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Biomedical subjects

M K Chung

Publications and source records attributed to M K Chung.

At least 55 records · Page 3Linked to original sources
PubMed1998

Pharmacokinetic analysis for assessing developmental toxicity of a new synthetic acetolactate synthase inhibitor, LGC-40863, in rats.

Effects of O-[2,6-bis[(4,6-dimethoxy-2pyrimidinyl)oxy]benzoyl]oxime (LGC-40863) on dams and embryonic development were examined at p.o. doses of 500, 1000 and 2000 mg/kg/day on days 6 to 15 of gestation in rats. No significant maternal or embryonic toxicity was observed at any of the doses. However, external fetal anomalies including brachycephaly, microcephaly, micrognathia, agnathia, lordosis and edema were observed at an incidence of 2.2% at the lowest dosage level but not at higher dosages. Because these malformations are not common as spontaneous variations in rats, we carried out a toxicokinetic study to clarify whether the fetal anomalies at 500 mg/kg are related to LGC-40863. During multiple p.o. administrations of LGC-40863 at the same doses used in the developmental toxicity study, LGC-40863 was not detected in the systemic circulation. Moreover, 3 months of multiple dosing did not alter its plasma level. In the pregnant rats receiving 500 mg/kg on 10 consecutive days of gestation, LGC-40863 was also undetectable. However, after i.v. administration, high levels of the drug were found in plasma, and these could be described by a two-compartment model. These results demonstrate that the bioavailability of LGC-40863 is negligible. To investigate a possible relevance of metabolite(s) to the fetal anomalies, we examined excretion of radioactivity after p.o. doses of 500 and 2000 mg/kg of LGC-40863 spiked with [14C]LGC-40863. For both doses, cumulative recovery up to 72 hr was approximately 80% and 9% in feces and urine, respectively, indicating dose linearity in the elimination kinetics. Overall, these toxicokinetic data suggest that the fetal anomalies observed at 500 mg/kg are not associated with LGC-40863 but are spontaneously generated. In conclusion, LGC-40863 had neither significant maternal nor developmental toxicity at any of the doses tested for p.o. exposure.

Abnormalities, Drug-Induced↗
PubMed1997

Three-dimensional mapping of the initiation of nonsustained ventricular tachycardia in the human heart.

BACKGROUND: Elucidation of the electrophysiological mechanisms of nonsustained ventricular tachycardia (VT) in humans is required to define the relationship between nonsustained VT and sustained VT. This goal requires, at least in part, analysis of transmural ventricular activation in patients with both sustained and nonsustained VTs. METHODS AND RESULTS: We analyzed three-dimensional intraoperative cardiac maps of extrastimuli and beats during 44 nonsustained VTs and the initiating beats of 6 sustained VTs from six patients with healed myocardial infarcts who were undergoing arrhythmia surgery. The coupling interval, total activation time, and diastolic interval of each extrastimulus and beat of nonsustained VT were compared with counterparts during sustained VT. Sites activated last during extrastimuli initiating nonsustained or sustained VTs occurred in the same region, and activation times were comparable. However, the site of earliest activation during the initial or subsequent beats of nonsustained VT was discordant from the site activated earliest during the first and subsequent beats of sustained VT in 74% of cases. The mean variance in coupling interval, but not total activation time or diastolic interval, was significantly greater for VT that terminated before the 10th cycle than for VT that sustained. When analyzed from the last extrastimulus up to the fifth VT cycle, the standard deviation of the coupling interval, but not of the total activation time, was greater for nonsustained than for sustained VTs. Electrode density was sufficient to define an arrhythmia mechanism for 36 beats of nonsustained VT. Twenty-one (58%) initiated in the subendocardium, midmyocardium, or epicardium by a macroreentrant mechanism, and 15 (42%) initiated in the subendocardium by a focal mechanism. CONCLUSIONS: Compared with sustained VT, nonsustained VT initiates at discordant sites, is characterized by oscillations in coupling interval but not in total activation time, and initiates by either a macroreentrant or a focal mechanism.

