Use of a conductance (volume) catheter and transient inferior vena caval occlusion for rapid determination of pressure-volume relationships in man

Parallel conductance determination in cardiac volumetry using dilution manoeuvres: theoretical analysis and practical implications

Left ventricular volume calibration based on the conductance catheter depends on the correct determination of the parallel conductance (Gp). Baan's saline manoeuvre procedure leads to Gp by finding the end-systolic (Ges) and end-diastolic (Ged) conductances, for each beat of the dilution curve rising limb. After plotting such values in an xy-system, their linear regression is back-projected to intersect the identity line, so yielding an estimated Gp. The objective is to theoretically analyse all possible lines, Ges = aGed + b (Baan's line) and, based on experimental results, to establish their limitations. This was attained by calculating the regression lines using, first Ged = f1(Ges) and thereafter, Ges = f2(Ged), which led to two values, Gp2 and Gp1, for the parallel conductance. The morphology of the saline curve was also modified to assess its effect on the extrapolation. Multiple dilutions were recorded in eight experimental dogs injecting different concentrations. Each curve was classified according to the maximum change (VAR) reached by the total average conductance. Over 138 manoeuvres, 276 regressions were processed yielding correlations higher than 0.65. Of this total, 92.4% gave positive parallel conductances. The rest produced negative values and, thus, were neglected. If the two (Ged, Ges) statistical relationships were ideal, they should yield Gp = Gp1 = Gp2; however, there were differences which, when Gp1 was studied against Gp2, led to: Gp1 = 0.97 Gp2 + 0.055, with r = 0.9476, and n = 85. The remaining 53 were discarded because either some Gp values were negative, or the correlation of Ges which Ged (or vice versa) was < 0.85, and/or VAR < 15%; the two latter conditions were found necessary for reliable calibration. Baan's line high correlation is not a unique condition to ensure the accuracy and precision of Gp determination because the slope a depends on VAR and, thus, different intersections with the identity line may be obtained. Its recommended that manoeuvres be used with at least eight data points, with VAR > 15% and, finally, with (Ges, Ged) correlation better than 0.85. Theoretical analysis of Baan's line offers a reference frame, which contains only a limited number of practical possibilities.

Use of transesophageal echocardiography for postoperative evaluation of right ventricular function

BACKGROUND

No method has been available to assess the right ventricular (RV) pressure-volume relation in the operating room or intensive care unit. Left ventricular cross-sectional area measured by echocardiography using the technology of automated border detection has been used to construct left ventricular pressure-area (P-A) loops. In the human right ventricle, however, this approach has not been validated.

METHODS

We recorded RV P-A loops in 14 patients in the intensive care unit using transesophageal echocardiography. Multiple RV P-A loops were obtained by reducing preload with intravenous nitroglycerin, thereby elucidating the end-systolic P-A relation.

RESULTS

With an incremental dose of dobutamine, the slope of the RV end-systolic P-A relation increased (from 4.56+/-2.42 to 7.34+/-3.62 mm Hg/cm2, p<0.01), with no change in the x-axis intercept, which implied increased contractility. Furthermore, in the operating room we validated the use of RV cross-sectional area as a surrogate for RV volume by demonstrating the close correlation between the stroke area (maximal RV area minus minimal RV area) and stroke volume (r = 0.962; p<0.0001).

CONCLUSIONS

Transesophageal echocardiography with automated border detection is a promising tool for elucidating RV function through the analysis of RV P-A loops.

Lack of desensitization and enhanced efficiency of calcium channel promoter in conscious dogs with heart failure

The goal of this study was to compare responses to a calcium promoter, BAY y 5959, and dobutamine (Dob) in heart failure (HF). Dogs (n = 9) were chronically instrumented and studied in the conscious state before and after pacing-induced HF. In the control state, BAY y 5959 (20 microgram. kg-1. min-1) increased the first derivative of left ventricular (LV) pressure (dP/dt) by 83 +/- 8% and mean arterial pressure (MAP) by 8 +/- 2% and decreased heart rate (HR) by 30 +/- 3%. With Dob (10 microgram. kg-1. min-1) LV dP/dt rose similarly (+80 +/- 6%), but HR also rose (+25 +/- 4%) (P < 0.05 vs. BAY y 5959). After HF developed, BAY y 5959 still increased LV dP/dt by 108 +/- 8% and MAP by 21 +/- 2% and decreased HR by 28 +/- 4%, whereas Dob increased LV dP/dt by only 50 +/- 7% (P < 0.05 vs. BAY y 5959) and MAP by 7 +/- 3%, and HR did not change (+3 +/- 3%) (P < 0.05 vs. BAY y 5959). In HF, cardiac work increased more (P < 0. 05) with BAY y 5959 (+105 +/- 13%) compared with Dob (+47 +/- 11%), yet myocardial oxygen consumption increased similarly with the two drugs. Accordingly, mechanical efficiency increased more (P < 0.05) with BAY y 5959 (+73 +/- 14%) than with Dob (+17 +/- 12%). These data indicate that 1) increases in contractility mediated directly by Ca2+ are relatively resistant to desensitization in HF; and 2) the calcium-channel promoter can produce increases in myocardial contractility and cardiac work similar to those of Dob at a significantly lower oxygen cost, thereby enhancing mechanical efficiency in HF.

Validation of a new intraoperative technique to evaluate load-independent indices of right ventricular performance in patients undergoing cardiac operations

BACKGROUND

Assessment of right ventricular performance in the perioperative period is difficult because there is no generally accepted method of measuring right ventricular volume. We set out to determine whether conductance technology could provide a valuable technique for the investigation of intraoperative right ventricular function.

METHODS AND RESULTS

Three validating studies were performed in 25 patients undergoing routine coronary revascularization. Study 1: The influence of conductance catheter position in the right ventricle was examined in 10 patients. Insertion of the conductance catheter through the outflow tract was associated with a larger gain constant and a smaller parallel conductance compared with insertion through the tricuspid valve. Study 2: The reproducibility of contractility measurements with the use of a conductance catheter was examined in 7 additional patients. Removal and reinsertion of the conductance catheter was not associated with any significant difference in right ventricular volume or contractile function. Study 3: Right ventricular performance before and after cardiopulmonary bypass was compared in 8 additional patients. There was a fall in the slope of the right ventricular preload recruitable stroke work from 15.6 (3.8) to 11.0 (5.1) mm Hg (P=.01) and an increase in the slope of the end-diastolic pressure-volume relations from 0.05 (0.02) to 0.11 (0.05) mm Hg/mL (P=.001).

CONCLUSIONS

The conductance technique can be used to study perioperative changes in right ventricular performance. Insertion of the conductance catheter through the outflow tract provides stable and reproducible data. There is significant impairment of right ventricular contractility in the early postoperative period.

Simultaneous LV and RV volumes by conductance catheter: effects of lung insufflation on parallel conductance

One aspect in the measurement of ventricular volume using the conductance catheter technique is the assessment of parallel electrical conductivity of structures extrinsic to the ventricular blood pool. Because it is sometimes necessary to make volume measurements during ventilation or spontaneous respiration, the extent to which parallel conductance may vary with lung insufflation was investigated. Anesthetized pigs (11-15 kg) were ventilated and instrumented with both left (LV) and right ventricular (RV) conductance and pressure-tip catheters and end-hole catheters for injection of hypertonic saline into the inferior vena cava and pulmonary artery. Data were recorded during ventilation with tidal volumes of 10 and 20 ml/kg, and the associated fluctuations to LV and RV end-diastolic (EDV) and stroke (SV) volumes were measured. With the use of a saline dilution technique, parallel conductance (Vc) was determined for each ventricle with the ventilator off and lungs insufflated to 0, 10, and 20 ml/kg. Whereas ventilation caused marked oscillations in LV and RV EDV and SV, these variations could not be attributed to Vc, which remained statistically unchanged from their baseline values of 34.1 +/- 3.1 in the LV and 31.1 +/- 4.4 in the RV. These results indicate that the fluctuations that occur in conductance catheter-derived LV and RV volume signals with ventilation are not caused by any significant changes to parallel conductance.

The effect of changing excitation frequency on parallel conductance in different sized hearts

OBJECTIVE

An important component of the ventricular volume measured using the conductance catheter technique is due to parallel conductance (Vc), which results from the extension of the electric field beyond the ventricular blood pool. Parallel conductance volume is normally estimated using the saline dilution method (Vc(saline dilution)), in which the conductivity of blood in the ventricle is transiently increased by injection of hypertonic saline. A simpler alternative has been reported by Gawne et al. [12]. Vc(dual frequency) is estimated from the difference in total conductance measured at two exciting frequencies and the method is based on the assumption that parallel conductance is mainly capacitive and hence is negligible at low frequency. The objective of this study was to determine whether the dual frequency technique could be used to substitute the saline dilution method to estimate Vc in different sized hearts.

METHODS

The accuracy and linearity of a custom-built conductance catheter (CC) system was initially assessed in vitro. Subsequently, a CC and micromanometer were inserted into the left ventricle of seven 5 kg pigs (group 1) and six 50 kg pigs (group 2). Cardiac output was determined using thermodilution (group 1) and an ultrasonic flow probe (group 2) from which the slope coefficient (alpha) was determined. Steady state measurements and Vc estimated using saline dilution were performed at frequencies in the range of 5-40 kHz. All measurements were made at end-expiration. Finally, Vc was estimated from the change in end-systolic conductance between 5 kHz and 40 kHz using the dual frequency technique of Gawne et al. [12].

