Lung disease affects exercise performance through a number of mechanisms, including
hypoxemia, abnormal ventilatory mechanics, abnormal ventilatory muscles, abnormal ventilatory patterns, abnormal right heart function and subjective
dyspnea. Supplemental
oxygen improves
hypoxemia and thus improves exercise impairment resulting from
hypoxemia-related reductions in
oxygen delivery. Supplemental
oxygen also reduces exercise ventilation. This, in turn, reduces ventilatory muscle work, and the concomitant permissive
hypercapnia may have beneficial effects at the cellular level. Additionally, in obstructive disease patients, an improved ventilatory pattern may reduce air trapping. Supplemental
oxygen may also improve
right ventricular dysfunction in patients with underlying
right ventricular dysfunction. Finally, supplemental
oxygen may reduce
dyspnea caused by
oxygen-related carotid body activity. Important questions remain. First, is long-term
oxygen use of benefit in patients with only exercise
hypoxemia? Second, is exercise conditioning possible in patients with exercise
hypoxemia? Third, does supplemental
oxygen enhance exercise conditioning efforts in those patients with CLD but without exercise
hypoxemia? If the answer to this last question is yes, what selection criteria should be used to identify those who would benefit? The answers to all of these questions will have enormous impact on our approach to the optimal management of CLD patients.