Does obstructive sleep apnea impair the cardiopulmonary response to exercise?

Effect of Sleep-Disordered Breathing on Exercise Capacity after Myocardial Infarction - A Cross-Sectional Study

Background

Exercise capacity reflects the cardiovascular risk after myocardial infarction (MI). The study aims to evaluate the impact of sleep-disordered breathing (SDB) on exercise capacity after MI.

Methods

Consecutive patients referring to outpatient cardiac rehabilitation up to 28 days after MI and participating in the Polish Managed Care after Acute Myocardial Infarction (MC-AMI) program were included. On admission, we assessed the presence and the severity of SDB using the home sleep apnea test (HSAT), patients' maximum exercise capacity on a treadmill exercise stress test (EST), and a 6-minute walk test (6MWT), as well as the effect of SDB on the results obtained. In the multivariate analysis, we verified the strength of the observed associations concerning age, anthropometric parameters, and left ventricular ejection fraction (LVEF).

Results

A total of 254 patients aged 60.00 (interquartile range 51.00-67.00), including 39 (15.4%) women, with technically adequate HSAT, constituted the study group. Mild SDB was found in 82 (32.3%), moderate in 54 (21.3%), and severe in 51 (20.1%) patients. Among those diagnosed with SDB, obstructive sleep apnea (OSA) was dominant in 167 (89.8%). With the worsening of SDB, the distance in 6MWT and the maximum physical exertion achieved in EST, expressed in metabolic equivalents (METs) and maximal heart rate (MHR), decreased. The linear regression analysis confirmed the following: (1) inversely proportional relationship between the respiratory event index and METs, MHR, and 6MWT distance (p = 0.005, p = 0.008, and p = 0.004), and the maximum apnea duration and MET and 6MWT distance (p = 0.042 and p = 0.002); and (2) directly proportional relationship between mean arterial oxygen saturation ( SpO 2 ) during sleep and MET, MHR, and 6MWT distance (p = 0.019, p = 0.006, and p = 0.013), and minimum SpO 2 and MET and MHR (p = 0.040 and p < 0.001). However, the independent risk factors for impaired exercise capacity, determined using multivariable regression analysis, were age, female sex, higher body mass index (BMI), and decreased LVEF, but not SDB parameters.

Conclusions

SDB negatively impacts exercise capacity after MI. However, the strength of this association may be less pronounced due to the interaction of risk factors common for SDB and impaired exercise capacity, e.g., sex, age, BMI, and LVEF.

Exercise capacity remains supernormal, though mildly reduced in middle-aged military personnel with Moderate to Severe Obstructive Sleep Apnea

INTRODUCTION

The relationship between moderate to severe OSA and exercise capacity remains unclear. Prior studies showing a reduction in VO₂ max in this population have mostly involved middle-aged, overweight patients. We aimed to study this relationship in a similarly aged population of military personnel with previously undiagnosed moderate to severe OSA.

METHODS

We studied late-career male military personnel who underwent CPET and polysomnography (PSG). Patients were categorized either into an OSA group (apnea-hypopnea index (AHI) ≥ 15 events/h) or a control group (AHI < 15 events/h). VO₂ max was compared between groups.

RESULTS

170 male military personnel met criteria for the study. Mean AHI was 29.0/h in the OSA group (n = 58) versus 7.4/h in the controls (n = 112) while SpO₂ nadir was slightly lower (86.0% vs. 89.0%). Patients were of similar age (53.1 vs. 53.7 years), and BMI was slightly higher in the OSA group (27.5 kg/m² vs. 26.3 kg/m²). Percent-predicted VO₂ max was supernormal in both groups, though it was comparatively lower in the OSA group (117% vs. 125%; p < 0.001).

CONCLUSIONS

Military personnel with moderate to severe OSA were able to achieve supernormal VO₂ max values, yet had an 8% decrement in exercise capacity compared to controls. These findings suggest that OSA without significant hypoxemia may not significantly influence exercise capacity. It remains likely that the effects of untreated OSA on exercise capacity are complex and are affected by several variables including BMI, degree of associated hypoxemia, and regularity of exercise. Statistically lower VO₂ max noted in this study may suggest that untreated OSA in less fit populations may lead to significant decrements in exercise capacity.

Turkish Thoracic Society Early Career Members Task Force Group's Virtual Congress Notes: European Respiratory Society International Congress 2020

In this article, Early Career Task Force Group members of the Turkish Thoracic Society summarize the European Respiratory Society 2020 virtual congress. Current developments in the field of respiratory diseases were compiled with the addition of sessions specific to coronavirus disease 2019 this year. Almost all of the congress sessions were examined, and the important and striking results of the congress were highlighted. Congress sessions were attended by expert researchers, and the prominent messages of each session were highlighted in short summaries. They were then grouped under relevant titles and ranked in order of meaning and relation. It was finalized by a team of researchers.