RESULTS

There was no change in measured volume of a simple insulated cylindrical model when the stimulating frequency was varied from 5-40 kHz. Vc(saline dilution) varied significantly with frequency in group 1 (8.63 +/- 2.74 ml at 5 kHz; 11.51 +/- 2.65 ml at 40 kHz) (p = 0.01). Similar results were obtained in group 2 (69.43 +/- 27.76 ml at 5 kHz; 101.24 +/- 15.21 ml at 40 kHz) (p < 0.001). However, the data indicate that the resistive component of the parallel conductance is substantial (Vc at 0 Hz estimated as 8.01 ml in group 1 and 62.3 ml in group 2). There was an increase in alpha with frequency in both groups but this did not reach significance. The correspondence between Vc(dual frequency) and Vc(saline dilution) methods was poor (group 1 R2 = 0.69; group 2 R2 = 0.22).

CONCLUSION

At a lower excitation frequency of 5 kHz a smaller percentage of the electric current extends beyond the blood pool so parallel conductance is reduced. While parallel conductance is frequency dependent, it has a substantial resistive component. The dual frequency method is based on the assumption that parallel conductance is negligible at low frequencies and this is clearly not the case. The results of this study confirm that the dual frequency technique cannot be used to substitute the saline dilution technique.

Brain damage and myocardial dysfunction: protective effects of magnesium in the newborn pig

BACKGROUND

Brain damage is associated with myocardial dysfunction resulting from excessive release of endogenous catecholamines and Ca2+ overload. Magnesium ion, a natural Ca2+ blocker, has recently been recognized as a myoprotective agent.

METHODS

Myocardial function was assessed in 3- to 7-day-old piglets from pressure-volume data (obtained by the conductance catheter/micromanometer technique) before and for 4 hours after ligation of the aortic arch vessels and was correlated with ultrastructural changes. Group a (n = 6) received MgSO4 immediately after induction of brain damage for 4 hours, whereas group b (n = 6) did not receive MgSO4 and served as control.

RESULTS

In both groups after induction of brain damage, there was a significant (p < 0.05) increase in end-systolic elastance and preload-recruitable stroke work that persisted for 1 hour. However, after 2 and 4 hours, there was a significant (p < 0.05) reduction in both variables in group b (end-systolic elastance, 74% +/- 5% and 59% +/- 6%, respectively, and preload-recruitable stroke work, 77% +/- 4% and 64% +/- 3%, respectively, compared with baseline), and in group a, the values returned to baseline. The chamber stiffness index rose significantly (p < 0.05) in group b 15 minutes after induction of brain damage and remained significantly (p < 0.05) higher for 4 hours versus no significant change in group a. Plasma levels of epinephrine and norepinephrine were similar in the groups before and after brain damage. Electron microscopic study showed severe ultrastructural changes in group b and significantly milder changes in group a.

CONCLUSIONS

We conclude that MgSO4 may protect the neonatal myocardium when administered immediately after brain damage.

Direct myocardial effects of OPC-18790 in human heart failure: beneficial effects on contractile and diastolic function demonstrated by intracoronary infusion with pressure-volume analysis

OBJECTIVES

We sought to determine the precise myocardial effects of OPC-18790 as demonstrated by intracoronary administration.

BACKGROUND

Although previous studies have determined the cardiovascular effects of a novel intravenous inotrope, OPC-18790, the observed benefits on contractile and diastolic function may have been confounded by the marked changes in peripheral loading associated with this drug when given intravenously.

METHODS

Eight heart failure patients received intracoronary OPC-18790 at 31.25 microg/min for 20 min, and then at 62.5 microg/min for another 20 min. Hemodynamic variables and pressure-volume indexes using the conductance catheter method were determined at baseline and then after the two doses.

RESULTS

There were no significant effects on heart rate, cardiac output or loading conditions, including afterload as determined by systemic vascular resistance and arterial elastance (Ea) and preload as determined by end-diastolic volume (EDV). There were significant increases in end-systolic elastance (Ees) from 0.74+/-0.11 to 0.90+/-0.16 mm Hg/ml at 31.25 microg/min and to 137+/-0.33 mm Hg/ml at 62.5 microg/min (p < 0.05 by analysis of variance [ANOVA]). Diastolic function improved, as determined by the time constant for isovolumetric relaxation tau, which decreased significantly from baseline to 31.25 microg/min (94+/-9 to 79+/-9 ms, p < 0.05), and did not shorten further at 62.5 microg/min (78+/-8 ms, p=NS). There were significant decreases in right atrial pressure (9+/-1 to 7+/-1 mm Hg, p < 0.01 by ANOVA) and mean pulmonary artery wedge pressure (21+/-3 to 16+/-2 mm Hg, p < 0.05 by ANOVA). This fall in filling pressures was not accompanied by any change in EDV. Inspection of the diastolic portion of the pressure-volume curve confirmed a downward shift consistent with pericardial release in five of the eight patients.

CONCLUSIONS

Intracoronary administration of OPC-18790 demonstrates that the direct myocardial effects of this agent include a modest increase in inotropy and improvement in diastolic function, both of which occur without increases in heart rate, indicating that this agent may be beneficial for the intravenous treatment of congestive heart failure.

ESPVR of in situ rat left ventricle shows contractility-dependent curvilinearity

We developed a miniaturized conductance catheter for in situ rat left ventricular (LV) volumetry. After the validation study of the conductance volumetry in 11 rats, we characterized the end-systolic pressure-volume relationship (ESPVR) in 24 sinoaortic-denervated, vagotomized and urethan-anesthetized rats. Stroke volume (SV) measured with the conductance catheter correlated closely with that measured by electromagnetic flowmetry (r > 0.95). No significant difference was found between the in situ LV end-diastolic volumes measured by conductance volumetry and postmortem morphometry; a linear regression analysis indicated that the correlation coefficient was 0.934, that the slope was not significantly different from 1, and that the intercept was not significantly different from 0. During cardiac sympathotonic conditions, the ESPVR was curvilinear. The estimated slope of ESPVR (end-systolic elastance, Ees) by quadratic curve fitting at end-systolic pressure of 100 mmHg was 2,647 +/- 846 mmHg/ml. Bilateral cervical and stellate ganglionectomy depressed contractility and made the ESPVR linear; a quadratic equation did not improve the fit. Ees was 946 +/- 55 mmHg/ml with the volume-axis (V0) intercept of 0.076 +/- 0.007 ml. Administration of propranolol (1 mg/kg) further reduced Ees (573 +/- 61 mmHg/ml, P < 0.001) and increased V0 slightly (0.091 +/- 0.011 ml). We conclude that the conductance catheter method is useful for the assessment of the ESPVR of the in situ rat left ventricle and that the ESPVR displays contractility-dependent curvilinearity.

A new technique to measure and track blood resistivity in intracardiac impedance volumetry

OBJECTIVE

To propose and verify a technique by which blood resistivity can be measured continuously and instantaneously with a conductance catheter used to measure ventricular volume by intracardiac impedance volumetry.

METHODS

Intracardiac impedance volumetry involves the measurement of ventricular blood volume using a multi-electrode conductance catheter. Ventricular volume measurement with the conductance catheter requires the value of blood resistivity. Previously, blood resistivity has been determined by drawing a sample of blood and measuring resistivity in a separate measuring cell. A new technique is proposed that allows the resistivity of blood to be measured with the conductance catheter itself. Two adjacent electrodes of the catheter are chosen to establish a localized electric field. With a localized field, the resistance measured between the adjacent electrodes bears a constant ratio (resistivity ratio) to the resistivity of blood. Finite element cylindrical models with exciting electrodes were created to determine the resistivity ratio. Blood resistivity was determined by dividing the resistance found due to the localized electric field by the resistivity ratio. The proposed scheme was verified in cylindrical physical models and in in vivo canine hearts.

RESULTS

Finite element simulations showed the resistivity ratio to be 1.30 and 1.43 for two custom-made catheters (Ohmeda Inc. and Biosensors Inc., respectively). The resistivity ratio remained constant as long as the cylindrical volume of blood around the adjacent electrodes had a radius larger than the electrode spacing. In addition, this ratio was found to be a function of electrode width. The new technique allowed us to measure saline resistivity with an error, -0.99+/-0.25% in a physical model, and blood resistivity with an error, -0.625+/-2.75% in an in vivo canine model.

CONCLUSION

The new in vivo technique can be used to measure and track blood resistivity instantaneously and continuously without drawing blood samples.

