2021 Volume 57 Issue 6 Pages 333-340
Spinal cord injury makes a person lose the desire to urinate and leads to difficulty in voiding of urine. Catheterization at an opportune time is recommended as a coping technique, however, the practice is not easy. We have developed an algorithm for deriving the moment of a urine volume increase in the bladder until the need to void, using the acoustic pulse wave （APW） induced-heart beat via the body trunk detected at the back surface. The APW was continuously measured, and the urine volume in the bladder and subjective desire to urinate were acquired in an intermittent manner for each healthy experimental participant in a relaxed sitting position. Two time-series gradient heart rates were calculated from the heartbeat intervals calculated from each subject’s APW by two methods. Three ultra-low/very-low frequency band powers were calculated from each gradient heart rate, and total six time-series data were obtained from each subject. The characteristic waveforms of the band powers at the moment of a urine volume increase were distinguished. An algorithm was identified the moments that similar characteristic waveforms appeared. The determined algorithm derived eight identified moments among six eligible participants. Those were compared at each moment of the urine volume increase or the growing desire to urinate. Seven true-positive moments were confirmed, while one false-positive moment was confirmed （13％ risk rate of type I error）. There were no false-negative results （no errors of type II）.
