Operator's Manual

3.3 Theory of operation
Tempus Pro User/Operator Manual - 41-2001EN-00 – Page 31
Right Side of the Tempus – Communications Connectors
3.3 Theory of operation
All of the measurements made by the Tempus Pro are displayed on the screen. Attaching a sensor to a
patient will initiate measurements by that particular parameter. Monitoring will continue until the sensor is
removed from the patient or the unit (and the consequent alarm is silenced). In the case of non-invasive
blood pressure, measurements start once the user presses the ‘start’ button and will continue on a regular
basis when in automatic mode until either the cycle is stopped by the user or the unit is unable to take a
reading e.g. cuff is removed.
3.3.1 Pulse rate and oxygen saturation (SpO
2
)
Pulse oximetry measures functional oxygen saturation.
Pulse oximetry is based on the following:
 The difference in the absorption of red and infrared light (spectrophotometry) by oxyhaemoglobin and
deoxyhaemoglobin
 Changes in the volume of arterial blood in tissue during the pulse cycle (plethysmography), and hence,
light absorption by that blood.
A pulse oximeter determines Spot Oxygen Saturation (SpO
2
) by passing red and infrared light into an
arteriolar bed and measures changes in light absorption during the pulsatile cycle. Red and infrared low
power light emitting diodes (LEDs) in the oximetry sensor serve as light sources; a photodiode serves as the
photo detector.
Since oxyhaemoglobin and deoxyhaemoglobin differ in light absorption, the amount of red and infrared light
absorbed by blood is related to haemoglobin oxygen saturation. To identify the oxygen saturation of arterial
haemoglobin, 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 monitor bases its SpO
2
measurements on the difference between maximum and minimum absorption
(measurements at systole and diastole). The focus of light absorption by pulsatile arterial blood eliminates
the effects of nonpulsatile absorbers such as tissue, bone, and venous blood.
Power socket
Two USB A sockets
for USB 1.0 & 2.0
communications
Headset socket
Ethernet RJ-45
socket
Tactical switch