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

Pulmonary Artery Diameter (PAD) and the Pulmonary Artery to Aorta Ratio (PAD/AAD) as Assessed by Non-contrast Cardiac CT: The Association with Left Ventricular (LV) Remodeling and the LV Function

Objective Dilatation of the pulmonary artery itself (PAD: pulmonary artery diameter) or in relation to the ascending aorta (PAD/AAD: pulmonary artery diameter to ascending aortic diameter ratio) has been reported to be associated with pulmonary hypertension and with a prognostic outcome of either heart failure or cardiovascular events. We herein aimed to assess the correlations between pulmonary hypertension-related parameters PAD (or PAD/AAD) and left ventricular (LV) remodeling and LV function. Methods This retrospective study included 193 patients (ages: 67±12 years) who underwent both coronary CT angiography (CCTA) and echocardiography. The PAD and the AAD were measured on a transaxial non-contrast CCTA image at the level of the pulmonary artery bifurcation. Left ventricular mass (LVM), relative wall thickness ratio (RWT), left ventricular ejection fraction (LVEF), left atrial volume (LAV), and early mitral inflow velocity to mitral annular early diastolic velocity ratio (E/e') were evaluated by echocardiography. The relationships between PAD (or PAD/AAD) and echocardiography parameters were assessed, and adjusted for the demographic data and cardiovascular disease (CVD) risk factors by a multivariable linear regression analysis. Results PAD (mean±SD: 2.6±0.4 cm) was positively correlated with LVM (r=0.34, p<0.001), LAV (r=0.41, p<0.001), and E/e' (r=0.29, p<0.001). PAD/AAD (mean±SD: 0.76±0.12 cm) was positively correlated with LVM (r=0.12, p=0.09), LAV (r=0.24, p<0.001), and E/e' (r=0.15, p=0.04). These correlations remained significant after adjusting for demographic data and CVD risk factors. PAD (or PAD/AAD) did not correlate with LVEF or RWT (p>0.05). Conclusion Greater PAD or PAD/AAD is significantly associated with LV remodeling and an impaired LV function.

Extent of load-independence of pressure-normalized stress in swine

A load-independent index of myocardial contractility provides a measure of cardiac function. Previous contractility indices have been shown to be either load-dependent or invasive. We sought to determine the extent of load (preload and afterload)-independence of dσ*/dtmax (σ* is pressure-normalized stress) in comparison with other well-established indices. Six anaesthetized pigs underwent left ventricular pressure-volume measurements under various load conditions. The average preload was decreased by 70.0 ± 15.0% (from 39.2 ± 6.4 mL to 11.7 ± 7.7 mL) and increased by 49.3 ± 5.9% (from 35.1 ± 7.4 mL to 51.7 ± 8.9 mL). The average afterload was increased by 74.3 ± 43.5% (from 3.3 ± 0.6 mmHg/mL to 5.7 ± 1.7 mmHg/mL). When preload was reduced within an average of 21.7% (39.2 ± 6.4 mL to 30.7 ± 6.2 mL) using occlusion of the inferior vena cava, dσ*/dt max did not change significantly (6.50 ± 1.10 s⁻¹ vs 6.60 ± 0.90 s⁻¹, P = non-significant [NS]). When preload was increased within an average of 29.3% (35.1 ± 7.4 mL to 45.4 ± 7.3 mL) from infusion of normal saline, dσ*/dt max did not change significantly (7.04 ± 1.00 s⁻¹ vs 7.29 ± 1.10 s⁻¹, P = NS). When afterload was increased within an average of 42.4% (3.3 ± 0.6 mmHg/mL to 4.7 ± 1.0 mmHg/mL) using intra-aortic balloon occlusion, dσ*/dtmax did not change significantly (6.72 ± 1.18 s⁻¹ vs 6.89 ± 1.28 s⁻¹, P = NS). As expected, dσ*/dtmax was significantly increased with dobutamine. A linear regression showed no correlation between dσ*/dtmax and preload (r² = 0.02, P = 0.17) within a maximum range of -30% to +50% of preload change, or between dσ*/dtmax and afterload (r² = 0.03, P = 0.36) within maximum range of 0-100% of afterload increase, respectively. In conclusion, dσ*/dtmax is independent of loading conditions within an average of 21.7% of preload decrease, 29.3% of preload increase, 42.4% of afterload increase, and sensitive to dobutamine infusion.

