Measurement Modules
Theory of Operation
A-6 Efficia CM Series Service Guide
• Manifold
• Filter
• Pressure measurement and control circuitry
Pressure data is converted to digital format and conveyed to the processor. The NBP
pump uses an oscillometric method that employs stepwise pressure deflation. Pump
software eliminates most ambient noise and motion interference. Applications are
neonatal, pediatric and adult patients. The blood pressure range is as follows:
• Systolic, 30 – 270 mmHg
• Diastolic, 10 – 245 mmHg
• Mean, 20 – 255 mmHg.
Accuracy is ±5 mmHg, with standard deviation no greater than 8 mmHg.
NBP processing uses an oscillometric technique to provide needed measurements at
selected intervals. This technique uses an inflatable sphygmomanometer cuff similar to
those used by clinicians in routine measurements. A motorized pump inflates the cuff
to approximately 160 mmHg (adult mode) initially, at which point the pressure
effectively stops the flow of blood. Then, under monitor control, the pressure in the
cuff is gradually reduced, while a pressure transducer detects the pressure and
transmits the parameter signal to the NBP input circuitry. As the pressure is reduced,
blood flows in the previously occluded artery, and changes the measurements made
by the transducer. The point at which oscillation increases sharply is defined as
systolic pressure. As the cuff continues to deflate, the oscillation amplitude increases
to a maximum, and then decreases. The peak oscillation amplitude is defined as the
mean arterial pressure. The point at which the system detects a rapid decrease in
oscillation is defined as the diastolic pressure.
Philips SpO
2
The SpO
2
module measures oxygen saturation in the blood using an optical
spectrophotometry technique. It is based on the differences in the absorption of red
and Infrared light by oxygenated and deoxygenated Hemoglobin.
A pulse oximeter passes red and infrared light into an arteriolar bed and measures
changes in light absorption during the pulsatile cycle. The light sources are red and
infrared light emitting diodes (LEDs). A photo diode provides detection.
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 vacuolar
bed, and both blood volume and light absorption increase. During diastole, blood
volume and light absorption reach their lowest point. The measurement is based on
the difference between maximum and minimum absorption, focusing on the pulsatile
arterial blood. In addition to the oximetry function, the measurement can also provide
the heart rate.
NellCor SpO
2
The monitoring system uses pulse oximetry to measure functional oxygen saturation in
the blood. Pulse oximetry works by applying a NellCor™ sensor to a pulsating arteriolar
vascular bed, such as a finger or toe. The sensor contains a dual light source and a
photodetector.
Bone, tissue, pigmentation, and venous vessels normally absorb a constant amount of
light over time. The arteriolar bed normally pulsates and absorbs variable amounts of
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