Portable ECG - Electrocardiogram
Electrocardiogram (ECG or EKG) is the record of the electrical activity of the heart over a period of time. The measurement required to produce an electrocardiogram involves detection of a variety of electrical potential readings from electrodes taped to the patient's skin. The electrical potential between a pair of electrodes passes through a highly precise instrumentation amplifier and is read by an A/D converter. Ordinary ECGs can only be used for short-term recording of patients’ electrocardiosignal because they are too big to carry. While portable ECGs, for example DCGs (Dynamic Electrocardiograph) and Holter monitors, could be easily carried by patients and record up to 100 thousand cardiac cycles uninterruptedly for 24 hours. Minimal weight, and extended battery life are essential for a portable ECG.
A portable ECG is basically composed of electrodes, an AFE (Analog Front End), a MCU/DSP, a ZigBee module, a SD card, a buzzer, a battery and a display. Electrodes detect electrocardiosignal from human bodies and send it to AFE for amplification and band-pass filtering (high pass and low pass), as well as A/D conversion. AFE can be categorized into AC coupling and DC coupling according to coupling implementation. DC coupling is the dominant design of ECGs’ AFE at present because of its low peak-to-peak noise performance within a diagnosis bandwidth and low power consumption at high precision. The digital output of AFE is processed by a processing unit which displays a real-time electrocardiogram on screen and stores in SD card. Meanwhile, the processing unit can implement a quadratic differential wavelet transforms algorithm to identify abnormal electrocardiographic QSR waves. And if any abnormal is found, an alarm will be raised through buzzer. In addition, ECG data could be transmitted to a remote monitoring center through ZigBee wireless network.
Future portable ECGs are expected to be featured with more capabilities such as automatic diagnosis and remote wireless communication. Automatic diagnosis can figure out a general condition of patients based on a software algorithm and the detected electrocardiosignal. And if any problem, for example heart attack is detected, the portable ECGs equipped with remote wireless communication modules such as a GSM module would send an alarm immediately to patients’ families or doctors.