EFFECTS OF HIGH ATMOSPHERIC-PRESSURE AND OXYGEN ON MIDDLE CEREBRAL BLOOD-FLOW VELOCITY IN HUMANS MEASURED BY TRANSCRANIAL DOPPLER

Background and Purpose-There are several reports that have studied the effects of hyperbaric oxygen (HBO) on cerebral blued flow (CBF). Howe ver, most of the reports have been of animal experiments, and human st udies are few so far. The aim of this study is to clarify the relation ship between HBO and CBF in humans. Methods-Middle cerebral arterial b lood now velocity (MCV) was measured using transcranial Doppler (TCD) technique in a multiplace hyperbaric chamber. The Doppler probe was fi xed on the temporal region by a head brit, and the transcutaneous gas measurement apparatus (tcPO(2) and tcPCO(2)) was fixed on the chest wa ll. MCV and transcutaneous gas were measured continuously in eight hea lthy volunteers under four various conditions: 1 atmosphere absolute ( ATA) air, I ATA oxygen (O-2), 2 ATA air, and 2 ATA O-2. On the nest st ep, the effect of environmental pressure was studied in another eight healthy volunteers, in whom the tcPO(2) was kept at almost the same le vel under conditions of both 1 ATA and 4 ATA ty inhaling oxygen at 1 A TA. Results-MCV of 1 ATA O-2, 2 ATA air, and 2 ATA O-2 decreased, and tcPO(2) increased significantly in comparison with thar: oi 1 ATA air, A significant difference in MCV was observed between the O-2 group an d he air group under the same pressure circumstance, On the other hand , there were Ilo differences in MCV or tcPO(2) between 4 ATA air and 1 ATA plus O-2, and the influence for the MCV of the environmental pres sure was not observed. Conclusions-We conclude that hyperoxemia caused by HBO reduces the CBF, but the high atmospheric pressure per se does not influence the CBF ill humans.