Gzrdiovascular Research ELSWIER Cardiovascular Research 32(1996)901-908 Does parallel conductance vary during systole in the human right ventricle? P.A. White a, R.R. Chaturvedi a, A.J. Bishop b, C.I.O. Brcmkes b, P. J. Older&w A.N. Redington a7* b, a Depurtment of Paediatric Cardiology, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, UK b Department of Adult Cardiology, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, UK Received7 February1996; accepted3 I May 19% Abstract Keywords: Parallel conductance; Conductance catheter; Human; Pressure-volume area Right ventricular (RV) contractile performance remains poorly characterised, particularly in humans. Measurement of ventricular volume is important in the investigation of ventricular function and the description of changes in left ventricular volume related to time and pressure has been fundamental in the development of current concepts of left ventricular performance. Numerous techniques have been used to measure right ventricular volume [l-5], but most require geometric assumptions and labour intensive off-line image contouring. The conductance technique has been developed to enable a real time, beat to beat assessment of left ventricular volume [6-91 and is a potentially useful technique for continuous measurement of right ventricular volume. Corresponding author. Tel. (+44-171) 351-8545. Time for primary 1. Introduction l 351-8546; Fax (+44-171) OCO8-6363/%/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved. PII SOOOS-6363(96)00132-O review 36 days. Downloaded from by guest on September 30, 2016 Objectives: Right ventricular (RV) contractile performance remains poorly characterised, particularly in humans. Conductance catheter techniques have the potential to overcome the geometric difficulties in RV volume measurementthat have hindered systematic studies of RV pressurevolume relations. The present study examines changes in parallel conductance(Vc) that may occur during the cardiac cycle in the human right ventricle. Methods: Using signals obtained from custom-built conductance catheters, six iscchronal systolic values of Vc (Vc(t)) were measuredduring hypertonic saline wash-in. Studies were performed in nine patients undergoing right heart catheterisation.Their agesranged from 7 to 39 years (median = 16) and their weights ranged from 20.3 to 84.7 kg (median = 50.0 kg). Measurementsof mean Vc and isochronal Vc(t) and its variability during systole were assessed.Mean Vc was measuredusing the Baan technique (Vc(Baan)), Vc(t) was measuredfrom six systolic isochrones obtained during the same period of hypertonic saline wash-in. Results: The temporal changes in Vc(t) were small (mean 5.8%, median = 4.4%, range = 0.6-17.9%) of total corrected end-diastolic volume (mean maximal variation of 7.7 ml). The value of Vc(t) obtained at dp/df,, (mean - 99.1 ml; median - 104.75 ml; range 20.15-196.7 ml) was not significantly different to that obtained at dp/dt,, (mean = 100.0 ml; median = 110.87 ml; range = 20.0-204.2 ml) (P > 0.05), but both were higher than the single Vc measurement(Vc(Baan)) obtained using the standard approach(P = 0.02). The correlation betweenVc(Baan) and Vc(t) for group data; (Vc(Baan) = 89.69 ml, s.d. = 43.73 ml; vc(t7 = 98.16 ml, s.d. = 50.16 ml) produces a regressionslope of 0.99 for all studies (P = 0.02). Conclusion: We conclude that parallel conductance does vary during systole in the human right ventricle of adults and older children after repair of congenital abnormalities but there is no significant difference in Vc(t) at dp/dr,i, and d p/dr,. However, there was a significant difference when the isochronal Vc(t) measurementis comparedwith the standardsingle value technique (Vc(Baan)) obtained using the hypertonic saline wash-in method.The excellent correlation between Vc(t) and Vc(Baan) suggeststhat the correction of Vc for the phaseof the cardiac cycle is unnecessaryfor most purposeswhen studying the human right ventricle. PA. White et al./ Cardiovascular Research 32 (1996) 901-908 902 A .,, ._ ,.. 4 _..._.....