Mindray DPM 4 Operator's Manual

11-9
 CONFIG >> You can select this option to access the SPO2 CONFIG
menu, in which you may select FACTORY CONFIG or
USER CONFIG. After finishing your selection and exiting
the menu, the system pops up a dialog box asking for your
confirmation.
11.3 Masimo SpO
2
Module
NOTE
z This section is only applicable to the monitor equipped with a Masimo SpO2
module.
11.3.1 Principles of Operation
The pulse oximetry measurement module (Masimo Set, which is called MS-7) is based on three
principles:
 Oxyhemoglobin and deoxyhemoglobin differ in their absorption of red and infrared light
(spectrophotometry).
 The volume of arterial blood in tissue and the light absorbed by the blood changes during
the pulse (plethysmography).
 Arterio-venous shunting is highly variable, and the fluctuating absorbance by venous blood
is a major component of noise during the pulse.
The working principle of MS-7 uses is similar to the traditional SpO
2
module. It calculates the
SpO
2
value by passing red and infrared light into a capillary bed and measuring changes in light
absorption during the pulsatile cycle. The red and infrared light-emitting diodes (LEDs) in
oximetry sensors serve as the light sources, and the photodiode serves as the photodetector.
Traditional pulse oximeter assumes that all pulsations in the light absorbance signal are caused by
oscillations in the arterial blood volume. This assumes that the blood flow in the region of the
sensor passes entirely through the capillary bed rather than through any arterio-venous shunts.
The traditional pulse oximeter calculates the ratio of pulsatile absorbance (AC) to the mean
absorbance (DC) at each of two wavelengths, 660 nm and 940 nm:
)660(/)660()660(Re DCACd =
)940(/)940()940( DCACIr =
This traditional instrument then calculates the ratio of these two arterial pulse-added absorbance
signals:
)940(/)660(Re IrdR =
This value of R is used to find the SpO
2
in a look-up table built into the instrument’s software.
The values in the look-up table are based upon human blood studies against a laboratory
co-oximeter on healthy adult volunteers in induced hypoxia studies.
This MS-7 assumes that arterio-venous shunting is highly variable and that fluctuating
absorbance by venous blood is the major component of noise during the pulse. The MS-7
decomposes S(660) and S(940) into an arterial signal plus a noise component and calculates the
ratio of the arterial signals without the noise:

Mindray DPM 4 Specifications

General

Brand	Mindray
Model	DPM 4
Category	Medical Equipment
Language	English