Pulmonary Vascular Function and Aerobic Exercise Capacity at Moderate Altitude.

PURPOSE: 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) allow 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 cardiopulmonary exercise test at sea level and at an altitude of 2250 m.
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 (V˙O2max), 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 (V˙E/V˙CO2) at sea level and at moderate altitude. Independent determinants of V˙O2max 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 V˙O2max 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.