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Biomedical subjects

A R Hill

Publications and source records attributed to A R Hill.

At least 19 recordsLinked to original sources
PubMed1992

Evaluation of two infrared autorefractors in pseudophakia.

We investigated the viability of using an objective infrared autorefractor to identify high corneal astigmatism (> 3.00 D) in a pseudophakic population. The eyes of 91 patients, who had recently undergone cataract extraction and intraocular lens implanation, were refracted manually and using two infrared autorefractors, a Canon RK-1 and a Nikon NR-2000. Autorefractor measurements were repeated to provide estimates of reliability for each instrument. LogMAR visual acuities were also recorded with both the manual and autorefractor corrections. Approximately 75% of repeat autorefractor measurements were within 0.50 D of the initial readings, and about 75% of measurements were within 1.00 D of the manual refractions. Visual acuities with manual corrections were, on average, one line better than with autorefractor corrections. By validating the autorefractors against manual refraction, the efficiency of the autorefractors for detecting astigmatism > 3.00 D was calculated. Setting the cut-off criterion to ensure high sensitivity (95%), so that almost all patients with > 3.00 D were detected, resulted in both instruments having a poor specificity of about 40%.

Adult↗
PubMed1991

Which 3-ribofuranosyl-substituted purine 5'-phosphates undergo template-directed oligomerization?

We have studied the oligomerization reactions of the 2-methylimidazolide derivatives of 3-isoisoguanosine 5'-phosphate (2) and 3-isoxanthosine 5'-phosphate (5) in the presence of a variety of homopolynucleotide templates. In no case did we observe a substantial template-facilitated production of long oligomers. Polyuridylic acid directed the synthesis of low molecular-weight products from both monomers. Polycytidylic acid, polyadenylic acid, polyinosinic acid, and polyguanylic acid were ineffective as templates in the systems that we investigated.

Chromatography, High Pressure Liquid↗
PubMed1991

Vistech VCTS 6500 charts--within- and between-session reliability.

The aim of the study was to measure the reliability of the Vistech VCTS 6500 charts, in test score units, in order to allow clinicians to derive estimates of what constitutes a clinically meaningful change in performance over time. The reliability of a more familiar test, Bailey-Lovie high contrast visual acuity, was also measured to provide a comparison. Patients with normal vision and with early or subtle eye disease were recruited so that the results would be representative of the population likely to present for primary vision screening. Patients were tested on all three VCTS charts on two separate occasions at least 3 weeks apart to give estimates of within- and between-session reliability. Reliability was found to be low in all circumstances; between-session reliability could be improved by using the mean score for the three charts, but the 95% range of difference scores still encompassed at least one-half of the total performance range of the test. It was concluded that Vistech charts are unlikely to be of use for clinical measurements or for research studies.

Adult↗
PubMed1991

Disseminated tuberculosis in the acquired immunodeficiency syndrome era.

To assess the influence of human immunodeficiency virus type 1 (HIV)-induced immunodeficiency on the clinical, radiographic, and pathologic features of disseminated tuberculosis (TB), we studied 79 patients presenting in 1984 through 1987 with miliary or focal disseminated disease due to Mycobacterium tuberculosis, as well as 4 additional non-HIV patients diagnosed after 1987. Clinically defined acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC) was present in 51 (Group 1). A total of 20 had TB unrelated to HIV disease (Group 2). The remaining 12 were excluded because the role of HIV could not be determined. Clinical features were similar between groups aside from younger age; lower hemoglobin, total leukocyte, lymphocyte, and platelet counts; and more frequent tuberculin anergy (90 versus 40%) in AIDS/ARC patients (p less than or equal to 0.03). Chest radiographs showed a miliary pattern in about half of each group. Pleural effusion occurred only in AIDS/ARC patients (24%, p = 0.02), but intrathoracic lymphadenopathy was present in about a third of each group. Tissue biopsies (n = 70) usually revealed necrotizing granulomatous inflammation in each group, with a tendency to greater necrosis and more numerous acid-fast bacilli in Group 1. Granulomas were usually poorly formed in AIDS/ARC patients (59 versus 18%, p = 0.01). Autopsy of 9 AIDS/ARC patients with overwhelming miliary TB revealed a "nonreactive" histologic pattern with poorly organized or absent granulomas, extensive necrosis, and numerous bacilli. HIV-related disseminated TB causes a major constitutional illness with a high short-term mortality (25%).(ABSTRACT TRUNCATED AT 250 WORDS)

