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Six challenges and measures of ECG design

Time:2010-10-17 11:39:24       Edietor: admin

The engineers can use ADI solutions to face major challenges of ECG subsystem design, including safe, common mode/differential mode interference, inputing dynamic range requirements, equipment reliability and protection, reducing the noise and EMC/RFI.

ECG is a common medical record. In many bad environment, it must be clear to read and remain accuracy. No matter it is in hospital, ambulance, aircraft, ships, clinic or home, interference sources is everywhere. The new generation of highly portable ECG technology makes us measure heart action in more environmental conditions. With ECG subsystem more and more being applicated in hospital outside, manafacturers are facing pressure of continuous reducing system cost, shorten developing time and remaining or inproving performance level. Therefore, a ECG subsystem is invented, which is safe and effective and face environmental challenges.

 First challenge: Achieve the highest safety standards and ensure ECG subsystem safe and effective.

Safe is always the first attention object of ECG designer. Designer must be prevent surge or pressure from Ac power. When the ECG subsystem or medical equipment connected with patients or operators happens fault, it maybe appear dangerous voltage or current. The ultimate goal of ECG design is that ensure patients and operation person security and don't injure by this voltage or current.

Before designing ECG, engineers must ensure itself clinical application, where it uses and storages equipment. The engineers have to estimate all equipment misuse situation which may lead to current applied to patients and potential external connection. As the added current is less than 10μA rms, operators and the patient's safety is no problem in the condition of single fault. It prevents patient getting an electric shock accidents and protects ECG equipment.

ECG system have to comply with federal law, international standard and the relevant countries/regions instruction requirement. The U.S. food and drug administration divide medical products into three categories: I, II and III. The different categories have different requirments for product design and the examination and approval process. For example, The portable dynamic monitor used for diagnosing heart rhythm is II equipment; The heart monitor and implement is III equipment which has ECG subsystem.

The humon heart is sensitive for 50Hz to 60Hz current. After provation, only 50 Hz/60Hz current of 34 μA rms flows through the heart and the heart will be damage. Considering that various program being possible execution as ECG system connect with patients, the current 50 Hz/60 Hz current limition is set as 10 μA rms. In ECG design, 10 μA rms is design parameters in no fault condition.

The designer must check current from electrodes to circuit or electrodes to floor and it maybe cause single fault and all cases which lead to the current is more than 10 μA rms. The corresponding frequency range of 10μA rms limits is DC to 1 KHZ. From 1kHz to 100 kHz, current level increses with frequency linear; As it is 1 kHz, it is 10μA rms; When it is 100 Khz, it is 1 mA rms. If it is more than 100 kHz, current is limit of 1 mA rms.

The solutions are that placed resistance in signal path or using limit current device.



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