[Analysis by computer simulation of double breathing during pressure support ventilation].
BACKGROUND
Pressure support ventilation (PSV) usually provides good patient-ventilator synchrony, but asynchrony is sometimes encountered. Double breathing is one form of asynchrony in which the ventilator assists two or more times during a single inspiration of the patient.


METHODS
Double breathing was analyzed using a computer simulation.


RESULTS
In an obstructive lung model, inspiratory support was terminated just after the beginning of the inspiration lasting until inspiratory effort triggering the ventilator again. One of the causes of this premature termination was that the compressed and consumed volume in the circuit created a high peak inspiratory flow setting. The other cause was oscillation of the airway pressure. Reducing the circuit volume, slowing the inspiratory rise time, or decreasing the termination criteria could prevent this phenomenon. In a restrictive lung model, the time-constant of the lung was so short that the inspiratory flow finished early and double breathing occurred. It was difficult to prevent this phenomenon by adjusting the circuit assembly or respiratory parameters.


CONCLUSIONS
Double breathing during PSV was considered to be closely associated with obstructive or restrictive lung. If the problem arises and cannot be resolved by adjusting ventilatory parameters, the ventilatory mode must be changed.
Ohtsuka
Masahide
M
Department of Anesthesiology, Yokohama City University, School of Medicine, Yokohama 236-0004.
Usuda
Yutaka
Y
Yamaguchi
Osamu
O
Yamada
Yoshitsugu
Y
D000403:Airway Resistance; D003198:Computer Simulation; D008170:Lung Compliance; D008954:Models, Biological; D011175:Positive-Pressure Respiration / Q000009:adverse effects*; D012119:Respiration