This paper proposes a circulatory condition-monitoring system with an air-pack sensor for ongoing measurement of pressure signals in supine patients with cervical spinal cord injuries. The system can be used to determine pulse pressure waves, pulse beats, respiratory waves and the augmentation index (AI). In this study, the physiological significance of signals obtained via the sensor was elucidated by comparing them with signals actually measured using commercial devices. The results showed a close correspondence between the signals obtained using the proposed system and the pulse pressure waves, breathing waveforms and RR-intervals. The AI values estimated using the air-pack sensor also displayed a high level correlation with those determined from radial artery pressure waveforms. To verify the performance of the proposed system, a patient with an injury was tested while asleep. The results confirmed that the system can be used to assess circulatory states of arteriosclerosis using the estimated AI values.
