Mindray PM-50, Operation Manual

Page: 21 / 60

15
Chapter 4 Measurement
4.1 Measuring Principle
The Pulse Oximeter is capable of measuring SpO
2
, PR and pulse
strength.
The Pulse Oximeter measures SpO
2
by a method called pulse oximetry.
It is a continuous, non-invasive method based on the different
absorption spectra of reduced hemoglobin and oxyhemoglobin. It
measures how much light, sent from light sources on one side of the
sensor, is transmitted through patient tissue (such as a finger or an ear),
to a receiver on the other side. The amount of light transmitted is
determined by multiple factors, most of which are fixed. The blood flow
in arteries is one of the factors that change with time, because it is
pulsating.
Usually, the wavelength of the light transmitted by a red-light LED can
be detected by the sensor is 660nm, and by an infrared LED is 940nm.
Maximum power output of the LED is 4mW.
The Pulse Oximeter measures the absorbed light during the pulsatile
period to acquire pulse rate and pulse strength as well as arterial
oxygen saturation, and then after a further processing, displays the
results on the LCD screen. The displayed SpO
2
value is of functional
saturation.