Within each day exists a cycle that affects attention, alertness, energy and mood of a human being. This internal rhythm is produced and regulated by a neurological mechanism called the circadian clock. In healthy humans, the secretion of cortisol from the adrenal glands follows a diurnal cycle with a profound increase after awakening. This increase after awakening, a phenomenon termed the cortisol awakening response, appears to be a distinct feature of the hypothalamus-pituitary-adrenal axis, superimposing the circadian rhythmicity of cortisol secretion. Another circadian effect is the morning surge of blood pressure. A sudden activation of the sympathetic nervous system is the primary mediator of the morning surge. Increased-mediated sympathetic vasoconstriction has been found in normal subjects. Whereas arousal from sleep is associated with a slight rise in plasma epinephrine, arising induces a significant rise both in epinephrine and norepinephrine.
In Panza et al., “Circadian variation in vascular tone and its relation to α-sympathetic vasoconstrictor activity”, N Engl J Med 1991; 325:986-990, it is described that there is a circadian rhythm in basal vascular tone, due either partly or entirely to increased alpha-sympathetic vasoconstrictor activity during the morning. This variation may contribute to higher blood pressure and the increased incidence of cardiovascular events at this time of day.
Current methods for circadian phase detection usually require obtrusive sampling methods. One the one hand, it is possible to derive information on the circadian phase from the core body temperature. The core body temperature can be measured with an intra body sensor, such as an e-pill. Having to swallow an e-pill and to retrieve it from excrements is cumbersome. Alternatively, the temperature in the mouth or in the armpit can be measured, which may also be inconvenient to the individual. On the other hand, it is possible to derive information on the circadian phase from a salivary melatonin test. The salivary testing of melatonin requires the regular sampling of saliva. This is a burden to the individual.
In DE 4221526 A1 a system for controlling, measuring and training psycho-emotional adaption processes is disclosed. The system serves for non-invasively verifying different psycho-emotional states like arousal, stress, fear, relaxation, impact of ataractics etc. The system evaluates the secretion of the perspiratory glands by means of pulsating direct current. The system is implemented in the form of a wristwatch and converts electric values of the skin conductance into analog angle readings. A high arousal (low skin conductance) corresponds to a high angle reading (high impulse frequency).
In Till Roenneberg: “Chronobiology: The human sleep project”, Nature, June 2013, a research activity at the University of Munich is presented. Researchers have gathered a database including entries for more than 150.000 individuals from all over the world that have provided the times at which they go to bed, prepare for sleep, fall asleep, wake-up and get up.
Consequently, it is desirable to provide an approach for unobtrusive circadian phase detection. Such an approach could be used to provide a gentle adaption of the circadian phase of a person to an external requirement.