Pulmonary Vascular Function and Aerobic Exercise Capacityat Moderate Altitude

There has been suggestion that a greater "pulmonary vascular reserve" defined by a low pulmonary vascular resistance (PVR) and a high lung diffusing capacity (DL) allows for a superior aerobic exercise capacity. How pulmonary vascular reserve might affect exercise capacity at moderate altitude is not known. METHODS: Thirty-eight healthy subjects underwent an exercise stress echocardiography of the pulmonary circulation, combined with measurements of DL for nitric oxide (NO) and carbon monoxide (CO) and a cardio-pulmonary exercise test at sea level and at the altitude of 2250m. RESULTS: At rest, moderate altitude decreased arterial oxygen content (CaO2) from 19.1±1.6 to 18.4±1.7 ml/dl, p<0.001 and slightly increased PVR, DLNO and DLCO. Exercise at moderate altitude was associated with decreases in maximum O2 uptake (VO2max), from 51±9 to 43±8 ml/kg/min, p<0.001 and CaO2 to 16.5±1.7 ml/dl, p<0.001 but no different cardiac output, PVR and pulmonary vascular distensibility. DLNO was inversely correlated to the ventilatory equivalent of CO2 (VE/VCO2) at sea level and at moderate altitude. Independent determinants of VO2max as determined by a multivariable analysis were the slope of mean pulmonary artery pressure-cardiac output relationship, resting stroke volume and resting DLNO at sea level as well as at moderate altitude. The magnitude of the decrease in VO2max at moderate altitude was independently predicted by more pronounced exercise-induced decrease in CaO2 at moderate altitude. CONCLUSION: Aerobic exercise capacity is similarly modulated by pulmonary vascular reserve at moderate altitude and at sea level. Decreased aerobic exercise capacity at moderate altitude is mainly explained by exercise-induced decrease in arterial oxygenation.