Exercise Intolerance in Untreated OSA: Role of Pulmonary Gas Exchange and Systemic Vascular Abnormalities

BACKGROUND

Reduced exercise capacity has been reported previously in patients with OSA hypopnea syndrome (OSAHS), although the underlying mechanisms are unclear.

RESEARCH QUESTION

What are the underlying mechanisms of reduced exercise capacity in untreated patients with OSAHS? Is there a role for systemic or pulmonary vascular abnormalities?

STUDY DESIGN AND METHODS

This was a cross-sectional observational study in which 14 patients with moderate to severe OSAHS and 10 control participants (matched for age, BMI, smoking history, and FEV1) underwent spirometry, incremental cycle cardiopulmonary exercise test (CPET) with arterial line, resting echocardiography, and assessment of arterial stiffness (pulse wave velocity [PWV] and augmentation index [AIx]).

RESULTS

Patients (age, 50 ± 11 years; BMI, 30.5 ± 2.7 kg/m2; smoking history, 2.4 ± 4.0 pack-years; FEV1 to FVC ratio, 0.78 ± 0.04; FEV1, 85 ± 14% predicted, mean ± SD for all) had mean ± SD apnea hypopnea index of 43 ± 19/h. At rest, PWV, AIx, and mean pulmonary artery pressure (PAP) were higher in patients vs control participants (P < .05). During CPET, patients showed lower peak work rate (WR) and oxygen uptake and greater dyspnea ratings compared with control participants (P < .05 for all). Minute ventilation (V·E), ventilatory equivalent for CO2 output (V·E/V·CO2), and dead space volume (VD) to tidal volume (VT) ratio were greater in patients vs control participants during exercise (P < .05 for all). Reduction in VD to VT ratio from rest to peak exercise was greater in control participants compared with patients (0.24 ± 0.08 vs 0.04 ± 0.14, respectively; P = .001). Dyspnea intensity at the highest equivalent WR correlated with corresponding values of V·E/V·CO2 (r = 0.65; P = .002), and dead space ventilation (r = 0.70; P = .001). Age, PWV, and mean PAP explained approximately 70% of the variance in peak WR, whereas predictors of dyspnea during CPET were rest-to-peak change in VD to VT ratio and PWV (R2 = 0.50; P < .001).

INTERPRETATION

Patients with OSAHS showed evidence of pulmonary gas exchange abnormalities during exercise (in the form of increased dead space) and resting systemic vascular dysfunction that may explain reduced exercise capacity and increased exertional dyspnea intensity.

Chronic Intermittent Hypoxia Induces Early-Stage Metabolic Dysfunction Independently of Adipose Tissue Deregulation

Several studies demonstrated a link between obstructive sleep apnea (OSA) and the development of insulin resistance. However, the main event triggering insulin resistance in OSA remains to be clarified. Herein, we investigated the effect of mild and severe chronic intermittent hypoxia (CIH) on whole-body metabolic deregulation and visceral adipose tissue dysfunction. Moreover, we studied the contribution of obesity to CIH-induced dysmetabolic states. Experiments were performed in male Wistar rats submitted to a control and high-fat (HF) diet. Two CIH protocols were tested: A mild CIH paradigm (5/6 hypoxic (5% O₂) cycles/h, 10.5 h/day) during 35 days and a severe CIH paradigm (30 hypoxic (5% O₂) cycles, 8 h/day) during 15 days. Fasting glycemia, insulinemia, insulin sensitivity, weight, and fat mass were assessed. Adipose tissue hypoxia, inflammation, angiogenesis, oxidative stress, and metabolism were investigated. Mild and severe CIH increased insulin levels and induced whole-body insulin resistance in control animals, effects not associated with weight gain. In control animals, CIH did not modify adipocytes perimeter as well as adipose tissue hypoxia, angiogenesis, inflammation or oxidative stress. In HF animals, severe CIH attenuated the increase in adipocytes perimeter, adipose tissue hypoxia, angiogenesis, and dysmetabolism. In conclusion, adipose tissue dysfunction is not the main trigger for initial dysmetabolism in CIH. CIH in an early stage might have a protective role against the deleterious effects of HF diet on adipose tissue metabolism.

