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Biomedical subjects

P A Rivas

Publications and source records attributed to P A Rivas.

10 recordsLinked to original sources

Real-time black-blood MRI using spatial presaturation.

A real-time interactive black-blood imaging system is described. Rapid blood suppression is achieved by exciting and dephasing slabs outside the imaging slice before each imaging excitation. Sharp-profiled radio frequency saturation pulses placed close to the imaging slice provide good blood suppression, even in views containing slow through-plane flow. In vivo results indicate that this technique improves endocardial border definition during systole in real-time cardiac wall-motion studies. Phantom and animal results indicate that this technique nearly eliminates flow artifacts in real-time intravascular studies. J. Magn. Reson. Imaging 2001;13:807-812.

Algorithms↗

Antibody-mediated hemolytic anemia following ABO-mismatched organ transplantation: contributory role of HLA matching and polyclonal antilymphocyte globulin.

We report three instances of antibody-mediated hemolytic anemia following ABO-mismatched, but compatible, renal (n = 2) and simultaneous pancreas-kidney (n = 1) transplantation. The two renal allograft recipients had received a 6-antigen matched transplant; one received polyclonal antilymphocyte globulin to treat an early rejection episode. The simultaneous pancreas-kidney transplant received polyclonal antilymphocyte globulin (ALG) as part of a quadruple therapy induction regimen. All three patients developed severe, but self-limited, antibody-mediated hemolytic anemia within two weeks of their transplants. Serologic testing demonstrated the hemolysis to be antibody mediated; furthermore, testing of the ALG lots demonstrated high titers of anti-red blood cell antibodies. The possible contribution of ALG and HLA matching to the hemolysis seen in these patients after ABO mismatched organ transplantation is discussed.

ABO Blood-Group System↗

The morphology and function of rabbit hepatocytes isolated using ethylenediaminetetraacetate.

The enzyme digestion technique using collagenase is used in most studies that describe hepatocyte isolation, including those in which hepatocytes are isolated for transplantation. The use of collagenase, however, has several drawbacks. We describe the use of a highly concentrated ethylenediaminetetraacetate solution for isolation of hepatocytes followed by purification using a Percoll gradient in the rabbit model. Isolated hepatocytes were then preserved at 4 degrees C for up to three days in either University of Wisconsin solution or Dulbecco's modified eagle's medium. Morphological studies of hepatocytes at 24 hr and 72 hr in either medium were performed using Papanicolaou and PAS stains of cytopreparations for the presence of glycogen. Similarly, functional studies of the preserved hepatocytes included LDH release, total tissue water content, and amount of 99m-technetium mebrofenin uptake. The use of EDTA perfusion for hepatocyte isolation was highly reproducible in this model. The cell yield was comparable to that achieved previously using collagenase. The morphologic studies demonstrated pure hepatocytes with well-preserved architecture when preserved for up to three days in UW solution. Functional studies showed a statistically significant lower LDH release and total tissue water content and a higher technetium-99m mebrofenin uptake for hepatocytes preserved in UW solution. We conclude that a pure and viable hepatocyte suspension can be obtained from rabbit livers using concentrated EDTA solutions. These hepatocytes can be well preserved at 4 degrees C for up to 72 hr in UW solution, based on morphologic and functional criteria.

Adenosine↗

Extracellular pH modulates block of both sodium and calcium channels by nicardipine.

Slowing of the recovery of the Na channel from local anesthetic block at low external pH has been well described. In contrast the Ca channel has been reported not to show such an effect. Because of the absence of this response, a two-site model for the interaction of Ca antagonists with the Ca channel has been proposed. We sought to determine whether these results were a consequence of utilizing the poorly lipid-soluble Ca antagonist diltiazem as the test drug. We have measured the time constants of recovery (tau r) of Na (INa) and Ca currents (ICa) recorded from rabbit atrial myocytes during control and exposure to the lipid-soluble Ca antagonist nicardipine as external pH was reduced from 7.8 to 6.9. In the absence of drug, tau r for INa decreased from 19 +/- 1.3 to 12.1 +/- 0.6 ms for the pH reduction. Similarly, tau r for ICa decreased from 53 +/- 7 to 33.6 +/- 7 ms. During exposure to nicardipine tau r for INa increased from 2.24 +/- 0.8 to 5.96 +/- 0.8 s as external pH was reduced. For ICa, tau r also increased from 1.43 +/- 0.55 to 2 +/- 0.32 s. For each channel type, the results are well explained by a single blocking site model with hydrophobic and hydrophilic pathways to a single membrane binding site as proposed by Hille (J. Gen. Physiol. 69: 497-517, 1977).

Animals↗

Pancreas-kidney transplantation for intensivists: perioperative care and complications.

Simultaneous pancreas-kidney transplantation is a therapeutic option for type I diabetics with end-stage renal disease. It aims to correct the uremic state, to normalize glucose hemeostasis, and to ameliorate diabetic complications. Careful donor-recipient selection and meticulous intra-operative and postoperative care will substantially impact recipient morbidity. An understanding of the technical aspects of the surgical procedure and its metabolic and immunological consequences is necessary to successfully manage a pancreas-kidney transplant recipient, many of whom are nursed in intensive care units. A successful outcome is predicted in early recognition of technical complications and aggressive management of rejection to achieve the current 1-year graft survival rates of 75% for pancreas transplants and 84% for kidney transplants.

Adult↗

Transplantation of hepatocytes: an in-vitro and in-vivo study in canines.

We isolated and transplanted hepatocytes in the canine, large animal model to evaluate hepatocyte yield and purity as well as the optimal site for hepatocyte engraftment (i.e., the spleen or the portal bed). We obtained viable, pure, single hepatocyte suspensions that were readily preserved at 4 degrees C in University of Wisconsin (UW) solution for up to 3 days. Both intrasplenic and portal vein injection were well tolerated, with minimal recipient morbidity and mortality when 1-2 x 10(9) hepatocytes were injected into immunosuppressed allogeneic hosts. We noted the embolization of hepatocytes into the parenchyma of the native liver within 7 days of intrasplenic transplantation that produced a mild reversible derangement of liver function and histology. These results warrant consideration prior to clinical trials of hepatocyte transplantation in man.

Adenosine↗