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D S Chang

Publications and source records attributed to D S Chang.

32 records · Page 2Linked to original sources
PubMed1996

Mechanoreceptive afferents exhibit functionally-specific activity dependent changes in conduction velocity.

Impulse activity in axons generates aftereffects on membrane excitability that can alter the conduction velocity of subsequently conducted impulses. We used a computerized stimulus pattern (a 1 Hz stimulus period followed by a period of repeated short bursts at 200 Hz) to assess in vivo activity-dependent changes in conduction latency of functionally identified rat cutaneous afferents conducting in the A beta range. Several different parameters of activity dependence were measured: burst supernormality, the average increase in conduction latency following conditioning with a single preceding impulse during high frequency burst stimulation; burst subnormality, the average latency increase during each burst; depression, a long-term increase in latency caused by the high frequency stimulation. The data show that different mechanosensitive A beta afferents with overlapping resting conduction velocities exhibit activity-dependent changes in conduction latency that are characteristic of their particular functions.

Animals↗
PubMed1996

Cutaneous microvascular flow in the foot during simulated variable gravities.

Our objective was to understand how weight bearing with varying gravitational fields affects blood perfusion in the sole of the foot. Human subjects underwent whole body tilting at four angles: upright [1 gravitational vector from head to foot (Gz)], 22 degrees (0.38 Gz), 10 degrees (0.17 Gz), and supine (0 Gz), simulating the gravitational fields of Earth, Mars, Moon, and microgravity, respectively. Cutaneous capillary blood flow was monitored on the plantar surface of the heel by laser Doppler flowmetry while weight-bearing load was measured. At each tilt angle, subjects increased weight bearing on one foot in graded load increments of 1 kg beginning with zero. The weight bearing at which null flow first occurred was determined as the closing load. Subsequently, the weight bearing was reduced in reverse steps until blood flow returned (opening load). Mean closing loads for simulated Earth gravity, Mars gravity, Moon gravity, and microgravity were 9.1, 4.6, 4.4, and 3.6 kg, respectively. Mean opening loads were 7.9, 4.1, 3.5, and 3.1 kg, respectively. Mean arterial pressures in the foot (MAP(foot)) calculated for each simulated gravitational field were 192, 127, 106, and 87 mmHg, respectively. Closing load and opening load were significantly correlated with MAP(foot) (r =0.70, 0.72, respectively) and were significantly different (P < 0.001) from each other. The data suggest that decreased local arterial pressure in the foot lowers tolerance to external compression. Consequently, the human foot sole may be more prone to cutaneous ischemia during load bearing in microgravity than on Earth.

Adolescent↗
PubMed1996

Comparison of diuretic effects of glycerol with furosemide after transurethral prostatectomy.

BACKGROUND: Diuretic therapy after transurethral prostatectomy (TURP) is primarily intended to induce diuresis against water intoxication and cystic clot retention. This study was undertaken to compare the diuretic effects of glycerol with furosemide after TURP. METHODS: Thirty patients (ASA I or II) undergoing TURP were studied. Spinal anesthesia was induced with bupivacaine. At the end of prostatic resection, the patients were randomly allocated into two groups. In one group (n = 15) the patients received furosemide 30 mg i.v., while in the other group (n = 15) they received glycerol 0.5 g/kg i.v. Blood samples were collected for measurements of osmolality, hematocrit, sodium and glucose concentration before anesthesia and after surgery. Urine output was also recorded after surgery in each group. RESULTS: Plasma osmolality in glycerol group was higher than furosemide group at 30 min (295.3 +/- 10.6 vs. 283.8 +/- 5.6 mOsm/kg, p < 0.01) and 1 h after operation (294.9 +/- 8.7 vs 286.3 +/- 6.7 mOsm/kg, p < 0.01). Blood glucose was higher in glycerol group than that in furosemide group at 2 h after operation (195.6 +/- 121.9 vs 152.9 +/- 70.1 mg/dl, p < 0.05). Measured urine output was significantly greater in furosemide group at 30 min after operation (904.6 +/- 491.5 vs. 248.4 +/- 143.4 ml, p < 0.05) but was greater in glycerol group at 12 h after operation. CONCLUSIONS: Since urine output is significantly less in glycerol group at 1 h after operation, glycerol is inferior to furosemide for preventing cystic clot retention after TURP. But glycerol may protect against water intoxication better for its merit of producing higher plasma osmolality.

Aged↗
PubMed1995

Ultrasound measurement of transcranial distance during head-down tilt.

Exposure to microgravity elevates blood pressure and flow in the head, which may increase intracranial volume (ICV) and intracranial pressure (ICP). Rhesus monkeys exposed to simulated microgravity in the form of 6 degrees head-down tilt (HDT) experience elevated ICP. With humans, twenty-four hours of 6 degrees HDT bed rest increases cerebral blood flow velocity relative to pre-HDT upright posture. Humans exposed to acute 6 degrees HDT experience increased ICP, measured with the tympanic membrane displacement (TMD) technique. Other studies suggest that increased ICP in humans and cats causes measurable cranial bone movement across the sagittal suture. Due to the slightly compliant nature of the cranium, elevation of ICP will increase ICV and transcranial distance. Currently, several non-invasive approaches to monitor ICP are being investigated. Such techniques include TMD and modal analysis of the skull. TMD may not be reliable over a large range of ICP and neither method is capable of measuring the small changes in intracranial volume that accompany changes in pressure. Ultrasound, however, may reliably measure small distance changes that accompany ICP fluctuations. The purpose of our study was to develop and evaluate an ultrasound technique to measure transcranial distance changes during HDT.

