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Cardiovascular Research 2000 48(3):455-463; doi:10.1016/S0008-6363(00)00203-0
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Copyright © 2000, European Society of Cardiology

A new approach to determine parallel conductance for left ventricular volume measurements

L Korneta,*, J.J Schreuderb, E.T van der Veldec, J Baanc and J.R.C Jansend

aDepartment of Physiology, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands
bDepartment of Cardiac Surgery, San Raffaele Hospital, Milan, Italy
cDepartment of Cardiology, Leiden University Medical Center, Leiden, The Netherlands
dDepartment of Intensive Care, Leiden University Medical Center, Leiden, The Netherlands

* Corresponding author. Tel.: +31-43-388-1209; fax: +31-43-388-4166 l.kornet{at}fys.unimaas.nl

Received 3 April 2000; accepted 21 July 2000


   Abstract
Top
 Abstract
1 Introduction
 2 Methods
 3 Experimental protocol...
 4 Results
 5 Discussion
 References
 
Objectives: To determine absolute ventricular volume with the conductance catheter technique, the electrical conductance of tissues and fluids (parallel conductance) around the ventricle should be determined precisely. Methods: A new objective method to estimate parallel conductance based on analysis of the dilution curve of hypertonic saline was investigated. The parallel conductances obtained with the new method (Gap) were compared to those obtained with the conventional method (Glp). The study was performed in the left ventricle of 12 patients. Results: Gap was not significantly different from Glp. For the Glp method the average percentage difference between duplicate values, both taken as absolute values, was 15.06% and for the Gap method it was 4.01%. Thus the reproducibility of the method is a factor four better than that of the method. This difference appeared to be significant. Conclusion: We conclude that a smaller number of injections will be required to obtain the same precision using our method.

KEYWORDS Cardiomyopathy; Cardiovascular surgery; Conduction (block); Contractile function; Heart failure


   1 Introduction
Top
 Abstract
 1 Introduction
2 Methods
 3 Experimental protocol...
 4 Results
 5 Discussion
 References
 
Assessment of cardiac function is of vital importance in clinical cardiology for diagnosis, monitoring, and treatment. A prerequisite for quantification of cardiac function is a reliable estimation of pressure–volume relationships of the ventricles. Therefore, besides pressure, absolute ventricular volume should be determined continuously. To determine the volume of the left or right ventricle in vivo the electrical conductance method has been used by positioning a catheter in the ventricles and measuring the electrical conductance [1–21]. This method has several advantages over other methods which determine intra-ventricular volumes. The results are obtained immediately, i.e. on-line, and precise geometric assumptions regarding the ventricle, or labor-intensive analyses are not required. However, the conductive tissues and fluids surrounding the ventricle contribute to the measured electrical conductance of the blood inside the ventricle, causing an offset in the relation between measured conductance and true intra-ventricular volume [2]. This offset is called parallel conductance. When parallel conductance is not quantified, only changes in conductance as a measure of changes in volume can be presented [1,22–24]. To extend the conductance method to absolute volume measurements, a method to determine tissue conductance has been introduced by Baan et al. [2]. They determined conductance of the tissues surrounding the blood in the ventricular cavity, by changing the specific conductivity ({sigma}b) of blood by injecting hypertonic saline into the pulmonary artery. The conductance signal was recorded and the successive conductance values at end-diastole (Gdias) were plotted versus the corresponding values at end-systole (Gsys). A linear regression line was fitted through Gsys–Gdias points and extrapolated to the identity line. The intersection point between the lines corresponds to a zero value of conductivity of blood ({sigma}b), and therefore, yields parallel-conductance (Gpl). A disadvantage of this extrapolation method is that a small variation in the determined Gdias and Gsys values will result in a large error in the extrapolated value of parallel conductance.

We evaluated a new objective method to estimate parallel conductance (Gpa), which is based on the integration of an area under a conductance (ion) dilution curve and the determination of flow and conductivity of blood. Paired measurements were performed in 12 patients undergoing left ventricular catheterization. Measurements were used to calculate parallel conductances with both the Gpa and the Gpl method. To compare the accuracy of our new method with that of the conventional method, the mean values of duplicates of our new method as well as the differences between those duplicates were compared to those of the conventional method.


