Development of a practicable non-contact bedside autonomic activation monitoring system using microwave radars and its clinical application in elderly people.

We developed a practicable, non-contact, autonomic activation monitoring system using microwave radars without imposing any stress on monitored individuals. Recently, the rapid increase in the aging population has raised concerns in developed countries. Thus, hospitals and care facilities will need to perform long-term health monitoring of elderly patients. The system allows monitoring of geriatric autonomic dysfunctions caused by chronic diseases, such as diabetes or myocardial infarction (MI), while measuring vital signs in non-contact way. The system measures heart rate variability (HRV) of elderly people in bed using dual, 24-GHz, compact microwave radars attached beneath the bed mattress. HRV parameters (LF, HF, and LF/HF) were determined from the cardiac peak-to-peak intervals, which were detected by radars using the maximum entropy method. We tested the system on 15 elderly people with and without diabetes or MI (72-99 years old) from 7:00 p.m. to 6:00 a.m. at a special nursing home in Tokyo. LF/HF obtained by the system correlated significantly (R = 0.89; p < 0.01) with those obtained by Holter electrocardiography (ECG). Diabetic subjects showed significantly lower LF (radar) than non-diabetic (119.8 ± 57.8 for diabetic, 405.9 ± 112.6 for non-diabetic, p < 0.01). HF (radar) of post-MI subjects was significantly lower than that of non-MI (219.7 ± 131.7 for post-MI and 580.0 ± 654.6 for non-MI, p < 0.05). Previous studies using conventional ECG reveal that diabetic neuropathy decreases LF, and also MI causes parasympathetic attenuation which leads to HF reduction. Our study showed that average SDNN of post-MI patients is smaller than 50 ms which is known to have high mortality. The non-contact autonomic activation monitoring system allows a long-term health management especially during sleeping hours for elderly people at healthcare facilities.