Analysis of the mechanisms of expiratory asynchrony in pressure support ventilation: a mathematical approach

Abstract

A mathematical model was developed to analyze the mechanisms of expiratory asynchrony during pressure support ventilation (PSV). Solving the model revealed several results. 1) Ratio of the flow at the end of patient neural inspiration to peak inspiratory flow (VTI/V(peak)) during PSV is determined by the ratio of time constant of the respiratory system (tau) to patient neural inspiratory time (TI) and the ratio of the set pressure support (Pps) level to maximal inspiratory muscle pressure (Pmus max). 2) VTI/V(peak) is affected more by tau/TI than by Pps/Pmus max. VTI/V(peak) increases in a sigmoidal relationship to tau/TI. An increase in Pps/Pmus max slightly shifts the VTI/V(peak)-tau/TI curve to the right, i.e., VTI/V(peak) becomes lower as Pps/Pmus max increases at the same tau/TI. 3) Under the selected adult respiratory mechanics, VTI/V(peak) ranges from 1 to 85% and has an excellent linear correlation with tau/TI. 4) In mechanical ventilators, single fixed levels of the flow termination criterion will always have chances of both synchronized termination and asynchronized termination, depending on patient mechanics. An increase in tau/TI causes more delayed and less premature termination opportunities. An increase in Pps/Pmus max narrows the synchronized zone, making inspiratory termination predisposed to be in asynchrony. Increasing the expiratory trigger sensitivity of a ventilator shifts the synchronized zone to the right, causing less delayed and more premature termination. Automation of expiratory trigger sensitivity in future mechanical ventilators may also be possible. In conclusion, our model provides a useful tool to analyze the mechanisms of expiratory asynchrony in PSV.

Neurally adjusted ventilatory assist (NAVA) improves patient–ventilator interaction during non-invasive ventilation delivered by face mask

“…Because patient and ventilator respiratory profiles differ, patientventilator asynchronies often occur during pressure support ventilation (PS) [4,5]. They are particularly frequent during PS-NIV because unavoidable leaks at the patient-ventilator interface interfere with pneumatic triggering (i.e.…”

Patient-Ventilator Interaction During Noninvasive Ventilation in Simulated COPD

“…Furthermore, our results show that the cycling setting must be individualized, since response time of the respiratory system, the interface, amount of pressure support, breathing frequency, and leakage will probably affect how a patient responds. 14,15 Careful analysis of flow and pressure tracings and derived parameters are necessary. We recommend raising cycling criteria above the conventional level as long as parameters suggesting delayed cycling (non-supported inspirations, prolonged mechanical inspiration time, and flow curve analysis) are detectable.…”

“…4 As has been shown for invasive ventilation, adjustment of cycling criteria improves patient ventilator synchronization and reduces intrinsic PEEP. 13,14 However, studies assessing cycling in depth 15 are lacking. The purpose of this lung model study with COPD settings was to systematically investigate how patient ventilator synchronization during NIV with 2 different interfaces (face mask and ventilation helmet) can be improved by adjusting cycling.…”

Dual Unscented Kalman Filter and Its Applications to Respiratory System Modelling

“…Pt is direct effects of the patients inspiratory muscles and can be approximated by the second-order polynominal function (Yamada & Du, 2000): T and T are the inspiration duration time and total duration of one cycle respiration respectively. They are set to constant values in the algorithm.…”