Cardiac output derived from left ventricular pressure during conductance catheter evaluations: an extended Modelflow method.
OBJECTIVE
The Modelflow method computes cardiac output (CO) from arterial pressure (CO-MFao) by simulating a non-linear three-element Windkessel model of aortic input impedance. We present a novel technique to apply the Modelflow method to the left ventricular pressure (Plv) signal, to obtain an estimation of CO (CO-MFlv).


METHODS
We extended the model by simulating the aortic valve as a resistance placed in series to the characteristic impedance. In our model the valve resistance is infinite in diastole, while it has a patient related value during systole. Twenty one patients with heart failure were studied with a combined pressure-conductance catheter positioned in the left ventricle and a micromanometer in the aorta. CO changes were induced during temporary sequential atrio-biventricular pacing with different atrio-ventricular and inter-ventricular intervals. After a single calibration we compared CO-MFlv with CO-MFao (516 measurement series) and with CO estimated by the conductance catheter volume technique (CO-cond) (267 series).


RESULTS
CO ranged from 2.42 to 7.59 l/min with an overall mean of 4.36 (1.38) l/min. Comparing the two Modelflow methods, the bias was -0.04 (0.36) l/min, with limits of agreement of -0.77 and 0.70 l/min, and a coefficient of variation of 8.4%. Of the 516 changes in CO from baseline values, 112 were greater than 0.5 l/min and 110 of these (98%) were scored in the same direction by both methods. For comparisons between CO-MFlv and CO-cond the bias was -0.10 (0.49), with limits of agreement of -1.12 and 0.90 l/min, and a coefficient of variation of 12.5%.


CONCLUSIONS
Cardiac output estimates by the modelflow method from aortic pressure and left ventricular pressure are interchangeable in patients without mitral and aortic abnormalities. After an initial calibration, CO-MFlv presents near zero bias and an adequate precision.
Valsecchi
Sergio
S
Medtronic Italia, Via Lucrezio Caro, Rome, Italy. sergio.valsecchi@medtronic.com
Perego
Giovanni B
GB
Schreuder
Jan J
JJ
Censi
Federica
F
Jansen
Jos R C
JR
D000368:Aged; D000369:Aged, 80 and over; D006328:Cardiac Catheterization; D002302:Cardiac Output; D005260:Female; D006333:Heart Failure / Q000503:physiopathology; D006334:Heart Function Tests / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D008991:Monitoring, Physiologic / Q000379:methods* / Q000706:statistics & numerical data; D017711:Nonlinear Dynamics; D016277:Ventricular Function, Left