Differential effects of chronic oral antihypertensive therapies on systemic arterial circulation and ventricular energetics in African-American patients

Gene-Gene Interactions Among PRKCA, NOS3 and BDKRB2 Polymorphisms Affect the Antihypertensive Effects of Enalapril

Protein kinase C (PKC) signalling is critically involved in the control of blood pressure. Angiotensin-converting enzyme inhibitors (ACEi) affect PKC expression and activity, which are partially associated with the responses to ACEi. We examined whether PRKCA (protein kinase C, alpha) polymorphisms (rs887797 C>T, rs1010544 T>C and rs16960228 G>A), or haplotypes, and gene-gene interactions within the ACEi pathway affect the antihypertensive responses in 104 hypertensive patients treated with enalapril as monotherapy. Patients were classified as poor responders (PR) or good responders (GR) to enalapril if their changes in mean arterial pressure were lower or higher than the median value, respectively. Multi-factor dimensionality reduction was used to characterize interactions among PRKCA, NOS3 (nitric oxide synthase 3) and BDKRB2 (bradykinin receptor B2) polymorphisms. The TC+CC genotypes for the rs1010544 polymorphism were more frequent in GR than in PR (p = 0.037). Conversely, the GA+AA genotypes for the rs16960228 polymorphism, and the CTA haplotype, were more frequent in PR than in GR (p = 0.040 and p = 0.008, respectively). Moreover, the GG genotype for the PRKCA rs16960228 polymorphism was associated with PR or GR depending on the genotypes for the rs2070744 (NOS3) and rs1799722 (BDKRB2) polymorphisms (p = 0.012). Our results suggest that PRKCA polymorphisms and gene-gene interactions within the ACEi pathway affect the antihypertensive responses to enalapril.

How to estimate aortic characteristic impedance from magnetic resonance and applanation tonometry data?

OBJECTIVES

Compare seven previous methods for the estimation of aortic characteristic impedance, which contributes to left ventricle pulsatile load, from phase-contrast cardiovascular magnetic resonance (CMR) and applanation tonometry data.

METHODS

We studied 77 healthy (43 ± 16 years) individuals and 16 hypertensive (61 ± 9 years) patients, who consecutively underwent ascending aorta CMR and carotid tonometry, resulting in flow and pressure waveforms, respectively. Characteristic impedance was semi-automatically estimated in time domain from these latter waveforms, using seven methods. The methods were based on the following: methods 1-4, magnitudes at specific times; method 5, early-systolic up-slope; method 6, time-derivatives peak; and method 7, pressure-flow loop early-systolic slope.

RESULTS

Aortic characteristic impedance was significantly increased in hypertensive patients when compared to elderly controls (n = 32) with a similar mean age of (59 ± 8 years) when using methods based on 95% of peak flow, up-slopes, and derivatives peaks (P < 0.05). When considering healthy individuals, impedance indices were significantly correlated to central pulse pressure for all methods (P < 0.005). Finally, characteristic impedance was correlated to the frequency-domain reference values (r > 0.65, P < 0.0001), with a slight superiority for the same three methods as above (r > 0.82, P < 0.0001).

CONCLUSIONS

This is the first study demonstrating phase-contrast CMR and tonometry usefulness in aortic characteristic impedance temporal estimation. Methods based on 95% of peak flow, as well as those based on derivative peaks and up-slopes, which are fast and independent of curve preprocessing, were slightly superior. They can be easily integrated in a clinical workflow and may help to understand the complementarity of this pulsatile index with other CMR aortic geometry and stiffness measures in the setting of left ventricle-aortic coupling.

Polymorphisms in VEGFA gene affect the antihypertensive responses to enalapril

PURPOSE

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor that affects blood pressure by promoting vasodilation mediated by nitric oxide. Angiotensin-converting enzyme inhibitors (ACEi) up-regulate the VEGF expression; thus, genetic polymorphisms in the VEGFA gene could affect the antihypertensive responses to these drugs.

METHODS

Hypertensive patients (n = 102) were prospectively treated only with the ACEi enalapril for 60 days. We compared the effect of VEGFA polymorphisms on changes in blood pressure after enalapril treatment. In addition, multiple linear regression analysis was carried out to assess the effect of covariates on blood pressure. Genotypes for g.-2578C>A (rs699947), g.-1154G>A (rs1570360), and g.-634G>C (rs2010963) VEGFA polymorphisms were determined, and haplotype frequencies were estimated.

RESULTS

Individuals carrying the CA and AA genotypes for the g.-2578C>A polymorphism and the AGG haplotype showed more intense decrease in blood pressure in response to enalapril 20 mg/day. A multiple linear regression analysis showed that the AA genotype for the g.-2578C>A polymorphism and the AGG haplotype are associated with more intense decrease in blood pressure in response to enalapril 20 mg/day, while the CC genotype for the g.-2578C>A polymorphism and the CGG haplotype are associated with the opposite effect.

CONCLUSIONS

These findings suggest that polymorphisms in VEGFA gene may affect the antihypertensive responses to enalapril.

