The volume-dependency of parallel conductance throughout the cardiac cycle and its consequence for volume estimation of the left ventricle in patients.
OBJECTIVE
To study the hypothesis that the electrical conductance of tissues and fluids (parallel conductance (G(p))) around the ventricle depends on left ventricular volume throughout the cardiac cycle.


METHODS
We extended a recently developed method to determine G(p) throughout the cardiac cycle. First, we compared the estimates of parallel conductances obtained with the new method (G(a)(p)) with those of the conventional one (G(1)(p)), both averaged over the cardiac cycles. Secondly, G(a)(p) was determined throughout the cardiac cycle and its volume dependency was assessed. Thirdly, the factor alpha was calculated as the ratio between stroke volume, obtained by the conductance method using G(1)(p), and that obtained by a thermodilution method. Because the non-homogeneous field was indicated to be the reason for the dependency of G(p) on left ventricular volume as well as for the need for alpha, we tested whether the hypothesis implies that a correction with alpha is not needed if G(p) is determined throughout the cardiac cycle.


RESULTS
We found a negative linear relation between G(p) and left ventricular volume. This relation appeared to be reproducible within each patient. Furthermore, we found that alpha deviates from 1 primarily due to the dependency of G(p) on left ventricular volume.


CONCLUSIONS
To obtain stroke volume or to determine absolute left ventricular volume continuously within a cardiac cycle, G(p) should be determined throughout each cardiac cycle and if a constant G(p) throughout the cardiac cycle is used a correction with the factor alpha should be made to correct for a possible influence of electrical field heterogeneity.
Kornet
L
L
Department of Physiology, Cardiovascular Research Institute Maastricht, Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands. l.kornet@fys.unimaas.nl
Schreuder
J J
JJ
van der Velde
E T
ET
Jansen
J R
JR
D002302:Cardiac Output; D004553:Electric Conductivity; D006329:Heart Conduction System / Q000503:physiopathology*; D006333:Heart Failure / Q000473:pathology / Q000503:physiopathology*; D006339:Heart Rate; D006352:Heart Ventricles / Q000473:pathology; D006801:Humans; D013318:Stroke Volume