Respiration Processing - Nellcor OxiMax N 5500 Service Manual

System Processing Description
Functional versus Fractional Saturation
This monitor measures functional saturation — oxygenated hemoglobin expressed as a
percentage of the hemoglobin that can transport oxygen. It does not detect significant
amounts of dysfunctional hemoglobin, such as carboxyhemoglobin or methemoglobin.
In contrast, hemoximeters such as the IL482 report fractional saturation — oxygenated
hemoglobin expressed as a percentage of all measured hemoglobin, including measured
dysfunctional hemoglobin. To compare functional saturation measurements to those
from an instrument that measures fractional saturation, fractional measurements must be
converted as follows:
fractional saturation
functional saturation = × 100
100 – (%carboxyhemoglobin + %methemoglobin)
OxiMax Technology
The N5500 SpO monitoring is designed to use Nellcor I brand sensors, which
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integrate the I technology. These sensors can be identified by their deep blue plug
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color. All I sensors contain a memory chip carrying information about the sensor
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which the monitor needs for correct operation, including the sensor's calibration data,
model type, troubleshooting codes, and error detection data. This unique oximetry
architecture enables several new features with the N5500. When an I sensor is
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connected to the N5500, the monitor will first read the information in the sensor
memory chip, check it to make sure that there are no errors, and then load the data to
begin monitoring. The monitor containing OxiMax Technology uses calibration data
contained in the sensor in calculating the patient' s SpO .
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10.6 Respiration Processing

The N5500 respiration monitoring is designed to use the variation of this thoracic
impedance. The chest contains various materials, ranging from bone to air. Each of
these materials has different electrical properties and is located in a different portion of
the chest. The materials of the chest vary in electrical resistivity (the amount of
electrical resistance between opposite faces of a cube of that material), which is an
important determinant of electrical impedance in the body.
Two of the major components of the chest, blood and air, are at opposite ends of the
scale. Furthermore, the volume of each of these materials varies with time over the
cardiac and breathing cycles. The variation of the thoracic impedance is caused by the
difference between air and blood in the thoracic impedance. Blood has relatively low
resistivity, which varies over the cardiac cycle owing to changing blood volumes in the
heart and in the vascular compartment. Air, on the other hand, has high electrical
resistivity and hence impedance, and it undergoes wide volume changes in the lungs
during normal breathing. i.e. the impedance of blood is 150 ohm/cm and the one of air
is 5000 ohm/cm.
The patient's respiration is detected by using two of the three leads of the ECG
electrodes (RA and LA, or RA and LL) and cable. The electrical impedance between a
N5500 Service Manual 91