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Biomedical subjects

W L Chan

Publications and source records attributed to W L Chan.

At least 55 records · Page 3Linked to original sources
PubMed1996

Rehabilitation challenges in craniospinal injury: two case reports.

Craniospinal injuries affect young patients with catastrophic morbidity and impact on society with regards to potential economic losses and medical costs. With improved neurosurgical and orthopaedic management, many more are surviving. Outcomes in this group of patients may be unpredictable because of the complex interactions between their cognitive, physical and behavioural deficits. Rehabilitation issues are often multiple and complex. An interdisciplinary approach to rehabilitation of these patients may aid them towards functional, community and vocational reintegration. We report the rehabilitation courses of 2 patients with combined traumatic brain and spinal cord injury.

Accidental Falls↗
PubMed1995

Transvenous permanent left ventricular pacing. A case report.

This case report presents a patient who inadvertently received transvenous permanent left ventricular pacing through an unexpected atrial septal defect. This lead malpositioning was proved by two-dimensional and transesophageal echocardiography. The abnormal pattern of electric activation was demonstrated by radionuclide phase image analysis. He has been followed up for a total of forty-three months with antiplatelet therapy and has been free from systemic embolic phenomena. A simple and readily available method that could lead to early recognition of lead malpositioning is reiterated and the various causes, methods of detection, and prognosis of left ventricular pacing are discussed.

Aged↗
PubMed1995

Immunization with class I human histocompatibility leukocyte antigen can protect macaques against challenge infection with SIVmac-32H.

OBJECTIVE: To evaluate the efficacy of immunopurified class I human histocompatibility leukocyte antigen (HLA) to protect against SIV infection. METHODS: HLA class I antigens were immunopurified from a human B-lymphoblastoid cell line. Groups of four macaques were vaccinated subcutaneously with four doses of the immunogen in adjuvant, or with adjuvant alone and subsequently challenged intravenously with 10 median monkey infectious doses of cell-free SIVmac-32H. Infection was determined by polymerase chain reaction for SIVmac proviral DNA and by virus isolation. Antigen-specific humoral and cellular immune responses were monitored. RESULTS: Macaques immunized with the HLA molecules produced anti-HLA class I antibodies that inhibited SIV replication in vitro and downregulated autologous T-cell proliferation against irradiated C8166 cells. They were partially protected (two out of four) from virus infection for at least 33 weeks when challenged with SIV grown in human cells. All four control animals were infected. CONCLUSIONS: This demonstration of partial protection, together with our previous work reporting that vaccination with allogenic cynomolgus lymphocytes can protect against challenge infection with SIV grown in simian cells, suggests that allogenic immune response induced before or during establishment of HIV infection may have important implications for AIDS disease progression.

Animals↗
PubMed1994

Minireview: trichosanthin--a protein with multiple pharmacological properties.

Trichosanthin (TCS), a protein isolated from the root tuber of the Chinese medicinal herb Trichosanthes kirilowii Maxim., is used to induce abortion in China. It also possesses immunomodulatory, anti-tumor and anti-human immunodeficiency virus properties. TCS is a member of the family of ribosome-inactivating proteins and inactivates eukaryotic ribosomes via its N-glycosidase activity. The gene encoding TCS has been cloned and over-expressed and the crystal structure of this protein resolved to 1.73A. In this review, the various pharmacological properties of TCS are discussed and assessed.

Abortifacient Agents↗
PubMed1993

A double-blind, placebo-controlled crossover trial of nadolol and verapamil in mild and moderately symptomatic hypertrophic cardiomyopathy.

