Compliance Calculations C-42 High Compliance /目 △ 2000mL Low Compliance 100ml/cm △(Pmg-Pan)20cm-0cm △ 2000mL ngs△(Pngs-pena (20cm-5cm)-(0cm-(-5)cm) Pressure(cmH2O) 200 ml/cm cm cm resp +0cm +20c +0cm 100200200 2 liters 4 liters
+20 cm + 0 cm -5 cm + 0 cm +5 cm 2 liters 4 liters P V C mL cm cm cm mL P P V C lungs air lungs resp 100 / 2 0 0 2000 ( ) mL cm cm cm cm cm mL P P V C lungs pleura lungs lungs 200 / [ (20 5 ) (0 ( 5) ) ] 2000 ( ) Cresp Clungs Cchest wall 1 1 1 200 1 200 1 100 1 Pressure (cmH2O) Volume (mL ) Low Compliance High Compliance Compliance Calculations
Resistance(R) and Time Constant(t) Resistance measured in presence of flow o R=AP/F where f= flou elastic z=RxC⊥△P△FCmH2O sec F△Pml/ sec cmh2O Where t= time constant tiime it takes for 64% of volume to be exhaled. normally r-2cmh2o per ml of air per sec and c=0.1 liter/ cmH2O so that t=2 sec. About 4t(0. 8 sec) needed for complete expiration Assumption: single unit emptying Endotracheal tubes and inhomgeneous ventilation can greatly slow emptying- multiple compartments. Anything which increases R or C increases exhalation time(both occur in obstructive lung disea
R = ΔP/F where F = flow PLung = Presistance + Pelastic Where τ = time constant tiime it takes for 64% of volume to be exhaled. Normally R=2cmH2O per ml of air per sec and C= 0.1 liter/cmH2O so that τ = .2 sec. About 4 τ (0.8 sec) needed for complete expiration. Assumption: single unit emptying. Endotracheal tubes and inhomgeneous ventilation can greatly slow emptying – multiple compartments. Anything which increases R or C increases exhalation time (both occur in obstructive lung disease.) sec /sec 2 2 cmH O ml ml cmH O P V F P R C Resistance measured in presence of flow