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Biomedical subjects

M R de Leval

Publications and source records attributed to M R de Leval.

At least 19 recordsLinked to original sources
PubMed2001

Double orifice right atrioventricular valve in atrioventricular septal defect: morphology and extension of the concept of fusion of leaflets.

A rare observation of a double orifice right atrioventricular valve in a partial form of atrioventricular septal defect is reported. The concept of leaflet fusion along part of their anticipated zones of apposition is used to explain the formation of this anomaly. We show that this concept can account for the different morphologic presentations of atrioventricular septal defect.

Adult↗
PubMed2000

Effects of respiration and gravity on infradiaphragmatic venous flow in normal and Fontan patients.

BACKGROUND: In the Fontan circulation, pulmonary and systemic vascular resistances are in series. The implications of this unique arrangement on infradiaphragmatic venous physiology are poorly understood. METHODS AND RESULTS: We studied the effects of respiration and gravity on infradiaphragmatic venous flows in 20 normal healthy volunteers (control) and 48 Fontan patients (atriopulmonary connection [APC] n=15, total cavopulmonary connection [TCPC] n=30). Hepatic venous (HV), subhepatic inferior vena caval (IVC), and portal venous (PV) flow rates were measured with Doppler ultrasonography during inspiration and expiration in both the supine and upright positions. The inspiratory-to-expiratory flow rate ratio was calculated to reflect the effect of respiration, and the supine-to-upright flow rate ratio was calculated to assess the effect of gravity. HV flow depended heavily on inspiration in TCPC compared with both control and APC subjects (inspiratory-to-expiratory flow rate ratio 3.4, 1.7, and 1.6, respectively; P:<0.0001). Normal PV flow was higher in expiration, but this effect was lost in TCPC and APC patients (inspiratory-to-expiratory flow rate ratio 0.8, 1.0, and 1.1, respectively; P:=0.01). The respiratory influence on IVC flow was the same in all groups. Gravity decreased HV flow more in APC than in TCPC patients (supine-to-upright flow rate ratio 3.2 versus 2.1, respectively; P:<0.04) but reduced PV flow equally in all groups. CONCLUSIONS: Gravity and respiration have important influences on infradiaphragmatic venous return in Fontan patients. Although gravity exerts a significant detrimental effect on lower body venous return, which is more marked in APC than in TCPC patients, the beneficial effects of respiration in TCPC patients are mediated primarily by an increase in HV flow. These effects may have important short- and long-term implications for the hemodynamics of the Fontan circulation.

Adolescent↗
PubMed2000

Use of mathematical model to predict hemodynamics in cavopulmonary anastomosis with persistent forward flow.

BACKGROUND: The bidirectional cavopulmonary anastomosis with additional pulmonary blood flow is used as a staged procedure or a definitive palliation of univentricular hearts. In this paper the flow competition occurring between the caval and the pulmonary flows is investigated. The hemodynamics in the superior vena cava and the blood flow distribution into the lungs, as well as the systemic arterial oxygen availability, are correlated with the severity of the right ventricle outflow tract obstruction and the pulmonary arteriolar resistance. MATERIALS AND METHODS: Computer models of the pre- and postoperative hemodynamics of univentricular hearts were developed. The effects of increasing severity of the right ventricle outflow tract obstruction, with a pulmonary arteriolar resistance ranging from 0.8 to 7.9 nonindexed Woods units, were simulated. RESULTS: The study indicates that the presence of an additional pulmonary blood flow from the native pulmonary artery may be beneficial. Since an excessive additional blood flow may cause central venous hypertension, its optimal value should be chosen according to the value of pulmonary arteriolar resistance. The model was utilized to simulate four clinical cases. CONCLUSIONS: The simulations show that the model can predict the postoperative hemodynamics and could therefore be usefully applied to predict quantitatively the effect of the native pulmonary blood flow following bidirectional cavopulmonary anastomosis.

Anastomosis, Surgical↗
PubMed2000

Computational model of the fluid dynamics in systemic-to-pulmonary shunts.

A systemic-to-pulmonary shunt is a connection created between the systemic and pulmonary arterial circulations in order to improve pulmonary perfusion in children with congenital heart diseases. Knowledge of the relationship between pressure and flow in this new, surgically created, cardiovascular district may be helpful in the clinical management of these patients, whose survival is critically dependent on the blood flow distribution between the pulmonary and systemic circulations. In this study a group of three-dimensional computational models of the shunt have been investigated under steady-state and pulsatile conditions by means of a finite element analysis. The model is used to quantify the effects of shunt diameter (D), curvature, angle, and pulsatility on the pressure-flow (DeltaP-Q) relationship of the shunt. Size of the shunt is the main regulator of pressure-flow relationship. Innominate arterial diameter and angles of insertion have less influence. Curvature of the shunt results in lower pressure drops. Inertial effects can be neglected. The following simplified formulae are derived: DeltaP=(0. 097Q+0.521Q(2))/D(4) and DeltaP=(0.096Q+0.393Q(2))/D(4) for the different shunt geometries investigated (straight and curved shunts, respectively).