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.

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.

Influence of obesity in pulmonary function and exercise tolerance in obese women with obstructive sleep apnea

OBJECTIVE

To evaluate the influence of obesity on pulmonary function and exercise tolerance in women with obstructive sleep apnea (OSA).

SUBJECTS AND METHODS

A descriptive analytic cross- sectional study was carried out. Thirty-nine (39) sedentary climacteric women, aged 45 to 60 years, were evaluated and submitted to polysomnography. The participants were divided into 4 groups: a) 'eutrophic non-OSA' (n = 13); b) 'eutrophic OSA' (n = 5); c) 'obese non-OSA' (n = 6); d) 'obese OSA' (n = 15). All subjects underwent clinical and anthropometric evaluation, followed by pulmonary function tests and 6-minute walk test (6MWT).

RESULTS

There was a significant difference in the predicted percentage values of FEV1/FVC when comparing 'eutrophic OSA' and 'obese OSA' (97.6% ± 6.1% vs. 105.7% ± 5.7%, respectively; p = 0.025). The other spirometric variables did not show any differences between the studied groups. There was no significant difference in the maximum distance walked when the 'eutrophic non-OSA', 'eutrophic OSA', 'obese non-OSA' and 'obese OSA' groups were compared.

CONCLUSION

Considering the results of this study, OSA itself did not influence pulmonary function or functional capacity parameters compared to eutrophic women. However, not only isolated obesity but also obesity associated with OSA can negatively impact sleep quality and lung function.

Prevalence of Obstructive Sleep Apnea and Obesity Among Middle-Aged Women: Implications for Exercise Capacity

STUDY OBJECTIVES

The aim of the current study was to evaluate the association between obstructive sleep apnea (OSA) and exercise capacity in middle-aged women.

METHODS

Consecutive middle-aged female subjects without cardiovascular disease, aged 45 to 65 years, from two gynecological clinics underwent detailed clinical evaluation, portable sleep study, and treadmill exercise test.

RESULTS

We studied 232 women (age: 55.6 ± 5.2 years; body mass index [BMI]: 28.0 ± 4.8 kg/m²). OSA (apnea-hypopnea index ≥ 5 events/h) was diagnosed in 90 (39%) and obesity (BMI > 30 kg/m²) in 76 (33%) women, respectively. Participants with OSA were older, had a higher BMI, and an increased frequency of arterial hypertension compared to women without OSA. Multiple logistic regression models were used to evaluate the association between OSA and exercise capacity, controlling for traditional risk factors including BMI, age, hypertension, diabetes, and sedentary lifestyle. In multivariate analysis, the presence of obesity without OSA was associated with low exercise capacity (odds ratio [OR] 2.88, 95% confidence interval [CI] 1.02-8.11, P = .045), whereas the presence of OSA without obesity was not (OR 1.07, 95% CI 0.31-3.69, P = .912). However, the coexistence of obesity and OSA increased markedly the odds of reduction in exercise capacity (OR 9.40, CI 3.79-23.3, P < .001).

CONCLUSIONS

Obesity and OSA are common conditions in middle-aged women and may interact to reduce exercise capacity. These results highlight the importance of obesity control programs among women, as well as the diagnosis of comorbid OSA in older women.

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.

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.

Exercise tolerance in obstructive sleep apnea-hypopnea (OSAH), before and after CPAP treatment: Effects of autonomic dysfunction improvement

BACKGROUND

Obstructive sleep apnea hypopnea (OSAH) is associated with decreased exercise tolerance and autonomic abnormalities and represents a risk for cardiovascular diseases. The aim of the study was to evaluate the effects of CPAP on cardiovascular autonomic abnormalities and exercise performance in patients with OSAH without changes in lifestyle and body weight during treatment.

METHODS

Twelve overweight subjects with OSAH underwent anthropometric measures, autonomic cardiovascular and incremental symptom-limited cardio-respiratory exercise tests before and after two months of treatment with CPAP.