Changes in Exercise Capacity of Patients With Obstructive Sleep Apnea Following Treatment With Continuous Positive Airway Pressure

Introduction: Patients with obstructive sleep apnea (OSA) frequently complain of fatigue during exercise. Treatment with continuous positive airway pressure (CPAP) ameliorates OSA-related symptoms and may reduce the burden of OSA on coexistent diseases. However, the role of CPAP on exercise capacity in OSA has not been fully investigated.

Aim: The aim of this study is to assess exercise capacity in a group of newly diagnosed OSA patients, without known comorbidities, following treatment with CPAP.

Methods: Consecutively diagnosed OSA patients by polysomnography completed the International Physical Activity Questionnaire (IPAQ) and underwent cardiopulmonary exercise testing (CPET) and pulmonary function testing at baseline of OSA diagnosis three months after adherence to CPAP treatment.

Results: A total of 40 OSA patients (Apnea-Hypopnea Index (ΑΗΙ)>15 events/hour) of whom 29 (72.5%) males with an average age of 42±2.5 years were enrolled in the study. OSA patients had a mean peak oxygen uptake (V̇O₂) value of 40.3 ±8.4 ml/kg/min (77.7±15%), which was improved after three months on CPAP treatment, 47.6±7.9 ml/kg/min (92.9±10.5%). (p=0.002). In addition, patients’ mean work (W) value increased significantly from baseline to three months of treatment with CPAP (101.5±30 watts vs 78.6±18.5 watts. p=0.015, respectively). There were no significant differences in terms of physical activity, as noted in IPAQ, before and after OSA therapy (p=0.075).

Conclusions: In the present study, OSA is associated with impaired exercise capacity, which seems to be improved after short-term treatment with PAP. Further evidence is warranted to elucidate whether CPET could be routinely used to monitor treatment responses of OSA with CPAP.

Obstructive Sleep Apnea Syndrome: The Effect of Acute and Chronic Responses of Exercise

Obstructive Sleep Apnea Syndrome (OSAS) is a sleep disorder with high prevalence in general population, but alarmingly low in clinicians' differential diagnosis. We reviewed the literature on PubMed and Scopus from June 1980–2021 in order to describe the altered systematic pathophysiologic mechanisms in OSAS patients as well as to propose an exercise program for these patients. Exercise prevents a dysregulation of both daytime and nighttime cardiovascular autonomic function, reduces body weight, halts the onset and progress of insulin resistance, while it ameliorates excessive daytime sleepiness, cognitive decline, and mood disturbances, contributing to an overall greater sleep quality and quality of life.

OSA and cardiorespiratory fitness: a review

The effects of untreated obstructive sleep apnea (OSA) on cardiopulmonary function remain unclear. Cardiorespiratory fitness (CRF), commonly reflected by VO₂ max measured during cardiopulmonary exercise testing, has gained popularity in evaluating numerous cardiopulmonary conditions and may provide a novel means of identifying OSA patients with the most clinically significant disease. This emerging testing modality provides simultaneous assessment of respiratory and cardiovascular function with results helping uncover evidence of evolving pathology in either organ system. In this review, we highlight the current state of the literature in regard to OSA and CRF with a specific focus on changes in cardiovascular function that have been previously noted. While OSA does not appear to limit respiratory function during exercise, studies seem to suggest an abnormal cardiovascular exercise response in this population including decreased cardiac output, a blunted heart rate response (ie, chronotropic incompetence), and exaggerated blood pressure response. Surprisingly, despite these observed changes in the cardiovascular response to exercise, results involving VO₂ max in OSA remain inconclusive. This is reflected by VO₂ max studies involving middle-aged OSA patients showing both normal and reduced CRF. As prior studies have not extensively characterized oxygen desaturation burden, we propose that reductions in VO₂ max may exist in OSA patients with only the most significant disease (as reflected by nocturnal hypoxia). Further characterizing this relationship remains important as some research suggests that positive airway pressure therapy or aerobic exercise may improve CRF in patients with OSA. In conclusion, while it likely that severe OSA, via an abnormal cardiovascular response to exercise, is associated with decreased CRF, further study is clearly warranted to include determining if OSA with decreased CRF is associated with increased morbidity or mortality.

