Acetazolamide and inhaled carbon dioxide reduce periodic breathing during exercise in patients with chronic heart failure

Exercise oscillatory ventilation: the past, present, and future

Exercise oscillatory ventilation (EOV) is a fascinating event that can be appreciated in the cardiopulmonary exercise test and is characterized by a cyclic fluctuation of minute ventilation, tidal volume, oxygen uptake, carbon dioxide production, and end-tidal pressure for oxygen and carbon dioxide. Its mechanisms stem from a dysregulation of the normal control feedback of ventilation involving one or more of its components, namely, chemoreflex delay, chemoreflex gain, plant delay, and plant gain. In this review, we intend to breakdown therapeutic targets according to pathophysiology and revise the prognostic value of exercise oscillatory ventilation in the setting of heart failure and other diagnoses.

Breathing pattern and pulmonary gas exchange in elderly patients with and without left ventricular dysfunction-modification with exercise-based cardiac rehabilitation and prognostic value

Background

Inefficient ventilation is an established prognostic marker in patients with heart failure. It is not known whether inefficient ventilation is also linked to poor prognosis in patients with left ventricular dysfunction (LVD) but without overt heart failure.

Objectives

To investigate whether inefficient ventilation in elderly patients with LVD is more common than in patients without LVD, whether it improves with exercise-based cardiac rehabilitation (exCR), and whether it is associated with major adverse cardiovascular events (MACE).

Methods

In this large multicentre observational longitudinal study, patients aged ≥65 years with acute or chronic coronary syndromes (ACS, CCS) without cardiac surgery who participated in a study on the effectiveness of exCR in seven European countries were included. Cardiopulmonary exercise testing (CPET) was performed before, at the termination of exCR, and at 12 months follow-up. Ventilation (VE), breathing frequency (BF), tidal volume (VT), and end-expiratory carbon dioxide pressure (PETCO2) were measured at rest, at the first ventilatory threshold, and at peak exercise. Ventilatory parameters were compared between patients with and without LVD (based on cardio-echography) and related to MACE at 12 month follow-up.

Results

In 818 patients, age was 72.5 ± 5.4 years, 21.9% were women, 79.8% had ACS, and 151 (18%) had LVD. Compared to noLVD, in LVD resting VE was increased by 8%, resting BF by 6%, peak VE, peak VT, and peak PETCO2 reduced by 6%, 8%, and 5%, respectively, and VE/VCO2 slope increased by 11%. From before to after exCR, resting VE decreased and peak PETCO2 increased significantly more in patients with compared to without LVD. In LVD, higher resting BF, higher nadir VE/VCO2, and lower peak PETCO2 at baseline were associated with MACE.

Conclusions

Similarly to patients with HF, in elderly patients with ischemic LVD, inefficient resting and exercise ventilation was associated with worse outcomes, and ExCR alleviated abnormal breathing patterns and gas exchange parameters.

Effects of acetazolamide on control of breathing in sleep apnea patients: Mechanistic insights using meta-analyses and physiological model simulations

Obstructive and central sleep apnea affects ~1 billion people globally and may lead to serious cardiovascular and neurocognitive consequences, but treatment options are limited. High loop gain (ventilatory instability) is a major pathophysiological mechanism underlying both types of sleep apnea and can be lowered pharmacologically with acetazolamide, thereby improving sleep apnea severity. However, individual responses vary and are strongly correlated with the loop gain reduction achieved by acetazolamide. To aid with patient selection for long-term trials and clinical care, our goal was to understand better the factors that determine the change in loop gain following acetazolamide in human subjects with sleep apnea. Thus, we (i) performed several meta-analyses to clarify how acetazolamide affects ventilatory control and loop gain (including its primary components controller/plant gain), and based on these results, we (ii) performed physiological model simulations to assess how different baseline conditions affect the change in loop gain. Our results suggest that (i) acetazolamide primarily causes a left shift of the chemosensitivity line thus lowering plant gain without substantially affecting controller gain; and (ii) higher controller gain, higher paCO2 at eupneic ventilation, and lower CO2 production at baseline result in a more pronounced loop gain reduction with acetazolamide. In summary, the combination of mechanistic meta-analyses with model simulations provides a unified framework of acetazolamide's effects on ventilatory control and revealed physiological predictors of response, which are consistent with empirical observations of acetazolamide's effects in different sleep apnea subgroups. Prospective studies are needed to validate these predictors and assess their value for patient selection.

