The effect of moist air on skin blood flow and temperature in subjects with and without diabetes.

Background: Endothelial function is known to be impaired in response to heat in people with diabetes, but little has been done to see how air humidity alters the skin blood flow response to heat. Methods: Seventeen male and female subjects were divided in two groups, one with type 2 diabetes and the other the control subjects without diabetes, age-matched to the diabetes group. All subjects participated in a series of experiments to determine the effect of the warming of the skin by air on skin temperature and skin blood flow. On different days, skin temperature was warmed with air that was 38 degrees C, 40 degrees C, or 42 degrees C for 20 min. Also, on different days, at each temperature, the air humidity was adjusted to 0%, 25%, 50%, 75%, or 100% humidity. Skin blood flow and temperature were measured throughout the exposure period. This allowed the interactions between air humidity and temperature to be assessed. Results: For the control subjects, the moisture in the air had no different effect on skin blood flow at air temperatures of 38 degrees C and 40 degrees C (analysis of variance, P > 0.05), although skin blood flow progressively increased at each air temperature that was applied. But for the warmest air temperature, 42 degrees C, although the four lower humidities had the same effect on skin blood flow, air at 100% humidity caused the largest increase in skin blood flow. In contrast, in the subjects with diabetes, blood flow was always significantly less at any air temperature applied to the skin than was observed in the control subjects (P < 0.05), and skin blood flow was significantly higher for the two higher humidities for the two higher air temperatures. Skin temperature paralleled these findings. Conclusion: These data show that individuals with diabetes do not tolerate moist, warm air above 50% humidity as well as controls without diabetes.