connected. Breathing circuit recognition is performed via three electrical connections on the heater wire adaptor. Re-configuring the electrical connection pins on a heated circuit and the way it connects to this adaptor identifies the type of heated circuit. In this way three separate heater wire circuits can be identified by the MR850.

4.2Humidifier Controls

4.2.1Power Button

The humidifier will power on if this button is held down briefly, but must be held for one second to turn the humidifier off.

Note: For software version 5.45, 5.70 the power button need only be pressed briefly to turn off the MR850.

CAUTION: Although the display is not illuminated, the unit may still be energized. Be sure to disconnect power from the MR850 before servicing.

After power-on the humidifier starts an internal diagnostic routine which checks for possible problems in the humidifier setup. If everything is working correctly, normal control is initiated.

4.2.2Mode Button

When held down for one second, the mode button toggles the humidifier between Non-Invasive and Invasive mode. The Mode indicator LED shows the user which mode is selected.

Invasive mode is for use with patients whose upper airways have been bypassed by either a tracheostomy or endotracheal tube. In this mode of operation the humidifier attempts to deliver optimal humidity to the patient (37 °C, 100 % RH). This mode is the default mode on power up of the humidifier.

The humidifier normally controls the chamber outlet temperature to 37 °C, and the airway temperature to 40 °C, maintaining a +3 °C temperature gradient along the inspiratory limb1.

If however this temperature gradient is not maintained, the chamber set point is reduced in 0.5 °C steps (minimum setting of 35.5 °C), in order to reduce condensate buildup in the breathing circuit2. If the chamber set point is less than 37 °C and sufficient temperature gradient has been maintained along the inspiratory limb, then the chamber set point is increased back up to 37 °C in 0.5 °C steps.

Non-Invasive mode is suitable only for patients whose natural humidification system (i.e. upper airways) has not been bypassed, but are receiving gas via a facemask or similar.

The humidifier normally controls the chamber outlet temperature to 31 °C, and the airway temperature to 34 °C, maintaining a +3 °C temperature gradient along the inspiratory limb1.

1If automatic or manual humidity compensation has been activated then the displayed temperature may be higher than 37 °C (Invasive mode) or 31 °C (Non-Invasive mode).

2The humidity compensation algorithm takes precedence over the condensation control algorithm.

16 MR850 Technical Manual * Revision J * Issued November 2005 * Ref. 185041340 (185041713 internal)