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Biomedical subjects

R K Chang

Publications and source records attributed to R K Chang.

13 recordsLinked to original sources
PubMed1995

Age- and anesthesia-related changes in accessory pathway conduction in children with Wolff-Parkinson-White syndrome.

The anterograde effective refractory period of the accessory pathway is age-dependent in pediatric patients with the WPW syndrome. Thus, age should be considered when developing electrophysiologic criteria for the risk of hypotensive arrhythmias in these patients. In addition, general anesthesia must also be considered in interpreting age-related changes in the anterograde APERP, especially in children.

Adolescent↗
PubMed1992

Physiological and behavioural thermoregulation in bigeye tuna (Thunnus obesus).

Tuna are unique among teleost fishes in being thermoconserving. Vascular counter-current heat exchangers maintain body temperatures above ambient water temperature, thereby improving locomotor muscle efficiency, especially at burst speeds and when pursuing prey below the thermocline. Because tuna also occasionally swim rapidly in warm surface waters, it has been hypothesized that tuna thermoregulate to accommodate changing activity levels or ambient temperatures. But previous field experiments have been unable to demonstrate definitively short-latency, mammalian-type physiological thermoregulation. Here we show using telemetered data that free-ranging bigeye tuna (Thunnus obesus) can rapidly alter whole-body thermal conductivity by two orders of magnitude. The heat exchangers are disengaged to allow rapid warming as the tuna ascend from cold water into warmer surface waters, and are reactivated to conserve heat when they return into the depths. Combining physiological and behavioural thermoregulation expands the foraging space of bigeye tuna into otherwise prohibitively cold, deep water.

Animals↗
PubMed1992

Serological detection of disease activity in SLE.

Laboratory tests are commonly used to aid in monitoring disease activity in patients with systemic lupus erythematosus. Typically, tests for antinative DNA, complement, acute phase reactants, and sometimes circulating immune complexes are used for this purpose. More recently, tests for complement activation products and immunocyte activation have been suggested. We measured antinative DNA, C4, Westergren sedimentation rate, iC3b, Bb, and sIL-2R levels in a group of 100 patients with SLE evaluated clinically for activity by a modified version of the Systemic Lupus Activity Measure (SLAM); iC3b and Bb were studied in 71 of the patients and sIL-2R in 52. We found that sIL-2R and sedimentation rate correlated best with SLAM, anti-DNA was intermediate, and C4, iC3b, and Bb correlated the least. None of the tests predicted severity of disease, but sIL-2R was highest in patients with active renal disease.

Adolescent↗
PubMed1992

Pulse oximetry and peak flow as indicators of wheezing severity in children and improvement following bronchodilator treatments.

This study examined the changes from the initial peak flows and oxygen saturations (OSAT) of wheezing children at presentation to the emergency department through their treatment in the emergency department. Data was collected prospectively on 785 patients 5 to 20 years of age during an 11-month period from November 1, 1990, to September 30, 1991. Both the initial OSAT and peak flows were correlated with the number of bronchodilator treatments required in the emergency department and with the need for hospitalization. Both the initial OSAT and the peak flows had a limited ability to predict the need for hospitalization. Oxygen saturation appears to be a valid measure of wheezing severity and is more easily obtained in children of all ages. Following bronchodilator treatment, peak flow results in a larger quantitative improvement than OSAT; however, this difference does not appear to have any significant advantage. Aerosolized albuterol and subcutaneous epinephrine resulted in a similar degree of improvement as measured by peak flow and by oxygen saturation, with clinically similar changes in heart rate.

Adolescent↗
PubMed1990

Effectiveness of testing for anti-DNA and the complement components iC3b, Bb, and C4 in the assessment of activity of systemic lupus erythematosus.

