Influence of a twofold voluntary hyperventilation on visually evoked cortical potentials and human pupillogram.

We studied the direct and aftereffects of twofold hyperventilation (HV) on pattern reversing VEPs and pupillograms (PGs) of 19 healthy volunteers. The VEP-N80 and P100 latencies increased during HV. Both peak times were maintained for a longer period, up to 20 minutes after HV-2 ended. In addition, the PG-latency time during HV and the PG-construction time during and after HV were increased. The results indicated a temporary delay of neural afferent transmission in the visual system during and after HV. A similar delay of the nervous transmission appeared in the efferent part of the system regulating the pupillary movements after HV ended. The observed changes of the VEP and PG parameters most probably resulted from the hypocapnia cased by HV and its effect on the brain vessels, although other explanations for the changes of the VEP- and PG-parameters may have been possible.