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Biomedical subjects

A Redington

Publications and source records attributed to A Redington.

At least 19 recordsLinked to original sources
PubMed2005

Measurement and modelling of air pollution and atmospheric chemistry in the U.K. West Midlands conurbation: overview of the PUMA Consortium project.

The PUMA (Pollution of the Urban Midlands Atmosphere) Consortium project involved intensive measurement campaigns in the Summer of 1999 and Winter of 1999/2000, respectively, in which a wide variety of air pollutants were measured in the UK West Midlands conurbation including detailed speciation of VOCs and major component analysis of aerosol. Measurements of the OH and HO2 free radicals by the FAGE technique demonstrated that winter concentrations of OH were approximately half of those measured during the summer despite a factor of 15 reduction in production through the photolysis of ozone. Detailed box modelling of the fast reaction chemistry revealed the decomposition of Criegee intermediates formed from ozone-alkene reactions to be responsible for the majority of the formation of hydroxyl in both the summer and winter campaigns, in contrast to earlier rural measurements in which ozone photolysis was predominant. The main sinks for hydroxyl are reactions with NO2, alkenes and oxygenates. Concentrations of the more stable hydrocarbons were found to be relatively invariant across the conurbation, but the impacts of photochemistry were evident through analyses of formaldehyde which showed the majority to be photochemical in origin as opposed to emitted from road traffic. Measurements on the upwind and downwind boundaries of the conurbation revealed substantial enhancements in NOx as a result of emissions within the conurbation, especially during westerly winds which carried relatively clean air. Using calcium as a tracer for crustal particles, it proved possible to reconstruct aerosol mass from the major chemical components with a fairly high degree of success. The organic to elemental carbon ratios showed a far greater influence of photochemistry in summer than winter, presumably resulting mainly from the greater availability of biogenic precursors during the summer campaign. Two urban airshed models were developed and applied to the conurbation, one Eulerian, the other Lagrangian. Both were able to give a good simulation of concentrations of both primary and secondary pollutants at urban background locations.

Acetone↗
PubMed2002

Transcatheter closure of atrial septal defect preserves right ventricular function.

OBJECTIVES: To determine the effects of atrial septal defects (ASD) and their closure on systolic and diastolic right and left ventricular function; and by comparing surgical closure with transcatheter device closure, to establish differences attributable to cardiopulmonary bypass. DESIGN: Cross sectionally guided M mode echocardiographic ventricular long axis function was measured prospectively before and within one week after ASD closure by device in 17 patients and by surgery in 12 patients, and compared with 18 normal subjects. RESULTS: All indices of right ventricular function were impaired after surgery: mean total excursion, -1.89 cm (95% confidence interval (CI), -2.18 to -1.59); peak shortening rate, -9.09 cm/s (-10.82 to -7.35); peak lengthening rate, -9.26 cm/s (-11.09 to -7.43). Total excursion and peak lengthening rate were preserved after device closure, at -0.12 cm (-0.28 to 0.05) and 0.01 cm/s (-2.29 to 2.31), respectively. Left ventricular free wall function was unchanged after closure by either method, while all septal measurements were reduced after closure by either method (changes ranging from -3.51 to -0.32; 95% CI ranging from -4.90 to -0.13). CONCLUSIONS: Left ventricular free wall function is unaffected by ASD closure, whereas septal function is impaired, irrespective of the method of closure. Right ventricular function, both systolic and diastolic, is impaired by cardiopulmonary bypass but preserved after device closure. These findings support the transcatheter approach to ASD closure in anatomically suitable defects.

Balloon Occlusion↗
PubMed2001

Vascular dysfunction after repair of coarctation of the aorta: impact of early surgery.

