Development of a New Ambulatory Monitoring System for Indirect Beat-to-Beat Arterial Blood Pressure Using the Volume-compensation Method

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A new portable instrument for the ambulatory monitoring of instantaneous arterial blood pressure using the volume-compensation method previously proposed by us has been developed in the first project year. The superficial temporal artery was chosen as a measuring site order to minimize restraint for a subject and to avoid venous congestion during the long-term monitoring. A disc-type cuff with a reflectance-type photo-sensor for blood volume detection was firmly placed to the subject's head using a belt and the subject carried a cuff-pressure (Pc) control (CPC) unit (32x65x110mm, 210g) and a microprocessor-based central processing & recording (MCPR) unit (85x185x200mm, 800g). An interactive software was also developed in this year for sequential measurement control and data storage in an automatic manner during the monitoring. The CPC unit consisted mainly of a micro air pump for compressed air supply and a miniature piezo-electric valve (PVAA8000120H, JUPITOR Co.) for Pc control. The … More MCPR unit performs the automatic setting of the servo-reference value and control of the servo-gain, processing and storing of beat-to-beat indirect systolic (Pcs), mean (Pcm) and diastolic blood pressure (Pcd) and instantaneous heart rate (HR). Altogether 60,000 beats of each data can be stored in a memory IC unit. After the monitoring, the stored data are reproduced and analyzed using a conventional personal computer or a specially ordered equipment for data analysis (ECM-1DS, ESCOM CO.) to obtain trend charts and histograms of Pcs, Pcm, Pcd and HR.In the second project year, the instrument was further improved as follows and the performance in an operation was evaluated through the clinical and dieldwork experiments. A nozzle-flapper type miniature electro-pneumatic converter for Pc control was newly designed, which was installed in the disc-type cuff together with a miniature pressure toansducer for Pc measurement. Through these modification, the frequency response of the Pc servocontrol system was highly and only the improved MCPR unit including a micro-air pump was carried by a subject. In order to evaluate the accuracy for blood pressure measurement by this instrument, simultaneous measurements of direct brachial and indirect superficial temporal arterial pressure were made in catheterised patients, showing fairly good agreements between these two values and pressure wave forms. With this instrument, ambulatory monitorings during fieldwork, highway driving, physicotherapeutics and so on, were successfully carried out, revealing that the instrument seems to have good operating performances and to be an useful means to monitor instantaneous variations of blood pressure in unrestricted subjects. Because the superficial temporal artery was adopted as a measuring site, the long-term monitoring could be made in the subjects being little affected by discomfort.The whole programs of this research project were completed within the project term with satisfactory results as described above. Less