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Biomedical subjects

J Wallwork

Publications and source records attributed to J Wallwork.

At least 73 records · Page 4Linked to original sources
PubMed1997

Left ventricular assist devices: current status and future applications.

Despite the advances in the medical management of heart failure over the last 20 years it remains a major cause of morbidity and mortality. While cardiac transplantation has evolved into an established mode of therapy, the number of patients with severe heart failure who could benefit from cardiac transplantation far exceeds the supply of donor organs. The development of an implantable left ventricular assist device (LVAD) began in the early 1970s in centres such as the Texas Heart Institute and was funded by the National Heart, Lung, and Blood Institute. Clinical trials of these devices began in the mid 1980s and several hundred patients have now been supported with one or other of these devices. Most patients have had an LVAD implanted as a bridge to cardiac transplantation. Recently there has also been interest in the use of an LVAD for (a) permanent ventricular support and (b) as a bridge to recovery in patients with potentially reversible causes of heart failure.

Heart Failure↗
PubMed1997

Human leukocyte antigen compatibility in heart transplantation: evidence for a differential role of HLA matching on short- and medium-term patient survival.

BACKGROUND: Studies of the influence of human leukocyte antigen (HLA) matching on cardiac transplant outcome have proved inconclusive, mainly due to the lack of well-matched grafts. However, a growing number of studies report improved clinical course and patient survival in cases with increased HLA compatibility. Opelz et al. believe these benefits justify the introduction of prospective HLA-matching strategies. METHODS: We performed univariate and multivariate analyses to examine the short- and medium-term influence of HLA matching on 556 consecutive primary heart transplants performed at a single center between 1983 and 1994. Overall graft survival at 1, 3, and 5 years was 80%, 74%, and 67% respectively. Sixteen (2.9%) grafts failed within 5 days and were not considered in the analysis of the HLA matching and graft survival data. RESULTS: Complete HLA-A, -B, and -DR typing data were available on 477 transplant pairs. The results demonstrate a 12% 1-year survival advantage for 31 patients with zero to two HLA antigen mismatches compared with three to six mismatches. The influence of each individual locus was 6.1%, 8.4%, and 5.4% for zero HLA-A, -B, and -DR mismatches, respectively, compared with two mismatches. However, when outcome from 1 to 5 years was considered, analysis of the role of each locus revealed marked differences. HLAA-matched grafts (n=45) had a 24% lower survival rate compared with two-antigen-mismatched grafts (n=148; 88% [SE 3.1] vs. 64% [SE 8.2], respectively; P=0.009). Furthermore, 34% of HLA-A-matched grafts failed between 1 and 5 years, compared with only 5% of HLA-B-matched grafts (P=0.013). CONCLUSIONS: These data suggest that although HLA matching is effective at reducing acute graft loss, in the longer term, HLA-A matching may impair survival. HLA-A may serve as a restriction element for indirect presentation of allopeptides or tissue-specific minor histocompatibility antigens, facilitating chronic graft loss. Therefore, we advocate a differential role for HLA matching over two epochs. A blanket approach to prospective matching for heart transplants may be premature for optimal long-term survival.

Adolescent↗
PubMed1997

Hyperacute lung rejection in a pig-to-human transplant model: the role of anti-pig antibody and complement.

BACKGROUND: The physiology of hyperacute rejection of pig lung by human blood and the role of antispecies antibody and complement in this phenomenon have not previously been characterized. METHODS: Human blood was perfused through an ex vivo pig heart-lung preparation. In the treatment groups, blood was either unmodified or modified to deplete alternative pathway complement (heat treatment), anti-pig antibody, or both. Control experiments were performed with unmodified and heat-treated pig blood. Physiologic parameters, organ survival, and immunohistology were the primary outcome measures assessed. RESULTS: Pig lung was consistently damaged by human blood within 45 min (median 20 min), as evidenced by elevated pulmonary vascular resistance and parenchymal injury. Immunohistologic studies of perfused lungs showed prominent deposition of IgM and classical pathway component, C4, and weaker deposition of alternative pathway component, properdin. Heat treatment did not impede the rise in pulmonary vascular resistance or significantly prolong survival. Depletion of anti-pig antibody prolonged survival (median 90 min) and attenuated the rise in pulmonary vascular resistance. Antibody absorption, combined with heat treatment of plasma, prevented the elevation in pulmonary vascular resistance and yielded median graft survival (210 min) similar to pig blood perfusion (approximately 240 min). CONCLUSIONS: These results show that elevated pulmonary vascular resistance and pulmonary parenchymal injury are mediated at least in part by antispecies antibody and heat-sensitive pathways. They are consistent with the hypothesis that complement activation contributes significantly to acute lung damage in the pig-to-human species combination.

Animals↗
PubMed1997

Bronchiolitis obliterans syndrome in heart-lung transplantation: surveillance biopsies.

Transbronchial biopsies (TBBs) are useful to diagnose acute rejection and infection in patients with lung transplants. The value of routine surveillance biopsies (S-TBBs) is not known, and such biopsies with a clinical indication are not without risk and are expensive. One hundred twenty-six 6-mo survivors of heart-lung transplantation (HLT) were studied to determine the effect of stopping S-TBBs on the development of bronchiolitis obliterans syndrome (BOS) and subsequent survival. Fifty-one received transplants while S-TBB was part of routine care (group A), and 75 received transplants after this practice was stopped (group B). There was no difference in patient characteristics. Group A had shorter graft ischemia (p < 0.01) and longer postoperative ventilation (p < 0.01). Maintenance immunosuppression was similar, but group A had more steroid pulses in the second 6 mo after HLT (p < 0.01). The number of patients free from any functional deterioration at 49 to 60 mo after HLT declined to 39% in group A and 64% in group B. The risk of developing BOS grade 1 in group A relative to group B was 1.63 (95% confidence intervals: 0.96-2.79, p = 0.07). Patient survival was similar in the two groups. A total of 86 TBBs were taken in the absence of any signs or symptoms and had low diagnostic yield. In summary, there was no increased incidence of BOS after stopping S-TBBs.

Actuarial Analysis↗
PubMed1997

Expression of human decay accelerating factor may protect pig lung from hyperacute rejection by human blood.

BACKGROUND: Hyperacute rejection currently prevents clinical application of discordant lung xenografts. Pigs transgenic for human regulators of complement activation offer one promising potential solution to this problem. METHODS: Using fresh human blood in an ex vivo lung perfusion model, we studied eight different strains of pigs transgenic for human decay accelerating factor. Survival (by blood flow and gas transfer criteria) were correlated with immunohistologic evidence of pulmonary human decay accelerating factor expression and complement activation. RESULTS: With human blood perfusion, blood flow through the unmodified pig lung rapidly falls and is not restored by continuous infusion or high-dose bolus of prostacyclin. Airway pressure also rises rapidly and is followed promptly by loss of gas transfer. Four of the transgenic pig strains showed no difference from this pattern. Immunohistochemistry for human decay accelerating factor revealed low or no pulmonary expression in these lungs. In contrast, two of five transgenic pig lungs that had significant decay accelerating factor expression demonstrated recovery of pulmonary blood flow within 1 hour, and rejection was delayed, from less than 20 minutes in controls to about 1 hour. Complement activation, particularly the alternative pathway, was inhibited in lungs with high levels of endothelial decay accelerating factor expression. CONCLUSIONS: Lungs from some strains of pig transgenic for human decay accelerating factor demonstrate incomplete physiologic and histologic protection from hyperacute rejection. Although complement-independent pathogenic mechanisms may present a formidable obstacle, pig lungs transgenic for human complement regulatory proteins may facilitate discordant lung transplantation in human beings.

Animals↗
PubMed1996

Pharmacodynamics of cyclosporine in heart and heart-lung transplant recipients. I: Blood cyclosporine concentrations and other risk factors for cardiac allograft rejection.

We have attempted to determine the optimal clinical use of cyclosporine during the first 3 months after heart transplantation. We used multiple logistic regression to quantify how blood cyclosporine concentrations and other potential risk factors influence the risk of histologically confirmed acute rejection in 111 heart transplant recipients. A 50% increase in cyclosporine concentration was associated with a 15% reduction in risk of rejection in the subsequent 5 days (P=0.002). Increasing oral corticosteroid dose also protected against rejection (P=0.01). Rejection was over 2.5 times more likely during the first 20 postoperative days, and patients with 2 HLA-DR mismatches who were transplanted for cardiomyopathy or who had multiple previous rejection episodes were predisposed to further rejection (P<0.01). High short-term variability in cyclosporine concentrations was weakly associated with risk of rejection (P=0.1). Investigation of threshold levels for the cyclosporine concentration-effect relationship suggested that concentrations above 375 microgram L(-1) provide optimal protection against acute cardiac allograft rejection. This result yields an objectively defined therapeutic threshold for targeting early cyclosporine concentrations following heart transplantation, although the upper end of the range will depend on the individual's susceptibility to nephrotoxicity and infection.

Analysis of Variance↗
PubMed1996

Pharmacodynamics of cyclosporine in heart and heart-lung transplant recipients. II: Blood cyclosporine concentrations and other risk factors for lung allograft rejection.

We have attempted to quantify the optimal clinical use of cyclosporine during the first 3 months after heart-lung transplantation. We used multiple logistic regression to investigate the influence of blood cyclosporine concentrations and other potential risk factors on histologically confirmed acute lung rejection in 50 heart-lung transplant recipients. A 50% increase in cyclosporine concentration was associated with a 25% reduction in risk of rejection in the subsequent 5 days (P=0.008). Increasing oral corticosteroid dose also protected against rejection (P=0.006). Rejection was over 4 times more likely to occur during the first 20 postoperative days (P=0.002). After 20 days, an FEV1 < or = 70% of the age-, sex-, and height-adjusted expected score was associated with a 4-fold increase in risk of rejection (P=0.01). Patients who had multiple previous rejection episodes were also predisposed to further rejection (P=0.005). An investigation of threshold levels for the cyclosporine concentration-effect relationship suggested that cyclosporine concentrations above 500 microg L(-1) provide optimal protection against acute lung allograft rejection. This result provides an objectively defined therapeutic threshold for targeting early cyclosporine concentrations following heart-lung transplantation.

Adult↗
PubMed1996

Development of bronchiolitis obliterans syndrome in recipients of heart-lung transplantation--early risk factors.

Given the internationally recognized definition of bronchiolitis obliterans syndrome (BOS) and longer follow up of heart-lung transplant recipients, it is possible to establish some of the major risk factors for development and progression of BOS. Between April 1984 and 31 December 1993, 157 patients underwent heart-lung transplantation; 126 survived at least six months after operation and so were at risk of developing BOS. The following early risk factors were assessed for development of BOS grade 1 (21-35% decline in FEV1) and progression from grade 1 to grade 2 (36-50% decline in FEV1): age, gender and underlying diagnosis of the recipient, evidence of acute rejection and cytomegalovirus (CMV) infection within 6 months of operation, peak FEV1 achieved, age and gender of the donor, cold ischemic time of the graft, and matching of CMV serological status and HLA antigens of donor and recipient. The number of acute rejection episodes observed remained the single most important determinant of development of BOS grade 1 (relative risk 1.17 (1.06, 1.29), P=0.002) and progression to BOS grade 2 (relative risk 1.58 (1.02, 2.46), P=0.03). No other factors were significantly related to development or progression of BOS, although both evidence of CMV infection and disease and the number of HLA mismatches increased the risk. Bronchiolitis obliterans syndrome is a major problem for medium-to-long-term survivors of cardiothoracic transplantation. Acute rejection early after transplantation is a sensitive prognostic indicator of subsequent functional decline and requires prompt attention.

Adolescent↗
PubMed1996

Bronchiolitis obliterans syndrome (BOS) following heart-lung transplantation.

With the increasing number of successfully performed lung transplants and a longer follow up of patients, there is an interest in the analysis of long-term complications and their impact on patient survival. Heart-lung transplantation was performed in 157 patients with 126 patients surviving at least 6 months. Early death was mainly caused by bacterial and viral infection. Long-term patient survival was decisively influenced by obliterative bronchiolitis. With the new international definition of bronchiolitis obliterans syndrome (BOS) based on an irreversible decline of FEV1 from baseline values, it became possible to analyse the incidence of BOS and the impact on patient mortality in long-term survivors. FEV1 reached a peak value of 102% predicted at a median of 219 days. In 106 of 126 patients (84%), FEV1 showed no decline within the first year. A total of 60 patients (47.6%) developed BOS grade 1 with progression to BOS grade 2 in 85% of these patients. The incidence of BOS was 12.6% at 1 year increasing to more than 50% 5 years after transplantation. Patient mortality due to obliterative bronchiolitis increased from 1% at 1 year to 18% more than 5 years after transplantation. Almost all deaths (86%; 32/37) more than 1 year after HLT were associated with bronchiolitis obliterans. In summary, bronchiolitis obliterans decisively contributes to long-term patient morbidity and mortality after heart-lung transplantation. Clinical and research efforts should be directed towards avoiding this important complication.

