Régis Rieu

Impact of systemic hypertension on the assessment of aortic stenosis

Objective: To determine the effect of systemic arterial hypertension on the indices of aortic stenosis (AS) severity. Methods: A severe supravalvar AS was created in 24 pigs. The maximum and mean pressure gradients across the stenosis were measured by Doppler echocardiography and by catheterisation. Both echocardiography and catheter data were used to calculate stenosis effective orifice area, energy loss coefficient, and peak systolic left ventricular wall stress. Measurements were taken both at normal aortic pressures and during hypertension induced by banding of the distal thoracic aorta in 14 pigs and by intravenous administration of phenylephrine in 10 pigs. Results: During hypertension, systemic arterial resistance downstream from the stenosis increased greatly (all animals: 71 (40)%), whereas total systemic arterial compliance decreased significantly (−38 (21)%). Hypertension resulted in a moderate increase in effective orifice area (29 (14)%) and energy loss coefficient (25 (17)%) and substantial decreases in catheter gradients (maximum: −40 (20)%; mean: −43 (20)%; peak to peak: −70 (23)%) and Doppler gradients (maximum: −35 (17)%; mean: −37 (16)%). In multivariate analysis, peak to peak gradient was significantly (p < 0.001) related to the energy loss coefficient, mean flow rate, and arterial compliance, whereas maximum and mean catheter gradients were related only to the energy loss coefficient and flow rate. Of major importance, maximum systolic left ventricular wall stress increased greatly during hypertension (43 (23)%). Conclusions: The severity of AS may be partially masked by the presence of coexisting hypertension. The markers of AS severity should thus be interpreted with caution in hypertensive patients and be re-evaluated when the patient is in a normotensive state.

Long-term Results with the Palmaz Stent in the Superficial Femoral Artery

Purpose: Femoral stenting has demonstrated inconsistent and often disappointing long-term results. To compare our experience, we retrospectively analyzed a series of patients who had Palmaz balloon-expandable stents placed exclusively for superficial femoral artery (SFA) lesions. Methods: From January 1990 to November 1993, 39 patients were evaluated for claudication (79%) or critical ischemia in 42 limbs. The culprit lesions were confined to the SFA: 24 (57%) occlusions and 18 (43%) stenoses, including 3 restenotic lesions. Stenting was elective in 12 (29%) cases: the 3 restenoses and 9 chronic, calcified occlusions. The remaining stents were applied for postangioplasty residual stenosis or angioscopic findings of thrombogenic luminal irregularities. A total of 55 prostheses were successfully implanted. All patients were maintained on ticlopidine and followed by routine duplex scanning. Follow-up angiography was performed in 28 (72%) patients between 4 and 45 months. Results: In the postprocedural period, two acute thromboses (4.8%) occurred within 48 hours in patients who had long occlusions and poor runoff; no other major complications were encountered, for a clinical success rate of 95%. Follow-up evaluation ranged from 4 months to 4 years with a mean of 25 months. The restenosis rate was 19% (34% in occlusions; 10% in stenotic lesions, p = NS). At 24 months, cumulative primary patency was 77% and secondary patency 89%. Conclusions: Palmaz stents performed well in the SFA, demonstrating a low acute thrombosis rate and good long-term patency. The incidence of restenosis is likely to be greater in occlusions than in stenoses.

Effects of cryopreservation on the viscoelastic properties of human arteries.

The purpose of this study was to use our newly developed mock circulation loop to determine the effects of cryopreservation on the common carotid artery (CCA) and the superficial femoral artery (SFA). Fourteen healthy arteries (7 CCA and 7 SFA) harvested from multiple organ donors between the ages of 18 and 35 years were tested before and after cryopreservation at −140° C using dimethyl sulfoxide and the vapor phase of liquid nitrogen. Mean storage time was 4.2 months. The mock pulse rate was 60 beats/min and the following four systolic/diastolic pressures settings were used: 50/110, 80/140, 110/170, and 140/200 mm Hg. Simultaneous measurements of intra-arterial pressure and external arterial diameter were made using an intra-arterial pressure sensor and external piezoelectric sensors. Measured data were used to calculate pulsatility, volumetric compliance, stiffness, midwall radial arterial stress, Youngs modulus, and the incremental modulus. After SFA cryopreservation, no significant changes were observed. Conversely, CCA cryopreservation led to a significant decrease in compliance and pulsatility and a significant increase in stiffness. Youngs modulus, the incremental modulus, and midwall radial arterial stress did not change significantly. A clearcut decrease in hysteresis was observed after cryopreservation in the CCA. No evidence of structural changes was detected on light and scanning electron microscopy. Baseline findings in this study were consistent with classification of the CCA as an elastic artery and the SFA as a muscular artery. Cryopreservation had no effect on the viscoelastic properties of muscular arteries (SFA). Cryopreservation affected only values related to the cylindrical shape of the elastic arteries (CCA). It had no effect on values related to wall structure.

