Respiratory response to the progressing expiratory loading and its effect on patient-ventilator synchronization

Objective To observe the changes of respiratory mechanics of normal adults under the condition of expiratory load and investigate the effect of expiratory load on patient-ventilator synchronization.Methods Nine normal adults were asked to breath under the expiratory load of 0,5,10 and 15 cm H2O,and the diaphragmatic electromyography(EMGdi),gastral pressure(Pgas),esophageal pressure(Peso),mouth pressure(Pm),transdiaphramatic pressure(Pdi) and Flow were measured.Results (1)As the expiratory loading increased,the nadir of Peso and Pm became deeper,while the peak of Pgas did not increase during inspiration;and all the peak of Pgas,Peso and Pm increased during expiration. (2)As the expiratory loading increased,the basic pressure of Pgas,Peso and Pm just before the onset of inspiration increased. (3)The onset of Peso,Pm and Pdi was later than that of EMGdi in the condition of lower or no expiratory loading.As the expiratory loading increased,the time interval difference was decreased;and when the expiratory loading was 10 or 15 cm H2O,the onset of Peso and Pm was earlier than that of EMGdi. As the expiratory loading increased,the onset of Pgas and Flow was later than that of EMGdi and the time interval difference between Pgas and EMGdi tended to increase. (4)As the expiratory loading increased,the time from the peak of inspiratory Flow (Fpeak-in),F75%Peak-in or F25%Peak-in to the onset of expiration Flow increased and the changing of time interval difference between F25%Peak-in to the onset of expiration Flow increased much more(P<0.05).Conclusions Both the activity of inspiratory and expiratory muscle increase in the condition of expiratory loading. The expiratory loading may lead to the higher value of Peso and Pm just before the beginning of inspiration,but dose not delay the onset of Flow. Expiratory loading could lead to the delay of expiration. Key words: Diaphragm; Electromyography; Expiratory loading; Patient-ventilator synchronism