The independent effects of hypovolaemia and pulmonary vasoconstriction on ventricular function and exercise capacity during acclimatisation to 3800 m

We aimed to determine the isolated and combined contribution of hypovolaemia and hypoxic pulmonary vasoconstriction in limiting left ventricular (LV) function and exercise capacity under chronic hypoxaemia at high altitude. In a double-blinded, randomised and placebo-controlled design, 12 healthy participants underwent echocardiography at rest and during submaximal exercise before completing a maximal test to exhaustion at sea level (SL; 344m) and after 5-10days at 3800m. Plasma volume was normalised to SL values, and hypoxic pulmonary vasoconstriction was reversed by administration of sildenafil (50mg) to create four unique experimental conditions that were compared with SL values: high altitude (HA), Plasma Volume Expansion (HA-PVX), Sildenafil (HA-SIL) and Plasma Volume Expansion with Sildenafil (HA-PVX-SIL). High altitude exposure reduced plasma volume by 11% (P<0.01) and increased pulmonary artery systolic pressure (19.64.3 vs. 26.05.4, P<0.001); these differences were abolished by PVX and SIL respectively. LV end-diastolic volume (EDV) and stroke volume (SV) were decreased upon ascent to high altitude, but were comparable to sea level in the HA-PVX trial. LV EDV and SV were also elevated in the HA-SIL and HA-PVX-SIL trials compared to HA, but to a lesser extent. Neither PVX nor SIL had a significant effect on the LV EDV and SV response to exercise, or the maximal oxygen consumption or peak power output. In summary, at 3800m both hypovolaemia and hypoxic pulmonary vasoconstriction contribute to the decrease in LV filling, but restoring LV filling does not confer an improvement in maximal exercise performance.