In vitro cytotoxicity of dental adhesive systems under simulated pulpal pressure

OBJECTIVES Most of the devices used to evaluate the cytotoxicity of resin-based composites in vitro use a dentin barrier test. However, it is difficult to obtain the number of freshly extracted teeth, all on the same day, that is necessary for powerful statistical analysis. Tooth cryopreservation provides a way to build up a supply of teeth. This in vitro study compared cryopreserved teeth and freshly extracted teeth in an evaluation of the cytotoxicity of resin-based composites. In addition, this study also evaluated the effects of pulsatile pressure and the importance of dentin permeability on the cytotoxic response to bonding resins. METHODS Forty freshly extracted and forty cryopreserved third molars were used. A standardized Class I cavity was prepared within the dentin. The hydraulic conductance of each tooth was recorded. The cavities were filled either with Scotchbond Multi-Purpose Plus and Z 100 (3M Dental Products) or with Optibond and Herculite (Kerr). A plexiglas device was designed to permit 24 h long contact between culture medium and the roof of the pulp chamber while a pulsatile pulpal pressure was simulated. The viability of L 929 cells cultured with a control medium and evaluated by an MTT assay was compared to that of L 929 cells cultured with medium which remained for 24 h in contact with the pulp chamber of restored teeth. A three-way ANOVA was used to compare the cytotoxicity among the different groups. A simple least-squares linear regression was used to seek a relationship between the hydraulic conductance of dentin and the cytotoxicity of composite restorative materials. RESULTS No significant differences in cytotoxicity were found between the freshly extracted teeth and the cryopreserved teeth (p = 0.53). The cytotoxicity of the resin adhesives was statistically higher when a pulsatile pulpal pressure was simulated (p = 0.04). A significant relationship was found between the hydraulic conductance of dentin and the cytotoxicity of resin-based composites (p = 0.02). SIGNIFICANCE Cryopreserved teeth can be used for in vitro evaluation of the cytotoxicity of resin adhesives. Pulsatile pulpal pressure simulations increased the in vitro cytotoxicity of the tested materials.

Velocity distribution along an elastic model of human arterial tree

An experimental investigation of an elastic model of the human arterial tree, has been performed for physiological type flow by pulsed Doppler ultrasonic velocimetry. The arterial tree model, fabricated in clear polyurethane, includes the aortic arch, with a Starr-Edwards ball valve mounted in the root of the aorta, the descending aorta and the iliac bifurcation. Our study showed that the velocity profile, a few centimeters beyond the valve, is skewed, with higher velocities towards the top and the inner wall (anatomically the posterior and left lateral wall). An inward shift of the maximum velocity and reverse flow are denoted along the inner wall of the aortic arch. The velocity profiles in the descending aorta are blunted. Downstream from the vertex of the iliac bifurcation, there is vorticity creation, but the branching effect is quickly damped by the pulsatility of the flow and the elasticity of the wall.

Doppler Vortography: A Color Doppler Approach to Quantification of Intraventricular Blood Flow Vortices

We propose a new approach to quantification of intracardiac vorticity based on conventional color Doppler images -Doppler vortography. Doppler vortography relies on the centrosymmetric properties of the vortices. Such properties induce particular symmetries in the Doppler flow data that can be exploited to describe the vortices quantitatively. For this purpose, a kernel filter was developed to derive a parameter, the blood vortex signature (BVS), that allows detection of the main intracardiac vortices and estimation of their core vorticities. The reliability of Doppler vortography was assessed in mock Doppler fields issued from simulations and in vitro data. Doppler vortography was also tested in patients and compared with vector flow mapping by echocardiography. Strong correlations were obtained between Doppler vortography-derived and ground-truth vorticities (in silico: r2 = 0.98, in vitro: r2 = 0.86, in vivo: r2 = 0.89). Our results indicate that Doppler vortography is a potentially promising echocardiographic tool for quantification of vortex flow in the left ventricle.

