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Dissanayake HU, Sutherland K, Phillips CL, Grunstein RR, Mihailidou AS, Cistulli PA. Comparative effects of CPAP and mandibular advancement splint therapy on blood pressure variability in moderate to severe obstructive sleep apnoea. Sleep Med 2021; 80:294-300. [PMID: 33610954 DOI: 10.1016/j.sleep.2021.01.059] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 01/17/2021] [Accepted: 01/28/2021] [Indexed: 10/22/2022]
Abstract
BACKGROUND Obstructive sleep apnoea (OSA) is associated with increased blood pressure variability (BPV) and are risk factors for cardiovascular disease. We aimed to assess the comparative effects of two OSA therapies, continuous positive airway pressure (CPAP) and mandibular advancement splint (MAS), on BPV. METHODS This is a secondary analysis of data collected as part of a previously published randomised crossover trial of one month each of CPAP and MAS therapy. BPV was determined from 24-h-ambulatory blood pressure recordings in 92 patients with moderate to severe OSA at baseline and after one month of optimised treatment with each modality. BPV was assessed by three measures: Standard deviation of the mean (SD), Coefficient of variation (CoV), and the Average Real Variability (ARV) index. RESULTS Neither CPAP nor MAS therapy improved BPV, with no difference between treatments. BPV did not change in hypertensive OSA patients, however, there was a reduction in ARV of diastolic blood pressure in the effectively treated compared to ineffectively treated CPAP patients, Δ ARV 24-h-DBP (mmHg), -0.72 ± 2.14, 0.34 ± 1.52, P = 0.02, respectively. There was no difference between effective versus ineffective MAS treatment, Δ ARV 24-h-DBP (mmHg), -0.04 ± 2.4, 0.02 ± 1.9, P = 1.00, respectively. CONCLUSIONS One month of optimised CPAP or MAS therapy did not improve short term BPV in patients with moderate to severe OSA. The subgroup of patients on effective CPAP showed some improvement in BPV with CPAP but not MAS. Further work on the effect of OSA therapy on BPV following long-term therapy is needed.
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Affiliation(s)
- Hasthi U Dissanayake
- Sleep Research Group, D 17 - Charles Perkins Centre, The University of Sydney, Australia; Faculty of Medicine and Health, Sydney Medical School, Northern Clinical School, The University of Sydney, Australia.
| | - Kate Sutherland
- Sleep Research Group, D 17 - Charles Perkins Centre, The University of Sydney, Australia; Faculty of Medicine and Health, Sydney Medical School, Northern Clinical School, The University of Sydney, Australia; Centre for Sleep Health & Research, Department of Respiratory Medicine, Royal North Shore Hospital, Australia
| | - Craig L Phillips
- Faculty of Medicine and Health, Sydney Medical School, Northern Clinical School, The University of Sydney, Australia
| | - Ronald R Grunstein
- Faculty of Medicine and Health, Sydney Medical School, Northern Clinical School, The University of Sydney, Australia; Woolcock Institute of Medical Research, Sydney, Australia
| | - Anastasia S Mihailidou
- Department of Cardiology and Kolling Institute, Royal North Shore Hospital, St Leonards, Australia; Faculty of Medicine and Health Sciences, Macquarie University, Sydney, Australia
| | - Peter A Cistulli
- Sleep Research Group, D 17 - Charles Perkins Centre, The University of Sydney, Australia; Faculty of Medicine and Health, Sydney Medical School, Northern Clinical School, The University of Sydney, Australia; Centre for Sleep Health & Research, Department of Respiratory Medicine, Royal North Shore Hospital, Australia
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Huber DA, Schreihofer AM. Exaggerated sympathoexcitatory reflexes develop with changes in the rostral ventrolateral medulla in obese Zucker rats. Am J Physiol Regul Integr Comp Physiol 2016; 311:R243-53. [PMID: 27280427 DOI: 10.1152/ajpregu.00085.2016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 06/01/2016] [Indexed: 11/22/2022]
Abstract
Obesity leads to altered autonomic reflexes that reduce stability of mean arterial pressure (MAP). Sympathoinhibitory reflexes such as baroreflexes are impaired, but reflexes that raise MAP appear to be augmented. In obese Zucker rats (OZR) sciatic nerve stimulation evokes larger increases in MAP by unknown mechanisms. We sought to determine the autonomic underpinnings of this enhanced somatic pressor reflex and whether other sympathoexcitatory reflexes are augmented. We also determined whether their final common pathway, glutamatergic activation of the rostral ventrolateral medulla (RVLM), was enhanced in male OZR compared with lean Zucker rats (LZR). Sciatic nerve stimulation or activation of the nasopharyngeal reflex evoked larger rises in splanchnic sympathetic nerve activity (SNA) (79% and 45% larger in OZR, respectively; P < 0.05) and MAP in urethane-anesthetized, ventilated, paralyzed adult OZR compared with LZR. After elimination of baroreflex feedback by pharmacological prevention of changes in MAP and heart rate, these two sympathoexcitatory reflexes were still exaggerated in OZR (167% and 69% larger, respectively, P < 0.05). In adult OZR microinjections of glutamate, AMPA, or NMDA into the RVLM produced larger rises in SNA (∼61% larger in OZR, P < 0.05 for each drug) and MAP, but stimulation of axonal fibers in the upper thoracic spinal cord yielded equivalent responses in OZR and LZR. In juvenile OZR and LZR, sympathoexcitatory reflexes and physiological responses to RVLM activation were comparable. These data suggest that the ability of glutamate to activate the RVLM becomes enhanced in adult OZR and may contribute to the development of exaggerated sympathoexcitatory responses independent of impaired baroreflexes.