Positionspapier „Schlafmedizin in der Kardiologie“, Update 2021

Es hat sich viel getan in der Welt der Schlafmedizin in der Kardiologie, weshalb eine vollwertige Überarbeitung des Positionspapiers „Schlafmedizin in der Kardiologie“ erforderlich wurde. In der aktuellen neuartigen Version finden sich nicht nur alle verfügbaren Studien, Literaturstellen und Updates zu Pathophysiologie, Diagnostik- und Therapieempfehlungen, sondern auch Ausblicke auf neue Entwicklungen und zukünftige Forschungserkenntnisse. Dieses überarbeitete Positionspapier gibt Empfehlungen für Diagnostik und Therapie von Patienten mit kardiovaskulären Erkrankungen mit schlafassoziierten Atmungsstörungen und erteilt darüber hinaus einen fundierten Überblick über verfügbare Therapien und Evidenzen, gibt aber ebenso Ratschläge wie mit Komorbiditäten umzugehen ist. Insbesondere enthält dieses überarbeitete Positionspapier aktualisierte Stellungnahmen zu schlafassoziierten Atmungsstörungen bei Patienten mit koronarer Herzerkrankung, Herzinsuffizienz, arterieller Hypertonie, aber auch für Patienten mit Vorhofflimmern. Darüber hinaus finden sich erstmals Empfehlungen zur Telemedizin als eigenes, neues Kapitel. Dieses Positionspapier bietet Kardiologen sowie Ärzten in der Behandlung von kardiovaskulären Patienten die Möglichkeit einer evidenzbasierten Behandlung der wachsend bedeutsamen und mit zunehmender Aufmerksamkeit behafteten Komorbidität schlafassoziierter Atmungsstörungen. Und nicht zuletzt besteht mit diesem neuen Positionspapier eine enge Verknüpfung mit dem neuen Curriculum Schlafmedizin der Deutschen Gesellschaft für Kardiologie, weshalb dieses Positionspapier eine Orientierung für die erworbenen Fähigkeiten des Curriculums im Umgang von kardiovaskulären Patienten mit schlafassoziierten Atmungsstörungen darstellt.

The role of acetazolamide in sleep apnea at sea level: a systematic review and meta-analysis

STUDY OBJECTIVES

The recognition of specific endotypes as drivers of sleep apnea suggests the need of therapies targeting individual mechanisms. Acetazolamide is known to stabilize respiration at high altitude but benefits at sea level are less well understood.

METHODS

All controlled studies of acetazolamide in obstructive sleep apnea and/or central sleep apnea (CSA) were evaluated. The primary outcome was the apnea-hypopnea index.

RESULTS

Fifteen trials with a total of 256 patients were pooled in our systematic review. Acetazolamide reduced the overall apnea-hypopnea index (mean difference [MD] -15.82, 95% CI: -21.91 to -9.74, P < .00001) in central sleep apnea (MD -22.60, 95% CI: -29.11 to -16.09, P < .00001), but not in obstructive sleep apnea (MD -10.29, 95% CI: -33.34 to 12.77, P = .38). Acetazolamide reduced the respiratory related arousal index (MD -0.82, 95% CI: -1.56 to -0.08, P = .03), improved partial arterial of oxygen (MD 11.62, 95% CI: 9.13-14.11, P < .00001), mean oxygen saturation (MD 1.78, 95% CI: 0.53-3.04, P = .005), total sleep time (MD 25.74, 95% CI: 4.10-47.38, P = .02), N2 sleep (MD 3.34, 95% CI: 0.12-6.56, P = .04) and sleep efficiency (MD 4.83, 95% CI: 0.53-9.13, P = .03).

CONCLUSIONS

Acetazolamide improves the apnea-hypopnea index and several sleep metrics in central sleep apnea. The drug may be of clinical benefit in patients with high loop gain apnea of various etiologies and patterns. The existence of high heterogeneity is an important limitation in applicability of our analysis.

SYSTEMATIC REVIEW REGISTRATION

Registry: PROSPERO; Name: The effect of acetazolamide in patients with sleep apnea at sea level: a systematic review and meta analysis; URL: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020163316; Identifier: CRD42020163316.

