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Malhotra D, Boyle SH, Gifford EJ, Sullivan BA, Nguyen Wenker TH, Abs ND, Ahmed ST, Upchurch J, Vahey J, Stafford C, Efird JT, Hunt SC, Bradford A, Sims KJ, Hauser ER, Helmer DA, Williams CD. Self-reported gastrointestinal disorders among veterans with gulf war illness with and without posttraumatic stress disorder. Neurogastroenterol Motil 2023; 35:e14548. [PMID: 36942766 DOI: 10.1111/nmo.14548] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2022] [Revised: 11/08/2022] [Accepted: 01/11/2023] [Indexed: 03/23/2023]
Abstract
BACKGROUND Gulf War Illness (GWI) is a chronic, multi-symptom disorder affecting 25%-32% of Gulf War veterans. Veterans with GWI disproportionately suffer from gastrointestinal (GI) disorders. Given the increasing evidence supporting a gut-brain axis, we explore the relationship between post-traumatic stress disorder (PTSD), GWI, and self-reported GI disorders among GW veterans. METHODS Veterans from the Gulf War Era Cohort and Biorepository responded to a mail-based survey (N = 1058). They were stratified by GWI (Centers for Disease Control definition) and PTSD status. This yielded three groups: GWI-, GWI+/PTSD-, and GWI+/PTSD+. Multivariable logistic regression adjusting for demographic and military characteristics examined associations between GWI/PTSD groups and GI disorders. Results were expressed as adjusted odds ratios (aOR) with 95% confidence intervals (95% CI). KEY RESULTS The most frequently reported GI disorders were irritable bowel syndrome (IBS), gastroesophageal reflux disease (GERD), and colon polyps (CP). The GWI+/PTSD+ group had a higher odds of these disorders than the GWI+/PTSD- group (aORIBS = 3.12, 95% CI: 1.93-5.05; aORGERD = 2.04, 95% CI: 1.44-2.90; aORCP = 1.85, 95% CI: 1.23-2.80), which had a higher odds of these disorders than the GWI- group (aORIBS = 4.38, 95% CI: 1.55-12.36; aORGERD = 2.51 95% CI: 1.63-3.87; aORCP = 2.57, 95% CI: 1.53-4.32). CONCLUSIONS & INFERENCES GW veterans with GWI and PTSD have significantly higher odds of specific self-reported GI disorders than the other groups. Given the known bidirectional influences of the gut and brain, these veterans may benefit from a holistic healthcare approach that considers biopsychosocial contributors to the assessment and management of disease.
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Affiliation(s)
- D Malhotra
- Duke University School of Medicine, Durham, North Carolina, USA
- Cooperative Studies Program Epidemiology Center, Durham VA Medical Center, Durham VA Health Care System, Durham, North Carolina, USA
| | - S H Boyle
- Cooperative Studies Program Epidemiology Center, Durham VA Medical Center, Durham VA Health Care System, Durham, North Carolina, USA
| | - E J Gifford
- Cooperative Studies Program Epidemiology Center, Durham VA Medical Center, Durham VA Health Care System, Durham, North Carolina, USA
- Center for Child and Family Policy, Duke Margolis Center for Health Policy, Duke University Sanford School of Public Policy, Durham, North Carolina, USA
| | - B A Sullivan
- Duke University School of Medicine, Durham, North Carolina, USA
- Cooperative Studies Program Epidemiology Center, Durham VA Medical Center, Durham VA Health Care System, Durham, North Carolina, USA
| | - T H Nguyen Wenker
- Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
- VA HSR&D Center for Innovations in Quality, Effectiveness and Safety (IQuEST), Michael E. DeBakey VA Medical Center, Houston, Texas, USA
| | - Nono-Djotsa Abs
- Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
- VA HSR&D Center for Innovations in Quality, Effectiveness and Safety (IQuEST), Michael E. DeBakey VA Medical Center, Houston, Texas, USA
- Big Data Scientist Training Enhancement Program (BD-STEP), VA Office of Research and Development, Washington, DC, Washington, USA
| | - S T Ahmed
- Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
- VA HSR&D Center for Innovations in Quality, Effectiveness and Safety (IQuEST), Michael E. DeBakey VA Medical Center, Houston, Texas, USA
| | - J Upchurch
- Cooperative Studies Program Epidemiology Center, Durham VA Medical Center, Durham VA Health Care System, Durham, North Carolina, USA
| | - J Vahey
- Cooperative Studies Program Epidemiology Center, Durham VA Medical Center, Durham VA Health Care System, Durham, North Carolina, USA
- Computational Biology and Bioinformatics Program, Duke University School of Medicine, Durham, North Carolina, USA
| | - C Stafford
- Cooperative Studies Program Epidemiology Center, Durham VA Medical Center, Durham VA Health Care System, Durham, North Carolina, USA
| | - J T Efird
- VA Cooperative Studies Program Coordinating Center, Boston, Massachusetts, USA
- Department of Radiation Oncology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA
| | - S C Hunt
- VA Puget Sound Health Care System, Seattle, Washington, USA
- Department of Medicine, University of Washington, Seattle, Washington, USA
| | - A Bradford
- Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
| | - K J Sims
- Cooperative Studies Program Epidemiology Center, Durham VA Medical Center, Durham VA Health Care System, Durham, North Carolina, USA
| | - E R Hauser
- Cooperative Studies Program Epidemiology Center, Durham VA Medical Center, Durham VA Health Care System, Durham, North Carolina, USA
- Department of Biostatistics and Bioinformatics, Duke University Medical Center, Duke Molecular Physiology Institute, Durham, North Carolina, USA
| | - D A Helmer
- Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
- VA HSR&D Center for Innovations in Quality, Effectiveness and Safety (IQuEST), Michael E. DeBakey VA Medical Center, Houston, Texas, USA
| | - C D Williams
- Cooperative Studies Program Epidemiology Center, Durham VA Medical Center, Durham VA Health Care System, Durham, North Carolina, USA
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Bradford A. Topic: AS03-Health Economics & Outcome Research/AS03b-Patient-reported outcomes. Leuk Res 2021. [DOI: 10.1016/j.leukres.2021.106681.12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Wencel D, Kaworek A, Abel T, Efremov V, Bradford A, Carthy D, Coady G, McMorrow RCN, McDonagh C. Optical Sensor for Real-Time pH Monitoring in Human Tissue. Small 2018; 14:e1803627. [PMID: 30427575 DOI: 10.1002/smll.201803627] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Revised: 10/29/2018] [Indexed: 05/21/2023]
Abstract
This article reports on a fiber-based ratiometric optical pH sensor for use in real-time and continuous in vivo pH monitoring in human tissue. Stable hybrid sol-gel-based pH sensing material is deposited on a highly flexible plastic optical fiber tip and integrated with excitation and detection electronics. The sensor is extensively tested in a laboratory environment before it is applied in vivo in a human model. The pH sensor performance in the laboratory environment outperforms the state-of-the-art reported in the current literature. It exhibits the highest sensitivity in the physiological pH range, resolution of 0.0013 pH units, excellent sensor to sensor reproducibility, long-term stability, short response time of <2 min, and drift of 0.003 pH units per 22 h. The sensor also exhibits promising performance in in vitro whole blood samples. In addition, human evaluations conducted under this project demonstrate successful short-term deployment of this sensor in vivo.
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Affiliation(s)
- Dorota Wencel
- School of Physical Science, Biomedical Diagnostic Institute, Dublin City University (DCU), Dublin 9, Ireland
| | - Alicja Kaworek
- BlueBridge Technologies, 3015 Lake Drive, Citywest Campus, Citywest, Dublin 24, Ireland
| | - Tobias Abel
- Roche Diagnostics International, Rotkreuz, Switzerland
| | - Vitaly Efremov
- Biomedical Diagnostic Institute, DCU, Dublin 9, 6343, Ireland
| | - Aidan Bradford
- Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, 123 St. Stephen's Green, Dublin 2, Ireland
| | - Denise Carthy
- Biomedical Diagnostic Institute, DCU, Dublin 9, 6343, Ireland
| | - Garret Coady
- BlueBridge Technologies, 3015 Lake Drive, Citywest Campus, Citywest, Dublin 24, Ireland
| | | | - Colette McDonagh
- School of Physical Science, Biomedical Diagnostic Institute, Dublin City University (DCU), Dublin 9, Ireland
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Doherty S, Knight JG, Backhouse T, Bradford A, Saunders F, Bourne RA, Chamberlain TW, Stones R, Clayton A, Lovelock K. Highly efficient aqueous phase reduction of nitroarenes catalyzed by phosphine-decorated polymer immobilized ionic liquid stabilized PdNPs. Catal Sci Technol 2018. [DOI: 10.1039/c7cy02557b] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Phosphino-decorated polymer immobilised ionic liquid-stabilised PdNPs are highly efficient catalysts for the aqueous phase hydrogenation and transfer hydrogenation of aromatic nitro compounds in batch and continuous flow.
