ALVEOLAR GAS CHANGES DURING BREATH HOLDING

Abstract

With inspired PO2 ranging from 69 to 694 mm. Hg, the alveolar pO2 and pCO2, and arterial saturation by the oximeter were recorded for 8 subjects before breath holding and at the breaking point. At high initial O2 tensions, the breath holding time was relatively long, the rate of O2 uptake from the lungs during apnoea was normal, but the R.Q. was as low as 0.1 owing to CO2 retention by the blood and tissues. At low initial 02 tensions, the breath-holding time was short, the rate of O2 uptake was about 25% of normal, and the R.Q. was about 1. When the R.Q. is less than 1 the lung vol. tends to decrease. If N2 is present this results in increasing pN2 so that pO2 decreases rapidly. When N2 is absent the decrease in vol. prevents the pO2 from falling. Application of Gray''s Multiple Factor theory indicates that the breaking point occurs when the total stimulus from low PO2 and high pCO2 is sufficient to produce an alveolar ventilation about 8 times the normal.