Assessment of the end-systolic pressure-volume relationship in human beings with the use of a time-varying elastance model

Organ-level validation of a cross-bridge cycling descriptor in a left ventricular finite element model: effects of ventricular loading on myocardial strains

Although detailed cell‐based descriptors of cross‐bridge cycling have been applied in finite element (FE) heart models to describe ventricular mechanics, these multiscale models have never been tested rigorously to determine if these descriptors, when scaled up to the organ‐level, are able to reproduce well‐established organ‐level physiological behaviors. To address this void, we here validate a left ventricular (LV) FE model that is driven by a cell‐based cross‐bridge cycling descriptor against key organ‐level heart physiology. The LV FE model was coupled to a closed‐loop lumped parameter circulatory model to simulate different ventricular loading conditions (preload and afterload) and contractilities. We show that our model is able to reproduce a linear end‐systolic pressure volume relationship, a curvilinear end‐diastolic pressure volume relationship and a linear relationship between myocardial oxygen consumption and pressure–volume area. We also show that the validated model can predict realistic LV strain‐time profiles in the longitudinal, circumferential, and radial directions. The predicted strain‐time profiles display key features that are consistent with those measured in humans, such as having similar peak strains, time‐to‐peak‐strain, and a rapid change in strain during atrial contraction at late‐diastole. Our model shows that the myocardial strains are sensitive to not only LV contractility, but also to the LV loading conditions, especially to a change in afterload. This result suggests that caution must be exercised when associating changes in myocardial strain with changes in LV contractility. The methodically validated multiscale model will be used in future studies to understand human heart diseases.

Physiological characterization of the SynCardia total artificial heart in a mock circulation system

The SynCardia total artificial heart (TAH) has emerged as an effective, life-saving biventricular replacement system for a wide variety of patients with end-stage heart failure. Although the clinical performance of the TAH is established, modern physiological characterization, in terms of elastance behavior and pressure-volume (PV) characterization has not been defined. Herein, we examine the TAH in terms of elastance using a nonejecting left ventricle, and then characterize the PV relation of the TAH by varying preload and afterload parameters using a Donovan Mock Circulatory System. We demonstrate that the TAH does not operate with time-varying elastance, differing from the human heart. Furthermore, we show that the TAH has a PV relation behavior that also differs from that of the human heart. The TAH does exhibit Starling-like behavior, with output increasing via preload-dependent mechanisms, without reliance on an alteration of inotropic state within the operating window of the TAH. Within our testing range, the TAH is insensitive to variations in afterload; however, this insensitivity has a limit, the limit being the maximum driving pressure of the pneumatic driver. Understanding the physiology of the TAH affords insight into the functional parameters that govern artificial heart behavior providing perspective on differences compared with the human heart.

Why Is Infarct Expansion Such an Elusive Therapeutic Target?

Myocardial infarct expansion has been associated with an increased risk of infarct rupture and progression to heart failure, motivating therapies such as infarct restraint and polymer injection that aim to limit infarct expansion. However, an exhaustive review of quantitative studies of infarct remodeling reveals that only half found chronic in-plane expansion, and many reported in-plane compaction. Using a finite element model, we demonstrate that the balance between scar stiffening due to collagen accumulation and increased wall stresses due to infarct thinning can produce either expansion or compaction in the pressurized heart-potentially explaining variability in the literature-and that loaded dimensions are much more sensitive to changes in thickness than in stiffness. Our analysis challenges the concept that in-plane expansion is a central feature of post-infarction remodeling; rather, available data suggest that radial thinning is the dominant process during infarct healing and may be an attractive therapeutic target.

Ejection Fraction and ESPVR. A study from a theoretical perspective

A formula derived by using large elastic deformation for the contraction of the myocardium is used to describe the pressure-volume relation (PVR) in the heart left ventricle, it is also used to calculate a mathematical expression for the non-linear end-systolic pressure-volume relation (ESPVR) in the left ventricle. An important feature of the mathematical formalism used is the inclusion of the isovolumic pressure Piso (equal active pressure generated by the myocardium) in the formalism describing the PVR. Relations between the ejection fraction (EF) and parameters describing the non-linear ESPVR are presented. It is shown that the non-linear ESPVR offers a rich collection of parameters that can be used to study the performance of the ventricles, like the areas under the ESPVR (units of energy) or the ordinates of the ESPVR (units of pressure), slopes and intercepts of the curves involved. The mathematical procedure can be easily implemented in a non-invasive way in routine clinical work when ratios of variables are calculated, it necessitates only the non-invasive measurement of the dimensions of the ventricles. Applications to clinical data published in the literature are presented, and they give results that show the consistency of the mathematical formalism used. The implications of the results of this research work on the study of the problem of heart failure with normal or preserved ejection fraction (HFpEF) are discussed.

The effect of a myocardial infarction on the normalized time-varying elastance curve

It has been suggested that the shape of the normalized time-varying elastance curve [E(n)(t(n))] is conserved in different cardiac pathologies. We hypothesize, however, that the E(n)(t(n)) differs quantitatively after myocardial infarction (MI). Sprague-Dawley rats (n = 9) were anesthetized, and the left anterior descending coronary artery was ligated to provoke the MI. A sham-operated control group (CTRL) (n = 10) was treated without the MI. Two months later, a conductance catheter was inserted into the left ventricle (LV). The LV pressure and volume were measured and the E(n)(t(n)) derived. Slopes of E(n)(t(n)) during the preejection period (alpha(PEP)), ejection period (alpha(EP)), and their ratio (beta = alpha(EP)/alpha(PEP)) were calculated, together with the characteristic decay time during isovolumic relaxation (tau) and the normalized elastance at end diastole (E(min)(n)). MI provoked significant LV chamber dilatation, thus a loss in cardiac output (-33%), ejection fraction (-40%), and stroke volume (-30%) (P < 0.05). Also, it caused significant calcium increase (17-fold), fibrosis (2-fold), and LV hypertrophy. End-systolic elastance dropped from 0.66 +/- 0.31 mmHg/microl (CTRL) to 0.34 +/- 0.11 mmHg/microl (MI) (P < 0.05). Normalized elastance was significantly reduced in the MI group during the preejection, ejection, and diastolic periods (P < 0.05). The slope of E(n)(t(n)) during the alpha(PEP) and beta were significantly altered after MI (P < 0.05). Furthermore, tau and end-diastolic E(min)(n) were both significantly augmented in the MI group. We conclude that the E(n)(t(n)) differs quantitatively in all phases of the heart cycle, between normal and hearts post-MI. This should be considered when utilizing the single-beat concept.

Impact of arterial elastance as a measure of vascular load on left ventricular geometry in hypertension

OBJECTIVE

Effective arterial elastance (Ea), integrating the pulsatile component of left ventricular (LV) afterload, is an estimate of aortic input impedance. We evaluated relationships of Ea with left ventricular anatomy and function in essential hypertension.

DESIGN

A cross-sectional analysis in 81 normotensive and 174 untreated hypertensive individuals enrolled in a referral hypertension centre.