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Lewis P, McMorrow C, Bradford A, O'Halloran KD. Improved tolerance of acute severe hypoxic stress in chronic hypoxic diaphragm is nitric oxide-dependent. J Physiol Sci 2015; 65:427-33. [PMID: 26001629 PMCID: PMC10717054 DOI: 10.1007/s12576-015-0381-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Accepted: 05/02/2015] [Indexed: 10/23/2022]
Abstract
The effects of chronic hypoxia (CH) on respiratory muscle performance have hardly been investigated, despite clinical relevance. Results from recent studies are indicative of unique adaptive strategies in hypoxic diaphragm. Respiratory muscle tolerance of acute severe hypoxic stress was examined in normoxic and CH diaphragm in the presence and absence of a nitric oxide (NO) synthase inhibitor. We tested the hypothesis that improved tolerance of severe hypoxic stress in CH diaphragm is NO-dependent. Wistar rats were exposed to normoxia (sea-level, n = 6) or CH (ambient pressure = 380 mmHg, n = 6) for 6 weeks. Diaphragm muscle functional properties were determined ex vivo under severe hypoxic conditions (gassed with 95%N2/5% CO2) with and without 1 mM L-N(G)-nitroarginine (L-NNA, nNOS inhibitor). Fatigue tolerance, but not force, was significantly improved in CH diaphragm (p = 0.008). CH exposure did not affect diaphragm muscle fibre oxidative capacity determined from cluster analysis of area-density plots of muscle fibre succinate dehydrogenase activity. Acute NOS inhibition reduced diaphragm peak tetanic force (p = 0.018), irrespective of gas treatment, and completely reversed improved fatigue tolerance of the CH diaphragm. We conclude that CH exposure improves fatigue tolerance during acute severe hypoxic stress in an NO-dependent manner, independent of muscle fibre oxidative capacity.
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Affiliation(s)
- Philip Lewis
- Department of Physiology, School of Medicine, Western Gateway Building, University College Cork, Western Road, Cork, Ireland,
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Shortt CM, Fredsted A, Chow HB, Williams R, Skelly JR, Edge D, Bradford A, O'Halloran KD. Reactive oxygen species mediated diaphragm fatigue in a rat model of chronic intermittent hypoxia. Exp Physiol 2014; 99:688-700. [PMID: 24443349 DOI: 10.1113/expphysiol.2013.076828] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Respiratory muscle dysfunction documented in sleep apnoea patients is perhaps due to oxidative stress secondary to chronic intermittent hypoxia (CIH). We sought to explore the effects of different CIH protocols on respiratory muscle form and function in a rodent model. Adult male Wistar rats were exposed to CIH (n = 32) consisting of 90 s normoxia-90 s hypoxia (either 10 or 5% oxygen at the nadir; arterial O2 saturation ∼ 90 or 80%, respectively] for 8 h per day or to sham treatment (air-air, n = 32) for 1 or 2 weeks. Three additional groups of CIH-treated rats (5% O2 for 2 weeks) had free access to water containing N-acetyl cysteine (1% NAC, n = 8), tempol (1 mM, n = 8) or apocynin (2 mM, n = 8). Functional properties of the diaphragm muscle were examined ex vivo at 35 °C. The myosin heavy chain and sarco(endo)plasmic reticulum Ca(2+)-ATPase isoform distribution, succinate dehydrogenase and glyercol phosphate dehydrogenase enzyme activities, Na(+)-K(+)-ATPase pump content, concentration of thiobarbituric acid reactive substances, DNA oxidation and antioxidant capacity were determined. Chronic intermittent hypoxia (5% oxygen at the nadir; 2 weeks) decreased diaphragm muscle force and endurance. All three drugs reversed the deleterious effects of CIH on diaphragm endurance, but only NAC prevented CIH-induced diaphragm weakness. Chronic intermittent hypoxia increased diaphragm muscle myosin heavy chain 2B areal density and oxidized glutathione/reduced glutathione (GSSG/GSH) ratio. We conclude that CIH-induced diaphragm dysfunction is reactive oxygen species dependent. N-Acetyl cysteine was most effective in reversing CIH-induced effects on diaphragm. Our results suggest that respiratory muscle dysfunction in sleep apnoea may be the result of oxidative stress and, as such, antioxidant treatment could prove a useful adjunctive therapy for the disorder.
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Affiliation(s)
- Christine M Shortt
- * Department of Physiology, Western Gateway Building, University College Cork, Cork 0, Ireland.
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7
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Edge D, McDonald FB, Jones JFX, Bradford A, O'Halloran KD. Effect of chronic intermittent hypoxia on the reflex recruitment of the genioglossus during airway obstruction in the anesthetized rat. Prog Brain Res 2014; 209:147-68. [PMID: 24746047 DOI: 10.1016/b978-0-444-63274-6.00008-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
We sought to test the hypothesis that chronic intermittent hypoxia (CIH)-a feature of sleep-disordered breathing in humans-impairs reflex recruitment of the genioglossus (GG, pharyngeal dilator) during obstructive airway events. Adult male Wistar rats were exposed to 20 cycles of normoxia and hypoxia (5% O2 at nadir) per hour, 8h a day for 7 days (CIH, N=7). The sham group (N=7) were exposed to normoxia in parallel. Following gas treatments, rats were anesthetized with an i.p. injection of urethane (1.5g/kg; 20%, w/v). Fine concentric needle electrodes were inserted into the GG and the costal diaphragm. Discriminated GG motor unit potentials and whole electromyograph (EMG), together with arterial blood pressure and arterial O2 saturation, were recorded during quiet basal breathing and during nasal airway occlusion. Airway occlusion significantly increased GG EMG activity in all animals; but there was no difference in the reflex response to airway occlusion between sham and CIH-treated animals (+105±22% vs. +105±17%, mean±SEM for area under the curve of integrated GG EMG, % increase from baseline, p=0.99). Occluded breaths were characterized by a significant increase in the firing frequency of phasically active units and the recruitment of large motor units that were quiescent under basal conditions. Though there are reports of impaired control of the upper airway following CIH in the rat, we conclude that reflexly evoked motor discharge to the GG is not affected by 7 days of CIH, a paradigm that we have shown increases apnea index in sleeping rats.
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Affiliation(s)
- Deirdre Edge
- UCD School of Medicine and Medical Science, University College Dublin, Dublin, Ireland.
| | - Fiona B McDonald
- UCD School of Medicine and Medical Science, University College Dublin, Dublin, Ireland
| | - James F X Jones
- UCD School of Medicine and Medical Science, University College Dublin, Dublin, Ireland
| | - Aidan Bradford
- Department of Physiology & Medical Physics, Royal College of Surgeons in Ireland, Dublin, Ireland
| | - Ken D O'Halloran
- Department of Physiology, Western Gateway Building, University College Cork, Cork, Ireland
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Carberry JC, McMorrow C, Bradford A, Jones JFX, O'Halloran KD. Effects of sustained hypoxia on sternohyoid and diaphragm muscle during development. Eur Respir J 2013; 43:1149-58. [PMID: 23766332 DOI: 10.1183/09031936.00139512] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Sustained hypoxia is a dominant feature of respiratory disease. Despite the clinical significance, the effects of sustained hypoxia on the form and function of respiratory muscle during development are relatively underexplored. Wistar rats were exposed to 1 week of sustained hypoxia (ambient pressure 450 mmHg) or normoxia at various time points during development. Sternohyoid and diaphragm muscle contractile and endurance properties were assessed in vitro. Muscle succinate dehydrogenase and myosin heavy chain composition were determined. The role of reactive oxygen species in hypoxia-induced muscle remodelling was assessed. Sustained hypoxia increased sternohyoid muscle force and fatigue in early but not late development, effects that persisted after return to normoxia. Hypoxia-induced sternohyoid muscle fatigue was not attributable to fibre type transitions or to a decrease in oxidative capacity. Chronic supplementation with the superoxide scavenger tempol did not prevent hypoxia-induced sternohyoid muscle fatigue, suggesting that mechanisms unrelated to oxidative stress underpin hypoxia-induced maladaptation in sternohyoid muscle. Sustained hypoxia had no effect on diaphragm muscle fatigue. We conclude that there are critical windows during development for hypoxia-induced airway dilator muscle maladaptation. Sustained hypoxia-induced impairment of upper airway muscle endurance may persist into later life. Upper airway muscle dysfunction could have deleterious consequences for the control of pharyngeal airway calibre in vivo.
