Oscillations and noise: Inherent instability of pressure support ventilation?

John R. Hotchkiss, Alexander B. Adams, Mary K. Stone, David J. Dries, John J. Marini, Philip S. Crooke

Research output: Contribution to journalArticlepeer-review

33 Scopus citations

Abstract

Pressure support ventilation (PSV) is almost universally employed in the management of actively breathing ventilated patients with acute respiratory failure. In this partial support mode of ventilation, a fixed pressure is applied to the airway opening, and flow delivery is monitored by the ventilator. Inspiration is terminated when measured inspiratory flow falls below a set fraction of the peak flow rate (flow cutoff); the ventilator then cycles to a lower pressure and expiration commences. We used linear and nonlinear mathematical models to investigate the dynamic behavior of pressure support ventilation and confirmed the predicted behavior using a test lung. Our mathematical and laboratory analyses indicate that pressure support ventilation in the setting of airflow obstruction can be accompanied by marked variations in tidal volume and end-expiratory alveolar pressure, even when subject effort is unvarying. Unstable behavior was observed in the simplest plausible linear mathematical model and is an inherent consequence of the underlying dynamics of this mode of ventilation. The mechanism underlying the observed instability is "feed forward" behavior mediated by oscillatory elevation in end-expiratory pressure. In both mathematical and mechanical models, unstable behavior occurred at impedance values and ventilator settings that are clinically realistic.

Original languageEnglish (US)
Pages (from-to)47-53
Number of pages7
JournalAmerican journal of respiratory and critical care medicine
Volume165
Issue number1
DOIs
StatePublished - Jan 1 2002

Keywords

  • Dynamics
  • Mathematical model
  • Mechanical ventilation

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