Effects of atenolol, perindopril and verapamil on haemodynamic and vascular function in Marfan syndrome - a randomised, double-blind, crossover trial

BACKGROUND

Aortic dilatation is the main therapeutic target in patients with Marfan syndrome. Standard treatment with a β-blocker may not lower central pulse pressure - the major objective - because it does not do so in hypertension, unlike angiotensin-converting enzyme inhibitors and calcium-channel blockers. We therefore performed a prospective, randomised, double-blind, crossover trial to compare the effects of these three agents on large artery function and central aortic pressure in patients with Marfan syndrome.

METHODS AND RESULTS

Eighteen patients had applanation tonometry, pulse wave analysis and echocardiography, before and after atenolol 75 mg, perindopril 4 mg and verapamil 240 mg, each given for 4 weeks, in a random order, with 2 weeks between medications. Fourteen patients completed the study. Within-drug comparisons demonstrated that perindopril (-10·3 mmHg, P = 0·002), verapamil (-9·2 mmHg, P = 0·003) and atenolol (-7·1 mmHg, P = 0·01) all reduced central systolic pressure and brachial pressure; central changes were least, and peripheral changes greatest with atenolol but between-drug comparisons (analysis of covariance) were not significant. There was a trend for augmentation to be reduced by perindopril (-6·3%, P = 0·05), verapamil (-5·5%, P = 0·07) and atenolol (-3·2%, P = 0·09). Only atenolol reduced heart rate (by 16%) and delayed expansion in the arch and abdominal aorta (by 8% and 11%) (P < 0·001, P < 0·01 and P < 0·05, respectively, for between-drug comparisons).

CONCLUSIONS

Perindopril, verapamil and atenolol all reduced peripheral and central systolic pressure. As atenolol slowed heart rate and delayed aortic wave travel, β-blockade may have a continuing role in the treatment of patients with Marfan syndrome.

Effect of captopril on serum lipid levels and cardiac mitochondrial oxygen consumption in experimentally-induced hypercholesterolemia in rabbits

Angiotensin converting enzyme inhibitors are widely used in therapy of cardiovascular diseases. However, the consensus on effects of these inhibitors in control of myocardial oxygen consumption during the process of experimental hypercholesterolemia and under the condition of endothelial dysfunction has not been reached. Here we examined effects of captopril, an angiotensin converting enzyme inhibitor, on serum lipid levels and oxygen consumption rate in mitochondria isolated from heart of rabbits treated by hypercholesterolemic diet. During the twelve-week period, the Chinchilla male rabbits were daily treated by saline (controls); 1 % cholesterol diet; 5 mg/kg/day captopril or 1 % cholesterol + 5 mg/kg/day captopril. Total- and high-density lipoprotein cholesterol and triglyceride in serum were measured spectrophotometrically. The left ventricle mitochondrial fraction was isolated and myocardial oxygen consumption was measured by Biological Oxygen Monitor. Mitochondria isolated from hearts of rabbits exposed to hypercholesterolemic diet showed significantly reduced respiration rates (state 3 and state 4) with altering adenosine diphosphate/oxygen ratio, whereas the respiratory control ratio was not affected when compared to controls. Mitochondria from cholesterol/captopril-treated animals showed significantly reduced respiration rates without altering adenosine diphosphate/oxygen ratio index or respiratory control ratio. Although captopril did not exert the favorable effect on serum lipid levels in cholesterol-treated animals, it restored the mitochondrial oxygen consumption. Further studies should be performed to define the underlying physiological and/or pathophysiological mechanisms and clinical implications.

Peripheral vascular decoupling in porcine endotoxic shock

Cardiac output measurement from arterial pressure waveforms presumes a defined relationship between the arterial pulse pressure (PP), vascular compliance (C), and resistance (R). Cardiac output estimates degrade if these assumptions are incorrect. We hypothesized that sepsis would differentially alter central and peripheral vasomotor tone, decoupling the usual pressure wave propagation from central to peripheral sites. We assessed arterial input impedance (Z), C, and R from central and peripheral arterial pressures, and aortic blood flow in an anesthetized porcine model (n = 19) of fluid resuscitated endotoxic shock induced by endotoxin infusion (7 μg·kg⁻¹·h⁻¹ increased to 14 and 20 μg·kg⁻¹·h⁻¹ every 10 min and stopped when mean arterial pressure <40 mmHg or Sv(O₂) < 45%). Aortic, femoral, and radial artery pressures and aortic and radial artery flows were measured. Z was calculated by FFT of flow and pressure data. R and C were derived using a two-element Windkessel model. Arterial PP increased from aortic to femoral and radial sites. During stable endotoxemia with fluid resuscitation, aortic and radial blood flows returned to or exceeded baseline while mean arterial pressure remained similarly decreased at all three sites. However, aortic PP exceeded both femoral and radial arterial PP. Although Z, R, and C derived from aortic and radial pressure and aortic flow were similar during baseline, Z increases and C decreases when derived from aortic pressure whereas Z decreases and C increases when derived from radial pressure, while R decreased similarly with both pressure signals. This central-to-peripheral vascular tone decoupling, as quantified by the difference in calculated Z and C from aortic and radial artery pressure, may explain the decreasing precision of peripheral arterial pressure profile algorithms in assessing cardiac output in septic shock patients and suggests that different algorithms taking this vascular decoupling into account may be necessary to improve their precision in this patient population.