   2 Methods
Top
 Abstract
 1 Introduction
 2 Methods
3 Experimental protocol...
 4 Results
 5 Discussion
 References
 
2.1 The conductance method
The general principles of the conductance method have been described extensively elsewhere [2,4]. Therefore, only the configuration needed for this study will be mentioned. The conductance catheter (7F, Sentron, CD Leycom, Zoetermeer, The Netherlands) for intra-ventricular volume measurements was equipped with 12 circular electrodes mounted at equal distances near the tip. The catheter was positioned in the left ventricle along the longitudinal axis. One alternating current (20 kHz, 30 µA RMS) was applied between the outermost electrodes (1 and 12); and one current (20 kHz, –10 µA RMS) was applied between the two adjacent electrodes (2 and 11). This dual-field configuration [14,15], which has been shown to improve the accuracy of the method, was used in all patients. The catheter was connected to a signal-processor system (Leycom CFL-512, CD Leycom).

For left ventricular measurements, the volume of a segment (Qsegment) between two measuring electrodes at any time t can be calculated as:


Formula (1)

Where the factor {alpha} is a correction factor accounting for the fact that the ventricle is not a regular cylinder, t is time, L the distance between two adjacent electrodes, {sigma}b the conductivity of blood, Gsegment(t) the time-varying conductance between two electrodes and Gp,segment (t) the time-varying parallel conductance for the corresponding segment. The conductivity of blood ({sigma}b) was determined by use of a measuring cell (CD Leycom). If {alpha} is 1, Eq. (1) can be rewritten as:


Formula (2)

Six adjacent electrodes were located in the ventricle, to determine five segmental ventricular conductances. Total left ventricular parallel conductance (Gp) was calculated from the sum of five segmental parallel conductances.


Formula (3)

Likewise, the total conductance can be calculated from the sum of the conductances of the segments according to:


Formula (4)

In this study parallel conductance has been determined using two methods: the conventional method (Glp) and the new method (Gap), both described below.

2.2 Parallel conductance obtained by extrapolation of the Gdias versus Gsys relationship
The assumptions for the conventional method to estimate parallel conductance Gpl [2,4] are that: (1) the injection of a hypertonic saline solution increases blood conductivity but does not affect ventricular volume; (2) parallel conductance does not change as a cause of the intervention; (3) the conductivity of the surrounding structures is the same at diastole and systole; (4) the conductivity of blood changes only in the filling phase of the ventricle when a new saline/blood mixture enters the left ventricle, and it is therefore the same at the beginning and the end of the ejection-phase of the ventricle; (5) in the ventricles the conductivity of blood is not influenced in a pulsatile way by orientation and deformation of erythrocytes because a non-unidirectional flow is present [2,4]. To obtain Glp, the two best identifiable points of the conductance signal in the cardiac cycle are used, i.e. the minimum value at end-diastole (Gdias) and maximum value at end-systole (Gsys). Because actual stroke volume (QV,sys–QV,dias) is assumed to be constant, changes in conductance are due to altered blood conductivity, not volume. From the Gsys versus Gdias plot, with {sigma}b increasing in the ascending limb of the dilution curve after the injection of hypertonic saline, parallel conductance was solved by extrapolation to that theoretical point where conductivity of blood is zero. Then the following holds:


Formula (5)

Thus Glp is the intersection point between the regression line of the relationship between Gdias and Gsys and the identity line (Gdias=Gsys). The precision of this method relies on the constancy of Gp during the intervention. Since salt might enter the coronary circulation, causing an increase in parallel conductance, only those Gsys and Gdias values were considered recorded during the increase in conductance [1,2,6]. To minimize errors at least eight data points were used [25]. The three criteria, used to select the range of Gsys–Gdias values, to determine parallel conductance [4], are (1) the linear regression line with the highest correlation coefficient through conductance values at systole versus those at diastole should be used, (2) the summed value of parallel conductances should approximate the parallel conductances determined with the total conductance signal and (3) parallel conductance obtained for each segment should be positive. Because these three criteria might conflict, the determination of parallel conductance in the ventricle may become observer-dependent. The software package CONDUCT-PC (CD Leycom) used to calculate Glp, provides a tool to reduce the observer-dependency.