Differential calcium handling in two canine models of right ventricular pressure overload

BACKGROUND

The purpose of this investigation was to characterize differential right atrial (RA) and ventricular (RV) molecular changes in Ca(2+)-handling proteins consequent to RV pressure overload and hypertrophy in two common, yet distinct models of pulmonary hypertension: dehydromonocrotaline (DMCT) toxicity and pulmonary artery (PA) banding.

METHODS

A total of 18 dogs underwent sternotomy in four groups: (1) DMCT toxicity (n = 5), (2) mild PA banding over 10 wk to match the RV pressure rise with DMCT (n = 5); (3) progressive PA banding to generate severe RV overload (n = 4); and (4) sternotomy only (n = 4).

RESULTS

In the right ventricle, with DMCT, there was no change in sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) or phospholamban (PLB), but we saw a trend toward down-regulation of phosphorylated PLB at serine-16 (p[Ser-16]PLB) (P = 0.07). Similarly, with mild PA banding, there was no change in SERCA or PLB, but p(Ser-16)PLB was down-regulated by 74% (P < 0.001). With severe PA banding, there was no change in PLB, but SERCA fell by 57% and p(Ser-16)PLB fell by 67% (P < 0.001). In the right atrium, with DMCT, there were no significant changes. With both mild and severe PA banding, p(Ser-16)PLB fell (P < 0.001), but SERCA and PLB did not change.

CONCLUSIONS

Perturbations in Ca(2+)-handling proteins depend on the degree of RV pressure overload and the model used to mimic the RV effects of pulmonary hypertension. They are similar, but blunted, in the atrium compared with the ventricle.

The Acute Effect of Intra-aortic Balloon Counterpulsation During Extracorporeal Life Support: An Experimental Study

Hemodynamically unstable patients supported by an extracorporeal life support (ECLS) circuit often receive additional support by intra-aortic balloon pump (IABP). However, it is not established whether support of the failing heart is improved by adjunctive IABP in both peripheral cannulation (PC) and central cannulation (CC) settings. Seven sheep were supported by an IABP and an ECLS system which were cannulated centrally as well as peripherally. In each cannulation configuration, hemodynamic and cardiac function indices were measured at baseline, ECLS, and ECLS plus IABP. The primary variables were mean coronary artery flow (Qcor), diastolic pressure time index (DPTI), left ventricular (LV) pressure-volume area (PVA), and tension time index (TTI). Additional IABP with ECLS support (CC/PC) decreased LV afterload (LV systolic peak pressure -4%, P<0.05/-8%, P<0.02), as well as TTI -2%/-10% and PVA -10%/-12% (P<0.03). Coronary perfusion was increased by additional IABP: CC, Qcor, +9%, and DPTI, +18% (P<0.02); PC, Qcor,+6%, and DPTI, +11% (P<0.05). IABP augmented the myocardial oxygen supply/demand ratios (CC/PC): Qcor/(PVA.heart rate) (+21%/+22%, P<0.02) and DPTI/TTI (+27%/+24%, P<0.03). In case of low arterial pressure (<50 mm Hg) and reduced ECLS flow, the overall hemodynamic profile improved only with central cannulation. We conclude that in both central and peripheral ECLS cannulation settings, adjunctive IABP improves the myocardial oxygen supply demand balance. In case of low cardiac output and insufficient extracorporeal flow with PC, adjunctive IABP may be contraindicated.

