MEASUREMENT OF THE THERMAL INERTIA OF THE SKIN USING SUCCESSIVE THERMOGRAMS TAKEN AT A STEPWISE CHANGE IN AMBIENT RADIATION TEMPERATURE

Skin thermal properties are difficult to measure in vivo in the steady state because there is a constant temperature gradient across the ski n surface. However, measurement of skin thermal properties is postulat ed in quantitative evaluation for thermographic observation. In this s tudy, imaging of the thermal inertia of the skin was attempted by ther mographic measurements at a stepwise change in ambient radiation tempe rature achieved by quickly switching two hoods maintained at different temperatures. Using this technique, a total of 65 thermograms were se quentially recorded at intervals of 0.5 s beginning 2 s before the ste pwise change. The image of skin thermal inertia was estimated by apply ing statistical curve fitting at each pixel of the thermograms. In add ition, the emissivity and true temperature of the skin were also deter mined, together with thermal inertia, in a single measurement. Measure ments were made at different sites on 10 subjects. The average values of thermal inertia of normal skin were scattered throughout a range fr om 1.4 x 10(3) to 2.1 x 10(3) W s(1/2) m(-2) K-1. Investigations of th e relationship between skin blood flow and thermal inertia were also m ade by imaging thermal inertia when skin blood flow was changed by app lying a vasodilator or vasoconstrictor on the skin surface. In a compa rison with the data measured by laser Doppler flowmetry, the average s lope of skin blood flow versus thermal inertia was 2.88 x 10(-4) V per W s(1/2) m(-2) K-1, and the thermal inertia of the skin with no blood how was 1.03 x 10(3) W s(1/2) m(-2) K-1. The results also show an alm ost linear correlation between skin blood flow and thermal inertia in each individual, but inter-individual differences were also observed. The results suggest that skin blood flow distribution can be estimated by non-contact imaging of thermal inertia.