BACKGROUND: Patients with repaired coarctation are at increased risk of hypertension and cardiovascular disease despite successful repair. We studied the function of conduit arteries in upper and lower limbs of patients late after successful coarctation repair and its relation to age at surgery. METHODS AND RESULTS: Flow-mediated dilatation (FMD) and the dilatation after sublingual nitroglycerin (NTG, 25 microgram) were measured by using high-resolution ultrasound in the brachial artery in 64 coarctation patients (44 males and 20 females, aged 19+/-10 years; median age at operation 4 months) and 45 control subjects (28 males and 17 females, aged 19+/-10 years) and in the posterior tibial artery in 37 patients and 22 control subjects. Arterial stiffness was determined by pulse-wave velocity (PWV) of the brachioradial and femoral-dorsalis pedis tracts. Patients, compared with control subjects, had lower brachial FMD (7.16+/-3.4% versus 8.62+/-2.3%, respectively; P=0.02) and NTG (11.46+/-4.3% versus 13.21+/-4.6%, respectively; P=0.046) and higher brachioradial PWV (9.17+/-3.1 versus 8.06+/-1.9 m/s, respectively; P=0.05). In contrast, posterior tibial FMD, NTG, and lower limb PWV were comparable. Age (months) at the time of repair was related to brachioradial PWV (r=0.42, P=0.002) but not to brachial FMD or NTG. CONCLUSIONS: Patients with repaired aortic coarctation have impaired conduit artery function, with abnormal responses to flow and NTG, and increased vascular stiffness confined to the upper part of the body. Early repair is associated with preserved elastic properties of conduit arteries, but reduced reactivity remains.

Adult↗
PubMed2001

Pulmonary artery occlusion from tuberculous lymphadenopathy in a child.

Occlusion of the pulmonary artery is a rare complication of mediastinal tuberculosis. We report on a 10-year-old girl who presented with a tuberculous pericardial effusion in whom subsequent imaging showed a totally occluded right pulmonary artery from tuberculous lymphadenopathy. Diagnosis was confirmed by polymerase chain reaction from a lymph node biopsy. Failure of medical therapy necessitated surgical reconstruction of her right pulmonary artery. Postoperatively she has normal perfusion of the right lung and normal lung function.

Arterial Occlusive Diseases↗
PubMed2000

Heterotrisomy, a significant contributing factor to ventricular septal defect associated with Down syndrome?

Down syndrome (DS; trisomy 21) is associated with a wide range of variable clinical features, one of the most common being congenital heart defects (CHD). We used molecular genetic techniques to study the inheritance of genes on chromosome 21 in children with DS and CHD. Polymorphic markers on the long arm of chromosome 21 were analysed in 99 families who had a child with DS. Of these, 60 children had a CHD and 39 children had no CHD. Heterotrisomy describes the inheritance of an allele from each of three different grandparents. In some cases heterotrisomy will involve the inheritance of three different alleles. Heterotrisomic regions were defined as those showing retention of non-disjoining parental heterozygosity at polymorphic loci in the non-disjoined chromosomes of children with DS. Using polymorphic non-coding markers, we identified a consistent 9.6-cM minimum region (D21S167-HMG14) of heterotrisomy in children with DS and ventricular septal defect (VSD). Comparing individuals with DS and VSD to all others with DS (those either with no CHD or with any other CHD combined) shows the individuals with DS and VSD to have significantly more non-reduction or heterotrisomy in this region (P=0.006, Fisher's exact test, two-tailed). We postulate that heterotrisomy for a gene or genes in this region is a contributing factor to the pathogenesis of VSD in trisomy 21 either through the presence of three different specific alleles or through the presence of specific combinations of alleles.

Adult↗
PubMed1999

Acute right ventricular dilatation in response to ischemia significantly impairs left ventricular systolic performance.