Hemodynamic effects of different lung-protective ventilation strategies in closed-chest pigs with normal lungs

OBJECTIVE

The benefits of lung-protective ventilation strategies used for acute respiratory distress syndrome in subjects with normal lungs are uncertain. The purpose of this study was to investigate the hemodynamic effects of conventional lung-protective ventilation (CLPV) and high-frequency oscillatory ventilation (HFOV) in a normal lung animal model.

DESIGN

Prospective laboratory investigation.

SETTING

Animal laboratory in a university medical center.

SUBJECTS

Seven landrace pigs (mean weight 41 kg).

INTERVENTIONS

Pigs were ventilated at random conventionally with positive end-expiratory pressure 2-3 cm H2O and tidal volume 10-12 mL/kg (control), with CLPV (positive end-expiratory pressure 10 cm H2O, tidal volume 6 mL/kg), or with HFOV. Hemodynamics were analyzed after insertion of biventricular conductance catheters and a pulmonary artery catheter.

MEASUREMENTS AND MAIN RESULTS

The protective strategies led to higher mean airway pressures and severe hypercapnia with acidosis, which was only significant with CLPV. Compared with control, oxygenation was worse with CLPV and HFOV. With HFOV and CLPV, mean arterial pressure, cardiac output, and stroke volume decreased significantly; pulmonary arterial elastance increased. The slope of the end-diastolic pressure volume relationship for the left and right ventricle remained unchanged (preserved ventricular function), whereas the intercept increased with both protective strategies (augmented intrathoracic pressure); left and right end-diastolic volumes decreased significantly.

CONCLUSIONS

In the absence of a fluid resuscitation strategy, CLPV and HFOV caused decreased mean arterial pressure, cardiac output, and stroke volume and worsened oxygenation in this normal lung animal model. This resulted primarily from a biventricular decrease in preload.

Miniature Intracardiac Assist Device Provides More Effective Cardiac Unloading and Circulatory Support During Severe Left Heart Failure Than Intraaortic Balloon Pumping

BACKGROUND

Hemodynamic assistance with a miniature intracardiac pump may fill the treatment gap between use of an intraaortic balloon pump (IABP) and the current, more invasive ventricular assist devices. The objective of this study was to compare the hemodynamic efficacy of a miniature intracardiac pump device with that of IABP.

METHODS AND RESULTS

Reversible acute mitral regurgitation (AMR) was induced in eight calves by stenting the mitral valve using a vena cava filter. Full and partial AMR assist were compared with maximum IABP support in each animal. In full-support mode, both assist systems increased cardiac output (miniature intracardiac pump, 13% [p < 0.05]; IABP, 3% [p < 0.05]), mean aortic pressure (miniature intracardiac pump, 13% [p < 0.05]; IABP, 8% [p < 0.05]), carotid artery flow (miniature intracardiac pump, 29% [p < 0.05]; IABP, 5% [difference not significant]), and coronary blood flow (miniature intracardiac pump, 25% [difference not significant]; IABP, 34% [p < 0.05]). Again in full-support mode, both systems reduced left atrial pressure (miniature intracardiac pump, 2.4 mm Hg [p < 0.05]; IABP, 0.7 mm Hg [p < 0.05]), peak left ventricular (LV) pressure (miniature intracardiac pump, 13% [p < 0.05]; IABP, 5% [p < 0.05]), and external LV work (miniature intracardiac pump, 29% [p < 0.05]; IABP, 3% [p < 0.05]). Only full miniature intracardiac pump support reduced both end-diastolic LV volume (7%; p < 0.05) and end-systolic LV volume (10%; p < 0.05). IABP mainly improved coronary perfusion, while the miniature intracardiac pump proved more capable of genuinely unloading the LV.

CONCLUSIONS

We conclude that during severe acute LV failure, the miniature intracardiac pump is capable of more effective cardiac unloading and circulatory support than IABP.

Efficacy of a new intraaortic propeller pump vs the intraaortic balloon pump: an animal study

OBJECTIVE

To compare the efficacy of a new intraaortic propeller pump (PP) to provide hemodynamic support to the intraaortic balloon pump (IABP) in an acute mitral regurgitation (MR) animal model.

