10-1
10 Theory of Operations
10.1
Overview
This chapter explains the theory behind operations of the Nellcor™ bedside SpO
2
patient monitoring system.
10.2
Theoretical Principles
The monitoring system uses pulse oximetry to measure functional oxygen satura-
tion in the blood. Pulse oximetry works by applying a Nellcor™ pulse oximetry sensor
to a pulsating arteriolar vascular bed, such as a finger or toe. The sensor contains a
dual light source and a photodetector.
Bone, tissue, pigmentation, and venous vessels normally absorb a constant amount
of light over time. The arteriolar bed normally pulsates and absorbs variable
amounts of light during the pulsations. The ratio of light absorbed is translated into
a measurement of functional oxygen saturation (SpO
2
).
Ambient conditions, sensor application, and patient conditions can influence the
ability of the pulse oximeter to accurately measure SpO
2
Pulse oximetry is based on two principles: oxyhemoglobin and deoxyhemoglobin
differ in their absorption of red and infrared light (measured using spectrophotom-
etry), and the volume of arterial blood in tissue (and hence, light absorption by that
blood) changes during the pulse (registered using plethysmography). A monitoring
system determines SpO
2
by passing red and infrared light into an arteriolar bed and
measuring changes in light absorption during the pulsatile cycle. Red and infrared
low-voltage light-emitting diodes (LED) in the sensor serve as light sources; a photo
diode serves as the photo detector.
Since oxyhemoglobin and deoxyhemoglobin differ in light absorption, the amount
of red and infrared light absorbed by blood is related to hemoglobin oxygen satura-
tion.
The monitoring system uses the pulsatile nature of arterial flow to identify the
oxygen saturation of arterial hemoglobin. During systole, a new pulse of arterial
Summary of Contents for Nellcor Series
Page 1: ...Operator s Manual Nellcor Bedside SpO2 Patient Monitoring System TM...
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Page 20: ...Introduction Page Left Intentionally Blank 1 8 Operator s Manual...
Page 36: ...Installation Page Left Intentionally Blank 3 8 Operator s Manual...
Page 118: ...Product Specifications Page Left Intentionally Blank 11 18 Operator s Manual...
Page 156: ...Clinical Studies Page Left Intentionally Blank A 38 Operator s Manual...
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