BACKGROUND: Right ventricular (RV) dilatation that occurs as a consequence of RV infarction is thought to produce hemodynamic instability by reducing left ventricular (LV) preload and compliance. We hypothesized that these geometric changes may also adversely affect LV systolic performance. METHODS AND RESULTS: Twelve 40-kg pigs were studied. Integrated conductance catheters and micromanometers were placed in both the LV and RV to allow simultaneous recordings of pressure and volume and derivation of indices of contractile function. RV ischemia was induced by balloon occlusion of the proximal right coronary artery (RCA) under 3 conditions: 1) with the pericardium intact, 2) with the pericardium intact and inotropic support, and 3) with the pericardium wide open. With an intact pericardium, RCA occlusion produced a decrease in LV end-diastolic volume associated with a marked decline in the contractile function. With the pericardium open, the same ischemic insult resulted in both LV and RV dilatation, which produced a significantly smaller negative effect on cardiac output (P=0.03), LV systolic pressure (P=0.02), LV preload-recruitable stroke work (P<0. 01), and LV end-systolic pressure-volume relations (P<0.01). Similarly, administration of dobutamine during RCA occlusion decreased the ventricular volume changes and produced a relative improvement in LV contractile performance. CONCLUSIONS: The hemodynamic compromise seen in association with acute RV dilatation within an intact pericardium is partly attributable to impaired LV systolic performance and cannot be wholly ascribed to changes in LV preload or compliance.

Animals↗
PubMed1999

Antioxidant protection against iron toxicity: plasma changes during cardiopulmonary bypass in neonates, infants, and children.

Cardiopulmonary bypass surgery is associated with the release of low molecular mass iron, which increases the saturation of plasma transferrin to over 50% in all adult patients treated. In a significant minority, however plasma transferrin becomes 100% iron saturated and non-transferrin bound iron can be detected in the plasma. An iron-saturated transferrin is also a common physiological finding in normal term and pre-term infants at a time when their plasma antioxidants, which protect against iron toxicity and radical scavenging, are profoundly different from those seen in adults. This study was conducted to assess the extent to which antioxidants, which protect against iron toxicity, are altered in neonates, infants, and children undergoing cardiopulmonary bypass surgery.

Antioxidants↗
PubMed1999

Use of self expanding stents in stenotic aortopulmonary shunts in adults with complex cyanotic heart disease.

OBJECTIVE: To describe the use of self expanding stents in treating long segment stenosis of aortopulmonary shunts (APS) in adults. DESIGN: Clinical records, catheterisation data, cineangiograms, and operation notes of four consecutive patients undergoing stent implantation since December 1994 were studied retrospectively. SETTING: A tertiary referral centre for cardiac disease. SUBJECTS: Four patients underwent cardiac catheterisation because of clinical deterioration. Their age ranged between 23 and 32 years. The underlying diagnosis was complex cyanotic heart disease in all. Three had a stenotic interposition graft, and one had a classic Blalock shunt. RESULTS: There was one technical failure owing to migration of the stent distal to an ostial stenosis. The ability index, resting oxygen saturation, and exercise tolerance improved in the remainder. Their medium term results have been excellent. CONCLUSIONS: This technique may further palliate adult patients with complex congenital heart disease, though the long term patency of stents is unknown.

Adult↗
PubMed1999

Transcatheter closure of atrial septal defect and interatrial communications with a new self expanding nitinol double disc device (Amplatzer septal occluder): multicentre UK experience.

