Mammals are equipped with a sophisticated system for controlling core temperature. This is achieved through the means of specialized vascular structures called arteriovenous anastomoses (AVAs) located in the hairless areas of the body, primarily the palms of the hands and soles of the feet. These areas of the human body possess two separate and distinct vascular beds: one for nutrient blood flow and the other, a high volume vascular bed, specifically utilized to bring large quantities of blood near the surface of the skin.

This second type of vascular bed is used by the body to shunt blood to the skin when the body is overheated. Conversely, when the body is exposed to cold and becomes hypothermic, these vascular beds constrict, thus shunting blood back to the core. Hypothermic individuals have minimal blood flow to the skin surface and especially to the areas of the palms of the hands and soles of the feet. A common complaint of cold patients is that their hands and/or feet feel cold. In a hypothermic patient, blood flow into the extremities can drop as much as 90% from the fully dilated state.

The body makes efficient use of its blood supply to control its core temperature. Heat is efficiently moved about the body by the circulation of the blood supply. The skin and fat that overlay the body act as an effective layer of insulation. This layer of insulation maintains the core temperature when the person is initially confronted by excessive heat or cold. When the blood supply to the skin is reduced, as in cases of hypothermia, external sources of heat (radiant, convection) are poorly conducted through the skin and fat.

The thermoregulatory system in humans can be compromised by many factors (anesthesia, trauma, environment, others) and may lead to the various thermal maladies and disease conditions. Upon induction of general anesthesia for instance, induced hypothermia may occur due to temperature redistribution from the core to the periphery from systemic vasodilation caused by the anesthetic agents. Thermal maladies, such as hypothermia and hyperthermia, can occur when the thermoregulatory system is overwhelmed by severe environmental conditions. Constriction of the AVAs thermally isolates the body core from the environment, while dilation of the AVAs promotes a free exchange of heat between the body core and the environment.

When a person becomes hypothermic, it is the vital organs in the body core that need to be warmed to counter the clinical consequences of the hypothermic state. Warming of skin and fat does little to improve mental status, reverse coagulopathy and decrease oxygen consumption. It is therefore imperative to get heat quickly to the core when treating a patient suffering from hypothermia.

Conventional methods of warming are slow at delivering heat to the body’s core and may be ineffective at times. These methods typically involve the application of blankets warmed either actively by convection (forced air warming) or conduction (fluid circulation warming), or passively (cotton blankets warmed in warming cabinets). The vitalHEAT™ vH²™ Temperature Management System warms the body core without requiring large areas of the patient’s body to be covered.

Future applications of CTR technology may include the treatment of hyperthermia — a condition in which the individual is unable to decrease body temperature within normal limits. Treatment of heat stroke is dependent on the ability to remove heat from the core rapidly. This process can be done more efficiently by maximal dilatation of the AVAs in the hands and feet. With these vascular structures maximally dilated and the application of cooling to the hand or foot, heat transfer out of the body may occur at an increased rate. This treatment approach might also be combined with other forms of therapy such as fluid resuscitation to increase effectiveness.