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Biomedical subjects

K Y Chan

Publications and source records attributed to K Y Chan.

At least 91 records · Page 5Linked to original sources
PubMed1991

Assessment of ventricular septal defect by colour flow mapping.

The purpose of this study was to evaluate the usefulness of colour flow mapping (CFM) in the diagnosis and classification of congenital ventricular septal defect (VSD) and in the confirmation of spontaneous and surgical closure. Between August 1988 and March 1990, a total of 102 patients with isolated VSD (82 preoperative and 20 postoperative), age ranging from one day to 14 years, were subjected to 176 echocardiographic examinations. Sequential cross sectional imaging and CFM were the main modalities of assessment with conventional Doppler interrogation for quantitative measurements. In the preoperative group, there were 56 (68.3%) perimembranous (pm) VSD, 14 (17.1%) muscular (m) VSD and 12 (14.6%) doubly committed subarterial (dcsa) VSD. Ventricular septal defect was detected by CFM only in 88.9% of m/VSD, 57.6% of dcsa/VSD and 11.8% of pm/VSD (p less than 0.01). Spontaneous closure rate was highest in m/VSD (28.6%) followed by pm/VSD (8.9%) (p = 0.05). None of the dcsa/VSD closed as assessed by CFM. In the postoperative group, CFM served to quickly confirm complete closure without residual left to right shunt in 20 patients. In addition, CFM was useful in the assessment of haemodynamics and flow directed Doppler interrogation. Hence, CFM is a useful adjunct to cross sectional imaging in the assessment of children with isolated VSD.

Adolescent↗
PubMed1990

Sonographic screening for renal tract anomalies associated with congenital heart disease.

The incidence of structural renal tract abnormalities in 109 children with documented congenital heart disease (CHD) was studied using real-time sonography. In these children, 11.9% had associated urologic anomalies, which included hydronephrosis, duplication, ectopia, agenesis, and dysplasia of kidneys. Children with associated extracardiac anomalies had a significantly higher incidence of renal tract anomalies (39.1%) compared to those with isolated CHD (4.7%). Therefore, sonographic screening of the renal tract should be performed routinely in patients with CHD, especially in those with multiple congenital defects.

Abnormalities, Multiple↗
PubMed1990

The antinociceptive activity of paracetamol in zymosan-induced peritonitis in mice: the role of prostacyclin and reactive oxygen species.

1. Oral administration of high doses of paracetamol (600 mg kg-1 or more) resulted in inhibition of the writhing and reduced the levels of prostacyclin (PGI2, measured as 6-keto-PGF1 alpha) induced by intraperitoneal administration of zymosan in mice. The high oral doses of paracetamol required were accompanied by behavioural toxicity which may have contributed to the inhibition of writhing. 2. The number of writhes per mouse and the proportion of mice writhing at least once correlated significantly with the levels of 6-keto-PGF1 alpha. However, inhibition of writhing by paracetamol occurred at higher levels of 6-keto-PGF1 alpha than was previously observed with acidic non-steroidal anti-inflammatory agents. 3. When injected i.p., PGI2, carbacyclin and iloprost (agonists at the PGI2 receptor) induced writhing. Intraperitoneal injection of PGI2 reversed the inhibition of writhing induced by indomethacin (1 mg kg-1, p.o.) but not that induced by oral administration of paracetamol. 4. Paracetamol at 800 mg kg-1, p.o., inhibited carbacyclin-induced writhing but indomethacin at 1 mg kg-1 p.o. did not. Paracetamol administered i.p. at 100 mg kg-1 reduced the peritoneal levels of 6-keto-PGF1 alpha and inhibited zymosan-induced but not carbacyclin-induced writhing and did not produce behavioural toxicity. 5. The in vitro potency of paracetamol as a prostaglandin synthesis inhibitor is known to be reduced by the presence of lipid peroxides. However, no lipid peroxides, measured as thiobarbituric acid reactive material, were detected in the peritoneal lavage fluid of zymosan-injected mice. 6. Intraperitoneal administration of a mixture of superoxide dismutase and catalase reduced detectable superoxide anion by 98% without inhibiting the writhing response to zymosan or the antinociceptive potency of paracetamol. 7. The data are consistent with the suggestion that inhibition of PGI2 synthesis in the peritoneal cavity by paracetamol is responsible for only a part of its antinociceptive activity in this test. However, extremely high oral doses of paracetamol were required which produced behavioural toxicity which clearly contributed to the inhibition of writhing. The low potency of paracetamol in this model cannot be attributed to the generation of lipid peroxides via the oxidative burst.