BACKGROUND

A new intraaortic PP (Reitan catheter pump; Jomed; Helsingborg, Sweden) recently has been introduced. The pump's aim is a reduction in afterload via a deployable propeller that is placed in the high descending aorta and can be set at rotational speeds of <or= 14,000 revolutions per minute (rpm).

METHODS

In nine calves, acute MR was created by placing a vena cava filter in the mitral valve. The PP was tested at 6,000, 10,000, and 14,000 rpm and was compared to 1:1 IABP support. Cardiac output, coronary blood flow, carotid artery flow, ascending and abdominal aortic pressure, left atrial pressure, and LV pressure-volume loops were recorded.

RESULTS

The PP caused an rpm-dependent reduction in the mean ascending aortic pressure reaching -10 mm Hg (p < 0.05) at 14,000 rpm. However, mean (+/- SD) cardiac output did not improve (2.6 +/- 0.7 to 2.5 +/- 1.1 L/min; p = not significant), and mean diastolic coronary flow and carotid flow (47 +/- 16 to 35 +/- 15 centiliters/min, p < 0.05) were reduced. The IABP improved cardiac output, and carotid and diastolic coronary flow.

CONCLUSIONS

In this acute MR animal model, the PP reduced afterload but left out positive effects on cardiac output, which resulted in reduced perfusion of the upper body and the coronary circulation. Therefore, the IABP gives better hemodynamic support than the new PP in calves with acute MR.

Intra-aortic balloon pumping in acute mitral regurgitation reduces aortic impedance and regurgitant fraction

Acute mitral regurgitation (MR) is present in 10% of patients presenting with cardiogenic shock. To stabilize these patients, intra-aortic balloon pumping (IABP) is recommended, but the mechanism of IABP support in these patients is unknown. This animal study was designed to describe the hemodynamic effect of intra-aortic balloon pumping during cardiogenic shock induced by acute MR. In eight calves, left ventricular pressure-volume loops, aortic and left atrial pressure, and aortic, carotid artery, and coronary blood flow were recorded. Acute MR (range 36%-79%) was created by placing a metal cage in the mitral valve. Hemodynamic data was obtained at control, during acute MR, and during acute MR with 1:1 IABP support. Acute MR caused a decrease in cardiac output (-32%, P = 0.018), blood pressure, and carotid artery flow, whereas left ventricular output (+127%, P = 0.018), end-diastolic volume, and left atrial pressure all significantly increased. Stroke work, ejection fraction, and coronary blood flow were not significantly changed, and no signs of ischemia were seen on the ECG. The IABP raised average cardiac output by 31% (P = 0.012) and significantly raised blood pressure and flow to the brain while decreasing systemic vascular resistance. Left ventricular function and mean coronary blood flow did not change, but diastolic coronary flow became more important as shown by the increase in diastolic fraction from 64% to 95%. (P = 0.028). Average MR dropped by 7.5% (P = 0.025). In conclusion, application of the IABP during acute MR lowers aortic impedance, resulting in less MR and more output toward the aorta without changing left ventricular function.

Validation of left ventricular end-diastolic volume from stroke volume and ejection fraction

The present study examines an innovative approach to measurement of left ventricular (LV) end-diastolic volume (LVEDV). Measurement of LVEDV is fundamental to the assessment of intraoperative systolic and diastolic LV function. We compared steady state LVEDV values obtained from stroke volume (SV) and ejection fraction (EF) with echocardiographic and postmortem LVEDV measurements. Five anesthetized pigs (40-45 kg) underwent median sternotomy and pericardiotomy. A transit time ultrasonic flow probe was placed on the ascending aorta to provide cardiac output. A micromanometer provided LV end-diastolic pressure. LV short axis cross sectional echocardiograms and electrocardiograms were also obtained. LV end-diastolic area (LVEDA) and end-systolic area (LVESA) were measured to obtain EF. LVEDVsv/ef was calculated from cardiac output, heart rate, and EF. LVEDVecho was determined using a three-plane echocardiography model. Postmortem (LVEDVpm/vv) volumes were also measured. LVEDVsv/ef correlated well with volumes obtained by echocardiography (r2 = 0.92) and postmortem (r2 = 0.73) measurements. Values of p < 0.05 indicated significant linearity of LVEDA-LVEDVsv/ef (r2 =0.93), LVEDA-LVEDVecho (r2 = 0.96), and LVEDA-LVEDVpm/vv (r2 = 0.81) relationships. Determination of LVEDV from SV and EF is valid and may facilitate real-time determination of LV mechanics.

