Ventilation-Perfusion Matching during Exercise

¹ The Department of Medicine, University of California San Diego, La Jolla.

Exercise in both normal subjects and patients with lung disease may alter gas exchange relationships by more than accounted for simply by increased total ventilation, cardiac output, Vo₂ and Vco₂. Thus, VA/Q mismatching and/or diffusion limitation may become more evident, depending on the setting as described above. In normal subjects, VA/Q inequality often develops but the reasons remain unclear. The principal explanation for the considerably increased P(A-a)O₂ appears to be alveolar-capillary diffusion limitation. In patients with lung disease, the effects of exercise are more numerous and variable, but both VA/Q mismatching and diffusion limitation may be important contributors to hypoxemia, depending on the pathologic condition.