6-Ketoprostaglandin F1 alpha↗
PubMed1990

Early diastolic clicks after the Fontan procedure for double inlet left ventricle: anatomical and physiological correlates.

M mode echocardiograms and simultaneous phonocardiograms were recorded in four patients with early diastolic clicks on auscultation. All had double inlet left ventricle and had undergone the Fontan procedure with closure of the right atrioventricular valve orifice by an artificial patch. The phonocardiogram confirmed a high frequency sound occurring 60-90 ms after aortic valve closure and coinciding with the time of maximal excursion of the atrioventricular valve patch towards the ventricular mass. One patient had coexisting congenital complete heart block. The M mode echocardiogram showed "reversed" motion of the patch towards the right atrium during atrial contraction. Doppler flow studies showed that coincident with this motion there was forward flow in the pulmonary artery with augmentation when atrial contraction coincided with ventricular systole. The early diastolic click in these patients was explained by abrupt cessation of the motion of the atrioventricular valve patch towards the ventricular mass in early diastole. In one patient atrial contraction led to a reversal of this motion and was associated with forward flow in the pulmonary artery.

Adolescent↗
PubMed1990

Quantitation of rabbit corneal epithelial cell outgrowth on polymeric substrates in vitro.

The outgrowth of corneal epithelial cells onto a polymeric substrate is expected to be the primary event in the epithelialization of a synthetic corneal graft. To study the effects of polymer surface properties on corneal epithelial cell outgrowth, a quantitative in vitro cell outgrowth assay was done. Polymers with systematic variations in hydroxyl content were used as outgrowth substrates. These polymers were characterized by electron spectroscopy for chemical analysis for elemental surface composition and by captive air-bubble contact angle for surface wettability. Circular corneal buttons were punched from excised rabbit corneas, placed onto these substrates, and incubated in a hormonally enriched culture medium. Outgrowth of the epithelial cells was allowed to proceed onto the substrates for 4 days. The outgrowth areas were measured, and an outgrowth index was calculated for each substrate by comparing it with tissue culture polystyrene substrate. The highest outgrowth generally occurred on substrates with intermediate wettabilities (captive air-bubble contact angles of approximately 45-75 degree); it was less on substrates of lower or higher wettabilities. Protein coatings of albumin, immunoglobulin G (IgG), fibronectin, and culture medium were found to lower the wettabilities of native substrates. Albumin and IgG precoating were shown to reduce epithelial cell outgrowth; fibronectin precoating was shown to improve outgrowth on most substrates. These results suggest that epithelial cell outgrowth is influenced by both substrate and protein interactions.

Actins↗
PubMed1990

A cryodamage model for studying corneal nerve regeneration.

This study used a transcorneal freezing technique to produce a 2-mm circular, central wound in the rabbit cornea for investigating corneal nerve regeneration. All the corneal cells, nerves, and associated Schwann cells were dead inside the wound, but the extracellular matrix components remained intact. The destroyed epithelium and endothelium were replaced in 1 and 5-7 days, respectively. The necrotic keratocytes and stromal and subepithelial nerves were removed completely in 1-3 days by invading macrophage-like cells. The wounded stroma was repopulated centripetally by migrating keratocytes between days 1-5. Two types of nerve growth were identified in the stroma. The first type was novel sprouting of straight, long neurites between days 2-21, initially from the undamaged, periwound nerves and later from regenerated stromal nerves inside the wound. These small-caliber neurites proliferated in a random and disorderly pattern both inside and outside the wound and sometimes terminated on stationary, stellate keratocytes. The second type was genuine regrowth of stromal and subepithelial nerves in a centripetal direction between days 3-7. Schwann cells appeared on the newly formed nerves starting on day 4 or 5. A near-normal pattern and size of the nerves were established in the wound as early as day 10. In the epithelium, transient, wound-oriented neurites (days 1-3), single nerves, and semileashes (days 4-10) appeared. A near-normal leash pattern was restored between days 10-21 only at the wound periphery. Thus, in this model, the major groundwork of nerve regeneration occurred between days 3-10, simultaneously, at all three levels of nerve organization. These data suggest that nerve-Schwann cell interaction contributes to the restoration of stromal and subepithelial nerves, whereas a reparative epithelium deficient in trophic activity may account for the incomplete regrowth of epithelial nerves. The cryodamage model offers an efficient and multifaceted system for the experimental study of corneal nerve regeneration.

