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Biomedical subjects

J M Harris

Publications and source records attributed to J M Harris.

At least 127 records · Page 7Linked to original sources
PubMed1995

Protein-rejecting ability of surface-bound dextran in end-on and side-on configurations: comparison to PEG.

There is much interest in attaching polyethylene glycol (PEG) and other hydrophilic, neutral polymers to surfaces to reduce the extent of protein and cell adsorption. Interestingly, these same surface-bound polymers are effective in masking surface charge and reducing electrokinetic effects such as particle electrophoretic mobility, streaming potential, and electroosmosis. It is apparent that similar molecular properties are responsible for both protein and cell rejection and reduction of electrokinetic effects. In this work we compared the fibrinogen-rejecting ability and the effect on electrophoretic mobility of three polymer coatings bound to polystyrene. The three polymers were side-bound dextran, end-bound dextran, and end-bound PEG. The results of these measurements were used to elucidate the importance of polymer packing density and polymer layer thickness on protein adsorption and reduction of electrokinetic effects. Protein adsorption appears not to be sensitive to polymer layer thickness or the presence of dilute polymer tails in a surface coating, while electrokinetic effects are. Protein adsorption is, however, very sensitive to the availability of exposed surface. Finally, the unique effectiveness of PEG is apparent in this research as in previous studies.

Adsorption↗
PubMed1995

Exposure to acid anhydrides in three resin and one cushioned flooring manufacturing plants.

Acid anhydrides are reactive organic chemicals of low molecular weight which cause occupational asthma. No previous research on the relationship between exposure to these chemicals and respiratory sensitization and development of occupational asthma has been reported. A retrospective cohort study was carried out in four factories (three alkyd resin factories and one cushioned flooring factory) to investigate the nature of exposure-response relationships for sensitization to phthalic anhydride (PA), trimellitic anhydride (TMA) and maleic anhydride (MA). This paper describes the results of full-shift and task-specific exposure measurements. Exposure to PA was low in relation to the Occupational Exposure Standard (OES). The highest full-shift PA exposures occurred among resin operators in the resin factory that used solid PA as compared to other resin factories where liquid PA was used. Arithmetic mean exposure levels to TMA and MA in the resin factories were well below their respective OESs. Short-term high exposures occurred during loading of acid anhydrides into the reactors and sampling and testing of the resin. Relatively high full-shift exposure to TMA occurred in the cushioned flooring factory, although no high peak exposures were detected.

Anhydrides↗
PubMed1995

Variation in rat urinary aeroallergen levels explained by differences in site, task and exposure group.

We describe how much of the variation in rat urinary aeroallergen (RUA) levels may be explained by differences in site and exposure group in research establishments and we identify task categories associated with high RUA levels. In this population 73% of the variability in RUA levels could be explained by exposure group, site and their interaction term. Exposure group alone explained the majority of the variation (69%). The task category associated with the highest RUA level was cleaning out, followed by indirect contact with rats and handling rats. The task categories associated with the lowest levels were slide production, post mortem and experiments. These results may help choose appropriate exposure measures for epidemiological studies in research establishments in the future and may help reduce the incidence of laboratory animal allergy.

Allergens↗
PubMed1995

Speed discrimination of motion-in-depth using binocular cues.

Although it is well known that motion-in-depth can be detected using binocular cues, it is not known whether those cues can be used to judge the speed of an object moving in depth. There are at least two possible binocular cues that could be used by the visual system to calculate three dimensional (3-D) speed: the rate of change of binocular disparity, or a comparison of the speeds of motion in the two eyes. We tested which of these cues is used to discriminate the speed of motion-in-depth. First, speed discrimination was measured for a dot moving away from the observer in depth (along the z-axis) and for a random dot stereogram in which a central square moved away from the observer in depth. These stimuli contained both disparity and monocular motion cues. Speed discrimination thresholds were as good for 3-D motion as for monocular sideways motion. Second, a dynamic random dot stereogram (in which the random dot pattern was replaced by a new dot pattern every frame) was used to remove consistent monocular cues. 3-D speed discrimination was now very poor, suggesting that the rate of change of disparity is not a good cue for 3-D speed. Finally, we tested whether observers were able to use the monocular motion cue from one eye to perform the speed discrimination task, or whether there had to be a comparison of the two eyes' monocular cues. By adding a small x-axis velocity component (with random direction) to the z-axis motion, it was possible to disrupt the monocular motion signals without altering the speed of the motion in 3-D. This manipulation did not disrupt the observers' performance, suggesting that monocular speed cues were not being used independently but that there was a comparison of monocular motion signals from the two eyes.