CITATION

Powell TA, Mysliwiec V, Brock MS, Morris MJ. OSA and cardiorespiratory fitness: a review. J Clin Sleep Med. 2022;18(1):279-288.

Exercise capacity and comorbidities in patients with obstructive sleep apnea

STUDY OBJECTIVES

There are few studies evaluating (1) exercise capacity as assessed by the 6-minute walking distance (6MWD) test in large populations with obstructive sleep apnea (OSA); and (2) correlations with patients' comorbidities.

METHODS

This study presents a cluster analysis performed on the data of 1,228 patients. Severity of exercise limitation was defined on the basis of 6MWD.

RESULTS

Sixty-one percent showed exercise limitation (29.2% and 31.9% mild and severe exercise limitation, respectively). About 60% and 40% of patients were included in cluster 1 (CL1) and 2 (CL2), respectively. CL1 included younger patients with high prevalence of apneas, desaturations, and hypertension with better exercise tolerance. CL2 included older patients, all with chronic obstructive pulmonary disease (COPD), high prevalence of chronic respiratory failure (CRF), fewer apneas but severe mean desaturation, daytime hypoxemia, more severe exercise limitation, and exercise-induced desaturations. Only CRF and COPD significantly (P < .001) correlated with 6MWD < 85% of predicted value. 6MWD correlated positively with apnea-hypopnea index, oxygen desaturation index, nocturnal pulse oxygen saturation (SpO₂), resting arterial oxygen tension, mean SpO₂ on exercise, and negatively with age, body mass index, time spent during night with SpO₂ < 90%, mean nocturnal desaturation, arterial carbon dioxide tension, and number of comorbidities. Patients without severe comorbidities had higher exercise capacity than those with severe comorbidities, (P < .001). Exercise limitation was significantly worse in OSA severity class I when compared to other classes (P < .001).

CONCLUSIONS

A large number of patients with OSA experience exercise limitation. Older age, comorbidities such as COPD and CRF, OSA severity class I, severe mean nocturnal desaturation, and daytime hypoxemia are associated with worse exercise tolerance.

Herrick J. Energy cost of walking and functional aerobic capacity during moderate intensity exercise in adults with obstructive sleep apnea: a cross-sectional study

Background

Autonomic dysregulation associated with obstructive sleep apnea (OSA) may limit cardiopulmonary responses to exercise, which, in turn, may impair functional aerobic capacity (FAC) and walking economy. We aimed to characterize walking economy and FAC in OSA patients compared with healthy adults (non-OSA) and examine their relationship with OSA severity (apnea-hypopnea index [AHI]).

Methods

A total of 26 adults (OSA, n = 13; non-OSA, n = 13) participated in this cross-sectional study. In this study, the participants with OSA were between the ages of 25 and 60 years, with a body mass index of 25 kg/m2 to 39 kg/m2, and who had undergone a recent third-party sleep study with an AHI of 5 or greater. Participants completed a maximal integrated cardiopulmonary exercise test, three separate exercise bouts of constant work rate (CWR) treadmill test at 85% of anaerobic threshold (AT), and a 10-min walk test (10MWT). Multiple linear regression analysis corrected for weight, age, and BMI were performed to examine the associations.

Results

There were significant differences between OSA and non-OSA participants in VO2peak (29.7 ± 5.6 mL/kg/min vs. 37.5 ± 6.5 mL/kg/min, p = 0.03) and Net VO2 during CWR (12.7 ± 5 vs.19 ± 6 mL/kg/min, p = 0.02). The 10MWT speed and distance were significantly lower in the OSA group (all p < 0.001). The energy cost of walking during submaximal exercise and 10-min walk test was higher among patients with OSA (all p < 0.001). The AHI scores were associated with 10MWT distance (R2 = 0.85, p < 0.001), energy cost of walking (R2 = 87, p < 0.001), and VO2 at anaerobic threshold (R2 = 0.92, p < 0.001).

Conclusions

The findings of this study show that patients with OSA have reduced FAC and a higher energy cost of walking. AHI explained 87% of variance in the energy cost of walking during the 10MWT. The results suggest that individuals with more severe obstructive sleep apnea experience greater impairment in functional performance.

The Association of Sleep Apnea and Cardiorespiratory Fitness With Long-Term Major Cardiovascular Events

OBJECTIVE

To determine the risk of long-term major adverse cardiovascular events (MACE) when sleep-disordered breathing (SDB) and decreased cardiorespiratory fitness (CRF) co-occur.