Adult↗
PubMed1995

The use of right gastroepiploic artery for the bypass of left anterior descending coronary artery--case reports.

The right gastroepiploic artery (RGEA), a branch of the gastroduodenal artery, supplies the greater curvature of the stomach. It is capable of easily reaching the posterior and lateral surface of the heart as a reliable arterial conduit when appropriately harvested. In the previous reports, it has usually been anastomosed to the right coronary artery (RCA) or left circumflex coronary artery (LCX). Here, we present two cases of ischemic heart disease undergoing coronary revascularization. The RGEA was anastomosed to the left anterior decending coronary artery (LAD), which is the most important coronary artery in terms of patient outcome. Thallium-201 myocardial scintigraphy has proven that the RGEA can provide sufficient blood flow to the territory of the LAD. Thus, in coronary artery bypass grafting (CABG), the RGEA is a reliable arterial conduit for LAD revascularization.

Aged↗
PubMed1994

Psychiatric disorders among elderly Koreans in the United States.

This study examines the lifetime prevalence of various psychiatric disorders among 100 Korean elderly in Los Angeles. The instrument used in this study is the Diagnostic Interview Schedule, Version III (DIS III, 1-10). The main finding is of relatively low prevalence of most DSM-III disorders with the exception of alcohol abuse and dependence. The rate of alcoholism is astonishingly high among elderly Korean males in Los Angeles. The findings are compared with the U.S. Epidemiological Catchment Area studies, and with other much larger community studies conducted in Korea. A comparison shows that there are no significant differences in the prevalence of mental disorders between elderly Koreans in Los Angeles and elderly Americans in St. Louis (N = 576) except for the prevalence of alcohol abuse and dependence. The lifetime prevalence of DSM-III disorders among Koreans in Korea (N = 5100) is generally higher than among elderly Koreans in Los Angeles.

Aged↗
PubMed1993

Simple purification method for a Vibrio vulnificus hemolysin by a hydrophobic column chromatography in the presence of a detergent.

A Vibrio vulnificus hemolysin (VVH) was purified by two steps of hydrophobic column chromatography on Phenyl-Sepharose HP. The first chromatography was carried out at pH 6.0. In this pH condition, VVH efficiently bound to the column, but the hemolysin fraction eluted was accompanied with colored substance(s). To eliminate this colored substance, the second chromatography was carried out at pH 9.8 in the presence of 1% 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS), a zwitterionic detergent. Homogeneity of the hemolysin thus obtained was shown by polyacrylamide gel electrophoresis. The specific activity increased 33,600 times and the yield was 35%. The method is simple and useful to supply enough VVH for study of the role of the hemolysin in the infection by V. vulnificus or on the mechanism of action of the hemolysin.

Chromatography↗
PubMed1989

The conviction to care. The McKinney Scholarship Fund.

In response to the AIDS crisis and the critical need for competent and trained health care providers for the growing number of persons with AIDS, the McKinney Scholarship Fund has been recently established with the Stewart B. McKinney Foundation, and will be announced in December. As the first fund of its kind in the country, the McKinney Scholarship Fund will provide funding and financial assistance to qualified individuals who have demonstrated the ability and desire to go to school to work in the medical field with persons with AIDS, but who cannot afford to do so. At the present time, it is sponsored and endorsed by the Connecticut State Medical Society, the Hartford County Medical Association, the Connecticut Nurses' Association, the Hartford County Bar Association, and the Insurance Association of Connecticut.

Acquired Immunodeficiency Syndrome↗
PubMed1983

Penicillin therapy of experimental endocarditis induced by tolerant Streptococcus sanguis and nontolerant Streptococcus mitis.

The response of tolerant Streptococcus sanguis and nontolerant Streptococcus mitis infections to penicillin therapy was compared in the rabbit model of endocarditis. The minimal inhibitory and bactericidal concentrations of penicillin were 0.1 and 0.1 mug/ml, respectively, for S. mitis and 0.05 and 6.2 mug/ml, respectively, for S. sanguis. Time-kill studies done in vitro with penicillin concentrations of 2 and 20 mug/ml demonstrated minimal killing of the tolerant strain, with a 3 log difference in survival between the two strains after 24 and 48 h. Both strains produced endocarditis with comparable bacterial densities on the valvular vegetations. Rabbits were treated with procaine penicillin G in two dosage regimens, 80,000 or 5,000 U/kg given every 8 h. There was no difference between bacterial densities in valvular vegetations removed from rabbits infected with either strain after 2, 4, or 6 days of treatment with the high-dose regimen (serum penicillin concentration at 0.5 h, 9.4 mug/ml), despite the fact that serum bactericidal activity against the tolerant strain at 0.5 h was minimal. With the low-dose penicillin regimen (serum concentration at 0.5 h, 2.5 mug/ml), therapy was significantly less effective in the tolerant group only after 6 days of treatment. Similar results were obtained when penicillin was administered in low and high doses to prevent infection. In this animal model of infection, penicillin tolerance was associated with a diminished response to penicillin therapy only when the dose was severely restricted. In the high-dose regimen, there was no difference in the response to penicillin therapy between animals infected with either strain, despite the presence of only minimal serum bactericidal activity in the rabbits infected with the tolerant strain.