Convenient automated conductance volumetric system

Conventional conductance volumetric systems require ex-vivo calibrations for blood conductivity and parallel conductance. It is often impractical to repeat blood sampling and hypertonic saline infusion for these calibrations. To overcome these limitations, we developed a useful, self-calibrating conductance volumetric system that does not require ex-vivo calibrations. On a conventional 6-electrode catheter, we added an extra electrode close to one of the recording electrodes to estimate blood conductivity. These two electrodes were placed close (0.5 mm) enough so that conductance between them reflected only blood conductivity regardless of cardiac volume. We estimated parallel conductance by the dual-frequency excitation (2 and 20 kHz) method. In 18 anesthetized rabbits, blood conductivity (sigma(est)) thus estimated agreed well with that (sigma(conv)) measured by the conventional ex-vivo blood sampling method (sigma(est) = 1.04sigma(conv)-0.25, R(2) = 0.98, SEE = 0.01 mS/cm, 1.2% error). Parallel conductance (G(p est)) estimated by dual-frequency excitation also agreed well with that (G(p conv)) estimated by the saline injection method (G(p est) = 0.95G(p conv)+4.25, R(2) = 0.87, SEE = 4.0 mS, 6.0% error). Estimated ventricular volume (V(est)) by our system agreed reasonably well with that (V(conv)) by the conventional method (V(est) = 0.93V(conv)+0.01, R(2) = 0.86, SEE = 0.22 ml, 14.7% error). The fact that this self-calibrating conductance volumetric system drastically simplifies volume measurement makes it an attractive tool for the assessment of cardiac function where significant changes in blood conductivity and parallel conductance are inevitable, such as in cardiac surgery.

Reducing errors in parallel conductance measurement

Conductance (COND) measures left ventricle (LV) and right ventricle (RV) volume continuously during the cardiac cycle. COND measurement of the ventricle can be impaired by electrically conductive factors extrinsic to the heart that cause an artifactual increase in COND. This is known as parallel COND. A hypertonic saline injection has traditionally been used to measure parallel COND. The entry of hypertonic saline into the ventricle causes a rise (ascending region) in ventricular COND tracing, whereas its dissipation causes a fall (descending region). The hypothesis of this study is that parallel COND measurement can vary based on the region of COND tracing (ascending versus descending versus both) chosen for calculations. Parallel COND was measured in the LV (15 pigs and 5 sheep) and the RV (13 pigs and 5 sheep). In the LV, average +/- standard error of mean (SEM) parallel COND measured from the ascending region (55.4 +/- 9.2) was significantly different (p < 0.05) from the descending region and from both regions (72.2 +/- 10.3 and 66.4 +/- 9.2, respectively). Additionally, LV parallel COND measured from the descending region and from both regions were not different (p = NS; 72.2 +/- 10.3 and 66.4 +/- 9.2, respectively). In the RV, there was no significant difference (p = NS) among parallel COND calculated from ascending, descending, and both regions (102.9 +/- 8.1, 105.6 +/- 10.0, and 103.9 +/- 7.5, respectively). Average +/- SEM number of points used for parallel COND calculation (N) in the LV for each region (ascending versus descending versus both) were significantly different (p < 0.05) from one another (8 +/- 1 vs 11 +/- 1 vs 18 +/- 1). Similarly, N values used for the calculation of RV parallel COND in ascending versus descending versus both regions were significantly different (p < 0.05) from one another (6 +/- 1 vs 9 +/- 1 vs 14 +/- 1). In conclusion, there were significant differences in parallel COND calculation based on varying regions of LV COND. This was not true for the RV. To reduce errors that are caused by the differences cited here, one region should be used consistently to measure parallel COND. More study will be required to determine the optimal region of the COND tracing for the determination of parallel COND.