Defibrillation efficacy with endocardial electrodes is influenced by reductions in cardiac preload

Little is known about the effects of cardiac preload and cardiac geometry on defibrillation efficacy with endocardial electrodes. We studied nine pigs implanted with an endocardial lead system in the normal and reduced preload state. In the reduced preload state, a balloon catheter was inflated in the inferior vena cava (IVC) for 20 seconds prior to the induction of ventricular fibrillation (VF). Complete occlusion of the IVC and reductions in preload were confirmed by observing deformation of the contrast-filled balloon, a reduction in cardiac size by fluoroscopy, and reductions in ventricular pressures. Biphasic shocks were delivered after 10 seconds of VF using a recursive up-down protocol. VF was induced 20 times for each preload state, and the 50% effective doses (ED50) for energy, current, and voltage were estimated by averaging all shocks for that state. At reduced preloads, energy decreased from 12.1 +/- 3.0 J (+/- SD) to 10.5 +/- 2.9 J (p < 0.01), voltage decreased from 415 +/- 51 V to 390 +/- 51 V (p < 0.05), and current decreased from 8.6 +/- 1.5 A to 7.6 +/- 1.5 A (p < 0.01), while impedance rose from 49.2 +/- 3.8 omega to 52.8 +/- 4.4 omega (p < 0.001). We conclude that reducing cardiac preload and cardiac size significantly lowers ED50 defibrillation energy, current, and voltage. This outcome may be caused directly by the decrease in blood volume as evidenced by increased impedance and/or may be due to changes in heart geometry and stretch.

Accuracy of the conductance catheter for measurement of ventricular volumes seen clinically: effects of electric field homogeneity and parallel conductance

The conductance-volume method is an important clinical tool which allows the assessment of left ventricular function in vivo. However, the accuracy of this method is limited by the homogeneity of electric field the conductance catheter produces and the parallel conductance of surrounding structures. This paper examines these sources of error in volumes seen clinically. The characteristics of electric field within a chamber were examined using computer simulation. Nonconductive and conductive models were constructed and experimental measurements obtained using both single-field (SF) and dual-field (DF) excitation. Results from computer simulations and in vitro measurements were compared to validate the purposed theoretical model of conductance-volume method. The effects of field homogeneity and significance of parallel conductance in volume measurement were then determined. The results of this study show that DF provide a more accurate measure of intraventricular volume than SF, especially at larger volumes. However, both significantly underestimate true volume at larger volumes. In addition, the parallel conductance due to the chamber wall is significant at small volumes, but diminishes at larger volumes. Furthermore, the effect of parallel conductance beyond the chamber wall may be negligible. This study demonstrates the limitations in applying current conductance technology to patients with dilated hearts.

Clinical application of the conductance catheter technique in the adult human right ventricle

This study examines the use of conductance catheters to assess human right ventricular volume. Ten patients undergoing diagnostic cardiac catheterisation underwent right heart catheterisation with a conductance catheter and micromanometer, and a thermodilution catheter before and after fluid loading. Parallel wall conductance (Vc), and the multiplication factor relating conductance and thermodilution derived stroke volumes (å) were derived at each steady state. Pressure-volume cycles were analyzed at steady state and during fluid loading. Fluid loading resulted in a significant increase in cardiac output, and change in maximum and minimum cycle volume. There was no significant change in å (mean 0.40 S.D. 0.20) or Vc (mean 126.4 S.D. 59.6 ml) at higher cardiac outputs or ventricular volumes. Right ventricular pressure-volume cycles were formed demonstrating characteristic lack of clear isovolumic contraction and relaxation phases, and low cycle efficiencies (mean 0.62 S.D. 0.16). Serial cycles recorded during volume loading defined an end systolic pressure-volume relation more reliably than a stroke work end diastolic volume relation. Thus, a conductance derived volume signal can be obtained in the human right ventricle which can be interpreted as a continuous and instantaneous index of right ventricular volume, allowing the construction of real time pressure-volume cycles.

Impairment of left ventricular function by acute cardiac lymphatic obstruction

OBJECTIVES

We performed the following study to define the effects of acute cardiac lymphatic obstruction on left ventricular (LV) systolic and diastolic function.

METHODS

Cardiac lymphatic obstruction was created in 8 pentobarbital-anesthetized dogs by identifying (Evans blue) and ligating the right and left epicardial lymphatics, the afferent and efferent lymphatics associated with the pretrachael and cardiac lymph nodes, and the thoracic duct. Left ventricular function was assessed by analysis of micromanometer-conductance catheter-derived LV pressure-volume relationships. Contractility was assessed by preload recruitable stroke work (PRSW). The active and passive phases of LV relaxation were assessed by the time constant o isovolumic relaxation (tau) and the end-diastolic pressure-volume relationship (stiffness), respectively.

RESULTS

PRSW decreased significantly and tau increased significantly from baseline at 1, 2, and 3 h after cardiac lymphatic obstruction (n = 8), but stiffness did not change. Cardiac lymphatic obstruction had similar effects on LV function in a group of autonomically blocked dogs (n = 5). Left ventricular function did not change in sham treated controls (n = 8). Cardiac lymphatic obstruction induced a significant increase in LV wet/dry weight ratios (3.58 +/- 0.01) when compared to the control group (3.53 +/- 0.02). Histopathology of the myocardium in the lymphatic obstruction groups revealed significant lymphangiectasis and increased interstitial spacing when compared to controls.

CONCLUSIONS

Acute cardiac lymphatic obstruction depresses contractility and active relaxation and causes mild LV myocardial edema, but does not alter diastolic stiffness.

Single-beat estimation of end-systolic pressure-volume relation in humans. A new method with the potential for noninvasive application

BACKGROUND

The end-systolic pressure-volume relation (ESPVR) provides a useful measure of contractile function. However, the need to acquire multiple cardiac cycles at varying loads limits its applicability. We therefore developed and tested a novel single-beat estimation method that is based on normalized human time-varying elastance curves [EN(tN)].

METHODS AND RESULTS

Pressure-volume (PV) data were measured by conductance catheter in 87 patients with normal or myopathic hearts. Time-varying elastance curves were generated from 72 PV loops (52 patients) and normalized both by amplitude and time to peak amplitude. The resulting EN(tN) curves were remarkably consistent despite variations in underlying cardiac disease, contractility, loading, and heart rate, with minimal interloop variance during the first 25% to 35% of contraction. On the basis of this finding and assuming ESPVR linearity and constant volume-intercept, ESPVRs were estimated from one beat with the use of PV data measured at normalized time (tN) and end systole (tmax) to predict intercept: Vo(SB) = [EN(tN) x P(tmax) x V(tN)-P(tN)x V(tmax)]/[EN(tN) x P(tmax)-P(tN)] and slope Emax(SB) = Pes/[Ves-Vo(SB)]. Single-beat estimates were highly correlated with measured ESPVR values obtained by standard multiple-beat analysis (including data from 35 additional patients). Emax(SB) accurately reflected acute inotropic change and was influenced little by loading. The new estimation method also predicted measured ESPVRs better than prior techniques and was applicable to noninvasive analysis.

CONCLUSIONS

ESPVRs can be reliably estimated in humans from single cardiac cycles by a new method that has a potential for noninvasive application.

In vitro and finite-element model investigation of the conductance technique for measurement of aortic segmental volume

This investigation examined the feasibility of applying the conductance catheter technique for measurement of absolute aortic segmental volume. Aortic segment volume was estimated simultaneously in vitro by using the conductance catheter technique and sonomicrometer crystals. Experiments were performed in five isolated canine aortas. Vessel diameter and pressure were altered, as were the conductive properties of the surrounding medium. In addition, a three-dimensional finite-element model of the vessel and apparatus was developed to examine the electric field and parallel conductance volume under different experimental conditions. The results indicated that in the absence of parallel conductance volume, the conductance catheter technique predicted absolute changes in segmental volumes and segmental pressure-volume relationships that agreed closely with those determined by sonomicrometry. The introduction of parallel conductance volume added a significant offset error to measurements of volume made with the conductance catheter that were nonlinearly related to the conductive properties of the surrounding medium. The finite-element model was able to predict measured resistance and parallel conductance volume, which correlated strongly with those measured in vitro. The results imply that absolute segmental volume and distensibility may be determined only if the parallel conductance volume is known. If the offset volume is not known precisely, the conductance catheter technique may still be applied to measure absolute changes in aortic segmental volume and compliance.

Validation of right and left ventricular conductance and echocardiography for cardiac function studies

BACKGROUND

Continuous estimation of left ventricular volume from instantaneous conductance has compared favorably with "gold standards," is less labor intensive, and provides real-time data. Little information exists, however, correlating right ventricular conductance with such gold standards or examining the effects of an electrical field generated in the opposite ventricle.

METHODS

In open-chested sheep, right and left ventricular conductance, two-dimensional echocardiography, and thermodilution cardiac outputs were measured at steady-state conditions. After these measurements, postmortem pressure-volume relations, ventricular mass, and ventricular casting were performed.

RESULTS

The corrected end-diastolic volume measured by conductance correlated well with volumes measured by echocardiography (r = 0.89), postmortem pressure-volume relations (r = 0.84), and casts (r = 0.85). Left ventricular end-diastolic volume measured by conductance did not differ significantly from other standards by analysis of variance. The presence of an electrical field in the opposite ventricle did not affect measured conductance in the studied ventricle.

CONCLUSIONS

Conductance is useful for the measurement of right and left ventricular end-diastolic volumes in the beating heart and is not affected by the presence of an electrical field in the opposite ventricle. Hence, conductance is a useful tool in studies involving interventricular dependence and function.