2.3 Parallel conductance obtained from the conductance dilution curve
The new approach to estimate parallel conductance is based on the dilution curve of hypertonic saline. Each injection of hypertonic saline was given near the entrance of the right atrium, and conductance was detected in the left ventricle (Fig. 1. upper panel). According to common practice, to eliminate the influence of ventilation on cardiac volume and blood flow, conductance was measured during a prolonged end-expiratory pause procedure. The indicator dilution method for hypertonic saline can be described by a mass balance, in which the amount of ions injected is the same as the change in amount of ions detected. The amount of injected ions, influencing conductance, is the product of the injected volume and the NaCl-ion concentration difference between the hypertonic saline and the blood before injection. The amount of detected ions is the product of flow and the integrated area under the NaCl-ion concentration, i.e. blood conductivity, dilution curve. Thus, if the injection is given as a bolus, if blood flow (Formula ) is constant and the assumption of complete mixing of indicator and blood is made, the following can be formulated:


Figure 1
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  		Fig. 1 Schematic of the new approach to determine parallel conductance. In the upper panel, the sites of injection and detection are given. In the lower panel the measured conductance dilution curve is shown. Within this curve, the conductance values averaged over a heart cycle are given by x. Through these points, the average conductance versus time dilution curve is drawn as a dashed line.

 

Formula (6)


Formula (7)

where Qi is the volume of the injectate, {sigma}i the electrical conductivity of the injectate at blood temperature, {sigma}b the conductivity of the blood before injection, t is time, t1 the time of injection, t2 the time when all indicator has passed the detector site and {Delta}{sigma}b the change in conductivity of the blood due to the injection of the hypertonic saline. Provided Formula is known Eq. (7) can be solved. If the beat to beat averaged left ventricular volume [Formula ] is constant during successive cardiac cycles between t1 and t2 at which hypertonic saline passes the ventricle, and a correction is made for a change in parallel conductance, due to salt entering the coronary circulation, a change in blood conductivity can be translated into a change in conductance. Thus:


Formula (8)

Conductance was averaged over the ejection period of each cardiac cycle [Formula(t)], i.e. average conductance was sampled with the frequency of the heart rate, and plotted versus time. Formula is the area under the beat to beat averaged conductance dilution curve (Fig. 1, lower panel). A small shift in baseline is usually present in the conductance dilution curve, measured in the left ventricle, due to saline entering the coronary circulation. The baseline conductance was subtracted to estimate the area under the dilution curve. From Eqs. (7) and (8) follows:


Formula (9)


Formula (10)

A combination of Eqs. (2) and (4), assuming Gp, G and Qv are averaged beat to beat, gives:


Formula (11)

Formula obtained in Eq. (10) can be substituted in Eq. (11) to obtain:


Formula (12)

Formulaap is the parallel conductance averaged beat to beat over the dilution curve during the ejection phase. Formula is the baseline conductance, estimated by averaging the conductance before the hypertonic saline passes the conductance catheter (Fig. 1. lower panel). We assume that the parallel conductance and total conductance before saline injection do not change between successive heart cycles and therefore Formulaap(t) can be written as Formulaap and Formula(t) as Formula. Because in this study, only values averaged over the heart cycle were used, Formulaap is written as Gap and Formula as G. We determined Formula by use of the thermodilution method [26–28]. Qi, the volume of the injectate, is known. The conductivity of the hypertonic injectate ({sigma}i) and that of blood ({sigma}b) with non-orientated and non-deformed erythrocytes was determined by use of a measuring cell (Leycom CFL-512, CD Leycom) at body temperature. It is assumed that in the ventricles, no overall orientation or deformation of erythrocytes occurs because a non-unidirectional flow is present [2,4].

