Automatic Calibration - Nellcor Oximax NPB-40 Operator's Manual

Principles of Operation
pulsatile cycle. Red and infrared low-voltage
light-emitting diodes (LED) in the oximetry O
sensor serve as light sources; a photo diode serves as the
photo detector.
Because oxyhemoglobin and deoxyhemoglobin differ 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 monitor 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 point. The pulse
oximeter bases its SpO
between maximum and minimum absorption
(measurements at systole and diastole). By doing so, it
focuses on light absorption by pulsatile arterial blood,
eliminating the effects of nonpulsatile absorbers such as
tissue, bone, and venous blood.

Automatic Calibration

Because light absorption by hemoglobin is wavelength
dependent and because the mean wavelength of LEDs
varies, an oximeter must know the mean wavelength of
the O M
XI
SpO .
2
During monitoring, the NPB-40's software selects
coefficients that are appropriate for the wavelength of
that individual O
coefficients are then used to determine SpO
Additionally, to compensate for differences in tissue
thickness, the light intensity of the O
is adjusted automatically.
120
measurements on the difference
2
sensor's red LED to accurately measure
AX
M sensor's red LED; these
XI AX
M
XI AX
.
2
M sensor's LEDs
XI AX