HYPOXIC VENTILATORY RESPONSE PREDICTS THE EXTENT OF MAXIMAL BREATH-HOLDS IN MAN

To understand the factors influencing breath-holding performance, we tested whether the hypoxic (HVR) and hypercapnic ventilatory responses (HCVR) were predictors of the extent of maximal breath-holds as measured by breath-hold duration, the lowest oxyhemoglobin saturation (Sp(O2min)), lowest calculated Pa-O2 (Pa-O2min) and highest end-tidal P-CO2 (PET(CO2max)) reached. Steady state isocapnic HVR and hyperoxic HCVR were measured in 17 human volunteers. Breath-holds were made at total lung capacity (TLC), at TLC following hyperventilation, at functional residual capacity, and at TLC with FIO2 = 0.15. Sp(O2) was measured continuously by pulse oximetry, and alveolar gas was measured at the end of breath-holds by mass spectrometry. Pa-O2min was calculated from Sp(O2min) and PET(CO2max). HVR was a significant predictor of both Sp(O2min) and Pa-O2min. HVR and forced vital capacity were predictors of breath-hold duration by multiple linear regression. HCVR had no significant predictive value. We conclude that HVR, but not HCVR, is a significant predictor of breath-holding performance.