An impedance catheter continuously measuring stroke volume and cardiac output showed excellent correlation with an electromagnetic flowmeter in vivo (r=0.95) and in vitro (r=0.99).
Does an impedance catheter accurately measure continuous stroke volume and cardiac output compared to an electromagnetic flowmeter in an artificial heart model and in dogs?
An impedance catheter accurately measures continuous stroke volume and cardiac output in vitro and in animal models, showing potential for human application during cardiac catheterization.
Effect estimate: r = 0.95 (in vivo)
To improve assessment of ventricular function during cardiac catheterisation there should be available a continuous registration of stroke volume and cardiac output in addition to ventricular pressure. To obtain the desired volumetric quantities a catheter has been developed which measures changes in intraventricular dimensions by electrical impedance. For this purpose, the catheter is equipped with eight electrodes spaced over a distance equal to the long axis of the left ventricle into which it is introduced. A constant current is imposed between the outermost electrodes while the inner six are used to measure resistance of volume segments of the blood contained within the ventricular cavity. The difference in resistance at the beginning and end of ejection is proportional to the contribution of each segment to stroke volume, which follows from addition to the segmental terms. Calibration is obtained by measuring electrical conductivity of a blood sample. The catheter was tested over a tenfold range of cardiac output, both in vitro, using an artificial heart model, while performance in vivo was evaluated in 12 dogs. In the animals study, stroke volume and cardiac output from the catheter were compared with flows obtained with an electromagnetic flowmeter. In both studies, linear regression analysis showed excellent correlation of cardiac output (r = 0.99, n = 10 in vitro, r = 0.95, n = 126 in vivo) while the regression equations were close to those of identity. Very good correlation (r = 0.98, n = 28) was also obtained for stroke volumes on a beat to beat basis during arrhythmia. It is concluded that the catheter, which has great potential for application in man, fulfills its primary aim of continuously recording stroke volume and cardiac output.
Baan et al. (1981) studied Assessment of ventricular function (n=12). Impedance catheter vs. Electromagnetic flowmeter was evaluated on Correlation of cardiac output and stroke volume between the impedance catheter and electromagnetic flowmeter (r = 0.95 (in vivo)). An impedance catheter continuously measuring stroke volume and cardiac output showed excellent correlation with an electromagnetic flowmeter in vivo (r=0.95) and in vitro (r=0.99).
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