Diagnosis and management of Marfan syndrome

Marfan syndrome (MFS) is a relatively common inherited connective tissue disorder with significant morbidity and mortality. Diagnosis of this syndrome can be difficult, as many of the findings of MFS are present in other syndromes, as well as in the general population. MFS is diagnosed using the Ghent criteria, a group of clinical findings that are specific for MFS. Children and adolescents can pose diagnostic dilemmas as the stigmata of MFS are not present at birth but can evolve through adulthood. Current treatment for MFS is limited to strict blood pressure control and careful selection of physical activity. Aggressive screening and early management could significantly improve the quality of life for these patients.

Cross-sectional characterization of all classes of antihypertensives in terms of central blood pressure in Japanese hypertensive patients

BACKGROUND

Central blood pressure (CBP) has been reported to be superior to brachial blood pressure (BP) as a cardiovascular risk predictor in hypertensive patients; however, the effects of antihypertensives on CBP have not been fully examined. This cross-sectional hypothesis-generating study aimed to tentatively characterize all classes of antihypertensives in relation to CBP.

METHODS

Calibrated tonometric radial artery pressure waveforms were recorded using an automated device in 1,727 treated hypertensive patients and 848 nonhypertensive (non-HT) participants. Radial artery late systolic BP (SBP) has been reported to reflect central SBP. The difference between late and peak SBPs (DeltaSBP2) was assessed with linear regression model-based adjustments. Separate regression models for DeltaSBP2 were constructed for both participant groups as well as specified sub-populations.

RESULTS

DeltaSBP2 was 3.3 mm Hg lower in patients treated with any single-vasodilating (VD) antihypertensive agent without significant interclass difference than with non-VD agents, and was 2.0 mm Hg lower than estimated in nonhypertensive subjects. Combinations of two vasodilators were 6.6 and 2.9 mm Hg lower in DeltaSBP2 than nonvasodilator combinations and nonhypertensive subjects, respectively (P < 0.001 for all comparisons). Nonvasodilators and their combination showed high DeltaSBP2, 1.1 and 3.7 mm Hg higher than in nonhypertensive subjects (P < 0.001 for both). Additional adjustment of the pulse rate reduced high DeltaSBP2 with beta-blockers (betaBLs).

CONCLUSIONS

This cross-sectional observation suggests that vasodilatory antihypertensives lower CBP independently of peripheral BP levels without evident class-specific differences, whereas nonvasodilators may raise CBP.

Emerging trends in minimally invasive haemodynamic monitoring and optimization of fluid therapy

BACKGROUND

For decades the pulmonary artery catheter has been the mainstay of cardiac output monitoring in critically ill patients, and pressure-based indices of ventricular filling have been used to gauge fluid requirements with acknowledged limitations. In recent years, alternative technologies have become available which are minimally invasive, allow beat-to-beat cardiac output monitoring and permit assessment of fluid requirements by volumetric means and by allowing assessment of heart-lung interaction in mechanically ventilated patients.

METHODS

A qualitative review of the basic science behind the transpulmonary dilution technique used in the measurement of cardiac output, global end-diastolic volume and extravascular lung water; the basic science and validation of pulse contour analysis methods of real-time cardiac output monitoring; the application and limitations of these technologies to guide rational fluid therapy in surgical and critically ill patients.

RESULTS

Transpulmonary dilution techniques correlate well with pulmonary artery catheter-derived measurement of cardiac output. Volumetric measures of preload appear to be superior to central venous and pulmonary artery occlusion pressures. Dynamic indices of preload responsiveness such as stroke volume variation are more useful than static measures in mechanically ventilated patients.

CONCLUSION

In fully mechanically ventilated patients, dynamic measurements of heart-lung interaction such as stroke volume variation are superior to static measures of preload in assessing whether a patient is volume-responsive (i.e. will increase stroke volume in response to a fluid challenge). For patients who are not fully mechanically ventilated, pulse contour analysis allows real-time assessment of increases in cardiac output in response to passive leg-raising.

Pulsatile flow in a coronary artery using multiphase kinetic theory

Pulsatile flow in a model of a right coronary artery (RCA) was previously modeled as a single-phase fluid and as a two-phase fluid using experimental rheological data for blood as a function of hematocrit and shear rate. Here we present a multiphase kinetic theory model which has been shown to compute correctly the viscosity of red blood cells (RBCs) and their migration away from vessel walls: the Fahraeus-Lindqvist effect. The computed RBC viscosity decreases with shear rate and vessel size, consistent with measurements. The pulsatile computations were performed using a typical cardiac waveform until a limit cycle was well established. The RBC volume fractions, shear stresses, shear stress gradients, granular temperatures, viscosities, and phase velocities varied with time and position during each cardiac cycle. Steady-state computations were also performed and were found to compare well with time-averaged transient results. The wall shear stress and wall shear stress gradients (both spatial and temporal) were found to be highest on the inside area of maximum curvature. Potential atherosclerosis sites are identified using these computational results.

