Ethnic stratification in northwest China: occupational differences between Han Chinese and national minorities in Xinjiang, 1982-1990

Skin color of free flaps can represent their vascular conditions after reconstructive surgery. Thus far, however, surgeons have subjectively inspected flap color changes. More precise and objective measurement is necessary for early detection of vascular insufficiency. In order to evaluate color changes of flaps we used a portable non-contact type colorimeter with a L*a*b* color space (L* is brightness and a*, b* are chromaticness) recommended by the CIE (Commission Internationale d'Eclairage). Initially, we successfully performed objective evaluation of flap color changes in rats with or without a tied femoral artery or vein. Vein failure showed a decrease in a* and b* soon after surgery, while the artery failure appeared as b* and L* after 12 and 24 hours, respectively. Then, the color differences between sites of clinical free flaps were examined and considered to be relatively negligible against the time-dependent changes using delta a*, delta b*, delta L*, which represents the difference in color of an objective point from a control point. Next, we demonstrated that the color of abdominal skin did not significantly differ from that of forearm skin using delta a*, delta b*, delta L*. The clinical free flaps were measured with these parameters pre- and post-operatively and their normal course of color changes was revealed. The findings showed that a* changed with characteristic ups and downs before and after elevation due to congestion.