Automatic Breath Detection in Gas Flow Analyzers
From Matthias van der Staay. Correctly selected trigger settings in a ventilator tester are important for the measurement accuracy of breath-based parameters in medical ventilators such as tidal volume, minute volume or breath rate. Depending on the patient circuit configuration and the selected ventilation mode or settings, adjustments to the trigger settings are usually required. To overcome this inconvenience during daily practice, the FlowAnalyser PF-300 PRO offers automatic breath detection based on adaptive waveform analysis. The algorithm automatically detects adult, pediatrics or even HFO ventilation and chooses appropriate trigger settings. Furthermore, leaks are automatically detected, and laborious readjustment is a thing of the past.
How does it work?
The automatic breath detection is based on a three-stage process
1. In the first stage, the flow is preprocessed to compensate for leak flow. The leak flow is estimated based on the pressure (because the leak flow varies based on pressure) and the measured flow. The flow and the pressure waveform over half a minute are mathematically evaluated, so the algorithm requires approx. 30 to 40 seconds to adapt.
2. The pressure and the leak compensated flow are analyzed during the last 35 seconds. Based on statistical evaluation, a pressure trigger threshold, a flow trigger threshold and the trigger delay are automatically calculated.
3.) The more reliable flow trigger is used as a primary trigger and the pressure trigger is used as a backup. This means that the automatic breath detection is based on the leak compensated flow trigger as long as breaths are still detected. If there are no breaths detected for 30 seconds, the pressure trigger becomes active automatically to handle unusual circuit configurations.
How to activate?
The automatic breath detection can be activated in the FlowAnalyser PRO by setting the trigger type to “Auto”. This setting is available on the user interface of the device and in the flow lab application (Options -> Trigger).