Alicia Barrio

Contribution of the Diastolic Vortex Ring to Left Ventricular Filling

BACKGROUND Intraventricular fluid dynamics can be assessed clinically using imaging. The contribution of vortex structures to left ventricular (LV) diastolic function has never been quantified in vivo. OBJECTIVES This study sought to understand the impact of intraventricular flow patterns on filling and to assess whether impaired fluid dynamics may be a source of diastolic dysfunction. METHODS Two-dimensional flow velocity fields from color Doppler echocardiographic sequences were obtained in 20 patients with nonischemic dilated cardiomyopathy (NIDCM), 20 patients with hypertrophic cardiomyopathy (HCM), and 20 control healthy volunteers. Using a flow decomposition method, we isolated the rotational velocity generated by the vortex ring from the surrounding flow in the left ventricle. RESULTS The vortex was responsible for entering 13 ± 6% of filling volume in the control group and 19 ± 8% in the NIDCM group (p = 0.004), but only 5 ± 5% in the HCM group (p < 0.0001 vs. controls). Favorable vortical effects on intraventricular pressure gradients were observed in the control and NIDCM groups but not in HCM patients. Differences in chamber sphericity explained variations in the vortex contribution to filling between groups (p < 0.005). CONCLUSIONS The diastolic vortex is responsible for entering a significant fraction of LV filling volume at no energetic or pressure cost. Thus, intraventricular fluid mechanics are an important determinant of global chamber LV operative stiffness. Reduced stiffness in NIDCM is partially related to enhanced vorticity. Conversely, impaired vortex generation is an unreported mechanism of diastolic dysfunction in HCM and probably other causes of concentric remodeling.

A computer-based approach to the rational discovery of new trichomonacidal drugs by atom-type linear indices

Computational approaches are developed to design or rationally select, from structural databases, new lead trichomonacidal compounds. First, a data set of 111 compounds was split (design) into training and predicting series using hierarchical and partitional cluster analyses. Later, two discriminant functions were derived with the use of non-stochastic and stochastic atom-type linear indices. The obtained LDA (linear discrimination analysis)-based QSAR (quantitative structure-activity relationship) models, using non-stochastic and stochastic descriptors were able to classify correctly 95.56% (90.48%) and 91.11% (85.71%) of the compounds in training (test) sets, respectively. The result of predictions on the 10% full-out cross-validation test also evidenced the quality (robustness, stability and predictive power) of the obtained models. These models were orthogonalized using the Randic orthogonalization procedure. Afterwards, a simulation experiment of virtual screening was conducted to test the possibilities of the classification models developed here in detecting antitrichomonal chemicals of diverse chemical structures. In this sense, the 100.00% and 77.77% of the screened compounds were detected by the LDA-based QSAR models (Eq. 13 and Eq. 14, correspondingly) as trichomonacidal. Finally, new lead trichomonacidals were discovered by prediction of their antirichomonal activity with obtained models. The most of tested chemicals exhibit the predicted antitrichomonal effect in the performed ligand-based virtual screening, yielding an accuracy of the 90.48% (19/21). These results support a role for TOMOCOMD-CARDD descriptors in the biosilico discovery of new compounds.

Systemic vascular load in calcific degenerative aortic valve stenosis: insight from percutaneous valve replacement.

BACKGROUND Systemic arterial load impacts the symptomatic status and outcome of patients with calcific degenerative aortic stenosis (AS). However, assessing vascular properties is challenging because the arterial trees behavior could be influenced by the valvular obstruction. OBJECTIVES This study sought to characterize the interaction between valvular and vascular functions in patients with AS by using transcatheter aortic valve replacement (TAVR) as a clinical model of isolated intervention. METHODS Aortic pressure and flow were measured simultaneously using high-fidelity sensors in 23 patients (mean 79 ± 7 years of age) before and after TAVR. Blood pressure and clinical response were registered at 6-month follow-up. RESULTS Systolic and pulse arterial pressures, as well as indices of vascular function (vascular resistance, aortic input impedance, compliance, and arterial elastance), were significantly modified by TAVR, exhibiting stiffer vascular behavior post-intervention (all, p < 0.05). Peak left ventricular pressure decreased after TAVR (186 ± 36 mm Hg vs. 162 ± 23 mm Hg, respectively; p = 0.003) but remained at >140 mm Hg in 70% of patients. Wave intensity analysis showed abnormally low forward and backward compression waves at baseline, increasing significantly after TAVR. Stroke volume decreased (-21 ± 19%; p < 0.001) and correlated with continuous and pulsatile indices of arterial load. In the 48 h following TAVR, a hypertensive response was observed in 12 patients (52%), and after 6-month follow-up, 5 patients required further intensification of discharge antihypertensive therapy. CONCLUSIONS Vascular function in calcific degenerative AS is conditioned by the upstream valvular obstruction that dampens forward and backward compression waves in the arterial tree. An increase in vascular load after TAVR limits the procedures acute afterload relief.