RESULTS

Lower frequency component of power spectrum of heart rate variability (59.5±24.2 msec² vs 43.2±25.9 msec²; p<0.05) and improvements of maximal workload (99.3±13.5 vs 108.3±16.8%pred.; p<0.05) and peak oxygen consumption (95.3±7.6 vs 105.5±7.9%pred.; p<0.05) were observed in these patients after CPAP, being their BMI unchanged.

CONCLUSIONS

CPAP-induced decrease of sympathetic hyperactivity is associated with better tolerance to the effort in OSAH patients that did not change their BMI and lifestyle, suggesting that OSAH limits per se the exercise capacity.

Neurogenic mechanisms underlying the rapid onset of sympathetic responses to intermittent hypoxia

Sleep apnea (SA) leads to metabolic abnormalities and cardiovascular dysfunction. Rodent models of nocturnal intermittent hypoxia (IH) are used to mimic arterial hypoxemias that occur during SA. This mini-review focuses on our work examining central nervous system (CNS) mechanisms whereby nocturnal IH results in increased sympathetic nerve discharge (SND) and hypertension (HTN) that persist throughout the 24-h diurnal period. Within the first 1-2 days of IH, arterial pressure (AP) increases even during non-IH periods of the day. Exposure to IH for 7 days biases nucleus tractus solitarius (NTS) neurons receiving arterial chemoreceptor inputs toward increased discharge, providing a substrate for persistent activation of sympathetic outflow. IH HTN is blunted by manipulations that reduce angiotensin II (ANG II) signaling within the forebrain lamina terminalis suggesting that central ANG II supports persistent IH HTN. Inhibition of the hypothalamic paraventricular nucleus (PVN) reduces ongoing SND and acutely lowers AP in IH-conditioned animals. These findings support a role for the PVN, which integrates information ascending from NTS and descending from the lamina terminalis, in sustaining IH HTN. In summary, our findings indicate that IH rapidly and persistently activates a central circuit that includes the NTS, forebrain lamina terminalis, and the PVN. Our working model holds that NTS neuromodulation increases transmission of arterial chemoreceptor inputs, increasing SND via connections with PVN and rostral ventrolateral medulla. Increased circulating ANG II sensed by the lamina terminalis generates yet another excitatory drive to PVN. Together with adaptations intrinsic to the PVN, these responses to IH support rapid onset neurogenic HTN.

Effects of positive airway pressure therapy on exercise parameters in obstructive sleep apnea

BACKGROUND AND OBJECTIVES

Obstructive sleep apnea (OSA) is common in adult population and may cause many adverse clinical results. We aimed to investigate possible changes in cardiopulmonary exercise capacity in OSA patients after positive airway pressure treatment.

DESIGN AND SETTINGS

Patients who were admitted to Gaziantep University Pulmonary Diseases Sleep Center and diagnosed OSA were included. Studies carried out between May 2010 and July 2011. Sixty-five consecutive patients were included in this prospective study.

PATIENTS AND METHODS

Sixty-five adult sleep clinic patients diagnosed with OSA by polysomnography and in whom continuous positive airway pressure (CPAP) ventilation therapy was indicated were included. Cardiopulmonary exercise capacity was assessed by bicycle ergometry during diagnostic workup and at least 4 weeks later.

RESULTS

There were 57 (87.7%) males. The mean age was 45.29 (10.57) years, apnea-hypopnea index 38.02 (23.19 events/h, body mass index 31.72 (4.87) kg/m2. Patients were grouped with respect to compliance with CPAP. The peak oxygen consumption (VO2) did not change in the CPAP compliant group (n=33) (22.52 [6.62] mL/[min.kg] to 21.32 [5.26] mL/[min.kg]; P=.111), and decreased from 21.31 (5.66) mL/(min.kg) to 19.92 (5.40) mL/(min.kg) (P=.05) in the CPAP noncompliant group. Work rate increased from 84.0% to 85.0% in the CPAP compliant group and decreased from 79.6% to 77.1% in the noncompliant group (P=.041). In the group that used the device, ventilation (VE)/VCO2 at anaerobic threshold (AT) declined from 28.42 to 27.36; however, it increased from 27.41 to 27.81 in the group that did not use the device (P=.033).

