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Biomedical subjects

M H Chan

Publications and source records attributed to M H Chan.

13 recordsLinked to original sources
PubMed2001

Effect of 3He on submonolayer superfluidity.

We have studied the superfluid response of 3He-4He mixture films adsorbed onto porous gold for a wide range of 3He and 4He coverages, focusing on submonolayer superfluidity. At T = 0, 3He appears to float on top of 4He and can be viewed as a second substrate that induces its own inert layer. Depending on the 4He content, the zero-temperature superfluid mass and the superfluid onset temperature either saturate or vanish with the addition of 3He. The T = 0 superfluid-insulator phase boundary, which can be described by a simple function, is found in the 3He-4He coverage plane.

Journal Article↗
PubMed2001

Normal pulse oximeter reading in a cyanotic infant.

A newborn infant who presented with central cyanosis was found to have hereditary methaemoglobinaemia. The pulse oximeter readings and physical findings were incompatible. Clinical assessment remains an important part in the management of such cases.

Cyanosis↗
PubMed2001

Simvastatin increases serum osteocalcin concentration in patients treated for hypercholesterolaemia.

Animal studies, experimental models on cell lines, and epidemiological case-control studies have all suggested the possibility that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors have a beneficial effect on bone metabolism. However, all epidemiological studies are not prospective in nature and based on either measurement of bone mineral density or fracture risk. They also differ in recruitment criteria, definition of statin exposure, and outcome assessment. We performed a first prospective study using specific biochemical bone markers on 17 hypercholesterolaemic non-osteoporotic subjects treated with a therapeutic dose of simvastatin 20 mg daily for 4 weeks. Our results show that serum osteocalcin concentration increased significantly (p-value < 0.05) 4 weeks after therapy, whereas other bone markers including serum bone-specific alkaline phosphatase activity, urine deoxypyridinoline, and urine cross-linked N-telopeptides of type I collagen did not show any significant changes. Our data support that simvastatin causes a beneficial effect on bone metabolism as reflected by an increase in serum osteocalcin concentration. This added beneficial effect of statins on bone metabolism could potentially allow statins to become the first effective anabolic agent for the treatment of osteoporosis. We urge that priority should be given to a randomised controlled study to re-evaluate this group of drugs.

Adult↗
PubMed2000

Lidocaine-induced alterations in agonist-induced ion transport of cultured swine tracheal submucosal gland cells.

It has been documented that topical administration of lidocaine can cause airway complications, although it is the most used local anesthetic for laryngotracheal anesthesia. Thus, in this study we investigated the local actions of lidocaine on basal and autonomic secretagogue-induced ion transport in cultured swine tracheal submucosal gland cells. Ion transport plays an important role in maintaining effective mucociliary clearance and pulmonary defense mechanisms. It was measured as short-circuit current (Isc) utilizing Ussing chamber methodology. Exposure of cultured gland cells to lidocaine evoked a transient response with an initial increase in Isc followed by a decrease. The increase in Isc induced by lidocaine (3 mM) was 8.0 +/- 1.5 microA/cm(2). The maximal increases in Isc induced by isoproterenol and acetylcholine were 9.4 +/- 0.6 and 38.3 +/- 2.3 microA/cm(2), respectively. However, lidocaine significantly decreased the isoproterenol-induced increases in Isc. Acetylcholine-induced responses were not changed by lidocaine. Atropine did not significantly affect lidocaine-evoked events in ion transport. These results suggest that lidocaine directly alters epithelial transport of ions and also inhibits the adrenergic stimulation of epithelial ion transport.

Acetylcholine↗
PubMed2000

Mercury intoxication presenting with tics.

A 5 year old Chinese boy presented with recurrent oral ulceration followed by motor and vocal tics. The Chinese herbal spray he used for his mouth ulcers was found to have a high mercury content. His blood mercury concentration was raised. Isolated tics as the sole presentation of mercury intoxication has not previously been reported.

Child, Preschool↗
PubMed2000

Alpha-fetoprotein variants in a case of pancreatoblastoma.

