MECHANICAL AND CHEMICAL CONTROL OF BREATH HOLDING

¹ Department of Physiology, University of Aberdeen, Aberdeen, Scotland

The relationship between the maximum duration of a voluntary breath hold (BHT) and the alveolar Pco₂ at the start and finish of the period of apnoea has been investigated in six subjects over a wide range of CO₂ tensions, for breath holds made at VC, 60 per cent VC, and FRC. Alveolar Po₂ was maintained above the level at which hypoxia is a significant factor in stimulating pulmonary ventilation. The results suggest that the relationship between BHT and Pco₂ at breaking point may be approximated by two straight line segments: for short breath holds (with a high initial Pco₂), BHT and breaking point Pco₂ are linearly related; for long breath holds (with a low initial Pco₂) final Pco₂ is independent of the duration of the breath hold. These results suggest that the mechanical component of the drive to resume breathing saturates during long breath holds, the level of saturation depending on the lung volume at which the breath is held.