Relationship between arterial oxygen desaturation and ventilation during maximal exercise

The purpose of the present study was to investigate the contribution of ventilation to arterial O₂ desaturation during maximal exercise. Nine untrained subjects and 22 trained long-distance runners [age 18-36 yr, maximal O₂ uptake (V̇O(2 max) 48-74 ml · min^-1 · kg^-1] volunteered to participate in the study. The subjects performed an incremental exhaustive cycle ergometry test at 70 rpm of pedaling frequency, during which arterial O₂ saturation (Sa(O₂)) and ventilatory data were collected every minute. Sa(O₂) was estimated with a pulse oximeter. A significant positive correlation was found between Sa(O₂) and end-tidal PO₂ (PET(O₂); r = 0.72, r² = 0.52, P < 0.001) during maximal exercise. These statistical results suggest that ~50% of the variability of Sa(O₂) can be accounted for by differences in PET(O₂), which reflects alveolar PO₂. Furthermore, PET(O₂) was highly correlated with the ventilatory equivalent for O₂ (VE/V̇O₂; r = 0.91, P < 0.001), which indicates that PET(O₂) could be the result of ventilation stimulated by maximal exercise. Finally, Sa(O₂) was positively related to V̇E/V̇O₂ durimg maximal exercise (r = 0.74, r² = 0.55, P < 0.001). Therefore, one-half of the arterial O₂ desaturation occurring during maximal exercise may be explained by less hyperventilation, specifically for our subjects, who demonstrated a wide range of trained states. Furthermore, we found an indirect positive correlation between Sa(O₂) and ventilatory response to CO₂ at rest (r = 0.45, P < 0.05), which was mediated by ventilation during maximal exercise. These data also suggest that ventilation is an important factor for arterial O₂ desaturation during maximal exercise.