Ventilatory response to carbon monoxide during exercise in hypoxia and hypercapnia.

We tested if the addition of CO to inspired gases with different inspired O and CO fractions (FO and FCO) stimulates ventilation at rest or during submaximal exercise. We measured minute ventilation (V) in goats breathing combinations of FO ranging from 0.21 to 0.06 and FCO from 0 to 0.05, both with and without inspired CO resulting in carboxyhemoglobin fractions (F) of 0.02 (no CO added), 0.15, or 0.45. We did this while they stood on a treadmill, walked at 1.4, or trotted at 2.5ms. Hypoxia, hypercapnia, and exercise, alone and in combination, increased ventilation compared to breathing air at rest. Both elevated F increased V compared with ambient F during exercise (increases of 1.50 and 5.53mlskg for F 0.15 and 0.45, respectively; P=0.035), but not at rest (P=0.958), when the ventilatory effects of FO and FCO are factored out. Additionally, F 0.45 (but not 0.15) increased V compared to F 0.02 for all FO and FCO when the ventilatory effects of exercise are factored out. Taken together, these data suggest that exercise intensity and F dose interact to stimulate ventilation during exercise.