The effect of High to Low Altitude Adaptation on the Multifocal Electroretinogram
Peter Kristian Kofoed 1*,
Birgit Sander 1,
Gustavo Zubieta-Calleja 2,
Line Kessel 1,
Kristian Klemp 1,
and
Michael Larsen 1
1 Department of Ophthalmology, Glostrup Hospital, University of Copenhagen, Glostrup, Denmark
2 High Altitude Pathology Institute, La Paz, Bolivia; Department of Ophthalmology, Glostrup Hospital, University of Copenhagen, Glostrup, Denmark
* To whom correspondence should be addressed. E-mail: peter.k{at}dadlnet.dk.
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Abstract |
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PURPOSE. To examine variations in retinal electrophysiology assessed by multifocal electroretinogram (mfERG) during acclimatization of native highlanders during adaptation to normobaric normoxia at sea level.
METHODS. Eight healthy residents of from the greater La Paz area in Bolivia (3600 m above sea level) were examined over 72 days after arriving in Copenhagen, Denmark (sea level). A control group of 8 healthy lowlanders was used for comparison.
RESULTS. During the period of observation hemoglobin decreased from 16.7 gm/dL to 15.0 gm/dL (p = 0.0031), erythrocytes decreased from 5.3 T/l to 4.6 T/l (p = 0.0006), and hematocrit decreased from 49.4% to 42.2% (p = 0.0008). At baseline, Day 2 after arrival, the amplitudes (N1, P1, N2) of the mfERG were 43.1-59.9% higher in the highlanders than in lowlanders (p < 0.017). During acclimatization the mfERG amplitudes increased 16.9 to 20.4% (p < 0.028) to a level 73.2-87.0% higher in the highlanders than in lowlanders (p < 0.0008). The increase in amplitude was inversely proportional to the decrease in erythrocyte concentration (p = 0.023, 0.053, 0.12 for N1, P1, N2 respectively).
CONCLUSIONS. Upon arrival at sea level, highlanders had markedly supernormal multifocal electroretinographic amplitudes that continued to increase during the 72 day period of observation where the highlanders' hematocrit normalized. Our results suggest that acclimatization after a change in altitude and hence in ambient oxygen tension involves intrinsic retinal mechanisms and that acclimatization had not been completed at the end of the study.
Key Words:
retinal metabolism, electroretinography, adaptation, high altitude