METHODS

We included consecutive patients who underwent symptom-limited cardiopulmonary exercise tests between January 1, 2005, and January 1, 2010, followed by first-time diagnostic polysomnography within 6 months. Patients were stratified based on the presence of moderate-to-severe SDB (apnea/hypopnea index ≥15 per hour) and decreased CRF defined as <70% predicted peak oxygen consumption (VO₂). Long-term MACE was a composite outcome of myocardial infarction (MI), coronary artery bypass graft (CABG), percutaneous coronary intervention (PCI), stroke or transient ischemic attack (TIA), and death, assessed until May 21, 2018. Cox-proportional hazard models were adjusted for factors known to influence CRF and MACE.

RESULTS

Of 498 included patients (60±13 years, 28.1% female), 175 (35%) had MACE (MI=17, PCI=14, CABG=13, stroke=20, TIA=12, deaths=99) at a median follow-up of 8.7 years (interquartile range=6.5 to 10.3 years). After adjusting for age, sex, beta blockers, systemic hypertension, diabetes mellitus, coronary artery disease, cardiac arrhythmia, chronic obstructive pulmonary disease, smoking, and use of positive airway pressure (PAP), decreased CRF alone (hazard ratio [HR]=1.91, 95% confidence interval [CI], 1.15 to 3.18; P=.01), but not SDB alone (HR=1.26, 95% CI, 0.75 to 2.13, P=.39) was associated with increased risk of MACE. Those with SDB and decreased CRF had greater risk of MACE compared with patients with decreased CRF alone (HR=1.85; 95% CI, 1.21 to 2.84; P<.005) after accounting for these confounders. The risk of MACE was attenuated in those with reduced CRF alone after additionally adjusting for adequate adherence to PAP (HR=1.59; 95% CI, 0.77 to 3.31; P=.21).

CONCLUSION

The incidence of MACE, especially mortality, was high in this sample. Moderate-to-severe SDB with concurrent decreased CRF was associated with higher risk of MACE than decreased CRF alone. These results highlight the importance of possibly including CRF in the risk assessment of patients with SDB and, conversely, that of screening for SDB in patients with low peak VO₂.

CPAP Effect on Cardiopulmonary Exercise Testing Performance in Patients with Moderate-Severe OSA and Cardiometabolic Comorbidities

Background and Objectives: Obstructive sleep apnea (OSA) is associated with daytime somnolence, cognitive impairment and high cardiovascular morbidity and mortality. Obesity, associated cardiovascular comorbidities, accelerated erythropoiesis and muscular mitochondrial energetic dysfunctions negatively influence exercise tolerance in moderate-severe OSA patients. The cardiopulmonary exercise testing (CPET) offers an integrated assessment of the individual's aerobic capacity and helps distinguish the main causes of exercise limitation. The purpose of this study is to evaluate the aerobic capacity of OSA patients, before and after short-term continuous positive airway pressure (CPAP). Materials and Methods: Our prospective study included 64 patients with newly diagnosed moderate-severe OSA (apnea hypopnea index (AHI) 39.96 ± 19.04 events/h) who underwent CPET before and after CPAP. Thirteen patients were unable to tolerate CPAP or were lost during follow-up. Results: 49.29% of our patients exhibited a moderate or severe decrease in functional capacity (Weber C or D). CPET performance was influenced by gender but not by apnea severity. Eight weeks of CPAP induced significant improvements in maximal exercise load (Δ = 14.23 W, p = 0.0004), maximum oxygen uptake (Δ = 203.87 mL/min, p = 0.004), anaerobic threshold (Δ = 316.4 mL/min, p = 0.001), minute ventilation (Δ = 5.1 L/min, p = 0.01) and peak oxygen pulse (Δ = 2.46, p = 0.007) as well as a decrease in basal metabolic rate (BMR) (Δ = -8.3 kCal/24 h, p = 0.04) and average Epworth score (Δ = -4.58 points, p < 0.000001). Conclusions: Patients with moderate-severe OSA have mediocre functional capacity. Apnea severity (AHI) was correlated with basal metabolic rate, resting heart rate and percent predicted maximum effort but not with anaerobic threshold or maximum oxygen uptake. Although CPET performance was similar in the two apnea severity subgroups, short-term CPAP therapy significantly improved most CPET parameters, suggesting that OSA per se has a negative influence on effort capacity.

Moderate to Severe Obstructive Sleep Apnea in Military Personnel Is Not Associated With Decreased Exercise Capacity

STUDY OBJECTIVES

Studies of older and less active patients with obstructive sleep apnea (OSA) have reported decreased exercise capacity as measured by peak oxygen uptake (VO₂ max) during cardiopulmonary exercise testing (CPET). We looked to determine whether VO₂ max was decreased in younger patients with OSA who regularly exercise as would be encountered in the military.

