European Heart Journal (1992) 13 (Supplement E), 28-34
Single and dual excitation of the conductance-volume catheter analysed in a spheroidal mathematical model of the canine left ventricle P. STEENDIJK, E. T. VAN DER VELDE AND J. BAAN
Laboratory of Clinical Physiology, Department of Cardiology, Leiden University Hospital, The Netherlands
KEY WORDS: Conductance-volume catheter, segmental volume, slope factor, spheroidal model.
Introduction
factor can be obtained only by comparing the conductance data with an independent measurement of (stroke) volThe conductance-volume method employs a multi-elec- ume. Reported values for the slope factor are generally trode catheter to measure intracavitary electrical conduc- less than 1 and may vary substantially between hearts, tances from which segmental and total LV volumes are especially in humans'2' (Odake et aL, this issue). estimated. Previous studies have generally shown good We recently introduced a modified conductance catheter linear correlations between (stroke) volumes obtained by technique, called dual excitation, which employs two addi1 31 the conductance catheter technique and other methods' " . tional electrodes on the conductance catheter to superHowever, theoretical studies!6-81 predict that non-linearities impose a second electrical field on the field which is may be present when volume is varied over a large range. generated conventionally via the most proximal and distal To some extent this was confirmed by recent experimental electrodes'12'. By changing the ratio of the two currents 9101 studies' . Theoretical work also indicated that the relawhich are used to generate the electrical field, the shape of tion between conductance and volume may vary between this combined (dual excitation) field can be manipulated. ventricular segments which makes calibration difficult. More specifically, its homogeneity can be improved. The Since techniques to measure segmental LV volume in vivo rationale is that with a more homogeneous field, the accurately are sparse, the problem of segmental calibration assumptions implicit in the algorithm converting conduc11 has attracted little attention' ' (Van Der Velde et al., this issue). tance to volume are better satisfied, resulting in more accuCalibration of the conductance technique to obtain rate volume estimates absolute volumes requires the estimation of two quantities: The present report describes our analysis of the single an offset term and a slope factor. The conductance of the left ventricular wall and surrounding structures introduces and dual excitation conductance methods with regard to an offset in the relationship between intracavitary volume (segmental) calibration and linearity in a spheroidal anaand measured conductance. This term, called parallel con- lytical model of a canine LV of which the volume was ductance, may be obtained in situ by a saline dilution varied over a large range. method'2'. Although the offset term may vary substantially between hearts, it has been shown to be estimated accurately by the saline dilution technique. The second Methods calibration factor is the slope of the relation between true volume and conductance-derived volume. Initially Baan CONDUCTANCE CATHETER et a/.'11 assumed this factor to be 1, based on a simplified The principles and techniques of estimating LV volume stacked cylinder model of the LV. Later, Mur and Baan'61 by measuring electrical conductance in the cavity have assessed the slope factor in a more sophisticated spheroidal been described previously!1-21. Briefly, a catheter with eight model of the LV and found a value of 0-69. In vivo the slope ring electrodes equidistantly spaced near the tip is positioned along the long axis of the LV. The electrode distance is chosen such that, with the distal electrode in the apex, the most proximal electrode is situated just above the Correspondence: Paul Steendijk, Leiden University Hospital, Department aortic valve. An electrical field is set up in the cavity by of Cardiology, P.O. Box 9600,2300 RC Leiden, The Netherlands. 0195-668X/92/0E0028 + 07 S08.00/0
© 1992 The European Society of Cardiology
Downloaded from http://eurheartj.oxfordjournals.org/ by guest on June 7, 2016
The conductance method employs a multi-electrode catheter to generate an electricalfieldand measure intracavitary segmental conductances. Left ventricular (LV) volumes are calculated using an algorithm which assumes the electrical field to be homogeneous. This assumption may be violated leading to a non-linear relation between conductancederived and true volumes. In addition, this relation may vary between segments. A new method is introduced which uses a more homogeneous field. Volume estimates using the conventional single excitation and the new dual excitation method were compared in a mathematical model of a canine LV, which was varied over a large volume range. With single excitation the slope factors, relating conductance-derived and true volumes, varied from 0-50 to 0-76 between segments and was 0-65 for total LV volume. Using dual excitation the segmental slope variability was reduced (range: 0-74-0-77) and the slope factor for total volume increased to 0-76. The linearity of the relation between conductancederived and true volume was improved with dual excitation and extended over a larger range.
Dual excitation in a spheroidal model
29
passing a current (20 kHz, 30 /iA RMS) via the most proximal and most distal electrodes. The six remaining electrodes delineate five segments. The voltage difference between each pair of electrodes is measured continuously and divided into the current to obtain an instantaneous segmental conductance. Time-varying segmental volume, V|(t), with i = 1 through 5, follows from measured segmental conductance, G((t), through: V,(t) = [I/as]
[Gs(t) - Gf]
(1)
where a, is a segmental slope factor,
Single and dual excitation of the conductance-volume catheter analysed in a spheroidal mathematical model of the canine left ventricle P. STEENDIJK, E. T. VAN DER VELDE AND J. BAAN
Laboratory of Clinical Physiology, Department of Cardiology, Leiden University Hospital, The Netherlands
KEY WORDS: Conductance-volume catheter, segmental volume, slope factor, spheroidal model.