METHODS

Using echocardiography we determined left ventricular mass index (LVMI), relative wall thickness (RWT), stroke volume (SV), endocardial (FSe) and midwall (FSm) fractional shortening and total peripheral resistance (TPR). Carotid pressure waveforms were obtained by arterial tonometry, and end-systolic pressure (Pes) was measured at the dicrotic notch. Ea index (EaI) was calculated as Pes/(SV index); LV elastance (Ees) was estimated as Pes/LV end-systolic volume, and ventriculo-arterial coupling was evaluated by the Ea/Ees ratio.

RESULTS

EaI was higher in hypertensives than in normotensives (3.02 +/- 0.63 versus 2.40 +/- 0.52 mmHg/l per m2; P< 0.0001). Using the 95% upper confidence limit in normotensives, hypertensives were divided in two groups with normal or elevated EaI. The 38 hypertensives with elevated EaI had higher RWT (0.41 +/- 0.06 versus 0.37 +/- 0.05), lower LVMI (87.5 +/- 18.5 versus 96.8 +/- 19.3 g/m2), higher TPR (2247 +/- 408 versus 1658 +/- 371 dynes/cm s(-5)) and lower FSe and FSm (35 +/- 5 versus 39 +/- 5 and 16 +/- 2 versus 18 +/- 2%; all P< 0.05) than patients with normal EaI. Ea/Ees ratio was increased and cardiac output was reduced in hypertensives with elevated EaI.

CONCLUSIONS

High values of EaI identify a minority of hypertensive patients characterized by elevated TPR, left ventricular concentric remodelling, depressed left ventricular systolic function and impaired ventriculo-arterial coupling.

Studying the mechanics of left ventricular contraction

Several interesting aspects of the ESPVR have been discussed in this study, including: a) A possibility to introduce, in an explicit manner, the active force of the myocardium in the formalism describing the PVR of the left ventricle. b) A possibility to express the ventriculo-arterial coupling by using the ratio Emax/eam in a way to distinguish between the normal physiological state and the mildly or severely depressed state of the heart. The possibility of also expressing this coupling by using directly different areas under ESPVR has been indicated. A third method, not discussed here, is to use the windkessel model (see [27, 53]). c) The relationship between oxygen consumption and all the areas under ESPVR. d) A possible mechanism of adaptation to short- or long-term variation in load condition by changing ESPVR in a way to create an SWR (see Fig. 4 and Table 2). e) A possibility to use different areas under ESPVR for clinical diagnostic purposes (see [20]); an example for SWR and SWR/SW is given in Table. 2. f) A possibility of noninvasive clinical application of various results of this study. Item (f) depends on the possibility of noninvasive measurement of the left ventricular pressure, which has been reported by Bourguignon and Wagner [61], and Sato, et al. [62]. Noninvasive measurement of left ventricular dimensions has been discussed by Teichholz, et al. [63], Grassman, et al. [64], Dumesnil et al [65], Dumesnil and Shoucri [66, 67]. Measurement of ESPVR from one loop of the contraction cycle has also been discussed by Takeuchi, et al. [68] and Nakamoto, et al. [69]. Further readings can be found in [70] and [71]. The list of references is not exhaustive, but has been chosen to illustrate various related aspects of the topics discussed.

Oxygen-saving effect of a new cardiotonic agent, MCI-154, in diseased human hearts

OBJECTIVES

The aim of this study was to examine the left ventricular mechanoenergetic effects of a novel Ca2+ sensitizing agent, MCI-154, on diseased human hearts compared with dobutamine.

BACKGROUND

Unlike conventional cardiotonic agents, a Ca2+ sensitizer that could produce a positive inotropic action by altering the responsiveness of myofilament to Ca2+ could generate force with smaller amounts of Ca2+; thus, it may potentially save energy expenditure.

METHODS

The left ventricular pressure-volume relation and myocardial oxygen consumption per beat (Vo2) were measured by a conductance (volume) catheter and a Webster catheter. Left ventricular contractility (Emax), systolic pressure-volume area (PVA [index of left ventricular total mechanical energy]) and Vo2 were assessed before and after infusion of MCI-154 or dobut-amine. The PVA-independent Vo2 (Vo2 mainly for excitation-contraction coupling) was assessed as the Vo2 at zero PVA.

RESULTS

Both agents increased Emax comparably (dobutamine: from 3.55 +/- 1.10 [mean +/- SD] to 5.04 +/- 1.16 mm Hg/ml per m2, p < 0.0001; MCI-154: from 3.36 +/- 1.26 to 5.37 +/- 2.14 mm Hg/ml per m2, p < 0.0001); dobutamine increased total Vo2 (from 0.22 +/- 0.08 to 0.27 +/- 0.09 ml O2, p < 0.05) and PVA-independent Vo2 (from 0.019 +/- 0.019 to 0.091 +/- 0.051 ml O2, p < 0.005); but MCI-154 did not change these variables significantly. Consequently, the oxygen cost of contractility (delta PVA-independent Vo2/delta Emax) was less with MCI-154 than with dobutamine (0.14 +/- 0.18 vs. 1.10 +/- 0.80 J/mm Hg per ml per m2, p < 0.05).

CONCLUSIONS

These results suggest that the cardiotonic action mediated by MCI-154 could provide an energetic advantage over the conventional cardiotonic action with currently used inotropic agents.

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.

Left ventricular pressure-volume relations with transesophageal echocardiographic automated border detection: comparison with conductance-catheter technique

Pressure-volume relations are important means used to assess left ventricular (LV) contractility; however, on-line volume acquisition has been limited to the invasive conductance catheter. The objective was to compare simultaneous measures of LV volume by transesophageal echocardiographic automated border detection (ABD) and conductance catheter and their respective pressure-volume relations during steady state and alterations in preload and contractility. Seven dogs had placement of high-fidelity pressure and conductance catheters, a vena caval balloon occluder, and a transesophageal probe. An automated Simpson's rule volume algorithm was used from the transverse four-chamber view. Inotropic modulation was induced with dobutamine in four dogs and propranolol in three. Relative changes in ABD volume were linearly related to conductance volume at steady state with group mean r = 0.93 +/- 0.03, standard error of estimate (SEE) = 10 +/- 2%. Changes in end-diastolic volume, end-systolic volume, and stroke work with caval occlusion were also significantly correlated:r = 0.93 =/- 0.04, SEE = 3.6 ml; r = 0.89 +/- 0.04, SEE = 3.8 +/- 1.9 ml; and r = 0.86 +/- 0.05, SEE = 40 +/- 21 mJ, respectively. The overall bias was for absolute ABD volume to be less. End-systolic and maximal elastance values by ABD were significantly higher than by the conductance method; baseline group average 4.97 +/- 0.92 mm Hg/ml versus 2.70 +/- 1.15 mm Hg/ml and 6.63 +/- 1.66 mm Hg/ml versus 3.20 +/- 1.37 mm Hg/ml (p<0.05), respectively. However, the direction and relative magnitude of changes in elastance with inotropic modulation were similar.