Animals↗
PubMed1990

Percutaneous transluminal balloon valvuloplasty: the treatment of choice for congenital valvar pulmonary stenosis.

Forty-eight children with suspected isolated pulmonary valvar stenosis were evaluated clinically and echocardiographically between January 1987 and December 1988. Fourteen patients with significant transpulmonary peak systolic pressure gradient greater than 30 mmHg on continuous-wave Doppler interrogation were subjected to right heart catheterisation. Percutaneous transluminal balloon valvuloplasty was performed in 11 of these patients with peak systolic pressure gradient than 40 mmHg across the pulmonary valve at cardiac catheterisation. Satisfactory reduction of systolic right ventricular pressure (110 +/- 43 to 46 +/- 17 mmHg, p less than 0.001) and peak systolic pressure gradient across pulmonary valve (92 +/- 44 to 27 +/- 16 mmHg, p less than 0.001), were achieved in all cases. The reduction of peak systolic pressure gradient (64 +/- 37 mmHg, range = 29-158 mmHg), was positively correlated with the initial right ventricular systolic pressure (r = 0.92, p less than 0.0002). There was no significant complication in this series and all patients were discharged the day after the procedure. Percutaneous transluminal balloon valvuloplasty is effective and safe. It should be the treatment of choice for significant valvar pulmonary stenosis in children.

Cardiac Catheterization↗
PubMed1989

Magnetic resonance investigations of non-acoustic petrous lesions.

Twenty cases of intrapetrous lesions were studied by a 1.5 T magnetic resonance (MR) unit. In all cases, comparisons were made between MR, CT and clinical findings. Our present material included 9 cholesteatomas, 1 cholesterol cyst, 3 primary epidermoid carcinomas, 2 metastatic neoplasms, 1 glomus jugulare tumor and 4 facial neurinomas. Gadolinium was injected in 7 cases and seemed to be the best method for studying the intrapetrous tumors. MR permitted accurate topographic study and assessment of tumoral extension, as well as a ready demonstration of tumor vascularity. The present findings also showed that MR is not capable of defining small bony detail or calcifications.

Adolescent↗
PubMed1989

Kawasaki syndrome in Chinese children.

A retrospective analysis of the clinical features and outcome of 39 Chinese children with Kawasaki syndrome was made. The mean age of onset was 2.7 years (range: 0.2-13 years). The male:female ratio was 2.9:1. One child presented with nephrotic syndrome. This renal manifestation has not been described in Kawasaki disease. Ten (32%) out of 31 patients were found to have coronary aneurysms by cross-sectional echocardiography. The only significant risk factor detected in this group of patients was anaemia (P less than 0.007). There was one (2.5%) death from acute myocardial infarction and the rest of the patients were clinically well with a mean follow-up period of 1 year (mean: 5-40 days). This study indicates that there is a high incidence of coronary aneurysm complicating Kawasaki syndrome in Chinese comparable with that reported in Japanese children.

Child, Preschool↗
PubMed1989

Antimicrobial susceptibilities of halophilic vibrios.

Two hundred and forty-four clinical and environmental strains of nine species of halophilic vibrios isolated in Hong Kong were tested for their susceptibilities to 23 antimicrobial agents by an agar dilution method using unsupplemented Mueller-Hinton agar, an inoculum size of 10(5) cfu per spot and incubation for 18 h at 30 degrees C. Most strains were resistant to sulphamethoxazole, trimethoprim, penicillins and older cephalosporins, and most were susceptible to chloramphenicol, tetracycline, cotrimoxazole, the aminoglycosides, the newer cephalosporins, aztreonam, imipenem and the quinolones. However, there were significant differences between species, especially in their patterns of beta-lactam susceptibility.

