The impact of moderate-altitude staging on pulmonary arterial hemodynamics after ascent to high altitude

Baggish, Aaron L., Charles S. Fulco, Stephen Muza, Paul B. Rock, Beth Beidleman, Allen Cymerman, Kibar Yared, Peter Fagenholz, David Systrom, Malissa J. Wood, Arthur E. Weyman, Michael H. Picard, and N. Stuart Harris The impact of moderate altitude on pulmonary arterial hemodynamics after ascent to high altitude. High Alt. Med. Biol. 11:139-145, 2010.-Staged ascent (SA), temporary residence at moderate altitude en route to high altitude, reduces the incidence and severity of noncardiopulmonary altitude illness such as acute mountain sickness. To date, the impact of SA on pulmonary arterial pressure (PAP) is unknown. We tested the hypothesis that SA would attenuate the PAP increase that occurs during rapid, direct ascent (DA). Transthoracic echocardiography was used to estimate mean PAP in 10 healthy males at sea level (SL, P_B≈760 torr), after DA to simulated high altitude (hypobaric chamber, P _B≈460 torr), and at 2 times points (90min and 4 days) during exposure to terrestrial high altitude (P_B≈460 torr) after SA (7 days, moderate altitude, P_B≈548 torr). Alveolar oxygen pressure (Pao₂) and arterial oxygenation saturation (Sao₂) were measured at each time point. Compared to mean PAP at SL (mean±SD, 14±3mmHg), mean PAP increased after DA to 37±8mmHg (Δ=24±10mmHg, p<0.001) and was negatively correlated with both Pao₂ (r²=0.57, p=0.011) and Sao₂ (r ²=0.64, p=0.005). In comparison, estimated mean PAP after SA increased to only 25±4mmHg (Δ=11±6mmHg, p<0.001), remained unchanged after 4 days of high altitude residence (24±5mmHg, p=not significant, or NS), and did not correlate with either parameter of oxygenation. SA significantly attenuated the PAP increase associated with continuous direct ascent to high altitude and appeared to uncouple PAP from both alveolar hypoxia and arterial hypoxemia.