Search PubMed⌕ Search

Biomedical subjects

M Rivera

Publications and source records attributed to M Rivera.

At least 235 records · Page 13Linked to original sources
PubMedDate not supplied

Prevalence and patterns of HGV/GBV-C infection in patients with suspected HCV-related hepatitis.

Hepatitis G virus (HGV) is a recently described hepatotropic parenterally transmitted flavivirus. The presence of HGV was tested in 61 patients with a request for confirmation of HCV active infection. Thirty-two patients were in haemodialysis and 29 were referred from wards other than nephrology. Active HCV and HGV infections were determined by detection of their viral RNA in serum. Evaluation of previous HGV infection was carried out by detection of antibodies to E2 antigen. HCV prevalence was 62.29% (38/61). HGV-active infection was found in 11.47% (7/61) of the population studied: in 18.7% (6/32) of the haemodialysed patients and in 3.4% (1/29) of patients belonging to the other group. HGV prevalence increased two-fold when previous infection was also considered. HGV clearance was prospectively detected in 5 out of the 7 patients with active infection, and at an earlier stage for those patients coinfected with HCV. Anti-E2 seropositivity was associated with HGV clearance in only two patients.

Female↗
PubMedDate not supplied

Synthesis and properties of the monomethyl ester of meso-dimercaptosuccinic acid and its chelates of lead (II), cadmium(II), and mercury(II).

The monomethyl ester of meso-dimercaptosuccinic acid (MoMeDMSA) and its chelates with lead(II), cadmium(II), and mercury(II) have been synthesized. The mercury(II) chelate of MoMeDMSA is formed by the coordination of the two sulfur atoms in MoMeDMSA, whereas the lead(II) and cadmium(II) chelates are formed by the coordination of one sulfur and one oxygen atom. The solubilities of the chelates are pH dependent; the mercury(II) chelate dissolves when the uncoordinated carboxylic acid dissociates, but the lead(II) and cadmium(II) chelates are solubilized only after the uncoordinated mercapto group is dissociated. The cadmium(II) chelate is dimeric and the lead(II) and mercury(II) chelates are monomeric at the concentrations and conditions used in this study. The acid dissociation constants of the chelating agent and the uncoordinated groups in its metal chelates have been determined in 50% v/v methanol-water. These acid-base properties in addition to the polarity of the chelating agent contribute to the effectiveness in the in vivo mobilization of intracellular in vivo deposits of cadmium. The biliary excretion of cadmium in rats increased by a factor of 173 upon administration of the relatively toxic, nonpolar dimethyl ester of DMSA whereas the administration of the less toxic, more polar monomethyl ester increased the biliary excretion of cadmium by a factor of 63. On the other hand, meso-DMSA which is highly polar and less toxic is known to be without effect on biliary excretion of cadmium. The monomethyl DMSA, therefore, appears to have properties that are intermediate between those of DMSA and its dimethyl ester, as far as both chelating properties and biliary excretion of cadmium are concerned.

Animals↗
PubMedDate not supplied

The dimethyl ester of meso-2,3-dimercaptosuccinic acid and its interactions with Cd2+ and rabbit liver metallothionein I.

The ion association complex formed with the cadmium chelate of the dimethyl ester of meso-2,3-dimercaptosuccinic acid and the tetramethylammonium cation, [(Me)4N]2[Cd(Di-MeDMSA)2], has been synthesized. The structures of the ion association complex and of the ligand (meso-DiMeDMSA) were determined by single-crystal X-ray diffraction. The two methyl ester groups and the two sulfhydryl groups in meso-DiMeDMSA were in a staggered conformation. The anion [Cd(DiMeDMSA)2]2- is essentially a distorted tetrahedron, with a mononuclear CdS4 kernel. The structure of the [Cd(DiMeDMSA)2]2- anion in solution was found to be similar to its structure in the solid state by multinuclear (1H, 13C, 113Cd) magnetic resonance spectroscopy. In the presence of rabbit liver metallothionein I (MT), meso-DiMeDMSA was found to coordinate Zn2+ and Cd2+ ions. 1H NMR spectroscopy proved to be an effective analytical technique for monitoring the competition between meso-DiMeDMSA and the protein for these metal ions. This was accomplished by probing the tertiary structure of MT with 1H NMR spectroscopy after incubation with meso-DiMeDMSA. In addition, the 1H NMR spectra of rabbit liver metallothionein I demonstrated that MT is more susceptible to oxidation at physiological pH after the metal ions have been removed. It appears that intra- as well as intermolecular disulfide cross-linkages are formed upon oxidation. When rabbit liver metallothionein I was incubated with meso-DiMeDMSA in a 20:1 (meso-DiMeDMSA:MT) mole ratio, 32% of the cadmium and 87% of the zinc bound to MT were removed.

