In Response to “Ankle-Brachial Index on Kilimanjaro: Lessons From High Altitude”

To the Editor:

I read with interest the recent article by Nault et al ¹ regarding changes in ankle-brachial index (ABI) among a group of healthy individuals traveling from sea level to the summit of Mount Kilimanjaro. The observation of increased ABIs on the summit is certainly interesting, but the authors’ assertion that this is a result of hypoxic sympathetic stimulus is not sufficiently supported by the data.

In the design of their study, Nault et al have not uncoupled the effects of altitude from those of strenuous lower extremity exercise. Thus, it is not possible to clearly ascribe the increase in ABIs to the effects of hypoxic stress. Proving the authors’ claim requires 2 further experiments: ABI measurement at altitude without exercise and ABI measurement at sea level after exercise. The former could be undertaken at 2 US mountain peaks that are accessible by car: Pike's Peak (Colorado, elevation 4302 m) and Mauna Kea (Hawaii, elevation 4207 m). The second study would involve a group of subjects having ABIs measured after an equivalent exercise effort but without altitude gain.