Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, 10903 New Hampshire Ave, Silver Spring, MD 20903, USA.
Biomed Eng Online. 2011 Jul 29;10:66. doi: 10.1186/1475-925X-10-66.
We studied the worst-case radiated radiofrequency (RF) susceptibility of automated external defibrillators (AEDs) based on the electromagnetic compatibility (EMC) requirements of a current standard for cardiac defibrillators, IEC 60601-2-4. Square wave modulation was used to mimic cardiac physiological frequencies of 1-3 Hz. Deviations from the IEC standard were a lower frequency limit of 30 MHz to explore frequencies where the patient-connected leads could resonate. Also testing up to 20 V/m was performed. We tested AEDs with ventricular fibrillation (V-Fib) and normal sinus rhythm signals on the patient leads to enable testing for false negatives (inappropriate "no shock advised" by the AED).
We performed radiated exposures in a 10 meter anechoic chamber using two broadband antennas to generate E fields in the 30-2500 MHz frequency range at 1% frequency steps. An AED patient simulator was housed in a shielded box and delivered normal and fibrillation waveforms to the AED's patient leads. We developed a technique to screen ECG waveforms stored in each AED for electromagnetic interference at all frequencies without waiting for the long cycle times between analyses (normally 20 to over 200 s).
Five of the seven AEDs tested were susceptible to RF interference, primarily at frequencies below 80 MHz. Some induced errors could cause AEDs to malfunction and effectively inhibit operator prompts to deliver a shock to a patient experiencing lethal fibrillation. Failures occurred in some AEDs exposed to E fields between 3 V/m and 20 V/m, in the 38 - 50 MHz range. These occurred when the patient simulator was delivering a V-Fib waveform to the AED. Also, we found it is not possible to test modern battery-only-operated AEDs for EMI using a patient simulator if the IEC 60601-2-4 defibrillator standard's simulated patient load is used.
AEDs experienced potentially life-threatening false-negative failures from radiated RF, primarily below the lower frequency limit of present AED standards. Field strengths causing failures were at levels as low as 3 V/m at frequencies below 80 MHz where resonance of the patient leads and the AED input circuitry occurred. This plus problems with the standard's' prescribed patient load make changes to the standard necessary.
我们根据当前心脏除颤器电磁兼容性 (EMC) 标准 IEC 60601-2-4 的要求，研究了自动体外除颤器 (AED) 的最坏辐射射频 (RF) 敏感度。采用方波调制模拟 1-3 Hz 的心脏生理频率。与 IEC 标准的偏差是下限频率为 30 MHz，以探索患者连接导联可能产生共振的频率。还进行了高达 20 V/m 的测试。我们在患者导联上用心室颤动 (V-Fib) 和正常窦性节律信号测试 AED，以测试假阴性（AED 给出不建议电击的不当“无电击建议”）。
我们在 10 米的无回声室中使用两个宽带天线进行辐射暴露，在 30-2500 MHz 的频率范围内以 1%的频率步长产生 E 场。AED 患者模拟器被放置在屏蔽盒中，并将正常和颤动波形传输到 AED 的患者导联。我们开发了一种技术，可以在不等待分析之间的长周期时间（通常为 20 到 200 多秒）的情况下，筛选存储在每个 AED 中的 ECG 波形，以查找所有频率的电磁干扰。
测试的 7 个 AED 中有 5 个易受 RF 干扰，主要在 80 MHz 以下的频率。一些感应误差可能导致 AED 出现故障，并有效抑制操作员提示向遭受致命颤动的患者提供电击。当患者模拟器向 AED 传输 V-Fib 波形时，某些 AED 在 3 V/m 至 20 V/m 的 E 场中会出现故障，频率在 38-50 MHz 范围内。当使用 IEC 60601-2-4 除颤器标准的模拟患者负载对 EMI 进行测试时，我们发现无法对现代仅使用电池运行的 AED 进行测试。
AED 受到辐射射频的潜在威胁生命的假阴性故障，主要是在现有 AED 标准的低频限制以下。导致故障的场强低至 3 V/m，频率低于 80 MHz，此时患者导联和 AED 输入电路发生共振。加上标准规定的患者负载问题，因此需要对标准进行修改。