Anti-Bacterial Agents↗
PubMed1989

Detection of cardiac problems among school children by health screening.

A study was undertaken to assess the types of cardiac diseases and dysrhythmias in a healthy population of 651,794 school children who underwent general health screening between January 1981 to December 1986. Congenital heart lesions were diagnosed in 1159 (0.18 per cent), the majority being mitral valve prolapse (MVP; 0.08 per cent), small ventricular septal defects (VSD; 0.04 per cent), mild pulmonary stenosis (PS; 0.03 per cent), and small atrial septal defects (ASD; 0.02 per cent). Other lesions detected were patent ductus arteriosus (PDA), coarctation of aorta (CoA), Fallot's Tetralogy (FT) and total anomalous pulmonary venous drainage (TAPVD). Of these, five had surgical closure of ASD, eight and ligation of PDA, and one had correction for TAPVD. Cardiac dysrhythmias were seen in 350 patients; consisting of premature ventricular contractions (PVC) in 186, right bundle branch block (RBBB) in 132, atrial ectopics (AE) in 17, sinus node dysfunction in five, atrioventricular (AV) block in seven, Wolff-Parkinson-White (WPW) syndrome in two, and paroxysmal atrial tachycardia (PAT) in one boy. Associated congenital heart lesions were found in 110 patients. The cardiac screening programme has resulted in a significant detection of cardiac abnormalities among apparently healthy school children. Early detection of cardiac disease has resulted in early remedial measures to be taken and thus improved cardiological care.

Arrhythmias, Cardiac↗
PubMed1989

Vibrio parahaemolyticus and other halophilic vibrios associated with seafood in Hong Kong.

The summer prevalence of Vibrio parahaemolyticus and other halophilic vibrios in seafood from Hong Kong markets was investigated. Halophilic vibrios were isolated from all seven types of seafood examined, and comprised 9.1%, 8% and 6.1% of contaminating aerobic heterotrophic bacteria from mussels, clams and oysters respectively. Sucrose-positive vibrios were more common than sucrose-negative varieties. Vibrio alginolyticus was the most frequently isolated species, followed by V. parahaemolyticus, V. harveyi, V. fluvialis, V. vulnificus, V. pelagius, V. campbellii, V. spendidus and V. marinus. Mussels contained the highest concentration of V. parahaemolyticus (4.6 x 10(4)/g); oysters and clams contained 3.4 x 10(4)/g and 6.5 x 10(3)/g respectively. The ubiquity and relatively high concentrations of V. parahaemolyticus and other pathogenic vibrios in shellfish is a potential public health hazard in Hong Kong and other subtropical Asian countries.

Animals↗
PubMed1989

Cardiac arrhythmias in paediatric practice.

Clinical data of patients with cardiac arrhythmias managed between May 1986 and March 1988 were reviewed to determine their mode of presentation and clinical course. Of the 5,768 admissions, 62 (1.07%) patients had arrhythmias. During the same period, 21 patients were managed as outpatients with 13 being new referrals. Thirty-eight patients had undergone corrective cardiac procedures, 8 others had congenital heart lesions, 3 were associated with acquired cardiac pathology and the remaining had isolated arrhythmias. The cardiac arrhythmias were: right bundle branch block 36, premature atrial and ventricular contractions 15, supraventricular tachycardia (SVT) 15, atrioventricular (AV) block 7, sinus bradycardia 3, atrial fibrillation 2, ventricular tachycardia and fibrillation 2, Wolff-Parkinson-White syndrome without SVT 2, bradytachyarrhythmia 1. There were 3 patients with foetal SVT, one persisting till day 1. High grade AV block occurred in 2 patients post-surgically and needed pacing. Only 2 others were symptomatic. Other than the 38 patients who underwent corrective procedures (2 had balloon valvuloplasty for pulmonary stenosis), 8 others had structural heart disease. There was 1 sudden death and 5 died from their primary heart disease.

Adolescent↗
PubMed1989

Corneal nerve regeneration. Correlation between morphology and restoration of sensitivity.

