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Biomedical subjects

A Yeung

Publications and source records attributed to A Yeung.

At least 37 records · Page 2Linked to original sources
PubMed1997

Effect of Shear on the Strength of Polymer-Induced Flocs

Micromechanics was used to show that the rupture strength of polymer-induced flocs varied with the hydrodynamic conditions at which the flocs were formed. A maximum floc strength at an intermediate shear rate was observed. The overall performance of the polymeric flocculants, as determined by two independent methods, showed that the conditions for optimal flocculation did not coincide with those for maximum floc strength. The amount of flocculation was explained in terms of the competing effects of the particle collision frequency and the destructive hydrodynamic forces. The contributing forces to the floc strength are, however, more likely to be densification of the floc by shear and the weakening of reattachment strengths. The evidence presented here may be useful for explaining flocculation data that depart from the constant yield stress theory. Thus, the notion of the floc strength varying with shear rate may offer an alternative to multilevel floc structure models in the description of flocculation kinetics. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed1997

Coronary AVE micro stents: serial quantitative angiography and histology in a canine model.

The AVE Micro Stent (AVE Inc., Santa Rosa, CA) is composed of helically welded 3 mm long, zigzag crowns with stent lengths from 6 to 39 mm and diameters from 2.5 to 4.5 mm. Quantitative coronary angiography and histologic analyses of acute and chronic implantation were obtained in 52 stented coronary segments of 18 dogs. Three hearts with 8 stented coronary segments were harvested after 24 hr, 3 hearts with 9 stented segments were harvested after 2 weeks, 6 hearts with 15 stented segments were harvested at 8 weeks, and 6 hearts with 20 stented segments were harvested at 24 weeks post-deployment. There were no procedural complications, deaths, or acute vessel closures. The average lumen diameter of the stented segment was largest at 2 weeks (3.3 +/- 0.3 mm). The smallest average diameters were observed at 8 weeks after the stent deployment (2.7 +/- 0.4, P < 0.05) with an increase again at 24 weeks (2.9 +/- 0.6). The pre-explant percent of stenosis was <30% in all animals. Histologically, a peak of inflammation was visible at 2 weeks; however, the extent of luminal narrowing reached its peak at 8 weeks and the lumen dimension increased somewhat at 24 weeks. The degree of intimal thickening remained relatively constant throughout the different time points (<200 microm). Overall, these data suggest that constrictive remodeling within the stented segment occurs at 8 weeks in this animal model. The later increase of the stented segment dimensions as well as higher net gain at 24 weeks compared to 8 weeks after deployment suggests that this constriction is a transitory phenomenon.

Angioplasty, Balloon, Coronary↗
PubMed1996

Resistive-load detection in healthy school-aged children.

The ability to detect changes in respiratory resistance, which may be important in acute and chronic adaptations to airways obstruction, has not been measured previously in children. Two methods were used to measure the resistive-load detection thresholds (the added resistance that produced a "just noticeable difference" in perception) in a group of 38 healthy children and adolescents aged 7-16 years. Total respiratory system resistance (Rrs), as measured by forced oscillation, was used as an index of each child's intrinsic baseline (pre-test) resistance. To determine thresholds a computer program added various percentages of baseline resistance according to response (first method) and then in random order (second method). Thresholds by at least one of the two methods were detectable in 32 of the children (84%), and failure to detect a threshold was less common in older than in young children. Thresholds obtained by each method were significantly related to one another (r = 0.54, P < 0.05). Baseline resistance accounted for a marginally significant proportion of the variation in thresholds as assessed by the tracking method (R2 = 0.12, P < 0.10) and a large proportion of the variation in thresholds as assessed by the random method (R2 = 0.66, P < 0.0001). Thresholds expressed in terms of percent of baseline resistance were found to have mean values of 100.4-105.0%, regardless of gender or age. Results from a comparison group of adults (n = 10) indicated lower threshold by both procedures (mean values, 71.90-76.50%). We conclude that perceptual thresholds for added resistive loads are determined, in part, by growth-related changes in intrinsic resistance.

Adolescent↗
PubMed1996

Conceptual and methodologic issues in quantifying perceptual accuracy in childhood asthma.

Delineated methodologic issues in the study of symptom perception in childhood asthma. A review of past and recent psychophysiological and clinical studies of both adults and children presents the methodologic and analytic approaches that have been applied to quantify perceptual accuracy. Peak expiratory flow rate, forced expiratory volume in the first second, and force expiratory flow can serve as objective measures of asthma. A visual analog scale, a numerical guess, and a categorical description as subjective measures all have clear strengths and weaknesses. Correlational analysis of subjective-objective data, arithmetic differences between subjective guess and objective value, and an error grid categorization can each be applied to calculate an accuracy index on an individual subject. Illustrative examples reveal that the same data lead to different indices depending on the method chosen. Empirical research is needed to standardize various methodologic approaches. Given the increasing prevalence, severity, and morbidity of pediatric asthma, the study of symptom perception may be a critical component in our understanding of asthma management, and will likely lead to useful clinical interventions.