Cues↗
PubMed1995

Papanicolaou smear recommendations, patient complaints, and patient satisfaction in managed-care medical organizations.

This study sought to determine whether primary-care physicians, practicing in different types of manage-care medical organizations, wer recommending Papanicolaou (Pap) smear screening to their patients. The author also wished to determine whether Pap smear recommendation rates correlated with characteristics of the organizations, with complaint rates, or with survey-based satisfaction measures. Randomly selected medical records (N = 10,978) were audited for women older than 18 years of age, insured by a single California health maintenance organization, who were being cared for by 81 medical organizations. It was determined whether women with an established primary-care physician were receiving recommendations for Pap smear testing within a 2-year period. Information on quality-related patient complaints from these organizations also was tabulated, and a telephone-based patient satisfaction survey on 1,700 members from the 46 largest organizations was performed. Overall, the study's Pap smear standard was met 83.2% of the time, with a range of 30% to 100% between organizations. Performance was unrelated to organization size, type, number of patients, percentage of board-certified physicians, or whether the organization permitted self-referral to an obstetrics/gynecology physician. Performance was also unrelated to complaint rates or survey measures of patient satisfaction. Performance was, however, positively correlated with the number of prepaid patients per primary care physician (r = 0.28, P = 0.01). Complaint rates and survey satisfaction measures were strongly correlated with each other (r = -0.48 and -0.57, P = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Angiotensin II regulates nephrogenesis and renal vascular development.

To test the hypothesis that angiotensin II (ANG II) is necessary for normal embryonic and postnatal kidney development, the effect of angiotensin receptor blockade or angiotensin converting enzyme inhibition on nephrovascular development was studied in newborn Sprague-Dawley rats and in Rana catesbeiana tadpoles undergoing prometamorphosis. Blockade of ANG II type 1 receptor (AT1) in newborn rats induced an arrest in nephrovascular maturation and renal growth, resulting in altered kidney architecture, characterized by fewer, thicker, and shorter afferent arterioles, reduced glomerular size and number, and tubular dilatation. Inhibition of ANG II generation in tadpoles induced even more marked developmental renal abnormalities. Blockade of ANG II type 2 receptor (AT2) in newborn rats did not alter renal growth or morphology. Results indicate that ANG II regulates nephrovascular development, a role that is conserved across species.

Angiotensin II↗
PubMed1995

Acute infective exacerbations of chronic bronchitis.

Patients with an acute infective exacerbation of chronic bronchitis (AECB) (n = 471) were enrolled into a computer-based general-practice study to determine whether features of past history, presenting symptoms, or findings on examination were predictive of failure to recover. The median age was 68, 56.3% were male, and 82% were current or ex-smokers. All had daily sputum production and 57.5% had moderate or severe airflow obstruction. During the AECB 11.5% were pyrexial, and 80.7% had abnormal auscultatory findings; about half had moderate to severe increases in dyspnoea and airflow obstruction, and the majority had increases in sputum volume and/or purulence. The median number of AECBs in the previous year was three, and one-third of patients had cardiopulmonary disease. The only factors significantly (p < 0.05) predicting failure to recover from an AECB were historical. Neither clinical features at presentation nor antibiotic treatment affected recovery. Coexistent cardiopulmonary disease was a risk factor for returning with a chest problem and for being referred to hospital. The number of chest infections in the previous 12 months was a risk factor for returning with a chest problem. The higher the number of chest infections, the higher the odds of returning with a chest problem. The best combination predicting return with a chest problem was history of cardiopulmonary disease and more than four previous AECBs in the last 12 months. The sensitivity was 75% and specificity 47%.

Acute Disease↗
PubMed1994

Mapping and characterization of non-HLA multigene assemblages in the human MHC class I region.

The major histocompatibility complex (MHC) class I region has been shown to be associated with a variety of immune and nonimmune disorders. In an effort to initiate steps designed to identify the idiopathic hemochromatosis disease gene (HFE), we have cloned and mapped two expressed messages using probes from the HLA-H subregion that lie immediately distal to the HLA-A9 breakpoint. Although the cDNA clones identify distinct multifragment families that are dispersed throughout the MHC, the gene sequences from which the two cDNA clones derive map centromeric to the HLA-B locus and are absent from the genomes of higher nonhuman primates. This suggests that a syntenic coding segment arose within a highly polymorphic region (TNF to HLA-B interval) as the result of an insertion event following the emergence of Homo sapiens. An additional syntenic cluster exists within a peak of linkage disequilibrium with the HFE gene and may define coding sequences that underlie the defect in genetic iron overload. These data generally support the concept that the class I region is potentially gene-rich and further highlight the possibility that these new coding sequences may play a role in the development of a variety of HLA-linked diseases. The observations presented suggest that interlocus exchanges have played a structural role in the genesis of the human class I region.