Exercising in Hypoxia and Other Stimuli: Heart Rate Variability and Ventilatory Oscillations

Periodic breathing is a respiratory phenomenon frequently observed in patients with heart failure and in normal subjects sleeping at high altitude. However, until recently, periodic breathing has not been studied in wakefulness and during exercise. This review relates the latest findings describing this ventilatory disorder when a healthy subject is submitted to simultaneous physiological (exercise) and environmental (hypoxia, hyperoxia, hypercapnia) or pharmacological (acetazolamide) stimuli. Preliminary studies have unveiled fundamental physiological mechanisms related to the genesis of periodic breathing characterized by a shorter period than those observed in patients (11~12 vs. 30~60 s). A mathematical model of the respiratory system functioning under the aforementioned stressors corroborated these data and pointed out other parameters, such as dead space, later confirmed in further research protocols. Finally, a cardiorespiratory interdependence between ventilatory oscillations and heart rate variability in the low frequency band may partly explain the origin of the augmented sympathetic activation at exercise in hypoxia. These nonlinear instabilities highlight the intrinsic "homeodynamic" system that allows any living organism to adapt, to a certain extent, to permanent environmental and internal perturbations.

Roles of periodic breathing and isocapnic buffering period during exercise in heart failure

In heart failure, exercise - induced periodic breathing and end tidal carbon dioxide pressure value during the isocapnic buffering period are two features identified at cardiopulmonary exercise testing strictly related to sympathetic activation. In the present review we analysed the physiology behind periodic breathing and the isocapnic buffering period and present the relevant prognostic value of both periodic breathing and the presence/absence of the identifiable isocapnic buffering period.

Acetazolamide for OSA and Central Sleep Apnea: A Comprehensive Systematic Review and Meta-Analysis

BACKGROUND

Therapy options for OSA and central sleep apnea (CSA) are limited, thus many patients remain untreated. Clinically, acetazolamide is sometimes used for CSA; however, given overlapping pathophysiologic properties of OSA and CSA, we hypothesized that acetazolamide is equally effective for both types. Prior reviews focused on specific subtypes of sleep apnea, study designs, and languages, thus including few studies (typically ≤3) limiting insights.

RESEARCH QUESTION

How efficacious is acetazolamide for sleep apnea, and is its effect modified by sleep apnea type or acetazolamide dose?

STUDY DESIGN AND METHODS

We queried MEDLINE, EMBASE, and ClinicalTrials.gov from inception until March 11, 2019. Any study in which adults with OSA/CSA received oral acetazolamide vs no acetazolamide (control) that reported sleep apnea-related outcomes was eligible, independent of study design or language. Two reviewers independently assessed eligibility and abstracted data. Primary outcomes were apnea-hypopnea index (AHI) and oxygen saturation nadir. Quality of evidence (QoE) was rated with the use of Grades of Recommendation Assessment, Development and Evaluation methods.

RESULTS

We included 28 studies (13 OSA/15 CSA; N_{Subjects,Acetazolamide} = 542; N_{Subjects,Control} = 553) that enabled meta-analyses for 24 outcomes. Acetazolamide doses ranged from 36 to 1000 mg/d and treatment duration from 1 to 90 d (median, 6 d). Overall, acetazolamide vs control lowered the AHI by -0.7 effect sizes (95% CI, -0.83 to -0.58; I² = 0%; moderate QoE) that corresponded to a reduction of 37.7% (95% CI, -44.7 to -31.3) or 13.8/h (95% CI, -16.3 to -11.4; AHI_Control = 36.5/h). The AHI reduction was similar in OSA vs CSA, but significantly greater with higher doses (at least up to 500 mg/d). Furthermore, acetazolamide improved oxygen saturation nadir by +4.4% (95% CI, 2.3 to 6.5; I² = 63%; no evidence of effect modification; very low QoE) and several secondary outcomes that included sleep quality measures and BP (mostly low QoE).

INTERPRETATION

Short-term acetazolamide improved both OSA and CSA. Rigorous studies with long-term follow up are warranted to assess Acetazolamide's value for the chronic treatment of patients with sleep apnea.

CLINICAL TRIAL REGISTRATION

PROSPERO (CRD42019147504).