Myocardial dysfunction and abnormal left ventricular exercise response in autonomic diabetic patients

In diabetic patients, the pathophysiologic mechanisms of exercise-induced left ventricular (LV) dysfunction remain controversial. In this study, the role of myocardial contractility recruitment in determining an abnormal LV response to isometric or dynamic exercise has been investigated in 14 diabetic patients with autonomic dysfunction. Ischemic heart disease was excluded by the absence of LV wall motion abnormalities induced by isotonic and isometric exercise and by coronary angiography. Left ventricular and myocardial function were studied at rest, and during isometric and isotonic exercise, by two-dimensional echocardiography; moreover, recruitment of an inotropic reserve was assessed by postextrasystolic potentiation at rest and at peak handgrip. An abnormal response of LV ejection fraction to isometric (9/14) or to dynamic (8/14) exercise was frequent in study patients. In these patients, baseline myocardial contractility was normal, and the significant increase in ejection fraction by postextrasystolic potentiation indicated a normal contractile reserve (65 +/- 7% vs. 74 +/- 6%, p = 0.001). Nevertheless, the downward displacement of LV ejection fraction-systolic wall stress relationships during exercise suggests an inadequate increase in myocardial contractility. However, the abnormal ejection fraction at peak handgrip was completely reversed by postextrasystolic potentiation (67 +/- 6% vs. 58.1 +/- 10%, p = 0.008), a potent inotropic stimulation independent of the integrity of adrenergic cardiac receptors. A defective inotropic recruitment, despite the presence of a normal LV contractile reserve, plays an important role in deexercise LV dysfunction in diabetic patients with autonomic neuropathy.

Left ventricular end-systolic elastance is incorrectly estimated by the use of stepwise afterload variations in conscious, unsedated, autonomically intact dogs

BACKGROUND

End-systolic elastance (Ees), the slope parameter of the end-systolic pressure (ESP)-volume (ESV) relation (ESPVR), is usually estimated in patients by producing stepwise, steady-state pharmacological afterload variations and collecting one ESP-ESV point from each step. The ESPVR is then constructed by fitting a linear equation to these points. In sedated, autonomically blocked dogs, it has been shown that when one point from control, one point from a state of increased afterload, and one point from a state of decreased afterload are used, the resulting Ees incorrectly estimates true Ees, defined as the slope of the ESPVR obtained by transient vena caval occlusion. We investigated if this was also the case in unsedated, autonomically intact dogs when the points used belonged to steady states of progressively decreasing or progressively increasing afterload pressure.

METHODS AND RESULTS

In 10 conscious dogs instrumented with left ventricular (LV) endocardial sonomicrometers to measure LV volume, a LV pressure transducer, and an inferior vena caval (IVC) occluder, two protocols were carried out on separate days. In each protocol, an ESPVR was generated by IVC occlusion in the control state and in two steady-state levels of afterload change produced by stepwise infusion of nitroprusside (protocol 1, afterload decrease) and angiotensin II (protocol 2, afterload increase). In each protocol, steady-state ESP-ESV data points were averaged from the control state and from each level of afterload variation. Linear equations were fitted to the three steady-state points from each protocol, and the estimated Ees values obtained (EesEST) were compared with the Ees values of the control ESPVRs obtained by IVC occlusion (EesTRUE). In protocol 1, EesEST underestimated EesTRUE by about 16% (EesEST, 6.49 +/- 1.55 mm Hg/mL; EesTRUE, 7.48 +/- 1.29 mm Hg/mL; P < .02). In protocol 2, EesEST overestimated EesTRUE by about 37% (EesEST, 9.99 +/- 3.97 mm Hg/mL; EesTRUE, 6.43 +/- 3.88 mm Hg/mL; P < .007).

CONCLUSIONS

In conscious, autonomically intact dogs, the use of stepwise, steady-state afterload variations to obtain ESP-ESV data points to construct the ESPVR incorrectly estimates Ees. In the case of afterload reduction, EesTRUE is underestimated an average of 16.3%, and in the case of afterload increase, EesTRUE is overestimated an average of 37.1%. These errors should be taken into account when interpreting clinical studies using this methodology.

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.

Assessment of regional myocardial performance with end-systolic pressure length and thickness relationships

Although end-systolic pressure length and thickness relationships (ESPLR, ESPTR) are now widely used as substitutes for the end-systolic pressure volume relationships, there are some reservations about their use as an index of left ventricular (LV) performance. This study addressed three issues, namely: (1) which loading technique (decreasing preload by inferior vena cava (IVC) balloon occlusion or increasing systolic pressure by aortic constriction) is the most likely to yield usable data; (2) reproducibility of these relationships over a 30 min period; and (3) whether by using end-ejection (zero aortic flow) as a definition of end-systole, ESPLR and ESPTR can be used to characterize myocardial performance independent of load. Thirteen anesthetized beagles, weighing 16-25 kg, were used for this study, and were instrumented with sonomicrometers. We found that when ESPLR and ESPTR were constructed from data derived during aortic constriction, the slopes of these relationships were steeper and more curvilinear than when they were constructed from data recorded during IVC occlusion. In addition, the mean between ESPLR, ESPTR obtained 30 min apart was small, although there was a fair degree of variability between the first and second measurements. Using end-ejection to define end-systole, both ESPLR and ESPTR were relatively insensitive to loading conditions (LV end-diastolic pressure of 8-12 mmHg and 14-18 mmHg, aortic systolic pressure of 7-10 mmHg and 20-25 mmHg above baseline (in terms of the slope and shift (leftward or rightward) in these relationships, but were sensitive to inotropic interventions (dobutamine 2.5 micrograms/kg per min and 5 micrograms/kg per min). We conclude that, ESPLR and ESPTR, defined from measurements at end-ejection, can be used as adequate descriptors of regional myocardial performance if they were constructed from data over a similar pressure range during IVC balloon occlusion.

Maximum stress-volume index ratio of the left ventricle in hypertrophic cardiomyopathy

To evaluate the left ventricular contractile state in patients with nonobstructive hypertrophic cardiomyopathy (HCM), we analyzed the maximum stress-volume index ratio (MSVR) using catheter-tip cineangiography in 11 patients with HCM and 16 normal subjects. The value of the MSVR in normal subjects was 6.48 +/- 1.25 kdyn/cm5/m2 (mean +/- SD) and we defined the range of the mean +/- 2 SD as the normal MSVR range. Six patients with HCM placed inside the normal MSVR range (IN), but the other 5 patients placed outside and to the right of the normal range (RIGHT). This suggests that the contractile states of the patients of the RIGHT group were depressed. Compared with IN, the end-diastolic and end-systolic volume indices of RIGHT were larger (EDVI; 69.3 +/- 6.9 vs. 96.1 +/- 11.1 ml/m2, p less than 0.01, ESVI; 18.2 +/- 3.2 vs. 29.1 +/- 8.3 ml/m2, p less than 0.05), but the ejection fraction did not differ (IN 73.5 +/- 5.7 vs. RIGHT 69.6 +/- 8.3%, NS). End-diastolic pressure of IN and RIGHT was higher than that of normal subjects (IN 16.5 +/- 4.5, RIGHT 16.7 +/- 4.6 vs. 8.3 +/- 2.5 mm Hg, both p less than 0.05), but there was no difference between the two groups in HCM. End-systolic pressure did not differ among the three groups.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Slope of the end-systolic pressure-volume relation derived from single beat analysis is not always sensitive to positive inotropic stimuli in humans