Protamine-induced hypotension in heart operations: application of the concept of ventricular-arterial coupling

Protamine sulfate often causes hypotension during heparin neutralization. The concept of ventricular-arterial coupling was applied to determine whether a negative inotropic effect or a vasodilating effect of protamine was the major contributing factor to this hypotension. Thirty-five patients who underwent cardiac operations were studied during operation by measuring instantaneous left ventricular pressure and aortic flow to examine the end-systolic pressure-volume relationship. We obtained end-systolic elastance and effective arterial elastance values in a beat-to-beat fashion with a single-beat estimation method. In 28 of the 35 patients (80%), mean arterial pressure decreased more than 10 mm Hg with protamine infusion. Parameters were compared at the following three points: before a decrease in mean arterial pressure (control), at maximally decreased mean arterial pressure (maximum), and at a middle point between control and maximum values (midpoint). At both midpoint and maximum, mean arterial pressure decreased significantly (control 79.6 +/- 12.6 mm Hg, midpoint 66.5 +/- 10.8 mm Hg, maximum 52.7 +/- 9.9 mm Hg; p < 0.01). Similar changes were observed in effective arterial elastance (control 2.00 +/- 0.75 mm Hg/ml, midpoint 1.60 +/- 0.53 mm Hg/ml, maximum 1.31 +/- 0.46 mm Hg/ml; p < 0.01). Although the decrease in end-systolic elastance at midpoint (control 3.08 +/- 1.61 mm Hg/ml, midpoint 2.92 +/- 1.68 mm Hg/ml) did not reach statistical significance, end-systolic elastance significantly decreased at maximum (2.63 +/- 1.46 mm Hg/ml; p < 0.01). Continuous measurements showed that the decreases in mean arterial pressure and effective arterial elastance always preceded the depression of end-systolic elastance and that afterload reduction by vasodilating effect of protamine was the mechanism most likely to have initiated the hypotension. Delayed decrease in contractility may be ascribed to reduced coronary perfusion pressure caused by vasodilation or to a direct effect of protamine.

Acute cardiovascular effects of OPC-18790 in patients with congestive heart failure. Time- and dose-dependence analysis based on pressure-volume relations

BACKGROUND

OPC-18790 is a water-soluble quinolinone derivative that shares the pharmacological properties of vesnarinone and that may be useful for treating heart failure. We studied the contribution and relative dose sensitivities of the inotropic, lusitropic, and vascular effects of OPC-18790 in patients with dilated cardiomyopathy.

METHODS AND RESULTS

Pressure-volume (PV) analysis was performed in 17 patients who received either 5 micrograms.kg-1.min-1 (low dose, n = 10) or 10 micrograms.kg-1.min-1 (high dose, n = 7) OPC-18790 by 1-hour IV infusion. Right heart pressures and flow and left heart PV relations (conductance catheter) were measured at baseline and every 15 minutes during infusion. Transient inferior vena caval obstruction was used to determine PV relations. Both doses produced venodilation reflected by a 10% decline in left ventricular end-diastolic volume and a 30% fall in atrial and pulmonary artery pressures. Arterial dilation was four times greater at the high dose, with an approximately 40% fall in effective arterial elastance and systemic resistance. Contractility rose by 25% to 100% (depending on PV index) with both doses. Ventricular-arterial coupling (ratio of ventricular end-systolic to arterial elastances) was approximately 0.25 at baseline and doubled (or tripled) at low (or high) dose, correlating with improved efficiency. Isovolumetric relaxation shortened, whereas the diastolic PV relation was generally unchanged. Heart rate was unaltered.

CONCLUSIONS

OPC-18790 has potent venous and arterial vasodilator effects and moderate inotropic and lusitropic effects without a change in heart rate. These combined actions suggest a unique potential of OPC-18790 for heart failure treatment.

Measurement of left ventricular volume by dual-field conductance catheter in humans--comparison with single-field conductance catheter

The single-field conductance (SF) method for continuous measurement of left ventricular (LV) volume has achieved widespread use. However, it has been shown theoretically that the ratio between the measured conductance and the actual volume varies between the different interelectrode segments of the catheter due to the convex shape of the equipotential planes at the apex and base. The dual-field conductance (DF) method has recently been introduced and reportedly provides a flatter equipotential plane within the LV. In 11 patients, we compared LV volume measured by biplane cineangiography with conductance volume by the SF and DF methods. Strong correlations were found for both the SF method (r = 0.98) and the DF method (r = 0.99). However, in comparison with the SF method, the DF method gave a regression line with a slope factor, alpha, that was closer to unity, and the intercept of the regression line was small (p < 0.01). The DF method gave a significantly greater segmental stroke volume (SV) in the apex and base than the SF method. The ratio of the DF segmental SV to the SF segmental SV in the apex increased in proportion to the end-diastolic volume (p < 0.05). In conclusion, the DF method may facilitate the accurate measurement of LV volume in the human heart.

Effects of acid aspiration-induced lung injury on left ventricular function

BACKGROUND

Acid aspiration-induced acute lung injury (AALI) leads to myocardial leukosequestration and edema in rats and hemodynamic depression in dogs, but the effects of AALI on left ventricular (LV) function have not been carefully studied.

METHODS

We examined the effects of 0.1 N HCl administration into the lung on LV function, leukosequestration, and edema in pentobarbital-anesthetized, atropinized (n = 8), or autonomically blocked (n = 7) dogs. Saline solution was administered into the lungs of a control group of autonomically blocked dogs (n = 6). LV contractility was assessed by end-systolic elastance (EES) and preload recruitable stroke work (PRSW). Active relaxation was assessed by the time constant of LV pressure decline (tau).

RESULTS

AALI resulted in significant (p < 0.05) decreases in mean arterial pressure and cardiac output and increases in pulmonary artery pressure and systemic vascular resistance in atropinized and autonomically blocked dogs but not in saline control group. In atropinized dogs tau did not change after injury, but EES and PRSW were increased significantly at 2 and 3 hours after injury, despite significant myeloperoxidase activity and extravascular fluid wet-dry weight ratios. EES, PRSW, and tau did not change in the autonomically blocked dogs in response to AALI or in the saline control group.

CONCLUSIONS

We concluded that AALI results in a baroreflex mediated enhancement of LV contractility in dogs, despite mild myocardial leukosequestration and edema formation.

The effect of nifedipine on ventriculoarterial coupling in old myocardial infarction

The effect of nifedipine on ventriculoarterial coupling was examined in 8 patients with old myocardial infarction who showed a depressed ejection fraction (37 +/- 7%). Left ventricular (LV) pressure and LV volume were determined simultaneously by micromanometer and conductance catheter, respectively. We measured the slope (Ees) of the end-systolic pressure-volume relation during transient inferior vena caval occlusion, the slope (Ea) of the end-systolic pressure-stroke volume relation, the ratio of Ea to Ees (Ea/Ees), and the work efficiency (the ratio of external work to the systolic pressure-volume area) at baseline and after the sublingual administration of nifedipine (10 mg). Nifedipine slightly increased the heart rate from 71 +/- 14 to 78 +/- 17 beats/min. Although nifedipine had little effect on Ees (2.54 +/- 0.68 vs 2.47 +/- 0.62 mmHg/ml/m2, ns), it significantly decreased Ea from 3.47 +/- 1.16 to 2.37 +/- 0.54 mmHg/ml/m2. Consequently, Ea/Ees decreased from 1.42 +/- 0.47 to 0.97 +/- 0.31 and work efficiency increased from 48 +/- 12 to 59 +/- 13% after nifedipine administration. These data suggest that nifedipine reduces afterload (Ea) and improves left ventriculoarterial coupling without depressing left ventricular contractility in patients with failing hearts due to old myocardial infarction.

Left ventricular mechanoenergetics during asynchronous left atrial-to-aortic bypass. Effects of pumping rate on cardiac workload and myocardial oxygen consumption

The purpose of this study was to analyze left ventricular energetics during asynchronous, pulsatile left atrial to aortic bypass in the failing heart with the use of the pressure-volume relationship. In 12 anesthetized Holstein calves (body weight 94 +/- 7 kg), 10 microns microspheres (3.3 x 10(7) +/- 1.1 x 10(7)/100 gm left ventricular weight) were injected into the left main coronary artery to induce heart failure. Baseline left ventricular end-systolic elastance significantly decreased from 7.9 +/- 0.7 to 5.5 +/- 0.4 mm Hg/ml 100 gm left ventricular weight. Left ventricular pressure was measured with a micromanometer, and ultrasonic dimension transducers measured left ventricular orthogonal diameters. Ellipsoidal geometry was used to calculate simultaneous left ventricular volume. End-systolic elastance, pressure-volume area, external work, potential energy, and myocardial oxygen consumption were analyzed during steady-state contractions. After pre-pulsatile left atrial to aortic bypass measurements were taken, the measurements were repeated during asynchronous pulsatile left atrial to aortic bypass at the maximal pumping rate (69 +/- 13 beats/min) termed 100%, and then 80%, 60%, and 40% of the maximal pumping rate in the full to empty mode. With increases in pumping rate, pressure-volume area and external work proportionally decreased, whereas potential energy remained unchanged except for 100% of maximal pumping rate. Pressure-volume area correlated linearly with myocardial oxygen consumption during asynchronous pulsatile left atrial to aortic bypass (r = 0.971). As a result, pumping rate correlated linearly with conservation of myocardial oxygen consumption (r = 0.998). In conclusion, decreased pressure-volume area accounts for the reduction in myocardial oxygen consumption during asynchronous pulsatile left atrial to aortic bypass. Conservation of myocardial oxygen consumption is mainly attributed to the reduction of external work.

