Cycling With Valve Circuits; Triggering With Mouthpiece Circuits - ResMed Astral Series Clinical Manual

Ventilation modes

Cycling with valve circuits

Cycling in the Astral device is based on flow and can be set to automatic or manual.
Automatic cycling adjustment
Allows for the duration of the inspiratory phase (Ti) to vary from one breath to another, according to the
characteristics of the patient's spontaneous breathing. Therefore, Ti varies according to the shape of the
flow curve and the maximum flow value.
In the figure below, a dotted line is drawn between the start of inspiration and point (A) marked at the
peak inspiratory flow (PIF) at 2.3 seconds. Cycling occurs when the decelerating flow curve intersects
with this dotted line (B). The two breaths in the figure have different PIF values and therefore different Ti
times.
Manual cycling adjustment
The manual cycling set point is expressed as a percentage of the maximum flow. Cycling to expiration
occurs when the decreasing patient respiratory flow reaches the set cycling threshold. The higher the
percentage, the more sensitive the cycling.
Note: Cycling is constrained within the limits of TiMin and TiMax. This means that the inspiratory period
cannot be less that TiMin or longer than TiMax.
To change between automatic and manual cycling features
1. From the Setup main menu, select Settings.
2. From the Settings menu, select the Main settings tab.
3. From the on-screen selections, press Cycle.

Triggering with mouthpiece circuits

When using a mouthpiece circuit, the Astral device monitors the flow during the expiration phase for
changes in the magnitude and shape of the flow measurement to improve trigger sensitivity.
There are four sensitivity levels: Low, Medium, High and Touch.
Low, Medium and High trigger sensitivity levels are based on the detection of a change in flow during
expiration indicating the start of a spontaneous breath. The higher the sensitivity selected, the smaller
the patient effort required to trigger inspiration.
The Touch trigger setting combines the standard trigger with ResMed's Touch trigger technology to
detect the patient engaging or blocking the mouthpiece to trigger inspiration.
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