VISUAL THRESHOLDS AS AN INDEX OF PHYSIOLOGICAL IMBALANCE DURING ANOXIA

Publisher Website
Google Scholar
Abstract
The differential sensitivity of the human fovea was studied in relation to light intensity under a normal O2 tension and during a constant degree of O2 deprivation (10.8% O2) in a low O2 chamber. Final measurements were made while the subjects breathed 100% O2 through a nasal catheter. 9 subjects were used in these expts. The data are presented in 2 ways: a) as the differential threshold [DELTA]I plotted against the intensity I, and b) as the ratio [DELTA]I/I plotted against intensity. Both plots, on a double logarithmic grid, are fitted with theoretical curves derived from Hecht''s equation. The reduced O2 tension resulted in a translation of the log [DELTA]I vs. log I curve to the right and upwards along a 45[degree] asymptote. As the illumination increased anoxia caused progressively smaller changes in the threshold. The effect on the log [DELTA]I/I vs. log I curve is a simple translation to the right. This means that to reach any given level of [DELTA]I/I during a given degree of anoxia, the intensity I must be multiplied by a constant factor. The mean magnitude of the shift during exposure to 10.8% O2 was 0.356 log10 units. This is comparable to results obtained with other visual functions during equivalent degrees of O2 deprivation. The manner in which the effect of anoxia on differential thresholds varies with the degree of O2 deprivation was studied on 2 subjects. The changes in visual sensitivity are plotted in relation to a) time, b) decrease in arterial O2 saturation, and c) equivalent altitude, corresponding to the O2 tension. The increase of the differential threshold is initially proportional to the loss of arterial O2 saturation, but then tends to level off so that smaller increases result from further losses. The changes in the differential threshold plotted against equivalent altitudes are described by a sigmoid curve. Changes in visual sensitivity are discussed as an index of physiological imbalance in the organism.

This publication has 10 references indexed in Scilit: