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Biomedical subjects

A Redington

Publications and source records attributed to A Redington.

At least 37 records · Page 2Linked to original sources
PubMed1997

Right ventricular dysfunction during coronary artery occlusion: pressure-volume analysis using conductance catheters during coronary angioplasty.

OBJECTIVE: To study the effects of coronary artery occlusion on the pressure-volume relations of the right ventricle. DESIGN: Right ventricular pressure-volume cycles were studied using conductance catheters and micromanometers in 19 subjects undergoing coronary angioplasty in a tertiary referral cardiac centre. RESULTS: Catheter occlusions of either the left anterior descending coronary artery or the right coronary artery were associated with a decline in stroke work (mean change (SD): left-13.3 (15.8)%, p = 0.008; right -13.5(16.5)%, p = 0.04). Two patterns of change were evident: an upward shift usually associated with occlusion in the left coronary artery, and a rightward shift in the right coronary artery. In the former there was an increase in maximum ventricular volume (mean change: 3.0(2.7)%, p = 0.004) and in minimum ventricular volume (mean change: 2.3(2.7)%, p = 0.01) and a fall in peak pressure (mean change: -4.8 (5.1)%, p = 0.04). In the latter there was an increase in peak pressure (mean change 9.9(16.3)%, p = 0.04) and an increase in minimum ventricular volume (mean change 3.7(5.0)%, p = 0.02) leading to a fall in stroke volume (mean change -13.3(15.8)%, p = 0.008). CONCLUSIONS: Occlusion of the left anterior descending coronary artery or the right coronary artery is associated with a decline in right ventricular work. However, different patterns of change in indices of preload and afterload lead to different effects on overall right ventricular pump function.

Angioplasty, Balloon, Coronary↗
PubMed1996

Use of computational fluid dynamics in the design of surgical procedures: application to the study of competitive flows in cavo-pulmonary connections.

Computational fluid dynamic methods based on a finite-element technique were applied to the study of (1) competition of flows in the inferior and superior venae cavae in total cavopulmonary connection, and (2) competition between flow in the superior vena cava and forward flow from a stenosed pulmonary artery in bidirectional cavopulmonary anastomosis. Models corresponding to various degrees of offsetting and shape of the inferior vena caval anastomosis were simulated to evaluate energy dissipation and flow distribution between the two lungs. A minimal energy loss with optimal flow distribution between the two lungs was obtained by enlarging the inferior vena caval anastomosis toward the right pulmonary artery. This modified technique of total cavopulmonary connection is described. A computational model of the operation was developed in an attempt to understand the mechanisms of postoperative failure. In tight pulmonary artery stenosis (75%), the pulsatile forward flow is primarily directed to the left pulmonary artery, with little influence on superior vena caval pressure and the right pulmonary artery. Pulsatile forward flows corresponding to 15%, 30%, 45%, and 60% of the systemic artery output increased the mean pulmonary artery and superior vena caval pressures by 1, 1.7, 2.4, and 3.6 mm Hg, respectively. Although the modeling studies were not able to determine the cause of postoperative failure, they emphasize the impact of local geometry on flow dynamics. More simulations are required for further investigation of the problem.

Anastomosis, Surgical↗
PubMed1996

Total UK multi-centre experience with a novel arterial occlusion device (Duct Occlud pfm).

OBJECTIVE: To report the total UK multicentre experience of a novel arterial occlusion device (Duct Occlud pfm). DESIGN: Descriptive study of selected non-randomised paediatric patients with a variety of aortopulmonary connections. SETTING: Five UK tertiary referral centres for congenital heart disease. PATIENTS AND METHODS: Between March 1994 and February 1995, 57 children aged 2 weeks to 14 years (median 50 months) underwent attempted closure of their aortopulmonary connection. Fifty one had persistent arterial ducts and 9 of them had had a Rashkind umbrella device implanted. Five patients had superfluous modified Blalock-Taussig shunts (mBTS). In one there was also a native major aortopulmonary collateral artery (MAPCA). Another patient had a native major aortopulmonary connection (APC). Transcatheter occlusion was attempted in all cases through a 4 F delivery catheter. RESULTS: Devices were successfully deployed in 49/57 (86%) patients. Seven of 51 cases with persistent arterial ducts were judged too large for the device and a Rashkind umbrella was used. 40 (91%) of the 44 in whom the detachable coil device was used had complete occlusion at 24 hours on colour flow Doppler echocardiography. Devices were successfully deployed in all 6 remaining patients (4 mBTS, 1 mBTS + MAPCA, and 1 APC). Embolisation of a device occurred on 4 occasions. Two devices were not retrieved but caused no apparent clinical problems. CONCLUSION: This novel detachable coil type occlusion system compares favourably with other methods of transcatheter occlusion of native, residual, or surgically created aortopulmonary shunts. The delivery system allows its use in small children.

Adolescent↗
PubMed1995

Characterization of right ventricular diastolic performance after complete repair of tetralogy of Fallot. Restrictive physiology predicts slow postoperative recovery.

BACKGROUND: Prolonged postoperative recovery caused by a low cardiac output state occurs in some patients after complete repair of tetralogy of Fallot. Biventricular systolic function is usually well preserved in these patients. The contribution of impaired diastolic function, particularly of the right ventricle, has not been studied in detail; therefore, we performed a prospective study of right ventricular diastolic function in this patient group. METHODS AND RESULTS: We studied biventricular systolic and diastolic function using Doppler echocardiographic examination. Tricuspid valve, superior vena caval, pulmonary arterial, and mitral valve Doppler spectrals were obtained during the first postoperative day in 35 patients aged 6 months to 45 years who underwent complete repair of tetralogy of Fallot. Biventricular systolic function was grossly normal in all patients. Isolated restrictive right ventricular physiology characterized by pulmonary arterial antegrade flow coincident with atrial systole and associated with prominent retrograde superior vena caval flow was seen in 17 of the 35 patients (group 1). This flow was augmented during the expiratory phase of positive pressure ventilation and abolished or greatly diminished during the inspiratory phase (P < .001). An increase in the duration of pulmonary regurgitation occurred during the inspiratory phase of positive pressure ventilation in these patients (P < .01). All patients with right ventricular restriction had a clinical picture compatible with a low cardiac output state, requiring prolonged stays in intensive care and the hospital. Clinical improvement was mirrored by resolution of the Doppler markers of right ventricular restriction in most of the patients. CONCLUSIONS: Isolated right ventricular restriction is characterized by antegrade diastolic pulmonary arterial flow on Doppler echocardiography and is responsible for the slower postoperative course and clinical evidence of low cardiac output state in some patients after complete repair of tetralogy of Fallot.

Adolescent↗
PubMed1995

Comparison of cardiopulmonary adaptation during exercise in children after the atriopulmonary and total cavopulmonary connection Fontan procedures.

BACKGROUND: There are several potential physiological differences between the atriopulmonary (AP) and the total cavopulmonary connection (TCPC) Fontan circulations. Studies suggest that the TCPC reduces energy loss due to turbulence and may have more dependence on respiratory movement for pulmonary blood flow. We compared cardiopulmonary physiology during rest and exercise in patients who had undergone the AP Fontan procedure with those who had undergone the TCPC Fontan procedure. METHODS AND RESULTS: Forty-three children were studied more than 6 months after undergoing a Fontan procedure (23 AP and 20 TCPC); 106 healthy children were also studied as a control group. Measurements of effective pulmonary blood flow, stroke volume, arteriovenous oxygen difference, minute ventilation, heart rate, and oxygen and carbon dioxide consumption were made with an Innovision quadrupole mass spectrometer. Data from the control group allowed calculation of z scores for the Fontan groups matched for age, sex, pubertal stage, and body surface area. Maximal exercise performance was equal in the two Fontan groups, but it was below normal. However, adaptation to exercise was different in the Fontan groups. After 9 minutes of exercise, pulmonary blood flow rose less in the AP group than in the TCPC group (P < .01), and the stroke volume in the AP group also tended to be lower (P = .057) and their arteriovenous oxygen difference was significantly greater (P < .01). Although minute ventilation per unit of carbon dioxide production was similar in the Fontan groups at this level of exercise, children in the TCPC group breathed faster by approximately 10 breaths per minute (P < .005). CONCLUSIONS: At submaximal exercise, children who had undergone the TCPC Fontan procedure had pulmonary hemodynamics superior to those of children who had undergone the AP procedure, largely because of respiratory adaptation that permitted blood to be "sucked" into the lungs. To achieve the same maximal exercise performance, children who had undergone the AP procedure had a superior metabolic adaptation to exercise stress.

Adaptation, Physiological↗
PubMed1994

Reopening of an arterial duct after total occlusion with Rashkind's double umbrella device.

Reopening of a previously totally occluded ductus arteriosus with the Rashkind umbrella device occurred in a 5-yr-old girl, a previously unreported occurrence. Total occlusion using a second device was successful. This report emphasizes the need for regular follow-up with color flow Doppler echocardiography to diagnose and exclude a residual ductus even when apparent early closure has occurred.

Catheterization↗
PubMed1994

Regional ventricular wall motion abnormalities in tricuspid atresia after the Fontan procedure: flawed methodology may lead to a spurious finding of hypokinesia.

We believe that the two-frame method described by Akagi et al. cannot adequately describe the highly abnormal wall motion characteristics of these post-Fontan ventricles, and the systolic hypokinesia they describe may be spurious. Our data show that the predominant abnormality is incoordinate relaxation of the ventricular wall, which in turn prolongs the time constant of relaxation and the isovolumetric relaxation time and leads to reduced early rapid filling. Indeed, it was these abnormalities of diastolic, not systolic, function that were the strongest predictor of poor exercise performance in our study of patients late after the Fontan procedure. We strongly believe that the analysis of ventricular wall motion requires sequential data throughout the cardiac cycle, with well defined reference points concerning the timing of cardiac events, so that misinterpretation can be avoided.

