Peak oxygen consumption and heart rate recovery in patients with the obstructive sleep apnea syndrome.

We would like to comment on the article recently published in CHEST (September 2008) by Vanhecke et al,1 who reported that morbidly obese patients with obstructive sleep apnea syndrome (OSAS) had lower peak oxygen consumption (V̇o2) and slower heart rate recovery than obese patients without OSAS. First, given that fat is a metabolically inactive indexing of peak V̇o2 to body weight in obese patients can be misleading with respect to the severity of functional impairment.2 Body weight is not cited in the article, but body mass index tended to be higher in OSAS patients1; therefore, we wondered whether absolute peak V̇o2 (expressed in liters per minute) or percent predicted peak V̇o2 (equations typically do not include weight) also differed between groups. Interestingly, the majority of patients were women who generally have less lean body mass than men. We also encourage the authors to report values for respiratory exchange ratio at peak exercise as this will help to interpret data. In a study among 81 less obese OSAS patients,3 which was quoted by Vanhecke et al1 (42 OSAS patients) as one of the studies “limited by small sample sizes,” we have found that percent predicted peak V̇o2 was normal in patients with mild, moderate, and severe OSAS. Notably, apnea-hypopnea index (AHI) was similar in both reports (mean AHI, 32.5 episodes/h; median AHI, 34 episodes/h).1,3 Second, the observation of a delayed heart rate recovery in OSAS patients1 is not novel but concurs very nicely with the findings of our previously published study4 revealing that OSAS severity expressed as AHI was independently associated with heart rate recovery 1 min after exercise termination. We further demonstrated in an uncontrolled trial5 that nasal continuous positive airway pressure ventilation for approximately 8 months led to an improvement in heart rate recovery 1 min after exercise termination and heart rate recovery 2 min after exercise termination in patients with severe OSAS.