Physical measurements

Abstract

Physical variables associated with biomedical systems are measured by a group of sensors known as physical sensors. Although many specific physical variables can be measured in biomedical systems, these can be categorized into a simple list as shown in Table 46.1. Sensors for these variables, whether they are measuring biomedical systems or other systems, are essentially the same. Thus, sensors of linear displacement can frequently be used equally well for measuring the displacement of the heart muscle during the cardiac cycle or the movement of a robot arm. There is, however, one notable exception regarding the similarity of these sensors: the packaging of the sensor and attachment to the system being measured. Although physical sensors used in nonbiomedical applications need to be packaged so as to be protected from their environment, few of these sensors have to deal with the harsh environment of biologic tissue, especially with the mechanisms inherent in this tissue for trying to eliminate the sensor as a foreign body. Another notable exception to this similarity of sensors for measuring physical quantities in biologic and nonbiologic systems are the sensors used for fluidic measurements such as pressure and flow. Special needs for these measurements in biologic systems have resulted in special sensors and instrumentation systems for these measurements that can be quite different from systems for measuring pressure and flow in nonbiologic environments.