Electrophysiology↗
PubMed1997

Termination of ventricular tachycardia in the human heart. Insights from three-dimensional mapping of nonsustained and sustained ventricular tachycardias.

BACKGROUND: To define the electrophysiological basis for the termination of ventricular tachycardia (VT), three-dimensional cardiac mapping and analysis of the terminal beats of nonsustained VT and beats of sustained VT were performed in six patients with healed myocardial infarcts. METHODS AND RESULTS: Termination of VT was due to activation from multiple initiation sites that were discordant from those responsible for the maintenance of sustained VT in 45% of cases, to repetitive activation from single sites that were discordant from those responsible for the maintenance of sustained VT in 24% of cases, or to activation from sites concordant with the sites of repetitive activation during sustained VT in 31% of cases. Sustained VT was characterized by occasional shifting of initiation sites, even after the tachycardia entered the stable monomorphic phase. Mapping was of sufficient density to define the mechanisms for 21 terminating beats of VT. In 5 cases, termination was due to intramural reentry, which initiated with the total activation time of the preceding beat of 204 +/- 11 milliseconds (ms) but terminated primarily because of a decrease in total activation time (144 +/- 23 ms, P = .03) that was associated with the development of intramural conduction block or with significant changes in the activation sequence along the reentrant circuit. In 16 cases, terminal beats were initiated by a focal mechanism on the basis of the absence of intervening electrical activity from the termination of the preceding beat to the initiation of the terminating beat (172 +/- 9 ms). Focal activation was associated with less conduction delay of the preceding beat (115 +/- 6 ms) than terminating reentrant beats (P < .001) and usually terminated suddenly without oscillations in cycle length or total activation time. CONCLUSIONS: Termination of VT is associated with alterations in initiation sites that are most often discordant from those maintaining sustained VT and is due to either reentrant or focal mechanisms.

Electrocardiography↗
PubMed1997

Cardioversion guided by transesophageal echocardiography: the ACUTE Pilot Study. A randomized, controlled trial. Assessment of Cardioversion Using Transesophageal Echocardiography.

BACKGROUND: Electrical cardioversion in patients with atrial fibrillation is associated with an increased risk for embolic stroke. Screening for atrial thrombi with transesophageal echocardiography (TEE) before cardioversion should, in many patients, safely permit cardioversion to be done earlier than would be possible with prolonged conventional, anticoagulation therapy. OBJECTIVE: To compare the feasibility and safety of TEE-guided early cardioversion with those of conventional management of cardioversion in patients with atrial fibrillation. DESIGN: Randomized, multicenter clinical trial. SETTING: 10 hospitals in the United States, Europe, and Australia. PATIENTS: 126 patients who had atrial fibrillation lasting longer than 2 days and were having electrical cardioversion. INTERVENTION: Conventional therapy or early, TEE-guided cardioversion with short-term anticoagulation therapy. OUTCOME MEASURES: Feasibility outcome variables were frequency of cardioversion and times to cardioversion and sinus rhythm. Safety outcomes were ischemic stroke, transient ischemic attack, systemic embolization, bleeding, and detected episodes of clinical hemodynamic instability occurring as long as 4 weeks after cardioversion. RESULTS: 62 patients were randomly assigned to receive TEE-guided cardioversion; TEE was done in 56 (90%) of these patients. Atrial thrombi were detected in 7 patients (13%) and led to the postponement of cardioversion. Cardioversion was successful in 38 of 45 patients (84%) who had early cardioversion. No embolization occurred with this strategy. Of the 64 patients receiving conventional therapy, 37 (58%) had cardioversion, which was successful in 28 patients (76%). One patient had a peripheral embolic event. The time to cardioversion was shorter in the TEE group (0.6 weeks [95% CI, 0.3 to 0.9 weeks] compared with 4.8 weeks [CI, 3.8 to 5.7 weeks]; P < 0.01). The incidence of clinical hemodynamic instability and bleeding complications tended to be greater in the conventional therapy group. CONCLUSIONS: These results suggest that TEE-guided cardioversion with short-term anticoagulation therapy is feasible and safe. The use of TEE may allow cardioversion to be done earlier, may decrease the risk for embolism associated with cardioversion, and may be associated with less clinical instability than conventional therapy. A large, multicenter study to confirm these findings is currently under way.