Mitigation of Exercise Oscillatory Ventilation Score by Cardiac Resynchronization Therapy

BACKGROUND

Exercise oscillatory ventilation (EOV) is a consequence of ventilatory control system instability and is commonly observed in patients with advanced heart failure (HF); it is associated with adverse prognosis. The goal of this study was to evaluate the effects of cardiac resynchronization therapy (CRT) on oscillatory ventilation as quantified by a proposed EOV score.

METHODS AND RESULTS

Consecutive patients with HF (N = 35) who underwent clinically indicated CRT, cardiopulmonary exercise testing and carbon dioxide (CO₂) chemosensitivity by rebreathe before and 4-6 months after CRT were included in this post hoc analysis. With CRT, EOV scores improved in 22 patients (63%). In these patients, left ventricular ejection fraction, left atrial volume, brain natriuretic peptide concentration, and CO₂ chemosensitivity significantly improved after CRT (P < 0.05). Furthermore, minute ventilation per unit CO₂ production significantly decreased, and end-tidal CO₂ increased at rest and at peak exercise post-CRT. Multiple regression analysis showed only the change of CO₂ chemosensitivity to be significantly associated with the improvement of the EOV score (b = 0.64; F = 11.3; P = 0.004). In the group without EOV score improvement (n = 13), though left ventricular ejection fraction significantly increased with CRT (P = 0.015), no significant changes in ventilation or gas exchange were observed.

CONCLUSION

The EOV score was mitigated by CRT and was associated with decreased CO₂ chemosensitivity.

Exertional Periodic Breathing in Heart Failure: Mechanisms and Clinical Implications

Periodic breathing (PB) during exercise is a slow, prominent, consistent fluctuation in ventilation and derived parameters that may be persistent for the entire exercise or present only in the early phases of exercise. It is associated with a negative prognosis, particularly if concomitant with PB during sleep. Little is known about exercise-induced PB physiology, but hyperventilation is likely due to an increased sympathetic activity combined with an enhanced stimulation of intrapulmonary, chemoreceptors and metaboreceptors, low cardiac output leading to increased circulatory delay, and cerebrovascular reactivity to CO2, all with have a definite role.

Acetazolamide Therapy in Patients with Heart Failure: A Meta-Analysis

Background and objectives: Fluid overload and central sleep apnea are highly prevalent in patients with heart failure (HF). We performed this meta-analysis to assess the effects of acetazolamide therapy on acid/base balance and apnea indexes. Methods: A literature search was conducted using EMBASE, MEDLINE, and Cochrane Database from inception through 18 November 2017 to identify studies evaluating the use of acetazolamide in HF. Study results were analyzed using a random effects model. The protocol for this systematic review is registered with PROSPERO (International Prospective Register of Systematic Reviews; no. CRD42017065401). Results: Nine studies (three randomized controlled trials and six cohort studies) with a total of 229 HF patients were enrolled. After acetazolamide treatment, there were significant decreases in serum pH (mean difference (MD) of −0.04 (95% CI, −0.06 to −0.02)), pCO₂ (MD of −2.06 mmHg (95% CI, −3.60 to −0.53 mmHg)), and serum bicarbonate levels (MD of −6.42 mmol/L (95% CI, −10.05 to −2.79 mmol/L)). When compared to a placebo, acetazolamide significantly increased natriuresis (standardized mean difference (SMD) of 0.67 (95% CI, 0.08 to 1.27)), and decreased the apnea-hypopnea index (AHI) (SMD of −1.06 (95% CI, −1.75 to −0.36)) and central apnea index (CAI) (SMD of −1.10 (95% CI, −1.80 to −0.40)). Egger’s regression asymmetry tests revealed no publication bias with p = 0.20, 0.75 and 0.59 for analysis of the changes in pH, pCO₂, and serum bicarbonate levels with use of acetazolamide in HF patients. Conclusion: Our study demonstrates significant reduction in serum pH, increase in natriuresis, and improvements in apnea indexes with use of acetazolamide among HF patients.