Biventricular systolic function in young lambs subject to chronic systemic right ventricular pressure overload

In various clinical situations of congenital heart disease, the right ventricle (RV) is subject to a chronic systemic pressure overload which affects biventricular function and may progress to the development of RV failure. Young lambs (2-3 wk old) underwent adjustable pulmonary artery banding (PAB) at systemic (aortic) level for 8 wk. Biventricular function was determined by using load-independent indexes of global ventricular contractile performance by the end-systolic pressure-volume relationship (ESPVR) using the conductance catheter at baseline and during dobutamine infusion. PAB resulted in a significant fivefold increase in RV end-systolic pressure (12-64 mmHg) and a doubling of the RV-to-left ventricular (LV) wall thickness ratio (P < 0.01). RV global contractile performance increased significantly, as indicated by an increased slope of the ESPVR. Compared with age-matched control lambs, cardiac output decreased from 2.6 to 1.6 l/min (P < 0.05) whereas heart rates were equal. In contrast with RV volume, LV volume decreased significantly after PAB (P < 0.01), whereas the LV-ESPVR slope was unchanged. In the PAB group, the RV, but not the LV, showed a reduced response to dobutamine. We concluded that chronic RV pressure overload for 8 wk results in diminished pump function despite compensatory increased RV global contractile performance.

Hypertonic saline method accurately determines parallel conductance for dual-field conductance catheter

Conversion of conductance catheter data to absolute ventricular volumes requires assessment of parallel conductance (G(P)). We determined the accuracy of GP obtained by the hypertonic saline method (G(P)saline) compared with angiographically derived GP (G(P)Angio) and quantified the variabilities of GP for the dual-field conductance catheter method in nine anesthetized sheep studied at baseline, treated with dobutamine, and subjected to volume loading and beta-blockade. G(P)saline and G(P)Angio showed an excellent linear correlation (G(P)saline = 1.002 x G(P)Angio + 0.001 Omega(-1), R2 = 0.92), and Bland-Altman analysis yielded a nonsignificant bias and narrow limits of agreement (bias +/- 2SD = 0.002 +/- 0.112 Omega(-1)). Within-animal variability of GP was very similar with both methods and was due to changes in blood conductivity rather than geometrical changes. Variability between animals was significant (26.3% of mean for G(P)saline and 25.7% for G(P)Angio) and thus warrants individual assessment. Variations during the cardiac cycle were not significantly different from zero. With biplane angiography used as gold standard, the hypertonic saline method accurately determines GP for the dual-field conductance catheter over a wide range of hemodynamic conditions.

Right ventricular support for off-pump coronary artery bypass grafting studied with bi-ventricular pressure--volume loops in sheep

OBJECTIVES

Tilting the heart during off-pump coronary artery bypass grafting (OPCABG) causes a strong decrease in cardiac output. It is hypothesized that this decrease is caused by reduced right ventricular filling and that right ventricular support is thus the best way to restore cardiac output. Simultaneous left and right ventricular pressure-volume loops were used to test this hypothesis.

METHODS

In seven sheep, the heart was tilted with the use of an Octopus device. After unsupported tilting, a novel right ventricular support, the Enabler, was activated at a pulsatile flow of 1.6 l/min. Pressure-volume loops of both ventricles were obtained using conductance catheters, and cardiac output was monitored with an aortic flow probe.

