Analysis of the process of falling asleep – literature review

Involuntary falling asleep at the wheel is the cause of many road accidents and is an important social problem. For this reason, it seems important to explore the physiological processes associated with human falling asleep. Particularly interesting are those physiological parameters, which changes accompany the transition from the state of full consciousness to sleep. Monitoring them could be used eg. in determining the level of driver drowsiness and therefore assesment of the risk of falling asleep at the wheel. In this article we present a summary of knowledge on changes in selected physiological parameters that occur on the border of allertness/ sleep and deep sleep. Significant changes are particularly evident in the incidence of brain waves in the EEG. In addition, decrease in the activity of the autonomic nervous system leads to a decrease in heart rate and blood pressure. Also respiratory rate decreases and tidal volume increases. Spectral analysis of heart rate variability (HRV) shows decrease in the amplitude of the power spectral density function in the low frequency range. Also transition of eye movement from saccade to slow wave occurs during sleep which correlates with EEG changes. In addition, eyelids vibration disappear. Electromiography (EMG) shows gradual muscle tension fall. Warming in distal parts of limbs is also observed when falling asleep. All these parameters tend to be useful for evaluating the fatigue of the driver. In this article, we also try to determine which of them are suitable for drivers drowsiness monitoring