LUNG DIFFUSION CAPACITY, OXYGEN-UPTAKE, CARDIAC-OUTPUT AND OXYGEN-TRANSPORT DURING EXERCISE BEFORE AND AFTER AN HIMALAYAN EXPEDITION

Studies were made of pulmonary diffusion capacity and oxygen transport before and after an expedition to altitudes at and above 4900 m. Maxi mum power (P-max) and maximal oxygen uptake (VO2max) were measured in 11 mountaineers in an incremental cycle ergometer test (25W . min(-1)) before and after return from basecamp (30 days at 4900 m or higher). In a second test, cardiac output (Q(c)) and lung diffusion capacity of carbon monoxide (D-L,D-CO) were measured by acetylene and CO rebreath ing at rest and during exercise at low, medium and submaximal intensit ies. After acclimatization, VO2max and P-max decreased by 5.1% [from 6 1.0 (SD 6.2) to 57.9 (SD 10.2) ml . kg(-1), n.s.] and 9.9%, [from 5.13 (SD 0.66) to 4.62 (SD 0.42) W . kg(-1) n.s.], respectively. The maxim al cardiac index and D-L,D-CO decreased significantly by 15.6% [14.1 ( SD 1.41) l . min(-1). m(-2) to 11.9 (SD 1.44) l . min(-1). m(-2) P < 0 .05] and 14.3% [85.9 (SD 4.36) ml . mmHg(-1) min(-1) to 73.6 (SD 15.2) ml . mmHg(-1). min(-1), P < 0.05], respectively. The expedition to hi gh altitude led to a decrease in maximal Q(c), oxygen uptake and D-L,D -CO. A decrease in muscle mass and capillarity may have been responsib le for the decrease in maximal Q(c) which may have resulted in a decre ase of D-L,D-CO and an increase in alveolar-arterial oxygen difference . The decrease in D-L,D-CO especially at lower exercise intensities af ter the expedition may have been due to a ventilation-perfusion mismat ch and changes in blood capacitance. At higher exercise intensities di ffusion limitation due to reduced pulmonary capillary contact time may also have occurred.