Although suited astronauts are currently cooled with a Liquid Cooled Ventilation Garment (LCVG), which can remove up to 85 percent of body heat, their effectiveness is limited because cooling must penetrate layers of skin, muscle, fat, bone, and tissue to reach the bloodstream, where its effect is prominent. Vasoconstriction further reduces the effectiveness by limiting arterial flow when exposed to cold (the frostbite response), resulting in a time constant on the order of 20 minutes from application to maximum effect. This delay can be crucial in severe exposure to hypo- or hyper-thermic conditions, compromising homeostasis.
The purpose of this innovation is to provide a lightweight, effective means of delivering heat or cold from an external source directly to the bloodstream. The effectiveness of this ECCREP (External Cooling Coupled to Reduced Extremity Pressure) device is based on not having to penetrate layers of skin, muscle, fat, and tissue, thereby avoiding the thermal lag associated with their mass and heat capacity. This is accomplished by means of an outer boot operating at a slightly reduced pressure than the rest of the body, combined with an inner boot cooled or heated by an external source via water or chemicals. Heat transfer from the external source to the foot takes place by means of circulating water or flexible heat pipes. The envisioned device, by applying its effect to only the foot or hand, has minimal power, flow, and mass requirements, making it attractive for the space/planetary operations environment and compatible with existing or modified extra-vehicular activity (EVA) suits, boots, and gloves.
In the glove configuration, the design may also have the added benefit of enhancing manual dexterity, a result of operating at a lower pressure than current EVA gloves. A boot configuration is preferable to a glove because the foot does not have any requirement for manual dexterity. The theoretical basis of the innovation is in the fact that heat transfer from the human body to its surroundings takes place largely in the extremities, especially the hands and feet. When exposed to heat, for example, large volumes of blood are directed to the hands and feet, which act as pin fin heat exchangers. This reaction is countermanded when extreme cold is applied to the skin to remove heat, as in the case of an LCVG, because extreme cold sets up vasoconstriction that limits bloodflow.
The theoretical basis of the innovation is that this countermand command is apparently bypassed in the presence of reduced pressure. The ECCREP device accelerates blood pooling in the capillaries and arterioles of the hand or foot due to reduced pressure, then applies cold or heat through an external source to turn the limb into a “super heat exchanger.”
The advantages of the device include the ability to deliver heat or cold more directly to the bloodstream, thus reducing the time lag of effectiveness; the ability to mitigate dehydration (sweat) and electrolyte loss; the potential to increase exercise performance and endurance (keys to operations in EVA and countermeasures while in orbit); and the possible mitigation of decrements in cognitive, motor, and immune system function associated with high-stress operations such as ascent, entry, and landing during long-duration and short-duration missions.
This work was done by Lawrence H. Kuznetz of Johnson Space Center. MSC-23849-1