Patent ID: 6837242

Claim:
A method of determining respiratory system resistance (R) in a patient receiving gas from a ventilatory assist device (ventilator), comprising: estimating the flow rate ({dot over (V)}) and volume (V) of gas received by the patient from the ventilator; estimating pressure near the airway of the patient (Paw); generating a signal that results in a step decrease (negative pulse) in the pressure and/or flow output of the ventilator during selected inflation cycles; measuring Paw, {dot over (V)} and V at a point (T O ) near the beginning of the pulse (Paw O , {dot over (V)}, V O ), at a point (T I ) near the trough of the negative pulse (Paw 1 , {dot over (V)} 1 , V 1 ), and at a point (T −1 ) preceding T O but after the onset of inspiratory effort (Paw −1 , {dot over (V)} −1 , V −1 ); and calculating the value of resistance (R) from the differences between Paw, {dot over (V)} and V at T O and at T I and where the change in patient generated pressure (Pmus) in the interval T O →T I (ΔPmus(T O →T I )) is estimated, by extrapolation, from the differences between Paw, {dot over (V)} and V at T O and at T −1 , in accordance with equation (8), as follows: R =[( Paw O −Paw 1 +(Δ t/Δt −I )( Paw O −Paw −1 ))− E ( V O −V 1 +(Δ t/Δt −I )( V O −V −1 ))]/( V O −V 1 +(Δ t/Δt −I )( {dot over (V)} O −{dot over (V)} −1 )) (8).