Transmission optical coherence tomography based measurement of optical material properties.

We present transmission optical coherence tomography (transmission OCT) as a versatile tool to measure optical material properties of turbid media. The transmission OCT signal is described in detail and it is demonstrated how the group refractive index (n(g)), group velocity dispersion (GVD) and optical attenuation can be determined from this signal. We experimentally validate the refractive index properties of glasses, liquids and glucose water solutions in terms of n(g) and GVD. Measurements of scattering coefficients are determined using transmission OCT for suspensions of silica particles. Quantitative agreement is obtained with a dependent scattering model, both for the average as well as the wavenumber resolved optical attenuation coefficient. Good agreement is observed between our measurements and literature values.

Clinical validation of an artificial neural network trained to identify acute allograft rejection in liver transplant recipients.

Artificial neural networks (ANNs) are techniques of nonlinear data modeling that have been studied in a wide variety of medical applications. An ANN was developed to assist in the diagnosis of acute rejection in liver transplant recipients. We investigated the diagnostic accuracy of this ANN on a new data set of patients from the same hospital. In addition, we compared the diagnostic accuracy of the ANN with that of the individual input variables (alanine aminotransferase [ALT] and bilirubin levels and day posttransplantation). Clinical and biochemical data were collected retrospectively for 124 consecutive liver transplantations (117 patients) over the first 3 months after transplantation. Diagnostic accuracy was calculated using receiver operating characteristic (ROC) curve analysis. The ANN differentiated rejection from rejection-free episodes in the new data set over the first 3 months posttransplantation with an area under the ROC curve of 0.902 and sensitivity and specificity of 80.0% and 90.1% at the optimum decision threshold, respectively. The ANN was significantly more specific than ALT or bilirubin level or day posttransplantation at their corresponding optimum decision thresholds (P <.0001). Peak ANN output occurred 1 day earlier than peak values for either ALT or bilirubin (P <.005). The diagnostic accuracy of the ANN was greater than that of any of the individual variables that had been used as inputs. It would be a useful adjunct to conventional liver function tests for monitoring liver transplant recipients in the early postoperative period.

The clinical validation of novel strategies for monitoring transplant recipients.

In the early postoperative period after solid organ transplantation, the patient is monitored intensively to detect the early development of surgical and infectious complications or allograft rejection. Laboratory tests form an essential component of the routine monitoring protocol-particularly those that are of diagnostic value in assessing graft function. In this paper, we illustrate how a new liver-function test, alpha-glutathione S-transferase immunoassay, was subjected to systematic technical and clinical evaluation in the liver-transplant population, including a randomized, controlled trial that provided the evidence for its introduction into the routine laboratory. We also illustrate how the carefully controlled monitoring in a clinical trial is difficult to reproduce under routine circumstances and the crucial role of audit in ensuring that recommendations governing the use of a new diagnostic test are adhered to in clinical practice. Finally, we describe an "equivalence study," whereby our rigorous validation of the alpha-glutathione S-transferase assay has enabled us to fast-track the development of a simpler and cheaper liver function test (fructose 1,6-bisphosphatase), which shares similar diagnostic characteristic to alpha-glutathione S-transferase, without the requirement for a further clinical trial.

Randomized trial of blood eosinophil count monitoring as a guide to corticosteroid dosage adjustment after heart transplantation.

BACKGROUND: Increases in blood eosinophil counts (EOS) beyond 0.06 x 10(9)/liter precede treated heart allograft rejection. An oral prednisolone dose of 0.35 mg/kg/day usually suppresses EOS below this threshold. METHODS: We designed a randomized trial to compare our empirical protocol for steroid dose adjustment with a novel protocol guided by EOS monitoring during the first 3 months after heart transplantation. Eighty patients were randomized to either have their EOS reported and used for steroid dose adjustment (RG; n=40), or not reported (NG; n=40). RG patients had their steroid dosage increased if EOS exceeded 0.06 x 10(9)/liter. RESULTS: RG patients had an 83% lower risk of treated rejection (P=0.035) and lower median intravenous dose of methyl-prednisolone (P=0.017) than NG during the first 6 postoperative weeks. The proportion of diagnostic increases in EOS that were followed within 2 weeks by treated rejection was 42% greater in NG than RG (P=0.0001), compatible with a direct impact of EOS-guided prednisolone dose adjustment on the risk of subsequent rejection. Overall, RG had less than half the risk of rejection of any grade (P<0.001) and significantly more rejection-free biopsies than NG (P=0.001). The mean oral prednisolone dosage was significantly greater in RG than NG during the first (P=0.014) and second (P=0.001) 6 weeks of follow-up. This did not increase the incidence of serious steroid-related side effects. CONCLUSIONS: EOS monitoring is a simple, cheap, and effective means of optimizing steroid immunosuppression. Restriction of the EOS-guided steroid dosing protocol to periods of prolonged hospitalisation during the first 3 postoperative months should limit the requirement for higher prednisolone dosage without affecting immunosuppressive efficacy.

