Non-contact Assessment of Cardiovascular and Thermoregulatory Function during Exercise after Sleep Deprivation

The number of deaths due to heat stroke has been increasing rapidly in recent years, and it is predicted that by 2050 there will be 2.5 times as many deaths as at present. One of the major causes of heat stroke is loss of autonomic nervous system activity. Autonomic nervous system activity is a function of thermoregulation as well as cardiovascular regulation. However, the only index mainly used to control body condition is the cardiovascular index centering on heart rate. In addition, a noncontact, easy-to-use measurement system is needed for daily physical condition management. The purpose of this study was to evaluate autonomic nervous system activity in terms of both cardiovascular and thermoregulatory functions. We also aimed to construct a system that can measure these functions in a noncontact manner. To observe the effects of autonomic nervous system dysfunction more clearly, the subjects were asked to exercise. We focused on cutaneous blood vessels, which are commonly involved in cardiovascular and thermoregulatory functions. For the measurement of skin blood vessels, we used an index called the G/B ratio, which we have been developing for some time. This system uses differences in light absorbance to extract the contraction and dilation characteristics of facial capillaries. As a validation experiment, an exercise task using a bicycle ergometer was performed. The exercise intensity was set at 40% and calculated using the Karvonen method. Two conditions were used: normal sleep (control) and sleep deprivation for more than 24 hours (SD) to create a state of autonomic inactivity. The following parameters were measured: heart rate, blood pressure, peripheral vascular resistance, and cardiac output as cardiovascular indices, and deep body temperature, skin temperature, and facial animation as thermoregulatory indices. The G/B ratio also showed different variations between the control and SD conditions. The G/B ratio also varied differently between the control and SD conditions, suggesting that the G/B ratio alone can measure the state of autonomic nervous system inactivity. Future plans include making the system environmentally robust so that it can be used in daily life, and constructing a physical condition management system after further data collection.