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Affiliation(s)
- Domitila A Huber
- Department of Integrative Physiology, University of North Texas Health Science Center, Fort Worth, Texas; and Department of Physiology, Medical College of Georgia,* Augusta, Georgia
| | - Ann M Schreihofer
- Department of Integrative Physiology, University of North Texas Health Science Center, Fort Worth, Texas; and Department of Physiology, Medical College of Georgia,* Augusta, Georgia
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Kai H, Kudo H, Takayama N, Yasuoka S, Aoki Y, Imaizumi T. Molecular mechanism of aggravation of hypertensive organ damages by short-term blood pressure variability. Curr Hypertens Rev 2015; 10:125-33. [PMID: 25544288 PMCID: PMC4428492 DOI: 10.2174/1573402111666141217112655] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2014] [Accepted: 12/12/2014] [Indexed: 11/22/2022]
Abstract
There is increasing evidence that not only the elevation of systolic and diastolic blood pressure (BP) but also the increase in BP variability (or fluctuation) are associated with hypertensive organ damages and the morbidity and mortality of cerebrovascular and cardiovascular events. However, the molecular mechanism whereby the increase in BP variability aggravates hypertensive organ damages remains unknown. Thus, we created a rat chronic model of a combination of hypertension and large BP variability by performing bilateral sino-aortic denervation in spontaneously hypertensive rat. A series of our studies using this model revealed that large BP variability induces chronic myocardial inflammation by activating local angiotensin II and mineralocorticoid receptor systems and thereby aggravates cardiac hypertrophy and myocardial fibrosis, leading to systolic dysfunction, in hypertensive hearts. In addition, large BP variability induces the aggravation of arteriolosclerotic changes and ischemic cortical fibrosis in hypertensive kidney via local angiotensin II system.
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Flythe JE, Inrig JK, Shafi T, Chang TI, Cape K, Dinesh K, Kunaparaju S, Brunelli SM. Association of intradialytic blood pressure variability with increased all-cause and cardiovascular mortality in patients treated with long-term hemodialysis. Am J Kidney Dis 2013; 61:966-74. [PMID: 23474007 DOI: 10.1053/j.ajkd.2012.12.023] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Accepted: 12/21/2012] [Indexed: 11/11/2022]
Abstract
BACKGROUND Blood pressure is known to fluctuate widely during hemodialysis; however, little is known about the association between intradialytic blood pressure variability and outcomes. STUDY DESIGN Retrospective observational cohort. SETTING & PARTICIPANTS A random sample of 6,393 adult, thrice-weekly, in-center, maintenance hemodialysis patients dialyzing at 1,026 dialysis units within a single large dialysis organization. PREDICTOR Intradialytic systolic blood pressure (SBP) variability. This was calculated using a mixed linear effects model. Peridialytic SBP phenomena were defined as starting SBP (regression intercept), systematic change in SBP over the course of dialysis (2 regression slopes), and random intradialytic SBP variability (absolute regression residual). OUTCOMES All-cause and cardiovascular mortality. MEASUREMENTS SBPs (n = 631,922) measured during hemodialysis treatments (n = 78,961) during the first 30 days in the study. Outcome data were obtained from the dialysis unit electronic medical record and were considered beginning on day 31. RESULTS High (ie, greater than the median) versus low SBP variability was associated with greater risk of all-cause mortality (adjusted HR, 1.26; 95% CI, 1.08-1.47). The association between high SBP variability and cardiovascular mortality was even more potent (adjusted HR, 1.32; 95% CI, 1.01-1.72). A dose-response trend was observed across quartiles of SBP variability for both all-cause (P = 0.001) and cardiovascular (P = 0.04) mortality. LIMITATIONS Inclusion of patients from a single large dialysis organization, over-representation of African Americans and patients with diabetes and heart failure, and lack of standardized SBP measurements. CONCLUSIONS Greater intradialytic SBP variability is associated independently with increased all-cause and cardiovascular mortality. Further prospective studies are needed to confirm findings and identify means of reducing SBP variability to facilitate randomized study.
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Affiliation(s)
- Jennifer E Flythe
- Renal Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA.