Influence of tooth cryopreservation on human dentin permeability, in vitro

OBJECTIVES In order to use cryopreserved teeth in laboratory studies, cryopreservation must not modify the functional properties of teeth, in particular dentin permeability. The purpose of this study was to evaluate the effects of tooth cryopreservation on human dentin permeability. METHODS Three hundred and sixty freshly extracted human noncarious third molars were used. The teeth were randomly assigned to two groups: 180 teeth were stored in phosphate-buffered saline at 4 degrees C and tested within 4 h of collection; 180 teeth were cryopreserved. Hydraulic conductance was calculated according to the method developed by Pashley (Outhwaite et al., 1976). RESULTS Cryopreserved teeth presented a hydraulic conductance of 8.97 x 10(-3) +/- 4.21 x 10(-3) microL.cm-2.min-1.cm.H(2)0(-1) slightly higher than the hydraulic conductance of the freshly extracted teeth of 8.03 x 10(-3) +/- 3.87 x 10(-3) microL.cm-2.min-1.cm.H(2)0(-1). No statistically significant difference was found between the two groups. SIGNIFICANCE Under the conditions of this study, cryopreservation did not modify dentin permeability.

Hemodynamic impact of mitral prosthesis-patient mismatch on pulmonary hypertension : an in silico study

Recent clinical studies reported that prosthesis-patient mismatch (PPM) becomes clinically relevant when the effective orifice area (EOA) indexed by the body surface area (iEOA) is <1.2-1.25 cm(2)/m(2). To examine the effect of PPM on transmitral pressure gradient and left atrial (LA) and pulmonary arterial (PA) pressures and to validate the PPM cutoff values, we used a lumped model to compute instantaneous pressures, volumes, and flows into the left-sided heart and the pulmonary and systemic circulations. We simulated hemodynamic conditions at low cardiac output, at rest, and at three levels of exercise. The iEOA was varied from 0.44 to 1.67 cm(2)/m(2). We normalized the mean pressure gradient by the square of mean mitral flow indexed by the body surface area to determine at which cutoff values of iEOA the impact of PPM becomes hemodynamically significant. In vivo data were used to validate the numerical study, which shows that small values of iEOA (severe PPM) induce high PA pressure (residual PA hypertension) and contribute to its nonnormalization following a valve replacement, providing a justification for implementation of operative strategies to prevent PPM. Furthermore, we emphasize the major impact of pulmonary resistance and compliance on PA pressure. The model suggests also that the cutoff iEOA that should be used to define PPM at rest in the mitral position is approximately 1.16 cm(2)/m(2). At higher levels of exercise, the threshold for iEOA is rather close to 1.5 cm(2)/m(2). Severe PPM should be considered when iEOA is <0.94 cm(2)/m(2) at rest.

In vitro study of a physiological type flow in a bifurcated vascular prosthesis

Using a cardiovascular simulator allowing the production of physiological conditions, velocity field and pressure-diameter relationship were determined in a bifurcated arterial graft for two geometric configurations of implantation. Velocity measurements give the surgeon attractive and useful information for finding out the best way to implant the graft. The study of the pressure-diameter relationship showed a particular behaviour of the graft; the wall motion of the graft, compared with the pressure wave, being different both in the mother branch at the upstream anastomosis and in the daughter branch.

Effect of oversizing and elliptical shape of aortic annulus on transcatheter valve hemodynamics: An in vitro study

BACKGROUND Transcatheter aortic valve implantation (TAVI) is often performed in patients with non-circular aortic annulus and in oversizing (OS) conditions. The impact of elliptical annulus shape and the consequences of oversizing/underdeployment on the hemodynamic performance are still debated. OBJECTIVE This in-vitro study aims to assess and compare the valve hemodynamic performances of the Edwards SAPIEN transcatheter heart valve (THV) in the different current conditions of use: important oversizing in small circular annuli and in elliptical annuli, moderate oversizing in circular and in elliptical annuli of various degrees of eccentricity. METHODS A pulsed cardiovascular simulator was used. Edwards SAPIEN 23 and 26 (mm) were implanted in different circular and elliptical annuli of various sizes and eccentricity. Transvalvular mean pressure gradients (TPGm), effective orifice area (EOA) after implantation of Edwards SAPIEN THV were measured by Doppler-echocardiography and the performance index (PI=100 × EOA/Annulus Area) was calculated. Para and transvalvular regurgitation was assessed by color-Doppler and leakage volume was quantified by flowmeter measurement. RESULTS For a given aortic annulus area, EOAs after implantation of Edwards SAPIEN THV were generally larger and TPGms lower with elliptical annuli compared to circular annuli. The PI was higher (p=0.047) for elliptical (48 ± 3%) than for circular annuli (43 ± 5%). Paravalvular regurgitation occurred only in the case of the SAPIEN 26 implanted in the elliptical annulus with highest eccentricity. CONCLUSION The results of this in-vitro study suggest that the EOAs of Edwards SAPIEN are better in elliptical than in circular annuli. No transvalvular regurgitation occurred and only one paravalvular regurgitation was observed after implantation of SAPIEN 26 in the highly eccentric annulus.