We describe a 6-year-old boy with histologically confirmed pancreatoblastoma and a markedly elevated serum alpha-fetoprotein (AFP) concentration. Due to local tumour invasion, cytotoxic chemotherapy was given to debulk the tumour before attempting surgical resection. Serial serum AFP concentrations were measured on this patient. During chemotherapy there was a > 95% fall in total AFP. Tumour-specific variants of AFP, detected by isoelectric focusing, also disappeared during chemotherapy but recurred when chemotherapy was withdrawn. It is suggested that although there was no change in overall size of the tumour, as assessed by various imaging techniques, the changes in serological markers may indicate that the treatment did in fact cause considerable tumour necrosis, AFP and its variants may be useful markers of tumour response in patients with pancreatoblastoma. The expression of AFP and its variants in pancreatoblastoma may be related to the embryonic origin of the pancreas.

Antineoplastic Agents↗
PubMed1998

An evaluation of the effectiveness of patient-controlled analgesia after spinal surgery.

The purpose of this study was to evaluate the effectiveness of patient-controlled analgesia (PCA) in patients undergoing spinal surgery. Sixty patients undergoing spinal surgery were randomly assigned to receive PCA or the standard approach to postoperative analgesia (intramuscular injections on an "as needed" basis). Information on pain intensity at rest and with activity, total daily amount of analgesia, presence of adverse effects, length of time to ambulation and length of hospital stay was collected on all patients. Patients in the PCA group reported lower levels of pain, both at rest and with activity, and were ambulating earlier than patients receiving standard analgesia. There were no differences between the groups in total daily analgesic intake, presence of adverse effects and length of hospital stay. These data suggest that PCA is a safe, effective approach to managing pain after spinal surgery.

Adolescent↗
PubMed1997

Reduction in the bioelectric properties of swine tracheal submucosal gland cells in culture after daily short-term exposure to cocaine.

Chronic use of cocaine has been associated with respiratory complications. In this study, we investigated the effects of daily short-term cocaine exposure on epithelial bioelectric properties and chloride secretion in response to secretagogues in primary culture of swine tracheal submucosal gland cells grown on microporous inserts. Cell cultures exposed continuously to cocaine for 24 h or intermittently for 30 min daily for up to 3 consecutive days, resulted in a concentration-dependent reduction in transwell voltage and transepithelial resistance. Cocaine (300 microM) treatment for 24 h decreased the voltage and resistance by 87 and 75%, respectively. The voltage and resistance were also substantially decreased after 3 days of intermittent cocaine (10-30 microM) exposure. Cocaine exposure protocols used here did not enhance lactate dehydrogenase (LDH) release. Chloride secretion was measured as short-circuit current utilizing Ussing chamber methodology. Cocaine exposure did not change the decreases in short-circuit current caused by amiloride (10 microM), but reduced the increases in short-circuit current induced by acetylcholine and isoproterenol. After 3 days of intermittent cocaine (30 microM) exposure, the maximal acetylcholine and isoproterenol responses were reduced by 67 and 71%, respectively. Therefore, cocaine exposure continuously for 24 h or intermittently for 30 min daily for up to 3 days decreased basal transepithelial voltage as well as resistance and reduced the responses to cholinergic and beta-adrenoceptor agonists. These results suggest that alterations in epithelial function can occur even after daily transient cocaine exposure.

Acetylcholine↗
PubMed1997

A study of postural hypotension in a Chinese elderly outpatient population: are there really associated risk factors?

Postural hypotension is reported to be a common finding in elderly patients with prevalence rates from 10% to 30% having been reported. Proposed risk factors for the development of postural hypotension in the elderly include a number of medical conditions and medications. However, little is known about Chinses populations. From July 1995 through November 1995, we conducted a cross-sectional study on a group of 400 elderly patients (>65 years) in a geriatric outpatient department. Nearly 23% experienced a drop of 20 mmHg or more in systolic blood pressure on going from a supine to standing position. The fall did not correlate well with known risk factors such as use of anti-hypertensive drugs, hypnotics, diabetics mellitus, parkinsonism, and history of a fall. No significant factors were found to be associated with postural hypotension. Our data suggest that the change is idiopathic and does not result in any significant clinical outcome such as falls, syncope, and dizziness.

Journal Article↗
PubMed1996

Cocaine inhibits chloride secretion by swine tracheal submucosal gland cells grown in culture.

Active ion transport by airway submucosal gland cells plays an important role in maintaining effective mucociliary clearance. Alterations in the clearance will affect normal airway functions. Nasal and airway mucosal surfaces are exposed to high concentrations of cocaine after snorting crystals or smoking the freebase form, causing respiratory complications. The actions of cocaine on airway gland cell ion transport were determined by measuring the basal electrical properties and ion transport activated by acetylcholine (ACh) and isoproterenol (ISO) in swine tracheal submucosal gland cells grown in culture. The cells were enzymatically isolated, purified on Percoll density gradients, and then grown on microporous inserts at an air interface. Chloride secretion was measured as short-circuit current (Isc) utilizing Ussing chamber methodology. Amiloride (10 microM) was added mucosally to block sodium reabsorption. The maximal changes in Isc (delta Isc) induced by ACh and ISO were 42.0 +/- 4.4 and 8.8 +/- 0.8 microA/cm2. Cocaine decreased basal Isc and the increase in Isc induced by ACh and ISO. The concentration-response relationships for ACh and ISO were shifted to the right by cocaine (1-3 mM) when applied serosally. The maximal increase in Isc induced by ISO was inhibited by serosal cocaine, but, the maximal response to ACh was not. Thus, cocaine inhibits ACh-induced increases in Isc by competitively blocking the receptor and the response to ISO by noncompetitive inhibition. Mucosal cocaine reduced the maximal response to ACh and ISO and also caused a rightward shift. We conclude that cocaine directly alters submucosal gland cell function by reducing the basal and stimulated ability to transport ions and fluid.

Acetylcholine↗
PubMed1993

Nerve conduction studies in healthy Chinese: correlation with age, sex, height and skin temperature.

We consecutively collected 68 normal subjects who assented to receive electrophysiological examination in four limbs. There were 50 men and 18 women, with a mean age of 50.8 +/- 17.9 years (range: 15-88) and a mean height of 162.72 +/- 9.05 cm (range: 138-180). Mean skin temperature was 32.75 +/- 1.51 degrees C (range: 29.4-35.6) at wrist and 30.9 +/- 1.1 degrees C (range: 29-33) at lower leg. The mean values with standard deviation of the nerve conduction parameters such as distal latency, nerve conduction velocity, amplitude, duration and area of compound muscle action potential and sensory action potential, minimal latencies of H reflexes and F responses, and their side-to-side differences were presented. Age was negatively correlated with motor nerve conduction velocity (P < 0.05, r = -0.37 to -0.46), amplitude of compound muscle action potential (P < 0.05, r = -0.32 to -0.43) and sensory action potential (P < 0.05, r = -0.33 to -0.65), but not with sensory nerve conduction velocity (P > 0.05). Height was correlated with minimal latencies of H-reflexes and F-responses (P < 0.05, r = 0.45 to 0.76). Gender and temperature were not correlated with any parameters (P > 0.05).

Adolescent↗
PubMed1986

Effect of triethyltin on enzyme activity in human adult and cord red cells.

Since organotin compounds represent an environmental health hazard, we determined the effect of triethyltin bromide (TTB) on red blood cell (RBC) enzyme activity. TTB produced a concentration-dependent inhibition of hexokinase and pyrimidine 5'-nucleotidase for both adult and cord RBC. D-Glucose, but not ATP or MgCl2, prevented the hexokinase inhibition by TTB. Glucose-6-phosphate dehydrogenase, adenylate kinase, and hypoxanthine-guanine phosphoribosyltransferase were also inhibited by TTB. Cord RBC enzymes were more resistant to the effects of TTB than were adult RBC enzymes. Although TTB is a potent inhibitor of hexokinase, physiologic concentrations of glucose appear to protect the RBC during clinical tin intoxication.

5'-Nucleotidase↗