Mechanism of adenosine-induced elevation of pulmonary capillary wedge pressure in humans

BACKGROUND

Continuous intravenous administration of adenosine to humans often results in a paradoxical rise in pulmonary capillary wedge pressure (PCWP), whereas arterial resistance is lowered and cardiac output and heart rate increase. This is believed to be due to diastolic stiffening of the ventricle or to a negative inotropic effect. In the present study, we tested these and other mechanisms by using pressure-volume (PV) analysis and echocardiography.

METHODS AND RESULTS

Fifteen patients with normal rest left ventricular function underwent cardiac catheterization and received adenosine at a rate of 140 micrograms/kg per minute IV for 6 to 10 minutes. PV relations were measured in 9 patients (without coronary artery disease) using the conductance catheter method. In 6 additional patients with coronary artery disease, echocardiograms were used to assess wall thickness and function, and aortic and coronary sinus blood, lactate, oxygen, and adenosine levels were measured. Adenosine increased PCWP by 19% (+2.6 mm Hg) in both patient groups while lowering arterial load by 30% and increasing cardiac output by 45% (all P < .001). There was no significant effect of adenosine on mean linear chamber compliance or monoexponential elastic stiffness, as the diastolic PV relation was unchanged in most patients. Diastolic wall thickness also was unaltered. Thus, the PCWP rise did not appear to be due to diastolic stiffening. Adenosine induced a rightward shift of the end-systolic PV relation (ESPVR) (+12.7 +/- 3.7 mL) without a slope change. This shift likely reflected effects of afterload reduction, as other indexes (stroke work-end-diastolic volume relation and dP/dtmax at matched preload) were either unchanged or increased. Furthermore, this modest shift in ESPVR was more than compensated for by vasodilation and tachycardia, so reduced systolic function could not explain the increase in PCWP. There also was no net lactate production to suggest ischemia. Rather than arising from direct myocardial effects, PCWP elevation was most easily explained by a change in vascular loading, as both left ventricular end-diastolic volume and right atrial pressure increased (P < .05). This suggests that adenosine induced a redistribution of blood volume toward the central thorax.

CONCLUSIONS

PCWP elevation in response to adenosine primarily results from changes in vascular loading rather than from direct effects on cardiac diastolic or systolic function.

The effects of medetomidine on cardiac contractility in autonomically blocked dogs

The effects of medetomidine on load-dependent and relatively load-independent indices of left ventricular contractility and hemodynamics were studied in 8 chloralose-anesthetized, autonomic-blocked dogs. Left ventricular contractility was assessed by the maximum rate of increase in pressure (dP/dtmax), the slope of the end-systolic pressure volume relationship (Ees), preload recruitable stroke work (PRSW), and dP/dtmax-end-diastolic volume relation (SdPV). Dogs received 5 or 10 micrograms/kg of medetomidine IV. The dP/dtmax decreased significantly 30 minutes after both doses of medetomidine. The Ees did not change. Both SdPV and PRSW increased 5 minutes after both doses of medetomidine. Mean arterial pressure, left-ventricular end-diastolic and end-systolic pressures, peripheral vascular resistance and effective arterial elastance increased 5 minutes after both doses of medetomidine. Stroke volume, cardiac output, and stroke work decreased 5 minutes after medetomidine administration. End-diastolic volume did not change. End-systolic volume increased but the difference was not significant. Our study suggests that medetomidine increases inotropy and vascular resistance in autonomic-blocked dogs and that both ventricular and vascular responses to pharmacological manipulation must be considered for a complete assessment of the inotropic effects of a drug.

Reverse remodeling from cardiomyoplasty in human heart failure. External constraint versus active assist

BACKGROUND

Cardiomyoplasty (CM) is a novel surgical therapy for dilated cardiomyopathy. In this procedure, the latissimus dorsi muscle is wrapped around the heart and chronically paced synchronously with ventricular systole. While studies have found symptomatic improvement from this therapy, the mechanisms by which CM confers benefit remain uncertain. This study sought to better define these mechanisms by means of serial pressure-volume relation analysis.

METHODS AND RESULTS

Serial pressure-volume studies were performed by the conductance catheter method in three patients (total to date) with dilated cardiomyopathy (New York Heart Association class III) who underwent CM. Data were measured at baseline (before surgery) and at 6 and 12 months after CM. Chronic left ventricular (LV) systolic and diastolic changes induced by CM were evaluated with the stimulator in its stable pacing mode (every other beat) and after temporarily suspending pacing. CM-stimulated beats were compared with pacing-off beats to evaluate active systolic assist effects of CM. In each patient, CM resulted in a chronic lowering of cardiac end-diastolic volume and an increased ejection fraction. Most notably, the end-systolic pressure-volume relation shifted leftward, consistent with reversal of chronic chamber remodeling. In contrast, the diastolic pressure-volume relation was minimally altered, and the loops shifted down along the same baseline relation. These marked chronic changes in LV function measurable with CM stimulation off contrasted to only minor acute effects observed when the muscle wrap was activated. This suggests that the benefit of CM derived less from active systolic assist than from remodeling, perhaps because of an external elastic constraint.

CONCLUSIONS

These data, while limited to a small number of patients, suggest that CM can reverse remodeling of the dilated failing heart. While systolic squeezing assist effects of CM may play a role in some patients, our study found that this was not required to achieve substantial benefits from the procedure. We speculate that CM may act more passively, like an elastic girdle around the heart, to help reverse chamber remodeling.

Linear end-systolic pressure-volume relationship during pulsatile left ventricular bypass represents native heart function

This study assessed whether the end-systolic pressure-volume relationship obtained without any interventions during pulsatile left ventricular bypass adequately represents native heart function. In 11 anesthetized Holstein calves, left ventricular pressure was measured with a micromanometer while left ventricular volume was simultaneously calculated from orthogonal left ventricular diameters measured with ultrasonic dimension transducers. End-systolic pressure and volume data were subjected to linear regression analysis to achieve an end-systolic pressure-volume relationship. Data from both caval occlusions and aortic occlusion were used for the control end-systolic pressure-volume relationship (median r = 0.941, slope = 7.4 +/- 0.8 mm Hg per milliliter per 100 gm left ventricular weight; mean +/- standard error of the mean). During left atrial-aortic bypass with a Pierce-Donachy pneumatic assist pump in the asynchronous mode, the end-systolic pressure-volume relationships were obtained without interventions to change ventricular loading conditions. During maximal ventricular unloading during full to empty pumping, termed 100%, the resulting narrow range of pressure and volume data did not yield highly linear end-systolic pressure-volume relationships (median r = 0.669, slope = 4.9 +/- 0.9 mm Hg per milliliter per 100 gm left ventricular weight). However, at reduced rates off pumping, the end-systolic pressure-volume relationships were considerably linear (80%, median r = 0.819; 60%, median r = 0.868; 40%, median r = 0.899). Slopes did not significantly differ from control values (80%, 6.9 +/- 1.1; 60%, 8.2 +/- 1.1; 40%, 7.8 +/- 1.1). The end-systolic pressure-volume relationship obtained without exogenous load changes during asynchronous, pulsatile left ventricular bypass represents native left ventricular systolic function.

A new methodology for non-invasive clinical assessment of cardiovascular system performance and of ventricular-arterial coupling during stress

The objective of the study was to develop a non-invasive method for the quantitative evaluation of cardiovascular performance and ventricular-arterial (VA) coupling during varying physiological states. VA-coupling was represented by the ratio between the arterial and ventricular elastances-Ea/Ees. Approximate indices of the relative change of Ees and VA-coupling during stress were developed and tested. These indices can be evaluated directly from non-invasive measurements of ejection fraction values (for VA-coupling) and measurements of stroke volumes and systolic and diastolic arterial pressures (for Ees). Additional relative indices can be evaluated from these data (e.g., stroke work, cardiac output) to yield a complete representation of the cardiovascular response to stress. The present methodology was applied to assess the exercise stress response in healthy subjects (H, n = 8) and in patients with left ventricular dysfunction (n = 24). Left ventricular volumes were determined by nuclear angiography and arterial pressures were measured non-invasively by a new, validated method. Using published data obtained invasively, we found that the relative indices of Ees and VA-coupling showed a high correlation with the invasive ones (r > 0.8, P < 0.01). The patients were subgrouped by their maximal exercise capacitance (P2-50W, P3-75W). At rest, the two patient groups had similar ejection fraction values (45 +/- 15% and 48 +/- 16%), which were significantly different from those of the healthy subjects (66 +/- 7%, P < 0.05). During stress, a larger increase in stroke work and cardiac output was found in the healthy subjects. All three groups showed similar relative increases in Ees and heart rate, but relative Ea increased in P2 and decreased in H, while the opposite was found for the end-diastolic volume. The relative VA-coupling index in P2 was significantly larger than that in P3 and H (P < 0.05). The present non-invasively based indices can be used to quantitatively monitor the individual cardiovascular response to stress testing or drug interventions and to evaluate the importance of VA-coupling in the clinical setting.

