The influence of varying inspired fractions of O2 and CO2 on the development of involuntary breathing movements during maximal apnoea

The growing urge to breathe that occurs during breath-holding results in development of involuntary breathing movements (IBMs). The present study determined whether IBMs are initiated at critical levels of hypercapnia and/or hypoxia during maximal apnoea. Arterial blood gasses at the onset of IBM were monitored during maximal voluntary breath-holds. Eleven healthy men performed breath holds after breathing air, hyperoxic-normocapnia, hypoxic-normocapnia, and normoxic-hypercapnia. Pre-breathing of the gas mixtures facilitated the IBM onset, reducing the time-to-onset for similar to 46% (hyperoxic condition) and for similar to 80% ( hypoxic condition) compared to the normoxic air breathing time. A strong correlation (R = 0.83,P = 0.002) between arterial partial pressure of CO2 (Pa-CO2) at IBM onset after pre-breathing hyperoxic and hypercapnic gas mixtures was observed, suggesting the existence of a possible IBM Pa-CO2 threshold level of similar to 6.5 +/- 0.5 kPa. No clear "threshold" was observed for partial pressure of arterial O-2 (Pa-CO2). However, we observed that IBM onset was influenced, in part, by an interaction between Pa-O2 and Pa-CO2 levels during maximal apnoea. This study demonstrated the complex interaction between arterial blood-gases and the physiological response to maximal breath holding. (C) 2012 Elsevier B.V. All rights reserved.