On-line non-invasive determination of patients and ventilator respiratory work during Proportional Assist Ventilation

The ventilator is a type of clinical life support apparatus which can help patients to enhance lung ventilation and accelerate metabolization. Proportional Assist Ventilation (PAV) is proposed with the concept of proportionally amplifying patientpsilas breathing effort. Knowing the patient component and ventilator component of work can help the physician to adjust the proportion of support by the ventilator and improve the patientpsilas therapeutic effect. According to the definition of the work, an algorithm that estimates the patient and ventilator work components of proportional assist ventilated patients is presented. The integral result of the product of pressure and flow in the inspiratory period is the work. The algorithm requires estimating the patientpsilas airway resistance(R) and elastance(E). The controlled mechanical ventilation method, the least squares method and the physiological method are analysed. Their deficiencies are pointed and an improved physiological method is used ultimately to estimate R and E. The algorithm and the estimate of E and R require the continuous measurement of inspiratory airflow rate and mouth pressure and it is suitable to be incorporated in ventilators for on-line non-invasive determination of the patient and the ventilator contributions to the total work of breathing. Test results of our mechanical ventilator Shangrila590 and active servo lung ASL5000 are also reported for the algorithm and show that the proposed algorithm is non-invasive and can be used in ventilators for continuous online determination of work component.