Purpose: To determine if and how hypoxia combined with elevated carboxyhaemoglobin fraction (F HbCO) affects peripheral diffusing capacity and O2 extraction in animals exercising at their maximal aerobic capacity (V̇ O2max). Methods: Six goats ran on a treadmill at speeds eliciting V̇ O2max while breathing inspired O2 fractions (F IO2) of 0.21 or 0.12 with F HbCO 0.02 or 0.30. We measured O2 consumption and arterial and mixed-venous blood variables to assess how hypoxia and elevated F HbCO individually, and in combination, alter O2 transport and utilisation. Results: Peripheral diffusing capacity did not differ among the four gas combinations (P = 0.867), whereas O2 extraction fraction increased with hypoxia [0.920 ± 0.018 (SD)] and decreased with elevated F HbCO (0.792 ± 0.038) compared to control (0.897 ± 0.032). Oxygen extraction increases with hypoxia due to the sigmoid relationship between O2 saturation (SO2) and O2 partial pressures (PO2) affecting low (hypoxia) and high (normoxia) PO 2 differently. Oxygen extraction decreases with elevated F HbCO because elevated F HbCO increases haemoglobin (Hb) affinity for O2 and raises SO2, especially at very low (mixed-venous) PO2. Pulmonary gas exchange was impaired only with combined hypoxia and elevated F HbCO due to hypoxia decreasing alveolar PO2 and O2 flux coupled with elevated F HbCO increasing Hb affinity for O2 and decreasing the rate of PO2 increase for a given rise in SO2. Conclusion: This study quantifies the mechanisms by which O2 delivery and peripheral diffusion interact to limit V̇ O2max when O2 delivery is reduced due to breathing hypoxic gas with elevated F HbCO.
- Aerobic capacity
- Carbon monoxide
- Oxygen transport
ASJC Scopus subject areas
- Public Health, Environmental and Occupational Health
- Orthopedics and Sports Medicine
- Physiology (medical)