METHODS

We evaluated military personnel who had undergone pulmonary function testing (PFT), CPET, and polysomnography (PSG) as part of the larger STAMPEDE III study for comprehensive evaluation of exertional dyspnea. For analysis, patients were classified into two groups, the OSA group with an apnea-hypopnea index (AHI) ≥ 15 events/h and a control group with an AHI < 15 events/h.

RESULTS

Mean AHI was 32.7 in the OSA group (n = 40) versus 5.8 in the control group (n = 58) with no significant difference in age (40.7 years versus 39.4 years) or body mass index (30.4 kg/m² versus 29.9 kg/m²). PFT was normal in both groups including diffusing capacity (100.7% versus 96.5%) and FEV₁ (89.2% versus 86.2%). VO₂ max was not significantly different in the OSA group compared to the control group (101.3% versus 102.8%; P = .60) with both groups having normal exercise capacity. Exercise blood pressure response was normal and peak heart rate trended toward a blunted response in the OSA group (166.0 bpm versus 171.6 bpm, P = .09).

CONCLUSIONS

Younger military personnel with moderate to severe OSA do not have decreased exercise capacity. The effect of OSA on exercise tolerance may be influenced by additional factors and is likely too small to be noted in this population.

COMMENTARY

A commentary on this article appears in this issue on page 819.

Does obstructive sleep apnea affect exercise capacity and the hemodynamic response to exercise? An individual patient data and aggregate meta-analysis

Obstructive sleep apnea (OSA) has been linked to altered cardiovascular response to exercise. A systematic review and individual patient data (IPD) meta-analysis were conducted to assess whether OSA patients present reduced exercise capacity. PubMed, Embase and Web of Science were searched until September 2018. Studies which performed sleep recording in both OSA patients and controls and measured maximal oxygen consumption (VO_2peak) via a maximal exercise test were included. IPD were provided for five trials upon the 18 eligible (N = 289) and a two-stage IPD meta-analysis model was used, allowing to standardize the apnea cutoff and adjust for confounders. IPD meta-analysis demonstrated that moderate to severe OSA patients had similar VO_2peak (mean difference: -1.03 mL·kg^-1 min^-1; 95% CI: -3.82 to 1.76; p = 0.47) and cardiovascular response to exercise compared to mild or non-OSA patients. By contrast, aggregate data (AD) meta-analysis including the 13 trials for which IPD were unavailable (N = 605) revealed that VO_2peak was reduced in OSA patients compared to controls (mean difference: -2.30 mL·kg^-1 min^-1; 95% CI: -3.96 to -0.63; p < 0.001) with high heterogeneity. In conclusion, IPD meta-analysis suggests that VO_2peak and the cardiovascular response to exercise are preserved in moderate to severe OSA patients while AD meta-analysis suggests lower VO_2peak in severe OSA.

Brief Review: Ergospirometry in Patients with Obstructive Sleep Apnea Syndrome

This brief review summarizes the available literature on the intersection of obstructive sleep apnea syndrome (OSAS) and ergospirometry. Ergospirometry provides an assessment of integrative exercise responses involving pulmonary, cardiovascular, neuropsychological, and skeletal muscle systems, which are not adequately reflected through the measurement of individual organ system functions. Sleep disorders, including OSAS, often exacerbate problems in the operation of the autonomic nervous system, heart function, lung mechanics, anxiety, and muscle metabolism. Patients with OSAS have low aerobic capacity due to dysfunction of these systems, which often affect quality of sleep. Further research is necessary to elucidate the precise mechanisms through which ergospirometry can be useful in the assessment and early identification of patients with OSAS.

Maximal exercise capacity in patients with obstructive sleep apnoea syndrome: a systematic review and meta-analysis

Maximal aerobic capacity is a strong health predictor and peak oxygen consumption (V'_O2peak) is considered a reflection of total body health. No systematic reviews or meta-analyses to date have synthesised the existing data regarding V'_O2peak in patients with obstructive sleep apnoea (OSA).A systematic review of English and French articles using PubMed/MEDLINE and Embase included studies assessing V'_O2peak in OSA patients either in mL·kg^-1·min^-1 compared with controls or in % predicted. Two independent reviewers analysed the studies, extracted the data and assessed the quality of evidence.Mean V'_O2peak expressed in mL·kg^-1·min^-1 was significantly lower in patients with OSA than in controls (mean difference -2.7 mL·kg^-1·min^-1; p<0.001; n=850). This reduction in V'_O2peak was found to be larger in non-obese patients (body mass index <30 kg·m^-2). Mean V'_O2peak % pred was 89.9% in OSA patients (n=643).OSA patients have reduced maximal aerobic capacity, which can be associated with increased cardiovascular risks and reduced survival in certain patient subgroups. Maximal exercise testing can be useful to characterise functional limitation and to evaluate health status in OSA patients.