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McLoone VI, Ringwood JV, Van Vliet BN. A multi-component model of the dynamics of salt-induced hypertension in Dahl-S rats. BMC PHYSIOLOGY 2009; 9:20. [PMID: 19874603 PMCID: PMC2785758 DOI: 10.1186/1472-6793-9-20] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/18/2009] [Accepted: 10/29/2009] [Indexed: 01/11/2023]
Abstract
BACKGROUND In humans, salt intake has been suggested to influence blood pressure (BP) on a wide range of time scales ranging from several hours or days to many months or years. Detailed time course data collected in the Dahl salt-sensitive rat strain suggest that the development of salt-induced hypertension may consist of several distinct phases or components that differ in their timing and reversibility. To better understand these components, the present study sought to model the dynamics of salt-induced hypertension in the Dahl salt sensitive (Dahl-S) rat using 3 sets of time course data. RESULTS The first component of the model ("Acute-Reversible") consisted of a linear transfer function to account for the rapid and reversible effects of salt on BP (ie. acute salt sensitivity, corresponding with a depressed slope of the chronic pressure natriuresis relationship). For the second component ("Progressive-Irreversible"), an integrator function was used to represent the relatively slow, progressive, and irreversible effect of high salt intake on BP (corresponding with a progressive salt-induced shift of the chronic pressure natriuresis relationship to higher BP levels). A third component ("Progressive-Reversible") consisted of an effect of high salt intake to progressively increase the acute salt-sensitivity of BP (ie. reduce the slope of the chronic pressure natriuresis relationship), amounting to a slow and progressive, yet reversible, component of salt-induced hypertension. While the 3 component model was limited in its ability to follow the BP response to rapid and/or brief transitions in salt intake, it was able to accurately follow the slower steady state components of salt-induced BP changes. This model exhibited low values of mean absolute error (1.92 +/- 0.23, 2.13 +/- 0.37, 2.03 +/- 0.3 mmHg for data sets 1 - 3), and its overall performance was significantly improved over that of an initial model having only 2 components. The 3 component model performed well when applied to data from hybrids of Dahl salt sensitive and Dahl salt resistant rats in which salt sensitivity varied greatly in its extent and character (mean absolute error = 1.11 +/- 0.08 mmHg). CONCLUSION Our results suggest that the slow process of development of salt-induced hypertension in Dahl-S rats over a period of many weeks can be well represented by a combination of three components that differ in their timing, reversibility, and their associated effect on the chronic pressure natriuresis relationship. These components are important to distinguish since each may represent a unique set of underlying mechanisms of salt-induced hypertension.
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Affiliation(s)
- Violeta I McLoone
- Department of Electronic Engineering, National University of Ireland Maynooth, Maynooth, Co. Kildare, Ireland
| | - John V Ringwood
- Department of Electronic Engineering, National University of Ireland Maynooth, Maynooth, Co. Kildare, Ireland
| | - Bruce N Van Vliet
- Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3V6, Canada
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Kudo H, Kai H, Kajimoto H, Koga M, Takayama N, Mori T, Ikeda A, Yasuoka S, Anegawa T, Mifune H, Kato S, Hirooka Y, Imaizumi T. Exaggerated blood pressure variability superimposed on hypertension aggravates cardiac remodeling in rats via angiotensin II system-mediated chronic inflammation. Hypertension 2009; 54:832-8. [PMID: 19704105 DOI: 10.1161/hypertensionaha.109.135905] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Hypertensive patients with large blood pressure variability (BPV) have aggravated end-organ damage. However, the pathogenesis remains unknown. We investigated whether exaggerated BPV aggravates hypertensive cardiac remodeling and function by activating inflammation and angiotensin II-mediated mechanisms. A model of exaggerated BPV superimposed on chronic hypertension was created by performing bilateral sinoaortic denervation (SAD) in spontaneously hypertensive rats (SHRs). SAD increased BPV to a similar extent in Wistar Kyoto rats and SHRs without significant changes in mean blood pressure. SAD aggravated left ventricular and myocyte hypertrophy and myocardial fibrosis to a greater extent and impaired left ventricular systolic function in SHRs. SAD induced monocyte chemoattractant protein-1, transforming growth factor-beta, and angiotensinogen mRNA upregulations and macrophage infiltration of the heart in SHRs. The effects of SAD on cardiac remodeling and inflammation were much smaller in Wistar Kyoto rats compared with SHRs. Circulating levels of norepinephrine, the active form of renin, and inflammatory cytokines were not affected by SAD in Wistar Kyoto rats and SHRs. A subdepressor dose of candesartan abolished the SAD-induced left ventricular/myocyte hypertrophy, myocardial fibrosis, macrophage infiltration, and inductions of monocyte chemoattractant protein-1, transforming growth factor-beta, and angiotensinogen and subsequently prevented systolic dysfunction in SHRs with SAD. These findings suggest that exaggerated BPV induces chronic myocardial inflammation and thereby aggravates cardiac remodeling and systolic function in hypertensive hearts. The cardiac angiotensin II system may play a role in the pathogenesis of cardiac remodeling and dysfunction induced by a combination of hypertension and exaggerated BPV.
