We studied the effects of bathing in warm water on cerebral blood flow (CBF). Seven healthy male volunteers were subjected to experiments. The subjects were bathed in warm water at 39°C for 20 minutes in a sitting position immersed up to the neck. Each subject received two CBF examinations: one under normal conditions and the other after taking a bath mentioned above. There was an interval of at least seven days between the two examinations. To measure CBF, we used the Patlak plot method with technetium-99m ethyl cysteinate dimer (99m-Tc ECD). To examine CBF after bathing, 99m-Tc ECD was injected within 10 minutes after bathing. Brain perfusion index (BPI) and regional CBF (rCBF) were used as indexes for evaluating CBF. The body temperature, pulse, blood pressure, arterial oxygen and carbon dioxide pressure, and hematocrit were also measured. Wilcoxon's signed rank test was used for statistical analyses. The following were observed:
1) BPI increased significantly after bathing (p<0.05).
2) rCBF in the cerebral cortex, particularly in the frontal lobe, tended to increase after bathing (p<0.05). No definite changes were observed in the cerebellar cortex, caudate nucleus, or thalamus.
3) The body temperature and pulse increased significantly after bathing. No definite changes were observed in blood pressure, arterial oxygen and carbon dioxide pressure, or hematocrit. From the above, we conclude that bathing in warm water causes the cerebral blood flow to increase in healthy subjects.