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9
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Abstract
Respiratory muscle remodeling occurs in human sleep apnea--a common respiratory disorder characterized by chronic intermittent hypoxia (CIH) due to recurrent apnea during sleep. We sought to determine if CIH causes remodeling in rat sternohyoid (upper airway dilator) and diaphragm muscles. Adult male Wistar rats were exposed to CIH (n=8), consisting of 90 sec of hypoxia (5% at the nadir; SaO₂ ~80%)/90 sec of normoxia, 8 hr per day, for 7 consecutive days. Sham animals (n=8) were exposed to alternating air/air cycles in parallel. The effect of CIH on myosin heavy-chain (MHC) isoform (1, 2a, 2x, 2b) distribution, sarcoplasmic reticulum calcium ATPase (SERCA) isoform distribution, succinate dehydrogenase activity, glycerol phosphate dehydrogenase activity, and Na⁺/K⁺ ATPase pump content was determined. Sternohyoid muscle structure was unaffected by CIH treatment. CIH did not alter oxidative/glycolytic capacity or the Na⁺/K⁺-ATPase pump content of the diaphragm. CIH significantly increased the areal density of MHC 2b fibers in the rat diaphragm, and this was associated with a shift in SERCA proteins from SERCA2 to SERCA1. We conclude that CIH causes a slow-to-fast fiber transition in the rat diaphragm after just 7 days of treatment. Respiratory muscle functional remodeling may drive aberrant functional plasticity such as decreased muscle endurance, which is a feature of human sleep apnea.
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Affiliation(s)
- Christine M Shortt
- UCD School of Medicine and Medical Science, University College Dublin, Dublin, Ireland.
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Bradford A. Transcranial magnetic stimulation - a potential unobtrusive, non-invasive and drug-free treatment for obstructive sleep apnoea. Exp Physiol 2013; 98:882. [DOI: 10.1113/expphysiol.2012.071514] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Ross L, Polotsky A, Bradford A, Lesh J, Chosich J, Santoro N. Female obesity: profoundly reduced estrogen excretion after aromatase inhibition may underscore exaggerated sensitivity to estrogen negative feedback. Fertil Steril 2012. [DOI: 10.1016/j.fertnstert.2012.07.090] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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O'Halloran KD, Bradford A, Jones JFX, Edge D. Genioglossus motor unit properties in a rat model of sleep apnoea. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.1147.7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Aidan Bradford
- Department of Physiology and Medical PhysicsRoyal College of Surgeons in IrelandDublinIreland
| | - James FX Jones
- School of Medicine and Medical ScienceUniversity College DublinDublinIreland
| | - Deirdre Edge
- School of Medicine and Medical ScienceUniversity College DublinDublinIreland
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El-Khoury R, Bradford A, O'Halloran KD. Chronic hypobaric hypoxia increases isolated rat fast-twitch and slow-twitch limb muscle force and fatigue. Physiol Res 2012; 61:195-201. [PMID: 22292723 DOI: 10.33549/physiolres.932140] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Chronic hypoxia alters respiratory muscle force and fatigue, effects that could be attributed to hypoxia and/or increased activation due to hyperventilation. We hypothesized that chronic hypoxia is associated with phenotypic change in non-respiratory muscles and therefore we tested the hypothesis that chronic hypobaric hypoxia increases limb muscle force and fatigue. Adult male Wistar rats were exposed to normoxia or hypobaric hypoxia (PB=450 mm Hg) for 6 weeks. At the end of the treatment period, soleus (SOL) and extensor digitorum longus (EDL) muscles were removed under pentobarbitone anaesthesia and strips were mounted for isometric force determination in Krebs solution in standard water-jacketed organ baths at 25 °C. Isometric twitch and tetanic force, contractile kinetics, force-frequency relationship and fatigue characteristics were determined in response to electrical field stimulation. Chronic hypoxia increased specific force in SOL and EDL compared to age-matched normoxic controls. Furthermore, chronic hypoxia decreased endurance in both limb muscles. We conclude that hypoxia elicits functional plasticity in limb muscles perhaps due to oxidative stress. Our results may have implications for respiratory disorders that are characterized by prolonged hypoxia such as chronic obstructive pulmonary disease (COPD).
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Affiliation(s)
- R El-Khoury
- Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, St. Stephen’s Green, Dublin, Ireland
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Skelly JR, Edge D, Shortt CM, Jones JFX, Bradford A, O'Halloran KD. Respiratory control and sternohyoid muscle structure and function in aged male rats: decreased susceptibility to chronic intermittent hypoxia. Respir Physiol Neurobiol 2011; 180:175-82. [PMID: 22122888 DOI: 10.1016/j.resp.2011.11.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Revised: 11/11/2011] [Accepted: 11/12/2011] [Indexed: 11/30/2022]
Abstract
Obstructive sleep apnoea syndrome (OSAS) is a common respiratory disorder characterized by chronic intermittent hypoxia (CIH). We have shown that CIH causes upper airway muscle dysfunction in the rat due to oxidative stress. Ageing is an independent risk factor for the development of OSAS perhaps due to respiratory muscle remodelling and increased susceptibility to hypoxia. We sought to examine the effects of CIH on breathing and pharyngeal dilator muscle structure and function in aged rats. Aged (18-20 months), male Wistar rats were exposed to alternating cycles of normoxia and hypoxia (90 s each; F(I)O(2)=5% O(2) at nadir) or sham treatment for 8h/day for 9 days. Following CIH exposure, breathing was assessed by whole-body plethysmography. In addition, sternohyoid muscle contractile and endurance properties were examined in vitro. Muscle fibre type and cross-sectional area, and the activity of key oxidative and glycolytic enzymes were determined. CIH had no effect on basal breathing or ventilatory responses to hypoxia or hypercapnia. CIH did not alter succinate dehydrogenase or glycerol phosphate dehydrogenase enzyme activities, myosin heavy chain fibre areal density or cross-sectional area. Sternohyoid muscle force and endurance were unaffected by CIH exposure. Since we have established that this CIH paradigm causes sternohyoid muscle weakness in adult male rats, we conclude that aged rats have decreased susceptibility to CIH-induced stress. We suggest that structural remodelling with improved hypoxic tolerance in upper airway muscles may partly compensate for impaired neural regulation of the upper airway and increased propensity for airway collapse in aged mammals.
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Affiliation(s)
- J Richard Skelly
- UCD School of Medicine and Medical Science, University College Dublin, Belfield, Dublin 4, Ireland.
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Skelly JR, Edge D, Shortt CM, Jones JFX, Bradford A, O'Halloran KD. Tempol ameliorates pharyngeal dilator muscle dysfunction in a rodent model of chronic intermittent hypoxia. Am J Respir Cell Mol Biol 2011; 46:139-48. [PMID: 21868712 DOI: 10.1165/rcmb.2011-0084oc] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Respiratory muscle dysfunction is implicated in the pathophysiology of obstructive sleep apnea syndrome (OSAS), an oxidative stress disorder prevalent in men. Pharmacotherapy for OSAS is an attractive option, and antioxidant treatments may prove beneficial. We examined the effects of chronic intermittent hypoxia (CIH) on breathing and pharyngeal dilator muscle structure and function in male and female rats. Additionally, we tested the efficacy of antioxidant treatment in preventing (chronic administration) or reversing (acute administration) CIH-induced effects in male rats. Adult male and female Wistar rats were exposed to alternating cycles of normoxia and hypoxia (90 s each; Fi(O(2)) = 5% O(2) at nadir; Sa(O(2)) ∼ 80%) or sham treatment for 8 h/d for 9 days. Tempol (1 mM, superoxide dismutase mimetic) was administered to subgroups of sham- and CIH-treated animals. Breathing was assessed by whole-body plethysmography. Sternohyoid muscle contractile and endurance properties were examined in vitro. Muscle fiber type and cross-sectional area and the activity of key metabolic enzymes were determined. CIH decreased sternohyoid muscle force in male rats only. This was not attributable to fiber transitions or alterations in oxidative or glycolytic enzyme activity. Muscle weakness after CIH was prevented by chronic Tempol supplementation and was reversed by acute antioxidant treatment in vitro. CIH increased normoxic ventilation in male rats only. Sex differences exist in the effects of CIH on the respiratory system, which may contribute to the higher prevalence of OSAS in male subjects. Antioxidant treatment may be beneficial as an adjunct OSAS therapy.
