Therapies... - Hydrotherapy - Effects on Circulation

Water temperature can influence blood movement. The key muscle organ that generates blood circulation in the body is the heart. However, this is only partly true for the blood flowing in the arterial system, namely the blood leaving the heart. The movement of venous blood returning to the heart is mainly facilitated by the contractile action of the muscular skeletal system, such as muscles of the legs and abdomen. In addition, the smooth muscle lining the arteriole walls, venules, and lymph vessels also contribute to the overall motion of blood flow. The capillaries in the peripheral circulation, although they do not have a muscular lining, can be induced to dilate and constrict.

As the skin contains many capillaries, skin temperature can cause a dilation or constriction on the peripheral blood vessels. The combined area of periphery capillary cross-sections is almost 800 times that of the aorta. Dilated peripheral vessels can thus serve as a storage for blood when it is drawn away from central circulation, up to a capacity that can almost shut down the heart by leaving it with hardly anything to pump. At the same time, abnormally constricted peripheral vessels can overload the central circulation for the heart. Therefore, the peripheral capillaries can be stimulated through the skin to expand or contract with the ultimate effect of serving as a peripheral pump for circulation.