Acetazolamide attenuates cardiac fibrosis induced by aortic constriction through inhibiting transforming growth factor-β1/Smad2 signaling pathway in mice

The effect and mechanism of acetazolamide on cardiac fibrosis induced by transverse aortic constriction (TAC) were investigated. C57BL/6 mice were subjected to TAC or sham operation and then were orally gavaged with acetazolamide (20 mg/kg/day). After 4 weeks of operation, cardiac function was detected by echocardiography. Interstitial fibrosis was stained with Masson's trichrome. The expression of α-smooth muscle actin (α-SMA), collagen I, transforming growth factor-β1 (TGF-β1) and Smad2 were measured by western blotting. The TAC mice displayed significant cardiac dysfunction and fibrosis. The expression of α-SMA, collagen I, TGF-β1 and p-Smad2 in the TAC group was higher than those in the sham group. By contrast, acetazolamide administration inhibited interstitial fibrosis, as well as improved cardiac dysfunction induced by TAC. Acetazolamide also reduced the expression of α-SMA, collagen I, TGF-β1 and p-Smad2 in the TAC mice. Acetazolamide was able to attenuate cardiac fibrosis and improve cardiac dysfunction. The molecular mechanism involved in the anti-fibrotic effect of acetazolamide possibly was through inhibiting TGF-β1/Smad2 signaling pathway.

Pulmonary Circulation Transvascular Fluid Fluxes Do Not Change during General Anesthesia in Dogs

General anesthesia (GA) can cause abnormal lung fluid redistribution. Pulmonary circulation transvascular fluid fluxes (J_VA) are attributed to changes in hydrostatic forces and erythrocyte volume (EV) regulation. Despite the very low hydraulic conductance of pulmonary microvasculature it is possible that GA may affect hydrostatic forces through changes in pulmonary vascular resistance (PVR), and EV through alteration of erythrocyte transmembrane ion fluxes (_ionJ_VA). Furosemide (Fur) was also used because of its potential to affect pulmonary hydrostatic forces and _ionJ_VA. A hypothesis was tested that J_VA, with or without furosemide treatment, will not change with time during GA. Twenty dogs that underwent castration/ovariectomy were randomly assigned to Fur (n = 10) (4 mg/kg IV) or placebo treated group (Con, n = 10). Baseline arterial (BL) and mixed venous blood were sampled during GA just before treatment with Fur or placebo and then at 15, 30 and 45 min post-treatment. Cardiac output (Q) and pulmonary artery pressure (P_AP) were measured. J_VA and _ionJ_VA were calculated from changes in plasma protein, hemoglobin, hematocrit, plasma and whole blood ions, and Q. Variables were analyzed using random intercept mixed model (P < 0.05). Data are expressed as means ± SE. Furosemide caused a significant volume depletion as evident from changes in plasma protein and hematocrit (P < 0.001). However; Q, P_AP, and J_VA were not affected by time or Fur, whereas erythrocyte fluid flux was affected by Fur (P = 0.03). Furosemide also affected erythrocyte transmembrane K⁺ and Cl⁻, and transvascular Cl⁻ metabolism (P ≤ 0.05). No other erythrocyte transmembrane or transvascular ion fluxes were affected by time of GA or Fur. Our hypothesis was verified as J_VA was not affected by GA or ion metabolism changes due to Fur treatment. Furosemide and 45 min of GA did not cause significant hydrostatic changes based on Q and P_AP. Inhibition of Na⁺/K⁺/2Cl⁻ cotransport caused by Fur treatment, which can alter EV regulation and J_VA, was offset by the Jacobs Stewart cycle. The results of this study indicate that the Jacobs Stewart cycle/erythrocyte Cl⁻ metabolism can also act as a safety factor for the stability of lung fluid redistribution preserving optimal diffusion distance across the blood gas barrier.

Pharmacologic Approaches to Electrolyte Abnormalities in Heart Failure

Electrolyte abnormalities are common in heart failure and can arise from a variety of etiologies. Neurohormonal activation from ventricular dysfunction, renal dysfunction, and heart failure medications can perturb electrolyte homeostasis which impact both heart failure-related morbidity and mortality. These include disturbances in serum sodium, chloride, acid-base, and potassium homeostasis. Pharmacological treatments differ for each electrolyte abnormality and vary from older, established treatments like the vaptans or acetazolamide, to experimental or theoretical treatments like hypertonic saline or urea, or to newer, novel agents like the potassium binders: patiromer and zirconium cyclosilicate. Pharmacologic approaches range from limiting electrolyte intake or directly repleting the electrolyte, to blocking or promoting their resorption, and to neurohormonal antagonism. Because of the prevalence and clinical impact of electrolyte abnormalities, understanding both the older and newer therapeutic options is and will continue to be necessity for the management of heart failure.