Blood Circulation↗
PubMed2000

Human factors and cardiac surgery: a multicenter study.

OBJECTIVE: To study the role of human factors on surgical outcomes, with a series of 243 arterial switch operations performed by 21 surgeons taken as a model. METHODS: The following data were collected: patient-specific and procedural variables, self-assessment questionnaires, and a written report from a human factors researcher who observed the operation. The relationship of patient-specific variables to outcomes (death and death and/or near miss) was used to develop a multivariable baseline model to analyze the role of human factors after adjustment for these variables. RESULTS: The overall mortality was 6.6% with 24.3% of cases resulting in death and death and/or near misses. The self-assessment questionnaires were found to be unhelpful. Major and minor human failures were extracted from the written report. Major negative events were potentially life-threatening failures, whereas minor events were failures that, in isolation, were not expected to have serious consequences. Major events were closely related to death (P <.001) and death and/or near misses (P <.001). Appropriate compensation, however, sharply reduced the risk of death (P =.003). The total number of minor events was also closely related to both death and death and/or near misses (P <.001). CONCLUSION: The study highlights the role of human factors in negative surgical outcomes. Even in the most eventful circumstances, however, appropriate human factors defense mechanisms can lead to a successful outcome.

Cardiac Surgical Procedures↗
PubMed2000

Calculating blood flow from Doppler measurements in the systemic-to-pulmonary artery shunt after the Norwood operation: a method based on computational fluid dynamics.

Hypoplastic left heart syndrome is currently the most lethal cardiac malformation of the newborn infant. Survival following a Norwood operation depends on the balance between systemic and pulmonary blood flow, which is highly dependent on the fluid dynamics through the interposition shunt between the two circulations. We used computational fluid dynamic (CFD) models to determine the velocity profile in a systemic-to-pulmonary artery shunt and suggested a simplified method of calculating the blood flow in the shunt based on Doppler measurements. CFD models of systemic-to-pulmonary shunts based on the finite element method were studied. The size of the shunt has been varied from 3 to 5 mm. Velocity profiles at proximal and distal positions were evaluated and correlations between maximum and mean spatial velocity were found. Twenty-one Doppler measurements in the proximal and distal part of the shunt were obtained from six patients with hypoplastic left heart syndrome. Combining Doppler velocities and CFD velocity profiles, blood flow rate in the shunt was calculated. Flow rate evaluated from aortic Doppler and oxygen saturation measurements were performed for comparison. Results showed that proximal shunt Doppler velocities were always greater than the correspondent distal ones (ratio equal to 1.15 +/- 0.11). CFD models showed a similar behaviour (ratio equal to 1.21 +/- 0.03). CFD models gave a V(mean)/V(max) ratio of 0. 480 at the proximal junction and of 0.579 at the distal one. The agreement between the flow evaluated in the proximal and distal areas of the shunt was good (0.576 +/- 0.150 vs. 0.610 +/- 0.166 l/min). Comparison of these data with saturation data and aortic Doppler measurements correlate less well (0.593 +/- 0.156 vs. 1.023 +/- 0.493 l/min). A formula easily to quantify shunt flow rate is proposed. This could be used to evaluate the effects of different therapeutic and pharmacological manoeuvres in this unique circulation.

Anastomosis, Surgical↗
PubMed1999

Computational fluid dynamic simulations of cavopulmonary connections with an extracardiac lateral conduit.

Complex congenital heart defects due to the absence of a ventricular chamber can often be treated by the Fontan surgical procedure. The objective of this work was to quantify the haemodynamics in the Fontan operation (cavopulmonary connection) with extracardiac lateral conduit. Four different models based on the finite element method were constructed with different lengths of inferior anastomosis (range 18-25 mm) and inclinations of the conduit (33 and 47.5 degrees). Mass conservation and Navier-Stokes equations were solved by means of the FIDAP code, based on the finite element method. The left-to-right pulmonary flow ratio and percentage inferior caval blood to the left lung were the highest with the smallest anastomosis and highest inclination: 1.35 and 83.26%, respectively. Dissipated power percentage was higher with the largest anastomosis than with the smallest (19.4 vs 15.8%). It was concluded that, when performing a total cavopulmonary connection, an extracardiac lateral conduit: (i) diverts more flow to the left lung, and (ii) shows higher energy losses when compared with a connection with intra-atrial tunnel. This study could be useful to evaluate the incidence of pulmonary arteriovenous malformations.

Arteriovenous Shunt, Surgical↗
PubMed1999

Computational fluid dynamic and magnetic resonance analyses of flow distribution between the lungs after total cavopulmonary connection.