Intraventricular vortex properties in nonischemic dilated cardiomyopathy

Vortices may have a role in optimizing the mechanical efficiency and blood mixing of the left ventricle (LV). We aimed to characterize the size, position, circulation, and kinetic energy (KE) of LV main vortex cores in patients with nonischemic dilated cardiomyopathy (NIDCM) and analyze their physiological correlates. We used digital processing of color-Doppler images to study flow evolution in 61 patients with NIDCM and 61 age-matched control subjects. Vortex features showed a characteristic biphasic temporal course during diastole. Because late filling contributed significantly to flow entrainment, vortex KE reached its maximum at the time of the peak A wave, storing 26 ± 20% of total KE delivered by inflow (range: 1-74%). Patients with NIDCM showed larger and stronger vortices than control subjects (circulation: 0.008 ± 0.007 vs. 0.006 ± 0.005 m(2)/s, respectively, P = 0.02; KE: 7 ± 8 vs. 5 ± 5 mJ/m, P = 0.04), even when corrected for LV size. This helped confining the filling jet in the dilated ventricle. The vortex Reynolds number was also higher in the NIDCM group. By multivariate analysis, vortex KE was related to the KE generated by inflow and to chamber short-axis diameter. In 21 patients studied head to head, Doppler measurements of circulation and KE closely correlated with phase-contract magnetic resonance values (intraclass correlation coefficient = 0.82 and 0.76, respectively). Thus, the biphasic nature of filling determines normal vortex physiology. Vortex formation is exaggerated in patients with NIDCM due to chamber remodeling, and enlarged vortices are helpful for ameliorating convective pressure losses and facilitating transport. These findings can be accurately studied using ultrasound.

Validation of Noninvasive Indices of Global Systolic Function in Patients With Normal and Abnormal Loading Conditions A Simultaneous Echocardiography Pressure-Volume Catheterization Study

Background—Noninvasive indices based on Doppler echocardiography are increasingly used in clinical cardiovascular research to evaluate left ventricular global systolic chamber function. Our objectives were to clinically validate ultrasound-based methods of global systolic chamber function to account for differences between patients in conditions of abnormal load, and to assess their sensitivity to load confounders. Methods and Results—Twenty-seven patients (8 dilated cardiomyopathy, 10 normal ejection fraction, and 9 end-stage liver disease) underwent simultaneous echocardiography and left heart catheterization with pressure-conductance instrumentation. The reference index, maximal elastance (Emax), was calculated from pressure–volume loop data obtained during acute inferior vena cava occlusion. A wide range of values were observed for left ventricular systolic chamber function (Emax: 2.8±1.0 mm Hg/mL), preload, and afterload. Among the noninvasive indices tested, the peak ejection intraventricular pressure difference showed the best correlation with Emax (R=0.75). A significant but weaker correlation with Emax was observed for ejection fraction (R=0.41), midwall fractional shortening (R=0.51), global circumferential strain (R=−0.53), and strain rate (R=−0.46). Longitudinal strain and strain rate failed to correlate with Emax, as did noninvasive single-beat estimations of this index. Principal component and multiple regression analyses demonstrated that peak ejection intraventricular pressure difference was less sensitive to load, whereas ejection fraction and longitudinal strain and strain rate were heavily influenced by afterload. Conclusions—Current ultrasound methods have limited accuracy to characterize global left ventricular systolic chamber function in a given patient. The Doppler-derived peak ejection intraventricular pressure difference should be preferred for this purpose because it best correlates with the reference index and is more robust in conditions of abnormal load.