Animals↗
PubMedDate not supplied

Synthesis, structure, and stability of the zinc complex of the dimethyl ester of meso-2,3-dimercaptosuccinic acid.

The dimethyl ester of meso-2,3-dimercaptosuccinic acid (meso-DiMeDMSA) reacts with Zn2+ ions to form protonated and polynuclear complexes. The species [Zn2L3H]- and [Zn2L3]2- are formed at pH values between 3 and 6.5 and have overall formation constants of 10(37.53) and 10(32.52), respectively, whereas the mononuclear complex [ZnL2]2- is formed at physiological pH and has a formation constant of 10(18.06). The mononuclear complex was synthesized and isolated as an ion association complex with the tetramethylammonium ion, [(Me)4N]2[Zn(DiMeDMSA)2], and its structure in solution was determined by low-temperature 1H and 13C NMR spectroscopy. In this structure the Zn2+ ion is tetrahedrally coordinated to four thiolate groups from two meso-DiMeDMSA molecules.

Hydrogen-Ion Concentration↗
PubMedDate not supplied

Determination and metabolism of dithiol chelating agents: the zinc chelate of the dimethyl ester of meso-2,3-dimercaptosuccinic acid increase biliary excretion of cadmium and platinum.

meso-2,3-Dimercaptosuccinic acid is an orally active chelating agent useful for the treatment of lead intoxication. Since it is believed to be extracellular in its distribution, analogs have been synthesized in a search for one that will enter the cell and successfully complete for firmly bound intracellular toxic heavy metals such as cadmium and platinum. The biological properties of the zinc chelate of DiMeDMSA, ([Zn(DiMeDMSA)2]2- with tetramethylammonium or sodium as the counterion, have been investigated in the rat. In short-term (hourly) experiments, [Zn(DiMeDMSA)2]2- increased the biliary excretion of cadmium and platinum. In experiments of longer duration (days), severe renal toxicity was noted even in the absence of any exogenously administered cadmium chloride or cis-dichlorodiammineplatinum(II). The zinc content of the kidneys of rats receiving Na2[Zn(DiMeDMSA)2]2- was found to be about 10-fold greater than rats receiving saline or meso-dimethyldimercaptosuccinic acid. Although it appears that the source of the zinc is the injected [Zn(DiMeDMSA)2]2-, at this time it is unknown as to whether the toxicity is due to the Zn chelate molecule, per se, or Zn derived from the molecule after its degradative biotransformation.

Animals↗
PubMedDate not supplied

Polycyclic aromatic hydrocarbon (PAH) residues on skin in relation to air levels among roofers.

To assess the utility of skin wipes as an index of exposure to polycyclic aromatic hydrocarbons (PAHs), simultaneous skin wipe and breathing zone air samples were obtained for 10 roofers. Samples were obtained during removal of an old coal-tar pitch roof and application of a new asphalt roof. Skin wipes were obtained immediately before and after the workshift. Anthracene was present in air but not skin samples. In air samples, the relative concentrations of seven PAHs were fluoranthene greater than pyrene greater than benzanthracene greater than benzo[a]pyrene greater than benzo[b]fluoranthene greater than benzo[ghi]perylene greater than benzo[k]fluoranthene. A similar pattern, or rank concentration, was observed in matching skin wipe samples. The amount (ng) of PAH (either total or individual compounds) found in skin wipes taken after the workday was significantly correlated with that in air samples (micrograms/m3, time-weighted average) for 8 of the 9 cases with air and skin samples taken the same day (r = 0.99 for total PAH). Skin wipe PAH residues were not significantly correlated with air samples taken 4 d earlier. These findings suggest that skin wipes can provide a useful measure of exposure to PAH.

Air Pollutants↗
PubMedDate not supplied

[Relationship between the 1993 Daugirdas Kt/V method and other methods to calculate the dialysis dose].

