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Operation
Auto-Trak™ Sensitivity Function
The ventilator monitors flow through the patient circuit to determine
whether the patient is inhaling or exhaling using Digital Auto-Trak™
Sensitivity technology. The BiPAP Focus System adjusts its output to
support breathing and compensates for normal leaks in the patient circuit
using Digital Auto-Trak™ leak compensation technology.
Leak Estimation
The system monitors the total flow in the patient circuit and estimates
patient leak using leak estimation algorithms.
Sensitivity
An essential feature of S/T mode is effective detection of spontaneous
breathing effort, which causes the ventilator to trigger to IPAP and cycle
to EPAP. Because no preset sensitivity threshold can ensure patient and
machine synchrony with changing breathing efforts and circuit leaks, the
BiPAP Focus continuously tracks patient breathing patterns and
automatically adjusts its sensitivity thresholds to ensure optimum
sensitivity as breathing patterns or circuit leaks change. The system uses
volume trigger, shape signal, and Spontaneous Expiratory Threshold
(SET) algorithms to ensure optimum sensitivity:
• The Volume Trigger algorithm triggers IPAP during spontaneous
and timed breaths. The volume trigger threshold is 6 mL of
accumulated patient inspiratory volume. When patient effort
generates inspiratory flow causing 6 mL of volume, IPAP is
triggered.
• The Shape Signal algorithm (Figure 17) continuously tracks patient
inspiratory and expiratory flow and adjusts the spontaneous trigger
and cycle thresholds for optimum sensitivity. The shape signal is a
shadow image of the patient's actual flow and functions as a
sensitivity threshold at either inspiration or exhalation. When the
patient's flow rate crosses the shape signal, the system changes
pressure levels. The shape signal is created by offsetting the signal
from the actual patient flow by 15 L/min and delaying it for 300
milliseconds. This causes the shape signal to be slightly behind the
patients flow rate. A sudden change in patient flow causes the
shape signal to be crossed, causing the pressure level to change.
30
®
BiPAP
Focus™ Noninvasive Ventilator System
1027404 Rev K
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