Determination of Time Delay Using Cross Correlation
Original Publication Date: 2002-Sep-01
Included in the Prior Art Database: 2003-Jul-23
Background: Pressure sensors are usually found in both the inspi- ration and the expiration branches of the gas flow circuit in a patient ventilator system. At any time in the breathing cycle there will exist a time delay be- tween pressure sensed by the different sensors. For example, during an inspiration phase the expiration sensor will measure a signal that is delayed with respect to that measured by the inspiration sensor. A ventilator is typically regulated using the combined contemporaneous outputs of these sensors, weighed dependent on the time delay. In the present system this time delay is measured only at the start of its operation but time dependant changes in the tubing system may cause this time delay to vary signifi- cantly during use.
As can be seen from the insert of Fig.1 that shows indetail the ringed region, the output from the expira-tion pressure sensor is delayed with respect to thatfrom� the� inspiration� pressure� sensor� by� a time, t d.This� � time, t d� is determined in a digital data processorfrom� a� cross� correlation� of� the� two� curves (1,2).Usefully, data processing may be limited to a timewindow during� which� large� pressure� changes� areexpected to be measured, for example at the begin-ning (t 0 ) or the end (t 1 ) of an inspiration phase. Thedata� processing� system� employed� to� perform thecross-correlation is therefor preferably operablyconnected� to� the� ventilator� so� as� to� collect and/oranalyse data from the pressure sensors in dependenceof signals from the control system of the ventilatorthat are provided in a timed relation with the opera-tion of the ventilator.
Determination of Time Delay UsingCross Correlation
Idee: Åke Larsson, SE–Solna
Pressure sensors are usually found in both the inspi-ration and the expiration branches of the gas flowcircuit in a patient ventilator system. At any time inthe breathing cycle there will exist a time delay be-tween pressure sensed by the different sensors. Forexample, during an inspiration phase the expirationsensor� will� measure� a� signal� that is delayed withrespect to that measured by the inspiration sensor. Aventilator is typically regulated using the combinedcontemporaneous outputs of these sensors, w...