Single beat estimation of the slope of the end-systolic pressure-volume relation assumes symmetric left ventricular pressure increase and decay and requires extrapolation of peak isovolumic developed pressure (Pmax) from the left ventricular pressure curve of an ejection contraction. To test the sensitivity of this slope to positive inotropic stimuli, biplane cineangiocardiography and simultaneous high-fidelity left ventricular pressure measurements were performed in 50 patients with heart disease. The end-systolic pressure-volume relations were assessed under baseline conditions and during norepinephrine infusion (n = 19) or after postextrasystolic potentiation (n = 24), or both (n = 7). Norepinephrine did not change left ventricular end-systolic volume despite significant elevations of end-systolic pressure. Postextrasystolic potentiation significantly decreased end-systolic volume in association with an unaltered left ventricular end-systolic pressure. The potentiation significantly decreased the pressure half-time of contraction, an index of the speed of the left ventricular pressure increase, while it increased the pressure half-time of relaxation, an index of the speed of the pressure decline, indicating asymmetric pressure increase and decay. The slope of the end-systolic pressure-volume relation increased from 3.3 to 4.4 mm Hg/ml/m2 (p less than 0.001) during norepinephrine infusion. In contrast, despite an augmented contractility, the slope decreased significantly from 3.2 to 2.4 mm Hg/ml/m2 (p less than 0.0001) after the potentiation. The slope showed a high correlation with Pmax (r = 0.86, p less than 0.0001, n = 107). Thus, the slope of the end-systolic pressure-volume relation derived from single beat analysis is not always sensitive to inotropic interventions.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in left ventricular mechanics, energetics, and contractile reserve in experimental heart failure

The contributions of changes in primary systolic and diastolic properties, limitations of contractile reserve, and alterations in energy efficiency to the left ventricular dysfunction seen with chronic pacing tachycardia were investigated. Seven dogs (heart failure group) were ventricularly paced at 250 beats per minute for 26.3 +/- 2.9 days and compared with a separate control group (n = 8). STudies were performed with isolated, metabolically supported hearts coupled to a computer-controlled loading system. Pressure-volume relations and myocardial oxygen consumption (MVO2) were measured to assess chamber systolic and diastolic properties and efficiency (relation between MVO2 and pressure-volume area [PVA]). Systolic function was reduced in failure hearts versus controls as assessed by the slope of the end-systolic pressure-volume relation (1.29 +/- 0.94 versus 2.71 +/- 0.98 mm Hg/ml, p less than 0.01) and lowered end-systolic stiffness at a matched stress (956.1 +/- 123.5 versus 1,401.7 +/- 431.7 g/cm2, p less than 0.05). Diastolic chamber and myocardial stiffness were unaltered in failure hearts, but the unstressed diastolic-arrested volume was significantly larger (33.3 +/- 3.9 versus 21.9 +/- 7.6 ml, p less than 0.01). Inotropic response to increased heart rate and exogenous beta-adrenergic stimulation (dobutamine HCl) was significantly impaired in failure compared with control hearts. Most interestingly, failure hearts had a lowered slope of the MVO2-PVA relation (2.1 +/- 1.1 versus 2.9 +/- 1.4 ml O2.mm Hg-1.ml-1.100 g left ventricle-1, p less than 0.001), indicating increased efficiency of chemomechanical energy conversion. The y intercept of the MVO2-PVA relation, which reflects oxygen costs of basal metabolism and excitation-contraction coupling, was unchanged in the two groups despite decreased contractility of the heart failure hearts. These results demonstrate reduced chamber and myocardial contractility, dilatation without alteration of passive myocardial properties, impaired contractile reserve, and novel alterations in cardiac efficiency in this model of heart failure.

Cardiac mechanics: basic and clinical contemporary research

This survey of cardiac hemodynamics updates evolving concepts of myocardial and ventricular systolic and diastolic loading and function. The pumping action of the heart and its interactions with arterial and venous systems in health and disease provide an extremely rich and challenging field of research, viewed from a fluid dynamic perspective. Many of the more important problems in this field, even if the fluid dynamics in them are considered in isolation, are found to raise questions which have not been asked in the history of fluid dynamics research. Biomedical engineering will increasingly contribute to their solution.

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.

The pressure-volume relation in the left ventricle and the pump function of the heart

The concept of body force (force per unit volume) is introduced to account for the effect of the force generated in the radial direction by the active state of the myocardium in an elastic model of the left ventricle represented as a thick-walled cylinder contracting symmetrically. Experimental evidence for the validity of the model is presented. It is shown how the radial force/unit area developed by the myocardium on its inner surface can be included in the equation of the pressure-volume relation (P-V relation) of the left ventricle according to the Suga-Sagawa model, as well as in the formalism that describes the pump function of the heart.

Effects of portal vein occlusion on myocardial contractility

We studied canine left ventricular contractile performance following 15 min of portal vein occlusion by analyzing the end-systolic pressure diameter relationship (ESPDR) which many investigators have reported as being independent of changes in preload and afterload but sensitive to changes in ventricular contractility. Portal vein occlusion for 15 min decreased the mean arterial pressure, left ventricular peak systolic pressure, and cardiac index, while the release of the occlusion gradually increased these values, although it did not restore them to the control values. The systemic vascular resistance index increased during portal vein occlusion and returned to the control values after release. Left ventricular end diastolic diameter decreased during portal clamping and returned to the control values after release. ESPDR and percent shortening were not significantly changed during or after portal clamping. These results indicate that the decrease in blood pressure during portal vein occlusion was not due to a reduction in myocardial contractility but rather was due to a reduction in preload.

Pump function of the heart as an optimal control problem

In order to model the pump function of the heart the left ventricle is represented as an elastic thick-walled cylinder contracting symmetrically. The acceleration is included in the mathematical formalism describing the contraction of the myocardium and optimal control theory is used to solve the differential equation of motion of the cylindrical wall in such a way as to minimize a given performance index. Application of the equations to experimental data published in the literature is discussed. The mathematical formalism presents a new way to study the time variation of the volume ejected from the left ventricle. Methods to quantify the pump function of the heart are suggested.

Comparison of noninvasive measures of contractility in dilated cardiomyopathy

Left ventricular performance is usually quantified by ejection phase indices such as ejection fraction, cardiac output, and fractional shortening. The load-dependence of these measures may result in inaccurate estimation of intrinsic myocardial contractility in states of chronic pressure or volume overload. End-systolic and stress-shortening relations have been proposed as measures of contractile state insofar as they are theoretically independent of preload and incorporate afterload. This article examines the behavior of these relations in response to changes in loading conditions and contractile state and reviews their application utilizing noninvasive methodology, particularly in the setting of dilated cardiomyopathy.

