Patent ID: 8160817

Claim:
A method for automatically determining the resistance of the respiratory system of a spontaneously breathing intubated patient, wherein the method is conducted with or without assisted ventilation and includes an occlusion period at the start of inspiration, the method comprising: inhaling through a breathing apparatus; blocking a flow through the breathing apparatus at a start of said inhaling, said blocking being performed during the occlusion period; measuring flow (V′) and airway pressure (P aw ) as a function of time; determining the airway pressure at the end of the occlusion period as end of occlusion airway pressure (P aw (t c )=P occl ); analyzing a time dependence of the flow starting at the end of the occlusion period to determine a transition time (t d ) at which the slope of the flow changes from a first high value to a second lower value, and/or analyzing a time dependence of the airway pressure starting at the end of the occlusion period to determine the transition time (t d ) at which the slope at the airway pressure changes from a first high value to a second lower value, or by detecting an increase of the airway pressure over a predetermined threshold value to determine the transition time (t d ); determining the flow at the transition time as transition time flow (V′(t d )=V′ peak ) and determining the airway pressure at the transition time as transition time pressure (P aw (t d )); calculating the resistance on the basis of the ratio of an estimated driving pressure at the transition time (P drv (t d )) and the transition time flow (V′ peak ), wherein the value of the transition time driving pressure (P drv (t d )) is calculated as sum of the transition time airway pressure (P aw (t d )) and a muscular effort pressure (P mus (t d )) at the transition time, which muscular effort pressure (P mus (t d )) is extrapolated based on a predetermined time dependence of muscular effort pressure (P mus (t)) during the occlusion period and based on value of the end of occlusion airway pressure (P occl ).