Ankle-Brachial Index on Kilimanjaro: Lessons from High Altitude

ObjectiveThis 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.MethodsTwenty 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 ∼4100 m. The data were analyzed using predictive analytics software SPSS 14.0. Data obtained at sea level were compared to those obtained at ∼4100 m, with participants serving as their own controls.ResultsAnkle-brachial indices measured at ∼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 ∼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 ∼4100 m (mean = 152) (t = −3.5, 95% CI: −29 to −7.4; P = .002).ConclusionsThis 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.