CONCLUSIONS

Decline in the exercise capacity was prevented in patients with OSA after 4 weeks of CPAP therapy. The changes in VE/VCO2 at AT suggest the reversal of pathophysiologic changes in OSA with the CPAP therapy that may improve cardiac function and cause more efficient ventilation.

Heart rate recovery post 6-minute walking test in obstructive sleep apnea: cycle ergometry versus 6-minute walking test in OSA patients

PURPOSE

To examine the clinical usefulness of heart rate recovery (HRR) post 6-minute walking test (6MWT) as a simple marker of cardiovascular risk in obstructive sleep apnea (OSA) patients in comparison to HRR post cycle ergometry, the validated and more sophisticated protocol.

METHODS

Seventy-four participants underwent full overnight polysomnography, cycle ergometry and 6MWT. The HRR at 1, 2 and 3 min (HRR-1, HRR-2 and HRR-3) 6MWT was compared to HRR at 1, 2, and 3 min post cycle ergometry in normal subjects and in moderate and severe OSA patients before and after 6-month CPAP treatment.

RESULTS

The HRR-1, HRR-2 and HRR-3 in 6MWT were significantly different between normal, moderate and severe OSA patients with higher rates achieved in normal. The higher the severity of OSA the lower the HRR was. There were also no differences found between work rate and distance walked during cycle ergometry or 6MWT, respectively, concerning normal, moderate and severe OSA patients. Heart rate recovery was further associated with minimum saturation of oxygen during sleep independently of the duration of apnea episodes of BMI and ESS. The treatment with CPAP had a beneficial effect on HRR both post-6MWT and post cycle ergometry.

CONCLUSIONS

Autonomic nervous system dysfunction in OSA can be found even with submaximal exertion. Heart rate recovery post-6MWT, such as HRR post cycle ergometry, was significantly impaired in OSA patients in comparison to normals and was favorably influenced from CPAP treatment. Furthermore, it was found to be more sensitive compared with distance walked in 6MWT in discriminating severity of OSA. The HRR post-6MWT was found to be an easily measured and reliable marker of OSA severity both before and after CPAP treatment.

Qualidade do sono e tolerância ao esforço em portadores de apneia obstrutiva do sono

INTRODUÇÃO: O sono é um estado natural e recorrente, no qual acontecem processos neurobiológicos importantes. A má qualidade do sono está diretamente associada com piores indicadores de saúde. A qualidade do sono pode ser medida objetiva e subjetivamente por métodos como a polissonografia, que é o padrão de referência, ou por meio de testes e questionários, como o índice de qualidade de sono de Pittsburgh (IQSP).OBJETIVO: Correlacionar a qualidade do sono com a tolerância ao esforço em pacientes portadores da síndrome da apneia/hipopneia obstrutiva do sono (SAHOS).MÉTODOS: Participaram do estudo 63 indivíduos (57 mulheres e seis homens), média de idade de 51,7 ± 6,6 anos; índice de massa corpórea (IMC) média de 28,2 ± 5,0 kg/m2); índice de apneia/hipopneia (IAH) médio de 7,3 ± 10,50 eventos/hora, verificado através da polissonografia. Para a avaliação da qualidade do sono, os participantes responderam ao IQSP, e para a avaliação da tolerância ao esforço, realizaram o teste de caminhada de 6 minutos (TC6M).RESULTADOS: Não houve correlação entre o IQSP e o TC6M (Rs= -0,103620, p = 0,419), assim como entre o IAH e o TC6M (Rs= -0, 000984, p = 0,9939). Podemos sugerir que a qualidade do sono e a gravidade da SAHOS não afetam a tolerância ao esforço dos indivíduos com SAHOS.CONCLUSÃO: Estudos com uma amostra maior, levando-se em consideração a estratificação pela gravidade da SAHOS e utilizando métodos mais acurados de avaliação da capacidade funcional, devem ser realizados, a fim de que resultados mais abrangentes possam ser obtidos.

