抄録
It is reported that drowning accidents occur when the person is fully clothed. The victim should take the back float position, because comfortable for breathing. However, it is considered to be feeling the discomfort by water, physiological changes will occur. In this study, the degree of discomfort is expressed by the heart rate of the victim. The experiment was carried out in the swimming pool at a water temperature of 10.5℃ and a room temperature of 14.2℃. Three subjects were selected. They continued to keep the back float position with fully clothes including the sweater and the rain jacket on the surface of water. In addition, the temperature loggers and a Holter monitor were attached to the subject. The duration of keeping the back float position on the surface of water was 15 minutes. The temperature and electrocardiography were analyzed by regression analysis. The heart rate for all subjects increased in a moment prior to the decrease with decreasing the temperature near the surface of the back. The high heart rate continued for 1 minute and then it decreased. First increasing is thought to be a result of discomfort of the subject who feels cold water at his back. On the other hand, decreasing following first increasing is thought be a result of promotion of the venous return by the water pressure, accompanied with habituation for cold water. These results suggest that discomfort of cold water may be a factor for the breaking the back float position.