__._......-............_.._._...._.__._..._.__..........~~~~~ ._...__............-................._.__....._.............~ ::.::,..:.:*I :.: :.:._ :.:.. :.:.: :.: : :iseo, ECG (BPW . ... 85 Volume (ml) 80 __.....-.. I __ .__.._ __. _. Pressure (mmHg) Pressure / Volume Time (Set) B End Diastolic Volume (ml) End Systolic Volume (nil) Downloaded from by guest on September 30, 2016 20.84 PA. White et al. /Cardiovascular We have previously shown that a conductancecatheter can reliably measurethe volume of right ventricular models made from human post-mortem hearts [lo]. A drawback of this technique in vivo is that structures such as the myocardium and left ventricular blood pool also conduct current, a phenomenon known as parallel conductance (Vc). There is no systematicevaluation of Vc in the human left or right ventricle and validation is neededto determine its stability during the cardiac cycle. The hypertonic saline wash-in technique for determining parallel conductance has been widely reported for the left ventricle in animal models [8,11]. This technique yields a single value for parallel conductancevolume, Vc(Baan), i.e., it assumesno significant variation during the cardiac cycle. Animal studies have suggestedthat any such variation is insignificant in the left ventricle [ 12,131but there are no data currently available for the right. In this study we present a method of determining parallel conductance throughout the systolic phase of the cardiac cycle to investigate the potential variation of Vc in the human right ventricle. 2.1. Preparation Studies were performed in nine patients undergoing cardiac catheterisation for a variety of clinical conditions. Their agesranged from 7 to 39 years (median = 16 years) and their weights ranged from 20.3 to 84.7 kg (median = 50.0 kg). There were seven males and two females. All patients were in sinus rhythm. Patient characteristics are detailed in Table 1. All had undergone surgical or tranTable 1 Patient demographicsand clinical condition Patient Age (years) Weight (kg) Sex Clinical condition (repaired) 1 2 3 4 5 6 7 8 9 15 16 I 18 30 21 39 16 14 40.95 50.00 20.30 59.15 84.70 80.10 38.05 60.00 46.00 M M M M M F F M M PA + VSD PS+PR AVSD + fallots Fallots Fallots + PS+ PR Fallots PS+ fallot + VSD Fallots PS+ pulmonary valvotomy PA = pulmonary atrcsia; VSD = ventricular septal defect; PS = pulmonary stenosis; PR = pulmonary regurgitation; AVSD = atriovennicular septal defect; Fallots = tetralogy of fallot. 903 scatheter treatment of congenital heart defects and were being re-evaluated as part of their routine follow-up. None had any evidence of residual intra- or extracardiac shunting, outflow tract obstruction, atrioventricular valve regurgitation or myocardial dysfunction. This study was approved by the hospital ethics committee and informed written consentwas obtained from all patients. The investigation conforms with the principles outlined in the Declaration of Helsinki [14]. All subjects were sedated, intubated and receiving intermittent positive pressure ventilation at the time of study. A 2.5 French Millar micromanometer (Millar Instruments Inc., Houston, TX, USA) and a 5 or 7 French custom-built “8-electrode” conductance catheter (Cordis-Webster, Roden, The Netherlands) with an appropriate total interelectrode distance to match the length from the apex to the tricuspid valve (range 5-8 cm), was advanced via the femoral vein into the right ventricle and positioned with the distal end in the apex. The catheter size was selected so that the most proximal electrode of the conductance catheter was at the level of the tricuspid valve. Correct placement of the conductance catheter was achieved mainly by fluoroscopy and verified by monitoring segmental volume phase relationships and counterclockwise pressure-volumeloop genesis. The conductance catheter was connected to a Sigma 5 DF signal conditioning and processing unit (Cardiodynamics, The Netherlands). Analogue signals representing the five segmental conductances, left ventricular pressure and ECG were digitised (12 bit, 250 Hz), monitored on line and stored on a microcomputer for later analysis using custom software. 