We analysed during the whole respiratory cycle, resistance, elastance, volume dependence of elastance, and flow dependence of resistance in ARDS patients,in three levels of PEEP,using three different modelings : Linear modeling, nonlinear modeling for flow dependence of resistance, and nonlinear modeling for volume dependence of elastance.
Airways opening pressure (P), flow (V’) and volume (V) signals were recorded in 18 patients with ARDS and in 15 patients without known respiratory disorder (control group), all artificially ventilated, at three levels of PEEP (0, 5, and 10 hPa). Data were analysed using multiple linear regression analysis according to the equations: (a) P=Ers*V+Rrs*V’+Po, (b) P=Ers*V+(k1+k2*V’)*V’+Po and (c) P=(E1+E2*V)*V+Rrs*V’+Po, where Ers and Rrs represent the respiratory system elastance and resistance, k1 the linear coefficient of resistance, k2 the flow dependent coefficient of resistance, E1 the linear coefficient of elastance, E2 the volume dependent coefficient of elastance and Po the end-expiratory pressure.
The respiratory resistance (controls: p=0.01, ARDS: p=0.001), the linear coefficient of resistance (controls: p=0.05, ARDS: p=0.02), and the flow depended coefficient of resistance (controls: p=0.04, ARDS: p=0.04) were diminished significantly with the application of PEEP in both groups of patients, especially at high levels of PEEP (10hPa). Concerning the elastance, PEEP influenced significantly only the volume dependend coefficient of elastance (E2) in the ARDS group (p=0.04), which increased with the application of PEEP. All the measured mechanical parameters were significantly higher in the ARDS group comparing to the controls.
Mechanical ventilation with PEEP application in ARDS patients is related with a decline of linear and non linear coefficients of respiratory resistance, during the respiratory cycle. The application of PEEP tends to increase the volume dependend coefficient of elastance in ARDS patients.
More complex models accounting for volume dependence of elastance and for the flow dependence of resistance,may improve the accuracy of measurements of respiratory mechanics and offer more efficient mechanical ventilation in ARDS.
P.K. Behrakis, None.