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Affiliation(s)
- Hiroshi Kudo
- Department of Internal Medicine, Division of Cardio-Vascular Medicine, Kurume University School of Medicine, 67 Asahimachi, Kurume, Japan
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Kai H, Kudo H, Takayama N, Yasuoka S, Kajimoto H, Imaizumi T. Large Blood Pressure Variability and Hypertensive Cardiac Remodeling Role of Cardiac Inflammation. Circ J 2009; 73:2198-203. [DOI: 10.1253/circj.cj-09-0741] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Hisashi Kai
- Department of Internal Medicine, Division of Cardio-Vascular Medicine, Kurume University School of Medicine
| | - Hiroshi Kudo
- Department of Internal Medicine, Division of Cardio-Vascular Medicine, Kurume University School of Medicine
| | - Narimasa Takayama
- Department of Internal Medicine, Division of Cardio-Vascular Medicine, Kurume University School of Medicine
| | - Suguru Yasuoka
- Department of Internal Medicine, Division of Cardio-Vascular Medicine, Kurume University School of Medicine
| | - Hidemi Kajimoto
- Department of Internal Medicine, Division of Cardio-Vascular Medicine, Kurume University School of Medicine
| | - Tsutomu Imaizumi
- Department of Internal Medicine, Division of Cardio-Vascular Medicine, Kurume University School of Medicine
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Guild SJ, Barrett CJ, McBryde FD, Van Vliet BN, Malpas SC. Sampling of cardiovascular data; how often and how much? Am J Physiol Regul Integr Comp Physiol 2008; 295:R510-5. [DOI: 10.1152/ajpregu.00139.2008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Long-term measurement of cardiovascular variables by telemetry in laboratory animals has become indispensable in recent years. However, limited battery life and management of large volumes of recorded data are major drawbacks. These limitations can often be overcome by intermittent sampling of data. The question is, how much data does one need to collect to accurately reflect the underlying average value? To investigate this, 24-h continuous recordings of rabbit heart rate, arterial pressure, and integrated renal sympathetic nerve activity (RSNA) were resampled using a variety of protocols that differed with respect to the number of individual sampling periods used and the total amount of time that was sampled. The absolute percentage errors of estimates of the daily mean, standard deviation, and interquartile range were calculated for each sampling protocol. A similar analysis was repeated using arterial pressure data from rats. The results show that the number of sampling periods spread throughout the day had more effect than the total amount of data recorded. For example, just 2 h of total sampling time spread over 12 evenly spaced 10-min periods gave estimates of the daily mean of blood pressure and heart rate with < 1% error and RSNA with < 3% error. We show that accurate estimates of the daily mean of arterial pressure, heart rate, and RSNA can all be made using scheduled recording, and we recommend recording a minimum of 2 h/day spread over a number of periods throughout the day.
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Ayer A, Antic V, Dulloo AG, Van Vliet BN, Montani JP. Hemodynamic consequences of chronic parasympathetic blockade with a peripheral muscarinic antagonist. Am J Physiol Heart Circ Physiol 2007; 293:H1265-72. [PMID: 17496215 DOI: 10.1152/ajpheart.00326.2007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Whereas the sympathetic nervous system has a well-established role in blood pressure (BP) regulation, it is not clear whether long-term levels of BP are affected by parasympathetic function or dysfunction. We tested the hypothesis that chronic blockade of the parasympathetic nervous system has sustained effects on BP, heart rate (HR), and BP variability (BPV). Sprague-Dawley rats were instrumented for monitoring of BP 22-h per day by telemetry and housed in metabolic cages. After the rats healed from surgery and a baseline control period, scopolamine methyl bromide (SMB), a peripheral muscarinic antagonist, was infused intravenously for 12 days. This was followed by a 10-day recovery period. SMB induced a rapid increase in mean BP from 98 ± 2 mmHg to a peak value of 108 ± 2 mmHg on day 2 of the SMB infusion and then stabilized at a plateau value of +3 ± 1 mmHg above control ( P < 0.05). After cessation of the infusion, the mean BP fell by 6 ± 1 mmHg. There was an immediate elevation in HR that remained significantly above control on the last day of SMB infusion. SMB also induced a decrease in short-term (within 30-min periods) HR variability and an increase in both short-term and long-term (between 30-min periods) BPV. The data suggest that chronic peripheral muscarinic blockade leads to modest, but sustained, increases in BP, HR, and BPV, which are known risk factors for cardiovascular morbidity.
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Affiliation(s)
- Antoine Ayer
- Department of Medicine/Division of Physiology, University of Fribourg, Rue du Musée 5, CH-1700 Fribourg, Switzerland
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Parati G, Faini A, Valentini M. Blood pressure variability: its measurement and significance in hypertension. Curr Hypertens Rep 2007; 8:199-204. [PMID: 17147917 DOI: 10.1007/s11906-006-0051-6] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Blood pressure (BP) fluctuations over time physiologically result from the complex interaction between environmental stimulation, genetic factors, and cardiovascular control mechanisms. Ambulatory BP-monitoring techniques, in particular systems providing beat-by-beat BP recording, have allowed a detailed description of the different components contributing to overall BP variability (BPV) over 24 hours, including short-lasting and more sustained BP changes. In hypertension, BPV increases with increasing BP levels, and evidence is available that its magnitude correlates closely with target-organ damage and with the incidence of cardiovascular events, independent of absolute BP levels. It has been suggested that drugs capable of providing smooth 24-hour BP control, reducing BPV, may confer additional target-organ protection. Mathematic indices, such as the trough-to-peak ratio and the smoothness index, represent useful measures of the homogeneity of the antihypertensive effect over 24 hours. Further studies are still needed to confirm that, in humans, interventions that can reduce BPV can also reduce the rate of cardiovascular events.
