Comparison of several G-tolerance measuring methods at various seatback angles.
The most commonly accepted endpoint indicative of impending "blackout" for subjects (Ss) exposed to +GZ on a centrifuge is peripheral light loss (PLL). A comparison was made using PLL and cessation of bloodflow in the temporal artery, as measured in eight Ss with an externally mounted ultrasonic flowmeter using the doppler effect. Each relaxed S was exposed to increasing G (onset rates of 0.1 and 0.3 G/s), while positioned at seatback angles of 15 degrees, 60 degrees, and 75 degrees. In addition to the flowmeter, arterial oxygen saturation was monitored with an ear oximeter, and respiration and ECG were recorded. Tolerance to G loads was slightly greater with the more rapid rate of G onset. While use of the flowmeter resulted in obtaining reliable G tolerance endpoints in all cases, in only about 75% of these cases was the same true for PLL. Responses obtained from the ear oximeter were variable and delayed, showing only slight decreases in arterial saturation, which became more pronounced as the G-load exposure duration increased.
D000054:Acceleration; D000328:Adult; D000337:Aerospace Medicine; D006112:Gravitation; D006801:Humans; D010092:Oximetry; D011187:Posture; D012039:Regional Blood Flow; D012212:Rheology; D013699:Temporal Arteries / Q000502:physiology; D014474:Unconsciousness / Q000503:physiopathology; D014785:Vision, Ocular