LEARNING OBJECTIVES

1. 1 list and describe what a sensor does

2. 2 identify the two types of transducers and describe examples of each type

3. 3 list and describe the sources of error in sensor systems

4. 4 list and describe the four types of electrodes (surface, micro, indwelling, and needle)

5. 5 list and describe the sensors that are used to record direct blood pressure and temperature

6. 6 list and describe impedance matching and patient impedance

7. 7 list and describe human periodic, static, and random signals

8. 8 characterize human signals as analog and medical devices as digital

9. 9 describe electrical noise, especially related to the clinical setting

Introduction

The most common activity in patient care is patient monitoring. The human body produces a variety of physiological signals, and physicians have learned to interpret these signals to provide information about the health of a patient. To measure or monitor these signals, there must be a connection between the patient and some (typically electronic) device. This type of activity is called in vivo monitoring, which refers to the living patient. This chapter explores the machine-human connection.

Sensors

Sensors (often called transducers – the difference is unimportant here) convert the energy of the patient (pressure, for example) into a form that can be used by an instrument.