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1 IGDP in Physiology and Noll Laboratory, Department of Kinesiology, Pennsylvania State University, University Park, Pennsylvania, United States
* To whom correspondence should be addressed. E-mail: dwd141{at}psu.edu.
Aged humans often exhibit an impaired defense of core temperature during cold stress. However, research documenting this response has typically used small subject samples and strong cold stimuli. The purpose of this study was to determine the responses of young and older subjects, matched for anthropometric characteristics, during mild cold stress. Thirty-sex young (YS; (23±1 years, range 18-30) and 46 older (OS; 71±1 years, range 65-89) subjects underwent a slow transient cold air exposure from a thermoneutral baseline, during which esophageal temperature (Tes), mean skin temperature (Tsk), O2 consumption, and skin blood flow (SkBF; laser-Doppler flowmetry) were measured. Cold exposure was terminated at the onset of visible sustained shivering. Net metabolic heat production (Mnet), heat debt, predicted change in mid-region temperature (
Tmid) and tissue insulation (It) were calculated. Cutaneous vascular conductance was calculated as laser-Doppler flux/mean arterial pressure, and expressed as percent change from baseline (CVC%base). There were no baseline group differences for Tes, but Mnet was lower (OS: 38.0±1.1; YS: 41.9±1.1 W.m-2, p<0.05). Tes was well maintained in YS but fell progressively in OS (p<0.01 for all timepoints after 35 min). The skin vasoconstrictor response to mild cold stress was attenuated in OS (42±3 vs. 53±4 CVC%base, p<0.01). There were no group differences for Tsk or It, while Mnet remained lower in OS (p<0.05). The Tmid did not account for the drop in Tes in OS. Healthy aged humans failed to maintain Tes however the mechanisms underlying this response are not clear.
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