Abstract
The aim of this investigation was to assess the changes of atrial volumes during and after prolonged high-altitude exposure, in relation to extracellular and total body water and plasma levels of atrial natriuretic peptide (ANP). The estimation of extracellular and total body water was obtained by bioelectrical impedance measurement in seven healthy male subjects aged 24.7 years (range 23-28). These were members of a Himalayan expedition (Pumori, 7135 m). Measurements were taken before departure, after 1 and 4 weeks at altitude over 5000 m, and upon return to sea level. In the same phases, right and left atrial volumes were determined by 2D-echocardiography and blood samples were drawn for ANP by radioimmunoassay.
At high altitude, body fluid depletion, as shown by reduction of extracellular and total body water, was related to reduction of left atrial volume, whereas the right atrium did not show any significant change. Upon return to sea level, the persistence of reduced extracellular and total body water went along with the persistence of decreased left atrial volume. Despite the wide variability in plasma levels of ANP among subjects, a clear-cut reduction was observed in all subjects after 4 weeks at high altitude, and a significant (p < .01) correlation was found between ANP concentrations and left atrial volumes, considering the subjects in all phases of research.
During prolonged high altitude exposure, progressive reduction of left atrial volume reflects body fluid depletion; after 4-week exposure, circulating ANP levels decrease concomitant with left atrial volume reduction.