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Biomedical subjects

R M Nelson

Publications and source records attributed to R M Nelson.

At least 37 records · Page 2Linked to original sources
PubMed1999

Variability in physician opinion on limiting pediatric life support.

OBJECTIVE: We conducted this study to investigate how physicians in a pediatric intensive care unit (ICU) currently make decisions to withdraw and withhold life support. Consultation with the patient's primary caregiver often precedes decisions about withdrawal and limitation of life support in chronically ill patients. In these scenarios, the patient's primary caregiver was the pediatric oncologist. To evaluate the influence of subspecialty training, we compared the attitudes of the pediatric intensivists and the oncologists using scenarios describing critically ill oncology patients. DESIGN: Cross-sectional survey. Each physician was randomly assigned 4 of 8 potential case scenarios. SETTING: A total of 29 American pediatric ICUs. PARTICIPANTS: Pediatric intensive care and oncology attendings and fellows. INTERVENTION: Systematic manipulation of patient characteristics in two hypothetical case scenarios describing 6-year-old female oncology patients presenting to the ICU after the institution of mechanical ventilator support for acute respiratory failure. Cases 1 through 4 described a patient who, before admission, had a 99% projected 1-year probability of survival from her underlying cancer and suffered from severe neurologic disabilities. Cases 5 through 8 described a patient who was neurologically normal before admission and had a <1% chance of surviving longer than 1 year because of her underlying cancer. Each physician was randomly assigned 2 cases from cases 1 through 4 and 2 cases from cases 5 through 8. Within each of these case scenarios, parental preferences (withdraw or advance support or look for guidance from the caregivers) and probability of survival (5% vs 40%) were manipulated. Before distribution, the survey instrument was pilot-tested and underwent a rigorous assessment for clinical sensibility. PRIMARY OUTCOME MEASURES: Physicians ratings of the importance of 10 factors considered in the decision to withdraw life support, and their decisions about the appropriate level of care to provide. Respondents were offered five management options representing five levels of care: 1) discontinue inotropes and mechanical ventilation but continue comfort measures; 2) discontinue inotropes and other maintenance therapy but continue mechanical ventilation and comfort measures; 3) continue with current management but add no new therapeutic intervention; 4) continue with current management, add additional inotropes, change antibiotics and the like as needed, but do not start dialysis; and 5) continue with full aggressive management and plan for dialysis if necessary. Respondents also were asked whether they would obtain an ethics consultation. RESULTS: A total of 270 physicians responded to our survey (165 of 198 potentially eligible pediatric intensivists and 105 of 178 pediatric oncologists for response rates of 83% and 59%, respectively). The respondents considered the probability of ICU survival and the wishes of the parents regarding the aggressiveness of care most important in the decision to limit life-support interventions. No clinically important differences were found when the responses of oncologists were compared with those of intensivists. In six of eight possible scenarios, the same level of intensity of care was chosen by less than half of all respondents. In three scenarios, >/=10% of respondents chose full aggressive management as the most appropriate level of care, whereas another >/=10% chose comfort measures only when viewing the same scenario. The most significant respondent factors affecting choices were professional status (attending vs fellow) and the self-rated importance of functional neurologic status. The majority of respondents (83%) believed that the intensive care and the oncology staff were usually in agreement at their institution about the level of intervention to recommend to the parents. (ABSTRACT TRUNCATED)

Child↗
PubMed1998

Detection system for reaction-rate analysis in a low-volume proteinase-inhibition assay.

High-throughput screening of large combinatorial chemical libraries in biochemical assays will benefit from reduced reagent volume and increased speed of measurement. Standard assays typically are performed in 96-well microtiter plates having 200-microL well volumes and up to an hour of incubation time. In this paper, we demonstrate a technique for precise and rapid measurement of the progress of an enzymatic reaction and its inhibition with reduced volume and time (for this work, the assay was mixed at the 200-microL level and detected in 2-microL volumes with minutes of total assay time). Directly measuring the enzyme activity in the small volume format yields a precise value for the median inhibitory concentration (IC50) of an inhibitor compound. The model assay is the endoproteolytic cleavage of a small fluorogenic peptide by human neutrophil collagenase (MMP-8). The fluorogenic peptide was labeled at one end with a UV/blue fluorophore (N-methylanthranilyl) and at the other end with a quencher (dinitrophenol). To generate inhibition data, a hydroxamate peptide analog inhibitor of collagenase, actinonin, was included in the reaction. The experiments were performed using ultraviolet laser illumination (325 nm wavelength) and parallel fluorescence detection by a cooled, charge-coupled-device camera system to increase sensitivity and speed. The assay volume was reduced to 2 microL for data collection, and the total time for mixing, incubation, and measurement was less than 6 min. For comparison to a standard format, the same assay was performed in a 96-well microtiter plate in 200 microL using 30 min of incubation and measurement in a microtiter plate fluorimeter. Median inhibitory concentrations (IC50) for actinonin of 73 +/- 16 and 100 +/- 14 nM were obtained in the 2- and 200-microL assays, respectively. One concern with assay miniaturization and increases in throughput is a potential loss of precision and accuracy. Laser excitation and parallel detection of fluorescence is a promising approach for increased speed and reduced cost without loss of precision for proteinase inhibition assays.

