Tissue viability imaging for assessment of pharmacologically induced vasodilation and vasoconstriction in human skin.

Tissue viability imaging (TIVI) is a novel polarization spectroscopy method for assessing dermal vascular viability. The purpose of the present study was to compare TIVI with laser Doppler flowmetry (LDF) for assessment of pharmacologically induced vasodilation and vasoconstriction in human skin. Eight individual skin sites on the backs of seven healthy volunteers were randomized to receive an intradermal injection of prostaglandin E2 (PGE2, 10(-6) to 10(-9)M), norepinephrine (NE, 10(-5) to 10(-7)M), or vehicle. Vascular responses were measured by TIVI and LDF at the injection sites at 1-min intervals starting 2min before and ending 15min after the skin challenge. TIVI and LDF demonstrated significant dose-dependent and time-related vasodilator responses to PGE2 and vasoconstrictor responses to NE, respectively (p<0.001). The time course and dose-response functions for LDF and TIVI showed notable differences. Dose-response data showed a significant reduction in TIVI signal with NE 10-7M (10(-6) NE with LDF) whereas PGE2 10(-6)M was required to elicit a significant increase in TIVI signal (10(-8)M PGE2 with LDF). TIVI demonstrated relative vascular response changes of 0.79 to 1.63 of baseline values at 15min with NE 10(-5)M or PGE2 10(-6)M compared to values of 0.59 to 8.38 with LDF. There was a modest though significant correlation between relative changes in vascular responses measured by the two methods (p<0.0001, r(2)=0.521). A Bland-Altman difference plot demonstrated significant underestimation of relative increase versus baseline measured by TIVI (r(2)=0.99, p<0.0001). We conclude that TIVI polarization spectroscopy is a sensitive method for measurement of NE-induced vascular responses but that it is less sensitive than LDF for measurement of the PGE2-induced reactions.