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Affiliation(s)
- J Richard Skelly
- Department of Physiology, University College Cork, Western Gateway Building, Western Road, Cork, Ireland
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McMorrow C, Fredsted A, Carberry J, O'Connell RA, Bradford A, Jones JFX, O'Halloran KD. Chronic hypoxia increases rat diaphragm muscle endurance and sodium-potassium ATPase pump content. Eur Respir J 2010; 37:1474-81. [PMID: 21148231 DOI: 10.1183/09031936.00079810] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The effects of chronic hypoxia (CH) on respiratory muscle are poorly understood. The aim of the present study was to examine the effects of CH on respiratory muscle structure and function, and to determine whether nitric oxide is implicated in respiratory muscle adaptation to CH. Male Wistar rats were exposed to CH for 1-6 weeks. Sternohyoid and diaphragm muscle contractile properties, muscle fibre type and size, the density of fibres expressing sarco/endoplasmic reticulum calcium-ATPase (SERCA) 2 and sodium-potassium ATPase (Na+,K+-ATPase) pump content were determined. Muscle succinate dehydrogenase (SDH) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) dehydrogenase activities were also assessed. Acute and chronic blockade of nitric oxide synthase (NOS) was employed to determine whether or not NO is critically involved in functional remodelling in CH muscles. CH improved diaphragm, but not sternohyoid, fatigue tolerance in a time-dependent fashion. This adaptation was not attributable to increased SDH or NADPH dehydrogenase activities. The areal density of muscle fibres and relative area of fibres expressing SERCA2 were unchanged. Na+,K+-ATPase pump content was significantly increased in CH diaphragm. Chronic NOS inhibition decreased diaphragm Na+,K+-ATPase pump content and prevented CH-induced increase in muscle endurance. This study provides novel insight into the mechanisms involved in CH-induced muscle plasticity. The results may be of relevance to respiratory disorders characterised by CH, such as chronic obstructive pulmonary disease.
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Affiliation(s)
- C McMorrow
- University College Dublin School of Medicine and Medical Science, C228 Health Sciences Centre, University College Dublin, Belfield, Dublin 4, Ireland
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Edge D, Skelly JR, Bradford A, O’Halloran KD. Respiratory Plasticity in the Behaving Rat Following Chronic Intermittent Hypoxia. Advances in Experimental Medicine and Biology 2010; 669:267-70. [DOI: 10.1007/978-1-4419-5692-7_54] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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Skelly JR, Bradford A, Jones JFX, O'Halloran KD. Superoxide scavengers improve rat pharyngeal dilator muscle performance. Am J Respir Cell Mol Biol 2009; 42:725-31. [PMID: 19635929 DOI: 10.1165/rcmb.2009-0160oc] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Obstructive sleep apnea is a common disorder associated with upper airway muscle dysfunction. Agents that improve respiratory muscle performance may be useful as an adjunct therapy. The aim of this study was to examine the effects of antioxidants on rat pharyngeal dilator muscle performance. Adult male Wistar rats were killed humanely and isometric contractile properties of isolated sternohyoid muscle strips were examined in physiological salt solution at 35 degrees C in vitro. Muscle strips were incubated in tissue baths under hyperoxic (95%O(2)/5%CO(2)) or hypoxic (95%N(2)/5%CO(2)) conditions in the absence (control) or presence of the antioxidants: N-acetylcysteine (10 mM), Tiron (10 mM), or Tempol (10 mM). Force-frequency relationship was determined in response to supramaximal stimulation (10-100 Hz in increments of 10-20 Hz, train duration: 300 ms). Isometric force was also recorded during repetitive muscle stimulation (40 Hz, 300 ms every 2 s for 2 min). Under hyperoxic conditions, Tiron and Tempol, but not N-acetylcysteine, significantly increased sternohyoid muscle force and caused a left-shift in the force-frequency relationship. In addition, Tempol had a significant positive inotropic effect over the initial 90 seconds of repeated muscle activation. Hypoxia caused a significant decrease in sternohyoid muscle force. Under hypoxic conditions, Tempol-incubated muscles generated significantly higher forces compared with control muscles and showed improved performance in the early phase of the fatigue trial. This study illustrates that superoxide scavengers increase upper airway muscle force and that this effect persists under hypoxic conditions. We conclude that antioxidant treatment may be beneficial as a therapy in obstructive sleep apnea.
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Affiliation(s)
- J Richard Skelly
- UCD School of Medicine and Medical Science, Room C228, Health Sciences Centre, University College Dublin, Belfield, Dublin 4, Ireland
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Edge D, Skelly JR, Bradford A, O'Halloran KD. Ventilatory drive is enhanced in male and female rats following chronic intermittent hypoxia. Adv Exp Med Biol 2009; 648:337-44. [PMID: 19536497 DOI: 10.1007/978-90-481-2259-2_38] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Obstructive sleep apnoea is characterized by chronic intermittent hypoxia (CIH) due to recurrent apnoea. We have developed a rat model of CIH, which shows evidence of impaired respiratory muscle function. In this study, we wished to characterize the ventilatory effects of CIH in conscious male and female animals. Adult male (n=14) and female (n=8) Wistar rats were used. Animals were placed in chambers daily for 8 h with free access to food and water. The gas supply to one half of the chambers alternated between air and nitrogen every 90 s, for 8 h per day, reducing ambient oxygen concentration in the chambers to 5% at the nadir (intermittent hypoxia; n=7 male, n=4 female). Air supplying the other chambers was switched every 90 s to air from a separate source, at the same flow rates, and animals in these chambers served as controls (n=7 male, n=4 female). Ventilatory measurements were made in conscious animals (typically sleeping) after 10 days using whole-body plethysmography. Normoxic ventilation was increased in both male and female CIH-treated rats compared to controls but this did not achieve statistical significance. However, ventilatory drive was increased in CIH-treated rats of both sexes as evidenced by significant increases in mean and peak inspiratory flow. Ventilatory responses to acute hypoxia (F(I)O(2) = 0.10; 6 min) and hyperoxic hypercapnia (F(I)CO(2) = 0.05; 6 min) were unaffected by CIH treatment in male and female rats (P>0.05, ANOVA). We conclude that CIH increases respiratory drive in adult rats. We speculate that this represents a form of neural plasticity that may compensate for respiratory muscle impairment that occurs in this animal model.
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Affiliation(s)
- D Edge
- UCD School of Medicine and Medical Science, University College Dublin, Dublin 4, Ireland
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Cathcart MC, Tamosiuniene R, Chen G, Neilan TG, Bradford A, O'Byrne KJ, Fitzgerald DJ, Pidgeon GP. Cyclooxygenase-2-Linked Attenuation of Hypoxia-Induced Pulmonary Hypertension and Intravascular Thrombosis. J Pharmacol Exp Ther 2008; 326:51-8. [DOI: 10.1124/jpet.107.134221] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Skelly JR, Mitchell GS, Bradford A, O'Halloran KD. Tempol, a SOD‐mimetic, improves rat pharyngeal dilator muscle performance during hyperoxia and hypoxia. FASEB J 2008. [DOI: 10.1096/fasebj.22.1_supplement.739.3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | - Aidan Bradford
- Physiology and Medical PhysicsRoyal College of Surgeons in IrelandDublinIreland
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O'Halloran KD, Mitchell GS, Bradford A, Carberry J. EFFECTS OF CHRONIC HYPOXIA ON UPPER AIRWAY AND DIAPHRAGM MUSCLE ENDURANCE IN THE DEVELOPING RAT. FASEB J 2008. [DOI: 10.1096/fasebj.22.1_supplement.1232.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | - Aidan Bradford
- PhysiologyRoyal College of Surgeons in IrelandDublinIreland
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Affiliation(s)
- Clodagh McMorrow
- School of Medicine and Medical SciencesUniversity College DublinDublinIreland
| | - Gordon S Mitchell
- Departement of Comparative BiosciencesUniversity of Wisconsin at MadisonMadisonWI
| | - Aidan Bradford
- Department of Physiology and Medical PhysicsRoyal College of Surgeon in IrelandDublinIreland
| | - Ken D O'Halloran
- School of Medicine and Medical SciencesUniversity College DublinDublinIreland
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Abstract
Although somewhat controversial, there is good evidence that long-distance travel in general is a risk factor for venous thromboembolism, even in the absence of other risk factors. This is probably due to effects consequent to prolonged sitting but air travel in particular may be associated with risk factors other than this. One likely factor is hypoxia caused by the low ambient pressure of aircraft cabins. There is an association between venous thromboembolism and the hypoxia of altitude, chronic respiratory disease, neonatal hypoxia, sleep apnoea and experimentally-induced hypoxia. Platelet number and/or function are altered in all of these circumstances. Platelet aggregation is pivotal to venous thromboembolism and hypoxia alters platelet number and function. The early-onset thrombocytosis caused by hypoxia may be due to increased release of platelets from megakaryocytes and the late-onset thrombocytopaenia may be due to decreased platelet production and/or stem cell competition between erythrocytes and megakaryocytes. Hypoxia-induced platelet activation and aggregation may be due to increased circulating catecholamine levels but it is not known whether hypoxia can affect platelets directly. There is a need for further studies on the possible involvement of hypoxia-induced changes in platelet number and function in air travel-related venous thromboembolism.
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Affiliation(s)
- A Bradford
- Department of Physiology, Royal College of Surgeons in Ireland, St. Stephen's Green, Dublin 2, Ireland.