Fluorescence↗
PubMed1998

Interaction of secretory leukocyte protease inhibitor with heparin inhibits proteases involved in asthma.

Protease inhibition by secretory leukocyte protease inhibitor (SLPI) is accelerated by the sulfated polysaccharides. The nature of the SLPI-polysaccharide interaction, explored with affinity chromatography, indicated that this interaction was sensitive to the charge and type of polysaccharide. Dextran and chondroitin had the lowest affinity for SLPI, followed by dermatan, heparan, and dextran sulfates. While heparin bound SLPI tightly, the highest affinity heparin chains unexpectedly contained a lower level of sulfation than more weakly interacting chains. Heparin oligosaccharides, prepared using heparin lyase I were SLPI-affinity fractionated. Surprisingly, undersulfated heparin oligosaccharides bound SLPI with the highest affinity, suggesting the importance of free hydroxyl groups for high affinity interaction. Isothermal titration calorimetry was used to determine the thermodynamics of SLPI interaction with a low molecular weight heparin, an undersulfated decasaccharide and a tetrasaccharide. The studies showed 12-14 saccharide units, corresponding to molecular weight of approximately 4,800, were required for a 1:1 (SLPI:heparin) binding stoichiometry. Furthermore, an undersulfated decasaccharide was able to bind SLPI tightly (Kd approximately 13 nM), resulting in its activation and the inhibition of neutrophil elastase and pancreatic chymotrypsin. The in vitro assessment of heparin and the decasaccharide and tetrasaccharide using stopped-flow kinetics suggested that heparin was the optimal choice to study SLPI-based in vivo protease inhibition. SLPI and heparin were co-administered by inhalation in therapy against antigen-induced airway hyperresponsiveness in a sheep bronchoprovocation model. Heparin, in combination with SLPI demonstrated in vivo efficacy reducing early and late phase bronchoconstriction. Heparin also increased the therapeutic activity of SLPI against antigen-induced airway hyperresponsiveness.

Animals↗
PubMed1998

Persistent pulmonary hypertension of the neonate and asymmetric growth restriction.

OBJECTIVE: To evaluate the possible associations between persistent pulmonary hypertension of the neonate, need for extra-corporeal membranous oxygenation, small for gestational age (SGA), and low ponderal index for gestational age in infants with persistent pulmonary hypertension of the neonate and in matched controls. METHODS: Eighty-six infants with persistent pulmonary hypertension of the neonate delivered from 1991 to 1994 at our hospital were matched with 430 contemporaneous control singleton neonates. Birth weight and ponderal indices (100 x weight/length3) less than the tenth percentile for gestational age and gender were defined as SGA and low ponderal index, respectively. We assessed associations between these markers, the presence of persistent pulmonary hypertension of the neonate, and the need for extracorporeal membranous oxygenation. RESULTS: Low ponderal index was associated with persistent pulmonary hypertension of the neonate (odds ratio [OR] 5.4), whereas SGA was not. Low ponderal index (OR 4.0) was an independent correlate of persistent pulmonary hypertension of the neonate after adjustment with logistic regression for 5-minute Apgar scores less than 7, umbilical arterial pH less than 7.10, and presence of meconium. Low ponderal index was associated with need for extracorporeal membranous oxygenation in neonates with persistent pulmonary hypertension (P < .001). CONCLUSION: Fetal developmental events may significantly affect neonatal pulmonary status. Diminished neonatal nutritional status, as measured by low ponderal index for gestational age, is associated with increased risk of persistent pulmonary hypertension of the neonate and severity of the disease process.

Case-Control Studies↗
PubMed1998

Functional aspects of skeletal muscle contractile apparatus and sarcoplasmic reticulum after fatigue.