Timing and velocity of ejection as major determinants of end-systolic pressure in isolated rabbit hearts

BACKGROUND

Systolic shortening is known to produce muscle deactivation. The present study was designed to analyze whether the velocity and the timing of ejection play a role on end-systolic pressure-volume relations (ESPVR).

METHODS AND RESULTS

In isolated rabbit hearts, left ventricular pressure and volume were recorded and digitized, and left ventricular volume was controlled by a servosystem (4-millisecond cycles) to alter the timing of ejection. A significant deficit in end-systolic pressure was observed when ejection was late in systole with respect to earlier ejection. This was associated with a significantly reduced end-systolic elastance. End-systolic pressure of beats with slow ejection was intermediate between that of the beats with early ejection and that of beats with late ejection with a significantly increased end-systolic volume compared with beats with early rapid ejection. The same results were obtained with hypertrophied hearts (abdominal aortic stenosis). Pressure-volume loop areas were significantly increased in beats with slow ejections and with rapid delayed ejections versus early rapid ejections. No change in the positive peak of dP/dt was observed when the timing and the velocity of ejection were modified.

CONCLUSIONS

ESPVR is modified by the ejection profile, with a decreased end-systolic pressure and an increased pressure-volume loop area related to the velocity and the amount of shortening during the end-systolic phase. These indices of ventricular function thus must be used with caution when the timing of ejection is altered, and the end-diastolic volume-peak dP/dt relation may be a better index of ventricular function.

Parallel tolerance between platelet cyclic GMP and preload effects of nitroglycerin in anaesthetized mini-pigs

The effects of acute intravenous nitroglycerin (NTG) administration on platelet cyclic GMP in relation to changes in indices of preload (end-diastolic volume) and afterload (effective arterial elastance) were evaluated in the anaesthetized mini-pig, using pressure-volume analysis. NTG (1-30 micrograms kg-1 min-1, i.v.) elicited a dose-dependent fall in preload and afterload, and an increase in arterial blood platelet cyclic GMP. Repeated doses of NTG (30 micrograms kg-1 min-1) resulted in tolerance to the preload but not afterload effects. The increases in platelet cyclic GMP were also attenuated, being highly correlated with the preload changes. Therefore, platelet cyclic GMP appears to reflect NTG-induced venous tolerance, rather than arterial responsiveness. The measurement of platelet cyclic GMP may represent a simple approach for monitoring the degree of venous tolerance to NTG in animals or patients, facilitating further mechanistic investigations.

Bedside assessment of myocardial performance in the critically ill

No measurement of myocardial performance currently available in the ICU can be regarded is ideal. Table 2 summarises the main features of the major monitoring techniques. As many of the indices of myocardial performance are interdependent, quantifying the contribution of each component to overall cardiac function is not possible currently, and the clinical utility of monitoring each individually is not therefore established. Bedside measurements of LV dimensions, volumes and ejection fraction, and the other indices of systolic and diastolic function can now be made, but the case for their routine use in influencing clinical practice remains unproven. Transoesophageal echocardiography has an important and established diagnostic role and has been used successfully for continuous monitoring during surgery, but practical considerations seriously limit its potential for routine use. Radionuclide techniques allow the measurement of many of the same parameters and have the potential for continuous use, but practical problems and the additional risk of radiation exposure may limit this application in the critical care environment. Doppler techniques are non-invasive, provide continuous data and are simple to operate, but the data provided has important limitations. Although the pulmonary artery catheter has been in use for over twenty years, questions regarding the information is provides concerning myocardial function remain and the extent to which it should influence therapeutic decisions is still controversial. However with the development of additional facilities, particularly the continuous measurement of cardiac output the pulmonary artery catheter seems likely to remain the mainstay of bedside monitoring of myocardial performance in the critically ill in the immediate future.

Effects of hypertonic saline on myocardial contractility in anaesthetized pigs

The cardiac effects of hypertonic saline (HS, 7.5% NaCl) were evaluated using a number of indices derived from the left ventricular (LV) pressure-volume relationship. Left ventricular end-systolic elastance (elastance), the slope of the end-systolic pressure-volume relationship, end-systolic elastance normalized for end-diastolic volume (elastance(norm)), the rate of rise of LV pressure (dP/dtmax), and dP/dtmax/end-diastolic volume were used to assess myocardial contractility. Pigs were anaesthetized with isoflurane and instrumented for haemodynamic measurements, LV pressure, and volume (conductance catheter) determinations. Elastance was determined during transient (8-10 s) caudal vena caval balloon occlusion. Following instrumentation, the end-tidal isoflurane concentration was reduced and maintained at 1 minimum alveolar concentration (1.5%). Pigs were randomly administered either 0.9% NaCl (n = 7) or HS (n = 9) at a dose of 4 ml/kg, over 3 min into the right atrium. There were no significant differences in LV or haemodynamic measurements between isotonic saline and HS treated pigs at any time point. Elastance, elastase(norm) and dP/dtmax/end-diastolic volume did not change in either treatment group. In contrast, dP/dtmax increased significantly (P < 0.015) at 5 min compared to baseline after treatment with HS. End-diastolic volume increased significantly from 5 to 30 min following treatment with HS. Left ventricular end-diastolic pressure increased significantly at 5 and 60 min in HS treated pigs. Central venous and pulmonary arterial wedge pressures,and cardiac index increased significantly at 5 min after treatment with HS. Total peripheral resistance decreased significantly at 5 min, followed by a return to baseline in the HS group.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventricular systolic assessment in patients with dilated cardiomyopathy by preload-adjusted maximal power. Validation and noninvasive application

BACKGROUND

Noninvasive cardiac-specific analysis of contractile function in patients with dilated heart failure remains problematic. This study tests whether maximal power divided by the square of end-diastolic volume (PWRmx/EDV2, or preload-adjusted PWRmx) can provide such assessment.

METHODS AND RESULTS

To validate the load insensitivity of the PWRmx index and determine its response to contractile change, 24 subjects with chronic dilated cardiomyopathy underwent invasive pressure-volume catheterization study using the conductance catheter technique. Preload was transiently reduced by 30% using balloon occlusion of the inferior vena cava, and afterload impedance was lowered by 50%, induced by a bolus injection of nitroglycerin. Contractile state was varied by intravenous dobutamine, verapamil, or esmolol. PWRmx was calculated from the simultaneous product of ventricular pressure and rate of volume change (dV/dt), the latter derived from the volume catheter signal. PWRmx varied directly with preload but was minimally influenced by afterload. However, PWRmx/EDV2 was not significantly altered by either loading change. PWRmx/EDV2 did vary with contractility, correlating closely with changes in the end-systolic pressure-volume relation (r = .91, P < .001). To test the noninvasive application of this index, 12 additional patients were studied, with PWRmx/EDV2 derived from nuclear ventriculography combined with a novel method to measure central arterial pressures. Subjects received intravenous nitroprusside or dobutamine in random order. Ejection fraction increased similarly with both agents (+42.9 +/- 8.9% for dobutamine and +29.4 +/- 5.3% for nitroprusside, both P < .01). In contrast, PWRmx/EDV2 did not significantly change with nitroprusside but increased by 126 +/- 16.1% with dobutamine (P < .01).

CONCLUSIONS

Preload-adjusted PWRmx is a steady-state index of ventricular systolic function that is sensitive to inotropic state and minimally influenced by physiological changes in afterload impedance or volume load. It appears useful for noninvasive cardiac-specific analysis of acute drug effects.

Changes in systolic and diastolic ventricular function with cold cardioplegic arrest in man. The Multicenter Study of Perioperative Ischemia (McSPI) Research Group

INTRODUCTION

Most of the cardiac surgery done today is performed with aortic cross-clamping and cardioplegic arrest. Despite improvements in cardioplegic techniques, ventricular dysfunction following cardioplegic arrest is a major cause of perioperative morbidity and mortality. This experiment will quantify the changes in left ventricular systolic function with cold cardioplegia. Four measures of cardiac function will be assessed with a volume conductance catheter.

METHODS AND RESULTS

Thirty patients undergoing coronary artery bypass graft surgery had volume conductance and micromanometer catheters placed in their left ventricles. Preload reduction was used to measure Ees (the slope of the end-systolic pressure-volume relationship), EdP/dtMax-EDV (slope of dP/dtMax end-diastolic volume relationship), EPLRSW (slope of stroke work end-diastolic volume relationship), Eed (slope of the end-diastolic pressure-volume relationship), and ENegdP/dtMax-EDV (slope of the negative dP/dtMax end-diastolic volume relationship). Ees decreased from 4.32 +/- 2.94 prebypass to 2.52 +/- 1.06 mmHg/mL postbypass.

CONCLUSION

Cold cardioplegic cardiac arrest is associated with postbypass systolic and diastolic ventricular dysfunction, which can be quantitated by volume conductance and micromanometer based measurements.

