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MR850 Technical Manual * Revision J * Issued November 2005 * Ref. 185041340 (185041713 internal)
12
4 Operating Modes and Controls
4.1 Humidifier Operation
The MR850 humidifier is designed to add heat and moisture to respiratory gases. The gas is
passed through a humidification chamber where it is warmed and humidified.
The MR850 has two heating systems. The first is a heater plate, which heats the water
contained in the humidification chamber, humidifying the air passing through it. The humidifier
monitors the temperature of the gas at the chamber outlet with the chamber probe, and controls
the amount of power delivered to the heater plate, in order to maintain the chamber set point.
Under normal conditions the gas is heated to 37 °C in the invasive mode, 31 °C for the non-
invasive mode.
4.1.1 Heater wire operation
Figure 4.1 Typical Heater Wire Humidifier Setup
Humidified gas from the chamber travels through the inspiratory limb, where its temperature
must be maintained in order to prevent the generated humidity from condensing. This is
achieved with a heater wire encapsulated within the inspiratory limb. The humidifier maintains
the temperature along the inspiratory limb by monitoring the temperature at the airway probe
and controlling the power delivered to the heater wire. Under normal conditions the gas is
heated to 40 °C in the invasive mode, 34 °C for the non-invasive mode.
An optional, second heater wire, located in the expiratory limb, minimises condensate in this
limb.
Temperature Probe
RT100 Breathing Circuit
Ventilator/Gas Supply
MR850 Humidifie
r
MR290 Chamber
Chamber Probe
Airway Probe
Heater Wire Adapter