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Biomedical subjects

G Nash

Publications and source records attributed to G Nash.

At least 19 recordsLinked to original sources
PubMed2001

Comparison of the effects of radiographic contrast media on dehydration and filterability of red blood cells from donors homozygous for hemoglobin A or hemoglobin S.

Iodinated radiographic contrast media have traditionally been contraindicated in patients with sickle cell disease because their high osmolality may induce osmotic shrinkage of red blood cells, impair blood flow through the microcirculation, and precipitate or exacerbate a sickle cell crisis. This study investigated that concept by comparing the hematological and rheological effects in vitro of four X-ray contrast media of differing osmolalities: Visipaque (290 mOsm/kg), Hexabrix (600 mOsm/kg), Omnipaque (844 mOsm/kg), and RenoCal-76 (1940 mOsm/kg). Blood was tested from 10 normal and 10 sickle cell donors at drug concentrations of 0, 1, 10, and 30% w/v in an attempt to approximate the relative concentrations of contrast medium to blood that might occur during the bolus-injection and circulation-diluted phases of drug administration. Parameters evaluated included hematology, red cell morphology, and red cell flow resistance through a micropore filter to approximate the microcirculatory effects. Significant hematological effects for both normal and sickle cell donors included a concentration dependent decrease in hematocrit and MCV, and increase in MCHC, all of which varied directly with the osmolality of the contrast media in the order of RenoCal-76 > Omnipaque > Hexabrix > Visipaque. The contrast media had minor effects on red blood cell morphology except for RenoCal-76, 10-30% in which marked echinocytosis was observed. There was no significant increase in the number of irreversibly sickled cells in donors with hemoglobin S. Filterability of red cell suspensions through capillary size pores was impaired in both normal and sickle cell samples in direct proportion to the osmolality of the contrast media, as listed above. Filterability effects were greater for sickle cells than for normal red cells. Visipaque, which was closest to isotonicity, had little effect on red cell volume and had no significant effect on filterability of normal or sickle cells. These results suggest that microcirculatory impairment following infusion of contrast media may occur in sickle patients because of the unusual rheological sensitivity of HbSS red cells, and may be avoided by choice of an isotonic medium.

Anemia, Sickle Cell↗
PubMed2000

Glial growth factor 2 induces proliferation and structural changes in ensheathing cells.

Ensheathing cells were isolated from neonatal rat olfactory bulbs and cultured in the presence of glial growth factor 2 (GGF2). Proliferation assay showed that at concentrations of up to 60 ng/ml GGF2, ensheathing cells underwent a modest increase in proliferation rate. This stimulation was not maintained at high doses of GGF2 at 100 ng/ml or more. Chemotaxis chambers and scanning electron microscopy were used to determine whether GGF2 was a chemoattractant for ensheathing cells. Although the results showed no chemotactic response to GGF2, ensheathing cells demonstrated structural changes when cultured in the presence of 20 ng/ml GGF2. Ultrastructural observations revealed that GGF2 promoted increased deposition of extracellular matrix on the cell membrane, more cytoskeletal elements in the processes and as a possible consequence, contributed to a more rigid support. Ensheathing cells cultured in the absence of GGF2 often extended thinner and curved processes. Reverse transcription-polymerase chain reaction confirmed the presence of GGF2 transcripts in ensheathing cells, suggesting that ensheathing cells themselves are a source of GGF2.

Animals↗
PubMed1997

Pulmonary aspergillosis in acquired immune deficiency syndrome: autopsy study of an emerging pulmonary complication of human immunodeficiency virus infection.

Pulmonary aspergillosis has recently been described as an emerging infection in patients with acquired immune deficiency syndrome (AIDS), but the pathological changes have not been well documented. In this autopsy study, 17 cases of AIDS-related pulmonary aspergillosis were identified from the files of two institutions. With the exception of hypersensitivity reactions, the entire spectrum of pulmonary aspergillosis was represented. Thirteen patients exhibited acute invasive aspergillosis, and seven patients had evidence of subacute or chronic invasive infection, four of whom also had areas of acute invasion. One patient had necrotizing bronchial aspergillosis as well as acute invasive infection, and one individual had saprophytic colonization of a cavity caused by previous Pneumocystis carinii pneumonia (PCP) without evidence of invasive aspergillosis. The same conditions known to predispose immunocompromised individuals without human immunodeficiency virus (HIV) infection to invasive pulmonary aspergillosis were also identified in these patients with AIDS and included neutropenia, steroid therapy, and underlying lung disease. Additional pulmonary conditions were identified in all but one case and consisted mainly of infection or some form of chronic lung disease. In particular, half of the cases were associated with pulmonary fibrosis related to prior PCP. All cases occurred in or after 1990, confirming the perception of the recent emergence of aspergillosis in AIDS. As suggested by this study, one reason for this may be that patients with AIDS are now living long enough to develop one or more of the predisposing conditions for pulmonary aspergillosis.

AIDS-Related Opportunistic Infections↗
PubMed1997

Prevention of remote organ injury in cardiopulmonary bypass: the impact of flow generation technique.

The purpose of this study was to investigate the effects of 3 different types of flow generation for cardiopulmonary bypass on gastrointestinal permeability and on neutrophil expression of CD11b, a surface marker of neutrophil activation. Fourteen patients undergoing elective coronary revascularization were selected randomly to receive 1 of the 3 flow generation techniques (roller, pulsatile, or centrifugal). Intestinal permeability was assessed by the fraction of an oral dose of 51chromium-ethylenediaminetetraacetate (51Cr-EDTA) recovered in the urine over 24 h. Neutrophil activation was determined by expression of CD11b markers at 6 time points. Overall, the 14 patients showed significant increases in intestinal permeability. It was not possible to demonstrate statistically significant differences among the flow generation groups; however, when compared to both roller pump groups, the centrifugal pump group showed a 3.2% reduction in intestinal permeability. There was no change in the expression of CD11b receptors throughout the time points, nor was there a relationship of CD11b markers to the flow generation technique.

Administration, Oral↗
PubMed1995

Do fish acclimated to low temperature improve microcirculatory perfusion by adapting red cell rheology?

We have measured the rheological properties of individual red blood cells from fishes inhabiting different thermal environments and have also investigated the effects on red cells of acute in vitro temperature changes. The membrane shear elastic modulus (rigidity) increased markedly with decreasing temperature, and the dependence was similar if temperature was varied acutely in vitro or if cells were measured at normal body temperatures. Red cells from trout and Notothenia coriiceps had almost equal membrane rigidity at comparable temperatures and showed similar temperature-sensitivity in acute experiments. Entry times of trout cells into narrow (approximately 4 microm diameter) micropipettes also increased during in vitro reduction of temperature, and this could be explained largely by the temperature-dependence expected of aqueous solutions. Perhaps surprisingly, entry times did not vary when trout living at different temperatures were tested at these temperatures. Transit times of individual cells through somewhat larger pores (5 microm) in oligopore filters again increased with decreasing temperature in vitro (partly due to increasing fluid viscosity), but such transit times did show a similar temperature-dependence for cells from trout living at different temperatures. Thus, the temperature-dependence of cellular flow resistance appears to arise from variations in membrane rigidity and in the viscosity of fluid components, along with unquantified variations in components such as microtubular structures (which we found did not influence membrane rigidity but did affect pore entry time) and the cell nucleus. Thermal acclimation did not involve adaptation to compensate for increased membrane rigidity or a large pore transit time, with, at most, minor compensation in entry times into smaller pores. We conclude that impaired cellular rheology is not a major factor influencing circulation in fish at low temperature.

Journal Article↗