2011 Volume 31 Issue 1 Pages 25-36
This research aims to maintain accurate determination of heart and respiratory rates despite a subject's change of position and sleeping posture in bed, in a non-contact vital signs monitoring system for elderly people using two microwave radars that are placed beneath the mattress of a bed. To challenge the three problems in the Doppler radar based measurement, that is, Null detection point problems, harmonics and intermodulation interference and the limitation in the coverage area of radars, we propose a new real time selection method to choose the best radar-output channel out of four signals (I and Q cannels of each radar). Based on a spectrum shape analysis (SSA), we select the most appropriate channel with the least number of large peaks and with the largest peak-to-peak ratio in the FFT spectrum. A prototype of the system was set up at a nursing home and field tests were carried out with elderly subjects. The result of eight hours clinical test showed high correlation coefficients (r=0.61∼0.73) between heart rate determined by the proposed system and that derived from Holter ECG in spite of the frequent positional change in bed. This method achieved higher accuracy of heart rate detection than that of conventional methods. This system without any psychological and physical burden on elderly people is ideal as a new monitoring system in this time of limited resources in healthcare.