This study examined the effects of fatigue on the functional aspects of the contractile apparatus and sarcoplasmic reticulum (SR). Frog semitendinosus muscles were stimulated to fatigue, and skinned fibers or a homogenate fraction was prepared from both fatigued and rested contralateral muscles. In fatigued fibers, maximal Ca2+-activated force of the contractile apparatus was unaltered, whereas maximal actomyosin-ATPase activity was depressed by 20%. The Ca2+ sensitivity of force was increased, whereas that of actomyosin-ATPase was not altered. Also, the rate constant for tension redevelopment was decreased at submaximal Ca2+ concentration. These latter findings suggest that fatigue slows the dissociation of force-generating myosin cross bridges. Ca2+ uptake and Ca2+-ATPase activity of the SR were depressed by 46 and 21%, respectively, in the fatigued muscles. Fatigue also reduced the rates of SR Ca2+ release evoked by AgNO3 and 4-chloro-m-cresol by 38 and 45%, respectively. During fatigue, the contractile apparatus and SR undergo intrinsic functional alterations. These changes likely result in altered force production and energy consumption by the intact muscle.

Animals↗
PubMed1997

Ethics in the intensive care unit. Creating an ethical environment.

This article discusses ethical issues that exist each and every day in interactions with patients, families, and fellow workers in the ICU, even in the absence of overt conflict or controversy. The creation of an ethical working environment in the ICU is a necessary precondition for dealing with the ethical issues raised by specific issues such as cardiopulmonary resuscitation, the limitation or withdrawal of life-sustaining treatment, the special care of children with disabilities, brain death, and organ procurement, and triage. The creation of an ethical working environment requires developing a collaborative relationship with patients, families, staff, and other health care professionals.

Adult↗
PubMed1997

Intraobserver and interobserver reliability of assessments of impairments and disabilities.

BACKGROUND AND PURPOSE: The purpose of this study was to evaluate the interobserver and intraobserver reliability of assessments of impairments and disabilities. SUBJECTS AND METHODS: One physical therapist's assessments were examined for intraobserver reliability. Judgments of two pairs of therapists were used to examine interobserver reliability. Reliability was assessed by Cohen's kappa. RESULTS: Of the 42 impairments and disabilities assessed by the physical therapist in the intraobserver reliability study, kappa values could be calculated for 33 items. For 31 items (94%), kappa values ranged from .40 to .91, and 2 items (6%) had kappa values of less than .40. To determine interobserver reliability, 37 items were assessed in one practice. Kappa values could be calculated for 34 items, with 30 items (88%) having kappa values ranging from .41 to .80 and 4 items (12%) showing "poor" agreement. In the second practice, 47 items were assessed for interobserver reliability. Kappa values could be calculated for 40 items, with 11 items (27.5%) having kappa values ranging from .41 to .84. Poor agreement was shown for the remaining 29 items (72.5%). CONCLUSION AND DISCUSSION: Assessments of impairments and disabilities are potentially reliable. The differences between practices of the interobserver reliability study can be explained by the fact that one of the therapists did not receive training in the use of the assessment form. More generalizable conclusions will require further study with more subjects and therapists.

Adolescent↗
PubMed1997

Inhibition of colon carcinoma cell lung colony formation by a soluble form of E-selectin.

During metastasis, tumor cells adhere to vascular endothelia. E-selectin is an adhesive protein expressed by cytokine-activated endothelium that can support adhesion of colon cancer cells through the recognition of specific carbohydrate ligands. Using a series of colon carcinoma cell lines that displayed E-selectin adhesiveness and an increased metastatic capacity in cytokine-treated mice, we examined possible inhibition of cytokine-dependent experimental lung metastasis by a soluble form of E-selectin, the recombinant fusion protein E-selectin-immunoglobulin. We found that E-selectin-immunoglobulin bound to the surfaces of HT-29 colon carcinoma cells and blocked the formation of cytokine-inducible experimental lung metastases; control L-selectin-immunoglobulin also bound to HT-29 cells but had no effect on tumor cell lung colonization. E-selectin-immunoglobulin was found to interfere with E-selectin-dependent adhesion of HT-29 cells to activated vascular endothelium and to block the retention of these cells in the lung, a process that implies tumor cell adhesive interactions with the host vasculature. Our results demonstrate that E-selectin-immunoglobulin inhibits adhesion and formation of lung metastases by colon carcinoma cells and suggest that impairment of tumor cell-endothelium adhesion might represent a therapeutic approach to the metastatic diffusion of tumors.

