2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
shift in hemoglobin saturation curve might also explain changes in SaO2. However,
any shift in hemoglobin saturation curve, which would be expected due to an
increased CO2 production, would shift the curve in a direction, where a similar PaO2
would result in a decrease, rather than an increase in SaO2.
It is postulated that the lack of difference in FeCO2 between the two experimental
conditions during hypoxia was due to the ability of subjects to increase their
ventilation in the CHO trial because of the additional CO2 produced by carbohydrate
metabolism in the CHO trial. This increase in ventilation accounted for the observed
increase in oxygen saturation and also for a lack of difference in FeCO2 between the
two trials.
An increase in heart rate was also observed following carbohydrate ingestion; this
result suggests that carbohydrates acted not only by increasing the ventilation, but also
through some direct effects on the central regulatory mechanisms. Namely, the
observed increase in heart rate might have been a consequence of an increased
demand for blood flow to the gut to absorb carbohydrates, however several studies
demonstrated that ingestion of carbohydrates also increases the activity in sympathetic
nervous system (Welle et al., 1981; Berne et al., 1989).
In the present study, there is no reason to expect that hemoglobin content changed
during the experiment, therefore an increase in SaO2 must have increased oxygen
content in the arterial blood. As it has been demonstrated that stroke volume is not
reduced during acute hypoxic exposure (Vogel and Harris, 1967), it is likely that the
observed increase in heart rate following carbohydrate ingestion increased cardiac
output in hypoxia. Such an increase in heart rate, combined with an increase in
oxygen saturation can improve oxygen delivery to the tissues in acute hypoxic
conditions.
REFERENCES
Berne, C., Fagius, J., Niklasson, F., 1989. Sympathetic response to oral carbohydrate
administration. Evidence from microelectrode nerve recordings. J. Clin. Invest.
84, 1403-1409.
Welle, S., Lilavivat, U., Campbell, R.G., 1981. Thermic effect of feeding in man:
increased plasma norepinephrine levels following glucose but not protein or fat
consumption. Metabolism. 30(10), 953-358.
Vogel, J.A., Harris, C.W., 1967. Cardiopulmonary responses of resting man during
early exposure to high altitude. J. Appl. Physiol. 22(6), 1124-1128.
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