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Abstract
BACKGROUND AND PURPOSE Arterial baroreflex is one of the most important mechanisms in the regulation of cardiovascular activities. Arterial baroreflex function can be expressed as baroreflex sensitivity (BRS). The present study was designed to test 2 hypotheses: (1) BRS is a new independent predictor for the incidence of stroke in hypertension, and (2) restoration of BRS can prevent stroke in hypertension. METHODS First, 82 stroke-prone spontaneously hypertensive rats (SHR-SP) aged 28 to 30 weeks were used. After measuring blood pressure and BRS, the survival time was observed. Second, 12 SHR-SP aged 8 months were used. Blood pressure and BRS were determined separately before and after intragastric administration of ketanserin (0.3 and 3.0 mg/kg). Third, SHR-SP aged 5 months were treated with ketanserin for 12 weeks (0.3 mg and 3.0 mg/kg per day). At the end of the treatment, blood pressure and BRS were determined and the end-organ damage was evaluated. Last, SHR-SP aged 3 months were treated with ketanserin (0.3 and 3.0 mg/kg per day) for life and the survival time was recorded. RESULTS Stroke was significantly delayed in rats with high BRS than those with low BRS (time to 50% death was 1.47-fold longer than low BRS group; P<0.01). Ketanserin of 3.0 mg/kg per day decreased blood pressure and enhanced BRS, whereas 0.3 mg/kg per day only enhanced the BRS. Fatal stroke incidences were markedly reduced by treatment with both doses (P<0.0001 versus control group). CONCLUSIONS The present study provides evidence that BRS is an independent predictor for stroke in hypertension. Restoration of BRS may be a new strategy for the prevention of stroke.
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Affiliation(s)
- Ai-Jun Liu
- Department of Pharmacology, School of Pharmacy, Second Military Medical University, Shanghai, China
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Van Vliet BN, Chafe LL, Halfyard SJ, Leonard AM. Distinct rapid and slow phases of salt-induced hypertension in Dahl salt-sensitive rats. J Hypertens 2007; 24:1599-606. [PMID: 16877963 DOI: 10.1097/01.hjh.0000239296.25260.e0] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
OBJECTIVE To test the hypothesis that Dahl salt-sensitive (Dahl-S) rats exhibit distinct and separable phases of salt sensitivity. METHODS Blood pressure (BP) telemetry was used to describe the detailed time course of salt-induced hypertension in Dahl-S rats and in hybrid rats derived from Dahl-S and Dahl salt-resistant strains. RESULTS Switching to a high salt (4% NaCl) diet led to a biphasic increase in BP. Phase-1 reached a plateau in 4 days whereas phase-2 progressed slowly over the subsequent 5 weeks. In hybrid rats, phase-1 was present in each rat whereas phase-2 was absent in many individuals. A correlation of the amplitude of the first and second phases was of borderline significance in Dahl-S rats (P = 0.053, R2 = 0.44, n = 9) but was clearly significant in hybrid rats (P < 0.0001, R2 = 0.78, n = 22). Increases in BP were reversible following 1 week of high salt but progressively less so after 4 and 7 weeks. Estimation of the chronic pressure-natriuresis relationship suggests that phase-1 is attributable to a reduced slope of this relationship. In contrast, phase-2 corresponds with a further reduction in slope and a progressive and irreversible resetting of the relationship to higher BP levels. CONCLUSIONS Two phases of salt sensitivity coexist and provide distinct contributions to salt-induced hypertension in Dahl-S rats. Our data also suggest that short-term measures of salt-sensitivity may be predictive of the effect of salt on the eventual progression of salt-induced hypertension.
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Affiliation(s)
- Bruce N Van Vliet
- Basic Medical Science Division, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
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Abstract
The kidney displays highly efficient autoregulation so that under steady-state conditions renal blood flow (RBF) is independent of blood pressure over a wide range of pressure. Autoregulation occurs in the preglomerular microcirculation and is mediated by two, perhaps three, mechanisms. The faster myogenic mechanism and the slower tubuloglomerular feedback contribute both directly and interactively to autoregulation of RBF and of glomerular capillary pressure. Multiple experiments have been used to study autoregulation and can be considered as variants of two basic designs. The first measures RBF after multiple stepwise changes in renal perfusion pressure to assess how a biological condition or experimental maneuver affects the overall pressure-flow relationship. The second uses time-series analysis to better understand the operation of multiple controllers operating in parallel on the same vascular smooth muscle. There are conceptual and experimental limitations to all current experimental designs so that no one design adequately describes autoregulation. In particular, it is clear that the efficiency of autoregulation varies with time and that most current techniques do not adequately address this issue. Also, the time-varying and nonadditive interaction between the myogenic mechanism and tubuloglomerular feedback underscores the difficulty of dissecting their contributions to autoregulation. We consider the modulation of autoregulation by nitric oxide and use it to illustrate the necessity for multiple experimental designs, often applied iteratively.
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Affiliation(s)
- William A Cupples
- Centre for Biomedical Research and Dept. of Biology, Univ. of Victoria, PO Box 3020, STN CSC, Victoria, BC, Canada.
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Barrett CJ, Guild SJ, Ramchandra R, Malpas SC. Baroreceptor denervation prevents sympathoinhibition during angiotensin II-induced hypertension. Hypertension 2005; 46:168-72. [PMID: 15911743 DOI: 10.1161/01.hyp.0000168047.09637.d4] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Arterial baroreflexes are well established to provide the basis for short-term control of arterial pressure; however, their role in long-term pressure control is more controversial. We proposed that if the sustained decrease in renal sympathetic nerve activity (RSNA) we observed previously in response to angiotensin II-induced hypertension is baroreflex mediated, then the decrease in RSNA in response to angiotensin II would not occur in sinoaortic-denervated (SAD) animals. Arterial pressure and RSNA were recorded continuously via telemetry in sham and SAD rabbits living in their home cages before, during, and after a 7-day infusion of angiotensin II (50 ng . kg(-1) . min(-1)). The arterial pressure responses in the 2 groups of rabbits were not significantly different (82+/-3 mm Hg sham versus 83+/-3 mm Hg SAD before angiotensin II infusion, and 101+/-6 mm Hg sham versus 100+/-4 mm Hg SAD day 6 of angiotensin II). In sham rabbits, there was a significant sustained decrease in RSNA (53+/-7% of baseline on day 2 and 65+/-7% on day 6 of the angiotensin II). On ceasing the angiotensin II, all variables recovered to baseline. In contrast, RSNA did not change in SAD rabbits with the angiotensin II infusion (RSNA was 98+/-8% of baseline on day 2 and 98+/-8% on day 6 of the angiotensin II infusion). These results support our hypothesis that the reduction in RSNA in response to a pressor dose of angiotensin II is dependent on an intact arterial baroreflex pathway.
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Barrett CJ, Malpas SC. Problems, possibilities, and pitfalls in studying the arterial baroreflexes’ influence over long-term control of blood pressure. Am J Physiol Regul Integr Comp Physiol 2005; 288:R837-45. [PMID: 15793037 DOI: 10.1152/ajpregu.00456.2004] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
While there is no disputing the critical role of baroreflexes in buffering rapid changes in arterial pressure, their role in long-term pressure control has become an area of controversy. Recent experiments using novel techniques have challenged the traditional view that arterial baroreflexes are not involved in setting chronic arterial pressure levels. Resetting of the arterial baroreflex, often used as an argument against the arterial baroreflex playing a role in long-term pressure control is rarely complete. The arterial baroreflex is just one of the many neural, hormonal, and intrinsic mechanisms involved in arterial pressure control and while the removal of the arterial baroreflex alone has little effect on mean arterial pressure it is too simplistic to suggest that the baroreflex has no role in long-term pressure control. Renal sympathetic nerve activity appears to be particularly resistant to resetting in response to ANG II-induced hypertension. Given the important role of the kidneys in long-term pressure control, we suggest there is a clear need to develop experimental techniques whereby sympathetic nerve activity to the kidneys and other organs can be monitored over periods of weeks to months.
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Affiliation(s)
- Carolyn J Barrett
- Circulatory Control Laboratory, Dept. of Physiology, Univ. of Auckland Medical School, Private Bag 92019, Auckland, New Zealand
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Eto M, Toba K, Akishita M, Kozaki K, Watanabe T, Kim S, Hashimoto M, Ako J, Iijima K, Sudoh N, Yoshizumi M, Ouchi Y. Impact of Blood Pressure Variability on Cardiovascular Events in Elderly Patients with Hypertension. Hypertens Res 2005; 28:1-7. [PMID: 15969248 DOI: 10.1291/hypres.28.1] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Blood pressure variability is one of the characteristic features of hypertension in the elderly. However, its clinical significance remains to be determined. We therefore examined the impact of blood pressure variability on the development of cardiovascular events in elderly hypertensive patients. A total of 106 consecutive hypertensive patients aged more than 60 years old (mean age, 73.9 +/- 8.1 years old; male, 54%), all of whom underwent 24-h ambulatory blood pressure monitoring, were followed up (median, 34 months; range, 3-60 months). During the follow-up period, 39 cardiovascular events were observed, including 14 cases of cerebral infarction and 7 cases of acute myocardial infarction. The coefficient of variation (CV) of 24-h systolic blood pressure (SBP) values was used as an index of blood pressure variability. The patients showed a mean CV value of 10.6%, and were divided into two groups according to this mean value as a cut-off point: a high CV group (n = 46) and a low CV group (n = 60). Although baseline clinical characteristics were similar in the two groups, Kaplan-Meier plots for event-free survival revealed that the rate of cardiovascular events was significantly higher in high CV group than in low CV group (p < 0.05). Cox's proportional hazards analysis showed that increased blood pressure variability (a high CV value of 24-h SBP) was an independent predictive variable for cardiovascular events. The CV value of daytime SBP and the SD value of both 24-h SBP and daytime SBP also had positive correlations with the onset of cardiovascular events. These results suggest that increased blood pressure variability may be an independent risk factor for cardiovascular events in elderly hypertensive patients.
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Affiliation(s)
- Masato Eto
- Department of Geriatric Medicine, Graduate School of Medicine, University of Tokyo, Tokyo, Japan
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Igosheva N, Klimova O, Anishchenko T, Glover V. Prenatal stress alters cardiovascular responses in adult rats. J Physiol 2004; 557:273-85. [PMID: 15034122 PMCID: PMC1665046 DOI: 10.1113/jphysiol.2003.056911] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Environmental factors in early life are clearly established risk factors for cardiovascular disease in later life. Most studies have focused on nutritional programming and analysed basal cardiovascular parameters rather than responses. In the present study we have investigated whether prenatal stress has long-term effects on cardiovascular responses in adult offspring. Female pregnant Sprague-Dawley rats were subjected to stress three times daily from day 15 to day 21 of gestation. Litters from stressed and control females were cross-fostered at birth to control for mothering effects. When the offspring were 6 months old, blood pressure was measured in the conscious rats through implanted catheters at rest, during restraint stress and during recovery. Basal haemodynamic parameters were similar in the different groups but the pattern of cardiovascular responses during stress and recovery differed markedly between prenatally stressed (PS) and control animals. PS rats had higher and longer-lasting systolic arterial pressure elevations to restraint stress than control animals. They also showed elevated systolic and diastolic blood pressure values during the recovery phase. PS rats demonstrated a greater increase in blood pressure variability compared with control animals during exposure to restraint stress, and showed more prolonged heart rate responses to acute stress and delayed recovery than controls. There was no effect of prenatal stress on baroreflex regulation of heart rate. PS females showed a greater increase in systolic arterial pressure and blood pressure variability and delayed heart rate recovery following return to the home cage then did PS males. These findings demonstrate for the first time that prenatal stress can induce long-term, sex-related changes in the sensitivity of the cardiovascular system to subsequent stress.
