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Biomedical subjects

M H Chan

Publications and source records attributed to M H Chan.

18 recordsLinked to original sources
PubMed2006

Fourier transform ultraviolet-visible spectrometer based on a beam-folding technique.

A beam-folding technique in optical interferometry, where the number of beam folds used can be very large, is reported. This technique can be used as a low-cost position-tracking method in a Fourier transform spectrometer (FTS) to cover the broad spectral range from UV to IR. The main advantage gained is the simple position-tracking algorithm used in sampling the interferogram. We have developed a UV-visible FTS, whose wavelength coverage is limited only by the optical elements (350 nm(-1) microm with off-the-shelf components). Preliminary results show that it can achieve a resolution of approximately 4 cm(-1) even with a ball-bearing translation stage.

Algorithms↗
PubMed2005

Acousto-optic measurements of tropospheric nitrogen dioxide column density by solar spectroscopy.

Measurements of column densities of atmospheric gases can be achieved by a solar spectroscopic method that uses differential optical absorption spectroscopy. Because of the scintillation of sunlight intensity in the atmosphere, the variation in intensity will introduce a low-frequency modification of the measured solar spectrum. A spectral capturing-type CCD spectrometer takes milliseconds to capture a solar spectrum, and the effect of sunlight scintillation is negligible. In contrast, without scintillation correction, a scanning-type spectrometer spending minutes to obtain a complete solar spectrum will introduce some amount of errors. We demonstrate an intensity-compensation technique in a scanning-type spectrometer, based on a solid-state acousto-optic tunable filter, for solar spectroscopic measurements.

Journal Article↗
PubMed2004

Role of beta-blockade in anaesthesia and postoperative pain management after hysterectomy.

BACKGROUND: Perioperative use of beta-blockers has been advocated as a strategy to prevent cardiac sequelae. This study evaluated the influence of perioperative esmolol administration upon anaesthesia and postoperative pain management amongst patients undergoing hysterectomy. METHODS: Ninety-seven ASA I-II patients, undergoing abdominal total hysterectomy, were randomly divided into one of two groups. Patients in the Esmolol group received an i.v. loading dose of esmolol 0.5 mg kg(-1) followed by infusion of 0.05 mg kg(-1) min(-1) before anaesthesia induction. The infusion was documented at the completion of surgery. The Control group received a volume of normal saline. After surgery, all patients were treated with patient-controlled i.v. analgesia (PCA), which was programmed to deliver 1 mg of morphine on demand for 3 consecutive days. Pain intensity on movement and at rest, sedation score, and side effects were recorded. RESULTS: The two groups were comparable with respect to their characteristics. Patients in the esmolol group received significantly lower end-tidal isoflurane concentrations (1.0 (0.3) vs 1.4 (0.5)%, respectively; P<0.001) and fentanyl (0.9 (0.2) vs 1.2 (0.5) microg kg(-1), respectively; P=0.006) during anaesthesia. They also showed a reduced heart rate and arterial pressure response to tracheal intubation, skin incision, and tracheal extubation. The Esmolol group consumed less PCA morphine in 3 days (37.3 (8.4) vs 54.7 (11.2) mg, respectively; P=0.005). Pain intensity and medication side effects were similar in the two groups. CONCLUSION: The results suggest that perioperative esmolol administration during anaesthesia reduces the intraoperative use of inhalation anaesthetic and fentanyl, decreases haemodynamic responses, and reduced morphine consumption for the first 3 postoperative days.

Adrenergic beta-Antagonists↗
PubMed2004

Acousto-optic differential optical absorption spectroscopy for atmospheric measurement of nitrogen dioxide in Hong Kong.

Measurement of the atmospheric concentration of nitrogen dioxide (NO(2)) pollutant was demonstrated by differential optical absorption spectroscopy (DOAS) using a visible acousto-optic tunable filter. In a traditional spectral scanning DOAS system for atmospheric concentration monitoring, a highly stable light source is required. When the light intensity fluctuates during scanning, the concentration retrieval will be inaccurate. In order to reduce the error due to intensity fluctuations, a modified DOAS system has been developed by introducing a broadband light intensity monitoring channel. Using the measured intensity of the broadband channel as the intensity of the light source, the spectrum can be de-biased and the residual intensity variation will primarily result from atmospheric extinction. In addition, by employing the lock-in detection technique, the background light interference is also removed in the modified DOAS system. The atmospheric NO(2) concentration measurement was performed at the campus of City University of Hong Kong, and the results were compared with the concentration reported from a nearby monitoring station in Sham Shui Po, operated by the Hong Kong Environmental Protection Department.

Absorption↗
PubMed2004

Pain and disability in a group of Chinese elderly out-patients in Hong Kong.

OBJECTIVE: To investigate the relationship between musculoskeletal pain and disability among a group of geriatric out-patients. DESIGN: Consecutive case series. SETTING: Regional hospital, Hong Kong. PARTICIPANTS: Attendees at a geriatric specialist out-patient clinic from October 2002 to February 2003. MAIN OUTCOME MEASURES: Pain duration, location, intensity, and frequency; use of analgesics; ability to identify the cause of pain; disability (Barthel index) and Lawton Instrumental Activities of Daily Living scale score; depressive symptoms (Geriatric Depression Scale score); and self-reported sleep quality. RESULTS: Of the 749 respondents, 461 (61.5%) had experienced pain in the previous 2 weeks. Among these patients, 51.3% had received a pain-relieving drug. Compared with men, women reported a higher pain intensity (5.87 versus 5.26; P=0.001), had a lower Barthel index (96.0 versus 97.9; P=0.005), and had a lower score on the Lawton Instrumental Activities of Daily Living scale (42.19 versus 44.52; P=0.008). Multivariate logistic regression showed that the presence of pain was associated with female sex (odds ratio=2.25), poor self-rated health (0.69), and depression (1.54). CONCLUSION: Pain is a common problem among the elderly population, but it is not associated with physical disability, and only half of the patients received analgesics. The study provides information for health care workers to develop strategies to better assess and manage pain problems among elderly people.

Activities of Daily Living↗
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↗