Effects of losartan + L-arginine on nitric oxide production, endothelial cell function, and hemodynamic variables in patients with heart failure secondary to coronary heart disease

The purpose of the present study was to evaluate the effects of losartan and the combination of losartan and L-arginine on endothelial function and hemodynamic variables in patients with heart failure (HF). Endothelium-dependent vasodilation is impaired in patients with HF. It was hypothesized that the administration of losartan and the combination of losartan and L-arginine might increase nitric oxide production and have a beneficial additive effect on endothelial function and hemodynamic variables in patients with HF. Nine patients with HF (ejection fraction<35%) were given losartan 50 mg orally on 2 consecutive days. On the second day, 1 hour after losartan 50 mg administration, L-arginine 20 g was given by intravenous infusion. Endothelial function in the form of endothelium-dependent brachial artery flow-mediated vasodilation (FMV) was measured by ultrasound. Hemodynamic variables were estimated using Doppler echocardiography at baseline and at 2 and 4 hours after losartan alone and after combination therapy. Urinary levels of nitrite (NO2) or nitrate (NO3) were measured. Four hours after losartan administration, significant reductions in systemic vascular resistance and estimated end-systolic elastase were observed. On the second day, 1 hour after L-arginine infusion, an additive hemodynamic effect was observed, with significant increases in the cardiac index and stroke volume and significant reductions in systemic vascular resistance and calculated left ventricular end-diastolic pressure. A trend toward improved FMV was observed with losartan alone, but without statistical significance. Combination therapy significantly improved postintervention FMV compared with baseline. The increase in urinary nitric oxide excretion after losartan treatment and combination therapy was significantly correlated with improved hemodynamic variables and improved FMV. In conclusion, losartan induces significant afterload reduction, reduced contractility, and increased nitric oxide urinary excretion. The combination of L-arginine and losartan seems to have superior effects on hemodynamic variables and endothelium-dependent vasodilation compared with losartan alone.

Hemodynamic Computation Using Multiphase Flow Dynamics in a Right Coronary Artery

Hemodynamic data on the roles of physiologically critical blood particulates are needed to better understand cardiovascular diseases. The blood flow patterns and particulate buildup were numerically simulated using the multiphase non-Newtonian theory of dense suspension hemodynamics in a realistic right coronary artery (RCA) having various cross sections. The local hemodynamic factors, such as wall shear stress (WSS), red blood cell (RBC) buildup, viscosity, and velocity, varied with the spatially nonuniform vessel structures and temporal cardiac cycles. The model generally predicted higher RBC buildup on the inside radius of curvature. A low WSS region was found in the high RBC buildup region, in particular, on the area of maximum curvature of a realistic human RCA. The complex recirculation patterns, the oscillatory flow with flow reversal, and vessel geometry resulted in RBC buildup due to the prolonged particulate residence time, specifically, at the end of the diastole cycle. The increase of the initial plasma viscosity caused the lower WSS. These predictions have significant implications for understanding the local hemodynamic phenomena that may contribute to the earliest stage of atherosclerosis, as clinically observed on the inside curvatures and torsion of coronary arteries.

Multiphase hemodynamic simulation of pulsatile flow in a coronary artery

A multiphase transient non-Newtonian three-dimensional (3-D) computational fluid dynamics (CFD) simulation has been performed for pulsatile hemodynamics in an idealized curved section of a human coronary artery. We present the first prediction, to the authors' knowledge, of particulate buildup on the inside curvature using the multiphase theory of dense suspension hemodynamics. In this study, the particulates are red blood cells (RBCs). The location of RBC buildup on the inside curvature correlates with lower wall shear stress (WSS) relative to the outside curvature. These predictions provide insight into how blood-borne particulates interact with artery walls and hence, have relevance for understanding atherogenesis since clinical observations show that atherosclerotic plaques generally form on the inside curvatures of arteries. The buildup of RBCs on the inside curvature is driven by the secondary flow and higher residence times. The higher viscosity in the central portion of the curved vessel tends to block their flow, causing them to migrate preferentially through the boundary layer. The reason for this is the nearly neutrally buoyant nature of the dense two-phase hemodynamic flow. The two-phase non-Newtonian viscosity model predicts greater shear thinning than the single-phase non-Newtonian model. Consequently, the secondary flow induced in the curvature is weaker. The waveforms for computed hemodynamic parameters, such as hematocrit, WSS, and viscosity, follow the prescribed inlet velocity waveforms. The lower oscillatory WSS produced on the inside curvature has implications for understanding thickening of the intimal layer.

The arterial system in pre-eclampsia and chronic hypertension with superimposed pre-eclampsia

OBJECTIVES

To determine if the normal gestational changes in mechanical properties of the arterial system are altered in pre-eclampsia.

DESIGN

Prospective controlled observational study.

SETTING

University urban tertiary medical centre.

POPULATION

Eleven pre-eclamptics and 10 chronic hypertensives with superimposed pre-eclampsia were compared with 14 normotensive gravidas experiencing preterm labour, all receiving MgSO(4). Two additional control groups were studied as well: (A) nine normal pregnant women receiving neither magnesium nor epidural, for baseline comparisons; and (B) eight normotensive gravidas receiving epidural anaesthesia.

METHODS

Two-dimensional targeted M-mode echocardiograms and continuous wave Doppler velocity were used to obtain instantaneous pressure and flow data. Total vascular resistance (TVR) quantified the steady component of systemic arterial load; pulsatile arterial load was characterised by global arterial compliance (AC), aortic input impedance spectrum (Z(1)) and characteristic impedance (Z(0)).

