Resting blood flow in the skin: does it exist, and what is the influence of temperature, aging, and diabetes?

Abstract

Measurement of resting blood flow to the skin and other organs is an important indicator of health and disease and a way to assess the reaction to various stimuli and pharmaceutical interventions. However, unlike plasma ions such as sodium or potassium, it is difficult to determine what the proper value for resting blood flow really is. Part of the problem is in the measurement of blood flow; various techniques yield very different measures of skin blood flow even in the same area. Even if there were common techniques, resting blood flow to tissue, such as the skin, is determined by the interaction of a plurality of factors, including the sympathetic nervous system, temperature, pressure, shear forces on blood vessels, tissue osmolality, and a variety of other stimuli. Compounding this variability, the blood flow response to any stressor is reduced by free radicals in the blood and diminished by aging and diabetes. Race also has an effect on resting blood flow to the skin. All these factors interact to make the exact resting blood flow difficult to determine in any one individual and at any one time. This review examines the main techniques to assess blood flow, the factors that alter blood flow in the skin, and how aging and diabetes affect blood flow. Recommendations for the measurement of resting blood flow are presented.

Figure 1

Vascular occlusion on the foot due to application of 30 s of pressure in three groups of subjects in 24 °C global temperature with standard deviation bars. Data were collected on 15 older subjects, 15 subjects with diabetes, and 15 younger subjects. Blood flow is measured in the skin by a laser Doppler flow meter. Reproduced with permission from Diabetes Technology & Therapeutics.

Figure 2

The blood flow of the arm from the elbow to the wrist assessed by venous occlusion plethysmography for 2 min after 4 min of vascular occlusion in young (triangle), older (squares), and people with diabetes (diamond). Thirty controls and 16 subjects with type 2 diabetes participated in this series of experiments to examine the interrelationships between age, diabetes, and endothelial cell function. The mean age of subjects with diabetes was 61.2 ± 10.1 years and for the nondiabetic group 55.3 ± 9.7 years. Reproduced with permission from BMC Endocrine Disorders.

Figure 3

Average blood flow response of the 30 subjects (± the appropriate SD) during heating by a thermode for 6 min for the leg: younger group (diamond), older group (square), and subjects with diabetes (triangle). Blood flow is measured by laser Doppler imager of the skin. The mean ages of the 10 subjects in each group was younger, 25.1 ± 2.2 years; older, 59.1 ± 6.1 years; and subjects with diabetes, 61.3 ± 7.9 years. The average duration of diabetes was 2–13 years, and the average hemoglobin A1c was 7.4 ± 1.3%. Reproduced with permission from Diabetes Technology & Therapeutics.

Figure 4

The blood flow response of the skin to heat at three temperatures with a dry and moist heat source. Blood flow is measured by laser Doppler imager of the skin. Data represent 20 young subjects, average age 24.1 ± 2.4 years. Reproduced with permission from Journal of Medical Engineering & Technology.

Figure 5

Excess in blood flow over rest during 2 min after vascular occlusion in younger and older people with and without type 2 diabetes. The regression equation for the subjects with diabetes is y = -0.3945x + 39.269 and for the older age-matched subjects is y = -0.5092x+ 77.707. There was no statistical difference between the slopes. Data are represented on 22 subjects with diabetes and 26 age-matched controls. Blood flow is measured on the arm by mercury in rubber plethysmography. Data are from Figure 2, calculated by integration as described in the text. Reproduced with permission from BMC Endocrine Disorders.

Figure 6

Blood flow response of the skin to heat over 6 min in two age-matched groups of young subjects; one group (squares) took vitamins for two weeks prior to measurements. Data are on 18 control subjects and 18 who took vitamins for two weeks. Blood flow is measured on the skin by a laser Doppler flow meter. Reproduced with permission from Anatomy & Physiology.

Figure 7

Mean ± standard deviation of blood flow (flux) measured during the exposure to heat at 42 °C in 10 Caucasians and 10 Koreans at rest and over a period of 360 s. Blood flow is measured by a laser Doppler flow meter. Reproduced with permission from Medical Science Monitor.

Figure 8

Mean ± standard deviation of blood flow (flux) measured during the 4 min period of occlusion and the 2 min period following the release of the occlusion cuff in 10 Caucasians and 10 Koreans. Blood flow was measured by a laser Doppler imager of the skin. Reproduced with permission from Medical Science Monitor.

Figure 9

Malondialdehyde is a measure of blood-born free radicals used to assess oxidative stress in the body. Illustrated here is the average malondialdehyde in venous blood in 10 Caucasians and 10 Koreans at baseline and 2 h after a high-fat and low-fat meal both before and after a 2-week vitamin regime. MDA, malondialdehyde.

Figure 10

Illustrated here is the blood flow response to 4 min of occlusion in 10 Koreans 2 h after a high-fat meal before vitamin administration. Blood flow was measured in the skin by a laser Doppler imager. Blood flow postocclusion was significantly lower after a high-fat meal (2 h post; analysis of variance p < .05).

Figure 11

Illustrated here is the blood flow response to 4 min of occlusion in 10 Koreans after a high-fat meal before and after two weeks of vitamin administration. Blood flow was measured in the skin by a laser Doppler imager. There was no significant difference in the blood flow response to occlusion before and after the high-fat meals (analysis of variance p > .05).