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Functional Aerobic Capacity in Patients With Sleep-Disordered Breathing
Study Questions:
Is decreased exercise capacity a possible consequence of sleep disordered breathing (SDB)?
Methods:
This single-center, retrospective, cross-sectional study was conducted 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. Most subjects were referred for an exercise test for the evaluation of fatigue, chest pain, or palpitations. Exclusions included those with complex heart, lung, or kidney disease. Subjects with known coronary disease were not excluded. Subjects were categorized by apnea-hypopnea index (AHI) into four groups: <5, 5-14, 15-29, 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), which was calculated based on a nomogram using age, sex, baseline activity, and observed duration of exercise.
Results:
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 systolic blood pressure (R2adj = 0.23, p = 0.03), and positively correlated with resting and peak diastolic blood pressure (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.
Conclusions:
The authors concluded that 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.
Perspective:
This is the largest study to date to explore the relationship between untreated SDB and decreased exercise capacity. The cohort contained a small number of subjects with baseline smoking, pulmonary, or structural heart disease. Pulmonary function data were not available in all subjects. Several possible mechanisms by which SDB may lead to abnormalities in exercise capacity include: hypoxia, hypertension, arrhythmias, impaired muscle metabolism, and deconditioning due to poor sleep hygiene. Since this was a referral cohort population to an exercise laboratory, findings here may not apply to all patients with SDB.
Keywords: Exercise Tolerance, Thioguanine, Multivariate Analysis, Cross-Sectional Studies, Referral and Consultation, Coronary Disease, Risk Factors, Heart Rate, Nomograms, Sleep Apnea Syndromes, Smoking, Heart Diseases, Kidney Diseases, Body Mass Index, Polysomnography, Chest Pain, Hypertension, Logistic Models, Diabetes Mellitus, Lung Diseases, Exercise Test
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