Noninvasive Estimation of the Rate of Relaxation by the Analysis of Intraventricular Pressure Gradients

Background—During late ejection, myocardial relaxation causes systolic flow to decelerate and stop, and this phenomenon is coupled with the generation of a pressure gradient inside the left ventricle (LV). We hypothesized that the peak reverse ejection intraventricular pressure difference (REIVPD) between the LV apex and the outflow tract could be a useful method to improve the assessment of LV relaxation using Doppler echocardiography. Methods and Results—Three sets of animal experiments and 1 clinical study were designed. In 6 pigs, a close relationship between REIVPD and the intensity of the relaxation wave (Rrm=0.89) was demonstrated using wave intensity analysis of high-fidelity pressure-volume-velocity data. In 19 animals, REIVPD sensitively detected modifications of the lusotropic state and closely correlated with the time constant of LV relaxation (&tgr;) within animals (Rrm=−0.93). Load-dependence analysis in 5 pigs showed that REIVPD remained stable up to values of 35% to 40% acute preload reduction. Clinical validation was tested in 50 patients (23 with normal systolic function) undergoing simultaneous Doppler echocardiography and high-fidelity LV pressure measurements on the same beat. REIVPD and tissue Doppler mitral annulus velocity (e′) were independently related to &tgr;, but the REIVPD · e′ product correlated better with &tgr; than either variable separately (bootstrap-corrected correlation coefficients: R=−0.84 versus −0.71, and −0.70, respectively, P<0.05). Area under the receiver operating characteristic curve to predict impaired relaxation (&tgr;>50 ms) for e′ · REIVPD was 0.96 (95% confidence interval, 0.85 to 0.99). Conclusions—The Doppler-derived REIVPD provides a sensitive, reliable, reproducible, and relatively load-independent index of the rate of LV relaxation. Combined with tissue Doppler measurements of longitudinal function, this method improves noninvasive assessment of LV relaxation in the clinical setting.

Diastolic chamber properties of the left ventricle assessed by global fitting of pressure-volume data: improving the gold standard of diastolic function

In cardiovascular research, relaxation and stiffness are calculated from pressure-volume (PV) curves by separately fitting the data during the isovolumic and end-diastolic phases (end-diastolic PV relationship), respectively. This method is limited because it assumes uncoupled active and passive properties during these phases, it penalizes statistical power, and it cannot account for elastic restoring forces. We aimed to improve this analysis by implementing a method based on global optimization of all PV diastolic data. In 1,000 Monte Carlo experiments, the optimization algorithm recovered entered parameters of diastolic properties below and above the equilibrium volume (intraclass correlation coefficients = 0.99). Inotropic modulation experiments in 26 pigs modified passive pressure generated by restoring forces due to changes in the operative and/or equilibrium volumes. Volume overload and coronary microembolization caused incomplete relaxation at end diastole (active pressure > 0.5 mmHg), rendering the end-diastolic PV relationship method ill-posed. In 28 patients undergoing PV cardiac catheterization, the new algorithm reduced the confidence intervals of stiffness parameters by one-fifth. The Jacobian matrix allowed visualizing the contribution of each property to instantaneous diastolic pressure on a per-patient basis. The algorithm allowed estimating stiffness from single-beat PV data (derivative of left ventricular pressure with respect to volume at end-diastolic volume intraclass correlation coefficient = 0.65, error = 0.07 ± 0.24 mmHg/ml). Thus, in clinical and preclinical research, global optimization algorithms provide the most complete, accurate, and reproducible assessment of global left ventricular diastolic chamber properties from PV data. Using global optimization, we were able to fully uncouple relaxation and passive PV curves for the first time in the intact heart.

