System for Measuring the Transthoracic Electrical Impedance to the Ecg Signal

This paper presents an electronic system for measuring the impedance of the electrocardiograph signal from its origin (heart) to the electrodes placed on the patient’s skin. The main advantages of this system are that the reading is taken at the frequency of the electrocardiographic signal and that it is a totally noninvasive method, as no external current is applied to the patient besides the amplifier polarisation currents. The developed system allows the measurement of a physiological parameter related with anthropometric variables such as height and body surface area, and reflects pathological conditions that theoretically can alter thoracic impedance such as chronic bronchitis and thoracic surgery. Besides, it allows a correction of the ECG derived parameters that increases the correlation with left ventricular mass and improves the senstitivity of ECG for the diagnosis of left ventricular hypertrophy.