Aged↗
PubMed1997

A case of biliary cystadenocarcinoma.

Biliary cystadenocarcinoma is a very rare cystic tumor that arises in the liver or, less frequently, in the extrahepatic biliary system. It has been shown to arise in congenital liver cysts, bile ducts, biliary cystadenoma, in the context of fibropolycystic disease and in the hepatoduodenal ligament. Common presenting symptoms include an abdominal mass, local pain, nausea, jaundice, fever or occasional ascites. Some patients are asymptomatic, the lesion being an incidental finding at autopsy or surgery. Approximately 50 cases have been reported in the literature. We report a case of biliary cystadenocarcinoma in a 63-year-old man with a review of the literature.

Biliary Tract Neoplasms↗
PubMed1996

Comparison of prediction models for the compression force on the lumbosacral disc.

The main objective of this research was to compare three representative methods of predicting the compressive forces on the lumbosacral disc: LP-based model, double LP-based model, and EMG-assisted model. Two subjects simulated lifting tasks that are frequently performed in the refractories industry of Korea, in which vertical and lateral distances, and weight of load were varied. To calculate the L5/S1 compressive forces, EMG signals from six trunk muscles were measured, and postural data and locations of load were recorded using the Motion Analysis System. The EMG-assisted model was shown to reflect well all three factors considered here, whereas the compressive forces from the two LP-based models were only significantly affected by weight of load. In addition, low lifting index (LI) values were observed for relatively high L5/S1 compressive forces from the EMG-assisted model, suggesting that the 1991 NIOSH lifting equations may not fully evaluate the risk of dynamic asymmetric lifting tasks.

Adult↗
PubMed1995

Prognosis of patients > or = 70 years of age with non-Q-wave acute myocardial infarction compared with younger patients with similar infarcts and with patients > or = 70 years of age with Q-wave acute myocardial infarction.

In this study, 70 patients > or = 70 years of age admitted to the coronary care unit with non-Q-wave acute myocardial infarction (AMI) were followed prospectively for 1 year, and the clinical course in these patients was compared with that in 61 patients < 70 years with non-Q-wave AMI and 56 patients > or = 70 years with Q-wave AMI. Compared with the younger patients with non-Q-wave AMI, older patients were more likely to develop atrial fibrillation (23% vs 8%; p < 0.05) and congestive heart failure (53% vs 30%; p < 0.01), and less likely to receive thrombolytic therapy (9% vs 28%; p < 0.01), cardiac catheterization (41% vs 72%; p < 0.01), and coronary angioplasty (20% vs 39%; p < 0.05). Hospital mortality did not differ significantly between older and younger non-Q-wave AMI patients (10% vs 3%), but 1-year mortality was higher in the elderly (36% vs 16%; p = 0.02). Elderly patients with Q-wave AMI had more in-hospital complications, including death (25% vs 10%; p < 0.05), than elderly patients with non-Q-wave AMI. In contrast, postdischarge mortality was higher in elderly patients with non-Q-wave AMI, so that total mortality at 1 year was similar in the 2 groups. Overall, elderly patients with non-Q-wave AMI accounted for 62% of all deaths occurring during the first year after discharge (relative risk 2.6 compared with other groups; p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1995

Effects of posture, weight and frequency on trunk muscular activity and fatigue during repetitive lifting tasks.

We examined the effects of posture, weight and frequency on trunk muscular activity and fatigue during repetitive dynamic lifting. Electromyographic (EMG) signals from eight primary trunk muscles were collected during 120 min for four different task conditions. The patterns of muscle recruitment and the levels of relative activation were analysed using the normalized EMG data. Median power frequency (MPF) shift patterns were analysed to examine muscular fatigue. The muscles in the dorsal part of the trunk were activated at the symmetric posture, while the muscles on the contralateral side to the workload were more strongly activated at the asymmetric posture. Decreasing trends of MPFs were found in some active muscles, and they were more pronounced for the asymmetric posture than for the symmetric posture. It was also seen that the muscles became fatigued faster for the light load-high frequency task than for the heavy load-low frequency task.

