Exercise-related change in airway blood flow in humans: relationship to changes in cardiac output and ventilation.

This study examined the relationship between airway blood flow (Q(aw)), ventilation (V(E)) and cardiac output (Q(tot)) during exercise in healthy humans (n=12, mean age 34+/-11 yr). Q(aw) was estimated from the uptake of the soluble gas dimethyl ether while V(E) and Q(tot) were measured using open circuit spirometry. Measurements were made prior to and during exercise at 34+/-5 W (Load 1) and 68+/-10 W (Load 2) and following the cessation of exercise (recovery). Q(aw) increased in a stepwise fashion (P<0.05) from rest (52.8+/-19.5 microl min(-1) ml(-1)) to exercise at Load 1 (67.0+/-20.3 microl min(-1) ml(-1)) and Load 2 (84.0+/-22.9 microl min(-1) ml(-1)) before returning to pre-exercise levels in recovery (51.7+/-13.2 microl min(-1) ml(-1)). Q(aw) was positively correlated with both Q(tot) (r=0.58, P<0.01) and V(E) (r=0.50, P<0.01). These results demonstrate that the increase in Q(aw) is linked to an exercise related increase in both Q(tot) and V(E) and may be necessary to prevent excessive airway cooling and drying.