Neuro-computing versus linear statistical techniques applied to liver transplant monitoring: a comparative study.

This paper explores the potential for the application of neurocomputing in on-line monitoring in the liver transplantation domain. It extends our previously documented work to provide both an assessment of the performance gains achievable by incorporating temporal and dynamical information about the measurements made on a patient as well as presenting a novel computerized clinical decision aid for this domain. A comparison of the performance of linear and nonlinear classification system is made and used to motivate the final selection of the diagnostic inputs.

Blood levels of TGFbeta1 in liver transplant recipients receiving either tacrolimus or micro-emulsified cyclosporine.

BACKGROUND: Transforming growth factor beta-1 (TGFbeta1) is pro-fibrotic in addition to being a potent immunosuppressive cytokine. Cyclosporine (cyclosporin A[CsA]) has been found to increase circulating TGFbeta1 levels in patients (1, 2). To determine whether tacrolimus (FK506) similarly increases TGFbeta1 we have measured TGFbeta levels in blood samples from liver graft recipients who were of known TGFbeta1-responder status. METHODS: Sequential serum and plasma samples were obtained from liver transplant recipients in the UK trial of tacrolimus versus microemulsified CsA, with a follow up period of between 50 and 265 days. Twelve patients received CsA and 13 received tacrolimus. Active and total TGFbeta1 protein were measured and plasma beta thromboglobulin (betaTG) levels were used as an indirect indication of platelet-derived TGFbeta contamination of samples. RESULTS: We found no correlation between trough drug levels and active TGFbeta1 levels in serum of either set of patients. Plasma beta thromboglobulin was detected in platelet-depleted plasma samples, indicative of platelet damage before plasma separation. CONCLUSION: Neither CsA nor tacrolimus induced active TGFbeta1 blood levels in liver transplant recipients during a follow up period of < or = 265 days.

Monitoring eosinophil activation and liver function after liver transplantation.

BACKGROUND: Portal tract eosinophil infiltration and an increase in the blood eosinophil count (EOS) have been shown to be specific markers of liver allograft rejection. The graft eosinophil infiltration is associated with the local release of eosinophil cationic protein. Therefore, serum eosinophil cationic protein concentration (ECP) is a potential marker for acute allograft rejection. We investigated the chronological relationship among and diagnostic value of serial changes in EOS, ECP, and liver function tests (LFTs) following liver transplantation. METHODS: EOS, ECP, serum alpha-glutathione S-transferase concentration, and conventional LFTs were measured in serial samples collected over the first 3 postoperative months following 58 liver transplants. The diagnostic potential of each test, alone or in combination, was reviewed over the entire follow-up period. RESULTS: EOS and ECP increased at a median period of 3.5 and 4 days, respectively, before the diagnosis of acute rejection, and this increase was significantly earlier than the corresponding changes in LFTs (P<0.05). There was a significant correlation between the day of the first increase in EOS and alpha-glutathione S-transferase (rs=0.535; P=0.009) and EOS and alanine transaminase (rs=0.629; P=0.004). The optimum combination of tests for the diagnosis of acute rejection was an increase in both EOS and GST with a predictive efficiency of 84%. CONCLUSIONS: Increases in EOS and ECP are early indicators of acute liver allograft rejection and precede evidence of hepatocellular damage. However, an increase in ECP was also frequently associated with infection. Therefore, we recommend the regular monitoring of EOS in conjunction with routine LFTs after liver transplantation as an aid to the early diagnosis of acute rejection.

Randomized trial to evaluate the clinical benefits of serum alpha-glutathione S-transferase concentration monitoring after liver transplantation.

