Ventilatory response to carbon monoxide during exercise in hypoxia and hypercapnia

We tested if the addition of CO to inspired gases with different inspired O2 and CO2 fractions (FIO2 and FICO2) stimulates ventilation at rest or during submaximal exercise. We measured minute ventilation (VE) in goats breathing combinations of FIO2 ranging from 0.21 to 0.06 and FICO2 from 0 to 0.05, both with and without inspired CO resulting in carboxyhemoglobin fractions (FHbCO) 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 2.5 m s−1. Hypoxia, hypercapnia, and exercise, alone and in combination, increased ventilation compared to breathing air at rest. Both elevated FHbCO increased VE compared with ambient FHbCO during exercise (increases of 1.50 and 5.53 ml s−1 kg−1 for FHbCO 0.15 and 0.45, respectively; P = 0.035), but not at rest (P = 0.958), when the ventilatory effects of FIO2 and FICO2 are factored out. Additionally, FHbCO 0.45 (but not 0.15) increased VE compared to FHbCO 0.02 for all FIO2 and FICO2 when the ventilatory effects of exercise are factored out. Taken together, these data suggest that exercise intensity and FHbCO dose interact to stimulate ventilation during exercise.