Physiological Dead Space and Alveolar Gas Pressures at Rest and during Muscular Exercise

Abstract

Summary. The respiratory dead space (physiological dead space) calculated from the B ohr formula on the basis of arterial pCO 2 has been determined on 4 young healthy subjects at rest and during light to heavy muscular work. It was found that the physiological dead space during work increased with the tidal volume from an average value of about 170 cc at rest to about 350 cc during work at a tidal volume of about 3.3 liters. The values were nearly the same when breathing atmospheric air and when breathing air with a low oxygen content (about 12.5% O 2 in inspired air). In muscular work with tidal volumes higher thait about 1.5 liters the arterial pCO 2 was found to be 2 to 3 mm Hg higher than the alveolar pCO 2 calculated from the B ohr formula using a constant dead space at modum K rogh and L indhard . The arterial pCO 2 was on the other hand in heavy work found to be about 3 mm Hg lower than the alveolar pCO 2 determined by direct sampling (end‐normal expiration method). The alveolar pCO 2 determined by direct sampling was in heavy work found to be ahout 6 mm Hg lower than the alveolar pCO 2 calculated from B ohr's forniula using the physiological dead space for CO 2 . The possible reasons for the differences are discussed in the text.