Computer simulation of the response of the human body to immersion in cold water.

Many military and civilian personnel are required to work in situations where there is a risk of accidental immersion in the sea. Since immediate rescue may not be possible, it is important to predict the time for which survivors may remain alive. A computer-based mathematical model may provide a means of simulating the change in body temperature with time. The need for such a model and the physiological basis for its development have been investigated. A mathematical model has been developed in which the human body is visualised as 15 cylindrical or spherical segments, each divided into 10 radial shells of tissue. Passive heat flows are simulated at the surface and internally. Transport of heat by blood flow is represented in 120 arterial and venous compartments. The physiological mechanisms of thermoregulation are simulated, using existing physiological data. The model is implemented in structured FORTRAN 77 code. Although it is primarily configured for cold water immersion, infrastructure is included to permit adaption to simulate heat or cold stress in air. Code has been included for heat transfer through clothing and for exercising as well as resting conditions. Comparisons of the model predictions have been made against experimental data obtained from semi-nude immersions in water at 12, 18 and 24°C. For subjects with a relatively high body mass and fat content, the predicted body core temperature is generally within plus or minus one standard error of the experimental mean. For small, thin subjects at 12 and 18°C, the prediction is within two standard errors. The model does not cope well with sudden large changes in exercise but predictions for clothed subjects appear adequate