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Affiliation(s)
- N Igosheva
- Department of Biology, University of Saratov, Saratov, Astrakhanskaya str. 83, 410026, Saratov, Russia.
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Lanfranchi PA, Somers VK. Arterial baroreflex function and cardiovascular variability: interactions and implications. Am J Physiol Regul Integr Comp Physiol 2002; 283:R815-26. [PMID: 12228049 DOI: 10.1152/ajpregu.00051.2002] [Citation(s) in RCA: 186] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The arterial baroreflex contributes importantly to the short-term regulation of blood pressure and cardiovascular variability. A number of factors (including reflex, humoral, behavioral, and environmental) may influence gain and effectiveness of the baroreflex, as well as cardiovascular variability. Many central neural structures are also involved in the regulation of the cardiovascular system and contribute to the integrity of the baroreflex. Consequently, brain injuries or ischemia may induce baroreflex impairment and deranged cardiovascular variability. Baroreflex dysfunction and deranged cardiovascular variability are also common findings in cardiovascular disease. A blunted baroreflex gain and impaired heart rate variability are predictive of poor outcome in patients with heart failure and myocardial infarction and may represent an early index of autonomic activation in left ventricular dysfunction. The mechanisms mediating these relationships are not well understood and may in part be the result of cardiac structural changes and/or altered central neural processing of baroreflex signals.
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Narkiewicz K, Winnicki M, Schroeder K, Phillips BG, Kato M, Cwalina E, Somers VK. Relationship between muscle sympathetic nerve activity and diurnal blood pressure profile. Hypertension 2002; 39:168-72. [PMID: 11799097 DOI: 10.1161/hy1201.097302] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The physiological mechanisms mediating the variability and diurnal rhythm of blood pressure are unclear. We tested the hypothesis that resting sympathetic activity is linked to the variability characteristics and 24-hour profile of ambulatory blood pressure measurements. We evaluated the relationship between muscle sympathetic nerve activity (MSNA) and the level, variability, and nocturnal fall of ambulatory blood pressure in 69 normal men. Subjects were subdivided according to the tertiles of MSNA distributions. Mean 24-hour blood pressure was not significantly different across the 3 groups. Compared with subjects in the first tertile (lowest MSNA, <18 bursts/min), subjects in the third tertile (highest MSNA, >25 bursts/min) had significantly greater daytime blood pressure variability, whether expressed as absolute values (10.2+/-0.5 versus 8.1+/-0.4 mm Hg for systolic blood pressure and 9.4+/-0.4 versus 7.2+/-0.4 mm Hg for diastolic blood pressure; P<0.01 for both comparisons) or as variation coefficients (8.1+/-0.4% versus 6.6+/-0.3% for systolic blood pressure and 12.7+/-0.7% versus 10.1+/-0.6% for diastolic blood pressure; P<0.01 for both comparisons). Subjects in the third tertile also had a more striking absolute and percentage fall in systolic blood pressure from daytime to nighttime than subjects in the first tertile (17+/-2 versus 10+/-2 mm Hg, P=0.02, or 13+/-1% versus 8.2+/-1.4%, P=0.02). In conclusion, higher resting measurements of sympathetic traffic are associated with greater daytime blood pressure variability and a more marked nocturnal decline in blood pressure in normal subjects. These findings suggest that sympathetic neural mechanisms may contribute importantly to the regulation of blood pressure over the 24-hour period.
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Affiliation(s)
- Krzysztof Narkiewicz
- Department of Hypertension and Diabetology, Medical University of Gdansk, Gdansk, Poland
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Pires SL, Barrès C, Sassard J, Julien C. Renal blood flow dynamics and arterial pressure lability in the conscious rat. Hypertension 2001; 38:147-52. [PMID: 11463776 DOI: 10.1161/01.hyp.38.1.147] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
It is not known whether renal blood flow (RBF) is still autoregulated when the kidney is exposed to large transient blood pressure (BP) fluctuations such as those occurring spontaneously in conscious sinoaortic baroreceptor-denervated (SAD) rats. In this study, BP and RBF were simultaneously recorded in 8 SAD rats (2 weeks before study) and 8 baroreceptor-intact rats during approximately 3 hours of spontaneous activity. The kidney used for RBF recordings was denervated to prevent the interference of changes in renal sympathetic tone with autoregulatory mechanisms. In intact rats, RBF variability (coefficient of variation 9.1+/-0.8%) was larger (P<0.02) than BP variability (5.9+/-0.2%). This was mainly because of slow changes in RBF that were unrelated to BP and also to a prominent oscillation of RBF of approximately 0.25-Hz frequency. Autoregulatory patterns were identified at frequencies <0.1 Hz and provided a modest attenuation of BP fluctuations. In SAD rats, RBF variability (12.4+/-1.6%) was lower (P<0.02) than BP variability (18.2+/-1.1%). Autoregulation powerfully attenuated BP changes <0.1 Hz (normalized transfer gain 0.21+/-0.02 in the 0.0015- to 0.01-Hz frequency range) but at the expense of an oscillation located at approximately 0.05 Hz that possibly reflected the operation of the tubuloglomerular feedback. Large transient hypertensive episodes were not translated into RBF changes in SAD rats. We conclude that autoregulatory mechanisms have an ample capacity to protect the kidney against spontaneous BP fluctuations in the conscious rat. This capacity is not fully used under normal conditions of low BP variability.