New Antitrichomonal Drug-like Chemicals Selected by Bond (Edge)-Based TOMOCOMD-CARDD Descriptors

Bond-based quadratic indices, new TOMOCOMD-CARDD molecular descriptors, and linear discriminant analysis (LDA) were used to discover novel lead trichomonacidals. The obtained LDA-based quantitative structure-activity relationships (QSAR) models, using nonstochastic and stochastic indices, were able to classify correctly 87.91% (87.50%) and 89.01% (84.38%) of the chemicals in training (test) sets, respectively. They showed large Matthews correlation coefficients of 0.75 (0.71) and 0.78 (0.65) for the training (test) sets, correspondingly. Later, both models were applied to the virtual screening of 21 chemicals to find new lead antitrichomonal agents. Predictions agreed with experimental results to a great extent because a correct classification for both models of 95.24% (20 of 21) of the chemicals was obtained. Of the 21 compounds that were screened and synthesized, 2 molecules (chemicals G-1, UC-245) showed high to moderate cytocidal activity at the concentration of 10 μg/ml, another 2 compounds (G-0 and CRIS-148) showed high cytocidal activity only at the concentration of 100 μg/ml, and the remaining chemicals (from CRIS-105 to CRIS-153, except CRIS-148) were inactive at these assayed concentrations. Finally, the best candidate, G-1 (cytocidal activity of 100% at 10 μg/ml) was in vivo assayed in ovariectomized Wistar rats achieving promising results as a trichomonacidal drug-like compound. (Journal of Biomolecular Screening 2008:785-794).

Validation of a modified fluorimetric assay for the screening of trichomonacidal drugs

A fluorimetric microassay that uses a redox dye to determine the viability of the flagellate Trichomonas vaginalis has been optimised to provide a more sensitive method to evaluate potential trichomonacidal compounds. Resazurin has been used in recent years to test drugs against different parasites, including trichomonadid protozoa; however, the reproducibility of these resazurin-based methods in our laboratory has been limited because the flagellate culture medium spontaneously reduces the resazurin. The objective of this work was to refine the fluorimetric microassay method previously developed by other research groups to reduce the fluorescence background generated by the media and increase the sensitivity of the screening assay. The experimental conditions, time of incubation, resazurin concentration and media used in the microtitre plates were adjusted. Different drug sensitivity studies against T. vaginalis were developed using the 5-nitroimidazole reference drugs, new 5-nitroindazolinones and 5-nitroindazole synthetic derivatives. Haemocytometer count results were compared with the resazurin assay using a 10% solution of 3 mM resazurin dissolved in phosphate buffered saline with glucose (1 mg/mL). The fluorimetric assay and the haemocytometer counts resulted in similar percentages of trichomonacidal activity in all the experiments, demonstrating that the fluorimetric microtitre assay has the necessary accuracy for high-throughput screening of new drugs against T. vaginalis.

The role of elastic restoring forces in right ventricular filling

AIMS The physiological determinants of RV diastolic function remain poorly understood. We aimed to quantify the contribution of elastic recoil to RV filling and determine its sensitivity to interventricular interaction. METHODS AND RESULTS High-fidelity pressure-volume loops and simultaneous 3-dimensional ultrasound sequences were obtained in 13 pigs undergoing inotropic modulation, volume overload, and acute pressure overload induced by endotoxin infusion. Using a validated method, we isolated elastic restoring forces from ongoing relaxation using conventional pressure-volume data. The RV contracted below the equilibrium volume in >75% of the data sets. Consequently, elastic recoil generated strong sub-atmospheric passive pressure at the onset of diastole [-3 (-4 to -2) mmHg at baseline]. Stronger restoring suction pressure was related to a shorter isovolumic relaxation period, a higher rapid filling fraction, and lower atrial pressures (all P < 0.05). Restoring forces were mostly determined by the position of operating volumes around the equilibrium volume. By this mechanism, the negative inotropic effect of beta-blockade reduced and sometimes abolished restoring forces. During acute pressure overload, restoring forces initially decreased, but recovered at advanced stages. This biphasic response was related to alterations of septal curvature induced by changes in the diastolic LV-RV pressure balance. The constant of elastic recoil was closely related to the constant of passive stiffness (R = 0.69). CONCLUSION The RV works as a suction pump, exploiting contraction energy to facilitate filling by means of strong elastic recoil. Restoring forces are influenced by the inotropic state and RV conformational changes mediated by direct ventricular interdependence.