Animals↗
PubMed1996

Literature and ethical medicine: five cases from common practice.

This essay is composed of five stories written by practicing physicians about their patients. Each clinical story describes a challenging ethical condition-potential abuse of medical power, gravely ill and probably over-treated newborns, iatrogenic narcotic addiction, deceived dying people. Rather than singling out one ethical conflict to resolve or adjudicate, the authors attempt, through literary methods, to grasp the singular experiences of their patients and to act according to the deep structures of their patients' lives. Examining these five stories with simple literary tools-attention to narrative frames, time, plot, and desire-reveals the mechanisms through which acts of writing and reading contribute to clinical clarity and ethical actions.

Adult↗
PubMed1995

Differential colon cancer cell adhesion to E-, P-, and L-selectin: role of mucin-type glycoproteins.

E-, P-, and L-selectin support the adhesion of leukocytes to the vessel wall through the recognition of specific carbohydrate ligands, which often contain sialylated, fucosylated lactosamines such as sialyl Lewis x [sLex; Neu5Ac alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc-]. E-selectin expressed by activated endothelium has been shown to support the adhesion of sLex-bearing colon cancer cells. In the present study, we examine the interactions of multiple colon cancer cell lines with all three selectins. Three colon cancer cell lines (LS 180, T84, and COLO 205) bound to recombinant purified E-, P-, and L-selectin. The colon cancer line COLO 320 bound to P- and L-selectin but not E-selectin; conversely, HT-29 cells bound E-selectin but not P- and L-selectin. Caco-2 showed little or no interaction with any of the three selectins. Treatment of the cells with O-sialoglycoprotease from Pasteurella haemolytica, an enzyme that selectively cleaves mucin-type O-linked glycoproteins, reduced binding to purified P- and L-selectin in all cases. In addition, recombinant soluble P- and L-selectin bound to affinity-purified mucins from all adherent tumor cell lines. Of the four tumor cell lines that interacted with E-selectin, O-glycoprotease treatment substantially diminished adhesion of LS 180 and T84, had little effect on COLO 205, and failed to inhibit the binding of HT-29. As predicted by these data, E-selectin showed substantial binding only to mucins purified from LS 180 and T84. These findings suggest that L- and P-selectin interact primarily with mucin-type ligands on colon cancers, whereas E-selectin can recognize both mucin and nonmucin ligands. Binding of the colon cancer lines to purified selectins correlates with their adhesion to activated endothelial cells (E-selectin-dependent), platelets (P-selectin-dependent), and neutrophils (L-selectin-dependent). These differential tumor cell-selectin interactions may influence metastatic spread and may also contribute to the observed variability in host response to tumor progression.

Animals↗
PubMed1995

Carbohydrate-protein interactions in vascular biology.

Carbohydrate-protein interactions participate in a wide variety of biological and pathological events. In recent years, particular attention has been paid to the carbohydrate-protein interactions that occur in vascular biology. Sialylated oligosaccharides are ligands of a structurally diverse group of proteins that include the selectins and members of the immunoglobulin superfamily. Various glycosaminoglycans can be recognized by an overlapping set of proteins that include two of the selectins and CD44. Emerging knowledge of carbohydrate-protein interactions in human pathophysiology are discussed.

Animals↗
PubMed1994

Inositol polyanions. Noncarbohydrate inhibitors of L- and P-selectin that block inflammation.

Selectins are cell adhesion molecules known to support the initial attachment of leukocytes to inflamed vascular endothelium through their recognition of carbohydrate ligands such as the tetrasaccharide sialyl Lewisx (Neu5Ac alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc-). In the present study, we describe the inhibition of L- and P-selectin function by inositol polyanions, simple 6-carbon ring structures that have multiple ester-linked phosphate or sulfate groups. In a purified component competition assay, binding of L- and P-selectin-Ig fusion proteins to immobilized bovine serum albumin-sialyl Lewisx neoglycoprotein was inhibited by inositol hexakisphosphate (InsP6, IC50 = 2.1 +/- 1.4 microM and 160 +/- 40 microM), by inositol pentakisphosphate (InsP5, IC50 = 1.4 +/- 0.2 and 260 +/- 40 microM), and by inositol hexakissulfate (InsS6, IC50 = 210 +/- 80 microM and 2.8 +/- 0.9 mM); E-selectin-Ig binding was unaffected. Inositol polyanions diminished the adhesion of LS180 colon carcinoma cells to plates coated with L- and P-selectin-Ig but not with E-selectin-Ig. Inositol polyanions blocked polymorphonuclear leukocyte (PMN) adhesion to COS cells expressing recombinant transmembrane P-selectin but not to those expressing E-selectin. In addition, inositol polyanions diminished PMN adhesion to activated endothelial cells under rotation-induced shear stress, a process known to require L-selectin function. In vivo, the effects of inositol polyanions were studied in two murine models of acute inflammation. Intravenously administered InsP6 (two doses of 40 mumol/kg) inhibited PMN accumulation in thioglycolate-induced inflammation (55 +/- 10% inhibition) and in zymosan-induced inflammation (61 +/- 4% inhibition). InsP5 and InsS6 also inhibited inflammation in these models, although higher doses were required for InsS6. In conclusion, inositol polyanions are noncarbohydrate small molecules that inhibit L- and P-selectin function in vitro and inflammation in vivo.