2.2. Conductance catheter The principles of the conductancetechnique to estimate ventricular volume have been described in detail elsewhere and extensively evaluated in the left ventricle [7-91. Briefly, the conductance catheter method to determine ventricular volume is based on the measurementof the electrical conductanceof blood in a ventricular cavity. The conductance catheter used in all measurementshad eight equally spacedplatinum ring electrodes. An electric current of 20 kHz and 30 PA is applied between the two outermost electrodes(electrodes 1 and 8) to generate an intracavitary electric field. The remaining electrodesare used to measurethe potential difference and therefore derive the time varying conductance(Gt) of five ventricular segments.Total right ventricular conductanceis calculated as the sum of the segmentalconductances.The Fig. 1. Determination of Vc(Baan) from the human right ventricle. (A) Data obtained dur!ng hypertonic saline wash-m. The hypertonic saline mixes with blood in the right ventricle producing a gradual transient increasein volume while true volume and pressureremain constant.(B) Regressionusing paired minimal versus maximal volumes generatesa linear relation between observedvolumes as a function of changing blood conductivity. Extrapolation to the line of identity (correspondingto o = 0) gives Vc(Baan) = 59.7 ml, R = 0.%9. Downloaded from by guest on September 30, 2016 2. Method Research 3;? (1996) 901-908 PA. White ef al. / Cardiovascular Research 32 (1996) 901-908 904 relationship between time varying volume (Vt) with Gt is given by the simple formula [7]: Vt = l/a. L2 p(Gt - Gp) (1) Where (Y is the dimensionless slope factor, p is the specific conductivity of blood measured from a blood sample, L is the interelectrode distance and Gp is the parallel conductance.Left and right ventricular tissue, fluid and the associatedpericardial tissues also contribute to the total measuredconductance.The offset volume, Vc, caused by the parallel conductance,Gp, is equal to Vc = ( 1/cz)(L2. p)Gp (2) Fig. 2. Pressurevolume loops obtained during a saline wash-in technique. The perceived volume increase is due to the increasing conductivity created by hypertonic saline. 2.3. Vc estimation V,, = mV,, + b (3) Where V,, = end systole and V,, = end diastole, m = slope, b = y-intercept. As actual stroke volume is constant, changes in these conductance values are due to altered blood conductivity and not volume. V,,, is plotted against the subsequent Vminof each beat during the ascendingphaseof the saline wash-in. The theoretical relationship between EDV and ESV represents a straight line thus we perform linear regression analysis on ESV and EDV. This line is used to extrapolate to the line of identity (A’). The volume at this point representsVc(Baan) (B’) (Fig. 1B). This volume is the result of current conducted through structures surrounding the right ventricle equals (Vc(Baan)) by: Vc(Baan) = b/( 1 - m) (4) where Vc(Baan) = parallel conductance, b = y-intercept, m = slope 2.4. Vcfd The method describedby Baan et al. [6] yields a single value based on measurementstaken at end systole and diastole. This does not take into account potential changes during the cardiac cycle. To assessvariability of parallel conductancein the right ventricle multiple estimateswere obtained during systole using a method previously described in dogs and mini-pigs in the left ventricle [ 12,131. Briefly, the systolic portion of four consecutive cardiac cycles from a hypertonic saline wash-in was divided into six equal time intervals (isochrones) from dp/dt,,, to dp/dt,,,,, and the apparent ventricular volume of each point was obtained by interpolation from the raw data. The data were then plotted as ventricular volume versus stroke volume for each cardiac cycle. Thus ventricular volume at each isochronal point can be linearly regressed against stroke volume. The volume where the regression line intercepts the y-axis corresponding to zero stroke volume or conductivity correspondsto the parallel conductance volume at each time interval (Vc(t)). If there were no change in Vc(t) then the intercept would be identical for each isochrone. 