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Biomedical subjects

P L Saunders

Publications and source records attributed to P L Saunders.

5 recordsLinked to original sources
PubMed1995

The effect of varying time at -Gz on subsequent +Gz physiological tolerance (push-pull effect).

INTRODUCTION: 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. CONCLUSION: During relaxed conditions, the push-pull effect is augmented by increasing duration of the preceding -Gz.

Adult↗
PubMed1994

The "push-pull effect".

The purpose of this study was to prove or refute previous authors' suggestions that tolerance to +Gz is reduced when preceded by 0 Gz or -Gz. Six men and six women were subjected to one session of acceleration stresses that varied between -2 and +2.25 Gz on the NAMRL Coriolis Acceleration Platform (CAP). At the beginning and end of each session, we exposed the relaxed subjects to identical control segments that were comprised of +1 Gz for 30 s, followed by +2.25 Gz for 15 s, and then return to +1 Gz. Subjects were also exposed to three experimental segments that were comprised of 0, -1, or -2 Gz for 10 s, followed by +2.25 Gz for 15 s, and then return to +1 Gz. Subjects verbally reported any decrements in peripheral vision during exposure to +2.25 Gz. Blood pressure (BP) was reduced during each 15-s period at +2.25 Gz. The minimum BP was progressively lower during the 15-s period as the preexposure experimental conditions became more negative (+1, 0, -1, and -2 Gz). Episodes of peripheral vision loss increased as the preceding -Gz became more negative. BP during exposure to +Gz was significantly affected by the preceding 10-s exposure to -Gz, and is indicative of reduced +Gz tolerance. As this "push-pull effect" may result in unexpected incapacitation, it has important implications for aviation safety.

Acceleration↗
PubMed1979

The physiological cost of carrying light and heavy loads.

Nine subjects walked on a treadmill with load weights equal to 10% and 40% of body weight carried on the back. Although the speed of the treadmill was selected so that the measured oxygen consumption (VO2) was the same for both load conditions, the heavier load placed an extra strain on the cardiopulmonary system and was perceived by all subjects as harder work than the lighter load. When the subjects worked at their own pace, walking on a level road or climbing stairs with load weights equal to 10% and 40% of body weight, they compensated for the heavier load by decreasing walking speed or climbing rate. Although the energy costs calculated from walking speed, body and load weight for self-paced walking and the external work of stair climbing were the same for both load conditions, the heavier load was again perceived as harder work. These findings are discussed as they relate to the definition of acceptable load weights.

Adult↗