Exercise oscillatory ventilation: Mechanisms and prognostic significance

Alteration in breathing patterns characterized by cyclic variation of ventilation during rest and during exercise has been recognized in patients with advanced heart failure (HF) for nearly two centuries. Periodic breathing (PB) during exercise is known as exercise oscillatory ventilation (EOV) and is characterized by the periods of hyperpnea and hypopnea without interposed apnea. EOV is a non-invasive parameter detected during submaximal cardiopulmonary exercise testing. Presence of EOV during exercise in HF patients indicates significant impairment in resting and exercise hemodynamic parameters. EOV is also an independent risk factor for poor prognosis in HF patients both with reduced and preserved ejection fraction irrespective of other gas exchange variables. Circulatory delay, increased chemosensitivity, pulmonary congestion and increased ergoreflex signaling have been proposed as the mechanisms underlying the generation of EOV in HF patients. There is no proven treatment of EOV but its reversal has been noted with phosphodiesterase inhibitors, exercise training and acetazolamide in relatively small studies. In this review, we discuss the mechanistic basis of PB during exercise and the clinical implications of recognizing PB patterns in patients with HF.

Altered breathing syndrome in heart failure: newer insights and treatment options

In patients with heart failure (HF), altered breathing patterns, including periodic breathing, Cheyne-Stokes breathing, and oscillatory ventilation, are seen in several situations. Since all forms of altered breathing cause similar detrimental effects on clinical outcomes, they may be considered collectively as an "altered breathing syndrome." Altered breathing syndrome should be recognized as a comorbid condition of HF and as a potential therapeutic target. In this review, we discuss mechanisms and therapeutic options of altered breathing while sleeping, while awake at rest, and during exercise.

The noncarbonic anhydrase inhibiting acetazolamide analog N-methylacetazolamide reduces the hypercapnic, but not hypoxic, ventilatory response

Previous studies have shown that the carbonic anhydrase (CA) inhibitors acetazolamide (AZ) and methazolamide (MZ) have inhibiting actions on breathing. Classically these have been attributed to CA inhibition, but other effects unrelated to CA inhibition have been identified in other tissues. To explore this possibility in the control of ventilation by the central nervous system, we investigated whether an AZ-analog without CA inhibiting properties, by virtue of a single methylation on the sulfonamide moiety, N-methylacetazolamide (NMA), would still display similar actions to acetazolamide and methazolamide. NMA (20 mg kg⁻¹) was given intravenously to anesthetized cats and we measured the responses to steady-state isocapnic hypoxia and stepwise changes in end-tidal pco₂ before and after infusion of this AZ analog using the technique of end-tidal forcing. NMA caused a large decrease in the apneic threshold and CO₂ sensitivity very similar to those previously observed with AZ and MZ, suggesting that these effects are mediated independently of CA inhibition. In contrast to acetazolamide, but similar to methazolamide, NMA did not affect the steady-state isocapnic hypoxic response. In conclusion, our data reveal complex effects of sulfonamides with very similar structure to AZ that reveal both CA-dependent and CA-independent effects, which need to be considered when using AZ as a probe for the role of CA in the control of ventilation.

Ventilatory oscillations at exercise: effects of hyperoxia, hypercapnia, and acetazolamide

Periodic breathing has been found in patients with heart failure and sleep apneas, and in healthy subjects in hypoxia, during sleep and wakefulness, at rest and, recently, at exercise. To unravel the cardiorespiratory parameters liable to modulate the amplitude and period of ventilatory oscillations, 26 healthy subjects were tested under physiological (exercise) and environmental (hypoxia, hyperoxia, hyperoxic hypercapnia) stresses, and under acetazolamide (ACZ) treatment. A fast Fourier transform spectral analysis of breath-by-breath ventilation evidenced an increase in peak power under hypercapnia (vs. normoxia and hyperoxia, P < 0.001) and a decrease under ACZ (vs. placebo, P < 0.001), whereas it was not modified in hyperoxia. period was shortened by exercise in all conditions (vs. rest, P < 0.01) and by hypercapnia (vs. normoxia, P < 0.05) but remained unchanged under ACZ (vs. placebo). peak power was positively related to cardiac output () and in hyperoxia (P < 0.01), in hypercapnia (P < 0.001) and under ACZ (P < 0.001). period was negatively related to and in hyperoxia (P < 0.01 and P < 0.001, respectively), in hypercapnia (P < 0.05 and P < 0.01, respectively) and under ACZ (P < 0.05 and P < 0.01, respectively). Total respiratory cycle time was the main factor responsible for changes in period. In conclusion, exercise, hypoxia, and hypercapnia increase ventilatory oscillations by increasing and , whereas ACZ decreases ventilatory instability in part by a contrasting action on O₂ and CO₂ sensing. An intrinsic oscillator might modulate ventilation through a complex system where peripheral chemoreflex would play a key role.