Animals↗
PubMed1994

Application of temperature-induced phase partitioning at ambient temperature for enzyme purification.

Aqueous two-phase partition and temperature-induced phase separation using a non-ionic, random copolymer composed of 20% ethylene oxide, 80% propylene oxide (EO20 PO80) has been used for purification of glucose-6-phosphate dehydrogenase, hexokinase and 3-phosphoglycerate kinase from bakers' yeast. This EO20PO80 copolymer has a cloud point of 18 degrees C, at which temperature it phase separates from water. Enzymes were first partitioned at 4 degrees C in an initial EO20PO80-dextran T500 aqueous two-phase system. This system had an upper copolymer-rich phase and a lower dextran-rich phase. After phase separation had occurred the upper EO20PO80-rich phase was removed and placed at 24 degrees C. This resulted in formation of a new two-phase system with an upper water phase and a lower phase containing 98% copolymer and 2% water. Enzymes were recovered exclusively in upper water phase leaving a polymer-rich lower phase free of contamination. The phase diagram for the system EO20PO80 and dextran T500 at 4 degrees C has been determined.

Chemical Phenomena↗
PubMed1994

Constraints on human stereo dot matching.

Statistical efficiency was used as a model-free measure of stereo performance to explore how well human observers perform for a range of stereoscopic stimuli with varying amounts of added disparity noise. When the stimulus was a random dot stereogram in which perturbations of disparity were applied independently to each dot, most of the dots had very different disparities from their neighbours and efficiency was found to fall as the level of disparity noise was increased. It was hypothesized that the fall of efficiency was due to difficulty with dot matching, so random-dot stereograms were created in which there was a significant correspondence problem but in which there were groups of dots that had locally the same disparity. For these targets, efficiency was fairly constant as noise was increased. When the stimulus consisted of a pair of vertical columns of dots, efficiency was also generally constant as noise was increased, perhaps because such stimuli do not present a severe correspondence problem. These experiments may allow the separation of one source of efficiency loss--that due to the difficulty of dot matching--from other sources of efficiency loss. These separate components of efficiency loss may describe components of performance that are suitable for comparison with the performance of stereo dot matching algorithms.

Depth Perception↗
PubMed1994

Objective evaluation of human and computational stereoscopic visual systems.

Several computational models have been proposed to account for the abilities of human observers in solving the stereo correspondence problem. Such models are often evaluated by counting the number of correct matches that the model makes when presented with a test stimulus, but this measure is difficult to compare with conventional psychophysical measures of human stereo performance. This paper develops an absolute comparison of human and model stereo correspondence by using the concept of statistical efficiency, through which the performance of both humans and models is compared against that of an ideal observer. Some important assumptions need to be examined before the efficiencies of human and model can be compared because these assumptions affect the statistical performance of models. One assumption involves the use of an epipolar constraint to help constrain the matching problem but it is unclear what the resolution (or "height") of an epipolar line should be. Experimental estimates were obtained of the vertical region over which dot position may be varied without disruption of human stereoacuity. These estimates constrained the effective "height" of the zone above and below an epipolar line. Two models of stereopsis were then compared against human performance: the first (due to Pollard, Mayhew & Frisby, Perception, 14, 449-470, 1985) uses local constraints to solve the correspondence problem; the second is a simple area-based correlation model. For nearly all the stimuli tested, both models show strong similarities with human observers. For one particular stimulus, the efficiency of the correlation model is different from that of humans and of the PMF algorithm. This implies that a more complex process than simple correlation may be required to account for human stereo processing and indicates other limitations of correlation models.

Algorithms↗
PubMed1994

Managing the quality of managed care delivery systems.

We have developed a quantitative "score card" for measuring the quality of 130 managed care organizations. This tool is currently being used in California as part of a large scale CQI process. When quality data are compared to cost data, we observe a negative correlation between cost and quality, consistent with the industrial model that better quality and lower cost can go hand in hand.

Ambulatory Care↗
PubMed1993

Stereo and motion disparities interfere with positional averaging.