2.5. Protocol Arterial, right atria1and pulmonary artery pressuresand ECG were continuously monitored. Having obtained an optimum conductancecatheter position in the right ventricle, blood resistivity, p, was measuredand entered into the signal conditioning and processing unit along with the Fig. 3. Isochronal plots for each of the six time intervals in each patient. Isochrones l-6 representequally spacedisochronesfrom maximum dp/dr to minimum dp/dr and the numerical value is reflected by the y-intercept for each regressionline. Downloaded from by guest on September 30, 2016 Determination of a value for the volume offset due to parallel conductance(Vc(Baan)) was performed by a dilution technique previously described by Baan et al. [6], whereby the conductivity of the blood was transiently increasedby a bolus injection of hypertonic saline (1-3 ml of 10%) into the femoral vein. After a short period of time the blood-saline mixture entered the right ventricle causing an increase in the right ventricular conductance and perceived increase in amplitude of the volume signal (Fig. 1A). The principal assumption inherent in this method is that infusion of a small bolus of hypertonic saline increasesthe blood conductivity but not the volume of blood in the right ventricular cavity, while the conductivity of surrounding structures remains constant. From the conductance signal, the two most easily identified points from each successivecycle are the points of maximum (V,,, or end-diastolic) and minimum (V,,,i, or end-systolic) volume according to PA. White et al. /Cardiovascular Research 32 (1996) 901-908 905 Patient 3 Patient 1 ______ Vc@un)-IOS.4ml &.a l-126.32ml 6 lo Patient 4 30 20 strolks volva 6 I 2 (WI] 3 Sxoka ‘ Voluma 5 6 7 (mll Patient 6 Patient 5 00 Lsa 3=63.84d Is0 4=63 mm1 3 00 Downloaded from by guest on September 30, 2016 5 Is0 6==62.94ml s a : 2 2 5 Q 70 Patient 7 Patient 8 Patient 9 40 Is0 I -I 32.39d LoZ-123.6Lhl Lua44-117.3Sml 20 lo 0 str.A. lrochtone ea lrochrone q 1 2 o lrochrone o ltochrons 3 4 o lrochrons o lrochrone 20 “oluan 5 6 (ml, 30 -0 1 2 3 S,rLa. ‘ v.aluala 5 6 (“0 7 6 906 PA. White et al. / Cardiovascular interelectrode distance. Parallel conductancewas measured during the injection of 3 ml of 10% saline into the femoral vein during continuous data acquisition. If ectopy occurred during data collection, we performed another injection in order to obtain at least two acceptable recordings. If changesin heart rate or ventricular pressurewere apparent during the saline injection, the injection was repeatedwith a smaller volume. Each dataset was acquired for approx. 20 s during suspendedventilation. 2.6. Data analysis/statistics The significance of variation from the mean of six isochronal values of Vc(t> during systole was assessed using analysis of variance. The Vc(t) values obtained at were also compared directly to those at dp/%,, dp/dtmi, using a paired sample t-test. The possibility of a relationship between the absolute measurement of Vc(Baan) and its deviation during the cardiac cycle was assessedby linear regression. The null hypothesis was rejected when P < 0.05. Fig. 2 shows an example of the pressurevolume loops recorded after injecting 3 ml of hypertonic saline into the femoral vein. The single value technique yielded values of Vc(Baan) which ranged from 19 to 166.4 ml (median = 99 ml, s.d. = 43.75 ml). The correlation coefficients (r) of the relationship when V,,,,, is plotted against the subsequent Vminto obtain Vc(Baan) ranged from 0.80 to 0.99 (mean = 0.93, s.d. = 0.07). The time varying Vc(t) determination was obtained from each of six isochrones during the systolic portion of the cardiac cycle (Fig. 3). Each of the lines displayed on the graph represents one of the isochrones ranging from minimum to maximum