Nonlinearity and load sensitivity of end-systolic pressure-volume relation of canine left ventricle in vivo

The effects of mechanical changes in loading conditions on the left ventricular end-systolic pressure-volume relation (ESPVR) were studied in nine open-chest dogs, including three dogs studied before and after beta-adrenergic blockade. Left ventricular pressure was measured with a micromanometer, and left ventricular volume was measured with a conductance catheter. ESPVRs were obtained by increasing left atrial inflow over wide volume ranges (as much as threefold) under three different conditions: control or high or low aortic impedance. High impedance was obtained by occlusion of the descending aorta, and low impedance was obtained by a shunt between the subclavian artery and the left atrium. In the unblocked animals in 21 of 28 runs, a second-order polynomial equation gave a better fit for the ESPVR than a linear relation. To quantify the effects of the changes in aortic impedance on the ESPVR, we calculated from the quadratic equation its volume intercept (V18) and its local slope (E18) at an end-systolic pressure (Pes) of 18 kPa. In the unblocked animals, a statistically significant difference was found in V18 between low impedance (21.50 +/- 6.27 ml) and high impedance (14.10 +/- 8.98 ml; p less than 0.005) and between control (19.14 +/- 9.58 ml) and high impedance (p less than 0.05). In most dogs, E18 was increased at high and decreased at low impedance, but not significantly. In the additional experiments with beta-blockade, the nonlinearity diminished somewhat, but the load dependency of the ESPVR remained present after beta-blockade because the same leftward shift of the ESPVR with high aortic impedance was found. Two other relations, namely, of dP/dtmax and of stroke work versus end-diastolic volume, were also investigated, which on the whole showed the same behavior as the ESPVR. These results indicate that the ESPVR and dP/dtmax-Ved and stroke work-end-diastolic volume relations, when studied over a wide volume range, are nonlinear and that changes in loading conditions influence indexes of contractility derived from these relations, especially the volume intercepts, in such a way that an increase in aortic impedance may be interpreted as an increase in contractility. Blocking the beta-adrenergic receptors did not influence the load dependency of the ESPVR but, in some cases, tended to decrease the nonlinearity in concordance with the relation between contractility and nonlinearity in isolated hearts.

Performance of left ventricle based on pressure-volume relation

The concept of body force (force per unit volume) is used to derive an expression for the radial force developed by the myocardium (active force) in a model of the left ventricle represented as an elastic thick-walled cylinder contracting symmetrically. This approach leads to a novel equation to describe the pressure-volume relation in the Suga-Sagawa model. New indices to describe the mechanics of the left ventricular contraction are derived. Results tend to demonstrate that the radial active force generated by the myocardium will reach its peak value near end-systole, and that this peak is related to the peak isovolumic pressure. The study was carried out within a quasi-static approximation of the contraction (inertia forces neglected).

Left ventricular end-systolic stress-volume index ratio in aortic and mitral regurgitation with normal ejection fraction

To evaluate the left ventricular contractile state in regurgitant valvular disease with normal ejection fraction, we analyzed the end-systolic stress-volume index relationship (ESSVR) by means of cineangiography in 15 normal subjects, 11 patients with aortic regurgitation (AR), and 10 patients with mitral regurgitation (MR) whose ejection fraction (EF) was 60% or more. The end-systolic stress-volume index ratio in normal subjects was 5.57 +/- 0.60 kdyne/cm5/m2 (mean +/- standard deviation), and we defined the range including +/- 2 standard deviations of the ratio as the normal ESSVR range. Six patients with AR and five patients with MR placed inside the normal ESSVR range, termed AR IN and MR IN, but the remaining five patients with AR and MR placed to the right of the normal range, termed AR OUT and MR OUT. EF did not differ between patients with AR IN and AR OUT (69.4 +/- 5.4 verus 70.7 +/- 6.1%) and between MR IN and MR OUT (71.6 +/- 3.6 versus 71.1 +/- 7.9%). The EF of the subdivided groups with AR and MR also did not differ from that of normal subjects (70.7 +/- 7.3%). This finding showed that the left ventricular contractile state was depressed in patients with AR OUT and MR OUT despite a normal EF. In AR and MR the end-systolic stress and end-systolic volume index of OUT did not differ from those of IN, but the end-diastolic volume index of OUT was larger than that of IN (AR OUT 156.8 +/- 27.9 versus AR IN 110.8 +/- 24.1 ml/m2, MR OUT 160.5 +/- 44.7 versus MR IN 101.0 +/ 16.6 ml/m2; both p less than 0.05), and the regurgitant fraction of OUT was higher than that of IN (AR OUT 52.6 +/- 13.6 versus AR IN 29.7 +/- 13.3%, MR OUT 52.9 +/- 10.2 versus MR IN 30.2 +/- 11.4%; both p less than 0.05). In addition, there was a linear inverse correlation between the end-systolic stress-volume index ratio and the end-diastolic volume index in all subjects (r = -0.82, n = 36). In normal subjects there was a linear inverse correlation between end-systolic stress and the EF (r = -0.91, n = 15), but this relationship failed to separate patients with OUT from those with IN. Results of the present study suggest that some patients with AR and MR whose EF was normal had a depressed contractile state, and these patients had a large end-diastolic volume index and a high regurgitant fraction.(ABSTRACT TRUNCATED AT 400 WORDS)

Is standardization of left ventricular chamber elastance necessary?

Because of the relation between left ventricular (LV) chamber elastance and heart size, it has been hypothesized that maximum time-varying elastance (Emax) must be standardized to differentiate between preserved and depressed LV systolic performance. To test this hypothesis, we studied 66 patients, of whom 25 had a normal LV, 20 had aortic regurgitation, 14 had mitral regurgitation, and seven had cardiomyopathy, with micromanometer-determined LV pressures and radionuclide angiograms during multiple LV loading conditions. Multiple regression analysis established that Emax was independently related to LV end-diastolic volume (r = -0.69). When the Emax and LV end-diastolic volume (EDV) data from all patients were plotted, a curvilinear relation was evident. Data transformation to the base e identified two distinct linear relations, one in the normal patients of lnEmax = -0.60 (lnEDV) +4.34 (r = -0.67, p less than 0.001); and one in the patients with cardiac pathology of lnEmax = -1.06 (lnEDV) +6.12 (r = -0.73, p less than 0.001), which differed from each other (p less than 0.01). When a mathematical standardization was applied to these data to eliminate the independent contribution of heart size to the reduction in lnEmax, the normal patients had a standardized lnEmax versus lnEDV slope of 0, whereas that in the patients with cardiac pathology remained negative and continued to differ from that in the normal patients (p less than 0.001). Dichotomization of patients with cardiac pathology into those with preserved and depressed LV chamber elastance by lnEmax or standardized lnEmax provided highly concordant data (k = 0.73, p less than 0.001). Moreover, the estimated contribution of LVEDV to the reduction in Emax in patients with cardiac pathology averaged only 14 +/- 7%. We conclude from these data that LV chamber elastance calculated with radionuclide angiography has an independent relation with LVEDV, that a mathematical standardization of Emax for heart size does not significantly alter the dichotomization of patients with cardiac pathology into those with preserved and depressed LV systolic performance, and that heart size makes a relatively small contribution to the reduction in this index of LV systolic performance. Thus, standardization for heart size may not be necessary to identify whether preserved or depressed LV chamber elastance exists in an individual adult patient with cardiac pathology compared with normal adult patients.

