THE INFLUENCE OF LUNG SHRINKAGE ON BREATH HOLDING TIME

The influence of lung shrinkage on the breath holding time was studied in three normal males. The rate of shrinkage was increased two to three fold either by slow expiration or by reducing gas density in a hypobaric chamber. For any given lung volume the relationship between breath holding time and pCO2 was defined by a rebreathing method which allowed breath holds to be performed at progressively increasing levels of pCO2. Hypoxia was avoided throughout and the ventilatory response to CO2 remained constant irrespective of ambient pressure.The breath holding time for any given pCO2 was usually longer the larger the lung volume. Increasing the rate of lung shrinkage by either method did not alter the relationship between breath holding time and pCO2. There was no constant relationship between the pCO2 and the lung volume at the breaking point of a breath hold. These findings are discussed in the light of previous work and it is concluded that the sensation arising during breath holding cannot be fully explained in terms of any combination of pCO2, lung volume and lung shrinkage.