Background: 

To maintain a stable core temperature the human body balances heat production and heat loss. Heat from the core to the skin is primarily transported through conduction and blood flow. Fat has low heat conductive properties; therefore humans with a high fat precentage show high tissue insulation. The magnitude of skin blood flow greatly influences heat loss to the environment. Especially glabrous skin, rich in arteriovenous anastomoses, is capable of facilitating high and low perfusion rates close to the skin surface. Hence, these areas are well adapted for regulating heat loss. This study for the first time explored the relation between gender and perfusion of glabrous skin of the hand to tissue insulation during cold exposure.

Methods:

Measurements of energy expenditure (indirect calorimetry), skin temperature (wireless thermistors), core temperature (telemetric pill), perfusion (laser Doppler flowmetry), fat percentage (DXA-scan) and surface area (DXA-scan) were performed on 16 young adults (18-28 yrs; 8M 8F). All females were measured during the pre-follicular phase of their menstrual period. Tissue insulation was calculated according to deGroot and Kenney I=Area*(T_core-T_skin)/(M_net+S) (°Cm²/W), where M_netis metabolic rate corrected for respiratory heat loss and S is heat storage. During a 15 minute baseline period skin temperature was clamped at 33.5°C by a water perfused suit; next subjects were mildly cooled for 15 minutes by progressively lowering water temperature in the suit.

Results: 

Females had a significantly larger fat percentage than males (p<0.001). At baseline tissue insulation between both genders differs significantly (males: 0.08±0.01 vs. females: 0.11±0.01 (p<0.05)). Tissue insulation did not correlate significantly with fat percentage. After 15 minutes of cooling no significant difference in tissue insulation between genders is observed anymore. No significant gender difference in vasoconstriction is observed. Log linear regression between tissue insulation and perfusion at glabrous skin of the hand shows highly significant relations for both genders (males: r²=0.89, p<0.001; females: r²=0.87, p<0.001).

Conclusion:

The results indicate that during baseline female tissue insulation is significantly higher than in men, which is not significantly correlated to body fat percentage. During whole body cooling the gender effect in tissue insulation disappears. Regression analysis indicates that variation in tissue insulation can mainly be explained by vasoconstriction at glabrous skin of the hand.