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During direct passive heating in young men, a dramatic increase in skin blood flow is achieved by a rise in cardiac output (Qc) and redistribution of flow from the splanchnic and renal vascular beds. To examine the effect of age on these responses, seven young (Y; 23 +/- 1 yr) and seven older (O; 70 +/- 3 yr) men were passively heated with water-perfused(More)
To test the hypothesis that unloading cardiopulmonary receptors improves human carotid baroreceptor responsiveness we measured heart rate (HR) and mean radial artery blood pressure (BP) responses elicited by trains of neck pressure and neck suction from +40 to -65 Torr during graded lower body negative pressure (LBNP) at -5, -10, -15, -20, -35, and -50 Torr(More)
Orthostatic intolerance is common when astronauts return to Earth: after brief spaceflight, up to two-thirds are unable to remain standing for 10 min. Previous research suggests that susceptible individuals are unable to increase their systemic vascular resistance and plasma noradrenaline concentrations above pre-flight upright levels. In this study, we(More)
The mean velocity of 9 out of 10 women's events during the U.S. Olympic Swimming Trials was greater in 1984 as compared to 1976. Three of the 10 men's events showed improvement. In 9 out of these 12 events, the increased velocity was accounted for by increased distance per stroke (range, -3 to -13%). In the women's 100-m butterfly and 100-m backstroke,(More)
Adaptation to head-down-tilt bed rest leads to an apparent abnormality of baroreflex regulation of cardiac period. We hypothesized that this "deconditioning response" could primarily be a result of hypovolemia, rather than a unique adaptation of the autonomic nervous system to bed rest. To test this hypothesis, nine healthy subjects underwent 2 wk of -6(More)
Power spectral and time based analyses were applied to the cardiac inter-beat interval (RRI) of 8 healthy men before and after 15 d of bed rest in the 6 degrees head-down tilt position (HDT) to determine changes in indices of cardiac parasympathetic and sympathetic activity after this exposure. At 24 h prior to HDT and on HDT day 15, a minimum of 256 RRI's(More)
Astronauts returning from space have reduced red blood cell masses, hypovolaemia and orthostatic intolerance, marked by greater cardio-acceleration during standing than before spaceflight, and in some, orthostatic hypotension and presyncope. Adaptation of the sympathetic nervous system occurring during spaceflight may be responsible for these postflight(More)
Ten male firefighters were tested on a treadmill to determine their heart rate (HR) x oxygen consumption (VO2) relationship. These men then performed a simulated fire suppression protocol during which HR and VO2 were measured simultaneously by a portable physiological monitoring system. Average VO2 in the simulated setting was 31.0 +/- 7.0 ml.kg-1.min-1 at(More)
We review the hypotheses presented to account for the anecdotal and literature-based reports that chronic endurance exercise training reduces orthostatic tolerance. The findings from cross-sectional investigations of unfit subjects and endurance athletes are examined, as well as limited data from recent investigations of the changes in orthostatic tolerance(More)
BACKGROUND The cardiovascular adaptation to bed rest leads to orthostatic intolerance, characterized by an excessive fall in stroke volume (SV) in the upright position. We hypothesized that this large fall in SV is due to a change in cardiac mechanics. METHODS AND RESULTS We measured pulmonary capillary wedge pressure (PCWP), SV, left ventricular(More)