MAIN OUTCOME MEASURES

TVR, AC, Z(1), Z(0).

RESULTS

Controls, pre-eclamptics and chronic hypertensives with superimposed pre-eclampsia, respectively: TVR index 1328 [299], 1973 [609]*, 2428 [562]*(,#) dyn second cm(-5) m(2); AC area index 1.69 [0.46], 1.19 [0.46]*, 0.93 [0.38]* mL mmHg(-1) m(-2); Z(0) index 253.2 [61.3], 327.0 [135.1], 307.5 [130.9] dyn second cm(-5) m(2); and Z(1) index 184.2 [56.5], 283.6 [81.6]*, 357.1 [119.5]* dyn second cm(-5) m(2) (*P < 0.05 vs control;(#)P < 0.05 vs pre-eclampsia). Normal gravidas (in secondary controls group A) had decreased mean systolic and diastolic blood pressures, and increased AC and cardiac indices, compared with women receiving magnesium tocolysis, verifying the need for these primary controls. No differences were noted between normotensive gravidas receiving epidural anaesthesia (secondary controls group B) and the non-anesthetised controls (group A), eliminating epidural as a confounder.

CONCLUSIONS

The normal gestational changes in systemic arterial mechanical properties are significantly altered in pre-eclampsia and these alterations are more marked with superimposed hypertensive disease.

Assessment of arterial ventricular coupling changes in patients under therapy with various antihypertensive agents by a non-invasive echocardiographic method

BACKGROUND

The integration between arterial and ventricular function has been studied by mostly invasive techniques. We considered assessing the influence of various antihypertensive medications on arterial-ventricular coupling (AVC) with the use of a non-invasive echocardiographic method.

METHODS

A total of 9037 patients, who had been under treatment for essential arterial hypertension were studied echocardiographically at baseline prior to therapy and after 6 months of antihypertensive monotherapy (diuretics, beta-blockers without intrinsic sympathomimetic activity (ISA), beta-blockers with ISA, a-blockers, angiotensin converting enzyme inhibitors (ACEI), angiotensin II receptor blockers (AIIRA), non-dihydropyridine calcium antagonists, and dihydropyridine calcium antagonists). The AVC was calculated by echocardiographic measurements based on the equation: AVC=ESV/SV (ESV, end systolic volume; SV, stroke volume).

RESULTS

ACEI, AIIRA, and dihydropyridine calcium antagonists decreased (P<0.0001 for all) while diuretics, alpha-blockers, both beta-blocker groups, and non-dihydropyridines increased significantly the AVC values compared to baseline measurements (P<0.0001 for all, except P=0.02 for alpha-blockers). Changes in AVC were the most highly correlated with changes in EF (r=-0.979, P<0.0001).

CONCLUSION

Various antihypertensive drugs have a differential effect on AVC with ACEI, AIIRA, and dihydropyridine calcium antagonists having the most favorable effect on this index. AVC provides a meaningful index of cardiovascular performance in hypertension and offers the possibility of wide employment and serial follow-up in large numbers of patients because of its completely non-invasive nature.

Contributions of heart rate and contractility to myocardial oxygen balance during exercise

The respective contributions of heart rate (HR) reduction and left ventricular (LV) negative inotropy to the effects of antianginal drugs are debated. Accordingly, eight instrumented dogs were investigated during exercise at spontaneous and paced HR (250 beats/min) after administration of either saline, atenolol, or ivabradine (selective pacemaker current channel blocker). During exercise, atenolol and ivabradine (both 1 mg/kg iv) similarly reduced HR (-30% from 222 +/- 5 beats/min), and LV mean ejection wall stress was not altered. LV dP/dt(max) was reduced by atenolol but not ivabradine. Diastolic time (DT) was increased by atenolol versus saline (195 +/- 6 vs. 123 +/- 4 ms, respectively) and to a greater extent by ivabradine (233 +/- 11 ms). Myocardial oxygen consumption (MVo(2)) was lower under ivabradine and atenolol versus saline (6.7 +/- 0.6 and 4.7 +/- 0.4 vs. 8.1 +/- 0.6 ml/min, respectively, P < 0.05). Under pacing, DT and MVo(2) were similar between ivabradine and saline but significantly reduced with atenolol. Thus HR reduction and negative inotropy equally contribute to the reduction in MVo(2) during exercise in the normal heart. The negative inotropy limits the increase in DT afforded by HR reduction.

Influence of wall stress and left ventricular geometry on the accuracy of dobutamine stress echocardiography

OBJECTIVE

The goal of this study was to determine whether wall stress at rest and during stress could explain the influence of left ventricular (LV) morphology on the accuracy of dobutamine stress echocardiography (DSE).

BACKGROUND

The sensitivity of DSE appears to be reduced in patients with concentric remodeling, but the cause of this finding is unclear.

METHODS

We studied 161 patients without resting wall motion abnormalities who underwent DSE and coronary angiography. Patients were classified into four groups according to relative wall thickness (normal <0.45) and LV mass (normal </=131 g/m(2) in men and </=100 g/m(2) in women): normal geometry, concentric remodeling, concentric hypertrophy, and eccentric hypertrophy. Significant coronary artery disease was defined as >/=50% stenosis. Circumferential (cESS) and meridional end-systolic wall stress (mESS) were calculated at rest and peak DSE.

RESULTS

Both false-negative and false-positive results for DSE were present in 35 patients (22%). The accuracy of DSE in patients with concentric remodeling (61%) was lower than that in patients with normal geometry (85%, p < 0.05) or concentric hypertrophy (86%, p < 0.05), but the accuracy with eccentric hypertrophy (64%, p < 0.05) was lower than with concentric hypertrophy. Patients in lowest quartile of cESS and mESS at peak had significantly lower sensitivity and accuracy than those in the highest quartile. A reduced cESS at peak (p = 0.012), presence of concentric remodeling (p = 0.044), and eccentric hypertrophy (p = 0.012) were significant predictors of both false-negative and false-positive results for DSE.

CONCLUSIONS

The accuracy of DSE is influenced by the LV geometric pattern and peak wall stress.

Equipment review: new techniques for cardiac output measurement--oesophageal Doppler, Fick principle using carbon dioxide, and pulse contour analysis

Measuring cardiac output is of paramount importance in the management of critically ill patients in the intensive care unit and of 'high risk' surgical patients in the operating room. Alternatives to thermodilution are now available and are gaining acceptance among practitioners who have been trained almost exclusively in the use of the pulmonary artery catheter. The present review focuses on the principles, advantages and limitations of oesophageal Doppler, Fick principle applied to carbon dioxide, and pulse contour analysis. No single method stands out or renders the others obsolete. By making cardiac output easily measurable, however, these techniques should all contribute to improvement in haemodynamic management.

Cardiac cycle-dependent changes in aortic area and distensibility are reduced in older patients with isolated diastolic heart failure and correlate with exercise intolerance

OBJECTIVES

The goal of this study was to determine if cardiac cycle-dependent changes in proximal thoracic aortic area and distensibility are associated with exercise intolerance in elderly patients with diastolic heart failure (DHF).

BACKGROUND

Aortic compliance declines substantially with age. We hypothesized that a reduction in cardiac cycle-dependent changes in thoracic aortic area and distensibility (above that which occurs with aging) could be associated with the exercise intolerance that is prominent in elderly diastolic heart failure patients.

METHODS

Thirty subjects (20 healthy individuals [10 < 30 years of age and 10 > 60 years of age] and 10 individuals > the age of 60 years with DHF) underwent a magnetic resonance imaging (MRI) study of the heart and proximal thoracic aorta followed within 48 h by maximal exercise ergometry with expired gas analysis.

RESULTS

The patients with DHF had higher resting brachial pulse and systolic blood pressure, left ventricular mass, aortic wall thickness and mean aortic flow velocity, and, compared with healthy older subjects, they had a significant reduction in MRI-assessed cardiac cycle-dependent change in aortic area and distensibility (p < 0.0001) that correlated with diminished peak exercise oxygen consumption (r = 0.79). After controlling for age and gender in a multivariate analysis, thoracic aortic distensibility was a significant predictor of peak exercise oxygen consumption (p < 0.04).

CONCLUSIONS

Older patients with isolated DHF have reduced cardiac cycle-dependent changes in proximal thoracic aortic area and distensibility (beyond that which occurs with normal aging), and this correlates with and may contribute to their severe exercise intolerance.

Evaluation of arterial stiffness in children with Williams syndrome: Does it play a role in evolving hypertension?

BACKGROUND

Pathologic studies and surgical observations of thickened aortic walls have suggested an increase in aortic stiffness in patients with Williams syndrome. However, in vivo objective evaluation of aortic and arterial stiffness in Williams syndrome are lacking. Moreover, systemic hypertension, although prevalent in Williams syndrome, does not have a well-defined mechanism in this syndrome. Therefore, the purpose of this study was to quantitate aortic stiffness and arterial compliance in an objective manner, as well as to determine their roles in development of hypertension, in children with Williams syndrome.

METHODS

We studied 13 patients with Williams syndrome (aged 3-12 years) and 16 age-matched control subjects. Aortic stiffness was calculated from the beta index as follows: beta = (ln[P(s)/P(d)])/ ([D(s) - D(d)]/D(d)), where P(s) and P(d) are systolic and diastolic blood pressures and D(s) and D(d) are systolic and diastolic aortic dimensions, respectively. Arterial compliance (C) was calculated by the area method: C= (A(d) x CO x CL) / (A(t) x [P(es) - P(d)]), where A(t) is the total area and A(d) is the area under the diastolic portion of the arterial pulse tracing, CO is the cardiac output, CL is the cycle length, and P(es) is aortic end-systolic pressure.

RESULTS

In patients with Williams syndrome, the beta index was 2-fold higher than in control patients (9.02 +/- 3.15 vs 4.43 +/- 0.96, P <.005). Moreover, there was a strong positive correlation between the beta index and the systolic blood pressure (r = 0.8 and P <.0001). Compliance was decreased by 42% (0.41 +/- 0.11 vs 0.71 +/- 0.10 mL/mm Hg, P <.05), suggesting decreased arterial compliance.

