The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

A Po.I Analyzer for bed side application : A prototype

Shinji Fukasawa RCET, Hiromi Suzuki^{1} CET, Jun Ueki^{2} MD, Teruo Miyagawa^{3} RRT, RPT, RCET, Toyoki Kugimiya^{4} MD Departments of Inhalation Therapy, Clinical Engineering^{1}. Respiratory Medicine^{2}, Anesthesiology^{4}, Juntendo University school of Medicine, Tokyo, Showa University^{3} school of Medicine, Tokyo Japan.

Introduction: Airway Occlusion Pressure (Po.I) is one of the important monitoring parameters for the respiratory management. The assessment of Po.1 is becoming more popular mainly as the improvement of the microprocessor built-in the ventilator. However, Po.I obtained by conventional analyzers and ventilators are rather unstable and the equipments are too large for the bed side monitoring. To solve these problems, we focused our effort on making computerized accurate prototype Po.I analyzer which is compact and easily usable. Method: A one-way closing shutter driven by a pulse motor was selected for the occlusion section, since the pulse motor is light, compact and has large torque. With these suitable characteristics, it was able to shut and open a shutter very quickly without disturbing measurement and, more importantly, the noise was minimum. To make the valve as light as possible, we chose thin aluminum plate. To minimize airway resistance, the diameter of airway was decided to be 22mm. The shutter was made of stainless steel and shaped like a half-closed fan with movable angel of 30 degrees to cover the airway completely. The shutter was connected to the controller which controls occlusion time. It can either be shut automatically just at the beginning of inspiration with each duration time of 0.01, 0.05, 0.1 or 0.2 seconds, or be manually shut for any desired duration. The process of the measurement was as follows: (1) detect a point when the speed of inhalation reaches 50ml/second, (2) generate a pulse for one measurement by turning on a switch, (3) send a pulse to the airway shutter controller, (4) make the controller send a command to the valve, (5) close the airway long enough to measure the pressure, (6) measure the occlusion pressure, (7) analyze the airway occlusion pressure with A/D conversion computer. A Macintosh (Power Book 150) is used for the wave analysis using software, 'Acknowledge' by Biopack System without any adjustment. Results: By using our prototype analyzer, mouth occlusion pressure was measured in 20 healthy volunteers with occlusion time of 0.01, 0.05, 0.1, 0.2 seconds. The mean occlusion pressure were less than -1 cmH_{2}O at the occlusion time of 0.1 (Po.I) and 0.2 seconds. The mouth occlusion pressure lines obtained at the occlusion time of 0.1 and 0.2 seconds were quite linear and showed good reproducibility.

Occlusion Time (second) Po.I (mean ± SD cmH2O)

0.01 -2.25±0.10

0.05 -1.33±0.46

0.1 -0.97±0.63

0.2 -0.65±0.84

Conclusion: Our prototype Po.I analyzer is accurate and compact, and is available as a movable bed side respiratory monitor. The priority in designing our prototype analyzer is the development of computerized valve closure system equipped with the large torque pulse motor.

Reference: OF-96-191

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