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Trilogy200 clinical manual
36
Triggering
The device can be set to trigger breaths using the Auto-Trak or Flow
Trigger sensitivity features.
Digital Auto-Trak Sensitivity
An important characteristic of the device is its ability to recognize
and compensate for unintentional leaks in the system and to
automatically adjust its trigger and cycle algorithms to maintain
optimum performance in the presence of leaks. This feature is known
as Digital Auto-Trak Sensitivity. The following sections examine this
function in detail by describing the leak tolerance function and
sensitivity.
Leak Tolerance
A microprocessor monitors the total ow of the patient circuit and
calculates patient ow values.
A. Leak Estimation: Average and Parabolic
The device uses two leak estimation algorithms. A conservation
of mass algorithm is used to compute the average leak for a given
pressure support relationship. This average leak is used when large
leak variations are present in the system. Average leak is a high
estimate during EPAP pressure and a low estimate during IPAP
pressure. A better leak estimate, enabled by the digital system, is the
parabolic leak algorithm. Parabolic leak is proportional to the square
of the patient pressure; therefore, the leak estimate is correlated to
the changing patient pressure. Both algorithms include unintentional
circuit leak and are averaged over several breaths.
B. Patient Flow
The total circuit ow is comprised of the circuit leak and the patient
ow. The calculated patient ow is the total ow minus the circuit
leak. Patient ow is a primary input into the triggering and cycling
mechanisms.