Adolescent↗
PubMed1995

Effects of technique modification on immediate results of high speed rotational atherectomy in 710 procedures on 656 patients.

Seven hundred ten high speed rotational atherectomy (HSRA) procedures were performed in a single consecutive series of 656 patients. Stand alone HSRA was performed in 253 patients (35%). HSRA with adjunctive low pressure (< or = 2 ATM) balloon angioplasty (LP BA) was performed in 221 patients (31%), and HSRA with adjunctive high pressure (> or = 4 ATM) balloon angioplasty (HP BA) was performed in 236 patients (34%). Prognostically unfavorable Type B2 and C lesions dominated the study group (74.7%). Procedural success rate was 96%. Emergency coronary artery bypass surgery was performed in 1.4% of cases, Q wave myocardial infarction occurred in 3.4% and death, related to procedure, was consequent in 0.5% of cases. Incidence of flow limiting dissections was 3.1%, distal spasm was 5.3%, and "no reflow" phenomenon was 1.8%. The recent technique modifications included continuous advancer/guiding catheter infusion of the nitroglycerin-verapamil mixture, limitation of duration of lesion engagement by the burr, stepwise increase in the burr size, decrease of rotational speed, and strict control of rpm drop during lesion ablation. Evolution of the interventional technique involved trends towards decrease of the use of HP BA in conjunction with steady increase in the percentage of SA and LP BA procedures over time. These technique changes resulted in complete absence of "no reflow" in 1994, as well as a generalized decrease in overall coronary vascular reactivity from all burr passes.

Adult↗
PubMed1995

Spirometric patterns in childhood asthma: peak flow compared with other indices.

The objective of this study was to determine patterns of pulmonary function abnormalities and to evaluate how adequately peak flow monitoring was correlated to other spirometric indices in childhood asthma. Ninety-one children, aged 8-15 years, with moderate-to-severe asthma were repeatedly tested in a summer camp. On-site medical staff permitted 24-hour-a-day supervision. Subjective and objective clinical evaluations of asthma status were made over 14 consecutive days. Detailed clinical history and clinical observations were made by an experienced staff, and a total of 2,663 pulmonary function tests were performed regularly three times daily and whenever a child sensed asthma symptoms. Patterns of obstruction were divided into large airway abnormalities and small airway abnormalities. There was a low concordance between standard large airway measures, such as the peak expiratory flow rate (PEFR) or the forced expiratory volume in 1 second (the FEV1), and measures of small airway obstruction, such as the forced expiratory flow rate 25-75% (FEF25-75). Normal PEFR measurements do not always indicate that all other pulmonary function measures are normal. In fact, 18% of children with a normal PEFR had abnormal FEF25-75 values. Results demonstrated that the FEF25-75 was the most specific and sensitive measure of airway obstruction. PEFR is widely used to monitor asthma symptoms objectively because it is technically simple to perform, relatively inexpensive, and helpful in most cases. It is, therefore, appropriate for asthma education programs to recommend PEFR as an objective measure to guide in making therapeutic decisions. Our data and clinical observations support the "Guidelines for the Diagnosis and Management of Asthma" of the NIH Health Asthma Education Program that suggest that children have more complete pulmonary function testing along with frequent PEFR measures. Many children may appear asymptomatic, while recording normal PEFR measures, and still having significant asthma. Repeated pulmonary function testing and evaluation of the pattern of respiratory obstruction aids in managing this challenging group. We recommend that efforts be made to develop a simple and inexpensive method of measuring FEF25-75 that will allow this measurement to be made even at home.

Adolescent↗
PubMed1995

Meta-analysis of randomized controlled trials of cranial electrostimulation. Efficacy in treating selected psychological and physiological conditions.

To clarify the diverse published results of cranial electrostimulation (CES) efficacy, we conducted an extensive literature review that identified 18 of the most carefully conducted randomized controlled trials of CES versus sham treatment. For the 14 trials that had sufficient data, we used the techniques of meta-analysis to pool the published results of treating each of four conditions: anxiety (eight trials), brain dysfunction (two trials), headache (two trials), and insomnia (two trials). Because studies utilized different outcome measures, we used an effect size method to normalize measures which we then pooled across studies within each condition. The meta-analysis of anxiety showed CES to be significantly more effective than sham treatment (p < .05). Pooling did not affect results that were individually positive (headache and pain under anesthesia) or negative (brain dysfunction and insomnia). Most studies failed to report all data necessary for meta-analysis. Moreover, in all but two trials, the therapist was not blinded and knew which patients were receiving CES or sham treatment. We strongly recommend that future trials of CES report complete data and incorporate therapist blinding to avoid possible bias.