CONCLUSIONS

Our study indicates that in vivo arterial stiffness is increased in patients with Williams syndrome. We speculate that increased arterial stiffness may be the predisposing cause of systemic hypertension in Williams syndrome.

Smooth muscle relaxation and local hydraulic impedance properties of the aorta

Smooth muscle relaxation is expected to yield beneficial effects on hydraulic impedance properties of large vessels. We investigated the effects of intravenous diltiazem infusion on aortic wall stiffness and local hydraulic impedance properties. In seven anesthetized, closed-chest dogs, instantaneous cross-sectional area and pressure of the descending thoracic aorta were measured using transesophageal echocardiography combined with acoustic quantification and a micromanometer, respectively. Data were acquired during a vena caval balloon inflation, both at the control condition and with diltiazem infusion. At the operating point, diltiazem reduced blood pressure in all dogs but did not alter aortic dimensions or wall stiffness. Over the observed pressure range, aortic area-pressure relationships were linear. Whereas diltiazem affected the slope of this relationship variably (no change in 3 dogs, increase in 1 dog, decrease in 3 dogs), the zero-pressure area intercept was significantly increased in every case such that higher area was observed at any given pressure. When comparisons were made at a common level of wall stress, wall stiffness was either increased or unchanged during diltiazem infusion. In contrast, diltiazem decreased wall stiffness in every case when comparisons were made at a common level of aortic midwall radius. Aortic characteristic impedance and pulse wave velocity, components of left ventricular hydraulic load that are determined by aortic elastic and geometric properties, were affected variably. A comparison of wall stiffness at matched wall stress appears inappropriate for assessing changes in smooth muscle tone. Because of the competing effects of changes in vessel diameter and wall stiffness, smooth muscle relaxation is not necessarily accompanied by the expected beneficial changes in local aortic hydraulic impedance. These results can be reconciled by recognizing that components other than vascular smooth muscle (e.g., elastin, collagen) contribute to aortic wall stiffness.

Influence of Aortic Elastic Properties on Pulse Pressure Changes Induced by Rapid Ventricular Pacing

The mechanism of aortic pulse pressure decline induced by acute rapid ventricular pacing remains incompletely understood. It has been ascribed to changes in stroke volume or aortic compliance. This becomes more complicated by the dependence of aortic compliance on the level of the mean aortic pressure as well as the aortic wall properties. To test the role of such mechanical factors, aortic pressure-diameter hemodynamics, derived from simultaneous tip-micromanometer aortic pressure recordings and high-fidelity ultrasonic intravascular aortic diameter recordings, were measured in 15 normal subjects during and after abrupt cessation of rapid ventricular pacing (up to 160 bpm). Immediately after terminating the pacing, diastolic aortic pressure declined (-9%, from 87.4 +/- 1.2 to 79.5 +/- 1.7 mmHg, P < 0.0001) while systolic aortic pressure increased (+19%, from 109.5 +/- 1.6 to 130.1 +/- 2.8 mmHg, P < 0.0001). Thus, pulse pressure increased from 22.1 +/- 2.2 to 50.6 +/- 3.1 mmHg, P < 0.0001. To quantify systolic and diastolic aortic pressure differences we compared the first postpaced beat (a) and the last paced beat (b). To estimate what the aortic pressure would have been for the paced beats had the aortic diameter differences due to the different heart rate not occurred we calculated the theoretical pressure of the paced beat P(b) = E(b). D(a), where E(b) was the instantaneous aortic elastance of the paced beat and D(a) was the aortic diameter for the postpaced beat. The corrected pressure difference was then calculated by the following: DeltaP(cor) = (D(a). E(b)) - P(a). It was found that systolic DeltaP(cor) was 25% of systolic DeltaP(raw) and diastolic DeltaP(cor) was 89% of diastolic DeltaP(raw). DeltaP(raw) was the pressure difference between paced and spontaneous beat measured from the raw data. DeltaP(cor) indicates the portion of DeltaP(raw) that results from a change in aortic stiffness as a consequence of viscous behavior or aorto-ventricular coupling. These data indicate that the majority of diastolic pressure decline after pacing was terminated, may reflect a change in aortic stiffness while the majority of systolic pressure rise, and may be attributable to differences in hemodynamics alone.

Pulsatile hemodynamics in hypertension

The hemodynamics of hypertension and antihypertensive therapy have generally been approached in terms of the steady-flow load on the heart. Recent evidence, however, suggests that the pulsatile component of hemodynamic load may play a fundamental role in both the development and progression of hypertensive cardiovascular disease and its clinical sequelae. Pulse pressure, a correlate of conduit vessel stiffness, has been shown to be an important independent predictor of clinical events in hypertensive patients and in the general population. Unrecognized effects on pulsatile hemodynamics may account for the differential effects of various agents on left ventricular mass and events. A better understanding of abnormalities in pulsatile load in hypertension will facilitate risk stratification in and treatment of patients with hypertension.

