The influence of age and diabetes on the skin blood flow response to local pressure.

BACKGROUND: Previous data has shown that when pressure is applied to the skin of the ankle and on the foot, there is a reactive increase in circulation. In the present investigation, these studies were expanded to look at the response of the hand, back, and foot to applied pressure. MATERIAL/METHODS: Ten young subjects whose average age was 26.5+/-3.3 yrs, 10 older subjects whose average age was 73.3+/-19.7 yrs and 10 people with diabetes whose average age was 60.1+/-5.7 yrs participated in the study. There was no statistical difference in the height or weight of the subjects. Hemoglobin A1c of the group with Diabetes averaged 6.98+/-1.15% with the mean duration of diabetes 13.6+/-9.5 yrs. An infrared laser Doppler flow meter was used to measure circulation on the hand, lower back, and on the bottom of the foot during applications of pressure at 15, 30, 45, and 60 kPa. RESULTS: For all three areas of the body, circulation was significantly less in the group with diabetes than the other two groups (p<0.05). When pressure was applied at 15 kPa, the blood flow to the skin initially decreased, but then increased in the younger subjects and in the older subjects but did not increase in subjects with diabetes for any area of the body. Further, after pressure was released, for any of the four pressures examined here, while the younger subjects showed a pronounced reactive hyperemia, subjects with diabetes showed a diminished hyperemia not proportional to the pressure that was applied. CONCLUSIONS: It appears that the normal protective mechanism of a pressure induced hyperemia is absent or diminished in patients with diabetes with more effect on the periphery than on the core area of the body. More importantly, after pressure was applied and released, subjects with diabetes lacked a proportional hyperemia to recovery form the transient ischemia of the pressure.

The influence of ageing on the ability of the skin to dissipate heat.

BACKGROUND: Ageing reduces the resting blood flow to the skin as well as the blood flow response to thermal stimuli. However, the interrelationships between skin thickness, subcutaneous fat, and skin blood flow in determining the heat dissipation characteristics of the skin have not been investigated. MATERIAL/METHODS: In the present investigation, 60 male and female subjects were examined with either a continuous 0.15 watt heat source or a 40 degrees C instantaneous heat source applied to the skin. Data was correlated to skin and subcutaneous fat thickness measured by ultrasound and to skin blood flow measured by a laser Doppler flow meter. RESULTS: The results of the experiments showed a significant negative correlation between age and skin thickness (p<0.0001) and between age and subcutaneous fat thickness (p<0.001). Blood flows in the skin, with the subject in a 24 degrees C, room were 61.8% less in the older subjects compared to the younger subjects. This was due to both a reduction in red cell concentration and red cell velocity. The lower concentration of red cells matches the reduction in skin thickness, implying a loss in the dermal layer of the skin associated with ageing. The skin blood flow response to continuous heat and to a single heat exposure were both reduced in the older subjects (p<0.01). Ageing also caused a slower response of the skin to heat stress. CONCLUSIONS: The results support a reduction in both the resting and post local heat skin blood flows associated with ageing. Some of this may be due to a reduction in dermal layer thickness due to ageing.

Skin heat dissipation: the influence of diabetes, skin thickness, and subcutaneous fat thickness.

BACKGROUND: It is well established that diabetes impairs vascular endothelial function. However, the impact of impaired endothelial function on thermal conductivity of the skin, especially in relation to a constant versus a sudden heat stress, has not been established. Further, there is some evidence that aging reduces skin dermal thickness and subcutaneous fat thickness. Since these are important determinates of heat dissipation by the skin, these parameters also need to be examined in people with diabetes. METHODS: Ninety subjects (30 younger individuals, 30 patients with diabetes, and 30 patients age-matched to the diabetes subjects) participated in two series of experiments to determine (1) the thickness of the subcutaneous fat layer and skin thickness and the skin response to a sudden heat stress and (2) the response to a continuous heat stress on the lower back. Skin thickness and subcutaneous fat thickness were assessed by ultrasound, and skin blood flow was examined by infrared laser Doppler flow meter. RESULTS: People with diabetes had significantly less resting blood flow, blood flow in response to a single or continuous heat load, less subcutaneous fat, and thinner skin than either age-matched controls or younger people (P < 0.05). Subjects with diabetes also had the lowest concentration of red blood cells in their skin, implying a reduction in the number of capillaries in the skin. CONCLUSIONS: Thinning of the skin and probably a reduction in capillaries in the dermal layer contribute to a reduction in the blood flow response to heat. People with diabetes, in particular, have reduced skin heat dissipation because of less resting blood flow and thinner skin than that seen in age-matched controls.