OBJECTIVE: To review the safety and efficacy of the Amplatzer septal occluder for transcatheter closure of interatrial communications (atrial septal defects (ASD), fenestrated Fontan (FF), patent foramen ovale (PFO)). DESIGN: Prospective study following a common protocol for patient selection and technique of deployment in all participating centres. SETTING: Multicentre study representing total United Kingdom experience. PATIENTS: First 100 consecutive patients in whom an Amplatzer septal occluder was used to close a clinically significant ASD or interatrial communication. INTERVENTIONS: All procedures performed under general anaesthesia with transoesophageal echocardiographic guidance. Interatrial communications were assessed by transoesophageal echocardiography with reference to size, position in the interatrial septum, proximity to surrounding structures, and adequacy of septal rim. Stretched diameter of the interatrial communications was determined by balloon sizing. Device selection was based on and matched to the stretched diameter of the communication. MAIN OUTCOME MEASURES: Success defined as deployment of device in a stable position to occlude the interatrial communication without inducing functional abnormality or anatomical obstruction. Occlusion status determined by transoesophageal echocardiography during procedure and by transthoracic echocardiography on follow up. Clinical status and occlusion rates assessed at 24 hours, one month, and three months. RESULTS: 101 procedures were performed in 100 patients (86 ASD, 7 FF, 7 PFO), age 1.7 to 64.3 years (mean (SD), 13.3 (13.9)), weight 9.2 to 100.0 kg (mean 32.5 (23.5)). Procedure time ranged from 30 to 180 minutes (mean 92.4 (29.0)) and fluoroscopy time from 6.0 to 49.0 minutes (mean 16.1 (8.0)). There were seven failures, all occurring in patients with ASD, and one embolisation requiring surgical removal. Immediate total occlusion rate was 20.4%, rising to 84.9% after 24 hours. Total occlusion rates at the one and three month follow up were 92.5% and 98.9%, respectively. Complications were: transient ST elevation (1), transient atrioventricular block (1), presumed deep vein thrombosis (1), presumed transient ischaemic attack (1). CONCLUSIONS: It appears feasible to close interatrial communications and atrial septal defects up to 26 mm stretched diameter safely with the Amplatzer septal occluder. Short term results confirm an early high occlusion rate with no major complications. Careful selection of cases based on the echocardiographic morphology of the ASD and accurate assessment of their stretched diameter is of utmost importance. Further experience with the larger devices and longer term results are required before a firm conclusion regarding its use can be made.

Adolescent↗
PubMed1999

Transcatheter closure of atrial septal defects in adults with the Amplatzer septal occluder.

OBJECTIVE: To assess the efficacy and complications of device occlusion of atrial septal defects in adults, using the Amplatzer septal occluder (ASO). DESIGN: A prospective interventional study. SETTING: Paediatric cardiology departments in two European teaching hospitals. PATIENTS: The first 20 patients accepted for atrial septal defect device occlusion, on the basis of transoesophageal echocardiography. Sixteen patients had larger defects with right heart dilatation, while the primary indication for closure in four was a history of early paradoxical embolism. INTERVENTIONS: Transcatheter atrial septal defect occlusions performed under transoesophageal echocardiography and fluoroscopic guidance between December 1996 and June 1998. OUTCOME MEASURES: Success of deployment of ASO devices, procedure and fluoroscopic times, complications, and symptoms. RESULTS: The ASO device was successfully implanted in all 20 patients (14 female), median age 44.2 years, with no complications. Of the 16 patients with right heart dilatation, the median Qp:Qs was 2.5:1. Defects measured 11-22 mm (median 18) on transoesophageal echocardiography, with balloon sized diameter (and device size) of 13-28 mm (median 20). For all 20 patients, the procedure time ranged from 38-78 minutes (median 61), and fluoroscopy 8.4-24.7 minutes (median 15.2). There were residual shunts in three patients at the end of the procedure, which were trivial (</= 1 mm) as assessed by transoesophageal echocardiography, and persisted for more than six months in only one patient. Follow up ranged from 0.1-1.5 years (median 0.7). There have been no late complications. CONCLUSIONS: The ASO device can be used successfully to close selected oval fossa defects in adults, with minimal procedural morbidity and excellent early results.

Adolescent↗
PubMed1997

Resting right ventricular function in patients with coronary artery disease: pressure volume analysis using conductance catheters.

Right ventricular pressure volume cycles from patients with coronary artery disease were created in order to assess their characteristics and the effects of peak ventricular pressure and right and left artery coronary disease. Thirty-three patients undergoing diagnostic catheterisation for ischaemic heart disease underwent right ventricular catheterisation with a micromanometer and a conductance catheter. Simultaneous pressure and volume signals were recorded and analysed as functions of time, and of each other, forming pressure volume cycles. A total of 19/33 (58%) patients had an abnormal pressure volume loop with a clear end systolic shoulder, and an isovolumic relaxation phase. The mean peak ventricular pressure for all patients was raised (35.2 S.D. 11.8 mmHg), but there was no correlation between indices of shape and peak systolic pressure. Values of dP/dtmax were also raised, but there was no significant difference in this or any other index between patients with left or right coronary artery disease. Thus, in patients with coronary artery disease, the right ventricular pressure volume loop is frequently abnormal in a pattern that is recognised as a feature of an increased ventricular afterload.