INTRODUCTION: There are several shortcut formulas to calculate Kt/V, the most widely used because of its simplicity is the logarithmic formula proposed by Lowrie in 1983. The DOQI report recommends use of the formula proposed by Daugirdas's in 1993 to estimate the Kt/V, it must be > or = 1.2. The aim of the present work was to analyse the concordance between the second generation Daugirdas's formula and the other shortcut formulas. MATERIAL AND METHODS: In 208 hemodialysis sessions performed on 61 patients, Kt/V was estimated by thirteen formulas: 10 single-pool modeling and three double-pool modeling. RESULTS: The Kt/V values obtained by Daugirdas's formula was different from those obtained with the other single-pool based formulas (p < 0.01). When the dialysis sessions were classified in 4 groups according to the Kt/V values calculated by Daugirdas's formula, most of the single-pool formulas gave Kt/V values statistically different from those given by Daugirda's formula in all ranges examined. The concordance among Kt/V calculated by every one of the single-pool formulas and Daugirdas's formula was variable. The highest agreement was with Keshaviah's and Lowrie's 1992 formulas and the lowest with Calzavare's and Lowrie's 1983 formulas. The linear multivariate analysis showed that the two factors which influenced the concordance were the Kt/V value obtained by the Daugirdas's formula, and the quotient between the postdialysis body weight and the ultrafiltration rate. Despite the weak concordance with Daugirdas's formula, the Kt/V obtained by Lowrie's 1983 formula and the urea reduction ratio (URR) are still useful tools to monitor the adequacy of dialysis: a Kt/V > 1.065 calculated by the Lowrie's 1983 formula and a PRV > 65% are equivalent to a Kt/V > or = 1.2 calculated by Daugirdas's formula. CONCLUSIONS: The shortcut formulas used to calculate Kt/V give different results with high inter-method variability. When Kt/V is reported it is absolutely necessary to indicate the formula used to calculate it. The Kt/V obtained by Lowrie's 1983 formula and the URR are useful tools to monitor dialysis adequacy.

Adult↗
PubMedDate not supplied

[Relationship between ionic dialysance and urea clearance].

INTRODUCTION: Ionic dialysance is a method of continuous on-line monitoring of delivered dialysis without blood sampling. To compare the results obtained by ionic dialysance and those obtained by the traditional measurements of the dialysis dose, it is necessary to know the relationship between the ionic dialysance and urea clearance. MATERIAL AND METHODS: Ionic dialysance and the urea clearance were determined in 18 patients (13 dialyzed with cuprophan and 5 patients with AN69). Urea clearance was measured by 6 different methods: urea clearance in whole blood calculated with the arteriovenous difference in the urea concentration rates and the arterial flow measured by the rolling pump (KBAVb) or by ultrasounds (KBAVu); urea clearance in whole blood measured by the urea concentration in the dialysate (KBD); urea blood water clearance measured by the arteriovenous difference in the concentration rates using the arterial flow measured by the roller pump (KwBAVb) or by ultrasounds (KwBAVu) and urea blood water clearance measured by the urea concentration in dialysate (KwBD). RESULTS: The mean arterial flow measured by the roller pump was 314.4 +/- 16.2 ml/min and 275.1 +/- 13.8 ml/min when measured by ultrasounds (p < 0.001). The data of ionic dialysance and urea clearances were as follow (ml/min): ionic dialysance 185.6 +/- 11.7; KBAVb 245.7 +/- 15.7; KBAVu 215.4 +/- 13.2; KBD 231.6 +/- 13.1; KwBAVb 218.1 +/- 14; KwBAVu 191.2 +/- 11.8; KwBD 183.1 +/- 11.7. The absolute difference of ionic dialysance with the KwBAVu was 8.4 +/- 6 ml/min (range between -17.8 and 11.5 ml) and with the KwBD was 7.6 +/- 5.4 ml (range between -12.9 and 21.4 ml). CONCLUSIONS: There was a relationship between ionic dialysance and urea blood water clearance. The best concordance was obtained when the clearance was calculated with the urea concentration of dialysate, or with the arteriovenous difference of the urea concentration rates and the arterial blood flow measured by ultrasounds.

Adult↗
PubMedDate not supplied

[Estimate of the dialysis dose using ionic dialysance].