Abdomen↗
PubMed1993

Prevention of readmission in elderly patients with congestive heart failure: results of a prospective, randomized pilot study.

OBJECTIVE: To determine the feasibility and potential impact of a non-pharmacologic multidisciplinary intervention for reducing hospital readmissions in elderly patients with congestive heart failure. DESIGN: Prospective, randomized clinical trial, with 2:1 assignment to the study intervention or usual care. SETTING: 550-bed secondary and tertiary care university teaching hospital. PATIENTS AND PARTICIPANTS: 98 patients > or = 70 years of age (mean 79 +/- 6 years) admitted with documented congestive heart failure. INTERVENTIONS: Comprehensive multidisciplinary treatment strategy consisting of intensive teaching by a geriatric cardiac nurse, a detailed review of medications by a geriatric cardiologist with specific recommendations designed to improve medication compliance and reduce side effects, early consultation with social services to facilitate discharge planning, dietary teaching by a hospital dietician, and close follow-up after discharge by home care and the study team. MEASUREMENTS AND MAIN RESULTS: All patients were followed for 90 days after initial hospital discharge. The primary study endpoints were rehospitalization within the 90-day interval and the cumulative number of days hospitalized during follow-up. The 90-day readmission rate was 33.3% (21.7%-44.9%) for the patients receiving the study intervention (n = 63) compared with 45.7% (29.2%-62.2%) for the control patients (n = 35). The mean number of days hospitalized was 4.3 +/- 1.1 (2.1-6.5) for the treated patients vs 5.7 +/- 2.0 (1.8-9.6) for the usual-care patients. In a prospectively defined subgroup of patients at intermediate risk for readmission (n = 61), readmissions were reduced by 42.2% (from 47.6% to 27.5%; p = 0.10), and the average number of hospital days during follow-up decreased from 6.7 +/- 3.2 days to 3.2 +/- 1.2 days (p = NS). CONCLUSIONS: These pilot data suggest that a comprehensive, multidisciplinary approach to reducing repetitive hospitalizations in elderly patients with congestive heart failure may lead to a reduction in readmissions and hospital days, particularly in patients at moderate risk for early rehospitalization. Further evaluation of this treatment strategy, including an assessment of the cost-effectiveness, is warranted.

Aged↗
PubMed1993

Therapeutic end points for the treatment of atrioventricular node reentrant tachycardia by catheter-guided radiofrequency current.

OBJECTIVES: The purpose of this prospective study was to test the hypothesis that the elimination of inducible repetitive atrioventricular (AV) node reentry despite the persistence of slow AV pathway conduction is a valid end point for radiofrequency catheter ablation procedures in patients with supraventricular tachycardia due to AV node reentry. BACKGROUND: Although modification of AV node physiology by radiofrequency current can eliminate AV node reentrant tachycardia, therapeutic end points that are definitive of a satisfactory result in patients undergoing modification of the slow AV pathway have not been established. Applications of radiofrequency current at selected sites may eliminate all evidence of slow pathway conduction or sufficiently modify the refractory properties of the slow pathway to preclude sustained arrhythmias. Accordingly, total abolition of dual AV node physiology may not be necessary to prevent arrhythmia recurrence. METHODS: Radiofrequency catheter ablation of the slow AV pathway was attempted in 59 patients with typical AV node reentry. Tissue ablation was performed with a continuous wave of 500-kHz radiofrequency current. Twenty-five to 35 W was applied for 60 s at the site selected for tissue destruction. RESULTS: Dual AV node physiology was eliminated completely in 35 patients (59%), persisted without inducible AV node reentry in 13 patients (22%) and persisted with inducible single AV reentrant beats in 11 patients (19%). In patients with persistent dual AV node physiology, the maximal difference between the effective refractory period of the fast and slow pathways was reduced from 104 +/- 62 ms before the procedure to 37 +/- 37 ms after AV conduction had been modified (p < 0.001). During a mean follow-up interval of 15 months (range 4 to 28), only one patient (2%) had a recurrence of the tachycardia. CONCLUSIONS: Results demonstrate that when complete elimination of dual AV node physiology is difficult, modification of slow pathway conduction to the extent that repetitive AV node reentry cannot be induced is a definitive end point that portends a good prognosis.