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Bavis RW, Powell FL, Bradford A, Hsia CCW, Peltonen JE, Soliz J, Zeis B, Fergusson EK, Fu Z, Gassmann M, Kim CB, Maurer J, McGuire M, Miller BM, O'Halloran KD, Paul RJ, Reid SG, Rusko HK, Tikkanen HO, Wilkinson KA. Respiratory plasticity in response to changes in oxygen supply and demand. Integr Comp Biol 2007; 47:532-51. [PMID: 21672862 DOI: 10.1093/icb/icm070] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Aerobic organisms maintain O(2) homeostasis by responding to changes in O(2) supply and demand in both short and long time domains. In this review, we introduce several specific examples of respiratory plasticity induced by chronic changes in O(2) supply (environmental hypoxia or hyperoxia) and demand (exercise-induced and temperature-induced changes in aerobic metabolism). These studies reveal that plasticity occurs throughout the respiratory system, including modifications to the gas exchanger, respiratory pigments, respiratory muscles, and the neural control systems responsible for ventilating the gas exchanger. While some of these responses appear appropriate (e.g., increases in lung surface area, blood O(2) capacity, and pulmonary ventilation in hypoxia), other responses are potentially harmful (e.g., increased muscle fatigability). Thus, it may be difficult to predict whole-animal performance based on the plasticity of a single system. Moreover, plastic responses may differ quantitatively and qualitatively at different developmental stages. Much of the current research in this field is focused on identifying the cellular and molecular mechanisms underlying respiratory plasticity. These studies suggest that a few key molecules, such as hypoxia inducible factor (HIF) and erythropoietin, may be involved in the expression of diverse forms of plasticity within and across species. Studying the various ways in which animals respond to respiratory challenges will enable a better understanding of the integrative response to chronic changes in O(2) supply and demand.
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Affiliation(s)
- Ryan W Bavis
- *Department of Biology, Bates College, Lewiston, ME 04240, USA; Department of Medicine, University of California, San Diego, CA, USA; White Mountain Research Station, University of California, San Diego, CA, USA; Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, St. Stephen's Green, Dublin 2, Ireland; Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Unit for Sports and Exercise Medicine, Institute of Clinical Medicine, University of Helsinki, Helsinki, Paasikivenkatu 4 00250, Finland; Institute of Veterinary Physiology, Vetsuisse Faculty, and Zurich Center for Integrative Human Physiology, University of Zurich, Winterthurerstrasse 260, CH-8057 Zurich, Switzerland; **Institut für Zoophysiologie, Universität Münster, Germany; Harvard Medical School, Brigham and Women's Hospital, 221 Longwood Avenue, Boston, MA 02115, USA; UCD School of Medicine and Medical Science, University College Dublin, Dublin, Ireland; Centre for the Neurobiology of Stress, Department of Life Sciences, University of Toronto, Scarborough; Department of Biology of Physical Activity, Faculty of Sport and Health Sciences, University of Jyväskylä, PO Box 35, 40014 Jyväskylä, Finland
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Raza A, Farrell T, O'Halloran KD, Bradford A. The Effects of Breath-Holds and Muller Manoeuvres on Upper Airway Carbon Dioxide Concentration in Humans. Respiration 2007; 74:533-6. [PMID: 17259692 DOI: 10.1159/000098884] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2006] [Accepted: 10/26/2006] [Indexed: 11/19/2022] Open
Abstract
<i>Background:</i> Obstructive sleep apnoea is caused by collapse of the upper airway. The presence of CO<sub>2</sub> in the upper airway lumen evokes a number of reflexes which favour upper airway re-opening, and we have proposed previously that CO<sub>2</sub> would build up in the upper airway following airway collapse and that this would contribute to reflex airway re-opening. However, it is not known if CO<sub>2</sub> can transfer from the alveoli to the anatomical dead space of the upper airway during apnoea. <i>Objectives:</i> To determine if alveolar CO<sub>2</sub> can enter the upper airway during breath-holds and Muller manoeuvres. <i>Material and Methods:</i> With local ethics committee approval, 6 male volunteers (aged 22–48 years), following a quiet inspiration, carried out breath-holds and Muller manoeuvres until breaking point. CO<sub>2</sub> was measured continuously in samples obtained from the hypopharynx using an infrared analyser with a sample rate of 50 ml/min. Muller manoeuvres (forced inspirations against a closed upper airway) mimic the respiratory efforts which occur during obstructive apnoeas. <i>Results:</i> In all cases, CO<sub>2</sub> increased progressively during apnoeas. There was a much larger increase in Muller manoeuvres (3.78 ± 0.51%, mean ± SEM at breaking point) compared to breath-holds. <i>Discussion:</i> These results show that upper airway CO<sub>2</sub> concentration rises substantially during apnoeas and suggest that transfer of CO<sub>2</sub> from the lungs to the upper airway may evoke a number of reflex effects which could affect breathing and upper airway re-opening during obstructive apnoeas.
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Affiliation(s)
- A Raza
- Department of Anatomy, Royal College of Surgeons in Ireland, University College Dublin, Dublin, Ireland
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Chang S, Bondi C, Bradford A, Bradford J, Williams C, Duldner J. 146. Ann Emerg Med 2006. [DOI: 10.1016/j.annemergmed.2006.07.600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Affiliation(s)
| | | | - C. Lewis
- a Department of Materials Science , U.C.N.W., Bangor
| | - A. Bradford
- a Department of Materials Science , U.C.N.W., Bangor
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Siriwardana G, Bradford A, Coy D, Zeitler P. Autocrine/paracrine regulation of breast cancer cell proliferation by growth hormone releasing hormone via Ras, Raf, and mitogen-activated protein kinase. Mol Endocrinol 2006; 20:2010-9. [PMID: 16613992 DOI: 10.1210/me.2005-0001] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Although GHRH has previously been shown to regulate proliferation of breast cancer cells and prevent apoptosis, the intracellular pathways mediating this effect have not been clarified. Exogenous GHRH stimulated a dose-dependent proliferative response within 24 h in MDA-231, as well as in T47D cells and in MCF-7 cells transfected with the GHRH receptor. The proliferation of MDA-MB-231 (MDA-231) cells was associated with an increase in tritiated thymidine uptake. In addition, phosphorylation of MAPK was rapidly stimulated by GHRH. The phosphorylation of MAPK by GHRH was prevented by transfection of the cells with dominant-negative Ras or Raf or by pretreatment of cells with Raf kinase 1 inhibitor. The inhibition of Ras and Raf, as well as the inhibition of MAPK phosphorylation by PD98059, also prevented GHRH-induced cell proliferation. Finally, pretreatment of cells with the somatostatin analog, BIM23014, also prevented GHRH-induced MAPK phosphorylation and cell proliferation. These results indicate that GHRH stimulates dose-dependent cell proliferation of MDA-231 breast cancer cells through a pathway that requires Ras, Raf, and MAPK phosphorylation. The results also provide support for a possible autocrine/paracrine antagonism between GHRH and somatostatin in the regulation of MDA-231 cell population maintenance. Taken together, the studies provide further insight into the possible role of GHRH as a growth factor in breast cancer.
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Affiliation(s)
- G Siriwardana
- Department of Pediatrics, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA
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Bradford A, McGuire M, O'Halloran KD. Does episodic hypoxia affect upper airway dilator muscle function? Implications for the pathophysiology of obstructive sleep apnoea. Respir Physiol Neurobiol 2005; 147:223-34. [PMID: 16087148 DOI: 10.1016/j.resp.2005.04.001] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2004] [Revised: 04/01/2005] [Accepted: 04/01/2005] [Indexed: 11/20/2022]
Abstract
Obstructive sleep apnoea (OSA) is characterised by repetitive collapse of the upper airway during sleep owing to a sleep-related decrement in upper airway muscle activity with consequent failure of the pharyngeal dilator muscles to oppose the collapsing pressure that is generated by the diaphragm and accessory muscles during inspiration. The causes of upper airway obstruction during sleep are multi-factorial but there is evidence implicating intrinsic upper airway muscle function and impaired central regulation of the upper airway muscles in the pathophysiology of OSA. The condition is associated with episodic hypoxia due to recurrent apnoea. However, despite its obvious importance very little is known about the effects of episodic hypoxia on upper airway muscle function. In this review, we examine the evidence that chronic intermittent hypoxia can affect upper airway muscle structure and function and impair CNS control of the pharyngeal dilator muscles. We review the literature and discuss results from our laboratory showing that episodic hypoxia/asphyxia reduces upper airway muscle endurance and selectively impairs pharyngeal dilator EMG responses to physiological stimulation. Our observations lead us to speculate that episodic hypoxia--a consequence of periodic airway occlusion--is responsible for progression of OSA through impairment of the neural control systems that regulate upper airway patency and through altered respiratory muscle contractile function, leading to the establishment of a vicious cycle of further airway obstruction and hypoxic insult that chronically exacerbates and perpetuates the condition. We conclude that chronic intermittent hypoxia/asphyxia contributes to the pathophysiology of sleep-disordered breathing.
