The most important of these factors include ventilation-perfusion (V/Q) inequality and diffusion limitation. The increase in Pa02 during arm crank exercise was associated with a nonsignificant widening of the P(A-a)Os (Table 4); this suggests an overall minimal effect on ventilation-perfusion matching in the lungs at this level of submaximal cardiopulmonary stress. Better perfusion of the lung apices resulting in a more even distribution of pulmonary blood flow was the explanation provided by Whipp and Wasserman for the decrease in P(A-a)02 from 7.4 at rest to 3.8 that they observed during submaximal leg exercise (Vo2= 1.6 L/min). ampicillin antibiotic

We observed a decrease in P(A-a)02 in some subjects, primarily those in whom P(A-a)02 was initially relatively high. This may reflect either the hyperventilation associated with the anticipation of exercise or an improvement in ventilation-perfusion matching. Wagner et al, using inert gas techniques, observed a modest increase in ventilation-perfusion inequality which did not affect the P(A-a)02 during leg exercise. In that study, it was hypothesized that the contribution of an increase in V/Q inequality to the P(A-a)02 was offset by alveolar hyperventilation. Whether arm crank exercise promotes enhanced apical distribution of pulmonary flow and thereby improving overall ventilation-perfusion matching is unknown.