An overview of the applied definitions and diagnostic methods to assess exercise oscillatory ventilation--a systematic review

The variable "exercise oscillatory ventilation" (EOV), assessed during cardiopulmonary exercise test (CPET), recently became a fundamental prognostic parameter in patients with heart failure. In literature, various definitions are suggested, but an uniformly accepted description to identify EOV still lacks. We performed a systematic review of the literature in order to determine the different definitions and diagnostic techniques to assess EOV. A systematic search strategy was established and executed in seven databases (PubMed, Google Scholar, Cochrane Clinical Trials, Science Direct, Pedro, Web Of Science library and Medline (Ovid)) resulting in 605 citations after de-duplication. Full-text articles (n=124) were assessed for eligibility, resulting in 75 citations. The review accounted 17,440 patients of whom 4,638 subjects presented EOV. Seven studies described EOV in a non-heart failure population accounting 168 EOV subjects. The definitions could be categorized in nine subdivisions of which four (n=43) referred to an original description. The other subdivisions were combinations of the original definitions (n=11), quantifications (n=4), computational (n=3), vaguely described (n=8) or not defined (n=6). Symptom limited maximal exercise tests were conducted to assess EOV, however the modes, protocols, software and data sampling were divers. Heterogeneity in the numerous definitions to identify EOV and the vaguely described assessment methods are hindering the evolution to a standardized uniformly accepted definition and technique to identify this abnormal breathing pattern. Unity in definition and international adopted assessment is warranted to strengthen its validity as a prognostic marker and could promote communication. It may facilitate clinical trials on pathophysiology and origin of EOV.

Sex and acetazolamide effects on chemoreflex and periodic breathing during sleep at altitude

OBJECTIVE

Nocturnal periodic breathing occurs more frequently in men than in women with various clinical and pathophysiologic conditions. The mechanisms accounting for this sex-related difference are not completely understood. Acetazolamide effectively counteracts nocturnal periodic breathing, but it has been investigated almost exclusively in men. Our aim was to explore possible determinants of nocturnal periodic breathing in a high-altitude setting both in men and in women. We hypothesized that increased hypoxic chemosensitivity in men could be associated with the development of nocturnal periodic breathing at altitude more frequently than in women, and that acetazolamide, by leftward shifting the CO2 ventilatory response, could improve nocturnal periodic breathing at altitude in a sex-independent manner.

METHODS

Forty-four healthy lowlanders (21 women), randomized to acetazolamide or placebo, underwent cardiorespiratory sleep studies at sea level off treatment and under treatment on the first night after arrival at a 4,559-m altitude. Hypoxic and hypercapnic chemosensitivities were assessed at sea level.

RESULTS

Men, more frequently than women, exhibited increased hypoxic chemosensitivity and displayed nocturnal periodic breathing at altitude. Acetazolamide leftward shifted the CO2 set point and, at altitude, improved oxygenation and reduced periodic breathing in both sexes, but to a larger extent in men. Hypoxic chemosensitivity directly correlated with the number of apneas/hypopneas at altitude in the placebo group but not in the acetazolamide group.

CONCLUSIONS

The greater severity of periodic breathing during sleep displayed by men at altitude could be attributed to their increased hypoxic chemosensitivity. Acetazolamide counteracted the occurrence of periodic breathing at altitude in both sexes, modifying the apneic threshold and improving oxygenation.

TRIAL REGISTRY

EU Clinical Trials Register, EudraCT; No.: 2010-019986-27; URL: https://www.clinicaltrialsregister.eu.