Effect of partial pressures of end expiratory gases on voluntary breath holding time

INTRODUCTION - The break point of voluntary breath hold is believed to be brought about by multiple factors including partial pressures of arterial pCO2 and pO2. This study aims to look at the effect of partial pressures of arterial blood gases on voluntary breath holding time (BHT). MATERIALS AND METHODS - Breath holding time after 3 different maneuvers (normal, after re-breathing, after voluntary hyperventilation) were employed on 13 subjects to obtain their end expiratory partial pressures of gases before breath hold and at break point. RESULTS - The breath holding times for normal, rebreathing and voluntary hyperventilation were significantly different from each other (p less than 0.03 in all three comparisons). A negative correlation was observed between end expiratory pCO2 (eECO2) before breath hold and BHT (r equals -0.728, p less than 0.0001). A positive correlation was seen between end expiratory pO2 (eEO2) before breath hold and BHT (r equals 0.682, p less than 0.0001). Analysis of partial pressures of gases at break point revealed comparatively smaller deviations for end expiratory pCO2 than that of pO2. A three dimensional plot of eECO2 before breath hold, eEO2 before breath hold and BHT showed that all the data points fall along a straight line. CONCLUSION - Our experiments suggest a more significant role for arterial pCO2 than arterial pO2. Strong negative correlations between eECO2 before breath hold and BHT, and between eEO2 and eECO2 (r equals -0.965, p less than 0.0001) could have resulted in a positive correlation between eEO2 before breath hold and BHT.