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Biomedical subjects

A T Cheung

Publications and source records attributed to A T Cheung.

At least 55 records · Page 3Linked to original sources
PubMed1994

Echocardiographic and hemodynamic indexes of left ventricular preload in patients with normal and abnormal ventricular function.

BACKGROUND: Transesophageal echocardiography (TEE) is used to diagnose hypovolemia despite the lack of validation studies. The objective was to determine the effects of acute graded hypovolemia on TEE and conventional hemodynamic determinants of left ventricular (LV) preload in anesthetized patients with normal and abnormal LV function. METHODS: Determinants of LV preload derived from TEE and hemodynamic monitoring were measured serially in 35 anesthetized cardiac surgical patients without valvular heart disease. Patients were stratified into two groups: those with normal LV function (group 1, n = 17) and those with LV wall motion abnormalities (group 2, n = 13). Patients in groups 1 and 2 were subjected to graded hypovolemia produced by collecting 6 aliquots of blood, each equal to 2.5% of their estimated blood volume (EBV). A third group of patients (group 3, n = 5), not subjected to graded hypovolemia, were studied to test for time-dependent changes. RESULTS: Group 2 had a significantly greater baseline (mean +/- SD) pulmonary artery occlusion pressure (17 +/- 6 vs. 11 +/- 6 mmHg), LV end-diastolic area (23 +/- 5 vs. 18 +/- 4 cm2), LV end-diastolic wall stress (23 +/- 10 vs. 14 +/- 6 x 10(3) dyne.cm-2), and smaller fractional area change (35 +/- 13 vs. 59 +/- 7%). In groups 1 and 2, the LV end-diastolic area, pulmonary artery occlusion pressure, and LV end-diastolic wall stress decreased linearly in response to blood loss in the range of 0-15% of the EBV. No significant changes in the measured parameters occurred in group 3. A significant decrease in the central venous pressure, pulmonary artery occlusion pressure, and LV end-diastolic area was detected in response to a 2.5% EBV deficit (approximately 1.75 ml.kg-1) in groups 1 and 2. The mean change in LV end-diastolic area (0.3 cm2/1.0% EBV deficit) in response to equivalent EBV deficits was the same in groups 1 and 2. In contrast, the mean change in cardiac output and LV end-diastolic wall stress was less in group 2 despite a greater decrease in pulmonary artery occlusion pressure. Compared to group 1, a greater EBV deficit (7.5% to 12.5% vs. 2.5% to 5%) was required in group 2 to cause a significant decrease in the cardiac output, stroke volume, mixed venous oxygen saturation, and LV end-diastolic wall stress. CONCLUSIONS: TEE and hemodynamic determinants of LV preload detected changes in LV function caused by acute blood loss. Acute blood loss caused directional changes in LV end-diastolic area, pulmonary artery occlusion pressure, and LV end-diastolic wall stress even in patients with LV wall motion abnormalities. Changes in LV end-diastolic wall stress, derived from both TEE and hemodynamic measurements corresponded to changes in cardiac output, stroke volume, and mixed venous oxygen saturation that occurred during acute blood loss.

Coronary Artery Bypass↗
PubMed1993

Chronic Pseudomonas aeruginosa endobronchitis in rhesus monkeys: II. A histopathologic analysis.

We have recently established a rhesus monkey model of chronic Pseudomonas aeruginosa (PA) endobronchitis by bronchoscopic instillation of PA-embedded agar beads. All experimental animals developed chronic neutrophilic endobronchitis similar to chronic PA endobronchitis in cystic fibrosis (CF). Histopathologic studies further confirmed similarities to chronic PA endobronchitis in CF, including marked peribronchial inflammation, epithelial damage, presence of degraded cilia and ciliary abnormalities, appearance of PA bacterial clusters, mucosal hyperplasia, goblet cell hypertrophy/hypersecretion, airway obstruction, alveolar abnormalities, bronchiectasis, and fibrosis.

Animals↗
PubMed1991

Induction of differentiation in human myeloblastic leukemia ML-1 cells by heptachlor, a chlorinated hydrocarbon insecticide.