Correlation of lung function and respiratory muscle strength with functional exercise capacity in obese individuals with obstructive sleep apnea syndrome

OBJECTIVE

To evaluate lung function and inspiratory muscle strength, correlating them with exercise tolerance, in obese individuals with obstructive sleep apnea syndrome (OSAS).

METHODS

The sample comprised 31 adult subjects with moderate-to-severe OSAS diagnosed by polysomnography. We used spirometry to measure FVC, FEV1, and FVC/FEV1 ratio, using pressure manometry to measure MIP and MEP. The incremental shuttle walk test (ISWT) and the six-minute walk test (6MWT) were used in order to determine functional exercise capacity.

RESULTS

In this sample, the mean values for FVC (% of predicted), FEV1 (% of predicted): MIP, and MEP were 76.4 ± 12.3%, 80.1 ± 6.3%, 60.0 ± 21.9 cmH2O, and 81.3 ± 22.2 cmH2O, respectively. The mean distances covered on the ISWT and 6MWT were 221 ± 97 m and 480.8 ± 67.3 m, respectively. The ISWT distance showed moderate positive correlations with FVC (r = 0.658; p = 0.001) and FEV1 (r = 0.522; p = 0.003).

CONCLUSIONS

In this sample of obese subjects with untreated OSAS, lung function, inspiratory muscle strength, and exercise tolerance were all below normal. In addition, we found that a decline in lung function, but not in respiratory muscle strength, was associated with exercise tolerance in these patients.

Obstructive Sleep Apnea Syndrome, Objectively Measured Physical Activity and Exercise Training Interventions: A Systematic Review and Meta-Analysis

A systematic review of English and French articles using Pubmed/Medline and Embase included studies assessing objective physical activity levels of obstructive sleep apnea (OSA) patients and exploring the effects of exercise training on OSA severity, body mass index (BMI), sleepiness, and cardiorespiratory fitness [peak oxygen consumption (VO2peak)]. Two independent reviewers analyzed the studies, extracted the data, and assessed the quality of evidence. For objective physical activity levels, eight studies were included. The mean number of steps per day across studies was 5,388 (95% CI: 3,831–6,945; p < 0.001), which was by far lower than the recommended threshold of 10,000 steps per day. For exercise training, six randomized trials were included. There was a significant decrease in apnea–hypopnea-index following exercise training (mean decrease of 8.9 events/h; 95% CI: −13.4 to −4.3; p < 0.01), which was accompanied by a reduction in subjective sleepiness, an increase in VO2peak and no change in BMI. OSA patients present low levels of physical activity and exercise training is associated with improved outcomes. Future interventions (including exercise training) focusing on increasing physical activity levels may have important clinical impacts on both OSA severity and the burden of associated co-morbidities. Objective measurement of physical activity in routine OSA management and well-designed clinical trials are recommended.

Registration # CRD42017057319 (Prospero).

Correlation of lung function and respiratory muscle strength with functional exercise capacity in obese individuals with obstructive sleep apnea syndrome

OBJECTIVE

To evaluate lung function and inspiratory muscle strength, correlating them with exercise tolerance, in obese individuals with obstructive sleep apnea syndrome (OSAS).

METHODS

The sample comprised 31 adult subjects with moderate-to-severe OSAS diagnosed by polysomnography. We used spirometry to measure FVC, FEV1, and FVC/FEV1 ratio, using pressure manometry to measure MIP and MEP. The incremental shuttle walk test (ISWT) and the six-minute walk test (6MWT) were used in order to determine functional exercise capacity.

RESULTS

In this sample, the mean values for FVC (% of predicted), FEV1 (% of predicted): MIP, and MEP were 76.4 ± 12.3%, 80.1 ± 6.3%, 60.0 ± 21.9 cmH2O, and 81.3 ± 22.2 cmH2O, respectively. The mean distances covered on the ISWT and 6MWT were 221 ± 97 m and 480.8 ± 67.3 m, respectively. The ISWT distance showed moderate positive correlations with FVC (r = 0.658; p = 0.001) and FEV1 (r = 0.522; p = 0.003).