Enhanced left ventricular contractility in autonomic failure: assessment using pressure-volume relations

Severe autonomic failure is usually characterized by both supine hypertension and orthostatic hypotension. Inadequate preload reserve, insufficient arterial resistance and abnormal cardiac performance have been postulated to contribute to the hypotension. To clarify these mechanisms, left ventricular performance and contractility were assessed using radionuclide ventriculography and systolic pressure-volume relations when supine and with graded head-up tilt in 11 patients with autonomic failure. Results were compared with those of 12 normal subjects, using phenylephrine infusion for pharmacologic afterload augmentation after autonomic blockade with atropine and propranolol. In a subset of four patients with autonomic failure, systolic pressure-volume relations were similar by both the tilt and phenylephrine methods. In autonomic failure, end-diastolic volume, end-systolic volume and stroke volume decreased with progressive degrees of tilt (p less than or equal to 0.007 for each). The supine radionuclide ejection fraction and cardiac output were similar to those of normal subjects (69% versus 68% and 5.4 versus 4.9 liters/min, respectively, p = NS). However, the slopes of the pressure-volume relations and the supine pressure/volume ratio in autonomic failure were much greater than normal (8.8 versus 2.5, and 6.3 versus 3.6 mm Hg/ml, respectively, p less than or equal to 0.04 for both). The baseline total peripheral resistance was greater than normal (24.9 versus 17.4 mm Hg.min-1/liter, p = 0.01), but the resistance at maximal tilt failed to increase (20.8 +/- 6.1 units). Plasma norepinephrine concentrations were lower than normal. Thus, patients with autonomic failure had hypercontractile left ventricular performance when assessed by pressure-volume relations, and their hearts were well matched to the elevated peripheral resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Dissociation of end systole from end ejection in patients with long-term mitral regurgitation

To determine whether left ventricular (LV) end systole and end ejection uncouple in patients with long-term mitral regurgitation, 59 patients (22 control patients with atypical chest pain, 21 patients with aortic regurgitation, and 16 patients with mitral regurgitation) were studied with micromanometer LV catheters and radionuclide angiograms. End systole was defined as the time of occurrence (Tmax) of the maximum time-varying elastance (Emax), and end ejection was defined as the time of occurrence of minimum ventricular volume (minV) and zero systolic flow as approximated by the aortic dicrotic notch (Aodi). The temporal relation between end systole and end ejection in the control patients was Tmax (331 +/- 42 [SD] msec), minV (336 +/- 36 msec), and then, zero systolic flow (355 +/- 23 msec). This temporal relation was maintained in the patients with aortic regurgitation. In contrast, in the patients with mitral regurgitation, the temporal relation was Tmax (266 +/- 49 msec), zero systolic flow (310 +/- 37 msec, p less than 0.01 vs. Tmax), and then, minV (355 +/- 37 msec, p less than 0.001 vs. Tmax and p less than 0.01 vs. Aodi). Additionally, the average Tmax occurred earlier in the patients with mitral regurgitation than in the control patients and patients with aortic regurgitation (p less than 0.01, for both), whereas the average time to minimum ventricular volume was similar in all three patient groups. Moreover, the average time to zero systolic flow also occurred earlier in the patients with mitral regurgitation than in the control patients (p less than 0.01) and patients with aortic regurgitation (p less than 0.05). Because of the dissociation of end systole from minimum ventricular volume in the patients with mitral regurgitation, the end-ejection pressure-volume relations calculated at minimum ventricular volume did not correlate (r = -0.09), whereas those calculated at zero systolic flow did correlate (r = 0.88) with the Emax slope values. We conclude that end ejection, defined as minimum ventricular volume, dissociates from end systole in patients with mitral regurgitation because of the shortened time to LV end systole in association with preservation of the time to LV end ejection due to the low impedance to ejection presented by the left atrium. Therefore, pressure-volume relations calculated at minimum ventricular volume might not be useful for assessing LV chamber performance in some patients with mitral regurgitation.

Responsiveness of the maximum time-varying elastance to alterations in left ventricular contractile state in man

This investigation was designed to establish the relative responsiveness of maximum time-varying elastance (Emax) slope values to alterations in left ventricular contractile state in comparison with isovolumic and ejection phase indices in man. Accordingly, nine patients had a bipolar right atrial pacing catheter and micromanometer left ventricular catheter placed and red blood cells tagged with technetium-99m for radionuclide angiography. Hemodynamic measurements and radionuclide angiograms were acquired simultaneously over a range of loading conditions produced by methoxamine or nitroprusside infusions during both the basal and enhanced contractile states. Enhanced left ventricular contractility was produced by a steady-state dobutamine infusion of 2 to 10 mu/kg/min. The mean (+)dP/dtmax increased from 1510 +/- 460 mm Hg/sec during the basal state to 2537 +/- 546 mm Hg/sec (p less than 0.001) during the dobutamine infusion. The mean Emax slope value also increased from 4.34 +/- 1.40 mm Hg/ml during the basal state to 6.41 +/- 1.90 mm Hg/ml (p less than 0.001) during the dobutamine infusion. The average percent change in the Emax slope value (51 +/- 26%) was less than those for the isovolumic indices (57% to 112%), while it was more than those for the ejection phase indices (11% to 53%). When the variability in the percent changes for each of these contractile indices was incorporated into the analysis, the Emax slope values demonstrated a greater responsiveness to changes in left ventricular contractility than did the isovolumic and ejection phase indices. In conclusion, the Emax slope value calculated by this method is a contractile index, which is less affected by measurement variability and the influences of loading conditions than are the isovolumic and ejection phase indices, and therefore may improve our ability to both detect and quantitate changes in left ventricular contractility in man.

Effects of methoxamine and phenylephrine on left ventricular contractility in rabbits

The end-systolic pressure-volume relation is employed to evaluate left ventricular contractility. In clinical studies, pharmacologic vasoconstriction is used to increase left ventricular systolic pressure to assess pressure-volume relations. However, the effect of vasoconstrictors on the ventricular contractile state is not well characterized. The effects of methoxamine and phenylephrine on systemic arterial pressure and left ventricular contractility in rabbits were studied with three protocols. In protocol 1, anesthetized rabbits (n = 10) were injected with incremental doses of methoxamine and phenylephrine intravenously. Methoxamine (4 mg) increased the mean arterial pressure by 50 +/- 12% (mean +/- SE) (n = 5, p = 0.001). Phenylephrine (0.2 mg) increased mean arterial pressure by 82 +/- 14% (n = 5, p = 0.004). In protocol 2, isolated blood-perfused hearts were injected with incremental doses of these drugs in the ascending aorta in amounts approximately equal to the concentrations injected in the intact rabbits. Methoxamine (2 mg) reduced isovolumic peak systolic left ventricular pressure by 43 +/- 9% (n = 7, p = 0.003), whereas phenylephrine (0.1 mg) increased the isovolumic pressure by 24 +/- 9% (n = 7, p less than 0.05). These responses indicated an enhanced contractile state with phenylephrine and a reduced contractile state with methoxamine. Pretreatment with propranolol blunted the effect of phenylephrine on isovolumic pressure (n = 6, p less than 0.02). In protocol 3, cross-circulation experiments allowed study of the effect of these drugs on isovolumic left ventricular pressure in the isolated heart and simultaneously on the systemic arterial pressure in the intact anesthetized rabbit (support rabbit).(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of end-systolic pressure-volume relations by intra-aortic balloon occlusion

A new situ technique has been developed for measuring peak end-systolic elastance, Emax, that does not alter intrinsic or reflex-stimulated cardiac contractility. Afterload is varied by the inflation of an intra-aortic balloon catheter positioned in the ascending aorta. Balloon inflation is timed to interrupt ventricular ejection transiently at different times during the ejection phase, therefore, producing contraction at different ventricular volumes. Simultaneous measurement of left ventricular pressure and aortic flow during the occlusion sequence allows pressure versus ejected volume loops to be generated, from which the end-systolic pressure-volume relation is determined. End-systolic pressure-volume relation (ESPVR) was measured in six anesthetized Dorsett sheep with normal and enhanced contractile states. ESPVR was analyzed using both linear and nonlinear techniques. Although nonlinear components were seen in ESPVR, for the pressure-volume data range produced by the transient occlusions, linear approximations of ESPVR fit the end-systolic data points well. In the normal state, Emax, the slope of the linear ESPVR, was 1.01-5.08 mm Hg/ml in animals with body weights of 23-32 kg. After epinephrine infusion, Emax increased from 3.07 +/- 1.49 to 5.79 +/- 1.97 mm Hg/ml, which is consistent with previous investigations. Linear and nonlinear volume intercepts had a small increase with positive inotropic stimulation. Furthermore, serial measurements of Emax tracked cardiac function in depressed hearts with rapidly changing contractility.