Effects of heptachlor, an organochlorine pesticide, on human myeloblastic leukemia ML-1 cells were determined. Similar to 12-O-tetradecanoylphorbol-13-acetate (TPA), a known tumor promoter, heptachlor induced cell adherence and formation of extended cytoplasmic pseudopodia in ML-1 cells. The growth of ML-1 was slightly stimulated by low concentrations (less than 30 nM) of heptachlor. A dose-responsive cell death was also observed when ML-1 cells were treated with heptachlor at concentrations greater than 80 microM. Examination by light microscopy of the cells treated with 80 microM heptachlor revealed a gradual appearance of differentiation characteristics in the culture. On Day 3 of the treatment, 41% of the cells remained unchanged as ML-1, 39% of the cells showed changes and apparent cell differentiation, and 20% of the cells were induced to differentiate to monocyte- or macrophage-like cell type. Electron microscopy also revealed cellular differentiation and the presence of monocyte- and macrophage-like cell types (22%) was confirmed by positive esterase staining.

Acute Disease↗
PubMed1991

Functional deficiency of polymorphonuclear leukocytes in simian acquired immunodeficiency syndrome.

The functional characteristics of polymorphonuclear leukocytes (PMN), considered to be the first line of host defense against infections, from rhesus macaques confirmed to have simian retrovirus (SRV)-induced simian acquired immunodeficiency syndrome (SAIDS), were evaluated. The PMN from SRV antibody-positive macaques without clinical signs were chemotactically responsive. Their phagocytic and killing capabilities were normal, and their cell membranes were highly deformable. However, PMN from SRV antibody-positive macaques and with persistent lymphadenopathy, as well as having at least 3 of the 11 common clinical signs of AIDS, were chemotactically nonresponsive. Their phagocytic and killing capabilities were compromised, and their cell membranes were rigid and nondeformable. In general, PMN from macaques with clinically confirmed SAIDS were functionally deficient. The results are similar to those obtained in other retroviral infections and can be clinically significant, because the host defense deficiency may be responsible for the recurrent and opportunistic infections in SAIDS.

Animals↗
PubMed1990

Reduced microbicidal activity of peripheral mononuclear phagocytic cells infected with Pasteurella multocida.

Pasteurella multocida inhibits the uptake and killing of Candida albicans and P. multocida by avian mononuclear phagocytic cells. The toxic outer membrane protein of P. multocida, which has been previously described, also inhibited the uptake and killing of C. albicans. Antibody specific for the toxic outer membrane protein reversed this effect resulting not only in an increase in uptake of C. albicans and P. multocida, but also in intracellular killing of P. multocida. This antibody, however, only partially restored killing of C. albicans. These data support the hypothesis that P. multocida is capable of intracellular survival in avian mononuclear phagocytic cells and that the toxic outer membrane protein is totally or partly responsible for this occurrence.

Animals↗
PubMed1989

Intravital microscopy: a new in vivo technique for visualizing and quantifying effects of regulatory peptides on choledochoduodenal junction motility.

Using intravital microscopy, we studied the in vivo effects of regulatory peptides on choledochoduodenal junction motility in guinea pigs. During basal and hormone-stimulated periods, intravital microscopy documented rhythmic, asymmetrical, "milking" contractions of the sphincter ductus choledochi (SDC) which occurred independent of sphincter ampullae (SA) contractions or were followed by SA contractions. Cholecystokinin octapeptide (CCK-8) (greater than or equal to 0.01 micrograms/kg) increased the frequency of SDC contractions and at higher doses (greater than or equal to 0.1 microgram/kg) increased the frequency of SA contractions. Pentagastrin (greater than or equal to 1.0 microgram/kg) and secretin (10 micrograms/kg) decreased the contraction frequencies of both sphincters. Biliary manometry demonstrated similar effects of these peptides on the frequency of the SDC and SA contractions, but also showed that CCK-8 (0.1 microgram/kg) increased the amplitude of SDC and SA contractions while pentagastrin (1 microgram/kg) decreased the amplitude of only SDC contractions. Tetrodotoxin and atropine did not affect hormone-induced changes in frequency, but tetrodotoxin reduced the increase in amplitude of contraction caused by CCK-8. We concluded that intravital microscopy provides a sensitive, in vivo technique to visualize and quantify the complex motility of a small structure like the choledochoduodenal junction.