2.4 Subject population
We performed the study in 12 heart failure patients with dilated cardiomyopathy who underwent cardiomyoplasty. Cardiomyoplasty gives a 40% reduction in left ventricular end-diastolic volume [20]. We obtained data from all these 12 patients during left ventricular catheterization after cardiomyoplasty. One patient was also studied before cardiomyoplasty (Table 1). Only measurements were used if the heart rhythm of the patient was regular during the measurement. Table 1 shows cardiac output, stroke volume and heart rate of the individual patients. The procedures performed in this study had been approved by the medical ethics committees of the various hospitals, where the patients were accommodated [20]. The investigation conformed to the principles outlined in the Declaration of Helsinki [29]. Informed patient consent was obtained for insertion of catheters and subsequent measuring. The patients were heparinized before catheterization. A Swan Ganz thermodilution catheter was positioned in the pulmonary artery and a lumen of this catheter, positioned near the entrance of the right atrium, was used for the injection of hypertonic saline or ice-cold glucose. The conductance catheter was inserted via a femoral artery into the left ventricle.


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  		Table 1 Time related to surgery and haemodynamic conditions such as heart rate, cardiac output and stroke volume as determined with thermodilution

 

   3 Experimental protocol ventricular measurements
Top
 Abstract
 1 Introduction
 2 Methods
 3 Experimental protocol...
4 Results
 5 Discussion
 References
 
To determine parallel conductance, an injection of NaCl solution (5 to 7.5 ml, 6–9%) was given in duplicate and a correction for temperature was made [30]. It was assumed that parallel conductance was constant during the paired measurements. The injection was given via the pulmonary arterial catheter near the entrance of the right atrium at the beginning of a prolonged end-expiratory pause of about 12 s. During the end-expiratory pauses, the conductance signal was acquired at a sample-frequency of 250 Hz and stored on disk for analysis. The same measurement was used to obtain Gap and Glp. By use of a paired t-test, the mean values of duplicates (new method) were compared to those of the conventional method. R is the correlation coefficient. Furthermore, the differences between the duplicates (new method) were compared to those of the conventional method. If zero was not included in a 95% confidence interval (95% C.I.), then it was significantly different from zero. 95% C.I.=mean±(t·standard error). The standard error is given as S.E. The value t depends on the size of the group and can be found in Altman [31]. The absolute average difference between duplicates as percentage of their mean was considered to be a measurement of reproducibility. The ratio between intra-subject variation (due to inaccuracy of the method and variation in haemodynamic condition) and inter-subject variation (intra-subject and variation between subjects) was considered to be a measurement of relative accuracy.

Cardiac output (CO) was determined by thermodilution (COM-2, Baxter) before the conductance measurements by injecting 10 ml of ice-cold glucose also, at the beginning of a prolonged end-expiratory pause. The results of five (CO) measurements were averaged.


   4 Results
Top
 Abstract
 1 Introduction
 2 Methods
 3 Experimental protocol...
 4 Results
5 Discussion
 References
 
In a total 30 measurements, i.e. 15 pairs, obtained in the left ventricle of 12 patients were used to calculate parallel conductance values with the conventional (Glp) and the new method (Gap). In one patient, for one pair of measurements and in one patient for one single measurement, i.e. in total three measurements, Glp was determined for four instead of five segments because one segment was located (partly) in the aorta and not in phase with the other segments. The correlation coefficients of the linear fits through the Gsys versus Gdias relation, to determine parallel conductance with the conventional method, were between 0.62 and 0.99. In Fig. 2A Gap was plotted versus Glp, both averaged for each pair of measurements (n = 15). The regression line through these values was Gap=37 (95% C.I.=5, 70)+Glp*0.72 (95% C.I.=0.50, 0.94), (R = 0.83), mean Glp=141±7 (S.E.), mean Gap=139±5 (S.E.). The square symbols indicate those values of which the deviation of the repeated measurements were less than 10% of their average value for the conventional method. In Fig. 2B, the percentage differences between Glp and Gap, both averaged for each pair of measurements, were plotted versus the mean of both averaged parallel conductances. A paired t-test showed that the mean percentage difference between Gap (averaged for a pair of measurements) and the corresponding value of Glp, was 0.94%±3.53% S.E. (95% C.I.=–6.58%, 8.47%, n = 15), indicating that the outcome of the two used methods was not significantly different.


