Pulmonary Vascular Reserve and Exercise Capacity at Sea Level and at High Altitude

Abstract

Abstract

Pavelescu, Adriana, Vitalie Faoro, Herve Guenard, Claire de Bisschop, Jean-Benoit Martinot, Christian Melot, Robert Naeije. Pulmonary vascular reserve and exercise capacity at sea level and at high altitude. High Alt. Med. Biol. 14:19–26, 2013.—It has been suggested that increased pulmonary vascular reserve, as defined by reduced pulmonary vascular resistance (PVR) and increased pulmonary transit of agitated contrast measured by echocardiography, might be associated with increased exercise capacity. Thus, at altitude, where PVR is increased because of hypoxic vasoconstriction, a reduced pulmonary vascular reserve could contribute to reduced exercise capacity. Furthermore, a lower PVR could be associated with higher capillary blood volume and an increased lung diffusing capacity. We reviewed echocardiographic estimates of PVR and measurements of lung diffusing capacity for nitric oxide (DL_NO) and for carbon monoxide (DL_CO) at rest, and incremental cardiopulmonary exercise tests in 64 healthy subjects at sea level and during 4 different medical expeditions at altitudes around 5000 m. Altitude exposure was associated with a decrease in maximum oxygen uptake (Vo₂max), from 42±10 to 32±8 mL/min/kg and increases in PVR, ventilatory equivalents for CO₂ (V_E/Vco₂), DL_NO, and DL_CO. By univariate linear regression Vo₂max at sea level and at altitude was associated with V_E/Vco₂ (p<0.001), mean pulmonary artery pressure (mPpa, p<0.05), stroke volume index (SVI, p<0.05), DL_NO (p<0.02), and DL_CO (p=0.05). By multivariable analysis, Vo₂max at sea level and at altitude was associated with V_E/Vco₂, mPpa, SVI, and DL_NO. The multivariable analysis also showed that the altitude-related decrease in Vo₂max was associated with increased PVR and V_E/Vco₂. These results suggest that pulmonary vascular reserve, defined by a combination of decreased PVR and increased DL_NO, allows for superior aerobic exercise capacity at a lower ventilatory cost, at sea level and at high altitude.