Introduction
factor can be obtained only by comparing the conductance data with an independent measurement of (stroke) volThe conductance-volume method employs a multi-elec- ume. Reported values for the slope factor are generally trode catheter to measure intracavitary electrical conduc- less than 1 and may vary substantially between hearts, tances from which segmental and total LV volumes are especially in humans'2' (Odake et aL, this issue). estimated. Previous studies have generally shown good We recently introduced a modified conductance catheter linear correlations between (stroke) volumes obtained by technique, called dual excitation, which employs two addi1 31 the conductance catheter technique and other methods' " . tional electrodes on the conductance catheter to superHowever, theoretical studies!6-81 predict that non-linearities impose a second electrical field on the field which is may be present when volume is varied over a large range. generated conventionally via the most proximal and distal To some extent this was confirmed by recent experimental electrodes'12'. By changing the ratio of the two currents 9101 studies' . Theoretical work also indicated that the relawhich are used to generate the electrical field, the shape of tion between conductance and volume may vary between this combined (dual excitation) field can be manipulated. ventricular segments which makes calibration difficult. More specifically, its homogeneity can be improved. The Since techniques to measure segmental LV volume in vivo rationale is that with a more homogeneous field, the accurately are sparse, the problem of segmental calibration assumptions implicit in the algorithm converting conduc11 has attracted little attention' ' (Van Der Velde et al., this issue). tance to volume are better satisfied, resulting in more accuCalibration of the conductance technique to obtain rate volume estimates absolute volumes requires the estimation of two quantities: The present report describes our analysis of the single an offset term and a slope factor. The conductance of the left ventricular wall and surrounding structures introduces and dual excitation conductance methods with regard to an offset in the relationship between intracavitary volume (segmental) calibration and linearity in a spheroidal anaand measured conductance. This term, called parallel con- lytical model of a canine LV of which the volume was ductance, may be obtained in situ by a saline dilution varied over a large range. method'2'. Although the offset term may vary substantially between hearts, it has been shown to be estimated accurately by the saline dilution technique. The second Methods calibration factor is the slope of the relation between true volume and conductance-derived volume. Initially Baan CONDUCTANCE CATHETER et a/.'11 assumed this factor to be 1, based on a simplified The principles and techniques of estimating LV volume stacked cylinder model of the LV. Later, Mur and Baan'61 by measuring electrical conductance in the cavity have assessed the slope factor in a more sophisticated spheroidal been described previously!1-21. Briefly, a catheter with eight model of the LV and found a value of 0-69. In vivo the slope ring electrodes equidistantly spaced near the tip is positioned along the long axis of the LV. The electrode distance is chosen such that, with the distal electrode in the apex, the most proximal electrode is situated just above the Correspondence: Paul Steendijk, Leiden University Hospital, Department aortic valve. An electrical field is set up in the cavity by of Cardiology, P.O. Box 9600,2300 RC Leiden, The Netherlands. 0195-668X/92/0E0028 + 07 S08.00/0
© 1992 The European Society of Cardiology
Downloaded from http://eurheartj.oxfordjournals.org/ by guest on June 7, 2016
The conductance method employs a multi-electrode catheter to generate an electricalfieldand measure intracavitary segmental conductances. Left ventricular (LV) volumes are calculated using an algorithm which assumes the electrical field to be homogeneous. This assumption may be violated leading to a non-linear relation between conductancederived and true volumes. In addition, this relation may vary between segments. A new method is introduced which uses a more homogeneous field. Volume estimates using the conventional single excitation and the new dual excitation method were compared in a mathematical model of a canine LV, which was varied over a large volume range. With single excitation the slope factors, relating conductance-derived and true volumes, varied from 0-50 to 0-76 between segments and was 0-65 for total LV volume. Using dual excitation the segmental slope variability was reduced (range: 0-74-0-77) and the slope factor for total volume increased to 0-76. The linearity of the relation between conductancederived and true volume was improved with dual excitation and extended over a larger range.
Dual excitation in a spheroidal model
29
passing a current (20 kHz, 30 /iA RMS) via the most proximal and most distal electrodes. The six remaining electrodes delineate five segments. The voltage difference between each pair of electrodes is measured continuously and divided into the current to obtain an instantaneous segmental conductance. Time-varying segmental volume, V|(t), with i = 1 through 5, follows from measured segmental conductance, G((t), through: V,(t) = [I/as]
[Gs(t) - Gf]
(1)
where a, is a segmental slope factor,
