Impact of hydrotherapy on skin blood flow: How much is due to moisture and how much is due to heat?

Abstract

Hydrotherapy and whirlpool are used to increase skin blood flow and warm tissue. However, recent evidence seems to show that part of the increase in skin blood flow is not due to the warmth itself but due to the moisture content of the heat. Therefore, two series of experiments were accomplished on 10 subjects with an average age of 24.2 +/- 9.7 years and free of diabetes and cardiovascular disease. Subjects sat in a 37 degrees C hydrotherapy pool under two conditions: one in which a thin membrane protecting their skin from moisture while their arm was submerged in water and the second where their arm was allowed to be exposed to the water for 15 minutes. During this period of time, skin and body temperature were measured as well as skin blood flow by a Laser Doppler Imager. The results of the experiments showed that the vapor barrier blocked any change in skin moisture content during submersion in water, and while skin temperature was the same as during exposure to the water, the blood flow with the arm exposed to water increased from 101.1 +/- 10.4 flux to 224.9 +/- 18.2 flux, whereas blood flow increased to only 118.7 +/- 11.4 flux if the moisture of the water was blocked. Thus, a substantial portion of the increase in skin blood flow associated with warm water therapy is probably associated with moisturizing of the skin rather than the heat itself.

The interrelationship between air temperature and humidity as applied locally to the skin: The resultant response on skin temperature and blood flow with age differences

“…Movement of heat to or from the skin is through the passive heat exchange properties of the skin and the ability of the circulation to change [9]. Skin circulation is controlled through the sympathetic nervous system [10], mediated by vascular endothelial cells releasing vasodilators such as nitric oxide [11]. When local heat is applied to the skin, these same vasodilators respond to increase skin circulation and protect the skin from damage [6,8].…”

Comparison of Different Heat Modalities for Treating Delayed-Onset Muscle Soreness in People with Diabetes

“…The heat modality used most commonly clinically is hydrocollator heat wraps. 30 This local heat source reduces cytokines and pain. [31][32][33] However, hydrocollator heat wraps are a clinical tool that cannot be used at home.…”

“…Two widespread heat modalities were used: a clinical heat modality, hydrotherapy, 43 and a common home modality, ThermaCare dry heat. [3][4][5] However, recent experiments published in the last few years showed that chemically generated moist heat is more effective in warming deep tissue than that seen with either of these standard therapy modalities, 30,36,37 and that is why all three modalities were tested in this study. This is highly relevant because chemical moist heat packs have not been tested on muscle soreness in people with diabetes.…”

“…43 Heat activates transient receptor potential vanillin-4 and -1 voltage-gated calcium channels in the skin, inhibiting P 2 X 2 purine pain receptors on tactile nerves. 16,30,38,50 However, because of the high temperatures and the brief duration of use of this type of hot pack, there is a risk of burns. Hydrocollator heat packs also have little effect on muscle temperature but do elicit an increase in skin blood flow (as seen here).…”

Skin Moisture and Heat Transfer

“…One of those was through conductive heat loss. Conductive heat loss, as described above, involves passive properties of the skin including skin fat content, moisture, and structure [ 64,85 ] . The other way of moving heat is related to skin blood fl ow [ 81 ] .…”