Load dependence of the single beat maximal pressure (stress)/volume ratios in humans

To determine whether the slopes of the single beat maximal pressure (stress)/volume ratios are sensitive to changes in loading conditions in humans, 16 patients without cardiac disease were studied with simultaneous micromanometer-determined left ventricular pressures and biplane contrast cineangiograms under control conditions and during methoxamine and nitroprusside infusions. Left ventricular volumes were calculated with use of a Simpson's rule algorithm, wall thickness was obtained iteratively, and both midwall circumferential and meridional stresses were computed frame by frame. The maximal pressure/volume and both circumferential and meridional maximal stress/volume ratios were calculated using a single beat from each loading condition assuming a zero volume-axis intercept. Mean left ventricular systolic pressure increased 47% during the methoxamine infusion and decreased 22% during the nitroprusside infusion compared with control (p less than 0.001 for both). Despite these changes in left ventricular systolic pressure, heart rate was eliminated as a confounding variable by right atrial pacing; and mean maximal rate of change of left ventricular pressure [(+)dP/dtmax] and rate of change at developed pressure 40 mm Hg [(+)(dP/dt) per DP40] values did not differ significantly. Mean single beat maximal pressure/volume ratios also did not differ significantly among the three loading conditions. In contrast, mean single beat circumferential and meridional maximal stress/volume ratios were 3.15 +/- 1.83 and 1.40 +/- 0.82 g/cm2 per ml at control; they increased to 4.47 +/- 2.44 and 2.21 +/- 1.25 g/cm2 per ml during the methoxamine infusion (p less than 0.001 for both), and they decreased during the nitroprusside infusion to 2.58 +/- 1.47 and 1.14 +/- 0.57 g/cm2 per ml (p less than 0.05 and p less than 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Radionuclide left ventricular contractile indices and their relationship to heart size in dogs

To identify possible mechanisms to explain differences between the maximum time-varying elastance (Emax) and end-systolic pressure-volume (Ees) slope values calculated with radionuclide angiography and to establish whether they have a relationship to heart size, we studied 16 dogs that were instrumented with micromanometer left ventricular catheters and had red blood cells tagged with technetium-99m for radionuclide angiography. Hemodynamics and radionuclide angiograms were obtained under control conditions and during six additional steady-state loading conditions. Isochronal Emax averaged 7.14 +/- 2.54 mm Hg/ml, while Ees averaged 5.68 +/- 1.88 mm Hg/ml (p less than 0.01), but they were highly correlated (r = 0.95, p less than 0.001). This observation was related to the assumption of linearity when curvilinearity was present and to the important influence of timing on these relationships. The Emax and Ees slope values were compared to dog weight; left ventricular weight, which ranged from 85 to 142 gm (mean 113 +/- 18 gm); and left ventricular end-diastolic volume, which ranged from 15 to 56 ml (mean 29 +/- 10 ml) using multiple regression analyses. The Emax and Ees slope values demonstrated a comparable inverse linear relationship with only left ventricular end-diastolic volume (r = 0.76 and -0.69, p less than 0.001 and p less than 0.01). We conclude that the differences between Emax and Ees slope values calculated with radionuclide angiography are related to the assumption of linearity when curvilinearity is present and to the importance of the timing of systolic events and that both Emax and Ees are comparably related to left ventricular end-diastolic volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Linearity of the left ventricular end-systolic pressure-volume relation in patients with severe heart failure

The left ventricular end-systolic pressure-volume relation is a relatively load-independent measure of left ventricular contractile function. Linearity of the relation derived from full left ventricular pressure-volume loops has not previously been demonstrated for patients with severe heart failure. Therefore, nine patients with markedly depressed left ventricular systolic function (ejection fraction 0.14 +/- 0.08) were studied with micromanometer left ventricular pressure measurement and simultaneous radionuclide ventriculography. Afterload was reduced with graded infusions of nitroprusside, allowing construction of pressure-volume loops under four afterload conditions in four patients and three afterload conditions in the other five patients. The end-systolic pressure-volume relation derived from the pressure-volume loops was found to be linear for the range of pressures and volumes examined, with correlation coefficients in individual patients ranging from 0.936 to 0.999 (mean 0.981). The mean slope of the relation (or end-systolic elastance) was 0.71 mm Hg/ml (range 0.42 to 1.52), and the extrapolated volume intercept at zero pressure was positive in all patients. An exponential relation between end-systolic elastance and ejection fraction was demonstrated for this group of patients. Approximations of end-systolic elastance obtained from measurements other than the full pressure-volume loops correlated variably with "true" elastance obtained from the pressure-volume loops. The relation between stroke work and end-diastolic volume was nonlinear in most patients. Thus, the end-systolic pressure-volume relation is linear in the "physiologic" range in patients with severe heart failure. This finding should permit construction of the relation from two loading conditions in clinical studies, facilitating its use as an index of contractile function in patients with heart failure.

Influence of contractile state on curvilinearity of in situ end-systolic pressure-volume relations

Although in situ end-systolic pressure-volume relations (ESPVRs) are approximately linear throughout a limited load range, they often yield seemingly "negative" volume axis intercepts (V0) and V0 shifts with inotropic interventions. We tested whether or not these findings could stem from in situ ESPVR nonlinearity, and we examined the physiologic meaning and limitations of linearized ESPVR variables frequently used for assessing contractile state. Continuous left ventricular pressures and volumes were obtained by micromanometer and conductance (volume) catheters in six open-chest dogs. Left ventricular loading was varied throughout a wide range by rapid left atrial hemorrhage into a reservoir. Propranolol and verapamil were administered to reduce inotropic state, with heart rate maintained by atrioventricular sequential pacing. ESPVRs were fit to nonlinear [Pes = a(Ves-V'0)2 + b(Ves-V'0)] and linear (Pes = Ees (Ves-V0)] models. Contractile state was assessed by the slope of the ESPVR at V'0 (b, of nonlinear model) and by two other ESPVR model-independent measures: the slope of the dP/dtmax and end-diastolic volume relation, and the slope of the stroke work and end-diastolic volume relation. ESPVR was frequently curvilinear, and a significant correlation existed between the extent of nonlinearity (a) and contractile state. Volume intercepts derived from linear fits to the high load ESPVR range were mostly negative and were dependent on changes in Ees. V0 estimates derived from the low load portion were positive and relatively insensitive to Ees. Thus, in situ ESPVR displays contractility-dependent curvilinearity. The contractility range throughout which ESPVRs are essentially linear is typical for isolated hearts, but the range represents low values for in situ ventricles. Despite curvilinearity, Ees determined in situ throughout limited load ranges can accurately assess inotropic state; however, comparisons between ESPVRs should consider potential nonlinearity, and if possible, they should be made within similar end-systolic pressure ranges.

