Breaking Point of Breath-Holding

Abstract

After voluntary breath-holding of max. duration, untrained subjects rebreathed a gas mixture containing 8.2% O2 and 7.5% of CO2. This mixture afforded sufficient relief from respiratory distress so that the subject could resume breath-holding for 2 additional periods of shorter duration, despite progressively decreasing degrees of arterial O2 satura-tion and increasing alveolar tension of CO2. After breath-holding, the 2d inspiration was of smaller vol. than the 1st, generally because of a reduction in mean rate of inspiratory flow. This result is not readily explained. The distress which terminated breath-holding was attributed to sensory patterns accompanying hypercapnia, the stimulation of breathing induced thereby, and the voluntary effort required to oppose involuntary breathing movements.