Total arterial compliance in ambulatory hypertension during selective beta1-adrenergic receptor blockade and angiotensin-converting enzyme inhibition

Aortic root flow and pressure estimates were obtained noninvasively with Doppler echocardiography and calibrated subclavian artery pulse tracing in 30 subjects with ambulatory hypertension in a randomized, crossover study with 4 weeks' treatment and washout periods. Total arterial compliance, assessed by use of a three-element Windkessel model of the arterial tree, increased 42% with atenolol (50-100 mg once daily), and 7% (p = NS) with captopril (25-50 mg twice daily). Atenolol reduced mean arterial pressure by 15%, heart rate by 22%, and cardiac output by 14%, and increased acceleration time of aortic root flow by 17% and stroke volume and ejection time each by 11%. Captopril reduced mean arterial pressure and total peripheral resistance each by 7%. Acceleration time of aortic root flow, ejection time, heart rate, stroke volume, and cardiac output were not significantly changed by captopril. We conclude that total arterial compliance, at the operational blood pressure, increases during selective beta1-adrenergic receptor blockade in subjects with ambulatory hypertension. Although the main mechanism may be a reduction in mean arterial pressure, it should be considered whether reduced heart rate may play an additional role. The nonsignificant increase in total arterial compliance during angiotensin-converting enzyme inhibition may primarily be a consequence of a modest reduction of the mean arterial pressure.

The heart and conduit vessels in hypertension

The heart and conduit vessels, integral components of a pulsatile pumping system, undergo complex adaptive and degenerative changes in response to the increased load of hypertension. Over the last two decades, great technological strides have been made with regards to further discovering the role of the heart and conduit vessels in hypertension. This article reviews the adaptation of the heart and vessels to hypertension, the clinical implications of these structural and functional changes, and the effects of therapy on cardiovascular function.

Arterial wave propagation phenomena, ventricular work, and power dissipation

The effects of wave propagation phenomena, namely global reflection coefficient (gamma G[omega]) and pulse wave velocity (Cph), are studied in a model of the coupled left ventricle/arterial system. The left ventricle consists of a time-varying elastance, while the arterial system is modeled as a single, uniform, elastic tube terminating in a complex load. Manipulation of model parameters allowed for the precise control of gamma G(omega) and Cph independent of each other, peripheral resistance, and characteristic impedance. Reduction of gamma G(omega) and Cph were achieved through increases in load compliance and tube compliance, respectively. The equations describing the system were solved for left ventricular and aortic pressures and aortic flow. From these, stroke volume (SV), left ventricular stroke work (SW), and steady (Ws), oscillatory (Wo), and total power dissipation (Wt) in the arterial system were calculated. An index of arterial system efficiency was the ratio Wo/Wt (%Wo), with lower values indicating higher efficiency. Reduction of gamma G(omega) yielded initial increases in Ws, while Wo increased for the entire range of gamma G(omega), resulting in increased %Wo. This reduced efficiency is imposed on the ventricle, resulting in increased SW without increased SV. On the other hand, decreased Cph yielded in a steady increase in Ws and a biphasic response in Wo, resulting in reduced %Wo for most of the range of reduced Cph. These results suggest that differential effects on arterial system efficiency can result from reductions of gamma G(omega) and Cph. In terms of compliance, changes in arterial compliance can have different effects on efficiency, depending on where the compliance change takes place. Reasons for these results are suggested, and the role of distributed compliances is raised as a new problem.

Improvement of cardiac performance by intravenous infusion of L-arginine in patients with moderate congestive heart failure

OBJECTIVES

The aim of this study was to evaluate the hemodynamic effect of L-arginine infusion in patients with congestive heart failure.

BACKGROUND

Endothelium-dependent vasodilation is impaired in patients with congestive heart failure. Nitric oxide, which was identified as endothelium-derived relaxing factor, is generated by nitric oxide synthase from L-arginine. Our hypothesis was that administration of L-arginine in patients with congestive heart failure may increase nitric oxide production and have a beneficial hemodynamic effect.

METHODS

Twelve patients with congestive heart failure (New York Heart Association class II or III) due to coronary artery disease (left ventricular ejection fraction < 35%) were given 20 g of L-arginine by intravenous infusion over 1 h at a constant rate. Stroke volume, cardiac output and left ventricular ejection fraction were determined with Doppler echocardiography at baseline and at 30 and 60 min and 1 h after the end of infusion. Blood and urinary levels of nitrite/nitrate (NO2/NO3), stable metabolites of nitric oxide, were measured and clearance was calculated.

RESULTS

One hour of infusion of L-arginine resulted in a significant increase in stroke volume (from 68 +/- 18 ml to 76 +/- 23 ml [mean +/- SD], p = 0.014) and cardiac output (from 4.07 +/- 1.22 liters/min to 4.7 +/- 1.42 liters/min, p = 0.006) without a change in heart rate. Mean arterial blood pressure decreased (from 102 +/- 11 mm Hg to 89 +/- 9.5 mm Hg, p < 0.002), and systemic vascular resistance decreased significantly. Within 1 h after cessation of L-arginine infusion, blood pressure, stroke volume, cardiac output and systemic vascular resistance were statistically not different from baseline values. Clearance of NO2/NO3 increased significantly during L-arginine administration (from 13.28 +/- 0.42 ml/min to 29.97 +/- 1.09 ml/min, p < 0.001).

CONCLUSIONS

Infusion of L-arginine in patients with congestive heart failure results in increased production of nitric oxide, peripheral vasodilation and increased cardiac output, suggesting a beneficial hemodynamic and possibly therapeutic profile.