Noncontact screening system with two microwave radars for the diagnosis of sleep apnea-hypopnea syndrome

There were two key problems in applying Doppler radar to a diagnosis system for sleep apnea-hypopnea syndrome. The first is noise associated with body movements and the second is the body positions in bed and the changes of the sleeping posture. We focused on the changes of the amplitude of the radar output signal corresponding to the changes in the tidal volume, and proposed a method of detecting the change of the respiratory amplitude value without the influence of body position in bed. In addition, we challenged the detection of the apnea-hypopnea event confirmed by accompanied rise of heart rates. To increase the accuracy of heart rate measurement, we propose a new automatic gain control and a real-time radar-output channel selection method based on a spectrum shape analysis. A prototype of the system was set up at a sleep disorder center in a hospital and field tests were carried out with eight subjects. Despite the subjects engaging in frequent body movements while sleeping, the system was quite effective in the diagnosis of sleep apnea-hypopnea syndrome (the correlation coefficient r = 0.98).