A Breathing Synchronization Strategy for the Non-Invasive Ventilator System

Abstract

The study presents a method to achieve a subject-ventilator synchronic pressure supply for a non-invasive ventilator (NIV) used for obstructive sleep apnea syndrome (OSAS), solely through controlling the blower instead of using expiratory relief valves. The controller used air flow signal to distinguish inspiratory and expiratory phases, and used a fast auto-forecast (AF) algorithm to predict the current inspiratory duration based on respiration periods distinguished previously. Then in a patient's late inspiration the mechanical expiratory state was triggered to release pressure in advance. Afterward, when the beginning of a patient's actual expiration was detected, a timer was used to trigger the end-expiratory state. As the index of patient-ventilator synchrony, subject's chest movement was detected by electrical impedance signal in experiments. The experimental results indicated that the previous state transition based on the prediction of inspiratory duration can eliminate the pressure overshoot spike, and then avoid excessive expiratory pressure to subjects. The fast auto-forecast with end expiratory positive airway pressure (AF-EEPAP) controlling strategy presented in this paper provided a mild pressure curve, which is consistent with the subject's respiratory physiology, and thus improved respiratory synchrony between subject and ventilator.