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

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 (DLNO) and for carbon monoxide (DLCO) 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 (V(O2)max), from 42 +/- 10 to 32 +/- 8mL/min/kg and increases in PVR, ventilatory equivalents for CO2 (V-E/V-CO2), DLNO, and DLCO. By univariate linear regression Vo(2)max at sea level and at altitude was associated with V-E/V-CO2 (p < 0.001), mean pulmonary artery pressure (mPpa, p < 0.05), stroke volume index (SVI, p < 0.05), DLNO (p < 0.02), and DLCO (p = 0.05). By multivariable analysis, V(O2)max at sea level and at altitude was associated with V-E/V-CO2, mPpa, SVI, and DLNO. The multivariable analysis also showed that the altitude-related decrease in V(O2)max was associated with increased PVR and V-E/V-CO2. These results suggest that pulmonary vascular reserve, defined by a combination of decreased PVR and increased DLNO, allows for superior aerobic exercise capacity at a lower ventilatory cost, at sea level and at high altitude.