Figure 2
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  		Fig. 2 (A) Gap[S], averaged for two measurements, plotted versus Glp[S], averaged for the corresponding two measurements. The square symbols indicate those values of which the deviation of the repeated measurements where less than 10% of their average for the conventional method. (B) Scatter diagram of the relative differences between Gap, and Glp, both averaged for two corresponding measurements. The square symbols indicate those values of which the deviation of the repeated measurements where less than 10% of their average for the conventional method.

 
To compare the variation in both methods, the difference in parallel conductances between the first and second measurement of each pair of measurements (n = 15) was calculated using both methods and was plotted (Fig. 3A and B), versus the mean of each corresponding pair of measurements. For the Glp method, the average percentage difference between the first and second measurement was 10.21%±5.72% S.E. (95% C.I.=–1.98%, 22.40%) and for the Gap method it was 0.77%±2.95% S.E. (95% C.I.=–5.52%, 7.06%), neither of which was significantly different from zero. Negative differences and positive differences should balance each other and the average difference should equal zero, if the first measurement does not influence the outcome of the second one. To obtain a measurement for variation, we averaged the absolute values of the differences. In two pairs of measurement, the first measurements differed markedly from the second ones, i.e. the differences between Glp(1) and Gap(1) as well as the differences between Glp(2) and Gap(2) were much smaller than the differences between Glp(1) and Glp(2) or between Gap(1) and Gap(2). We therefore assumed that the condition of the patients had changed in between those measurements. In one of the two cases, the time between two measurements was too long, i.e. 3 h, instead of several minutes and the measurements could not be considered as duplicates anymore. In the other case, the difference was induced by a leg-lifting procedure, performed just before the duplicate measurement, probably changing the intraventricular conductance catheter position. Therefore these two results were excluded, as indicated by arrows in the Fig. 3A and B. For the Glpmethod, the average percentage difference between first and second measurement (n = 13), both taken as absolute values, was 15.06%±3.80% S.E., (95% C.I.=6.86%, 23.27%) and for the Gap method (n = 13) it was 4.01%±1.17% S.E., (95% C.I.=1.49%, 6.54%). Thus the reproducibility of the method is a factor four better than that of the method and this difference appeared to be significant [15.06%–4.01%=11.05%±3.52% S.E., (95% C.I.=3.45%, 18.65%)].


Figure 3
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  		Fig. 3 (A) Relative difference in Glp between two measurements [Glp(1)–Glp(2)]/[Glp(1)/2+Glp(2)/2]*100% versus their averaged value. (B) Relative difference in Gap between two measurements [Gap(1)–Gap(2)]/[Gap(1)/2+Gap(2)/2]*100% versus their averaged value. For the arrows, see Section 4.

 
The inter-subject variation (i.e. the standard error calculated of the 12 values, averaged for each individual) was 7.4% for both the Glpmethod and the Gap method. The intra-subject variation (i.e. the standard error calculated for each individual and averaged for the 12 individuals), was 7.7% for the Glp method and 3.3% for the Gap method. Thus the ratio between intra- and inter-subject variation was 1.0 for the Glp method and 0.5 for the Gap method.


   5 Discussion
Top
 Abstract
 1 Introduction
 2 Methods
 3 Experimental protocol...
 4 Results
 5 Discussion
References
 
A new method (Gap) to measure parallel conductance was studied in heart failure patients and compared to the conventional method (Glp). The average estimates of parallel conductance obtained by use of both parallel conductance estimation methods were similar. The reproducibility of the new method appeared to be a factor four better than that of the conventional method and this difference appeared to be significant.