Dose-related effects of magnesium on myocardial function in the neonate

The antagonistic effects of magnesium ion as a calcium ion blocker may decrease calcium influx associated with ischemia. However, the effect of magnesium on the preischemic neonatal myocardium has not been investigated previously. The purpose of this study was to investigate the effects of the administration of increasing doses of magnesium on left ventricular performance in the neonate. We assessed left ventricular function (pressure-volume data obtained by the conductance catheter/micromanometer technique) in three groups (n = 6 in each) of newborn pigs (3 to 5 days old) differing with respect to magnesium concentrations. End-systolic elastance did not change during infusion in group A (magnesium = 1.2 mmol/L), whereas in groups B (magnesium = 8 mmol/L) and C (magnesium = 16 mmol/L) it decreased significantly (P < .05) to 67 +/- 6% and 44 +/- 8% of baseline, respectively. The decrease in end-systolic elastance was associated with a significant reduction in cardiac output (P < .05) and stroke work (P < .05) in group C. After administration of magnesium, end-systolic elastance returned to baseline in group B in contrast to group C (78 +/- 3% of baseline value, P < .05). The slope constant of the end-diastolic pressure-volume relation decreased significantly (P < .05) from the preinfusion baseline values of 0.42 +/- 0.08 mL-1 in group B and 0.46 +/- 0.05 mL-1 in group C to 0.3 +/- 0.04 and 0.26 +/- 0.03 mL-1, respectively, versus no change in group A.(ABSTRACT TRUNCATED AT 250 WORDS)

Pressure-volume loops: a dynamic approach to the assessment of ventricular function

Analysis of ventricular function in terms of pressure-volume or pressure-dimension relationships allows global and regional ventricular dynamics to be fully analyzed. In addition, this approach allows the relationships between muscle function (contractility, stiffness, potential energy) and pump function (stroke volume, stroke work) to be determined and predicted. Alterations in ventricular loading conditions can also be examined in terms of muscle and pump function. However, this analysis is more complex than initially thought and considerable care must be taken especially when regional ischemia is concerned. Moreover, some of the early assumptions have been disproved and conclusions can only be drawn from studies in which full assessment of changes in pressure and dimensions is available.

Diminished contractile response to increased heart rate in intact human left ventricular hypertrophy. Systolic versus diastolic determinants

BACKGROUND

Experimental studies indicate that in addition to diastolic dysfunction, hypertrophied myocardium can display depressed contractile responses, particularly at rapid heart rates, compounding reserve limitations. This study tests whether such abnormalities exist in intact human subjects at physiological paced rates and, if so, whether they are linked to simultaneous rate-dependent deterioration in diastolic function.

METHODS AND RESULTS

Ten subjects with left ventricular hypertrophy (LVH) and 8 normal control subjects were studied. Most LVH patients presented with dyspnea and/or pulmonary edema and had concentric hypertrophy. Since rapid pacing simultaneously alters cardiac filling volumes and pressures, pressure-volume relation analysis was used to better define changes in contractile response. Patients were instrumented with a conductance catheter and micromanometer for pressure-volume data recording and a balloon occluder at the right atrial-inferior vena caval junction to vary filling and thus generate function relations. Data were obtained at baseline and at three atrial pacing rates (100, 120, 150 min-1). In addition, single-beat force-interval data were used to indirectly examine calcium cycling kinetics. LVH subjects demonstrated baseline diastolic abnormalities, including prolonged relaxation, elevated end-diastolic pressure, and reduced chamber compliance. However, systolic function was similar to that in control subjects. With rapid pacing, normal subjects displayed a positive contractile response, whereas this was markedly diminished in LVH subjects. With abrupt termination of pacing and return to slower sinus rhythm, LVH subjects displayed greater initial potentiation followed by a more rapid decline than control subjects, suggesting abnormalities of calcium handling. Despite contractile abnormalities, diastolic function did not further deteriorate with rapid pacing and thus did not appear to be tightly linked to the systolic changes.

CONCLUSIONS

Pacing stress in intact human LVH can result in systolic impairment superimposed on preexisting but not worsened diastolic dysfunction. Abnormal calcium handling probably contributes prominently to this response.

Bolus intravenous nitroglycerin predominantly reduces afterload in patients with excessive arterial elastance

OBJECTIVES

We hypothesized that bolus intravenous nitroglycerin would be an afterload-reducing agent in patients with excessive initial afterload for their level of left ventricular systolic function. Conversely, bolus intravenous nitroglycerin should be a preload-reducing agent in patients without excessive initial afterload.

BACKGROUND

Although nitroglycerin has both preload- and afterload-reducing actions, methods to predict its predominant site of action in an individual patient have not been previously described.

METHODS

Left ventricular pressure-volume relations were recorded with micromanometer and conductance catheters during bolus injection of intravenous nitroglycerin in 27 patients with both normal left ventricular systolic function and varying degrees of congestive heart failure. Preload was determined by end-diastolic volume, afterload by effective arterial elastance, left ventricular systolic function by end-systolic elastance and coupling of afterload and ventricular function by the ratio of effective arterial elastance to end-systolic elastance (Ea/Ees ratio). An Ea/Ees ratio > 1 was defined as excessive afterload for the level of ventricular function.

RESULTS

Patients with an initial Ea/Ees ratio < 1 (Group 1) constituted a group of normotensive patients with intact ventricular function who exhibited a predominant reduction in preload in response to intravenous nitroglycerin. Those with an initial Ea/Ees ratio > 1 and normal or mildly depressed ventricular function (Group 2a) constituted a group of patients, most of whom were hypertensive, who exhibited a predominant afterload reduction. Finally, those with an initial Ea/Ees ratio > 1 and abnormal ventricular function (Group 2b) constituted a group of patients with clinical congestive heart failure who exhibited both preload and afterload reduction but a predominant afterload reduction because stroke volume increased.

CONCLUSIONS

Patients with normal arterial elastance and ventricular function respond to nitroglycerin with a predominant preload reduction, whereas patients with either excessive arterial elastance or abnormal ventricular function respond with a predominant afterload reduction.

Tedisamil (KC 8857) is a new specific bradycardic drug: does it also influence myocardial contractility? Analysis by the conductance (volume) technique in coronary artery disease

To determine whether inotropism influences the bradycardic action of tedisamil, hemodynamic assessment was performed in 13 patients with ischemic coronary artery disease including analysis of end-systolic pressure-volume relationships after an infusion of tedisamil, 0.3 mg/kg, at rest, and during paced tachycardia stress. Slope Emax fell by 14% at rest (13 patients) and by 10% during tachycardia (6/13 patients), whereas loops of end-systolic pressure-volume relationships moved rightward; all parameter changes indicated a lack of significant inotropism loss with tedisamil (p > 0.05). Although the mean heart rate decreased from 77.5 to 64.7 beats/min and QTc duration increased by 14% (p < 0.05), filling pressure and dp/dtmin remained unchanged and vascular resistance increased by 30%. Parameters of left ventricular pump function (ejection fraction, stroke volume, left ventricular efficiency) decreased slightly (between 3% and 13%), whereas left ventricular volumes increased (end-diastolic volume by 6%, end-systolic volume by 23%). The respective parameter changes during tachycardia were comparable in tendency, and angina could no longer be induced during postdrug pacing stress. We concluded that the bradycardic effects of tedisamil are selectively generated without impairing either ventricular pump function or contractility in a clinically relevant fashion, whereas the postdrug anginal threshold appears elevated. Thus tedisamil can be used safely in ischemic coronary artery disease.

Validation of a method for noninvasive measurement of central arterial pressure

The goal of this study was to validate a newly improved noninvasive method for calibrated measurement of the ascending portion of the central arterial pressure wave in humans. Noninvasive pressure waveforms were generated by measuring the time delay between the R wave of the electrocardiogram and onset of brachial artery flow (by Doppler) during computer-controlled upper arm cuff deflation. This delay shortens with falling cuff pressure (becoming near constant at and below diastolic pressure), so that a plot of pressure versus time delay yields the ascending portion of the arterial waveform. These waveforms were compared with simultaneous invasive ascending aortic pressures in 57 adult patients (31 by fluid manometer [group A] and 26 by catheter-tipped micromanometer [group B]) during routine cardiac catheterization. Patient age ranged from 26 to 77 years. Eighty percent of group A patients and 40% of group B had coronary artery disease. Noninvasive systolic and diastolic pressures were very similar to invasive values in both groups (Pni = 0.98 x Pi, r = 0.99, p < 0.0001). Instantaneous pressure differences between waveforms were also similar in both groups, averaging between 4.5 and 5.5 mm Hg. Micromanometer and noninvasive pressure data were also obtained before and after intravenous nitroglycerin (n = 5) and isometric handgrip (n = 8) and demonstrated good agreement. A potential application of these pressures is for estimating maximal ventricular power to assess systolic function. This was tested using invasive pressure-volume data from four patients under a variety of conditions (exercise, pacing, etc.).(ABSTRACT TRUNCATED AT 250 WORDS)

Effective arterial elastance as index of arterial vascular load in humans

BACKGROUND

This study tested whether the simple ratio of ventricular end-systolic pressure to stroke volume, known as the effective arterial elastance (Ea), provides a valid measure of arterial load in humans with normal and aged hypertensive vasculatures.