Total cavopulmonary connection is a surgical procedure adopted to treat complex congenital malformations of the right heart. It consists basically in a connection of both venae cavae directly to the right pulmonary artery. In this paper a three-dimensional model of this connection is presented, which is based on in vivo measurements performed by means of magnetic resonance. The model was developed by means of computational fluid dynamics techniques, namely the finite element method. The aim of this study was to verify the capability of such a model to predict the distribution of the blood flow into the pulmonary arteries, by comparison with in vivo velocity measurements. Different simulations were performed on a single clinical case to test the sensitivity of the model to different boundary conditions, in terms of inlet velocity profiles as well as outlet pressure levels. Results showed that the flow distribution between the lungs is slightly affected by the shape of inlet velocity profiles, whereas it is influenced by different pressure levels to a greater extent.

Adolescent↗
PubMed1998

Primary arterial switch operation for transposition of the great arteries with intact ventricular septum in infants older than 21 days.

OBJECTIVES: The aim of this study was to assess the surgical outcome of the primary arterial switch operation (ASO) in infants 3 weeks to 2 months old. BACKGROUND: The surgical management of transposition of the great arteries and intact ventricular septum (TGA/IVS) beyond 2 to 3 weeks of age is controversial. Concern that regression of the left ventricular (LV) myocardial mass will render the left ventricle incapable of coping with the acutely increased work of systemic perfusion has been considered a contraindication to a primary ASO. METHODS: We used retrospective analysis of 37 patients 3 weeks to 2 months old and 156 patients <3 weeks old who underwent primary ASO with TGA/IVS to determine the surgical outcomes. RESULTS: Between January 1990 and December 1996, primary ASO was performed in 37 patients 21 to 61 days old (late ASO group) and 156 patients <21 days old (early ASO group) with TGA/IVS. One (2.7%, 95% confidence interval [CI] 0.07% to 14.2%) of 37 patients and 13 (8.3%, 95% CI 4.5% to 13.8%) of 156 patients died. One late death occurred in each group. Mechanical LV support was required in 1 (2.7%, 95% CI 0.07% to 14.2%) of 37 late ASO and 6 (3.8%, 95% CI 1.4% to 8.2%) of 156 early ASO group patients postoperatively. Neither death nor the need for mechanical LV support in the late ASO group patients could be attributed to LV failure. In the late ASO group, age, LV geometry, LV mass index, LV posterior wall thickness index, LV volume index, LV mass/volume ratio, patent arterial duct or pattern of coronary anatomy did not predict death, duration of postoperative ventilation or inotropic support or time in intensive care. Moreover, there was no difference in duration of ventilation, duration of inotropic support or the time spent in intensive care in comparison to a random sample of 37 neonates from the early ASO group. CONCLUSIONS: Primary ASO may be appropriate treatment for infants with TGA/IVS < or = 2 months old, regardless of preoperative echocardiographic variables. The upper age limit for which primary ASO is indicated in TGA/IVS is not yet defined.

Age Factors↗
PubMed1997

Outcomes after delayed sternal closure in pediatric heart operations: a 10-year experience.

BACKGROUND: Open heart operations in young children may lead to myocardial swelling and increased lung water. Decreased intrathoracic space may then make sternal closure difficult. Delayed sternal closure may be beneficial in this setting. Potential risks of delayed sternal closure are sepsis and sternal instability. METHODS: To assess these risks, we reviewed retrospectively 150 consecutive children who underwent delayed sternal closure after repair of complex congenital cardiac defects. RESULTS: Diagnoses included transposition of the great arteries (66), total anomalous pulmonary venous drainage (11), and complete atrioventricular septal defects (10). Age at operation was 229 +/- 51 days (mean +/- standard error of mean). Sixteen patients required extracorporeal membrane oxygenation. Survival was 88% (133 patients). The sternum was left open for 3.86 +/- 0.29 days. Fifteen patients had minor wound infections requiring antibiotics. No patient required reexploration for mediastinitis and no patient had an unstable sternum. CONCLUSIONS: Delayed sternal closure with sternal stenting and silicone membrane skin closure is a safe procedure in infants and children with compromised cardiac output after repair of congenital cardiac defects.

Cardiac Surgical Procedures↗
PubMed1997

Atrioventricular septal defect and tetralogy of Fallot: a 15-year experience.