Adolescent↗
PubMed1993

Teratogenicity study (segment II) of recombinant granulocyte-macrophage colony stimulating factors (LBD-005) in rats.

A teratogenicity study was carried out in Sprague-Dawley rats subcutaneously injected recombinant Granulocyte-Macrophage Colony Stimulating Factors (LBD-005), the growth of stem cell and the development of the hematopoietic cell, at dose levels of 250, 500 and 1000 micrograms/kg/day for a period of 11 days from day 7 to day 17 of gestation. Two-thirds of the pregnant females in each group were sacrificed on day 20 of gestation and their fetuses were examined. The remaining dams were allowed to litter naturally, and the postnatal development of the offspring was observed. The incidences of external, internal and skeletal anomalies were not significantly increased in the fetuses of any treated groups. Recombinant GM-CSF caused no effects on parturition, lactation, postnatal growth and reproductive ability of the male and female offsprings.

Abnormalities, Drug-Induced↗
PubMed1993

Peri- and postnatal study (segment III) of recombinant granulocyte-macrophage colony stimulating factors (LBD-005) in rats.

A perinatal and postnatal study was carried out in Sprague-Dawley rats subcutaneously injected recombinant Granulocyte-Macrophage Colony Stimulating Factors (LBD-005), the growth of stem cell and the development of the hematopoietic cell, at dose levels of 250, 500 and 1000 micrograms/kg/day for a period from day 17 of gestation to day 21 after delivery. All pregnant dams were allowed to litter naturally, and the postnatal development of the offsprings was observed. The incidences of external, internal and skeletal anomalies were not significantly increased in the F1 and F2 fetuses of any treated groups. Recombinant GM-CSF caused no effects on parturition, lactation, postnatal growth and differentiation, behaviour and reproductive ability of the male and female offsprings.

Animals↗
PubMed1993

A case of primary intestinal lymphangiectasia.

A 26-year-old male patient who had an 8 years history of recurrent peripheral edema with diarrhea and hypoproteinemia was evaluated. Endoscopic jejunal and ileal biopsy revealed markedly dilated mucosal lymph vessels with no evidence of inflammation. 99mTc-labeled human serum albumin (HSA) scintigraphy showed significant activity accumulating in the gastrointestinal tract to represent 99mTc-HSA leakage into the bowel lumen. A diagnosis of protein losing enteropathy and intestinal lymphangiectasia could be made. After treatment with a high protein and fat restricted diet, his symptoms subsided and the serum protein level was normalized.

Adult↗
PubMed1992

Is age an independent predictor of early and late mortality in patients with acute myocardial infarction?

