The effect of varying time at -Gz on subsequent +Gz physiological tolerance (push-pull effect).
BACKGROUND
Previous studies have demonstrated decreased +Gz tolerance when preceded by 0 Gz or -Gz, referred to as the "push-pull effect." The purpose of this experiment was to observe the effect of varying time duration at -Gz on the push-pull effect.


METHODS
During single sessions, six subjects (three men, three women) were subjected to five relaxed exposures to +2.25 Gz on the NAMRL Coriolis Acceleration Platform (CAP). The first and last exposures were control runs that were preceded by +1 Gz. Each experimental run was preceded by -2 Gz for 2, 5, or 15 s. Blood pressure (BP) was monitored using the Finapres at the level of the clavicle. Visual light loss was assessed at +2.25 Gz using a light bar.


RESULTS
Mean BP was significantly reduced when the +2.25 Gz exposures were preceded by -2 Gz. Following 15 s of -2 Gz, mean BP decreased more and was slower to recover than for 2 and 5 s of -2 Gz. Reported incidents of visual light loss were: 1 following 2 s, 2 following 5 s, and 4 following 15 s at -2 Gz. There were no reports of visual light loss during control runs.


CONCLUSIONS
During relaxed conditions, the push-pull effect is augmented by increasing duration of the preceding -Gz.
D000328:Adult; D000337:Aerospace Medicine; D001794:Blood Pressure / Q000502:physiology*; D005260:Female; D006801:Humans; D018471:Hypergravity; D018472:Hypogravity; D008297:Male; D013997:Time Factors; D015354:Vision, Low / Q000209:etiology*