BACKGROUND: An increase in serum alpha-glutathione S-transferase concentration (GST) has been shown to be a more sensitive and specific marker of hepatocellular damage than equivalent increases in transaminase activities. A randomized clinical trial of 60 liver transplants in 49 patients was carried out to assess the clinical benefits of GST monitoring as a supplementary test to routine liver function tests during the first 3 postoperative months after liver transplantation. METHODS: Mortality and morbidity were compared in graft recipients who had their GST reported daily to the ward (reporting group) and graft recipients who did not. RESULTS: The 3-month survival rate was significantly greater in the reporting group (P=0.033) and the risk of graft loss was halved (relative hazard ratio=0.50; P=0.29). The reporting group also had significantly more patients who spent less than 3 weeks in the hospital throughout the follow-up period (P=0.036). In addition, the reporting group experienced a lower frequency of biopsies per graft (P=0.038), less severe rejection (P=0.015), and a lower incidence of infection episodes per graft (P=0.03). GST increased by >50% above the upper limit of the reference range at a median of 1 day before the equivalent change in alanine transaminase in association with allograft rejection in the combined groups (95% confidence interval=1 to 2 days) but was lower on the day of diagnosis of rejection in the reporting group (P=0.02). This is compatible with the earlier diagnosis of rejection in the reporting group. CONCLUSIONS: We conclude that the monitoring of GST may improve patient care, reducing both mortality and morbidity.

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.

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.

Evaluation of an enzyme-immunometric assay for serum alpha-glutathione S-transferase.

A commercially available enzyme-immunometric assay for serum alpha-glutathione S-transferase (GST) was evaluated. Endogenous serum alpha-GST diluted linearly within the calibration range. However, we recommend that the sample and second antibody reagent are always added sequentially in the assay to avoid hook effect. Between-assay variability was below 7% across the calibration range and the upper limit of the reference range in adults (n = 219) was 11.4 micrograms/L. Within-individual variability in serum alpha-GST concentrations measured over a 4-6 week period in 4 healthy adults was small. Serum alpha-GST concentrations did not change significantly 6 h after a therapeutic dose of paracetamol. Studies in two patients after liver transplantation showed that serum alpha-GST is a better discriminant of acute changes in liver function than conventional tests. Serum alpha-GST concentrations were unaffected by gross muscle damage, extrahepatic inflammation, or haemolysis and thus appear to be more liver specific than transaminase activities. The effect of renal impairment on serum alpha-GST concentrations requires further investigation.

Blood cyclosporine concentrations and cytomegalovirus infection following heart transplantation.

We have attempted to identify major risk factors for cytomegalovirus (CMV) infection and disease following heart transplantation, with emphasis on the degree and type of immunosuppression used. One hundred and eleven consecutive heart transplant recipients were studied for the first 4 months. Data from the 95 who survived at least 1 month were analyzed using multiple Cox regression. Blood cyclosporine concentrations (CsAbc) > 550 micrograms L-1 were associated with a 4.4-fold increase in risk of CMV infection during the next week (95% confidence interval = 1.2-16.2). Other significant risk factors for CMV infection included antirejection treatment in the past 14 days, a drop in white blood cell count, receiving a CMV antibody-positive donor organ, and primary diagnosis other than cardiomyopathy. We found that patients experiencing a CMV infection were at 3 times the risk of subsequently developing symptomatic CMV disease (95% confidence interval = 1.1-9.7). In addition, the proportion of patients developing symptomatic CMV disease was significantly higher amongst those with a median CsAbc > 550 micrograms L-1 for at least 1 week (29% vs. 10%; P = 0.02) or who had been treated for rejection more frequently than once every 6 weeks (31% vs. 12%; P = 0.04) during the first 4 months. CMV antibody-negative recipients of antibody-positive donor organs had a higher rate of symptomatic CMV disease than did other serological combinations (67% vs. 10%; P = 0.0001). We conclude that the risk of CMV infection and symptomatic disease following heart transplantation may be critically influenced by early management of immunosuppression as well as by donor serology.

Absorption of cyclosporin from conventional and new microemulsion oral formulations in liver transplant recipients with external biliary diversion.

1. Less than 5% of a dose of the conventional oral formulation of cyclosporin, Sandimmun, is absorbed in liver transplant recipients with external biliary drainage, necessitating intravenous administration of the drug and exposing the patient to increased risk of severe side-effects. 2. We compared the pharmacokinetics of the conventional oral formulation of cyclosporin with that of the new microemulsion formulation, Neoral, in eight liver transplant recipients with external biliary diversion. Patients were maintained on a continuous infusion of cyclosporin until steady-state conditions had been achieved. They were then given a test dose (10 mg kg-1) of either the conventional or microemulsion formulation (randomised order) followed by the same dose of the other formulation. Parent cyclosporin concentrations were measured in whole blood samples collected at timed intervals over the 24 h after the oral doses and pharmacokinetic parameters calculated. 3. The bioavailability of cyclosporin from the microemulsion formulation was, on average, 6.5-fold (95% C.I. 1.9 to 11.1-fold) greater than that of the conventional formulation, indicating the improved absorption characteristics of the new oral microemulsion formulation during external bile drainage. 4. A significant negative correlation was found between the external bile drainage volume and bioavailability of cyclosporin from the microemulsion formulation (r = -0.8; P = 0.016), suggesting that variability in cyclosporin absorption from the microemulsion formulation may still be at least partly attributable to bile- dependence.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary fat on the pharmacokinetics and pharmacodynamics of cyclosporine in kidney transplant recipients.