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Affiliation(s)
- Aidan Bradford
- Department of Physiology, Royal College of Surgeons in Ireland, St. Stephen's Green, Dublin 2, Ireland
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Abstract
Sleep-disordered breathing is associated with chronic intermittent asphyxia and with a variety of cardiovascular abnormalities. Cardiovascular morbidity and mortality are linked to altered platelet function, and platelet function is affected in sleep-disordered breathing. As there is evidence that chronic continuous hypoxia may alter platelet number and function, the aim of the present study was to test the hypothesis that chronic intermittent asphyxia affects platelet count, activation and aggregation. Rats were treated with a hypercapnic hypoxic gas mixture (minimum of 6-8% O2, maximum of 10-14% CO2) for 15 s, twice per minute for 8 h per day for 3 weeks. Blood was analysed for platelet count, platelet activation (CD62p expression using flow cytometry), response to low dose ADP, haematocrit, red cell count and haemoglobin concentration. A platelet function analyser measured the closure time of an aperture, dependent on platelet aggregation. Compared to controls (n = 16), chronic intermittent asphyxia (n = 13) reduced body weight and increased right ventricular weight but had no significant effect on platelet count (control, 880.4 +/- 20.1; treated: 914.1 +/- 35.2 x 10(3) microl(-1); mean +/- S.E.M.), on the reduction in platelet count in response to ADP (control, reduced to 206.7 +/- 49.0; treated, reduced to 193.8 +/- 35.9 x 10(3) microl(-1)), or on the percentage of platelets positive for CD62p (control, 5.2 +/- 0.7; treated, 6.0 +/- 0.8%). Chronic intermittent asphyxia significantly (P = 0.037) reduced the closure time (control, 90.9 +/- 7.7; treated, 77.7 +/- 3.8 s), indicating greater adhesion and aggregation. There was no significant difference in haematocrit, red cell count and haemoglobin concentration. In conclusion, chronic intermittent asphyxia has no effect on platelet count but does increase platelet aggegation in rats. These data support the idea that chronic intermittent asphyxia alters platelet function in sleep-disordered breathing.
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Affiliation(s)
- M Dunleavy
- Department of Physiology Royal College of Surgeons in Ireland St. Stephen's Green, Dublin 2, Ireland
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Martial FP, Dunleavy M, Nolan P, McNicholas WT, O'Regan RG, Bradford A. Simultaneous recording of breathing and respiratory related neuronal activity in the brainstem of conscious rats. Respir Physiol Neurobiol 2005; 145:301-6. [PMID: 15705544 DOI: 10.1016/j.resp.2004.09.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/17/2004] [Indexed: 11/25/2022]
Abstract
One aim of integrative neurophysiology is to understand the relationship between neuronal activity and normal evolution of other physiological parameters. In this respect, anaesthetics or paralyzing agents, that have been shown to have a significant effect on several vital physiological processes, can be seen as a real problem for the interpretation of observations. Eletrophysiological recording in awake animals avoids this problem. Recordings in forebrain areas are now used routinely but a number of specific difficulties have limited their application to the medullary areas. In this paper, we describe a preparation that allows us to simultaneously record neuronal activity in the dorsal brainstem and respiratory activity in awake rats, while applying different types of respiratory challenges.
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Affiliation(s)
- Franck P Martial
- Department of Physiology, Royal College of Surgeons, 123, St. Stephen's Green, Dublin 2, Ireland
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Ennaceur A, Michalikova S, Bradford A, Ahmed S. Detailed analysis of the behavior of Lister and Wistar rats in anxiety, object recognition and object location tasks. Behav Brain Res 2004; 159:247-66. [PMID: 15817188 DOI: 10.1016/j.bbr.2004.11.006] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2004] [Revised: 11/02/2004] [Accepted: 11/04/2004] [Indexed: 10/26/2022]
Abstract
The present study, examines some issues in the measure and analysis of behavior in animals. Two strains of rats of both genders were used to illustrate and discuss these issues. We examined to what extent various behavioral measures reflect different or identical emotional or cognitive factors and, how sensitive are the various parameters of a task to differences between strains and genders. Wistar and Lister males and females rats were tested in an anxiety test then in the object recognition task followed by the object location task. Taking advantage of a simple computer program it is possible to: (1) record several parameters of theses tasks and examine the pattern of animal responses toward novelty and/or familiarity; (2) examine whether different measurements of the same response would reflect anxiety response to novelty and, can they discriminate between novelty and familiarity responses to objects; and (3) examine if changes in the pattern of animal responses are reflected by these measurements and, whether anxiety or discrimination is evident mainly during the first minute of the test. The results on the anxiety test show that different measures of the same response proved concordant and revealed significant differences between Lister males and Wistar males. Lister males approached more frequently an object and spent more time on an object in each approach compared to Wistar males in the first 5 min of test and in the total 10 min. They have also shorter latencies between approaches compared to Wistar males. The examination of performance over different time bins was significant with the measure of frequency. Lister male rats approached less frequently the object in the last 5 min of the test compared to the first 5 min. Their performance, however, did not differ from that of the other groups in this last 5 min. In the memory tasks, the measure of the frequency of approaches suggests that Lister male rats were able to discriminate between novel and familiar objects and, between novel and familiar location of objects. The measure of latency of first approach shows that Wistar female rats were able to discriminate between objects only in the spatial memory test. Discrimination in the object recognition task was observed in the first and second minute, and in the total 3 min sessions. Discrimination in the object location task was observed with the measure of frequency of approaches, in the first minute, and in the total 3 min sessions. Results from the total 3 min sessions were more concordant between the different measures of discrimination than results from separate 1 min bins. The results from the two memory tasks show that novelty prevented habituation to re-exposure to the testing environment. In many cases, novelty increased exploration of the objects in the choice phase compared to the sample phase. However, this lack of habituation or increased exploration in the choice phase is not concordant with most results of discrimination between novelty and familiarity from the same type of measurements.
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Affiliation(s)
- A Ennaceur
- School of Pharmacy, University of Sunderland, Wharncliffe Street, Sunderland SR13SD, UK.
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Pidgeon GP, Tamosiuniene R, Chen G, Leonard I, Belton O, Bradford A, Fitzgerald DJ. Intravascular thrombosis after hypoxia-induced pulmonary hypertension: regulation by cyclooxygenase-2. Circulation 2004; 110:2701-7. [PMID: 15492320 DOI: 10.1161/01.cir.0000145613.01188.0b] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Pulmonary hypertension induced by chronic hypoxia is characterized by thickening of pulmonary artery walls, elevated pulmonary vascular resistance, and right-heart failure. Prostacyclin analogues reduce pulmonary pressures in this condition; raising the possibility that cycloxygenase-2 (COX-2) modulates the response of the pulmonary vasculature to hypoxia. METHODS AND RESULTS Sprague-Dawley rats in which pulmonary hypertension was induced by hypobaric hypoxia for 14 days were treated concurrently with the selective COX-2 inhibitor SC236 or vehicle. Mean pulmonary arterial pressure (mPAP) was elevated after hypoxia (28.1+/-3.2 versus 17.2+/-3.1 mm Hg; n=8, P<0.01), with thickening of small pulmonary arteries and increased COX-2 expression and prostacyclin formation. Selective inhibition of COX-2 aggravated the increase in mPAP (42.8+/-5.9 mm Hg; n=8, P<0.05), an effect that was attenuated by the thromboxane (TX) A2/prostaglandin endoperoxide receptor antagonist ifetroban. Urinary TXB2 increased during hypoxia (5.9+/-0.9 versus 1.2+/-0.2 ng/mg creatinine; n=6, P<0.01) and was further increased by COX-2 inhibition (8.5+/-0.7 ng/mg creatinine; n=6, P< 0.05). In contrast, urinary excretion of the prostacyclin metabolite 6-ketoprostaglandin F1alpha decreased with COX-2 inhibition (8.6+/-3.0 versus 27.0+/-4.8 ng/mg creatinine; n=6, P< 0.05). Platelet activation was enhanced after chronic hypoxia. COX-2 inhibition further reduced the PFA-100 closure time and enhanced platelet deposition in the smaller pulmonary arteries, effects that were attenuated by ifetroban. Mice with targeted disruption of the COX-2 gene exposed to chronic hypoxia had exacerbated right ventricular end-systolic pressure, whereas targeted disruption of COX-1 had no effect. CONCLUSIONS COX-2 expression is increased and regulates platelet activity and intravascular thrombosis in hypoxia-induced pulmonary hypertension.
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Affiliation(s)
- Graham P Pidgeon
- Department of Clinical Pharmacology, Royal College of Surgeons Ireland, 123 St. Stephens Green, Dublin 2, Ireland.