Anxiety Disorders↗
PubMed1994

Symptom perception and self-management in childhood asthma.

Asthma self-management, an increasingly important component of the treatment of pediatric asthma, entails accurate perception of respiratory symptoms. This review summarizes what is known about symptom perception in both adults and children. The literature on visceral autonomic perception, laboratory studies of respiratory perception, and clinical work with asthmatic patients is reviewed.

Asthma↗
PubMed1994

A pictorial visual analog scale for rating severity of childhood asthma episodes.

The purpose of this study was to determine whether the use of pictorial anchors improved a visual analog scale (VAS) designed to assess asthma episodes. The sample consisted of 77 children with moderate to severe asthma attending a summer camp. They rated one of two VASs, either nonpictorial (39 subjects in year 1) or pictorial (38 subjects in year 2), three times a day for 2 weeks to report the severity of their asthma symptoms. Immediately after the subjects rated the VAS, pulmonary function testing was obtained. The mean VAS scores increased 64% using the pictorial VAS while the mean PEFRs in the 2 years were almost identical, suggesting that changes on the VAS were not due to differences in pulmonary functioning. For boys, the increase in individual mean VAS score in year 2 using the pictorial VAS was 44%; for girls, the increase in individual mean VAS scores was 112%. Use of a pictorial VAS increases the range of severity of symptoms reported by children with asthma. The instrument may be a useful tool in the systematic quantifiable assessment of subjective symptomatology in pediatric asthma.

Adolescent↗
PubMed1992

Circadian rhythms and coronary events: implications for therapy.

Obstructive coronary disease has many clinical expressions and some are used as useful indicators of risk. Apart from symptoms, transient ischaemia occurs during daily life, is mostly silent and represents one measure of risk. Ambulatory monitoring of the electrocardiogram shows that ischaemia occurs with increased frequency during the morning hours while waking and rising. This coincides with other damaging vascular events, increased sympathetic activity and changes in coronary blood supply and myocardial oxygen demand that may favour a lower threshold to ischaemia. Calcium blockers, beta-blockers and aspirin can favourably affect this process and long-acting drugs appear to be a more rational approach given the variability of ischaemia over time.

Circadian Rhythm↗
PubMed1991

Time-dependent recovery of passive neutrophils after large deformation.

Experiments are performed in which a passive human neutrophil is deformed into an elongated "sausage" shape by aspirating it into a small glass pipette. When expelled from the pipette the neutrophil recovers its natural spherical shape in approximately 1 minute. This recovery process is analyzed according to a Newtonian, liquid-drop model in which a variational method is used to simultaneously solve the hydrodynamic equations for low Reynolds-number flow and the equations for membrane equilibrium with a constant membrane tension. The theoretical model gives a good fit to the experimental data for a ratio of membrane cortical tension to cytoplasmic viscosity of approximately 1.7 x 10(-5) cm/s (0.17 micron/s). However, when the cell is held in the pipette for only a short time period of 5 s or less, and then expelled, the cell undergoes an initial, rapid elastic rebound suggesting that the cell behaves in this instance as a Maxwell viscoelastic liquid rather than a Newtonian liquid with constant cortical tension.

Elasticity↗
PubMed1991

Polylysine conjugates of Bowman-Birk protease inhibitor as targeted anti-carcinogenic agents.

Bowman-Birk protease inhibitor (BBI), an 8000 mol. wt polypeptide with anti-carcinogenic activity, was coupled to poly(D-lysine) (BBI-SS-PDL) and poly(L-glutamate) (BBI-SS-PLG) with a disulfide-cross-linking agent, N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP). In vitro transformation assays showed that BBI-SS-PDL, but not BBI-SS-PLG, retained the full anticarcinogenic activity of BBI. When administered i.v. to Balb/c mice, a selective localization in the lungs was found with BBI-SS-PDL but not with BBI or BBI-SS-PLG. At 30 min, 3 h and 24 h after the injection of BBI-SS-PDL, the amounts of BBI in the lungs were 118%, 74% and 19% of the injected dose/g of tissue respectively. At the same time points, the amount of radioactivity in the lungs of mice injected with BBI was 5%, 3% and 1% of the injected dose/g of tissue respectively. Therefore, higher amounts of BBI could be targeted to the lungs by injecting BBI as a PDL conjugate. BBI-SS-PDL was also retained in the lungs for a longer period of time than free BBI. In previous studies, BBI has been shown to suppress lung carcinogenesis. The results presented here suggest that BBI-SS-PDL could be more effective than BBI as an anti-carcinogenic agent for the lung.

