7
Principles of Operation
Pulse Oximeter adopts non-invasive double wavelength to measure SpO
2
and PR. It can
perform spot measuring and continuous measuring for a short time.
The system is consisted of Central Processing Unit, Signal Collection, Signal Input, Data
Output, Display and User Input module, shown as follows:
System Principle
Communication between the oximeter and external devices is through RS-232 interface.
7.1 Pulse Oximetry Measuring
The oximeter uses oximetry to measure functional oxygen saturation in the blood. Pulse
oximetry works by applying sensor to a pulsating arteriolar vascular bed, such as a finger
or toe. The sensor contains a dual light source and a photonic detector.
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 light
during the pulsations. The ratio of light absorbed is translated into a measurement of
functional oxygen saturation (SpO
2
). Because a measurement of SpO
2
is dependent upon
light from the sensor, excessive ambient light can interfere with this measurement.Pulse
oximetry is based on two principles:
Oxyhemoglobin and deoxyhemoglobin differ in their absorption of red and infrared
light (spectrophotometry).
The volume of arterial blood in tissue (hence light absorption by the blood)
changes during the pulse (plethysmography).
The oximeter determines SpO
2
by passing red and infrared light into an arteriolar bed and
measuring changes in light absorption during the pulsatile cycle. Red and infrared low-
Signal Input
Signal
Collection
Display
User Input
CPU
Data Output
Summary of Contents for VITAL TEST
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