UNLABELLED: The Diascan equipment (Hospal) measures ionic dialysance from which it derives the Kt/V. It is automatic, does not need blood samples and displays the results in real time. The aim of the present study was to compare the Diascan Kt/V with the Kt/V obtained with four simple formulas: two based on a single pool model of urea kinetics (Lowrie 1983 and Daugirdas 1993) and the other based on the two pool model (Maduell formulation applied to Lowrie Kt/V and that proposed by Daugirdas 1995). We have analyzed the inter-method variability, the degree of relationship among the different procedures for Kt/V calculation and the intra-individual variability. The intermethod variability between Kt/V Diascan and Kt/V calculated by the four simple formulas were studied in one hemodialysis session in 19 patients. The Kt/V Diascan was statistically different from that calculated by the four formulas (1,021 +/- 0.140 Diascan vs 1,147 +/- 0.124 for Lowrie-83; vs 1,373 +/- 0.164 for Daugirdas-93; vs 0.963 +/- 0.105 for Maduell and vs 1,173 +/- 0.143 for Daugirdas-95, p < 0.01). The lowest inter-method variability was obtained with the Maduell's Kt/V (relative difference 9%) but even in this case 37% of patients had a variability above 10%. The correlation coefficient was not high enough to allow an estimation of the different Kt/V measurements from the Diascan Kt/V by a regression equation. To study the individual relationship between the Diascan Kt/V and the Kt/V calculated by the four formulations, we have determined the Kt/V every 30 minutes in one hemodialysis session in 30 patients. In all patients we observed a good relationship between the Diascan Kt/V and the other four (correlation coefficient of 0.9952 for Lowrie-83, 0.9976 for Daugirdas-93, 0.9961 for Maduell and 0.9971 for Daugirdas-95); with these correlation coefficientes it was possible to derive regression equations and to obtain an estimation of the four Kt/V's from the Diascan Kt/V. To study the individual variability of each procedure used in the Kt/V calculations we determined the coefficient of variation of the different methods in 5 consecutive hemodialysis sessions performed under identical conditions in 19 patients. The coefficient of variation was 3.7 +/- 1.8% for the Diascan Kt/V; 6.0 +/- 2.8 for the Lowrie-83 Kt/V; 5.8 +/- 2.4 for the Daugirdas-93 Kt/V; 6.5 +/- 2.6% for the Maduell Kt/V; and 5.7 +/- 2.2% for the Daugirdas-95 Kt/V (p < 0.01 between the Diascan Kt/V and the other four). CONCLUSIONS: Although the Diascan Kt/V was statistically different from the other four Kt/V's calculated by the usual formulas, the Diascan Kt/V has an excellent correlation with all of them and showed a lower intra-individual variability. It is possible to obtain an estimation of the calculated Kt/V for each patient by linear regression equation.

Electrophysiology↗
PubMedDate not supplied

Cardiac surgery on Jehova's Witnesses at Instituto Cardiovascular-Hospital Pavia.

Jehovah's Witnesses (J.W.) can undergo successful cardiac operations. We have operated five J.W. patients. Of these patients, two had coronary artery bypass surgery and three had correction of congenital anomalies. These included an atrial septal defect with infundibular pulmonic stenosis, a tetralogy of Fallot and a patient with a ventricular septal defect. Our treatment protocol includes a meticulous surgery, the use of early heparinization to collect all shed blood into the pump oxygenator, observation in the operating room for early exploration if the patient bleeds and administration of iron preparations. Recombinant human erythropoietin, although available and in our treatment protocol, has not been used yet. All patients survived the operation and left the hospital with an excellent hemoglobin and hematocrit. The length of stay varied from 7 to 15 days.

Adolescent↗
PubMedDate not supplied

[Ionic dialysance to control the dose of dialysis. One year experience].

The Diascan equipment (Hospal) measures ionic dialysane which it derives the K and the Kt. If we divide the Kt obtained with Diascan between the Kt/V obtained by a simplified formula, it result a value of V for every patient. Entering this V in the Diascan software we can obtain a Kt/V (Diascan Kt/V), similar in theory to the simplified Kt/V. In the year 2002 we have controlled the delivered dialysis in our unit with the Diascan Kt/V. The aim of the present study was to study the agreement between de Diascan Kt/V and the Lowrie Kt/V. During the year 2002, 63 patients have been dialyzed in monitors with Diascan equipment. We calculated the V of each patient by dividing the Kt Diascan between the Lowrie Kt/V in the same dialysis session. The mea of the two consecutive measurements was considered the V value. Throughout the year 2002, 7 agreement studies were realized. The inter-method variability was assessed by the relative difference (absolute difference Diascan Kt/V-Lowrie Kt/V, divided by the average of both tests). A good agreement was considered when the relative difference was equal or lower than 10%. In the 7 agreement studies realized, the mean of the relative difference oscilled between 5.2 and 6.6%, and the percentage of patients with a relative difference equal or lower than 10% oscilled between 83 and 91%. During a month, the Diascan Kt/V was controlled in all dialysis sessions in 41 patients (554 sessions in total). Failure in the lecture of Kt/V Diascan was observed in 41 sessions (7%). A Diascan Kt/V greater than 1 (the minimum delivered dialysis considered in our unit) was obtained in 93% of the valid sessions. 38 of 41 patients had a mean monthly Diascan Kt/V greater than 1. The coefficient of variability of any patient oscilled between 2.1 and 12.4% (mean 5.1%). Diascan Kt/V is good procedure for the monitoring the delivered dialysis without blood sampling or any additional costs.

Evaluation Studies as Topic↗