Changes in Cerebral Blood Flow on Performance of a Diving Reaction in Humans

Cerebral blood flow was studied in humans during performance of a diving reaction simulated by cold + hypoxia + hypercapnia, as well as in a cold test, on respiration of a 7% hypercapnic mix, and in the Genche test (breath-holding). A total of 18 subjects (18–22 years old with no special physical training were studied. Cerebral blood fl ow was recorded by transcranial dopplerography. Simulated diving increased the linear cerebral blood fl ow rate by 82.3 ± 15.2% and decreased the pulse index by 77.2 ± 13.1%. In the cold test, the linear blood fl ow rate remained unaltered, while the pulse index increased. There were no significant changes in these values on respiration of the 7% hypercapnic mix. In the Genche test, the linear blood flow rate increased by 52.3 ± 12.5% and the pulse index decreased by 64.5 ± 15%. The latent period of changes in cerebral blood flow in simulated diving (14–43 sec) indicated that the regulatory influences altering blood flow were metabolic in nature.