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Abstract
Sleep-disordered breathing in humans is a common condition associated with serious cardiovascular and other abnormalities. The prevalence and pathogenesis of increased haematocrit and pulmonary hypertension is controversial and it has been suggested that these changes only occur in patients who also have daytime continuous hypoxaemia. The hypothesis tested here is that the chronic intermittent hypoxia and asphyxia associated with sleep-disordered breathing causes erythropoiesis and pulmonary hypertension and that this occurs in the absence of periods of continuous hypoxia. In humans and animals with obstructive sleep apnoea, there are abnormalities of upper airway muscle structure that have been ascribed to increased load placed on these muscles. An alternative hypothesis is that chronic intermittent hypoxia and asphyxia cause changes in upper airway muscle structure and function. To test these hypotheses, rats were exposed to intermittent hypoxia and asphyxia for 8 h per day for 5 weeks. This caused an increase in haematocrit, right ventricular weight and pulmonary arterial pressure. There were only slight changes in diaphragm, upper airway and limb muscle structure and force production but in general, muscle fatigability was increased. In conclusion chronic intermittent hypoxia and asphyxia cause an increase in haematocrit and pulmonary arterial pressure in the absence of periods of continuous hypoxia. Chronic intermittent hypoxia and asphyxia have little effect on skeletal muscle structure and force production but increase muscle fatigue. Increased upper airway muscle fatigue could lead to a vicious cycle of further compromise in upper airway patency and further hypoxia and asphyxia.
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Affiliation(s)
- Aidan Bradford
- Department of Physiology, Royal College of Surgeons in Ireland, St Stephen's Green, Dublin 2, Ireland.
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O'Halloran KD, McGuire M, O'Hare T, MacDermott M, Bradford A. Upper airway EMG responses to acute hypoxia and asphyxia are impaired in streptozotocin-induced diabetic rats. Respir Physiol Neurobiol 2004; 138:301-8. [PMID: 14609518 DOI: 10.1016/j.resp.2003.09.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Obstructive sleep apnoea (OSA) is a major clinical disorder that is characterised by multiple episodes of upper airway obstruction due to failure of the upper airway dilator muscles to maintain upper airway patency. The incidence of OSA is high in many endocrine disorders including both insulin-dependent and non-insulin-dependent diabetes but the reasons for this are not known. We wished to test the hypothesis that central respiratory motor output to the upper airway muscles is preferentially impaired in a rat model of diabetes mellitus. Sternohyoid (SH) and diaphragm (DIA) EMG activities were recorded in control and streptozotocin (STZ)-induced diabetic rats during normoxia, hypoxia (7.5% O2 in N2) and asphyxia (7.5% O2 and 3% CO2) under pentobarbitone anaesthesia. SH EMG responses to acute hypoxia and asphyxia were significantly impaired in STZ-induced diabetic rats compared to control animals (+47.1 +/- 5.7 vs. +11.7 +/- 1.9% during hypoxia in control and diabetic animals respectively and +56.5 +/- 7.9 vs. +15.7 +/- 5.0% during asphyxia). However, DIA EMG responses to hypoxia and asphyxia were not different for the two groups. We propose that the higher prevalence of OSA in diabetic patients is related to preferential impairment of cranial motor output to the dilator muscles of the upper airway in response to physiological stimuli.
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Affiliation(s)
- K D O'Halloran
- Department of Human Anatomy and Physiology, University College Dublin, Earlsfort Terrace, Dublin 2, Ireland.
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Abstract
The effects of vitamin E on the activity of membrane-dependent enzymes suggest that it acts indirectly by modifying some properties of the lipid host. The effects of alpha-tocopherol (alpha-T) and alpha-tocopherol hemisuccinate (alpha-THS) on phospholipid monolayer structure, curvature, and bending elasticity were examined using X-ray diffraction and the osmotic stress method. These ligands were mixed with the hexagonal phase-forming lipid, dioleoylphosphatidylethanolamine (DOPE). Increasing levels up to 50 mol% alpha-T in DOPE in excess water result in a systematic decrease in the lattice dimension. Analysis of the structural changes imposed by alpha-T shows that it contributes a spontaneous radius of curvature of -13.7 A. This unusually negative value is comparable to diacylglycerols. alpha-T does not affect the bending elasticity of these monolayers. alpha-THS in its charged form decreases membrane curvature, but in its undissociated neutral form has a qualitatively similar but reduced effect on monolayer curvature, as does alpha-T. We discuss these results in terms of the local stresses such ligands would produce in the vicinity of a membrane protein, and how one might expect proteins to respond to such stress.
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Affiliation(s)
- A Bradford
- Department of Biological Sciences, Brock University, St. Catharines, Ontario, Canada L2S 3A1
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El-Khoury R, O'Halloran KD, Bradford A. Effects of chronic hypobaric hypoxia on contractile properties of rat sternohyoid and diaphragm muscles. Clin Exp Pharmacol Physiol 2003; 30:551-4. [PMID: 12890176 DOI: 10.1046/j.1440-1681.2003.03874.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
1. Chronic hypoxia occurs in a variety of circumstances, including respiratory disease and exposure to altitude, and is known to affect respiratory muscle structure. However, little is known about its effects on respiratory muscle contractile properties. 2. Rats were exposed to normoxia (n = 16) or hypobaric hypoxia (n = 16; barometric pressure 450 mmHg) for 6 weeks. Contractile properties were measured in isolated sternohyoid and diaphragm muscles in warmed, oxygenated Krebs' solution. Isometric twitch and tetanic tension, contraction time, half-relaxation time and tension-frequency relationship were determined using field stimulation with platinum electrodes. Fatigue was induced by stimulation at 40 Hz with 300 msec trains of 0.5 Hz for 5 min. 3. Chronic hypoxia had no effect on bodyweight, but did increase haematocrit. Chronic hypoxia increased specific force development in both muscles and increased sternohyoid fatigue. Chronic hypoxia had no effect on contractile kinetics in either muscle, but shifted the tension-frequency relationship to the left in the diaphragm. 4. Therefore, chronic hypoxia alters rat respiratory muscle force and fatigue, either due to the direct effects of hypoxia or to increased muscle activation.
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Affiliation(s)
- R El-Khoury
- Department of Physiology, Royal College of Surgeons in Ireland, Dublin, Ireland
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Abstract
OBJECTIVE In obstructive sleep apnea (OSA), there is intermittent upper airway (UA) collapse due to an imbalance between the collapsing force generated by the diaphragm and the stabilizing force of the UA muscles. This results in chronic intermittent asphyxia (CIA). We have previously shown that CIA affects UA muscle fatigue, but little is known about the effects of chronic hypoxia on diaphragm or on limb muscle contractile properties and structure. DESIGN Rats were exposed to asphyxia and normoxia twice per minute for 8 h/d for 5 weeks to simulate the intermittent asphyxia of OSA in humans. Isometric contractile properties were determined from strips of isolated diaphragm, extensor digitorum longus (EDL), and soleus muscles in Krebs solution at 30 degrees C. EDL and soleus type 1 (slow, fatigue resistant), type 2A (fast, fatigue resistant), and type 2B (fast, fatigable) fiber distribution was determined using adenosine triphosphatase staining. RESULTS CIA caused a significant increase in diaphragm, EDL, and soleus fatigue, and reduced recovery from fatigue. Most of the other contractile properties were unaffected aside from a small reduction in diaphragm half-relaxation time and EDL twitch tension and a small shift to the left in the EDL force-frequency curve. There was no change in soleus fiber-type distribution and a small increase in EDL type 2A fibers (46.1 +/- 1.2% vs 49.9 +/- 1.4%, control vs CIA [mean +/- SD]). CONCLUSIONS CIA increases diaphragm, EDL, and soleus muscle fatigue. We speculate that if this also occurs in OSA, it would contribute to the pathophysiology of the condition.
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Affiliation(s)
- Michelle McGuire
- Department of Physiology, Royal College of Surgeons in Ireland, Dublin, Ireland
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Martial FP, Dunleavy M, Jones JFX, Nolan P, O'Regan RG, McNicholas W, Bradford A. Activity of Dorsal Medullary Respiratory Neurons in Awake Rats. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 536:445-53. [PMID: 14635698 DOI: 10.1007/978-1-4419-9280-2_56] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/27/2023]
Affiliation(s)
- F P Martial
- Department of Physiology, Royal College of Surgeons in Ireland, Ireland
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Hughes K, Pickering M, O'Leary DM, Bradford A, O'Regan RG, Jones JFX. The Paraganglia of the Rat Superior Laryngeal Nerve. Advances in Experimental Medicine and Biology 2003; 536:239-46. [PMID: 14635673 DOI: 10.1007/978-1-4419-9280-2_31] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Affiliation(s)
- Kris Hughes
- Department of Human Anatomy and Physiology, University College Dublin, Earlsfort Terrace, Dublin 2, Ireland
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Abstract
1. In humans, the effects of dietary creatine supplementation are controversial, with some studies showing increased muscle force and fatigue resistance and others reporting no effect on exercise performance. Little is known about the effects of creatine on muscle contractile properties. 2. Rats were fed a standard diet, creatine for 10 days or beta-guanidinopropionate, which depletes muscle creatine, for 7 days. Contractile properties were measured in isolated extensor digitorum longus and sternohyoid muscle as representative limb and upper airway dilator muscles, respectively. 3. Creatine had no effect on specific twitch and tetanic tension, contractile kinetics, twitch/tetanus tension ratio, the tension-frequency relationship or fatigue in both muscles. beta-Guanidinopropionate had no effect on the twitch and tetanic tension, contractile kinetics, twitch/tetanus tension ratio or tension-frequency relationship, but significantly increased (P < 0.05, anova) fatigue in both muscles. 4. Therefore, although creatine depletion increases fatigue, creatine loading has no effects on extensor digitorum longus and sternohyoid muscle contractile properties.