Corneal nerve regeneration was determined in albino rabbits after deepithelialization of the cornea using heptanol. Regeneration was monitored up to 10 weeks by measuring corneal tactile sensitivity using an esthesiometer and by examining stromal and intraepithelial nerve patterns following gold chloride impregnation and acetylcholinesterase staining. Tactile sensitivity was much reduced, possibly absent, up to 2 weeks after wounding. From 2.5-4 weeks, sensitivity recovered rapidly to 60% of prewounding levels and remained unchanged thereafter. In control corneas, a distinct orientation of the basoepithelial leashes towards the nasal-most limbus was observed in the central two-thirds of the cornea. Three days after wounding, neurites that were oriented radially towards the wound center extended into the periphery of the wound area from just beyond the wound margin. At 1 week, regenerating axons were present as single neurites and in the form of modified leashes, mainly at the periphery of the wound area but also more towards the center. At 3 weeks, neurites, regenerated leashes and networks of terminals with terminal endings were found throughout the regenerated epithelium. Regional changes in the orientation of the regenerated leashes were observed also. No further change in the intraepithelial nerve pattern was detectable thereafter up to 10 weeks after wounding. It was concluded that partial restoration of tactile sensitivity following deepithelialization of the cornea is a function of the establishment of a near-normal nerve pattern in the regenerated epithelium and is correlated with the subnormal neural density observed in a previous study.

Acetylcholinesterase↗
PubMed1989

Increased axonal transport of trigeminal ganglion proteins in an electrode model.

This investigation uses an electrical stimulation model of ocular herpes simplex virus (HSV) reactivation to elucidate the relationship between neuronal protein synthesis, axonal transport and electrical stimulation. In this study, healthy adult albino rabbits were implanted with electrodes over the trigeminal ganglion (TG) and stimulated chronically twice a week for 28-34 days (previously shown to induce HSV reactivation in infected rabbits). The TG was visualized surgically and injected with 3H-proline to label newly synthesized protein. After various times, the TG, corneas and ophthalmic nerve were analyzed for labeled proteins. In nonimplanted and implanted rabbits (whether stimulated or not), the rate of fast anterograde axonal transport in the ophthalmic nerve was 347 mm/day and 326 mm/day, respectively. A lag period of 45 min occurred between initiation of protein labeling and onset of axonal transport. Only a small percentage of newly synthesized neuronal proteins were transported in the ophthalmic nerve (1-4% in the proximal 10 mm) or deposited in the cornea (less than 0.5%) after 24 hr. Neither the rate of protein synthesis in the TG nor the rate of axonal transport was changed by electrical stimulation. However, the amount of radioactively labeled proteins undergoing axonal transport in the stimulated group was five times that of the sham control group. Thus, the routing and loading of TG proteins for axonal transport is enhanced in the electrical stimulation model.

Animals↗
PubMed1989

Time-lapse videomicroscopic study of in vitro wound closure in rabbit corneal cells.

This study used video time-lapse recording to characterize the dynamic features of corneal epithelial cells and keratocytes during in vitro wound closure. Confluent cultures of these two cell types from rabbits were established in Rose chambers. A wound 4 or 10 mm in diameter was produced in the center of each culture by mechanical removal of cells. Wound closure was recorded by videomicroscopy for 2-3 days and reviewed at a playback speed of 400 times normal. The epithelial cells at the wound margin initiated migration by extending lamellipodia with undulatory motions. Successive tiers of cells moved as a continuous sheet in a unified and coordinated manner while maintaining intercellular linkage. The migration was unidirectional, toward the wound center. The mean migration rate of the leading cells was 104 microns/hr. The trailing cells migrated at successively slower rates, inversely proportional to their distance from the wound margin. Mitosis was rare during migration but did occur simultaneously. The mitotic rate was 3.7 mitoses/100 cells. The relative mitotic frequency was 0.23 mitosis/hr. By contrast, in keratocyte cultures, the cells around the wound margin migrated individually and asynchronously without intercellular connection. Initially the cells moved generally toward the wound space, but later, different cells migrated in different directions. The mean migration rate was 15 microns/hr. Mitosis occurred frequently. The mitotic rate was 25.3 mitoses/100 cells, and the relative mitotic frequency was 1.33 mitoses/hr. The cell cycle duration was 9.9 hr. Thus corneal epithelial cells and keratocytes showed fundamentally different characteristics and mechanisms of wound closure in vitro.

Animals↗