Lung diffusion capacity, oxygen uptake, cardiac output and oxygen transport during exercise before and after an Himalayan expedition

Abstract

Studies were made of pulmonary diffusion capacity and oxygen transport before and after an expedition to altitudes at and above 4900 m. Maximum power (P _max) and maximal oxygen uptake (VO _2max) 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,CO) were measured by acetylene and CO rebreathing at rest and during exercise at low, medium and submaximal intensities. After acclimatization, VO_2max and P _max decreased by 5.1% [from 61.0 (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 maximal cardiac index and DL,co decreased significantly by 15.6% [14.1 (SD 1.41) 1·min⁻¹ · m⁻² to 11.9 (SD 1.44)1·min⁻¹ m⁻², P<0.05] and 14.3% [85.9 (SD 4.36)ml·mmHg⁻¹ min^−t to 73.6 (SD 15.2) ml · mmHg⁻¹ -min⁻¹, P<0.05], respectively. The expedition to high altitude led to a decrease in maximal Q _c, oxygen uptake and D_L,CO. A decrease in muscle mass and capillarity may have been responsible for the decrease in maximal Q_c which may have resulted in a decrease of D _L,CO and an increase in alveolar-arterial oxygen difference. The decrease in D _L,CO especially at lower exercise intensities after the expedition may have been due to a ventilation-perfusion mismatch and changes in blood capacitance. At higher exercise intensities diffusion limitation due to reduced pulmonary capillary contact time may also have occurred.