Seventy-one patients with systemic lupus erythematosus (SLE), seen in an outpatient setting for follow-up evaluation during a 3-mo period, were tested (in addition to routine lupus monitoring studies) with enzyme immunoassays (EIAs) for anti-DNA, iC3b, and factor Bb to determine the relationship of these test results to disease activity. SLE activity was scored by four previously reported scoring systems, and six patients were identified as active by all four systems. We found that the EIA for anti-DNA was the best indicator of disease activity and that iC3b and Bb were not informative for this purpose in this group of patients. Mean iC3b levels were higher in a subset of seven patients with past biopsy evidence of severe (WHO class IV) glomerulonephritis than in the rest of the study population, even though none of these patients had active disease at the time of this study.

Adolescent↗
PubMed1989

Predictive value of antinative DNA for systemic lupus erythematosus: comparison of radioimmunoassay and enzyme immunoassay.

Positive predictive values for the diagnosis of systemic lupus erythematosus (SLE) were determined for two antinative DNA assays: a Farr-type radioimmunoassay (RIA) and a solid-phase enzyme immunoassay (EIA). The study population consisted of all patients whose EIA anti-DNA results were positive (greater than 250 IU) during a 150 day period; in addition all patients whose EIA anti-DNA results were 100-250 IU during the first 25 days of this period were also included. Simultaneous Farr RIA were performed on all sera, and the Crithidia luciliae immunofluorescent assay was also carried out on those with positive RIA and/or EIA results. Diagnoses were established by chart review, and disease activity was scored for SLE patients. Positive predictive values for SLE were dependent on the level of test positivity, and "normal" limits of 10% binding for the Farr RIA and 800 IU for the EIA gave comparable results. Combination with Crithidia luciliae immunofluorescence increased the sensitivity of both assays, especially the EIA. Results of both assays correlated significantly with activity scores in SLE patients.

Antibodies, Antinuclear↗
PubMed1988

Aliphatic polyesters and cellulose-based polymers for controlled release applications.

The general technologies for fabricating drug delivery systems are briefly discussed in the present review. Furthermore, two types of commonly used polymers, biodegradable aliphatic polyesters for parenteral administration and cellulose-based polymers for oral uses, are presented by means of selected examples of their properties and applications to control drug release.

Cellulose↗
PubMed1985

Quantitation of herpes simplex virus in rabbit corneal epithelium.

The authors have developed an objective method for quantitation of herpes simplex virus in the corneal epithelium of rabbits. At appropriate times postinfection, full-thickness rabbit corneas were removed by trephination and subjected to one cycle of freezing and thawing. The corneal epithelium was then disrupted by sonication. The amount of infectious virus recovered from sonicated specimens was determined by an in vitro plaque assay, providing a measure of the quantity of virus present during the acute stage of herpetic keratitis. Using this technique, the authors found that the mean virus titer was reduced from 1.5 X 10(5) plaque forming units (pfu) per cornea in control rabbits to less than 200 pfu per cornea in rabbits treated topically for 2 days with 1% trifluridine. In contrast, instillation of 1% prednisolone acetate resulted in the persistence of higher levels of virus (275 pfu) than those observed in control rabbits (3 pfu) 4 days after the cessation of therapy.

Animals↗
PubMed1984

Gel tears. A new medication for the treatment of dry eyes.

Gel Tears, a clear, semisolid formulation of synthetic, high molecular weight, cross-linked polymers of acrylic acid, persists in the conjunctival sac for hours after topical instillation, slowly melting while absorbing fluid and retaining it locally. In the present study of 55 patients (106 eyes) with severe dry eyes, who were unable to obtain ocular comfort with frequent administration of a wide variety of commercially available artificial tear preparations, 78% were improved by Gel Tear therapy. Subjective symptoms such as burning, stinging, foreign body sensation, dryness, and photophobia were significantly (P less than 0.001) alleviated, while objective signs concurrently improved but to a lesser degree. No patient required Gel Tears more often than four times daily. Most maintained optimal comfort on a dose of twice daily or less, and several patients previously unable to obtain ocular comfort with hourly administered conventional artificial tears required Gel Tears less than once a day.

Acrylic Resins↗