AIDS-Related Complex↗
PubMed1991

Respiratory muscle function in asthma.

Asthma increases the load on the ventilatory pump by causing simultaneous increases in airway resistance, lung volume, and minute ventilation. The inspiratory muscles bear the majority of this load, whereas expiratory muscle recruitment is relatively minor. Respiratory muscle strength and endurance appear to be normal in stable asthmatics. During acute attacks, airway closure and expiratory airflow limitation result in a dynamic increase in end-expiratory lung volume. In turn, hyperinflation compromises the function of inspiratory muscles, especially that of the diaphragm, by reducing their force-generating capacity (muscle shortening) and impairing their mechanical advantage on the chest wall. Thus, exacerbations of asthma cause an acute increase in mechanical load together with decreased ventilatory capacity, thereby predisposing to inspiratory muscle fatigue and precipitating hypercapnic respiratory failure in severe cases. Management of ventilatory failure in asthma consists of mechanical unloading of the inspiratory muscles by positive pressure ventilation together with pharmacotherapy (anti-inflammatory and bronchodilating agents) to improve airway function. The strategy of mechanical ventilation is aimed at minimizing dynamic hyperinflation, which increases inspiratory muscle load as well as promotes barotrauma.

Adrenal Cortex Hormones↗
PubMed1990

Altered water metabolism in tuberculosis: role of vasopressin.

PURPOSE: Patients with hyponatremia due to tuberculosis have shown variable responses to water loading in previous small studies, ranging from persistent antidiuresis to a normal diuresis. Although tuberculosis is considered a cause of the syndrome of inappropriate antidiuretic hormone secretion (SIADH), circulating vasopressin has been documented in only a few cases. We studied a larger group of patients to determine whether it can be suppressed by a short-term reduction in osmolality. PATIENTS AND METHODS: Twenty-eight hyponatremic patients (mean age +/- SD: 40 +/- 10 years) with pulmonary or miliary tuberculosis underwent a clinical evaluation, measurement of blood and urine chemistry values, and (in 22) a water load of 20 mL/kg. Volume status was evaluated by urine sodium concentration, blood and urine urea nitrogen, and plasma renin activity. Endocrine, renal, and other recognized causes of SIADH were excluded. RESULTS: All 22 patients exhibited a decline in urine osmolality and an increase in free water clearance after water loading. Water excretion was fully normal in seven of 22, with the remainder showing variable impairment of diluting ability and/or volume excreted. Plasma vasopressin, measured in 11 of 22 patients as well as in six others not subjected to water loading, was detectable despite hypo-osmolality in 16 of 17. Vasopressin levels declined after water loading, from 1.85 +/- 1.32 to 0.77 +/- 0.25 pg/mL (p less than 0.05). The majority of patients had the euthyroid sick syndrome but normal adrenal responses to cosyntropin. Although several patients had mild volume depletion when studied, this factor did not appear to explain the defect in water excretion. Hyponatremia resolved predictably within days to weeks of antituberculous therapy. CONCLUSIONS: Circulating vasopressin remains detectable in hyponatremic patients with tuberculosis and is responsive to changes in osmolality. A downsetting of osmoregulation induced by active tuberculosis ("reset osmostat") could explain this abnormality, but we cannot exclude an unidentified non-osmotic stimulus that can be counteracted by water loading.

Adult↗
PubMed1988

Human lens nuclear colour matching and brunescence grading in vivo.