If required to judge the spatial separation between features that are sub-parts of larger objects, observers are biased in the direction of reporting the separation between the centroids of the objects. We predicted that this bias would be overcome by separating the target features from the larger objects, either by stereoscopic disparity or by relative motion. We measured the observer's perceptual biases for the "cluster illusion" with the target dots specified by: (1) contrast alone, (2) contrast and disparity, (3) disparity alone, (4) contrast and motion, and (5) motion alone. Disparity had the effect predicted, but the effects of motion were less clear.

Contrast Sensitivity↗
PubMed1993

Myenteric plexus neurons have developmentally acquired differences in the medium molecular weight subunit of neurofilament protein.

We have previously shown that neurofilaments in enteric neurons are immunologically distinct from those found in the central nervous system. In particular, one monoclonal antibody to the medium molecular weight neurofilament subunit, called NN18, stained the perikarya of enteric neurons very weakly, if at all, although other medium molecular weight neurofilament subunit antibodies clearly showed the presence of significant amounts of medium molecular weight neurofilament subunit. We have since located the epitope for NN18 in a peptide sequence at the carboxy terminal tail of medium molecular weight neurofilament subunit and have now looked for further neurofilament antibodies that stain the same region. We found two monoclonal antibodies, RMO1 and RMO59, that recognize the same peptide. These antibodies also show much reduced staining in myenteric neurons compared to those in the central nervous system, suggesting that this region of the medium molecular weight neurofilament subunit is specifically modified in certain cells. In the developing enteric nervous system, we found that all the antibodies show strong staining of enteric neurons in the neonatal rat, but that with NN18, RMO1, and RMO59, the staining intensity decreases during further development, and by postnatal day 21 all three demonstrate decreased or absent staining identical to the adult. These results indicate that myenteric neurons, in contrast to the brain, have a developmentally regulated modification in a specific region of the medium molecular weight neurofilament subunit, which may reflect adaptation to structural stress by myenteric neurons.

Alkaline Phosphatase↗
PubMed1993

Quantitation of tissue- and sex-specific induction of rat GSH transferase subunits by dietary 1,2-dithiole-3-thiones.

Male and female Sprague--Dawley rats were maintained for 5 days on control diet or diet containing 0.075% (w/w) 1,2-dithiole-3-thione (D3T) or 5-(2-pyrazinyl)-4-methyl-1,2-dithiole-3-thione (oltipraz). The content of GSH transferase (GST) subunits 1a, 1b, 2, 3, 4, 6, 7, 8, 10 and 11 in the soluble fraction of liver, kidney, small intestine, stomach and lung of control and D3T-fed animals was determined. Liver and kidney were similarly analysed for the oltipraz-fed animals. Significant induction of GST subunits by D3T was seen in all tissues, the most substantial being subunit 7 in male liver (approximately 50-fold) and subunits 1b, 3 and 10 in male and female small intestine (5- to 16-fold). Generally subunits 7, 10, 1b and 3 were most affected, while subunits 6 and 8 were hardly inducible. Oltipraz caused qualitatively similar inductions in the liver and kidney. The effect of GSH transferase induction on the hepatic capacity for GSH conjugation of aflatoxin B1 exo-8,9-oxide is assessed.

Animals↗
PubMed1993

Clinical significance of Mallory-Weiss tears.

OBJECTIVES: To assess course and outcome of patients with endoscopically diagnosed Mallory-Weiss tear bleeding. SUBJECTS: Thirty-four subjects seen during a 5-yr period formed the study group. RESULTS: Available follow-up after index bleed was 27.5 months +/- 2.7 SEM. There was no antecedent explanation for the tear, such as nausea, retching, abdominal pain, or vomiting in 12/28 (42.9%). Hematemesis on first emesis was noted in 13/26 (50%). Mean transfusion requirements were 2.6 +/- 1.0 (SEM) units of packed cells (range, 0-28), and 9/34 (26.5%) received four or more units. Two had therapeutic endoscopy and three required surgery to control bleeding. Thirty-day mortality noted four deaths, all multiorgan system failure related to the bleed. Patients who died had other endoscopic abnormalities, such as ulcers or varices, and all had an alcohol history. Two patients of 20 contacted had recurrent bleeding. One had another tear. The other had intermittent recurrent bleeding and refused care. CONCLUSIONS: Mallory-Weiss tear bleeding may be significant and recurrent. It may cause death or require transfusion, therapeutic endoscopy, and surgery.

Adolescent↗