CONCLUSIONS

In this sample of obese subjects with untreated OSAS, lung function, inspiratory muscle strength, and exercise tolerance were all below normal. In addition, we found that a decline in lung function, but not in respiratory muscle strength, was associated with exercise tolerance in these patients.

Effectiveness of inspiratory muscle training on sleep and functional capacity to exercise in obstructive sleep apnea: a randomized controlled trial

PURPOSE

The aim of this study was to evaluate the effectiveness of inspiratory muscle training (IMT) on sleep and functional capacity to exercise in subjects with obstructive sleep apnea (OSA).

METHODS

This is a controlled, randomized, double-blind study conducted in 16 OSA patients divided into two groups: training (IMT: n = 8) and placebo-IMT (P-IMT: n = 8). IMT was conducted during 12 weeks with a moderate load (50-60% of maximal inspiratory pressure-MIP), while P-IMT used a load < 20% of MPI. Total daily IMT time for both groups was 30 min, 7 days per week, twice a day.

RESULTS

There was no difference comparing IMT to P-IMT group after training for lung function (p > 0.05) and respiratory muscle strength (p > 0.05). Maximal oxygen uptake (VO_2Max) was not significantly different between IMT and P-IMT group (mean difference - 1.76, confidence interval (CI) - 7.93 to 4.41, p = 0.71). The same was observed for the other ventilatory and cardiometabolic variables measured (p > 0.05). A significant improvement in sleep quality was found when Pittsburgh Sleep Quality Index (PSQI) values of IMT and P-IMT group after training were compared (mean difference: 3.7, confidence interval 95% (CI95%) 0.6 to 6.9, p = 0.02) but no significant changes were seen in daytime sleepiness between both groups after the intervention (mean difference: 3.4, CI 95%: - 3.3 to 10.0; p = 0.29).

CONCLUSION

According to these results, 12 weeks of moderate load IMT resulted in improved sleep quality, but there were no significant repercussions on functional capacity to exercise or excessive daytime sleepiness.

The effects of exercise modality and intensity on energy expenditure and cardiorespiratory response in adults with obesity and treated obstructive sleep apnoea

To inform recommendations for the exercise component of a healthy lifestyle intervention for adults with obesity and treated obstructive sleep apnoea (OSA), we investigated the total energy expenditure (EE) and cardiorespiratory response to weight-supported (cycling) and unsupported (walking) exercise. Individuals with treated OSA and a body mass index (BMI) > 30 kg/m² performed an incremental cardiopulmonary exercise test on a cycle ergometer and a treadmill to determine the peak oxygen uptake [Formula: see text]. Participants subsequently completed two endurance tests on each modality, matched at 80% and 60% of the highest [Formula: see text] determined by the incremental tests, to intolerance. The cardiorespiratory response was measured and total EE was estimated from the [Formula: see text]. Sixteen participants completed all six tests: mean [SD] age 57 [13] years and median [IQ range] BMI 33.3 [30.8-35.3] kg/m². Total EE during treadmill walking was greater than cycling at both high (158 [101] vs. 29 [15] kcal; p < 0.001) and moderate (178 [100] vs. 85 [59] kcal; p = 0.002) intensities, respectively, with similar cardiorespiratory responses and pattern of EE during rest, exercise and recovery. Contrary to current guidelines, walking might be the preferred training modality to achieve the combination of weight loss and increased cardiorespiratory fitness in adults with obesity and treated OSA.

The Effect of Changes in Cardiorespiratory Fitness and Weight on Obstructive Sleep Apnea Severity in Overweight Adults with Type 2 Diabetes

STUDY OBJECTIVES

To examine the effect of changes in cardiorespiratory fitness on obstructive sleep apnea (OSA) severity prior to and following adjustment for changes in weight over the course of a 4-y weight loss intervention.

METHODS

As secondary analyses of a randomized controlled trial, 263 overweight/obese adults with type 2 diabetes and OSA participated in an intensive lifestyle intervention or education control condition. Measures of OSA severity, cardiorespiratory fitness, and body weight were obtained at baseline, year 1, and year 4. Change in the apnea-hypopnea index (AHI) served as the primary outcome. The percentage change in fitness (submaximal metabolic equivalents [METs]) and change in weight (kg) were the primary independent variables. Primary analyses collapsed intervention conditions with statistical adjustment for treatment group and baseline METs, weight, and AHI among other relevant covariates.