The Gap versus Glp values as plotted in Fig. 2A, were not significantly different. The square symbols in Fig. 2A, indicating those values from which the repeated measurements being smaller than 10% of their average for the conventional method, were in four out of five cases near the line of identity. This indicates that variation in the Gap–Glp values is mainly due to variation in the Glp values. The improved precision of the Gap method as compared to that of the Glpmethod, can probably be attributed to using the integration technique of the total area under the dilution curve instead of an extrapolation of a linear regression line derived from this curve, as well as the use of extra information, i.e. the flow and the conductivity of blood. Using the new method, the assumption that the injected volume does not influence the conductivity of surrounding tissues is not required because a baseline correction is made. It was assumed that no overall orientation or deformation of erythrocytes occurred either in the conductivity measuring cell or in the ventricles because a non-unidirectional flow is present in the ventricle [1,2,4]. It should be noted that although an error in the determination of the conductivity of blood, due to unexpected flow behavior of erythrocytes might influence Gap it would not influence calculated volume, if the conductivity of blood averaged over the ejection phase of a cardiac cycle is constant for subsequent heart cycles. Therefore in spite of pulsatile behavior of erythrocytes in large blood vessels [32], volume can also be determined with the new method in large blood vessels [33]. In our experiments the cardiac output was determined 3–15 min before the determination of the parallel conductance. To obtain a more reliable Gap-value, the hypertonic saline injection should be given as a combined bolus for the thermodilution curve and the electrical dilution curve. In that case, the assumption of invariant ventricular volume is less disputable, because cardiac output, which might change following the bolus injection of hypertonic saline, will be determined during the change, i.e. during the time that parallel conductance is determined. A further advantage of the Gap-method is that it is observer-independent thus allowing full automation of the procedure. The inter-observer variation of the Glp-method was found to be 7% [34] in a previous study.

Intra-subject variation is determined by inaccuracy of the method and variation in the haemodynamic condition. Inter-observer variation is caused by volume variations between subjects and intra-subject variation. The ratio between intra- and inter-subject variation is therefore smaller if the method is more accurate. The ratio between intra- and inter-subject variation was a factor two lower for the Gap-method than for the Glp-method. This indicates that the Gap-method is more accurate relative to the Glp-method. Unfortunately, we were not able to test the absolute accuracy of both conductance methods in the left ventricle, due to the absence of a ‘gold standard’ for left ventricular measurements. Previously, the accuracy of the conventional conductance method to determine left ventricular volumes was tested by comparison of the conductance obtained volume with a volume determined by cineventriculography and with thermodilution and electromagnetic flow determinations of stroke volume [2,12]. However, the flow methods do not determine absolute volumes. Furthermore, cineventriculography in the left ventricle has a deviation of 22%, being a factor five larger than the new method to determine parallel conductance [35]. We considered using non-invasive two-dimensional echo, but this method also has a standard deviation of 22% of the average for measurements in the left ventricle [36,37]. The conductance method has also been evaluated with balloon measurements [3]. However this was done in an isolated heart, which might influence parallel conductance and its variability.

Because assessment of ventricular volume is of clinical importance to patients with heart failure, we performed the study in patients after cardiomyoplasty. Though cardiomyoplasty reduces ventricular dimensions, the ventricles were still enlarged compared to normal values [20]. The catheters were adapted to the size of the ventricles, to obtain a linear relation between conductance and volume and to eliminate a possible influence of the size of the ventricle on the reliability of our parallel conductance measurements [32,38]. The conventional method is sensitive to irregularities in heart rhythm, because it influences the relation between conductance at systole and conductance at diastole. To reduce errors in the conventional method, which was used as comparison, measurements were only used whenever heart rhythm was regular. We suppose that the effect of an arrhythmia is negligible when a dilution curve of averaged conductance will be used to determine parallel conductance. Because many heart failure patients show frequently arrhythmia, the new method might improve the accuracy of the conductance catheter method in these critically ill patients.

We conclude that the new approach has a better reproducibility than the conventional method and therefore a smaller number of injections is required to obtain the same accuracy. Future studies are needed to test the absolute accuracy of the new approach and to test the applicability of the new method in patients with arrhythmia.

Time for primary review 31 days.


   References
Top
 Abstract
 1 Introduction
 2 Methods
 3 Experimental protocol...
 4 Results
 5 Discussion
 References
 

