Ankle-brachial index on Kilimanjaro: lessons from high altitude

This study investigated the effects of a high-sympathetic stimulus environment (high-altitude hypoxia) on limb-specific systolic blood pressure (sBP) and ankle-brachial index (ABI) in normal volunteers. We hypothesized that currently accepted normal values for ABI may in fact not reflect an actual normal vascular state in all patients.

Twenty climbers (17 males, 3 females) from Gatineau-Hull (Québec, Canada) participated in this study and ascended Mount Kilimanjaro, Africa. Ankle-brachial index measurements were performed at sea level and on Mount Kilimanjaro at approximately 4100 m. The data were analyzed using predictive analytics software SPSS 14.0. Data obtained at sea level were compared to those obtained at approximately 4100 m, with participants serving as their own controls.

Ankle-brachial indices measured at approximately 4100 m (mean = 1.20) were greater than those measured at sea level (mean = 0.97) (n = -6.23; 95% CI: -.32 to -.17; P < .001). There were no significant differences between the systolic brachial pressures at approximately 4100 m when compared to those at sea level (P = .814). Contrarily, systolic ankle pressures at sea level (mean = 132) were significantly greater than those measured at approximately 4100 m (mean = 152) (t = -3.5, 95% CI: -29 to -7.4; P = .002).

This study is the first to physiologically demonstrate that in response to a high adrenergic stimulus in healthy volunteers there is a greater increase in sBP in the legs vs the arms.