title: Expiratory asynchrony in proportional assist ventilation.
abstract: One of the proposed advantages of proportional assist ventilation (PAV) has been the automatic synchrony between the end of the patient's inspiratory effort and the ventilator cycle (i.e., expiratory synchrony). However, recent clinical studies have shown a prolonged ventilator inspiratory time or even a "runaway" phenomenon with the normal use of PAV. We hypothesize that control-system delay may account for this, because in reality there is always some degree of delays between control-system's input and output in all ventilators. Computer simulation study to date has not taken into account the potential effect of control-system delay on expiratory synchrony. We therefore created a computer model in which the parameter of control-system delay time was introduced. We found that significant expiratory asynchrony may occur with this more realistic model of PAV. The ventilator flow termination may fall behind the completion of the patient inspiration by as long as 0.33 seconds under the selected simulation conditions. The inspiratory termination delay time is in proportion to the control-system delay time, the respiratory time constant, and the assist gain settings. In conclusion, this model indicates that due to the unavoidable control-system delay in the ventilators, expiratory asynchrony may be an inherent shortcoming associated with PAV.
authors.affiliation: Clinical Research Department, Newport Medical Instruments Inc., Newport Beach, California 92658, USA. HLDu@nmitkb.com
authors.forename: Hong-Lin
authors.initials: HL
authors.lastname: Du
authors.forename: Mikiya
authors.initials: M
authors.lastname: Ohtsuji
authors.forename: Masaki
authors.initials: M
authors.lastname: Shigeta
authors.forename: David C
authors.initials: DC
authors.lastname: Chao
authors.forename: Katsunori
authors.initials: K
authors.lastname: Sasaki
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Usuda
authors.forename: Yoshitsugu
authors.initials: Y
authors.lastname: Yamada
mesh_terms: D003198:Computer Simulation; D006801:Humans; D008168:Lung / Q000502:physiology; D008953:Models, Anatomic; D012119:Respiration; D012121:Respiration, Artificial / Q000379:methods; D012132:Respiratory Muscles / Q000502:physiology