dp/dt and the numerical value is reflected by the y-intercept for each regression line. Isochrone 1 represents maximum positive dp/dt and isochrone 6, minimum dp/dt. Each isochrone in between can be identified from its y-intercept. The six Vc(t) values, Vc(t) at dp/d& and dp/dr,,,, and from the normal saline technique (Vc(Baan)) are summarised in Table 2. The close correlation betweenVc(Baan) and Vc( t) for group data (Vc(Baan) = 89.69 ml, s.d. = 43.74 ml; Vc( t) = 98.16 ml, s.d. = 50.16 ml) producesa regression slope of 0.99 and an intercept of - 3.93 ml (P = 0.02). Fig. 3 details the changesin Vc(t> that occurred during cardiac systole in all nine patients. The mean initial value for group data, at dp/dt,,,, of 0.96 + 4.36 ml above the mean decreased to a minimum of - 2.60 I!I 5.30 ml at midsystole changing at d p/d tmin to 1.90 f 4.37 ml. However, the value at dp/dr,,, was not significantly different from that at dp/dt,i, (P > 0.05) but both exceededmean Vc(Baan) (P = 0.02). Table 2 Mean Vc(Baan) determined by hypertonic saline with mean Vdt) nine patients Patient Vc(Baan) vc(t) Vdt) (dp/dr,,,) Vc(t) (dp/dr,,,) 1 2 3 4 5 6 7 8 9 Mean (ml) s.d. (ml) P 105.4 85.7 46.6 59.7 101.2 166.4 124.2 99.0 19.0 89.7 43.7 0.02 121.7 93.6 48.0 62.8 111.1 192.3 123.5 109.8 20.8 98.2 50.2 121.5 92.4 46.9 62.9 110.9 204.2 129.1 112.4 20.0 100.1 53.7 ns. 126.3 90.0 47.3 63.1 111.3 196.7 132.4 104.7 20.2 99.1 52.3 for Vc(Baan), single value parallel conductance; vc(t), mean of time varying parallel conductance from dp/dt,,, to dp/dt,,; Vc(t) dp/dt,i,, mean parallel conductance at dp/dr,,,; V&j dp/dt,,,, mean parallel conductance at dp/dr,,,. Comparison of Vc(Baan) with vc(t) and Vc(t) dp/dt,i, to V&) dp/dr,,, was by a paired I-test (P-values shown). There was a significant relationship (r = 0.59, P < 0.05) with the difference between maximum and minimum Vc(t) [AVc(t)] and the Vc( t) averaged from all of the six isochrones.This suggeststhat the magnitude of variability is proportional to the amount of parallel conductanceitself. However, overall the Vc(t) averaged for the group represented 5.73% (s.d. = 5.75%) of total corrected end-diastolic volume (mean maximal variation of 7.66 ml), and 2.47% (s.d. = 2.23%) as a percentageof Vc(t). 4. Discussion The conductancetechnique has been widely applied to the study of left ventricular pressure-volumerelationships in animals [8,15,16] and adults with a variety of heart diseases[7,11]. Extensive validation has been published and it has been recently demonstratedthat left ventricular parallel conductance remains fairly constant during the cardiac cycle [ 12,131.There is no theoretical reason why this technique should not be applied to study human right ventricular function. A prerequisite of this technique is the determination of the parallel conductanceor volume offset (Vc) due to the conductivity of tissues surrounding the ventricular blood pool. Early studies assumedthis offset to be constant [6,17], but there are several potential sources of Vc variability including respiration, atria1 filling, right ventricular ejection, and myocardial blood volume changes. Of these, in clinical practice, changeswith respiration are the largest and were even more marked in this study of right ventricular volumes than we have seen in the left ventricle. For this reason all measurementsmadeusing this technique should be recorded during suspendedventilation. Downloaded from by guest on September 30, 2016 3. Results Research 32 (1996~901-908 PA. White et al./Cardiovascular 907 lished b,y Szwarc et al. [13] in the much smaller left ventricle of anaesthetisedclosed chest mini-pigs. In this study a small but significant variation in Vc(t) was found using the isochronal method in the left ventricle of closed chest pigs, although there was no significant difference between Vc(t> at dp/dt,,, and dp/dr,,,,. However, a comparison with the single value method was not made in their study. Implicit in our analysis is an unchanged gain constant (a) throughout the cardiac cycle. There are remarkably