Animals↗
PubMed1989

Bile flow rates and biliary motility quantitated by intravital microscopy.

Intravital microscopy was adapted to document and quantitate in vivo biliary motility and bile flow rates in guinea pigs. The movement of 10 microns diameter fluorescent beads in the bile duct was used to measure bile flow rates. Using this method, bile flow rates were comparable to those determined by measuring the volume of bile collected from the papilla, but greater (P less than 0.01) than the volume of bile collected from a bile duct cannula. During intravital microscopy, biliary contractions were only detected at the choledochoduodenal junction. While fasting, the sphincter ductus choledochi contracted at 6.0 +/- 1.0 per min and the ampulla at 1.2 +/- 0.2 per min. Postprandially, sphincter contractions had a decreased frequency and an increased duration while both duration and frequency of ampullary contractions increased. The volume of bile collected from a bile duct cannula postprandially did not change. This data suggested that the choledochoduodenal junction had a propulsive function and postprandial changes in motility were due to neurohumoral factors rather than passive response to changes in bile flow rates. Intravital microscopy proved to be a sensitive in vivo technique in which to quantitate bile flow rates and biliary motility.

Animals↗
PubMed1989

Development of methodology for recording colonic myoelectrical activity in the infant primate.

In order to study developmental aspects of colonic motility, we have developed a miniaturized electrophysiologic recording system for use in the infant primate rhesus (Macaca mulatta). Technical considerations including absence of rectal valves, decreased tissue thickness and small colonic diameter limit application of standard non-surgical recording methodology in this model. In-vivo testing with 4 different bipolar electrode probe configurations yielded satisfactory quality recordings only with silver chloride suction electrodes. Using this system, colonic slow waves and spike action potentials were studied in 6 infant primates (ages 1 to 7 months) both fasting and following a standard liquid meal of 10 cc/kg. In response to feeding, colonic spike potentials increased from 7.8 +/- 1.7 to 14.2 +/- 4.1 within 15 minutes (mean spikes +/- SEM/5 min interval). The observed response of the distal colon to a meal in this model is similar to the response reported in adult humans using intraluminal recording techniques. Utilizing the described methodology, the infant primate appears to be a suitable model for investigation of developmental aspects of gastrointestinal motility and electrophysiology. These techniques have important direct applications for investigation in the human infant.

Animals↗
PubMed1988

The ontogeny of pulmonary defenses: alveolar macrophage function in neonatal and juvenile rhesus monkeys.

Using the technique of bronchoalveolar lavage, we isolated alveolar macrophages (AM) from the lower respiratory tract of newborn (1-4 days of age), infant (6-10 days of age), juvenile (3-6 months of age), and adult rhesus monkeys. The AM thus obtained were assayed in vitro to determine their chemotactic, phagocytic, and candidicidal capabilities. The predominant (greater than or equal to 89%) cell type in bronchoalveolar lavage effluent in all ages was the AM. Chemotaxis, phagocytosis, and killing of Candida albicans were markedly impaired in neonatal AM as compared with those from infants, juveniles, and adults. AM chemotactic activity achieved normal adult values by 6 days of age. Phagocytosis, and to a lesser extent candidicidal activity, were significantly improved in 6-day-old animals, but adult levels were still not achieved even by 6 months of age.

Aging↗
PubMed1987

Quantitative microscopy: I. A computer-assisted approach to the study of polymorphonuclear leukocyte (PMN) chemotaxis.

A computer-assisted approach has been designed to analyze and quantitate polymorphonuclear leukocyte (PMN) chemotaxis. This approach involves a rapid, objective, and semiautomated (user-directed) image-analysis system that is video- and microscope-based. The entire system consists of a microvideo set-up that is put on line with a Digital DEC-LSI-11/73 microcomputer, interfaced with a Datacube analog-digital/digital-analog converter. Video signals of PMN movement are digitized by the system at a resolution of 240 pixels vertically by 320 pixels horizontally (at 256 gray levels) and stored in a 76,800-byte frame buffer. The digitized data are stored for later use or utilized immediately for image segmentation, image display, movement, and morphometric computations for each PMN in a maximum phase field (at 645 X high dry) of 50 PMNs at 10-second intervals. The digitized data are used for computation of cell perimeter, surface area, optical density, contour-ratio, position, speed, and direction of locomotion with the utilization of micro-image-analysis programs written in FORTRAN and MACRO assembly language, with the computer operating under RT-11/TSX+. The reliability, objectivity, and reproducibility of measurements made with this quantitative approach have been tested by comparing with manual-tracing measurements of PMN movement. A correlation factor of 0.99 has been obtained. However, the quantitative-microscopic approach is much faster, more objective, less tedious, and much easier to operate than the conventional manual-tracing method.