Bronchiolitis Obliterans↗
PubMed1996

Lipids, lipoprotein (a) and coronary artery disease in patients following cardiac transplantation.

Cardiac allograft vascular disease (CAVD) is the most important cause of late mortality in cardiac transplant recipients. While the pathogenesis of the disease is believed to be immunological, other factors like hyperlipidaemia may contribute. Total cholesterol, LDL cholesterol. HDL cholesterol, triglycerides, apolipoprotein A1 and B and Lp(a) levels were measured in 174 cardiac transplant recipients attending our clinic for routine follow-up. Univariate and multivariate logistic regression analysis was carried out to assess the relationship of the variables studied to the presence of CAVD diagnosed with coronary angiography. CAVD was present in 42 of the 174 patients. The group with CAVD had a higher total cholesterol (6.8 vs 6.3 mmol/l), lower HDL cholesterol (0.8 vs 0.9 mmol/l), higher triglyceride (2.8 vs 2.0 mmol/l) and higher Lp(a) level (317.5 vs 95 mg/l) than the group without CAVD. In multivariate analysis, after adjusting for gender, hypertension, time from transplantation, preoperative diagnosis and lipid-lowering therapy, Lp(a), total cholesterol, HDL cholesterol and triglycerides remained significantly correlated with CAVD. The results indicate a significant association between hyperlipidaemia, Lp(a) levels and allograft vascular disease. Further studies are needed to show whether treatment of hyperlidaemia in this population delays the onset or slows the progression of CAVD.

Adult↗
PubMed1996

An approach to the retrieval of thoracic organs for transplantation.

A critical, worldwide shortage of thoracic organs exists. The donor management program at Papworth Hospital, National Health Service Trust, Cambridge, United Kingdom, allows satisfactory transplantation of thoracic organs that initially appear unsuitable. The perioperative organ retrieval team members assess the cardiovascular status of all potential donors and manage suboptimal hemodynamics with hormonal replacement therapy consisting of triiodothyronine, antidiuretic hormone, epinephrine, and insulin. These donors' cardiovascular and pulmonary functions must be within acceptable limits at the time of organ excision. Our standardized approach facilitates objective decision making regarding the appropriate use of donor organs and has increased the number of available donor organs at Papworth Hospital by 30%. Morbidity and mortality rates in thoracic organ recipients have not increased since the authors developed the standardized approach, and more patients have benefited from thoracic organ transplantation.

Decision Making, Organizational↗
PubMed1996

Excellent outcome of cardiac transplantation using domino donor hearts.

OBJECTIVE: Domino cardiac transplantation affords flexible and optimal organ utilization, provides hearts unaffected by brain death, allows prospective tissue matching, and subsequent transplantation with short allograft ischemic times. A retrospective review of our experience with domino cardiac transplantation has been made. METHODS: Seventy-two of 119 patients who underwent heart-lung transplantation from 1988 on served as domino cardiac donors (40 males, 32 females; mean age of 32 years; mean weight of 51 kg). The domino donor diagnoses were cystic fibrosis (n = 47), bronchiectasis (n = 9), primary pulmonary hypertension (n = 6), emphysema (n = 7), pulmonary fibrosis (n = 2) and Eisenmenger's syndrome (n = 1). Forty-seven domino hearts were transplanted at our institution and 25 were exported to other centres in the United Kingdom. The 72 domino cardiac recipients were 62 males and 10 females, mean age of 47 years, mean weight of 60 kg, with ischemic heart disease (n = 32), cardiomyopathy (n = 36) and other conditions (n = 4). RESULTS: There were four deaths (5.6%) at less than 30 days (2 from multiple organ failure, 1 from primary allograft failure and 1 from acute rejection). Actuarial survival estimates and 1 and 5 years were 77 +/- 5.2% nd 69 +/- 6.3%, respectively. This compared favourably with survival data obtained in 234 non-domino cardiac recipients. In the patients transplanted at Papworth, there was no difference in the incidence of rejection (0.6 +/- 0.05 versus 0.7 +/- 0.03 events per 100 patient days for the first 12 months) or in the freedom from graft atherosclerosis (74 +/- 3% versus 70 +/- 3% at 5 years) between the domino and non-domino groups. CONCLUSIONS: The use of domino hearts donated by recipients of heart-lung transplants is beneficial and is associated with an excellent early and longer-term outcome.

Actuarial Analysis↗