PERFUSION OF THE VISUAL-CORTEX DURING PRESSURE BREATHING AT DIFFERENTHIGH-G STRESS PROFILES

The effects of pressure breathing for G protection (PBG) on perfusion of the visual cortex were studied in a subject during various high-G s tress profiles. Blood flow velocity was measured in the posterior cere bral artery using a transcranial Doppler (TCD) ultrasound instrument. The G profiles examined included gradual and rapid onset rates. Mean c erebral blood flow velocity (MCBFV) declined with increasing +G(z) wit h G-suit protection alone. The MCBFV increased in direct proportion wi th increase in +G(z) acceleration with PBG. The mediating mechanisms f or the effects of PBG may include improved gaseous exchange, the dimin ished sympathicoadrenal discharges, and cardiopulmonary reflexes. A ro le for TCD in further research is indicated.