Accutorr Plus Service Manual 0070-10-0691 1 - 11
Theory of Operation SpO
2
Processor Circuit Boards
1.3 SpO
2
Processor Circuit Boards
The Accutorr Plus can be equipped with one of two optional technologies:
•Nellcor
®
SpO
2
system
•Masimo
®
SpO
2
system
Each technology uses proprietary sensors and interface cables. There are no “adapters”
possible or available.
1.3.1 SpO
2
General Theory Of Operation
Regardless of manufacturer, SpO
2
determination is based on the relative attenuation of a
red and an infrared light source. A sensor from the instrument contains two sets of LEDs
to illuminate a portion of the body (for example, a fingertip) and a single photo sensor
detects the light returned. The LEDs are alternately pulsed, red and infrared. Since
hemoglobin is the carrier of oxygen in the blood and the relative attenuation of the light
sources is proportional to the amount of oxygen carried by the hemoglobin, a relative level
of saturated hemoglobin can be determined. Since we are measuring the ratio of red and
infrared return from the circulatory system, the detection method is substantially
independent of skin color or total skin attenuation. Since the blood flow has a pulsatile
characteristic, a pulse rate can also be computed from this information.
NOTE: There is no calibration possible for the
determination of the SpO
2
% or of the pulse rate
derived. As mentioned above, we are measuring a
ratio of intensity of two light sources to
determine the % of saturated hemoglobin. The
determination is based on proprietary software
interpretation of the reflected light ratios, and it
is validated against strict clinical trials where
fresh arterial blood is examined with a clinical
blood gas analyzer. Once the software is
finalized, the SpO
2
monitor accuracy is fixed and
there are no possible adjustments.
NOTE: The wavelengths of the light emitted are
nominally 660nm and 890nm with the energy not
exceeding 15mV.
1.3.2 Nellcor
®
Nell-3 SpO
2
Circuit Board Theory of Operation
The Nell-3 is a complete SpO
2
detection and determination circuit, proprietary of
Nellcor
®
Puritan Bennett. Patient data is processed for serial transmission to the host
system.
To Next Page
Loading...
