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 μl min−1 ml−1) to exercise at Load 1 (67.0 ± 20.3 μl min−1 ml−1) and Load 2 (84.0 ± 22.9 μl min−1 ml−1) before returning to pre-exercise levels in recovery (51.7 ± 13.2 μl 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.