RESULTS

Tilting reduced cardiac output by 31% (4.4--3.1 l/min, P=0.001) and right ventricular end-diastolic volume by 44% (86--51 ml, P=0.005), while right ventricular end-diastolic pressure did not decrease. Left ventricular systolic pressure was not significantly reduced upon tilting and even increased in two animals. During Enabler right ventricular support, the cardiac output remained 23% lower than pre-tilting values (3.4 vs. 4.4 l/min, P=0.001).

CONCLUSIONS

Restricted right ventricular filling is the primary cause of the strong decrease in cardiac output during tilting. The Enabler right ventricular support can currently not restore cardiac output to pre-tilting values, mainly caused by its limited output and a decrease in right ventricular output upon Enabler activation. Constant monitoring of cardiac output is crucial during (unsupported or supported) tilting as blood pressure alone may not reflect the extent of the reduction in cardiac function.

Enhanced systolic function of the right ventricle during respiratory distress syndrome in newborn lambs

Respiratory distress syndrome (RDS) causes pulmonary hypertension. It is often suggested that this increased afterload for the right ventricle (RV) might lead to cardiac dysfunction. To examine this, we studied biventricular function in an experimental model. RDS was induced by lung lavages in seven newborn lambs. Five additional lambs served as controls. Cardiac function was quantified by indexes derived from end-systolic pressure-volume relations obtained by pressure-conductance catheters. After lung lavages, a twofold increase of mean pulmonary arterial pressure (from 15 to 34 mmHg) was obtained and lasted for the full 4-h study period. Stroke volume was maintained (5.2 +/- 0.6 ml at baseline and 6.1 +/- 1.4 ml at 4 h of RDS), while RV end-diastolic volume showed only a slight increase (from 6.5 +/- 2.3 ml at baseline to 7.7 +/- 1.3 ml at 4 h RDS). RV systolic function improved significantly, as indicated by a leftward shift and increased slope of the end-systolic pressure-volume relation. Left ventricular systolic function showed no changes. In control animals, pulmonary arterial pressure did not increase and right and left ventricular systolic function remained unaffected. In the face of increased RV afterload, the newborn heart is able to maintain cardiac output, primarily by improving systolic RV function through homeometric autoregulation.

A novel arresting solution for study of postmortem pressure--volume curves of the rat left ventricle

OBJECTIVE

We have found diastolic properties of the rat heart extremely sensitive to the method used to induce arrest. Accordingly, we sought to develop a reliable solution for measuring the LV pressure-volume relationship (LVPVR) in the rat.

MATERIALS AND METHODS

The study had five phases: (i) K120Na100, consisting of KCl (120 mEq/L) in NaCl (100 mEq/L) diluted with distilled water was developed in preliminary experiments. (ii) ACI rats were arrested with 3 cc of 4 degreesC KCl (n = 6) or K120Na100 (n = 6) infused into the aortic root. The LVPVR was expressed as normalized volume (Vn) at standardized pressures. Myocardial water content (%MWC) was determined. (iii) Six hearts were arrested with K120Na100 and LVPVRs observed over 1 h. (iv) Four hearts were instrumented with sonomicrometry crystals to compare in vivo and postmortem pressure diameter data. (v) The relation between body weight and dry heart weight was determined in 48 animals.

RESULTS

In hearts arrested with KCl, mean Vn at pressures of 10, 15, and 20 mmHg (206 +/- 26, 306 +/- 21, and 336 +/- 25 microl, respectively) was significantly reduced vs K120Na100 hearts (345 +/- 11, 407 +/- 12, and 472 +/- 18 microl) (P < 0.05). Mean %MWC changed insignificantly. Vn at 20 mm Hg became significantly smaller vs initial data 60 min after arrest with K120Na100 (P < 0.05, ANOVA). No differences between in vivo and postmortem mean normalized diameter were observed. The correlation coefficient for the relation between body weight and dry heart weight was 0.80. Conclusions. K120Na100 at 4 degreesC reliably preserves LV diastolic properties in the rat heart for 30 min. Normalization of LV volume to body weight is justified.