RESULTS

At baseline, greater METs were associated with lower AHI (B [SE] = -1.48 [0.71], P = 0.038), but this relationship no longer existed (B [SE] = -0.24 [0.73], P = 0.75) after adjustment for weight (B [SE] = 0.31 [0.07], P < 0.0001). Fitness significantly increased at year 1 (+16.53 ± 28.71% relative to baseline), but returned to near-baseline levels by year 4 (+1.81 ± 24.48%). In mixed-model analyses of AHI change over time without consideration of weight change, increased fitness at year 1 (B [SE] = -0.15 [0.04], P < 0.0001), but not at year 4 (B [SE] = 0.04 [0.05], P = 0.48), was associated with AHI reduction. However, with weight change in the model, greater weight loss was associated with AHI reduction at years 1 and 4 (B [SE] = 0.81 [0.16] and 0.60 [0.16], both P < 0.0001), rendering the association between fitness and AHI change at year 1 nonsignificant (B [SE] = -0.04 [0.04], P = 0.31).

CONCLUSIONS

Among overweight/obese adults with type 2 diabetes, fitness change did not influence OSA severity change when weight change was taken into account.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identification number NCT00194259.

Sleep, death, and the heart

Obstructive and central sleep apnea have been associated with increased risk of adverse cardiovascular events and mortality. Sympathetic dysregulation occurring as a result of the respiratory disturbance is thought to play a role in this increased risk. Sleep apnea increases the risk of arrhythmias, myocardial ischemia/infarction, stroke, and heart failure, all of which may increase mortality risk. A higher incidence of nocturnal arrhythmias, cardiac ischemia, and sudden death has been noted in subjects with sleep-disordered breathing (SDB). In this review, the association between SDB and each of these conditions is discussed, as well as the potential mechanisms underlying these risks and the effects of treatment of SDB. Particular emphasis is placed on the relationship between SDB and nocturnal atrial and ventricular arrhythmias, myocardial ischemia/infarction and sudden death.

Chemoreflexes, sleep apnea, and sympathetic dysregulation

Obstructive sleep apnea (OSA) and hypertension are closely linked conditions. Disordered breathing events in OSA are characterized by increasing efforts against an occluded airway while asleep, resulting in a marked sympathetic response. This is predominantly due to hypoxemia activating the chemoreflexes, resulting in reflex increases in sympathetic neural outflow. In addition, apnea - and the consequent lack of inhibition of the sympathetic system that occurs with lung inflation during normal breathing - potentiates central sympathetic outflow. Sympathetic activation persists into the daytime, and is thought to contribute to hypertension and other adverse cardiovascular outcomes. This review discusses chemoreflex physiology and sympathetic modulation during normal sleep, as well as the sympathetic dysregulation seen in OSA, its extension into wakefulness, and changes after treatment. Evidence supporting the role of the peripheral chemoreflex in the sympathetic dysregulation seen in OSA, including in the context of comorbid obesity, metabolic syndrome, and systemic hypertension, is reviewed. Finally, alterations in cardiovascular variability and other potential mechanisms that may play a role in the autonomic imbalance in OSA are also discussed.

Obstructive sleep apnea is associated with impaired exercise capacity: a cross-sectional study

OBJECTIVE

Obstructive sleep apnea (OSA) is associated with increased risk of adverse cardiovascular events. Because cardiopulmonary exercise testing (CPET) aids in prognostic assessment of heart disease, there is rising interest in its utility for cardiovascular risk stratification of patients with OSA. However, the relationship between OSA and exercise capacity is unclear. This study was conducted to test the hypothesis that OSA is associated with impaired exercise capacity.

METHODS

Fifteen subjects with moderate-to-severe OSA (apnea-hypopnea index [AHI] ≥15 events/h) and 19 controls with mild or no OSA (AHI <15 events/h) were enrolled. Subjects underwent standard polysomnography to determine AHI and exclude other sleep disorders. Resting metabolic rate was measured via indirect calorimetry, followed by maximum, symptom-limited CPET. Subjects completed a sleep diary and physical activity questionnaire characterizing behaviors in the week prior to testing.

RESULTS

Percent predicted peak oxygen uptake (V˙O2) was significantly lower in OSA subjects than controls (70.1%±17.5% vs 83.8%±13.9%; p = 0.02). Each 1-unit increase in log-transformed AHI was associated with a decrease in percent predicted peak V˙O2 of 3.20 (95% CI 0.53-5.88; p = 0.02). After adjusting for baseline differences, this association remained significant (p < 0.01). AHI alone explained 16.1% of the variability observed in percent predicted peak V˙O2 (p = 0.02).

CONCLUSIONS

OSA is associated with impaired exercise capacity. Further study is needed to evaluate the utility of CPET for prognostic assessment of patients with OSA.