Pulmonary Physiology & Rehabilitation Section
Exercise tolerance in untreated sleep apnea
Numerous cardiovascular, respiratory, neuromuscular, and perceptual factors determine exercise tolerance. This makes designing a study to isolate the contribution of one factor difficult.
A recently published study (Elbehairy, et al. Chest. 2022; published online September 29, 2022) explores exercise tolerance in patients with untreated OSA compared with age- and weight-matched controls. The authors found that at an equivalent work rate, patients with OSA had greater minute ventilation, principally due to higher breathing frequency. Dead space volume, dead space ventilation, and dead space to tidal volume ratio (VD/VT) were higher in patients with OSA, likely due to a reduction in pulmonary vessel recruitment relative to ventilation. VD/VT decreased more from rest to peak in controls than in patients with OSA, an adaptation that is expected with exercise. Patients with OSA had greater arterial stiffness measured by pulse wave velocity and higher blood pressures, which may have affected cardiac output augmentation. Patients with OSA also had higher resting mean pulmonary artery pressures and exercise dyspnea scores. Regression models predicting peak oxygen uptake and peak work rate were statistically significant, with predictors being age, pulse wave velocity, and resting mean pulmonary artery pressure. The role of diastolic dysfunction remains to be determined.
Prior studies have shown that some effects of OSA on exercise may be reversed with CPAP treatment (Arias, et al. Eur Heart J. 2006;27[9]:1106-1113; Chalegre, et al. Sleep Breath. 2021;25[3]:1195-1202). Understanding the mechanisms of exercise limitation in OSA will help physicians address symptoms, reinforce CPAP adherence, and design tailored pulmonary rehabilitation programs.
Fatima Zeba, MD
Fellow-in-Training