Chemotaxis, Leukocyte↗
PubMed1987

Long-term marginal zinc deprivation in rhesus monkeys. I. Effects on adult female breeders before conception.

To assess long-term effects of marginal zinc deprivation on pregnancy, adult non-pregnant female rhesus monkeys were fed diets containing 100 or 4 ppm zinc for 1 yr. then mated; effects on pregnancy and its outcome are under study. During this year, food intake was not depressed in zinc-deprived (ZD) monkeys, and there were relatively few effects on biochemical or hematological indices. By the end of the year, plasma zinc concentration was somewhat lower in ZD monkeys than in controls. Several immune variables, including serum IgM and IgG levels and polymorphonuclear leukocyte (PMN) function, were depressed in the ZD group, changes closely reflecting circannual fluctuations in plasma zinc levels in both diet groups. Endotoxin-activated plasma from ZD monkeys had less potential to promote chemotaxis than that from control monkeys, suggesting that defective PMN function may relate to a plasma effect. Marginal zinc deprivation may thus influence immune function before other variables are affected.

Animals↗
PubMed1987

A computer-assisted image-analysis system for analyzing polymorphonuclear leukocyte chemotaxis in patients with diabetes mellitus.

A computer-assisted image-analysis system that precisely tracks the cell movements of up to 50 polymorphonuclear leukocytes (PMNLs) was developed and used to quantitatively measure cellular chemokinesis and chemotaxis in normal individuals and in diabetic patients with hyperglycemia. The PMNLs were tested in Zigmond chambers with or without a gradient of 10(-7) M n-formylmethionylleucylphenylalanine (f-Met-Leu-Phe). Cellular movement was recorded on videotape by using a videocamera mounted on the microscope. The videotapes were analyzed by computer programs to calculate the speed and direction of each PMNL at 10-sec intervals. Average rates of chemokinesis were 19.6 microns/min without and 25.3 microns/min with f-Met-Leu-Phe. McCutcheon indices, which measure chemotaxis, were 0.01 without and 0.48 with f-Met-Leu-Phe. Similar values were observed in diabetic patients after fasting (average glucose, 217 mg/100 ml) and 2 hr after glucose challenge (average glucose, 309 mg/100 ml). These values demonstrate that PMNLs from diabetic patients with hyperglycemia move at normal rates and respond appropriately to f-Met-Leu-Phe.

Adolescent↗
PubMed1987

Effects of growth and maturation on biliary structures of guinea pigs.

The biliary system and major duodenal papilla of male guinea pigs were examined in vivo using intravital microscopy. Study of the photomicrographs and videotape recordings indicated that biliary organs changed with age and growth of the guinea pigs. Physiological data including the frequency of sphincteric contractions were recorded and efforts were made to correlate these data with changes in structure thought to be due to maturation. The volume of smooth muscle in the bile duct sphincter (measured using histological sections) increased with age as did surface area of the mucosa. The bile duct was separate from the pancreatic duct in each of 28 guinea pigs. Study of the guinea pig extrahepatic biliary system (EBS) allowed the isolated examination of effects of maturation on bile duct capacity. The anatomical reason for this is that the ampulla of the bile duct emptied into the duodenum (independently of the pancreatic duct) at the major duodenal papilla. The duct of the pancreas entered the duodenum distally (caudally) to the major duodenal papilla on the minor duodenal papilla. The separation of biliary and pancreatic ducts simplified the making of casts of the EBS. It is important to consider this feature in selection of a model for studies of bile duct function in living animals. Three anatomical techniques were selected to focus from differing perspectives on growth-related changes that occurred among the EBS of neonatal, juvenile and adult animals. These techniques were: The capacity (volume) of bile contained within the EBS was determined using plastic casts of the system.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