Angina Pectoris↗
PubMed1997

Clinical application of the conductance catheter technique in the adult human right ventricle.

This study examines the use of conductance catheters to assess human right ventricular volume. Ten patients undergoing diagnostic cardiac catheterisation underwent right heart catheterisation with a conductance catheter and micromanometer, and a thermodilution catheter before and after fluid loading. Parallel wall conductance (Vc), and the multiplication factor relating conductance and thermodilution derived stroke volumes (å) were derived at each steady state. Pressure-volume cycles were analyzed at steady state and during fluid loading. Fluid loading resulted in a significant increase in cardiac output, and change in maximum and minimum cycle volume. There was no significant change in å (mean 0.40 S.D. 0.20) or Vc (mean 126.4 S.D. 59.6 ml) at higher cardiac outputs or ventricular volumes. Right ventricular pressure-volume cycles were formed demonstrating characteristic lack of clear isovolumic contraction and relaxation phases, and low cycle efficiencies (mean 0.62 S.D. 0.16). Serial cycles recorded during volume loading defined an end systolic pressure-volume relation more reliably than a stroke work end diastolic volume relation. Thus, a conductance derived volume signal can be obtained in the human right ventricle which can be interpreted as a continuous and instantaneous index of right ventricular volume, allowing the construction of real time pressure-volume cycles.

Adult↗
PubMed1997

Cardiopulmonary physiology after surgical closure of asymptomatic secundum atrial septal defects in childhood. Exercise performance is unaffected by age at repair.

AIMS: Most secundum atrial septal defects, once diagnosed, are corrected at a young age. The evidence to justify early vs delayed or even non-closure is equivocal and little is known regarding long-term effects of later closure. This is particularly pertinent to those patients awaiting transcatheter closure of their defect for whom a device is only just becoming available. We examined the exercise cardiorespiratory physiology of children surgically treated for an isolated secundum defect. METHODS AND RESULTS: One hundred and six healthy control children and 22 children more than 6 months after surgical repair for an isolated secundum atrial septal defect were studied. All were asymptomatic. Measurements of effective pulmonary blood flow, stroke volume, arteriovenous oxygen difference, minute ventilation, heart rate, oxygen consumption and carbon dioxide production were made using a quadrupole mass spectrometer during rest and graded exercise. Data from the normal children allowed calculation of z scores for the atrial septal defect group matched for age, sex, pubertal stage and surface area. Maximal exercise performance was equal between control and atrial septal defect groups, however, the atrial septal defect group had a significantly greater effective pulmonary blood flow and stroke volume but a lower heart rate than controls at a given exercise stage. Stroke volume abnormalities were most closely related to duration of follow-up (29% of the variance explained, P < 0.01) rather than age at surgery. CONCLUSIONS: We were unable to show a medium term benefit from early surgery for an asymptomatic secundum atrial septal defect during exercise. The clinical relevance of the haemodynamic differences that do exist remains unclear.

Adolescent↗
PubMed1997

Cardiovascular effects of intravenous midazolam after open heart surgery.

Midazolam is the sedating agent of choice in many paediatric intensive care units, and is usually administered as a continuous intravenous infusion with or without a preceding bolus dose. Ten haemodynamically stable children, ventilated in the early postoperative period after cardiac surgery and receiving intravenous morphine infusions, were given an intravenous bolus followed by a continuous infusion of midazolam. Haemodynamic data were recorded before the bolus, and 15 minutes and one hour later. A bolus of midazolam lowered the cardiac output by 24.1%. Arterial blood pressure, oxygen consumption, and mixed venous oxygen content fell significantly. There was a tendency for all variables subsequently to recover towards baseline values, within one hour, during a continuous infusion. An intravenous bolus of midazolam causes a transient but unwanted fall in cardiac output. It is suggested that in children who are receiving intravenous opiates, its use in the early postoperative period be limited to a continuous infusion.

Adolescent↗