  1. Baan J, Jong T.T.A, Kerkhof P.L.M, et al. Continuous stroke volume and cardiac output from intra-ventricular dimensions obtained with impedance catheter. Cardiovasc Res (1981) 15(6):328–334.[Abstract/Free Full Text]
  2. Baan J, van der Velde E.T, de Bruin H.G, et al. Continuous measurement of left ventricular volume in animals and humans by conductance catheter. Circulation (1984) 70(5):812–823.[Abstract/Free Full Text]
  3. Burkhoff D, van der Velde E, Kass D, et al. Accuracy of volume measurement by conductance catheter in isolated, ejecting canine hearts. Circulation (1985) 72(2):440–447.[Abstract/Free Full Text]
  4. Baan J, van der Velde E.T, Steendijk P, Koops J. Calibration and application of the conductance catheter for ventricular volume measurement. Automed (1989) 11:357–365.
  5. Kass D.A, Yamazaki T, Burkhoff D, Maughan W.L, Sagawa K. Determination of left ventricular end-systolic pressure–volume relationships by the conductance (volume) catheter technique. Circulation (1986) 73(3):586–595.[Abstract/Free Full Text]
  6. Baan J, van der Velde E.T. Sensitivity of left ventricular end-systolic pressure–volume relation to type of loading intervention in dogs. Circ Res (1988) 62(6):1247–1258.[Abstract/Free Full Text]
  7. Boltwood C.M.J, Appleyard R.F, Glantz S.A. Left ventricular volume measurement by conductance catheter in intact dogs. Parallel conductance volume depends on left ventricular size. Circulation (1989) 80(5):1360–1377.[Abstract/Free Full Text]
  8. Applegate R.J, Cheng C.P, Little W.C. Simultaneous conductance catheter and dimension assessment of left ventricle volume in the intact animal. Circulation (1990) 81(2):638–648. see comments.[Abstract/Free Full Text]
  9. Teitel D.F, Klautz R, Steendijk P, et al. The end-systolic pressure–volume relationship in the newborn lamb: effects of loading and inotropic interventions. Pediat Res (1991) 29(5):473–482.[ISI][Medline]
  10. Cassidy S.C, Teitel D.F. The conductance volume catheter technique for measurement of left ventricular volume in young piglets. Pediat Res (1992) 31(1):85–90.[ISI][Medline]
  11. Odake M, Takeuchi M, Takaoka M, et al. Determination of left ventricular volume using a conductance catheter in the diseased human heart. Eur Heart J (1992) 13(E):22–27.[Abstract/Free Full Text]
  12. Van der Velde E.T, van Dijk A.D, Steendijk P, et al. Left ventricular segmental volume by conductance catheter and Cine-CT. Eur Heart J (1992) 13(Suppl_E):15–21.[Abstract/Free Full Text]
  13. Solda P.L, Pantaleo P, Perlini S, et al. Continuous monitoring of right ventricular volume changes using a conductance catheter in the rabbit. J Appl Phys (1992) 73(5):1770–1775.[Abstract/Free Full Text]
  14. Steendijk P, Van der Velde E.T, Baan J. Left ventricular stroke volume by single and dual excitation of conductance catheter in dogs. Am J Phys (1993) 264(6 Pt 2):H2198–2207.
  15. Steendijk P, van der Velde E.T, Baan J. Single and dual excitation of the conductance-volume catheter analysed in a spheroidal mathematical model of the canine left ventricle. Eur Heart J (1992) 13(Suppl E):28–34.[Abstract/Free Full Text]
  16. Szwarc R.S, Mickleborough L.L, Mizuno S, et al. Conductance catheter measurements of left ventricular volume in the intact dog: parallel conductance is independent of left ventricular size. Cardiovasc Res (1994) 28(2):252–258.[Abstract/Free Full Text]
  17. Dickstein M.L, Yano O, Spotnitz H.M, Burkhoff D. Assessment of right ventricular contractile state with the conductance catheter technique in the pig. Cardiovasc Res (1995) 29:820–826.[Abstract/Free Full Text]
  18. White P.A, Bishop A.J, Conroy B, Oldershaw P.J, Redington A.N. The determination of volume of right ventricular casts using a conductance catheter. Eur Heart J (1995) 16:1425–1429.[Abstract/Free Full Text]
  19. White P.A, Chaturvedi R.R, Bishop A.J, et al. Does parallel conductance vary during systole in the human right ventricle. Cardiovasc Res (1996) 32:901–908.[Abstract/Free Full Text]
