Pressure Regulation in a Mechanical Breathing Aid
Original Publication Date: 2002-Apr-01
Included in the Prior Art Database: 2003-Jul-23
Pressure Regulation in a Mechani-cal Breathing Aid
Idee: Kiomars Fathollahzadeh, S-Solna
In order to regulate patient pressure, particularly in apressure controlled mode of ventilation, it is commonto employ a control algorithm that uses both inspira-tion and expiration pressure signals simultaneously.Since the pressure measurements are made in differ-ent locations a large time difference exists betweeninspiration and expiration pressure readings. Moreo-ver, the time difference is also dependent on thelengths of tubing used in the inspiration and expira-tions sides of the external pneumatic circuit thatconnects a patient to the breathing aid. Thus the timedifference can typically vary from one or two milli-seconds to several tens of milliseconds.
This time difference causes different phase shifts atdifferent frequencies of the measured pressures. Thismakes it impossible for the regulation to functionsatisfactorily if it is not adaptable to the particulartubing lengths. If adaptation does not occur then thesystem becomes unstable and oscillations in pressureoccur at about typically 100 Hz.
If the pressure regulation is based only on the inspi-ration pressure, that is the expiration pressure de-pendency is removed from the control algorithm,then the patient will experience only a slow pressureapplication; this is clinically unacceptable.
On the other hand, if the pressure regulation is basedonly on the expiration pressure then...