Animals↗
PubMed1983

Synergy of combinations of vancomycin, gentamicin, and rifampin against methicillin-resistant, coagulase-negative staphylococci.

The activity of combinations of vancomycin (2 or 10 micrograms/ml), gentamicin (0.3 micrograms/ml), and rifampin (0.03 micrograms/ml) against methicillin-resistant, coagulase-negative staphylococcal isolates was determined by the time-kill method. Combinations of rifampin with gentamicin or with vancomycin 2 micrograms/ml demonstrated enhanced killing against 13 of 17 and 13 of 25 strains, respectively. However, rifampin-resistant strains were selected with the latter combination in the remaining 12 of 25 studies.

Coagulase↗
PubMed1983

Reliability of in vitro susceptibility tests for detecting coagulase-negative staphylococcal resistance to penicillinase-resistant semisynthetic penicillins.

The reliabilities of five in vitro susceptibility tests (agar dilution, broth microdilution, automated MS-2, Kirby-Bauer disk diffusion, and ability to grow on methicillin-containing agar) to predict the susceptibility of 204 coagulase-negative staphylococcal isolates to penicillinase-resistant semisynthetic penicillins were compared. There was wide variation in susceptibility, with results ranging from 86.3% susceptible by MS-2 to 38.2% by growth on methicillin-containing agar. The results of the broth dilution techniques, including the MS-2, were significantly different (P less than 0.02) from the remaining tests. Nafcillin disks were less effective (P less than 0.02) than oxacillin disks in predicting resistance. Kirby-Bauer oxacillin disks and the ability to grow on methicillin-containing agar were the most reliable predictors of resistance. The MS-2 did not reliably predict resistance.

Coagulase↗
PubMed1983

Effect of penicillin on the adherence of Streptococcus sanguis in vitro and in the rabbit model of endocarditis.

The effect of penicillin treatment of Streptococcus sanguis in vitro, on subsequent bacterial density in the bloodstream and on cardiac valves in the rabbit model of endocarditis was studied. As experimental tools for this study, isogenic pairs of S. sanguis differing in resistance to streptomycin or rifampin were prepared by genetic transformation. Rabbits with traumatized heart valves received an intravenous inoculation of penicillin treated (1 mug/ml) and untreated S. sanguis, each marked by resistance to either streptomycin or rifampin. The number of penicillin-treated and untreated bacteria attached to the valvular surfaces was determined by differential counting on streptomycin or rifampin containing media. Penicillin pretreatment reduced cardiac valve colonization 5 min after inoculation ("adherence ratio" x 10(8) was 4.11 for the control and 3.66 for the penicillin-treated bacteria, P < 0.001). The results were not due to differences in serum killing or bacterial densities in the bloodstream. There was no difference in valvular bacterial densities 24 h after bacterial inoculation (adherence ratio x 10(8), 7.26 untreated vs. 6.34 penicillin-pretreated, P > 0.10). In vitro experiments were performed using platelet-fibrin surfaces to test the possibility that penicillin-induced loss of lipoteichoic acid was responsible for decreased streptococcal adherence. Pretreatment of S. sanguis cultures with inhibitory concentrations of penicillin or with antiserum against lipoteichoic acid and precoating of the platelet-fibrin surfaces with lipoteichoic acid, all caused reduction in bacterial adherence. The findings are interpreted as support for the role of lipoteichoic acid as an adhesin in S. sanguis interactions with particular host tissue surfaces.

Adhesiveness↗
PubMed1983

Influence of sodium perchlorate on thiourylene antithyroid drug accumulation in mice.

Radiolabelled [35S]propylthiouracil and [35S]methimazole were shown to accumulate in mouse thyroid gland in vivo, with maximal tissue/plasma ratios and maximal intrathyroidal levels of 35S-labelled drug being seen at the lowest dose of drug studied (0.1 micrograms/animal). Pretreatment with sodium perchlorate (10 mg) abolished iodide trapping by the thyroid and caused a fall in accumulation of both [35S]methimazole and [35S]propylthiouracil, although this effect was not seen at higher doses of drug, when tissue/plasma ratios approached unity. These data suggest that thiourylene antithyroid drug accumulation by the thyroid gland does not depend directly on the anion trap, and it is suggested that this accumulation might depend on subsequent intrathyroidal drug metabolism.

Animals↗