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Affiliation(s)
- S L Pires
- Département de Physiologie et Pharmacologie Clinique, CNRS UMR 5014, Institut Fédératif de Recherche Cardio-Vasculaire No. 39, Université Claude Bernard, Lyon, France
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Van Vliet BN, Chafe LL, Montani JP. Contribution of baroreceptors and chemoreceptors to ventricular hypertrophy produced by sino-aortic denervation in rats. J Physiol 1999; 516 ( Pt 3):885-95. [PMID: 10200434 PMCID: PMC2269302 DOI: 10.1111/j.1469-7793.1999.0885u.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. To test whether sino-aortic denervation (SAD)-induced right ventricular hypertrophy (RVH) is a consequence of baroreceptor or chemoreceptor denervation, we compared the effects of aortic denervation (AD), carotid denervation (CD), SAD and a SAD procedure modified to spare the carotid chemoreceptors (mSAD), 6 weeks after denervation surgery in rats. A sham surgery group served as the control. 2. The blood pressure (BP) level was unaffected by AD, CD or SAD, but increased (9 %) following mSAD. The mean heart rate level was not affected. Short-term BP variability was elevated following AD (81 %), SAD (144 %) and mSAD (146 %), but not after CD. Baroreflex heart rate responses to phenylephrine were attenuated in all denervation groups. 3. Significant RVH occurred only following CD and SAD. These procedures also produced high mortality (CD and SAD) and significant increases in right ventricular pressures and haematocrit (CD). 4. Significant left ventricular hypertrophy occurred following CD, SAD and mSAD. Normalized left ventricular weight was significantly correlated with indices of BP variability. 5. These results suggest that SAD-induced RVH is a consequence of chemoreceptor, not baroreceptor, denervation. Our results also demonstrate that a mSAD procedure designed to spare the carotid chemoreceptors produced profound baroreflex dysfunction and significant left, but not right, ventricular hypertrophy.
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Affiliation(s)
- B N Van Vliet
- Faculty of Medicine, Memorial University of Newfoundland, St John's, Newfoundland, Canada,A1B 3V6.
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Narkiewicz K, Montano N, Cogliati C, van de Borne PJ, Dyken ME, Somers VK. Altered cardiovascular variability in obstructive sleep apnea. Circulation 1998; 98:1071-7. [PMID: 9736593 DOI: 10.1161/01.cir.98.11.1071] [Citation(s) in RCA: 370] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Altered cardiovascular variability is a prognostic indicator for cardiovascular events. Patients with obstructive sleep apnea (OSA) are at an increased risk for cardiovascular disease. We tested the hypothesis that OSA is accompanied by alterations in cardiovascular variability, even in the absence of overt cardiovascular disease. METHODS AND RESULTS Spectral analysis of variability of muscle sympathetic nerve activity, RR interval, and blood pressure were obtained during undisturbed supine rest in 15 patients with moderate-to-severe OSA, 18 patients with mild OSA, and 16 healthy control subjects in whom sleep disordered breathing was excluded by complete overnight polysomnography. Patients with OSA were newly diagnosed, never treated for OSA, and free of any other known diseases. Patients with moderate-to-severe OSA had shorter RR intervals (793+/-27 ms) and increased sympathetic burst frequency (49+/-4 bursts/min) compared with control subjects (947+/-42 ms; 24+/-3 bursts/min; P=0.008 and P<0.001, respectively). In these patients, total variance of RR was reduced (P=0.01) and spectral analysis of RR variability showed an increase in low frequency normalized units, a decrease in high frequency normalized units, and an increase in the ratio of low to high frequency (all P<0.05). Even though blood pressure was similar to that of the control subjects, blood pressure variance in patients with moderate-to-severe OSA was more than double the variance in control subjects (P=0.01). Patients with mild OSA also had a reduction in RR variance (P=0.02) in the absence of any significant difference in absolute RR interval. For all patients with OSA, linear regression showed a positive correlation (r=0.40; P=0.02) between sleep apnea severity and blood pressure variance. CONCLUSIONS Cardiovascular variability is altered in patients with OSA. This alteration is evident even in the absence of hypertension, heart failure, or other disease states and may be linked to the severity of OSA. Abnormalities in cardiovascular variability may be implicated in the subsequent development of overt cardiovascular disease in patients with OSA.
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Affiliation(s)
- K Narkiewicz
- From the Departments of Internal Medicine and Neurology, Cardiovascular Division, University of Iowa, Iowa City, IA 52242, USA
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