Impaired defense of core temperature in aged humans during mild cold stress

Abstract

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-six 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 (T(es)) and mean skin temperatures (T(sk)), O(2) 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 (M(net)), heat debt, predicted change in midregion temperature (DeltaT(mid)), and tissue insulation (I(t)) were calculated. Cutaneous vascular conductance (CVC) was calculated as laser-Doppler flux/mean arterial pressure and expressed as percent change from baseline (DeltaCVC(%base)). There were no baseline group differences for T(es), but OS M(net) was lower (OS: 38.0 +/- 1.1; YS: 41.9 +/- 1.1 W . m(-2), P < 0.05). T(es) 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 DeltaCVC(%base), P < 0.01). There were no group differences for T(sk) or I(t), while M(net) remained lower in OS (P < 0.05). The DeltaT(mid) did not account for the drop in T(es) in OS. Healthy aged humans failed to maintain T(es); however, the mechanisms underlying this response are not clear.

Cutaneous Infrared Thermometry for Detecting Febrile Patients

“…Our study identifi ed age as a variable that interferes with cutaneous measurement, but the role of gender is less obvious. Older persons showed impaired defense (stability) of core temperatures during cold and heat stresses, and their cutaneous vascular reactivity was reduced (12,13). Use of a simple infrared thermometry, rather than sophisticated imaging, should not be considered a limitation because this method concerns the relationship between cutaneous and central core temperatures.…”

Sex differences in age-related changes on peripheral warm and cold innocuous thermal sensitivity

“…Age-dependent neural degeneration observed in thermoreceptors can reduce both physiological and perceptual thermal sensitivity. Impaired cutaneous vascular function and delays in the sweating and shivering thresholds have been reported in age comparison studies [2,3,4,5,6]. Likewise, reduced thermal sensations in older adults have been reported, alongside a number of other tactile responses (touch, pressure and noxious thermal sensitivity) [7,8,9,10,11].…”

Extremity cooling for heat stress mitigation in military and occupational settings

“…It should be noted, however, that heart rate differences persisted into subsequent work bouts in the aforementioned studies (Khomenok et al, 2008;Selkirk et al, 2004), suggesting that more than postural differences are involved. No previous studies have reported changes in skin blood flow or stroke volume changes during extremity immersion cooling; however using cold air exposure or water-perfused suit models, it is well-established that skin temperature and skin blood flow are directly related (DeGroot and Kenney, 2006;Stephens et al, 2001). Therefore, considering the reduction in heart rate reported in several studies, it is reasonable to speculate that skin blood flow requirements are reduced, peripheral pooling is reduced, and stroke volume is maintained.…”