Perfusion of the visual cortex during pressure breathing at different high-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 stress profiles. Blood flow velocity was measured in the posterior cerebral artery using a transcranial Doppler (TCD) ultrasound instrument. The G profiles examined included gradual and rapid onset rates. Mean cerebral blood flow velocity (MCBFV) declined with increasing +Gz with G-suit protection alone. The MCBFV increased in direct proportion with increase in +Gz acceleration with PBG. The mediating mechanisms for the effects of PBG may include improved gaseous exchange, the diminished sympathicoadrenal discharges, and cardiopulmonary reflexes. A role for TCD in further research is indicated.