METHODS AND RESULTS

Ventricular pressure-volume and invasive aortic pressure and flow were simultaneously determined in 10 subjects (four young normotensive and six older hypertensive). Measurements were obtained at rest, during mechanically reduced preload, and after pharmacological interventions. Two measures of arterial load were compared: One was derived from aortic input impedance and arterial compliance data using an algebraic expression based on a three-element Windkessel model of the arterial system [Ea(Z)], and the other was more simply measured as the ratio of ventricular end-systolic pressure to stroke volume [Ea(PV)]. Although derived from completely different data sources and despite the simplifying assumptions of Ea(PV), both Ea(Z) and Ea(PV) were virtually identical over a broad range of altered conditions: Ea(PV) = 0.97.Ea(Z) + 0.17; n = 33, r2 = 0.98, SEE = 0.09, p less than 0.0001. Whereas Ea(PV) also correlated with mean arterial resistance, it exceeded resistance by as much as 25% in older hypertensive subjects (because of reduced compliance and wave reflections), which better indexed the arterial load effects on the ventricle. Simple methods to estimate Ea (PV) from routine arterial pressures were tested and validated.

CONCLUSIONS

Ea(PV) provides a convenient, useful method to assess arterial load and its impact on the human ventricle. These results highlight effects of increased pulsatile load caused by aging or hypertension on the pressure-volume loop and indicate that this load and its effects on cardiac performance are often underestimated by mean arterial resistance but are better accounted for by Ea.

Comparison of preload recruitable stroke work, end-systolic pressure-volume and dP/dtmax-end-diastolic volume relations as indexes of left ventricular contractile performance in patients undergoing routine cardiac catheterization

The end-systolic pressure-volume relation, the relation between stroke work and end-diastolic volume, termed the preload recruitable stroke work relation, and the relation between the peak of the first derivative of left ventricular pressure (dP/dtmax) and end-diastolic volume have been employed as linear indexes of left ventricular contractile performance in laboratory animals. The purpose of this study was to examine the relative utility of these indexes during routine cardiac catheterization in seven human subjects (mean age 48 +/- 18 [SD] years) with a normal left ventriculogram and coronary angiogram. Left ventricular pressure was recorded continuously with a micromanometer catheter, and left ventricular volume was derived from digital subtraction contrast ventriculograms obtained at 30-ms intervals. Transient occlusion of the inferior vena cava with a balloon-tipped catheter was employed to obtain beat to beat reductions in left ventricular pressure and volume over 8.7 +/- 1.7 cardiac cycles. Stroke work declined by 49 +/- 13% during vena caval occlusion, but end-systolic pressure fell by only 26 +/- 11%, and changes in dP/dtmax were small and inconsistent (12 +/- 22%). Consequently, the range of data available for determination of the preload recruitable stroke work relation greatly exceeded that for the end-systolic pressure-volume relation and the dP/dtmax-end-diastolic volume relation, and much less linear extrapolation from the measured data was required to determine the volume-axis intercept. Preload recruitable stroke work relations were highly linear (r = 0.95 +/- 0.07), and much more so than end-systolic pressure-volume relations (r = 0.79 +/- 0.23).(ABSTRACT TRUNCATED AT 250 WORDS)

Role of atrial contraction and synchrony of ventricular contraction in the optimisation of ventriculoarterial coupling in humans

OBJECTIVE

To examine the effects of pacing modes on the interaction between the left ventricle and arterial system in humans.

DESIGN

The slope of the end systolic pressure-volume relation (end systolic elastance), effective arterial elastance, the ratio of effective arterial elastance to end systolic elastance, and mechanical energy efficiency were compared under different pacing modes (atrial, atrioventricular, and ventricular).

PATIENTS

Nine male patients with sick sinus syndrome who had cardiac catheterisation for diagnosis and to see whether they needed a pacemaker.

INTERVENTIONS

A conductance catheter with tip-manometer was inserted into the left ventricle to obtain pressure-volume loops, and two pacing catheters were inserted into the right atrium and into the right ventricle respectively.

RESULTS

End systolic elastance was lower in atrioventricular pacing than in atrial pacing, but effective arterial elastance was not significantly different. End systolic elastance was lower in ventricular pacing than in atrioventricular pacing, and effective arterial elastance was higher in ventricular pacing than in atrioventricular pacing. Consequently the ratio of effective arterial elastance to end systolic elastance was lowest in atrial pacing and highest in ventricular pacing, and mechanical energy efficiency was highest in atrial pacing and lowest in ventricular pacing.

CONCLUSIONS

Atrial contraction and synchronous ventricular contraction independently optimise ventriculoarterial coupling in terms of a transfer of energy. Thus atrial pacing gives the best ventriculo-arterial coupling among these pacing modes.

Reduced left ventricular compliance in human mitral stenosis. Role of reversible internal constraint

BACKGROUND

The mechanisms of depressed left ventricular (LV) pump performance in human mitral stenosis (MS) remain poorly understood, because reduced filling alone affects many hemodynamic measurements. Therefore, pressure-volume relations were examined in nine subjects with MS and compared with eight age-matched normal controls.

METHODS AND RESULTS

Data were obtained by conductance catheter/micromanometer technique with transient inferior vena cava occlusion used to alter load and generate pressure-volume relations. In a subset of patients (n = 5), data were obtained both acutely and at 3 months (n = 4) after balloon valvuloplasty. MS patients had reduced cardiac output (3.3 +/- 0.9 versus 5.6 +/- 1.7 l/min) and end-diastolic volume (68.0 +/- 6.9 versus 115 +/- 31 ml) versus controls (p less than 0.001), with a mean transvalvular gradient of 14 +/- 6 mm Hg and estimated valve area of 0.6 +/- 0.2 cm2. Systolic function as assessed by the end-systolic pressure-volume relation was virtually the same in MS and control subjects. In contrast, end-diastolic pressure-volume relations in MS were consistently shifted leftward and had an increased slope (lower compliance) at matched pressure ranges (6.5 +/- 3.0 versus 2.2 +/- 0.53 ml/mm Hg at a mean diastolic pressure of 8 mm Hg, p less than 0.001). This change was not a result of reduced LV filling or probably of increased right heart loading. Valvuloplasty acutely returned chamber compliance to near normal, a change that was sustained at 3-month follow-up. Systolic function was little altered at this time.

CONCLUSIONS

These data indicate an impairment of diastolic function in human MS that can be acutely reversed by balloon valvuloplasty. Lowered LV compliance probably results from a functional restriction caused by ventricular attachment to a thickened and immobile valve apparatus.

Adverse effects of epinephrine in patients with advanced left ventricular dysfunction: analysis of ventriculo-arterial coupling

We examined the response of ventriculo-arterial coupling to epinephrine in 19 patients with normal left ventricular function and with left ventricular dysfunction of various degrees using a conductance catheter. They were divided into three groups: group I, seven patients without left ventricular wall motion abnormality; group II, six patients with ejection fraction of 45-60%; group III, six patients with ejection fraction of 28-40%. Changes in the slope of the end-systolic pressure-volume relationship (end-systolic elastance), the effective arterial elastance, the ratio of effective arterial elastance to end-systolic elastance and the ventricular work efficiency during administration of two different doses of epinephrine (0.05 and 0.1 micrograms/kg/min) were compared among the three groups. At baseline there were no significant differences among the three groups in the ratio of effective arterial elastance to end-systolic elastance, or ventricular work efficiency. At the lower dose of epinephrine, the mean ratio of effective arterial elastance to end-systolic elastance decreased and the mean ventricular work efficiency increased in any groups. At the higher dose of epinephrine the mean ratio of effective arterial elastance to end-systolic elastance further decreased and the mean ventricular work efficiency further increased in groups I and II. However, the mean ratio of effective arterial elastance to end-systolic elastance did not decrease but the mean ventricular work efficiency even decreased in group III. Thus, in patients with advanced left ventricular dysfunction, even a high dose of epinephrine does not modulate the ventriculo-arterial coupling to increase ventricular work efficiency.

Ventriculo-arterial coupling: concepts, assumptions, and applications

Recent investigations have yielded new insights into the interaction of the left ventricle with the arterial system. These studies have employed a variety of coupling frameworks to quantify this interaction, and each makes several simplifying assumptions. In this article, we review these frameworks, their major findings, assumptions, and clinical applications, and examine future directions for this research.

Influence of angiotensin converting enzyme inhibition on pump function and cardiac contractility in patients with chronic congestive heart failure

Eleven patients with coronary artery disease and chronic heart failure were studied before and three months after the angiotensin converting enzyme inhibitor enalapril was added to their frusemide medication. The following were measured: left ventricular pressure and volume with transient occlusion of the inferior vena cava, radionuclide angiography, and hormone concentrations in plasma. As in other reported studies, the clinical condition of the patients improved and their exercise tolerance increased moderately. Addition of enalapril reduced end diastolic and systolic pressure, reduced ventricular volume, and concomitantly increased the ejection fraction. The end systolic pressure-volume relation shifted to the left as it did in a similar animal study. In the animal study unloading by a vasodilator did not induce a leftward shift, so it can be inferred that in the present study unloading combined with a decrease in the angiotensin concentration was instrumental in remodelling the heart. Though unloading was expected to have a beneficial effect on the oxygen supply/demand ratio of the heart, the patients still showed the same drop in the ejection fraction during exercise as they did before treatment with enalapril, and early diastolic filling did not improve. Normally, regression of cardiac dilatation is only found if pump function improves; the present study showed that unloading in combination with angiotensin converting enzyme inhibition reshapes the ventricle without improving intrinsic pump function.