Retinal vessel diameters in relation to hematocrit variation during acclimatization of highlanders to sea level altitude.

PURPOSE

To examine variations in retinal vessel diameters during acclimatization of native highlanders to normobaric normoxia at sea level.

METHODS

Fifteen healthy residents of the greater La Paz region in Bolivia (3600 m above sea level) were examined thrice over a 72-day period, after having traveled by airplane to Copenhagen, Denmark, near sea level.

RESULTS

In the study subjects, hematocrit decreased from 49.6% (day 2) to 45.9% (P = 0.0066, day 23) and 41.7% (P < 0.0001, day 72); from days 2 to 23, retinal vein diameter increased by 2.68% (P = 0.0079); whereas retinal artery and vein diameters were indistinguishable from baseline after 72 days. No funduscopic signs of retinopathy were observed. Arterial blood pressure remained stable throughout the study.

CONCLUSIONS

Although a 16% reduction in hematocrit occurred between days 2 and 72 after arrival at sea level, the only significant excursion observed was that the diameter of the veins was larger at day 23 than at days 2 and 72. Retinal vessel diameters demonstrated a wide homeostatic range during acclimatization-driven hematocrit variation.