The effect of local-scale physical heterogeneity and nonlinear, rate-limited sorption/desorption on contaminant transport in porous media.

Nonideal transport of contaminants in porous media has often been observed in laboratory characterization studies. It has long been recognized that multiple processes associated with both physical and chemical factors can contribute to this nonideal transport behavior. To fully understand system behavior, it is important to determine the relative contributions of these multiple factors when conducting contaminant transport and fate studies. In this study, the relative contribution of physical-heterogeneity-related processes versus those of nonlinear, rate-limited sorption/desorption to the observed nonideal transport of trichloroethene in an undisturbed aquifer core was determined through a series of miscible-displacement experiments. The results of experiments conducted using the undisturbed core, collected from a Superfund site in Tucson, AZ, were compared to those obtained from experiments conducted using the same aquifer material packed homogeneously. The results indicate that both physical and chemical factors, specifically preferential flow and associated rate-limited diffusive mass-transfer and rate-limited sorption/desorption, respectively, contributed to the nonideal behavior observed for trichloroethene transport in the undisturbed core. A successful prediction of trichloroethene transport in the undisturbed core was made employing a mathematical model incorporating multiple sources of nonideal transport, using independently determined model parameters to account for the multiple factors contributing to the nonideal transport behavior. The simulation results indicate that local-scale physical heterogeneity controlled the nonideal transport behavior of trichloroethene in the undisturbed core, and that nonlinear, rate-limited sorption/desorption were of secondary importance.

Cranial base changes following coronal suturectomy in craniosynostotic rabbits.

It has been suggested that surgical release of synostosed sutures may ameliorate various cranial base abnormalities in craniosynostotic patients. The present study was designed to test this hypothesis in a rabbit model with familial coronal suture synostosis (CSS). Data were collected from 56 New Zealand White rabbits: 32 unaffected controls, 11 with unoperated CSS, and 13 with CSS released by suturectomy performed at 25 days of age. Serial radiographs were taken at 25, 42 and 84 days. Linear, angular and triangular shape cranial base measurements were compared using ANOVA and tensor biometric analysis. Results revealed that at 84 days, both groups of CSS rabbits had significantly (p < 0.05) different anterior and total cranial base lengths, flatter cranial base angles, and dysmorphic anterior cranial base shapes when compared with normals. Significant (p < 0.05) differences were noted only for palatal and cranial base angles and posterior cranial base shape between CSS rabbits with and without suturectomy. However, significant (p < 0.05) changes were noted between pre- and postoperative measurements in posterior and total cranial base lengths and anterior and posterior cranial base shapes in CSS rabbits with suturectomy. Results revealed that surgical release of synostosed coronal sutures through suturectomy did not normalize cranial base growth patterns in CSS rabbits. These findings may be explained by the relatively late age of surgical release or suturectomy site resynostosis with continued dysmorphic cranial base growth. Alternatively, cranial base abnormalities seen in CSS rabbits may be early primary malformations, not secondary deformations amenable to surgical modification.

Incidence of stroke among chronic hemodialysis patients with nonrheumatic atrial fibrillation.

In general, nonrheumatic atrial fibrillation is associated with a high risk of stroke. However, its impact on stroke in the setting of chronic hemodialysis treatment is insufficiently addressed in the literature. We assessed the incidence of stroke among 430 chronic hemodialysis patients and the impact of atrial fibrillation and various other potential risk factors on stroke in a retrospective study covering 1,111.16 patient-years. The overall incidence of stroke was 3.78/100 patient-years. Among patients with chronic atrial fibrillation without any antithrombotic therapy besides regular dialysis anticoagulation, the stroke incidence was 1.0/100 patient-years and did not differ statistically significantly from the rate among patients without this arrhythmia, in whom the incidence was 2.8/100 patient-years (p = 0.220). Conversely, the overall rate of stroke incidence per 100 patient-years was statistically significantly higher in patients with diabetic nephropathy (6.46, p = 0.0036), age > 65 years (5.90, p = 0.0001), moderate to severe hypertension (6.8, p = 0.0017), weight gain of > 2 kg between dialyses as a marker of poor patient compliance (6.47, p = 0.0433), and antithrombotic therapy with salicylates or warfarin (8.33, p = 0.0002), as compared with corresponding groups without these risk factors. Our data suggest that in contrast to other risk factors nonrheumatic atrial fibrillation in itself is not associated with an increased risk of stroke in patients on maintenance hemodialysis treatment.

Search for characteristic structural features of mammalian mitochondrial tRNAs.

A number of mitochondrial (mt) tRNAs have strong structural deviations from the classical tRNA cloverleaf secondary structure and from the conventional L-shaped tertiary structure. As a consequence, there is a general trend to consider all mitochondrial tRNAs as "bizarre" tRNAs. Here, a large sequence comparison of the 22 tRNA genes within 31 fully sequenced mammalian mt genomes has been performed to define the structural characteristics of this specific group of tRNAs. Vertical alignments define the degree of conservation/variability of primary sequences and secondary structures and search for potential tertiary interactions within each of the 22 families. Further horizontal alignments ascertain that, with the exception of serine-specific tRNAs, mammalian mt tRNAs do fold into cloverleaf structures with mostly classical features. However, deviations exist and concern large variations in size of the D- and T-loops. The predominant absence of the conserved nucleotides G18G19 and T54T55C56, respectively in these loops, suggests that classical tertiary interactions between both domains do not take place. Classification of the tRNA sequences according to their genomic origin (G-rich or G-poor DNA strand) highlight specific features such as richness/poorness in mismatches or G-T pairs in stems and extremely low G-content or C-content in the D- and T-loops. The resulting 22 "typical" mammalian mitochondrial sequences built up a phylogenetic basis for experimental structural and functional investigations. Moreover, they are expected to help in the evaluation of the possible impacts of those point mutations detected in human mitochondrial tRNA genes and correlated with pathologies.

Renal hemodynamic effects of L-arginine and sodium nitroprusside in heart transplant recipients.

BACKGROUND: Long-term treatment with cyclosporine A (CsA) induces vasoconstriction in the kidney and causes renal impairment. An altered L-arginine (L-Arg)/nitric oxide (NO) pathway may play a key role in CsA nephrotoxicity. METHODS: We studied the effect of L-Arg (dosage, 17 mg/kg/min over 30 min), the precursor of NO synthesis, and sodium nitroprusside (SNP; dosage, 1.0 microgram/kg/min over 30 min) on renal hemodynamics in a double-blind, placebo-controlled, randomized, three-way cross-over study comprising 12 stable cardiac transplant recipients on long-term CsA treatment, 10 patients with chronic nephropathy not receiving CsA, and 13 healthy controls. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were measured by paraaminohippurate (PAH) and the inulin clearance method, respectively. RESULTS: In healthy subjects, L-Arg induced an increase in RPF (P = 0.009) and GFR (P = 0.001). By contrast, L-Arg did not induce renal hemodynamic effects in heart transplant patients or patients with chronic nephropathy. SNP reduced RPF (P = 0.050) and GFR (P = 0.005) in patients with chronic nephropathy but did not affect renal hemodynamics in heart transplant recipients or in healthy subjects. CONCLUSIONS: These data indicate that L-Arg cannot be used to reverse CsA-induced renal vasoconstriction in heart transplant recipients under long-term CsA treatment, although these patients have a normal renal response to SNP.

Value of cardiopulmonary exercise testing and big endothelin plasma levels to predict short-term prognosis of patients with chronic heart failure.

OBJECTIVES: We tested the hypothesis that, in patients with stable heart failure, measuring big endothelin-1 (ET-1) plasma level at rest predicts short-term prognosis better than peak oxygen consumption (VO2max) at exercise. BACKGROUND: Cardiopulmonary exercise testing and evaluation of neurohumoral plasma factors are established tools to estimate survival in patients with heart failure. No data, however, exist comparing the prognostic value of both marker categories simultaneously. METHODS: Two hundred twenty-six heart failure patients were studied in regard to a combined end point of death and prioritization for urgent cardiac transplantation within 1 year follow-up. RESULTS: During the study period 149 patients were without cardiac events (group A), 69 patients died or were urgently transplanted (group B) and 8 patients were alive after a nonurgent heart transplant operation. Norepinephrine (p < 0.0001), atrial natriuretic peptide (p < 0.001), big endothelin plasma levels (p < 0.0001 as well as workload, VO2max and achieved percentage of predicted peak oxygen consumption (pVO2max) (all p < 0.0001) differed significantly between groups A and B. In multivariate stepwise regression analysis, however, only big ET-1 plasma concentration (chi2=74.4, p < 0.0001), New York Heart Association function class (chi2=33.9, p < 0.0001), maximal workload (chi2=7.2, p < 0.01, and plasma atrial natriuretic peptide (ANP) concentration (chi2=4.6, p < 0.05) were independently related to outcome. Peak oxygen consumption or pVO2max did not reach statistical significance in this model. Event-free survival rates were significantly lower in patients with a big ET-1 level of 4.3 fmol/ml or more than with lower big ET-1 levels (p < 0.0001). CONCLUSION: We conclude that in patients with chronic heart failure who are stable on oral therapy measuring big ET-1 and ANP plasma levels may be a valuable noninvasive adjunct to improve the prognostic accuracy of detecting high risk patients compared with exercise testing alone.

Multiple-dose pharmacokinetics of cefpirome in long-term hemodialysis with high-flux membranes.

Cefpirome is a cephalosporin eliminated primarily by kidneys that requires dosage reduction in patients with renal failure. The pharmacokinetic parameters were studied in 10 patients with end-stage renal disease who were receiving hemodialysis. Repeated intravenous administration of 2 gm cefpirome three times a week resulted in trough levels of 12.2 +/- 5.4 micrograms/ml and peak serum concentrations of 99.6 +/- 82.1 micrograms/ml. After 3 1/2 hours of hemodialysis with polysulfone high-flux membranes, 62.3% +/- 23.3% of cefpirome was removed. The interdialytic half-life was 9.35 +/- 0.99 hours, and the intradialytic half-life was 2.02 +/- 0.7 hours.

Update: abdominal tuberculosis--unusual findings on CT.

To update our knowledge of abdominal tuberculosis as manifested on computed tomography (CT), we reviewed the CT scans of 12 patients with proven abdominal tuberculosis. The nature, range and extent of abdominal involvement was determined. The CT findings were compared to those reported in the literature. The aetiologic agent was Mycobacterium tuberculosis in all patients. One patient had an increased risk because of AIDS. In nine patients, tuberculosis was limited to the abdomen, and three patients had previously unknown thoracic tuberculous disease. Characteristic features in our patients included low density ascites and uncommon patterns of adenopathy. Findings reported to be typical in abdominal tuberculosis were present in only five of our 12 patients. Unusual findings in our patients included solitary and multiple pelvic, adrenal, splenic and hepatic lesions. In six of 12 patients, those findings mimicked malignancy. We conclude that knowledge and early recognition of these unusual manifestations of abdominal tuberculosis should help to optimize clinical management of the disease and avoid misdiagnosis.

Primary pulmonary hypertension in pregnancy: a case report.

Primary pulmonary hypertension is a rare, incurable, and progressive disease. When it is associated with pregnancy, the mortality rises to > 50%. We report a patient who was diagnosed with severe pulmonary hypertension of unknown cause in the twenty-second week of gestation. She was treated with an oral calcium-channel blocker and low-molecular-weight heparin and underwent delivery by cesarean section with good maternal and fetal outcome. Patients with severe pulmonary hypertension should, however, avoid pregnancy because of the high mortality, although cases have been reported with positive outcome.