few data in this regard. Most investigators, in left ventricular studies, like us in the right ventricle either ignore ct (assuming it to be constant even over a wide range of conditions [8,17]) or calibrate the conductancesignal using angiographic [7] or thermodilution measurements[7,1l] (both of which have inherent limitations). In a novel study, examining (Y and its potential variation throughout the cardiac cycle and over a broad volume range, Stamatoet al. [20] examined seven open and closed chest pigs. The gain constant, cx, did not change significantly during the cardiac cycle. However, when stroke volume was compared with that obtained by either thermodilution or pulmonary flow probe (in the open chest animal), over a wide range of volumes, an inverse relation was observed between right ventricular volume and o. Although the exact relationship between a variable 01 and a variable Vc has not been definitively described, no matter what this relationship, the overall effect is small when assessedin this clinical preparation. The effects of hypertonic saline in the myocardial blood vessels were overcome by taking systolic isochronesduring the ascending limb of the saline wash-in. This is important, as Baan et al. [7] showed that a transient decreasein left ventricular pressure and in maximal left ventricular dp/dt occurred when 1.5 ml of 0.6 M of saline was injected directly into the main stem left coronary artery of dogs. Furthermore, there was a transient increase in left ventricular diameter and conductance, amounting to 2% of end-diastolic dimension. Lankford et al. [ 121 <andApplegate et al. [21] also observed that the descendingphase of the saline wash-in is often accompanied by a slight fall in left ventricular pressure,presumably becauseof the myocardial depressanteffect of the concentrated saline. To avoid these changes,apparently causedby an effect on the myocardium, Vc was measuredduring the rising limb of the hypertonic saline wash-in in all right ventricular parallel conductancemeasurementsas penetration of salt into the wall during this period is limited. Our results are important in a number of respects.The temporal variation in Vc(t) in the right ventricle is small and appearsto be of the same order of magnitude as that seenin the left ventricle [ 12,131,although it is theoretically possible that we did not detect larger changesby examining only six isochrones. Nonetheless,despite the potential effects of right atria1 filling, varying right ventricular chamber geometry during systole and left sided events, Downloaded from by guest on September 30, 2016 We have previously shown that a conductancecatheter can reliably measurethe volume of human right ventricular casts[lo], and Dickstein et al. [ 181in a recent study in open chest pigs suggestedthe technique may be particularly useful for the study of RV function in vivo. In their study a consistent change in RV end-systolic P-V relationships with loading and inotropic intervention was shown. Parallel conductancein the study of Dickstein et al. [ 181 was measuredusing the single value, linear technique first describedby Baan et al. (Vc(Baan)) [7]. Validation studies in animals [ 18,191with structurally normal right ventricles suggestthat Vc measuredusing Baan’s technique is relatively stable over a wide volume range. This commonly usedmethod of estimating Vc has the theoretical disadvantage of utilising only two points in the cardiac cycle and does not, therefore, allow for change in Vc that may occur between these times. Parallel conductance determination tends to be higher in the right ventricle [ 181,presumably reflecting a greater current leakage through the thin wall and proximity to mediastinal structures. This may introduce the potential for a greater error in absolute volume determination. Furthermore, the thin ventricular wall makes Vc measurementsmore sensitive to changes that occur within the cardiac cycle, e.g., atria1filling and LV ejection. To date, however, there are no animal or human data concerning right