Heart↗
PubMed1993

Juxtaductal aortic atresia masquerading as coarctation.

Two cases of juxtaductal aortic atresia diagnosed as coarctation on clinical and Doppler echocardiographic grounds are presented. The misleading nature of the Doppler flow velocity characteristics in this condition is discussed and raises questions as to the source of these flow velocities in coarctation.

Aorta, Thoracic↗
PubMed1990

Respiratory muscle function in cystic fibrosis.

Maximal static expiratory and inspiratory mouth pressures (PEmax and PImax) and quadriceps femoris muscle strength were measured in 25 patients aged 16-28 years with cystic fibrosis (mean FEV1 46% predicted). Mean (SD) PEmax was 64% (18%) predicted (below 75% predicted in 16 of the 25 patients), and PImax was 64% (24%) predicted (below 75% predicted in 14 patients). Quadriceps muscle strength was 68% (20%) predicted (below 75% predicted in 17 patients). The relatively small reduction in respiratory muscle strength in these patients was unlikely to have contributed appreciably to their respiratory problems.

Adolescent↗
PubMedDate not supplied

Outcome of pulmonary atresia and ventricular septal defect during infancy.

We evaluated 54 patients with pulmonary atresia and ventricular septal defect who were referred during the first year of life between 1972 and 1992. Particular emphasis was given to the nature of the pulmonary blood supply and its influence on outcome. Ductal supply of confluent pulmonary arteries was present in 30 patients (55.6%, group I), whereas 24 patients (44.4%, group II) had a pulmonary blood supply that was entirely (31.4%) or predominantly (13.0%) dependent on systemic collateral arteries. Over the 20 years there was no significant difference in actuarial survival between the two groups. Corrective surgery was performed in 8 of 30 patients in group I (26.7%)-significantly more than in group II (4 of 24, 16.7%). Arborization abnormalities of the pulmonary arteries (stenosis of unbranched and intrapulmonary arteries) were almost exclusively present in patients with systemic collateral arteries (p < 0.03), accounting for the lower probability of undergoing corrective surgery in group II patients. During the first decade of this study (1973-1983) corrective surgery was attempted in 9.6% of patients, with 42% mortality; and during the second decade (1983-1993) surgery was performed in 39.1% of patients, with 26% mortality, a significantly lower figure. Improving surgical results, complete preoperative demarcation of the pulmonary blood supply, and a more aggressive approach with early unifocalization of the pulmonary blood supply may invalidate comparison with retrospective data on the advisability of attempting to correct this anomaly. The present paper provides data against which treatment of infants with pulmonary atresia and ventricular septal defect presenting during the next decade can be compared.

Cardiac Catheterization↗
PubMedDate not supplied

Left ventricular pannus causing inflow obstruction late after mitral valve replacement for endocardial fibroelastosis.

A case of mitral stenosis following mitral valve replacement in a patient with endocardial fibroelastosis is reported. A 14-year-old boy presented with cardiac failure. He had been diagnosed as having endocardial fibroelastosis at the age of 7 months and had undergone resection of endocardial fibrous tissue in the left ventricle at that time. Five years later his mitral valve was resected owing to mitral stenosis, with Bjork-Shiley valve replacement. Cross-sectional echocardiography on this admission showed restrictive left ventricular inflow due to a thickened immobile prosthetic valve with severely dyskinetic left ventricle (ejection fraction 8%). The electrocardiogram showed atrioventricular reentry tachycardia. Despite direct current cardioversion and continual amiodarone infusion he suffered a cardiac arrest and died 12 days after admission. Postmortem examination showed left ventricular endocardial fibroelastosis with severe inflow obstruction due to the formation of a complete fibrous ring of pannus/fibrosis around the prosthetic margin on the ventricular aspect of the left ventricle. This complication has not previously been described in children after mitral valve replacement.

Adolescent↗
PubMedDate not supplied

Induction of nitric oxide synthase in asthma.

Nitric oxide (NO) is a mediator of vasodilatation and bronchodilatation synthesised from L-arginine by the enzyme NO synthase, which is either constitutive or induced by lipopolysaccharides and/or cytokines. The presence and function of NO synthase in normal or diseased lung is not yet clear. Asthma is characterised by bronchial hyperresponsiveness, epithelial damage, inflammation, and increased cytokine production. To investigate the presence of NO synthase in asthma, we immunostained bronchial biopsies from non-steroid-treated people with asthma and non-asthmatic controls with specific polyvalent antisera to purified inducible NO synthase and to a selected peptide sequence of the same enzyme. Immunoreactivity was seen in the epithelium and some inflammatory cells in 22 of 23 biopsies from people with asthma, but in only 2 of 20 controls. To assess the relation of cytokines to NO synthase induction, bronchial epithelial cells in culture were stimulated with tumour necrosis factor (TNF alpha). Inducible enzyme immunoreactivity was found only in the treated cells. The existence of inducible NO synthase in human lungs suggests that increased production of NO, probably induced by cytokines, may be relevant to the pathology of asthma.

Adult↗