OBJECTIVE: To investigate the effect of dietary fat on the pharmacokinetics and pharmacodynamics of cyclosporine. METHODS: Sixteen stable kidney transplants recipients (mean age, 50.4 years; age range, 19 to 63 years; six women) who were maintained on oral cyclosporine therapy were randomized to receive a high- or low-fat diet for periods of 7 days in a balanced crossover study. The crossover was separated by a 7-day washout period, when the usual diet was followed. Oral cyclosporine was taken once daily with breakfast. Twenty-four-hour pharmacokinetic studies were conducted during each dietary period on day 6 after oral cyclosporine and on day 7 after a 3-hour intravenous cyclosporine infusion (30% of oral dose). Sequential blood samples were also taken after the oral dose on day 6 for lymphocyte transformation studies. RESULTS: The mean breakfast fat intake and total daily fat intake were 6.5 and 5.5 times higher, respectively, during the high-fat diet than during the low-fat diet. The bioavailability and clearance of cyclosporine were found to be significantly higher during the high-fat diet (p = 0.02 and p = 0.01, respectively). As a consequence, the area under the blood concentration-time curve (AUC) after the oral dose was not significantly different between the two diets. There were no significant differences in concanavalin A-stimulated proliferation of peripheral blood lymphocytes between the high- and low-fat diets. CONCLUSIONS: An increased fat content of food significantly increases cyclosporine bioavailability and clearance. However, this is unlikely to be of clinical importance during oral administration because the AUC and pharmacodynamics of cyclosporine are not affected significantly.

Relative bioavailability of cyclosporin from conventional and microemulsion formulations in heart-lung transplant candidates with cystic fibrosis.

Patients with cystic fibrosis absorb cyclosporin poorly and erratically. We have compared the relative bioavailability of cyclosporin from conventional and microemulsion formulations in 5 adult heart-lung transplant candidates with cystic fibrosis. Relative bioavailability was compared at two dose levels (200 mg and 800 mg). A randomized 4-period cross-over study was performed with at least a 7 day washout period between each single dose pharmacokinetic study. Blood cyclosporin concentrations were measured by a selective monoclonal antibody-based radioimmunoassay. The bioavailability of cyclosporin from the microemulsion formulation was 1.84 (95% C.I. 1.05 to 3.22; P = 0.04) and 2.09 (95% C.I. 0.95 to 4.61; P = 0.06) times higher compared with the conventional formulation at 200 mg and 800 mg respectively. Cmax following the microemulsion formulation was 3.38 (C.I. 1.14 to 10.59; P = 0.04) and 2.77 (C.I. 1.48 to 5.19; P = 0.01) times higher compared with the conventional formulation at 200 mg and 800 mg respectively. The higher Cmax following the microemulsion formulation was accompanied by shorter tmax. An enhancement of cyclosporin absorption with the microemulsion formulation was demonstrated in each patient for at least one dose level. We conclude that rate and extent of cyclosporin absorption from the microemulsion formulation is greater compared with the conventional formulation in patients with cystic fibrosis. The potential therapeutic and economic benefits of the microemulsion formulation should be evaluated in cystic fibrosis patients following heart-lung transplantation.

Serum alpha-glutathione S-transferase--a sensitive marker of hepatocellular damage associated with acute liver allograft rejection.

The wide hepatic distribution, high cytosolic concentration, and short in vivo plasma half-life of serum alpha-glutathione s-transferase are properties which may make monitoring this enzyme more clinically useful than conventional biochemical liver function tests as a marker of hepatocellular damage associated with acute liver allograft rejection. In a prospective longitudinal study of 58 liver transplants in 45 patients, serum alpha-glutathione S-transferase concentrations rose significantly more consistently and more rapidly than conventional liver function tests in association with acute rejection. However, a rise in alpha-glutathione S-transferase was less specific for rejection than conventional liver function tests although none of the tests had a positive predictive value for rejection of greater than 32%. Compatible with the particularly short in vivo plasma half-life of this enzyme, alpha-glutathione S-transferase concentrations fell to or toward normal more rapidly than conventional liver function test measurements following uncomplicated transplantation as well as during high-dose steroid treatment of rejection. This may be valuable, both in improving the resolution of biochemical changes associated with early rejection episodes and in determining when treatment of rejection has been successful. Further studies are warranted, however, to assess whether the fall in GST during rejection treatment does genuinely reflect the histological resolution of rejection.