AIM: Atrioventricular septal defect and tetralogy of Fallot is a relatively uncommon lesion in which there is a risk of right ventricular dysfunction related to inlet and outlet valve problems. For this reason, conservative management involving an initial palliative procedure is often chosen. The aim of this report is to retrospectively review our experience with this lesion. PATIENT POPULATION: 35 patients with atrioventricular septal defect and tetralogy of Fallot have been surgically managed at this institution between January 1980 and June 1995. Twenty-one (60%) of these patients underwent 28 initial palliative shunt procedures. Fourteen (40%) patients underwent primary definitive repair. The criteria for choosing one management strategy over another was based on a number of factors, including age at presentation, anatomy of the lesion, and severity of symptoms. Of the 21 patients who underwent an initial shunt procedure, 15 have undergone definitive operation. Of the 6 patients who did not undergo definitive operation, three died (two directly related to complications of the shunt procedure), two are awaiting operation, and one was lost to follow-up. RESULTS: The primary indication for operation in all patients was cyanosis. Freedom from reoperation at 5 years after definitive operation was 65.1% for all patients; most reoperations were related to left atrioventricular valve regurgitation or residual leaks across the ventricular septal defect patch. The operative mortality at definitive operation was 10.3% (70% CL 4.5-20%) for all patients. The actuarial estimate of survival 7 years following definitive repair was 77.3% (70% CL 68.7-85.9%) for all patients. The actuarial estimate of survival at 7 years was 84.4% (70% CL 73.8-95%) in the patients undergoing primary repair and 65% (70% CL 52.4-77.6%) in patients initially palliated if the mortality of the palliative shunt procedure is included (P = 0.35). CONCLUSION: Patients with atrioventricular septal defect and tetralogy of Fallot can be successfully managed with a variety of surgical strategies. Primary repair may be a reasonable option in carefully selected patients, as this eliminates the morbidity and mortality of an initial shunt procedure and the subsequent interval between initial palliation and definitive repair.

Abnormalities, Multiple↗
PubMed1997

Computational transient simulations with varying degree and shape of pulmonic stenosis in models of the bidirectional cavopulmonary anastomosis.

The bidirectional cavopulmonary anastomosis is a surgical technique utilized to treat severe congenital malformations of the right part of the heart. It is obtained by anastomosing the superior vena cava to the superior aspect of the undivided right pulmonary artery. Transient simulations with a three-dimensional model of the bidirectional cavopulmonary anastomosis were carried out to evaluate the haemodynamics of different types of pulmonic stenosis (shape and severity of the obstruction). Models with a tunnel-like (supravalvar) or discrete (valvar) pulmonic stenosis with different values of reduction of cross-sectional area (60 and 75%) were investigated and compared to a model without stenosis. Calculations were based on a finite element method analysis. The results showed that a tighter stenosis can lead to a blood volume flow to the left lung reaching 70% of the total pulmonary flow. Moreover, the flow fields are highly influenced by the presence and shape of the pulmonic stenosis; the most intense jets in the left pulmonary artery occur for a discrete pulmonic stenosis of 75%. The flow in the right pulmonary artery is nearly steady because it is damped down by the steady caval flow.

Anastomosis, Surgical↗
PubMed1997

A mathematical model of circulation in the presence of the bidirectional cavopulmonary anastomosis in children with a univentricular heart.

The bidirectional cavopulmonary anastomosis is used as a staged procedure or a definitive palliation of univentricular hearts. It is often performed in the presence of an additional blood flow arising from the native pulmonary outflow tract. In this paper, the effects of the severity of the pulmonary outflow obstruction and the pulmonary arteriolar resistance are analysed with regard to the haemodynamics in the superior vena cava and the blood distribution into the lungs. A computer model has been developed, which can represent both the preoperative and the postoperative (systemic and pulmonary) circulations in a patient with a double-outlet univentricular heart. It is particularly detailed in the region of the large vessels and includes components that account for local three-dimensional effects due to the actual shape of the anastomosis. Results have indicated that the mean pressure in the superior vena cava increases from 8.2 to 19.2 mmHg with pulmonary arteriolar resistance ranging from 0.8 to 7.9 Woods units and pulmonary outflow obstruction ranging from 50 to 100%. The percentage flow distribution to the right lung has turned out to be heavily affected by the flow competition and has ranged from 43 to 50% of the total flow to the lungs in the systolic phase, and from 51 to 62% in the diastolic phase. The model allows routinely used clinical indices to be computed, as well as the evaluation of new indices, which is potentially helpful in the clinical assessment of postoperative haemodynamics (e.g. the right-to-left lung flow ratio and the superior vena cava-to-pulmonary flow ratio).

Biophysical Phenomena↗
PubMed1997

Heart-lung transplantation for patients under 10 with cystic fibrosis.

The outcome of patients with cystic fibrosis aged under 10 years referred for heart-lung transplantation assessment (n = 58) was determined and compared with older children (n = 109). Similar proportions were placed on to the active waiting list (64% v 71%) and received transplants (35% v 31%). Three year post-transplantation survival figures were also similar (41% v 46%), as were the figures for overall survival for those placed on to the active list (27% v 29%). Paediatricians should not be deterred from referring younger patients for transplantation.

Adolescent↗