A hypertensive response to exercise is prominent in patients with obstructive sleep apnea and hypertension: a controlled study

Blood pressure (BP) behavior during exercise is not clear in hypertensive patients with obstructive sleep apnea (OSA). The authors studied 57 men with newly diagnosed essential hypertension and untreated OSA (apnea-hypopnea index [AHI] ≥5) but without daytime sleepiness (Epworth Sleepiness Scale score ≤10), and an equal number of hypertensive controls without OSA matched for age, body mass index, and office systolic BP. All patients underwent ambulatory BP measurements, transthoracic echocardiography, and exercise treadmill testing according to the Bruce protocol. A hypertensive response to exercise (HRE) was defined as peak systolic BP ≥210 mm Hg. Patients with OSA and control patients had similar ambulatory and resting BP, ejection fraction, and left ventricular mass. Peak systolic BP was significantly higher in patients with OSA (197.6±25.6 mm Hg vs 187.8±23.6 mm Hg; P=.03), while peak diastolic BP and heart rate did not differ between groups. Furthermore, an HRE was more prevalent in patients with OSA (44% vs 19%; P=.009). Multiple logistic regression revealed that an HRE is independently predicted by both the logAHI and minimum oxygen saturation during sleep (odds ratio, 3.94; confidence interval, 1.69-9.18; P=.001 and odds ratio, 0.94; confidence interval, 0.89-0.99; P=.02, respectively). Exaggerated BP response is more prevalent in nonsleepy hypertensives with OSA compared with their nonapneic counterparts. This finding may have distinct diagnostic and prognostic implications.

Functional aerobic capacity in patients with sleep-disordered breathing

Few studies have examined exercise capacity or cardiovascular responses to maximal exercise testing and recovery in patients with sleep-disordered breathing (SDB), and results from these studies are conflicting. The objective of this cross-sectional study conducted at a tertiary referral center was to examine the association between SDB and exercise testing outcomes independent of body mass index (BMI) and other cardiopulmonary risk factors. Between January 1, 2005 and January 1, 2010, 1,424 adults underwent exercise testing and within 6 months before first-time diagnostic polysomnography. Subjects were categorized by apnea-hypopnea index (AHI) into 4 groups: <5, 5 to 14, 15 to 29, and ≥30. A logistic regression model incorporated age, gender, BMI, smoking, hypertension, diabetes, beta-blocker use, and cardiac and pulmonary disease as covariates. The primary variable of interest was functional aerobic capacity (FAC). Mean age was 56.4 ± 12.4 years; 75% were men. Mean BMI was 32.4 ± 7.1 kg/m², and mean AHI 19.5 ± 22.1 per hour. On multivariate analysis, AHI as a continuous variable showed a negative correlation with FAC (R²adj = 0.30, p <0.001) and postexercise SBP (R²adj = 0.23, p = 0.03), and positively correlated with resting and peak DBP (R²adj = 0.09, p = 0.01 and R²adj = 0.09, p = 0.04 respectively). When comparing patients with severe SDB (AHI ≥30) with those without SDB (AHI <5), FAC and heart rate recovery were significantly lower, and resting, peak, and postexercise DBP were higher in those with severe apnea (all p <0.05), after accounting for confounders. In conclusion, SDB severity was associated with reduced FAC and increased resting and peak DBP. Even after accounting for confounders, severe SDB was associated with attenuated FAC, impaired heart rate recovery, and higher resting, peak, and postexercise DBP.

Rats selectively bred for differences in aerobic capacity have similar hypertensive responses to chronic intermittent hypoxia

Exposure to chronic intermittent hypoxia (CIH) is an animal model that mimics the repetitive bouts of hypoxemia experienced by humans with sleep apnea. Rats exposed to CIH develop hypertension that depends on the activation of sympathetic nerve activity (SNA). Since obesity and metabolic syndrome have been linked to neurogenic hypertension and sleep apnea, and because sleep apnea can adversely affect aerobic exercise capacity, we tested the hypothesis that rats bred for selection of low aerobic capacity running (LCR) would have a greater hypertensive response to CIH than rats bred for high aerobic capacity running (HCR). Blockade of ganglionic transmission was performed to compare the contribution of SNA to the maintenance of resting mean arterial pressure (MAP). Next, hypertensive responses to 7 days of CIH were compared across LCR and HCR rats (14-16 mo old). Finally, the contribution of the hypothalamic paraventricular nucleus (PVN) to the maintenance of SNA and hypertension after CIH was determined and compared across groups. Although LCR rats were less active and had greater body weights than HCR rats, resting MAP, the contribution of ongoing SNA to the maintenance of MAP, and hypertensive responses to CIH were similar between groups. Contrary to our hypothesis, chemical inhibition of the PVN with muscimol (1 mmol/100 nl) caused a larger fall of MAP in HCR rats than in LCR rats. We conclude that LCR rats do not have resting hypertension or an exaggerated hypertensive response to CIH. Interestingly, the maintenance of CIH hypertension in LCR rats compared with HCR rats appears less reliant on ongoing PVN neuronal activity.