The nuclear colour of in vivo human lenses has been investigated by means of a colour matching technique, using 'Munsell' colour samples. Observations covered an extended age range, and included all degrees of nuclear pigmentation. A positive correlation was noted between increasing nuclear pigmentation and age. The colour matching data generated was used as a basis for establishing a system of nuclear brunescence grading. The system of grading consists of a Grade 0 for absence of brunescence, and Grade 1 to Grade 5 for increasing brunescence. The 'Munsell' notation for samples representing these grades are: Grade 0 (5GY 6/1), Grade 1 (5Y 7/4), Grade 2 (2.5Y 7/8), Grade 3 (7.5YR 6/8), Grade 4 (5YR 4/6), and Grade 5 (2.5YR 2.5/2). Assessments of both inter- and intra-observer variability in the use of the derived scale have shown the new colour grading system to be reliable. The measure is simple to use during biomicroscopic slit-lamp examination of the lens, and has the potential for routine clinical application as well as for use in clinical trials where detailed documentation of lens morphology is required. The new colour scale may be used either as an isolated measure, or as part of a battery of lens measures in the Oxford Clinical Cataract Classification and Grading system.

Aging↗
PubMed1988

Inter-observer and intra-observer variability of the Oxford clinical cataract classification and grading system.

Intra-observer (within observers) and inter-observer (between observers) variability of the Oxford Clinical Cataract Classification and Grading System were studied. Twenty cataracts were examined and scored independently by four observers. On a separate occasion two of the observers repeated the assessments of the same cataracts in the absence of information from the initial observations. The chance corrected and weighted kappa statistics for observer agreement, both for inter-observer and intra-observer variability demonstrated satisfactory repeatability of the cataract grading system. The overall intra-observer mean weighted kappa was kappa w = +0.68 (range SE kappa = 0.012-0.052) and the overall inter-observer mean weighted kappa was kappa w = +0.55 (range SE kappa = 0.011-0.043).

Cataract↗
PubMed1988

Template-directed oligomerization of 3-isoadenosine 5'-phosphate.

Template-directed oligomerization of an activated derivative of 3-isoadenosine 5'-phosphate (piA) on polyuridylic acid [poly(U)] was studied. The reaction of ImpiA is more efficient than the corresponding reaction of ImpA, and produces 3'-5'-linked oligomers while the reaction of ImpA gives only 2'-5'-linked oligomers. The base pairing between piA and poly(U) in this system is probably of the Hoogsteen type (involving the 6-amino group and N7 of 3-isoadenosine) rather than of the Watson-Crick type.

Adenosine Monophosphate↗
PubMed1988

Huematic--an automated scorer for the Farnsworth-Munsell 100 hue test.

A cheap, portable automated scorer for the Farnsworth-Munsell (FM) 100 hue test has been developed. It consists of a light pen, a series of omni-directional bar-codes attached to the reverse of the FM 100 hue caps and a small micro-computer. The print-out includes patient details, a linear histogram of the partial errors by cap position, indication of the peak error positions for congenital colour vision deficiencies and appropriate statistical analysis of the total error score. All the results are available within four minutes of completing the testing procedure.

Adolescent↗
PubMed1988

Test-retest reliability of the Arden Grating Test: inter-tester variability.

The aim of this study was to investigate the test-retest reliability of the Arden Grating Test (AGT), and to assess the extent to which any variance in AGT score on retest can be attributed to intra-subject and inter-tester differences. Twelve patients with various pathologies and whose contrast sensitivity covered a wide range were each tested twice by six testers. It was shown that variance attributable to testing by different clinicians accounted for approximately 25% of the total variance, and that the 95% confidence limits about any observed score were +/- 15 AGT units, which is about one quarter of the total dynamic range of the test. The large range of scores encompassed by the 95% confidence limits represents considerable unreliability, the consequence of which is a high misclassification rate, i.e. many false positives and false negatives, especially in the context of primary vision screening for which it was designed.

Adult↗