  20. Schreuder J.J, van der Veen F.H, van der Velde E.T, et al. Left ventricular pressure-volume relationships before and after cardiomyoplasty in patients with heart failure. Circulation (1997) 96(9):2978–2986.[Abstract/Free Full Text]
  21. Bishop A, White P, Oldershaw P, et al. Clinical application of the conductance catheter technique in the adult human right ventricle. Int J Cardiol (1997) 58(3):211–221.[CrossRef][ISI][Medline]
  22. Clavin O.E, Spinelli J.C, Alonso H, et al. Left intraventricular pressure–impedance diagrams (DPZ) to assess cardiac function. Part 1: morphology and potential sources of artifacts. Med Progn Technol (1986) 11:17–24.
  23. McKay R.G, Spears J.R, Aroesty J.M, et al. Instantaneous measurement of left and right ventricular stroke volume and pressure–volume relationships with an impedance catheter. Circulation (1984) 69(4):703–710.[Abstract/Free Full Text]
  24. Spinelli J.C, Clavin O.E, Cabrera E.I, et al. Left intraventricular pressure–impedance diagrams (DPZ) to assess cardiac function. Part II: determination of end-systolic loci. Med Progn Technol (1986) 11(1):25–32.
  25. Herrera M.C, Olivera J.M, Valentinuzzi M.E. Parallel conductance determination in cardiac volumetry using dilution manoeuvres: theoretical analysis and practical implications. Med Biol Eng Comp (1999) 37(2):169–174.[ISI][Medline]
  26. Jansen J.R.C, Schreuder J.J, Boogaard J.M, van Rooyen W, Versprille A. Thermodilution technique for measurement of cardiac output during artificial ventilation. J Appl Phys (1981) 50(3):584–591.
  27. Jansen J.R.C, Boogaard J.M, Versprille A. Extrapolation of thermodilution curves obtained during a pause in artificial ventilation. J Appl Phys (1987) 63(4):1551–1557.[Abstract/Free Full Text]
  28. Jansen J.R.C, Schreuder J.J, Settels J.J, Kloek J.J, Versprille A. An adequate strategy for the thermodilution technique in patients during mechanical ventilation. Int Care Med (1990) 16(7):422–425.[CrossRef][ISI][Medline]
  29. World Medical Association Declaration, Helsinki. Recommendations guiding physicians in biomedical research involving human subjects. Cardiovasc Res (1997) 35(1):2–3.[Free Full Text]
  30. Herrera M.C, Olivera J.M, Valentinuzzi M.E. Parallel conductance estimation by hypertonic dilution method with conductance catheter: effects of the bolus concentration and temperature. IEEE Trans Biomed Eng (1999) 46(7):830–837.[CrossRef][ISI][Medline]
  31. Altman D.G. Practical statistics for medical research. (1991) London: Chapman and Hall. 293–294.
  32. Kornet L, Jansen J.R.C, Gussenhoven E.J, et al. The conductance method for the measurement of cross-sectional areas of the aorta. Ann Biomed Eng (1999) April:141–150.
  33. Kornet L, Jansen J.R.C, Gussenhoven E.J, Versprille A. Determination of the mean cross-sectional area of the thoracic aorta using a double indicator dilution technique. Plugers Arch (1996) 432:1069–1073.[CrossRef][ISI][Medline]
  34. Kornet L. Extensions and improvements of the conductance method. (1996) Rotterdam, The Netherlands: Erasmus University.
  35. Keogh A.M, Eberl S, Yeates M.G, et al. Reproducibility of radionuclide left ventricular ejection fraction in patients awaiting cardiac transplantation. Clin Nucl Med (1990) 15(1):25–28.[CrossRef][ISI][Medline]
  36. Germain P, Roul G, Kastler B, et al. Inter-study variability in left ventricular mass measurement. Comparison between M-mode echography and MRI. Eur Heart J (1992) 13(8):1011–1019.[Abstract/Free Full Text]
  37. Otterstad J.E, Froeland G, St John Sutton M, Holme I. Accuracy and reproducibility of biplane two-dimensional echocardiographic measurements of left ventricular dimensions and function. Eur Heart J (1997) 18(3):507–513.[Abstract/Free Full Text]
  38. Hettrick D.A, Battocletti J.H, Linehan J.H, Warltier D.C. In vivo measurement of aortic pressure–diameter relationships using the conductance catheter technique. Annals Biomed Eng (1996) 25:S21.

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