The study will compare the rewarming effectiveness of heat donation through the distal arms and legs during rewarming of mildly hypothermic subjects. Warming will be accomplished through either warm water immersion; and fluidotherapy. The investigators hypothesize that fluidotherapy will be as, or more, effective compared to warm water immersion

Dr. Gordon Giesbrecht is studying/comparing the effectiveness of heat donation through the distal arms and legs in rewarming a mildly hypothermic individual. Warming will be accomplished through either warm water immersion; and fluidotherapy.

Procedure. Eight participants will be cooled in 8°C water on three occasions and then warmed by each of three warming conditions. The study will include following specific procedures: Anthropometric data which includes age, weight, height, and measurements of skinfold thickness at four sites- biceps, triceps, subscapularis, and suprailiac will be collected. Participant's heart rate and electrocardiogram will be monitored continuously throughout the experiment.

Participants will be instrumented as follows:

1. About 12 heat flux disks (2 cm in diameter) will be taped to the skin on the arms, legs, torso, head etc. to measure skin temperature and heat transfer from the skin.
2. Three ECG leads will be affixed to the skin.
3. Core temperature will be measured with a disposable esophageal thermocouple. A thin, flexible tube will be inserted through the nose, to midway down the esophagus at the level of the heart.
4. Oxygen consumption will be continuously measured with a metabolic cart. Participants will be asked to wear a face mask which will collect the expired breath during the cooling as well as the rewarming periods.

Conditions: The three treatment methods are as follows.

A. Spontaneous rewarming (Shivering only) - In this control condition, no external heat will be provided and the participant will rewarm spontaneously with the heat produced from shivering.

B. Warm water distal extremities immersion - Distal arms and legs will be immersed in warm water at 45°C for rewarming.

C.Fluidotherapy distal extremities rewarming - Distal arms and legs will be immersed in Fluidotherapy equipment for rewarming at 50°C.

Rewarming procedures will be administered either for a period of 60 minutes or until core temperature returns to normal values ( ̴ 36.5-37˚C). Following that, participants will be placed in a warm water bath (40-42˚C).

Research Design: Each of the three experimental trials, separated by at least 48 hours. On each of the three trials, participants will be immersed up to the level of the sternal notch in 8˚C for up to 60 minutes or until the core temperature falls to 35˚C. The participant will then exit the water, be dried off and rewarmed with either lie inside a vapor barrier within a hooded sleeping bag with the head inside the hood, or sitting with their distal arms and legs immersed in either Fluidotherapy at 50°C or warm water at 45°C. The rewarming will be administered for 60 minutes or until the core temperature returns to normal values (̴36.5-37˚C). The order of warming methods will follow a balanced design.

Inclusion Criteria:

• 18-45 yrs old, males or females, healthy

Exclusion Criteria:

• cardiopulmonary disease
• any symptoms caused by cold exposure