RELATIONSHIPS BETWEEN SWEATING RATE AND SKIN BLOOD FLOW IN PREPUBERTAL BOYS AND YOUNG MEN 780

Two potential mechanisms, reduced skin blood flow (SBF) and sweating rate (SR), may be responsible for elevated intestinal temperature (Tin) during exercise after bed rest and spaceflight. Seven men underwent 13 days of 6° head-down bed rest. Pre- and post-bed rest, subjects completed supine submaximal cycle ergometry (20 min at 40% and 20 min at 65% of pre-bed rest supine peak exercise capacity) in a thermoneutral room. After bed rest, Tin was elevated at rest (+0.31 ± 0.12°C) and at the end of exercise (+0.33 ± 0.07°C). Percent increase in SBF during exercise was less after bed rest (211 ± 53 vs. 96 ± 31%; P ≤ 0.05), SBF/Tin threshold was greater (37.09 ± 0.16 vs. 37.33 ± 0.13°C; P ≤ 0.05), and slope of SBF/Tin tended to be reduced (536 ± 184 vs. 201 ± 46%/°C; P = 0.08). SR/Tin threshold was delayed (37.06 ± 0.11 vs. 37.34 ± 0.06°C; P ≤ 0.05), but the slope of SR/Tin(3.45 ± 1.22 vs. 2.58 ± 0.71 mg · min−1 · cm−2 · °C−1) and total sweat loss (0.42 ± 0.06 vs. 0.44 ± 0.08 kg) were not changed. The higher resting and exercise Tin and delayed onset of SBF and SR suggest a centrally mediated elevation in the thermoregulatory set point during bed rest exposure.

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Age alters the cardiovascular response to direct passive heating

Journal of Applied Physiology ◽

10.1152/jappl.1998.84.4.1323 ◽

1998 ◽

Vol 84 (4) ◽

pp. 1323-1332 ◽

Cited By ~ 161

Author(s):

Christopher T. Minson ◽

Stacey L. Wladkowski ◽

Anthony F. Cardell ◽

James A. Pawelczyk ◽

W. Larry Kenney

Keyword(s):

Blood Flow ◽

Skin Blood Flow ◽

Thermal Tolerance ◽

Cardiovascular Response ◽

Venous Pressure ◽

Young Men ◽

Older Men ◽

Venous Occlusion ◽

Passive Heating ◽

Total Blood

During direct passive heating in young men, a dramatic increase in skin blood flow is achieved by a rise in cardiac output (Q˙c) 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 suits to their individual limit of thermal tolerance. Measurements included heart rate (HR),Q˙c (by acetylene rebreathing), central venous pressure (via peripherally inserted central catheter), blood pressures (by brachial auscultation), skin blood flow (from increases in forearm blood flow by venous occlusion plethysmography), splanchnic blood flow (by indocyanine green clearance), renal blood flow (by p-aminohippurate clearance), and esophageal and mean skin temperatures.Q˙c was significantly lower in the older than in the young men (11.1 ± 0.7 and 7.4 ± 0.2 l/min in Y and O, respectively, at the limit of thermal tolerance; P < 0.05), despite similar increases in esophageal and mean skin temperatures and time to reach the limit of thermal tolerance. A lower stroke volume (99 ± 7 and 68 ± 4 ml/beat in Y and O, respectively, P < 0.05), most likely due to an attenuated increase in inotropic function during heating, was the primary factor for the lowerQ˙c observed in the older men. Increases in HR were similar in the young and older men; however, when expressed as a percentage of maximal HR, the older men relied on a greater proportion of their chronotropic reserve to obtain the same HR response (62 ± 3 and 75 ± 4% maximal HR in Y and O, respectively, P < 0.05). Furthermore, the older men redistributed less blood flow from the combined splanchnic and renal circulations at the limit of thermal tolerance (960 ± 80 and 720 ± 100 ml/min in Y and O, respectively, P < 0.05). As a result of these combined attenuated responses, the older men had a significantly lower increase in total blood flow directed to the skin.

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