Animals↗
PubMed1994

Development of secondary sex characteristics in male rats after fetal and perinatal cimetidine exposure.

Cimetidine has been reported to cause antiandrogenic effects in male pups of female rats receiving cimetidine during gestation. Because of conflicting reports of cimetidine causing permanent antiandrogenic effects in male rats, we studied the sexual development of male rats born to females receiving cimetidine. Water or water and cimetidine (194 mg/kg of body weight per day) were administered to pregnant rats from day 12 of gestation through weaning. A total of 130 male pups were studied. Testicular prostate gland/seminal vesicle weights, anogenital distance, serum testosterone and dihydrotestosterone levels, and seminiferous tubule areas were compared between the two groups. Transfer of cimetidine across the placenta and though breast milk was confirmed by HPLC analysis of serum from female littermates at 0, 10, and 20 days of age. With the exception of a smaller anogenital distance (p < 0.03) and a lower anogenital index (p < 0.05) in the cimetidine-exposed newborn rats, no statistically significant differences were observed in the measured parameters between the cimetidine-exposed and control groups. Cimetidine exposure during the fetal and perinatal periods did not alter the development of secondary sex characteristics in male rat pups.

Animals↗
PubMed1994

Loop diuretic derivative L-644,711 inhibits K(+)-stimulated cellular injury in neonatal guinea pig cortical astrocytes.

An early pathological rise in extracellular K+ following acute hypoxia results in Cl- uptake into astrocytes through the Cl/HCO3- exchanger with an osmotic equivalent of water. This study addressed effects of the anion transport inhibitor, L-644,711, (5,6,-dichloro-2,3, 9,9a-tetrahydro-3-oxo-9a-propyl-1H-fluroen-7-yl)oxyacetic acid. Confluent primary cultures from neonatal guinea pigs, characterized as > 95% astrocytes with antiserum to glial fibrillary acidic protein, were manipulated by incubation in either basal buffer (BB) with the ionic composition of Dulbecco's minimum essential media (DMEM) or one with high extracellular K+ (HiK). Incubation in 27 or 60 mM Hik significantly reduced cell viability and precipitated a time-dose dependent increase in lactate dehydrogenase (LDH) efflux (30 min to 4 h). L-644,711 was not cytotoxic, and significantly inhibited HiK-stimulated LDH efflux. The optimal effective dose of L-644,711 for preventing injury in guinea pig astrocytes was 10(-11)M when administered simultaneously with the HiK paradigm or in reversing injury when administered 30 min after exposing cells to HiK. These findings indicate the potential usefulness of agents which modify ion transport processes in hypoxic-ischemic cerebral injury.

Animals↗
PubMed1994

Endothelial-leukocyte adhesion molecules in human disease.

An effective host response to infection or tissue damage requires focal accumulation of leukocytes. Leukocyte adhesion to the vessel wall, a key step in this process, depends on the ordered expression of specific endothelial cell surface molecules. The endothelial molecules that support adhesion include selectins that recognize leukocyte cell surface glycoconjugates as well as members of the immunoglobulin superfamily that interact with leukocyte integrins. Although inflammation can occur with minimal damage to the vessel wall and surrounding tissues, control mechanisms sometimes appear to fail, and the inflammatory response itself becomes a significant clinical problem. In this review, we discuss endothelial-leukocyte adhesion molecules with particular emphasis on their expression and function in human disease. Pathophysiological processes presented include atherosclerosis, ischemia-reperfusion injury, acute lung injury, rheumatoid arthritis, and graft rejection. A more detailed description of the discovery and characterization of the key molecules appears in the antecedent article entitled "Endothelial-Leukocyte Adhesion Molecules".

Cell Adhesion↗