Technical Discussion; Oximetry Overview - Nellcor OxiMax N-600x Service Manual

T e c h n i c a l D i s c u s s i o n

Oximetry Overview

O M N-600x Service Manual
XI AX
The N-600x uses pulse oximetry to measure functional oxygen saturation in the
blood. Pulse oximetry works by applying an O
arteriolar vascular bed, such as a finger or toe. The O
light source and a photo detector.
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
Since a measurement of %SpO
excessive ambient light can interfere with this measurement.
Specific information about ambient conditions, O
patient conditions is contained throughout this manual.
Pulse oximetry is based on two principles; oxyhemoglobin and deoxyhemoglobin.
These principles differ in their absorption of red and infrared light (i.e.,
spectrophotometry), and the volume of arterial blood in tissue (and hence, light
absorption by that blood) changes during the pulse (i.e., Plethysmography). A
pulse oximeter determines %SpO
arteriolar bed and measuring changes in light absorption during the pulsatile
cycle. Red and infrared low-voltage light-emitting diodes (LED) in the oximetry
O M sensor serve as light sources; a photo diode serves as the photo detector.
XI AX
Since oxyhemoglobin and deoxyhemoglobin differ in light absorption, the amount
of red and infrared light absorbed by blood is related to hemoglobin oxygen
saturation. The pulse oximeter uses the pulsatile nature of arterial flow to identify
the oxygen saturation of arterial hemoglobin. During systole, a new pulse of
arterial blood enters the vascular bed, causing both the blood volume and light
absorption to increase. During diastole, blood volume and light absorption reach
their lowest point. The pulse oximeter bases its %SpO
difference between maximum and minimum absorption (i.e., measurements at
systole and diastole). The oximeter focuses on light absorption by pulsatile
arterial blood, eliminating the effects of nonpulsatile absorbers such as tissue,
bone, and venous blood.
M sensor to a pulsating
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is dependent upon light from the O
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by passing red and infrared light into an
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Technical Discussion

sensor contains a dual
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sensor application, and
measurements on the
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