Powell TA; Mysliwiec V; Brock MS; Morris MJ

Journal of Clinical Sleep Medicine. 18(1):279-288, 2022 01 01.
VI 1

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.