The effect of head and neck suction on G tolerance.
A device was constructed which allowed subatomospheric pressures of up to -50 mm Hg to be applied to the neck, or to the head plus neck, of volunteer subjects riding on the USAFSAM centrifuge. Breathing pressures were always atmospheric. The G tolerance was measured during gradual (0.1 G.s-1) and rapid onset (1.0 G.s-1) runs and heart rate was monitored. Neck suction decreased tolerance to an extent explicable by carotid sinus activation (about -0.8 G at -50 mm Hg), while combined head and neck suction of -25 mm Hg increased tolerance to an extent greater than predicted from pressure effects on the eye and carotid sinus. Neck suction of -50 mm Hg induced less bradycardia when applied at +3 Gz than under 1-G conditions. These results were discussed in relation to intraocular tension, baroreceptor responsiveness, and jugular venous siphon effect.
USAF School of Aerospace Medicine, Crew Technology Division, Brooks Air Force Base, Texas.
D H
DH
Glaister
J B
JB
Lenox
D000054:Acceleration; D000328:Adult; D001794:Blood Pressure; D002560:Cerebrovascular Circulation; D004562:Electrocardiography; D006112:Gravitation; D006260:Head Protective Devices; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D011311:Pressoreceptors / Q000502:physiology*; D011482:Protective Devices; D013396:Suction / Q000295:instrumentation*; D014794:Visual Fields