Influence of age on left ventricular contractility

Controversy exists about whether left ventricular (LV) function is affected by aging. Therefore, peak systolic pressure to end-systolic diameter, peak systolic pressure to end-systolic volume, systolic wall stress to fractional shortening and systolic wall stress to end-systolic diameter relations were calculated in the left ventricle of 10 healthy subjects greater than 65 years old (age 70 +/- 4 years) (group B). They were compared with a control group composed by 10 healthy subjects (group A, age 22 +/- 1 years). LV measurements were obtained with M-mode echocardiography and an automatic cuff was used to determine blood pressure. Changes in the load conditions were obtained by 15 mg sublingual isosorbide dinitrate. There were no differences in resting end-systolic diameter, end-systolic volume, end-diastolic diameter, end-diastolic volume, fractional shortening, ejection fraction or systolic wall stress. Older subjects had higher values of resting peak systolic pressure (p less than 0.05) and lower heart rates (p less than 0.05). Young subjects had a steeper peak systolic pressure to end-systolic diameter slope (92 +/- 11 vs 51 +/- 11 mm Hg/cm; p less than 0.001) and peak systolic pressure to end-systolic volume slope (3.4 +/- 0.7 vs 1.9 +/- 0.6 mm Hg/ml; p less than 0.001). There was a slight difference in systolic wall stress to fractional shortening slopes between both groups (group A -0.215 vs group B -0.49%/10(3) dynes/cm2, p = 0.02) but not between systolic wall stress to end-systolic diameter slopes (group A 0.013 vs group B 0.019 cm/10(3) dynes/cm2, difference not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Combined influence of ventricular loading and relaxation on the transmitral flow velocity profile in dogs measured by Doppler echocardiography

The relation of the Doppler transmitral flow velocity profile to left ventricular loading conditions and diastolic properties remains poorly described. We studied seven adult mongrel dogs with an open-chest right heart bypass model in which left atrial pressure, representing preload, was varied by controlling blood flow into the pulmonary artery and left ventricular systolic pressure, representing afterload, was controlled independently by pumping blood into or from the femoral arteries. Heart rate was kept constant by crushing the sinus node and pacing the right atrium. Mitral inflow velocity profiles were measured by pulsed-wave Doppler echocardiography at multiple left atrial and left ventricular systolic pressures. In individual dogs, the peak E-wave velocity increased linearly with increasing left atrial V-wave pressure at constant left ventricular systolic pressure and decreased with increasing left ventricular systolic pressure at constant left atrial pressure. Stepwise multiple linear regression analysis of data pooled from all experimental stages in all dogs identified left atrial V-wave pressure, the time constant of relaxation (TL), and left ventricular systolic pressure, in order of decreasing significance, as predictors of the peak E-wave velocity (n = 82, multiple r = 0.87, p less than 0.0001). Multivariate analysis with the same three factors in individual dogs yielded higher r values (mean r = 0.89; range, 0.85-0.97), suggesting the presence of important interdog differences that were not accounted for by these three factors alone. When the values of codeterminant hemodynamic factors were kept within narrower limits, correlations between peak E-wave velocity and left atrial V-wave pressure (n = 35, multiple r = 0.83, p less than 0.0001), TL (n = 76, multiple r = -0.54, p less than 0.0001) and left ventricular systolic pressure (n = 20, multiple r = -0.59, p less than 0.005) improved substantially. In the pooled data, the relation of the peak E-wave velocity to left atrial V-wave pressure was shifted downward by an increase in TL (reduced relaxation rate), and the relation of the peak E-wave velocity to TL was shifted upward by an increase in left atrial V-wave pressure. Multivariate analysis also selected left atrial V-wave pressure and TL as the two most significant correlates of the velocity-time integral and deceleration rate of the E wave.(ABSTRACT TRUNCATED AT 400 WORDS)

Valvular-ventricular interaction: the importance of the mitral chordae tendineae in terms of global left ventricular systolic function

While conventional mitral valve replacement (MVR) for patients with chronic mitral regurgitation has been associated with relatively high operative mortality rates and incidence of late postoperative left ventricular (LV) failure and death, chordal-sparing mitral valve operations (valve repair/reconstruction or MVR with preservation of the chordae tendineae) subjectively appear to portend lower operative morbidity and mortality rates, better functional results, and improved long-term survival rates. Such empirical clinical observations have provided the basis for the concept of valvular-ventricular interaction, namely, that the intact mitral chordae are important mediators of more efficient and forceful ventricular contraction that enhances LV performance. This paper reviews the pertinent basic physiology and dynamics of the chordae tendineae and papillary muscles and examines critically the available experimental and clinical data regarding valvular-ventricular interaction. The problems inherent in quantifying LV contractility are central to this discussion and are also examined. While earlier experimental studies have produced conflicting results, more recent experiments utilizing load-independent measures of ventricular performance (particularly in isovolumic preparations) have conclusively demonstrated the importance of chordal integrity for optimal LV systolic function in normal animal hearts. The balance of the clinical evidence is also suggestive (although by no means conclusive) regarding the importance of valvular-ventricular interaction. Recent experimental evidence suggests that the mitral chordae enhance LV systolic function by means of regional afterload reduction. The mechanism(s) responsible for valvular-ventricular interaction, however, remains incompletely characterized at the present time, which underscores the urgent need for further experimental and, most importantly, clinical studies.

Radionuclide determination of the relationship between left ventricular contractile state and ejection fraction

To determine whether the relationship between various measures of left ventricular (LV) contractile state and ejection fraction (EF) is linear in man, we studied 30 patients during right atrial pacing over a range of loading conditions. With the use of micromanometer LV pressures and radionuclide LV volumes, pressure-volume (P-V) loops were generated for each loading condition. Then isochronal, instantaneous P-V data points were obtained by linear regression analysis to attain the maximum slope (Emax) of these time-varying isochrones. Other measures of LV end systole were also used to calculate end-systolic P-V relations in a similar fashion, and indirect P-V relations were obtained from the linear regression analysis of brachial artery peak pressure vs minimum LV volume data points. When the slopes of these LV contractile measures were compared to the radionuclide LV EFs, the linear correlation coefficients ranged from 0.53 to 0.67. After natural log transformation of the LV contractile state and EF data, the correlation coefficients for the polynomial curve fits ranged from 0.80 to 0.88. When the correlation coefficients for the polynomial curve fits of the natural log transformed data were compared to those for the linear regression analyses of the raw data, significant improvements were evident (p less than 0.05). Thus the relationship between various measures of LV contractile state and EF obtained with radionuclide angiography is best approximated by a complex, curvilinear relationship that is due, in part, to the wide range of LV contractile states within the relatively narrow normal range of LV ejection fractions.