ventricular parallel conductance during the cardiac cycle. Lankford et al. [12] devised a method for estimating changesin Vc during the cardiac cycle which, they argue, is more robust and less susceptible to noise within the system. By using 20 isochrones throughout systole they were able to demonstrate, in the isolated heart, minimal changesin left ventricular Vc(t), although there were more marked changes which approximated 4% of the end-diastolic volume, in the in situ preparations. Despite this temporal variation there remained an extremely good correlation between Vc(Baan) and Vc(t). It was also shown that the conductance volume signal was only minimally sensitive to changesin the blood content of the surrounding myocardium. We used a similar method to examine changesin Vc(t) that occur during the cardiac cycle in the human right ventricle. Our data show that small changes in parallel conductanceoccur during systole, representing 6% of the end-diastolic volume, but no significant difference between Vc(t) at dp/dr,,, and dp/d&. Interestingly, in common with the study of left ventricular parallel conductance by Lankford et al. [ 121,the parallel conductanceat both of thesepoints and the Vc( t) from the six systolic isochrones exceededthat obtained using the single value Baan technique (Vc(Baan)). Importantly, however, there was a close linear relationship between Vc(t) and Vc(Baan) (r = 0.99). Thus for most clinical and experimental preparations,where relative volume is important, either method will allow durable, repeatableand comparable results. These findings are very similar to those recently pub- Research 32 (1996) 901-908 908 PA. White et al. / Cardiovascular Acknowledgements This work was supportedby the Scott Rhodes Research Fund and Clinical Research Committee, Royal Brompton Hospital NHS Trust. Thanks must also be given to Dr. R. Szwarc for provision of the analysis software used in this paper. References 111 Ferlinz J. Measurement of right ventricular volumes in man from single plane cineangiograms. A comparison to the biplane approach. Am. Heart J 19749487-96. 121 Redington A, Gray H, H&on M, Rigby M, Oldershaw P. Characterisation of the normal right ventricular pressure-volume relation by biplane angiography and simultaneous micromanometer pressure measurements. Br. Heart J 1988;59:23-30. [3] Foale R, Nihoyannopoulos P, Mckenna W, et al. Echocardiographic measurement of the normal adult right ventricle. Br. Heart J 1986;56:33-44. [4] Markiewicz W, Sechtem U, Higgins C. Evaluation of the right ventricle by magnetic resonance imaging. Am Heart J 1987;113:815. [5] Schnjen F, Herringuez A, Renondo J, Poincelot F, Pichene M. Inter- 32 (1996) 901-908 and intrasubject variability of the thermodilution measurement of right ventricular ejection fraction and volume in patients with chronic obstructive pulmonary disease. Cardiovasc Res 1990;24:33-36. t61Baan J, Jong TTA, Kerkhof PLM, Moene RJ, Van Dijk AD, Van der Velde ET, Koops J. Continuous stroke volume and cardiac output from intra-ventricular dimensions obtained with impedance catheter. Cardiovasc Res 1981;15:328-334. [71 Baan J, Van der Velde ET, Hein G, et al. Continuous measurement of left ventricular volume in animals and humans by conductance catheter. Circulation 1984;70(5):812-823. h31Burkhoff D, Van der Velde ET, Kass D, Baan J, Maughan WL, Sagawa K. Accuracy of volume measurement by conductance ejecting canine hearts. Circulation catheter in isolated, 1985;72(2):440-447. 191 Baan J, Van der Velde ET, Steendijk P, Koops J. Calibration and application of the conductance catheter for ventricular volume measurement. Automedica 1989;11:357-365. [IO1White PA, Bishop AJ, Conroy B, Otdershaw PJ, Redington AN. The determination of volume of right ventricular casts using a conductance catheter. Eur Heart J 1995; 16: 1425- 1429. llll Kass DA, Midei M, Graves W, Brinker JA, Maughan WL. Use of a conductance (volume) catheter and transient inferior caval occlusion for rapid determination of pressure-volume relationships in man. Cathet Cardiovasc Diag 1988; 15: 192-202. l121Lankford EB, Kass DA, Maughan WL, Shoukas AA. Does volume catheter parallel wall conductance vary during the cardiac cycle. Am J. Physiol 1990;258 (Heart Circ PhysiolU):Hl9331942. 