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Key words: automatic external defibrillators, intelligent medical devices
Automatic External Defibrillators (AEDs) are in a class of devices known as intelligent medical devices. These devices include internal decision-making electronics (microcomputers and special software) that allows the devices to interpret physiologic signals, make medical diagnoses, and, in many cases, automatically apply therapy. Complete testing of this class of device is extremely difficult because of the wide range of possible signals that the device may see. The Automatic External Defibrillator Test System Development Project is intended to provide CDRH with the ability to objectively assess the performance of AEDs using a small set of simulated waveforms as the input signals (as opposed to actual physiologic signals collected in the clinic). In addition, this project is intended to demonstrate to the medical device community the feasibility of developing a bench test method for assessing the arrhythmia detection capability of AEDs.
A test system for AEDs was developed in FY 95. In FY 96, this test system was improved by increasing the fidelity of cardiac signal simulation. A database of simulated cardiac signal segments was developed which allowed comparative testing of AEDs. Public domain literature, patents, and standards were accumulated in order to ensure that the cardiac signals generated by the test system will accurately simulate the wide variety of signals that AEDs are expected to encounter. Figure 18 shows one such simulated signal. [PreME, PostMS, Stds]
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Key words: apnea, physiologic waveforms
The Apnea Monitor Physiologic Waveform Test Method Development project is intended to provide CDRH and the medical device community with a standard bench test method for determining the ability of an apnea monitor to detect apnea (the cessation of breathing) and its physiologic consequences. In this effort, OST engineers are working closely with clinicians and manufacturers through the Association for the Advancement of Medical Instrumentation's (AAMI) Apnea Monitoring Committee, which is co-chaired by the CDRH representative. This multi-year development project consists of the following steps:
In FY 96, effort focused on the development of signal acquisition hardware and the development of software for use in hardware evaluation and troubleshooting. Prototype boards were fabricated, tested, and found to perform within specifications. Also in FY 96, the principal investigator for clinical signal acquisition at the SIDS Institute, University of Maryland at Baltimore, received a one-year (renewable) Investigational Review Board (IRB) approval for the portion of the project to collect pilot data. In addition, OST received (conditional) approval for clinical signal acquisition from the CDRH Research in Human Subjects Committee (RIHSC) and is in the process of seeking FDA RIHSC approval. A contract to commence data-taking in FY 97 at the SIDS Institute has been awarded. [PreME, PostMS, Enf]
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Key words: pulse oximetry
Pulse oximeters are intelligent medical devices that can noninvasively assess the function of the heart and lungs during critical care and surgical procedures. They do this by calculating an indicator of oxygen saturation that is based on measuring the amount of light energy lost in a tissue bed perfused by pulsatile blood. More and more clinicians are coming to depend upon oximeters to issue an alert when the patient is in trouble, resulting in an exponential rise in oximeter use. The ability to assess the performance of oximeters to insure their safe and effective operation, including accuracy and immunity to noise and artifact, is therefore very important. The American Society for Testing and Materials (ASTM), the International Standards Organization (ISO), and the European Normalization Committee (CEN) all have addressed the need for a standard to insure the reliable and safe function of oximeters. All three standards, ASTM F1514, ISO pr9919, and CEN prEN 865, are similar in content and all three are unable to identify an adequate test method to support their requirements. OST is addressing the lack of test capability by developing an electronic simulator that uses recorded physiological waveforms adjusted for each oximeter's particular requirements, to reproducibly and without the use of blood samples challenge the performance of the device. Based on a previous FDA contract with the University of Washington, the prototype feasibility simulator is being improved and a new, higher performing clinical signal collection system is being developed.
OST was requested by CEN to provide technical assistance in support of their simulator development efforts. An OST scientist served as the Project Officer and principal engineer of the FDA simulator, presented the technical theory of operation and specifications to the CEN group during CENs biannual meeting in Athens, Greece, and has been requested to continue participating and contributing technical guidance until the test method for pulse oximeters has been completed and the standards can be amended to include it. A collaborative effort is underway to record highfidelity clinical waveforms that are representative of the expected physiological information and environmental noise and artifact, to develop a high fidelity, nonblood-based simulator, and to develop a test protocol so that both the quality of the calibration of the oximeter and its ability to function in its intended-use environment can be assessed. The goal of this work is to have all three international standards activities and the FDA regulatory process harmonized by having a single accepted test method used in each. [PreME, PostMS, Stds]