Alveolar and peripheral venous gas changes during breath-hold diving

Two fit young men were tested in a laboratory pool at 22 degrees C and 1 m depth before and after hyperventilation/breath-hold diving lasting 90 seconds. The percentages of alveolar oxygen and carbon dioxide were determined on a Polygas analyser and converted to partial pressures (PAO2 and PACO2) at an atmospheric pressure of 86 kPa at 20 degrees C, room temperature. PAO2 and PACO2 values were cross-checked by collecting expiratory gas in a Douglas bag and using the Haldane gas analyser. Peripheral venous blood was 'arterialized' and analysed for CO2 (PVCO2) using the Radiometer ABL1 gas analyser. For ethical reasons, arterial punctures were not considered in these healthy subjects. Peripheral venous blood was obtained under near steady-state conditions from the dorsum of the hand, which was warmed to 38 degrees C. The results of hyperventilation/breath-hold diving are illustrated. PAO2 increased after hyperventilation and decreased to below 5 kPa after the dive. PACO2 decreased after hyperventilation and increased after the dive. PVCO2 decreased after hyperventilation and increased after the dive. All values approached a common point between 3 and 5 kPa after the 90-second dive. The CO2 content of arterialized peripheral venous blood closely follows that of alveolar air.