Diagnosis and therapy

Abstract

This chapter provides an introduction to the two types of electrical medical devices—medical instruments and electrical stimulators. A medical instrument is a medical device that makes measurements, often for the diagnosis of disease. The physiologic quantity, property, or condition that the system measures is the measurand. The energy or information from a measurand is converted to another form by a transducer. If the transducer output is an electrical signal, then the transducer is a sensor. Commonly used sensors are the surface electrode, pressure sensor, thermistor, and photodiode. An external electrical stimulator requires a power source such as standard line 60-Hz/120-V or lithium batteries. Based on user input, the processing module activates a waveform circuit that discharges an appropriate waveform through electrodes to the patient. If the waveform is discharged over the skin, the surface electrodes are used, with electrode cables connecting the stimulator to the electrodes. An implantable electrical stimulator is used for chronic disease management. The three parts of an implantable electrical stimulator are the leads, pulse generator, and programer. Medical electrical stimulators are often also electronic instruments, such as early implantable pacemakers always paced the right ventricle at a steady rate.