PURPOSE: To determine whether advancing age is an independent predictor of increased mortality following acute myocardial infarction or simply a marker for more extensive cardiac disease, a higher prevalence of comorbid conditions, and/or differences in therapeutic approach. PATIENTS: A total of 261 consecutive patients with documented acute myocardial infarction admitted to a university teaching hospital during a 1-year interval. METHODS: Seventy-four variables were analyzed to determine univariate predictors of inhospital and 1-year post-discharge mortality. Multiple linear regression models were constructed to determine independent predictors of early and late mortality after adjusting for baseline and therapeutic differences between younger and older patients. RESULTS: Compared with patients less than 70 years (n = 124), patients greater than or equal to 70 years (n = 137) were more likely (all p less than 0.05) to be female and have a prior history of ischemic heart disease. New York Heart Association functional class and Killip class on admission were higher in older patients, as were the admission serum creatinine and blood urea nitrogen levels. Serum albumin and peak creatine kinase levels were lower in older patients, but older patients were more likely to exhibit left ventricular hypertrophy or atrioventricular block on the initial electrocardiogram. Finally, younger patients were three times as likely to receive a thrombolytic agent and 66% more likely to receive intravenous beta-blockade than older patients, and younger patients were also more likely to receive heparin and intravenous nitroglycerin. Hospital mortality was 5.6% in patients less than 70 years versus 16.1% in patients greater than or equal to 70 years (p = 0.013). After adjusting for baseline and therapeutic differences, independent predictors of hospital mortality were systolic blood pressure on admission (inverse correlation, p = 0.0095), beta-blocker therapy (inverse correlation, p = 0.01), age (p = 0.014), peak creatine kinase level (p = 0.015), and Killip class (p = 0.035). Among hospital survivors, 1-year post discharge mortality was 6.8% in patients less than 70 years versus 19.1% in those greater than or equal to 70 years (p = 0.001). Independent predictors of post-discharge mortality after adjusting for age-related baseline and therapeutic differences were admission heart rate (p = 0.0004), age (p = 0.011), left ventricular ejection fraction (inverse correlation, p = 0.012), initial non-Q-wave myocardial infarction (p = 0.026), and the blood urea nitrogen level (p = 0.036). CONCLUSION: After adjusting for multiple baseline and therapeutic differences between older and younger patients, age per se remains a strong independent predictor of both inhospital and 1-year post-discharge mortality rates in patients with acute myocardial infarction.

Age Factors↗
PubMed1992

Isoresponse time regions for the evaluation of visual search performance in ergonomic interface models.

Computer-aided ergonomic evaluation models often provide a limited function of visual performance, usually in the form of visibility tests at any given location. It is, however, of great importance to complete a visual task in a predetermined time successfully or to predict the time to complete the task, e.g., a task of high-level control such as aircraft flight operations. In this study, isoresponse time regions which have an effect on visual performance in real-life situations are presented as an effort to complement aforementioned shortcomings of ergonomic interface models. A multiple regression was used to provide equal response time regions, being asymmetrical in shape. In addition, the fuzzy linear regression (FLR) model was introduced to provide a fuzzy set from which a decision-maker might select appropriately. It provided similar fitted values with having the advantage of utilizing the interval of those fitted values over the conventional regression model. The results can be applied effectively to the design of an interface for diverse visual tasks in real situations.

Adult↗
PubMed1991

Stability over time of variables measuring heart rate variability in normal subjects.

Both time and frequency domain measures of heart rate (HR) variability have been used to assess autonomic tone in a variety of clinical conditions. Few studies in normal subjects have been performed to determine the stability of HR variability over time, or the correlation between and within time and frequency domain measures of HR variability. Fourteen normal subjects aged 20 to 55 years were studied with baseline and placebo 24-hour ambulatory electrocardiograms performed 3 to 65 days apart to assess the reproducibility of the following time domain measures of cycle length variability: the standard deviation of all normal cycle intervals; mean normal cycle interval; mean day normal cycle interval; night/day difference in mean normal cycle interval; root-mean-square successive cycle interval difference; percentage of differences between adjacent normal cycle length intervals that are greater than 50 ms computed over the entire 24-hour electrocardiographic recording (proportion of adjacent intervals greater than 50 ms); and the frequency domain measures of high (0.15 to 40 Hz), low (0.003 to 0.15) and total (0.003 to 0.40) power. The mean and standard deviations of these measures were virtually identical between placebo and baseline measurements and within the studied time range. Variables strongly dependent on vagal tone (high-frequency, low-frequency and total power, root-mean-square successive difference, and percentage of differences between adjacent normal cycle intervals greater than 50 ms computed over the entire 24-hour electrocardiographic recording) were highly correlated (r greater than 0.8). It is concluded that measures of HR variability are stable over short periods of time.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