Does obstructive sleep apnea impair the cardiopulmonary response to exercise?

STUDY OBJECTIVES

The aim of this study was to evaluate cardiopulmonary exercise performance in lean and obese patients with obstructive sleep apnea (OSA) compared with controls.

DESIGN

Case-control study.

SETTING

The study was carried out in Sao Paulo Sleep Institute, Sao Paulo, Brazil.

PATIENTS AND PARTICIPANTS

INDIVIDUALS WITH SIMILAR AGES WERE ALLOCATED INTO GROUPS: 22 to the lean OSA group, 36 to the lean control group, 31 to the obese OSA group, and 26 to the obese control group.

INTERVENTIONS

The participants underwent a clinical evaluation, polysomnography, a maximum limited symptom cardiopulmonary exercise test, two-dimensional transthoracic echocardiography, and spirometry.

MEASUREMENTS AND RESULTS

The apnea-hypopnea index, arousal index, lowest arterial oxygen saturation (SaO2) and time of SaO2 < 90% were different among the groups. There were differences in functional capacity based on the following variables: maximal oxygen uptake (VO2max), P < 0.01 and maximal carbon dioxide production (VCO2max), P < 0.01. The obese patients with OSA and obese controls presented significantly lower VO2max and VCO2max values. However, the respiratory exchange ratio (RER) and anaerobic threshold (AT) did not differ between groups. Peak diastolic blood pressure (BP) was higher among the obese patients with OSA but was not accompanied by changes in peak systolic BP and heart rate (HR). When multiple regression was performed, body mass index (P < 0.001) and male sex in conjunction with diabetes (P < 0.001) independently predicted VO2max (mL/kg/min).

CONCLUSIONS

The results of this study suggest that obesity alone and sex, when associated with diabetes but not OSA, influenced exercise cardiorespiratory function.

Cysteine: a potential biomarker for obstructive sleep apnea

OBJECTIVE

Obstructive sleep apnea (OSA) is a risk factor for a number of cardiovascular conditions. Although homocysteine (Hcy) and cysteine (Cys) are regarded as cardiovascular risk factors, few studies have analyzed Hcy and Cys plasma concentrations in patients with OSA. The aim of this study was to evaluate the role of Hcy and Cys in OSA in comparison with subjects without OSA and to determine the possible influence of obesity on these variables.

METHODS

Patients who submitted to polysomnography studies were recruited to engage in an 8-h fasting period for blood sample withdrawal, physical examination, ECG, and echocardiogram. A subgroup of lean patients with OSA (BMI < 25 kg/m(2)) were analyzed to rule out the influence of obesity. Fifteen patients were randomly assigned to participate in a continuous positive airway pressure (CPAP) protocol to assess the influence of OSA treatment on the obtained measurements.

RESULTS

A total of 75 patients and 75 control subjects matched for age and sex were analyzed. The Cys plasma levels were higher in patients with OSA compared with control subjects (490.16 ± 67.00 μmol/L vs 439.81 ± 76.12 μmol/L, respectively, P < .01); however, the Hcy plasma levels did not differ between groups. Cys plasma levels were also higher in the OSA lean subgroup when compared with lean control subjects (484.21 ± 71.99 μmol/L vs 412.01 ± 70.73 μmol/L, respectively, P = .009). There was a significant decrease of Cys plasma levels after 6 months of CPAP effective therapy.

CONCLUSION

Cys is a potential biomarker of OSA in obese and nonobese patients and is reduced after effective OSA treatment.