Brain Natriuretic Peptide Levels and the Occurrence of Subclinical Pulmonary Edema in Healthy Lowlanders at High Altitude

Background: High altitude (HA) pulmonary edema (PE) results from complex and misunderstood interactions between adaptation mechanisms. We assessed the occurrence of subclinical PE and brain natriuretic peptide (BNP) levels among nonacclimatized individuals during an expedition on Mount Elbrus (5642 m). Methods: Seven subjects underwent assessment of vital signs, Lake Louise Score, ultrasound lung comets using handheld echography and circulating BNP using capillary testing at different stages of ascension, in addition to baseline echocardiography. Friedman tests were used to compare serial measurements. Results: Heart rate, Lake Louise Score (P < 0.0001) and blood pressure (P = 0.037) increased during ascension; oxygen saturation decreased (P < 0.0001). BNP increased (40.7 +/- 16.8 vs 19.7 +/- 3.04 pg/mL; P < 0.01) after the summit, as did ultrasound lung comet count throughout ascension (P < 0.0001), but both parameters were not correlated (r = 0.36; P = 0.42). Post-summit peak BNP correlated with baseline left ventricular mass index (r = -0.79; P = 0.033). Conclusion: This study confirms the high incidence of subclinical PE during subacute exposure to hypobaric hypoxia and enhancement of this phenomenon after exertion. Although not correlated with the degree of PE, BNP levels increased after sustained effort at HA, but not at rest. Further investigation is needed to determine the mechanisms underlying the BNP response at HA and its usefulness as a monitoring tool during expeditions.