Changes in body water distribution and phase angle following rapid ascent to 3,680 m and their association with acute mountain sickness: a prospective cohort study.

AMS incidence was 61.76% among healthy individuals who rapidly ascended from 500 m to 3,680 m by flight.

• A total of 34 participants were included in the prospective cohort study.
• AMS was diagnosed and severity assessed using the Lake Louise Score System (LLSS).
• Participants flew from plain (500 m) to plateau (3,680 m).
• Body composition was measured within 24 h before and 24 h after ascent using multi-frequency bioelectrical impedance analysis.

Phase angle (PhA) decreased significantly following rapid ascent to high altitude compared to plain baseline.

• PhA decrease was statistically significant (t = -4.78, p < 0.001).
• The decrease in PhA indicates pronounced cellular-level dysfunction following acute high-altitude exposure.
• This finding remained significant after analysis.

Extracellular-to-intracellular water ratio (ECW/ICW) decreased significantly after rapid ascent to high altitude.

• ECW/ICW decrease was statistically significant before correction (t = -2.41, p = 0.022).
• However, results for ECW/ICW and ΔECW/ICW showed no statistically significant difference after Bonferroni correction.
• The decrease in ECW/ICW suggests body water shifted into cells following high-altitude exposure.

Participants with AMS exhibited a greater magnitude of decrease in both ΔECW/ICW and ΔPhA compared to those without AMS.

• ΔECW/ICW difference between AMS and non-AMS groups: Z = -2.14, p = 0.032.
• ΔPhA difference between AMS and non-AMS groups: Z = -3.01, p = 0.003.
• Results for ΔECW/ICW showed no statistically significant difference after Bonferroni correction.
• Susceptible individuals with AMS exhibited a more pronounced decrease in PhA.

Both ΔECW/ICW and ΔPhA were negatively correlated with LLSS score by Spearman correlation analysis.

• ΔECW/ICW correlation with LLSS: r = -0.447, p = 0.008.
• ΔPhA correlation with LLSS: r = -0.646, p < 0.001.
• Results for ECW/ICW and ΔECW/ICW showed no statistically significant association after Bonferroni correction.
• A greater decrease in PhA was associated with higher (more severe) LLSS scores.

ΔPhA was an independent predictor of LLSS score in multiple linear regression analysis, whereas ΔECW/ICW was not.

• ΔPhA: β = -0.507, p = 0.001 in multiple linear regression.
• ΔECW/ICW did not emerge as an independent predictor of LLSS score.
• The authors conclude that monitoring ΔPhA may provide an effective, non-invasive method for early risk warning of AMS.