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Affiliation(s)
- M Gagnon
- Department of Physiology, Royal College of Surgeons in Ireland, St Stephenís Green, Dublin, Ireland
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McGuire M, MacDermott M, Bradford A. The effects of chronic episodic hypercapnic hypoxia on rat upper airway muscle contractile properties and fiber-type distribution. Chest 2002; 122:1400-6. [PMID: 12377871 DOI: 10.1378/chest.122.4.1400] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
OBJECTIVE Obstructive sleep apnea (OSA) is caused by episodes of upper airway (UA) obstruction due to an inability of UA muscles such as the geniohyoids and sternohyoids to maintain airway patency. This results in chronic episodic hypercapnic hypoxia. Chronic continuous hypoxia and episodic hypocapnic hypoxia affect skeletal muscle structure and function, but the effects of chronic episodic hypercapnic hypoxia on UA muscle structure and function are unknown. DESIGN Rats breathed air and hypercapnic hypoxic gas twice per minute for 8 h/d for 5 weeks in order to mimic the intermittent hypercapnic hypoxia of OSA in humans. Isometric contractile properties were determined using strips of isolated geniohyoid and sternohyoid muscles in physiologic saline solution at 30 degrees C. Fiber-type distribution was determined by adenosine triphosphatase staining. RESULTS For both muscles, chronic episodic hypercapnic hypoxia had no significant effect on twitch or tetanic tension, twitch/tetanic tension ratio, and tension-frequency relationship. There was a significant (p < 0.05) increase in geniohyoid fatigue (50.5 +/- 6.6% vs 43.6 +/- 5.8% of initial tension), but sternohyoid fatigue was reduced (31.5 +/- 5.2% vs 37.8 +/- 6.0% of initial tension). Geniohyoid type 1 fibers were reduced and type 2B fibers increased, whereas sternohyoid muscle had an increase in type 1 and 2A fibers and a decrease in type 2B fibers. CONCLUSIONS Chronic episodic hypercapnic hypoxia alters UA muscle structure and function, changes that may affect the regulation of UA patency.
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Affiliation(s)
- Michelle McGuire
- Department of Physiology, Royal College of Surgeons in Ireland, St. Stephen's Green, Dublin 2, Ireland
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Abstract
1. Creatine feeding increases the oxidative capacity of type 1 skeletal muscle fibres and, in soleus muscles, consisting mainly of type 1 fibres, increases fatigue resistance. The diaphragm contains a relatively large content of type 1 fibres and respiratory muscle fatigue is a cause of respiratory failure. The aim of the present study was to determine whether creatine supplements increase fatigue resistance in the diaphragm. 2. Rats were given creatine monohydrate (2.55 g/L) in the drinking water. After 5-6 days, isometric contractile properties were measured in strips of costal diaphragm in Krebs' solution at 30 degrees C. Measurements were also made in soleus muscle strips. Values for strips from creatine-fed rats were compared with those from control rats. 3. Creatine feeding did not increase fatigue resistance and had no effect on twitch or tetanic tension or twitch kinetics in the diaphragm. Creatine increased fatigue resistance in soleus muscles, as reported previously.
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Affiliation(s)
- M McGuire
- Department of Physiology, Royal College of Surgeons in Ireland, 123 St Stephens Green, Dublin 2, Ireland
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McGuire M, MacDermott M, Bradford A. Effects of chronic episodic hypoxia on rat upper airway muscle contractile properties and fiber-type distribution. Chest 2002; 122:1012-7. [PMID: 12226048 DOI: 10.1378/chest.122.3.1012] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
OBJECTIVE Contraction of upper airway (UA) muscles such as the geniohyoids and sternohyoids dilates and/or stabilizes the UA, thereby maintaining its patency. Obstructive sleep apnea (OSA) is caused by episodes of UA collapse, and this results in chronic episodic hypoxia. Chronic continuous hypoxia affects skeletal muscle structure and function, but the effects of chronic episodic hypoxia on UA muscle structure and function are unknown. DESIGN Rats were exposed to alternating periods of hypoxia and normoxia twice per minute for 8 h/d for 5 weeks in order to mimic the intermittent hypoxia of OSA in humans. Isometric contractile properties were determined using strips of isolated geniohyoid and sternohyoid muscles in physiologic saline solution at 30 degrees C. Fiber-type distribution was determined using adenosine triphosphatase staining. RESULTS Chronic episodic hypoxia had no significant effect on twitch or tetanic tension, twitch/tetanic tension ratio, contractile kinetics, tension-frequency relationship, or fiber-type distribution for either the sternohyoid or geniohyoid muscle. However, chronic episodic hypoxia did significantly increase sternohyoid and geniohyoid fatigue and reduced recovery from fatigue. CONCLUSIONS Chronic episodic hypoxia increases UA muscle fatigue, an effect that may compromise the maintenance of UA patency.
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Affiliation(s)
- Michelle McGuire
- Department of Physiology, Royal College of Surgeons in Ireland, St. Stephen's Green, Dublin, Ireland
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O'Halloran KD, McGuire M, O'Hare T, Bradford A. Chronic intermittent asphyxia impairs rat upper airway muscle responses to acute hypoxia and asphyxia. Chest 2002; 122:269-75. [PMID: 12114369 DOI: 10.1378/chest.122.1.269] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
BACKGROUND Obstructive sleep apnea (OSA) is a major clinical disorder that is characterized by multiple episodes of upper airway obstruction due to the failure of the upper airway dilator muscles to maintain upper airway patency. This results in chronic intermittent asphyxia (CIA) due to repetitive apneas, but very little is known about the effects of CIA on upper airway muscle function. OBJECTIVE To test the hypothesis that CIA affects upper airway muscle activity and electromyogram (EMG) responses to acute hypoxia and asphyxia. DESIGN Record upper airway EMG responses to acute hypoxia and asphyxia in control and CIA-treated rats. SETTING Department of Physiology, Royal College of Surgeons in Ireland, Dublin, Ireland. MEASUREMENTS Sternohyoid (SH) muscle and diaphragm (DIA) muscle EMG activities were recorded in both groups during normoxia, hypoxia (7.5% O(2) in N(2)), and asphyxia (7.5% O(2) and 3% CO(2)) under pentobarbitone anesthesia. RESULTS Baseline SH EMG activity was significantly elevated in the CIA-treated rats compared to the controls, whereas DIA EMG activity was similar in the two groups. In addition, CIA significantly reduced SH EMG but not DIA EMG responses to acute hypoxia and asphyxia. CONCLUSIONS The elevated upper airway muscle activity associated with OSA in humans during wakefulness is due at least in part to CIA. We propose that a reduction in the response of upper airway dilator muscles to acute asphyxia following upper airway obstruction is likely to cause further asphyxic insult, leading to a vicious feed-forward cycle exacerbating the condition. Our results suggest that CIA contributes to the pathophysiology of sleep-disordered breathing.
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Affiliation(s)
- Ken D O'Halloran
- Department of Human Anatomy and Physiology, University College Dublin, Dublin, Ireland.
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Abstract
BACKGROUND Diaphragm muscle force and fatigue are key factors in the development of respiratory failure. Almitrine is used to improve ventilatory drive and ventilation-perfusion matching in respiratory failure. Recently, it has also been shown to improve diaphragm muscle force and endurance in young rats, but it is not known if this effect persists with ageing. OBJECTIVES To determine the effects of almitrine on diaphragm contractile properties in young and old rats. METHODS In young and old rats, isometric contractile properties were measured in strips of isolated diaphragm muscle in physiological saline solution at 30 degrees C with or without almitrine. RESULTS In young animals, almitrine increased twitch tension, reduced half-relaxation time and increased endurance, but had no effect on tetanic tension, contraction time or tension-frequency relationship. Ageing had no effect on endurance, but did reduce twitch and tetanic tension and contraction and half-relaxation time. Almitrine had no effect on contractile tension and kinetics, tension-frequency relationship or on endurance in the old animals. CONCLUSIONS Ageing negates the beneficial effects of almitrine on diaphragm muscle force and endurance.
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Affiliation(s)
- M McGuire
- Department of Physiology, Royal College of Surgeons in Ireland, St. Stephen's Green, Dublin, Ireland
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