Animals↗
PubMed1991

Relations between heart rate, ischemia, and drug therapy during daily life in patients with coronary artery disease.

BACKGROUND: Previous studies have shown that little if any increase in heart rate occurs 1 minute before the onset of ischemia in ambulant patients with coronary artery disease. This study tested the hypothesis that there are characteristic relations between heart rate and ischemia in ambulant patients with coronary artery disease. METHODS AND RESULTS: Twenty-one patients with proven coronary disease demonstrated 212 episodes of ischemia during 504 hours of continuous monitoring of the electrocardiogram. An important increase in heart rate (from 74 +/- 11 to 90 +/- 14 beats/min, p less than 0.001) occurred between 5 and 30 minutes (not 1 minute) before the onset of ischemia. A significantly higher heart rate at onset of ischemia was seen during Bruce protocol exercise testing than during daily life (117 +/- 12 versus 95 +/- 15 beats/min, p less than 0.01). However, when a less-strenuous, but more prolonged, exercise protocol was used in a subgroup of patients (n = 12), ischemia occurred at a heart rate that was significantly lower than during the Bruce protocol (88 +/- 14 versus 103 +/- 15 beats/min, p less than 0.05) and was not significantly different from the threshold heart rate at onset of ischemia during daily life (88 +/- 14 versus 84 +/- 12 beats/min, p = NS). As part of two placebo-controlled trials, treatment with both propranolol and nitroglycerin altered the distribution of ischemic events by heart rate but in opposite directions. Although propranolol largely eliminated events occurring at high (greater than 100 beats/min) and moderate (80-100 beats/min) heart rates, the number of events at low (less than 80 beats/min) heart rates was increased. In contrast, nitroglycerin reduced episodes at low and moderate heart rates only. CONCLUSIONS: Important increases in heart rate occur before the onset of ischemia during daily life, but this increase occurs much earlier than has been reported. Duration of heart rate increase appears to influence the heart rate threshold for ischemia, and this may contribute to the occurrence of ischemia at lower heart rates during daily life than during standard exercise testing. Last, different classes of drugs appear to have characteristic effects on ischemia occurring at different heart rates that may be useful in planning therapy.

Activities of Daily Living↗
PubMed1991

Diurnal rhythms and clinical events in coronary artery disease.

Patients with coronary atherosclerosis present with angina, myocardial infarction and sudden death, most often caused by atherosclerotic stenosis complicated by spasm and/or occlusive thrombosis. All of these events have been shown to exhibit similar diurnal rhythms, with a peak incidence in the morning after waking and rising. Other cardiovascular parameters also show a similar diurnal rhythm associated with increased sympathetic outflow and circulating catecholamines, producing increases in heart rate, blood pressure, myocardial contractility and oxygen demand soon after waking and rising. Experimental and clinical research has recently pointed to several possible mechanisms that might be responsible for these events. In patients with atherosclerosis, dysfunction of the endothelium in the epicardial coronary arteries results in a failure to limit the constrictor response to catecholamines. Catecholamines can also alter the procoagulant nature of vascular surfaces. We speculate that the interaction between increased sympathetic activity and the procoagulant and vasoconstrictor states of atherosclerotic coronary stenoses may lead to a lower threshold to ischaemia in the waking hours, with a corresponding increase in angina, myocardial infarction and sudden death. These factors may be important considerations for the selection of suitable therapies and for future research.

Cardiovascular System↗
PubMed1989

A cytostatic protein isolated from the conditioned medium of mouse monocytic leukemia WEHI-3 cell cultures.

A cytostatic factor (CF) with a molecular mass of 50 kDa was purified to more than 16,000-fold from the conditioned medium of LPS-treated mouse myelomonocytic leukemia (WEHI-3) cell cultures. The activity of CF was completely destroyed by heating at 70 degrees C for 10 min, 50 degrees C for 30 min, or by the treatment in pH 3 buffer for 2 h. CF showed a strong growth inhibitory effect on CHO cells, as well as several other unrelated cell lines, e.g., K562 and L1210, but not on L929 cells. It also inhibited Con A-induced mitogenesis in mouse and rat spleen cells. The growth inhibitory effect of CF, however, was highly reversible; CHO cells were able to regain the normal growth after removal of the factor from the culture medium. Our results suggest that CF is a protein secreted by WEHI-3 cells, which is distinct from other known macrophage- or tumor-derived cytotoxic proteins.

Animals↗