Product Manual

Principles of Operation
N-560 Operator’s Manual 91
Principles of Operation
Oximetry Overview
The N-560 uses pulse oximetry to measure functional oxygen
saturation in the blood. Pulse oximetry works by applying a sensor to
a pulsating arteriolar vascular bed, such as a finger or toe. The sensor
contains a dual light source and a photo detector.
Bone, tissue, pigmentation, and ven
ous 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).
Because a measurement of SpO
2 is dependent upon light from the
sensor, excessive ambient light can interfere with this measurement.
Specific information about ambient cond
itions, sensor application,
and patient conditions is contained throughout this manual.
Pulse oximetry is based on two principles: that oxyh
emoglobin and
deoxyhemoglobin differ in their absorption of red and infrared light
(spectrophotometry), and that the volume of arterial blood in tissue
(and hence, light absorption by that blood) changes during the pulse
(plethysmography). A pulse oximeter 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 oximetry sensor serve
as light sources; a photo diode serves as the photo detector.
Because oxyhemoglobin and deoxyhemoglobin dif
fer in light
absorption, the amount of red and infrared light absorbed by blood is
related to hemoglobin oxygen saturation. To identify the oxygen
saturation of arterial hemoglobin, the N-560 uses the pulsatile nature
of arterial flow. During systole, a new pulse of arterial blood enters
the vascular bed, and blood volume and light absorption increase.
During diastole, blood volume and light absorption reach their lowest