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(Stroke. 2008;39:336.)
© 2008 American Heart Association, Inc.

Original Contributions

Cerebrovascular Responses to Hypoxia and Hypocapnia in Ethiopian High Altitude Dwellers

Victoria E. Claydon, PhD; Giosué Gulli, MD, PhD; Marat Slessarev, MSc; Otto Appenzeller, MD, PhD; Guta Zenebe, MD; Amha Gebremedhin, MD Roger Hainsworth, MB, PhD, DSc

From ICORD (V.E.C.), University of British Columbia, Vancouver, Canada; the Institute for Cardiovascular Research (V.E.C., G.G., R.H.), University of Leeds, UK; the Department of Physiology (M.S.), University of Toronto and Department of Anaesthesia, Toronto General Hospital, Ontario, Canada; the New Mexico Health Enhancement and Marathon Clinics (NMHEMC) Research Foundation (O.A.), Albuquerque, NM; the Department of Neurology (G.Z.), Yehuleshet Higher Clinic, University of Addis Ababa, Ethiopia; and the Department of Medicine (A.G.), University of Addis Ababa, Ethiopia.

Correspondence to Victoria E Claydon, International Collaboration On Repair Discoveries (ICORD), 6270 University Boulevard, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada. E-mail claydon{at}icord.org

Background and Purpose— Cerebrovascular responses to hypoxia and hypocapnia in Peruvian altitude dwellers are impaired. This could contribute to the high incidence of altitude-related illness in Andeans. Ethiopian high altitude dwellers may show a different pattern of adaptation to high altitude. We aimed to examine cerebral reactivity to hypoxia and hypocapnia in healthy Ethiopian high altitude dwellers. Responses were compared with our previous data from Peruvians.

Methods— We studied 9 Ethiopian men at their permanent residence of 3622 m, and one day after descent to 794 m. We continuously recorded cerebral blood flow velocity (CBFV; transcranial Doppler). End-tidal oxygen (P_ETo₂) was decreased from 100 mm Hg to 50 mm Hg with end-tidal carbon dioxide (P_ETco₂) clamped at the subject’s resting level. P_ETco₂ was then manipulated by voluntary hyper- and hypoventilation, with P_ETo₂ clamped at 100 mm Hg (normoxia) and 50 mm Hg (hypoxia).

Results— During spontaneous breathing, P_ETco₂ increased after descent, from 38.2±1.0 mm Hg to 49.8±0.6 mm Hg (P<0.001). There was no significant response of CBFV to hypoxia at either high (–0.19±3.1%) or low (1.1±2.9%) altitudes. Cerebrovascular reactivity to normoxic hypocapnia at high and low altitudes was 3.92±0.5%.mm Hg^–1 and 3.09±0.4%.mm Hg^–1; reactivity to hypoxic hypocapnia was 4.83±0.7%.mm Hg^–1 and 2.82±0.5%.mm Hg^–1. Responses to hypoxic hypocapnia were significantly smaller at low altitude.

Conclusions— The cerebral circulation of Ethiopian high altitude dwellers is insensitive to hypoxia, unlike Peruvian high altitude dwellers. Cerebrovascular responses to P_ETco₂ were greater in Ethiopians than Peruvians, particularly at high altitude. This, coupled with their high P_ETco₂ levels, would lead to high cerebral blood flows, and may be advantageous for altitude living.

Key Words: cerebrovascular responses • Ethiopia • high altitude • hypoxia