Effects of dichloroacetate on exercise performance in healthy volunteers.

Dichloroacetate (DCA), a stimulator of the pyruvate dehydrogenase complex, decreases lactate levels and peripheral resistance and increases cardiac output. This study was performed to examine the effects of DCA on exercise performance in humans. Eight healthy male volunteers (age 20-28 years) were tested by bicycle spiro-ergometry using a microprocessor-controlled gas analysis system after infusion of DCA (50 mg/kg body weight) or saline. Prior infusion of DCA significantly reduced the increase of lactate levels during exercise when compared with infusion of saline (1.40 +/- 0.21 vs 2.10 +/- 0.09 mmol.l-1 at 50% of the expected maximal working capacity, P < 0.05; 8.53 +/- 0.45 vs 9.92 +/- 0.59 mmol.l-1 at maximal working capacity, P < 0.05). Oxygen uptake increased significantly after DCA when compared with saline from 7.5 +/- 0.4 vs 7.4 +/- 0.5 to 27.2 +/- 1.5 vs 23.7 +/- 1.7 (P < 0.05) at anaerobic threshold and to 35.6 +/- 1.7 vs 30.5 +/- 1.0 ml.kg-1 min-1 (P < 0.05) at maximal exercise capacity. Following DCA infusion the workload at which the anaerobic threshold was reached was significantly higher (160 +/- 7 vs 120 +/- 5 W, P < 0.05) and the maximal working capacity was significantly increased (230 +/- 9 vs 209 +/- 8 W, P < 0.05). In summary, DCA reduced the increase of lactate levels during exercise and increased oxygen uptake at the anaerobic threshold and at maximal working capacity, which was significantly increased. These results warrant further studies on a potential therapeutic application of DCA in patients with reduced exercise capacity.

Biocompatibility of high-flux membranes.

Standard dialysis with cuprophane membranes is known to stimulate the immune system. As a result of activation of macrophages various interleukins and tumor necrosis factor (TNF) are secreted, presenting further evidence of the poor biocompatibility of cuprophane. We investigated the immunogenic properties of three modern high-flux membranes. Seven patients were studied during hemodiafiltration sessions using either a polysulfone (F60, Fresenius), a polymethylmetacrylate (BK 2.1, Toray) or a cellulose triacetate (FB-210 U, Nipro) dialyzer in a hemodiafiltration procedure. Serial measurements were made during each treatment of interleukin-1 beta (II-1 beta), TNF, soluble IL-2 receptor (sII-2r), soluble CD4 (sCD4), soluble CD8 (sCD8), interferon gamma (IFNg) and neopterin. In contrast to the known increase of IL-1 beta, IL-2r and TNF with cuprophane membranes, none of the modern high-flux dialyzers stimulated the production of these factors. Significant decreases of neopterin and sCD4 were observed. IFNg and sCD8 did not change significantly. Our results suggest that the modern high-flux dialyzers are non-immunogenic, and thus provide further evidence of the superior biocompatibility of synthetic or semisynthetic membranes over the conventional cuprophane.

[Cerebral bilharziasis caused by Schistosoma mansoni]. / Bilharziose cérébrale à Schistosoma mansoni.

A 21-year-old French serviceman who had been posted to black Africa on several occasions between 1978 and 1981 was hospitalized in August 1981 with generalized convulsive seizures. The only abnormal finding on clinical, paraclinical and biological investigation was blood hypereosinophilia. A further generalized convulsive fit occurred in August 1982. A CT scan then showed a poorly defined hyperdense occipital area. Pathological examination of the operative specimen confirmed that the lesion was due to schistosoma mansoni. Investigation failed to detect clinical or biological evidence of other parasitic lesions. Specific serology was negative.