1131 Szwarc RS, Mickleborough LL, Mizuno SI, Wilson GJ, Liu P, Mohamed S. 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. [141 Declaration of Helsinki. Br Med J 1964;ii: 177. 1151 Kass DA, Yamazaki T, Burkhoff D, Maughan WL, Sagawa K. Determination of left ventricular end-systolic pressure-volume relationships by the conductance (volume) catheter technique. Circulation 1986;73:586-595. 1161McKay RG, Miller MJ, Ferguson JJ, et al. Assessment of left ventricular end-systolic pressure-volume relations with an impedance catheter and transient inferior vena cava occlusion: use of this system in the evaluation of the cardiotonic effects of dobutamine, mihinone, posicor, and epinehrine. J Am Co11Cardiol 1986,8: 11521160. [171 Mckay RG, Spears JR, Aroesty JM, et al. Instantaneous measurement of left and right ventricular stroke volume and pressure-volume relationships with an impedance catheter. Circulation 1984;69:703710. [18] Dickstein ML, Yano 0, Spotnitz HM, Burkhoff D. Assessment of right ventricular contractile state with the conductance catheter technique in the pig. Cardiovasc Res 1995;29:820-826. [19] Wocdard JC, Bertram CD, Gow BS. Detecting right ventricular volume changes using the conductance catheter. Pace 1992;15:2283-2294. [20] Stamato TM, Szwarc RS, Benson LN. Measurement of right ventricular volume by conductance catheter in closed-chest pigs. Am J Physiol 1995;269 (Heart Circ Physiol 38):H869-H876. [21] Applegate RJ, Cheng CP, Little WC. Simultaneous conductance catheter and dimension assessment of left ventricle volume in the intact animal. Circulation 1990;81:638-648. [22] Bohwood CM, Appleyard RF, Glantz SA. Left ventricular volume measurement by conductance catheter in intact dogs: parallel conductance volume depends on left ventricular size. Circulation 1989;80:1360- 1377. [23] White PA, Chaturvedi RR, Bishop AJ, Redington AN. Development and validation of a conductance technique for measuring pulmonary valve regurgitation. In: Proceedings of the Institution of Physics and Engineering in Medicine and Biology, 1st Annual Scientific Conference, 1995;98 (Abstr.). Downloaded from by guest on September 30, 2016 Vc(t) remains reasonably constant, and so estimations of Vc in the right ventricle should be as accurate as those in the left ventricle. Although these results are encouraging it must be realised that they do not imply that Vc remains constant under all conditions. Indeed Boltwood et al. [22] have demonstrateda significant fall in Vc during extreme off-loading in the canine left ventricle, while Applegate et al. [21] observed a greater decreasein conductancevolume as compared to ultrasonic volume during caval occlusion, implying that Vc decreasedwith extreme preload reduction. However, we have found no significant change in Vc under the more physiological changes seen during fluid loading in humans [23]. Until these findings have been investigated further it remains important, therefore,to make repeatedmeasurementsof Vc during acute interventions. In conclusion we have shown that while Vc(t) varies throughout the cardiac cycle in the human right ventricle of adults and older children after repair of congenital abnormalities, there is no significant difference in Vc(t) at dP/dtmin ad dP/dtrnax- The fact that the small changes observedin Vc(t) during systole are similar in both the RV and LV suggests that the anatomy of the RV does not preclude the use of conductancecathetertechnology in the assessmentof RV function. Finally, the excellent correlation between Vc(Baan) and Vc(t) suggeststhat the correction of Vc for the phaseof the cardiac cycle is unnecessary for the purposesof most data analysis. These results provide further evidence that the application of conductancetechnology to the study of human right ventricular function is both possible and useful. Research