OBJECTIVES: The aim of this study was to determine whether therapy with a beta-adrenergic or calcium channel blocking agent can improve the functional capacity and quality of life of patients with mild or moderately symptomatic hypertrophic cardiomyopathy. BACKGROUND: Both beta-blockers and calcium channel blockers may alleviate symptoms in hypertrophic cardiomyopathy, but previous studies have been performed in hospitalized patients or have been open studies without control subjects. METHODS: A randomized, double-blind crossover trial of nadolol, verapamil and placebo, administered for periods of 4 weeks each, was performed in 18 patients with mild or moderately symptomatic hypertrophic cardiomyopathy (10 men, 8 women; mean age +/- SD 39 +/- 17 years). A detailed symptom assessment, bicycle exercise testing, echocardiography and Holter monitoring were performed in each period. RESULTS: Two patients withdrew from the study owing to symptomatic sinus bradycardia during nadolol therapy. Neither drug improved maximal oxygen consumption (placebo 26 +/- 8, verapamil 23 +/- 6, nadolol 21 +/- 7 ml/kg per min; p = 0.1). Peak exercise work load was reduced by > or = 10 W in 13 patients (81%) during nadolol therapy and in 4 patients (25%) during verapamil therapy (p = 0.005, nadolol vs. verapamil). Despite the effects on exercise capacity, 13 patients (81%) preferred drug treatment (8 verapamil, 5 nadolol) over placebo (p = 0.001). Verapamil improved reported performance at work compared with nadolol (p = 0.01) and tended to improve other measures of health-related behavior and symptoms compared with nadolol and placebo. CONCLUSIONS: In patients with mild or moderately symptomatic hypertrophic cardiomyopathy, exercise capacity was not improved by nadolol or verapamil, and individuals were more often impaired by nadolol than with verapamil. Nevertheless, many patients derived symptomatic benefit from drug therapy, especially with verapamil.

Adolescent↗
PubMed1993

Autonomic function in hypertrophic cardiomyopathy.

BACKGROUND: Autonomic dysfunction has been found to be a powerful predictor of arrhythmic events and sudden death after myocardial infarction. Hypertrophic cardiomyopathy carries a risk of sudden death and this risk is increased by the occurrence of syncope. OBJECTIVES: To determine if autonomic dysfunction occurs in patients with hypertrophic cardiomyopathy and if it is associated with the occurrence of syncope. PATIENTS AND METHODS: Autonomic function was measured in 30 patients with hypertrophic cardiomyopathy, 15 with and 15 without a history of syncope, and in 28 healthy volunteers. RESULTS: Tests of parasympathetic activity showed that the mean (SD) variation in heart rate during deep breathing was reduced in patients compared with controls, 17 (9) v 22 (9) beats/min, p = 0.03, the Valsalva ratio was also reduced in patients, 1.52 (0.33) v 1.70 (0.36), p = 0.05 but the immediate heart rate response to standing, the 30:15 ratio, was similar in both groups. Tests of sympathetic activity--namely the diastolic blood pressure response to sustained handgrip and the change in systolic blood pressure on standing--did not differ between patients and controls. There was no significant difference in autonomic function between patients with and without a history of syncope. A secondary predetermined analysis showed that the degree of impairment in variation of heart rate with breathing was correlated with the severity of left ventricular hypertrophy, r = 0.39, p = 0.03. CONCLUSIONS: Patients with hypertrophic cardiomyopathy have a selective impairment of variability of heart rate with deep breathing and the Valsalva manoeuvre indicating decreased cardiac parasympathetic activity. The data suggest that the afferent limb of these reflexes is impaired and that the severity of impairment is related to the degree of left ventricular hypertrophy.

Adolescent↗
PubMed1992

Protection in simian immunodeficiency virus-vaccinated monkeys correlates with anti-HLA class I antibody response.

Our earlier reports demonstrated that Cynomolgus macaques vaccinated with either inactivated partially purified simian immunodeficiency virus (SIV), fixed SIV-infected C8166 (a human T lymphoblastoid cell line) cells, or fixed uninfected C8166 cells can be protected against a challenge infection with the 32H isolate of SIVmac 251 (grown in C8166) (Stott, E. J., W. L. Chan, K. H. G. Mills, M. Page, F. Taffs, M. Cranage, P. Greenway, and P. Kitchin. 1990. Lancet. 336:1538; Stott, E. J., P. A. Kitchin, M. Page, B. Flanagan, L. F. Taffs, W. L. Chan, K. H. G. Mills, P. Silvera, and A. Rodgers. 1991. Nature [Lond.]. 353:393). Protection is correlated with the levels of antibody response to cellular antigens in the human cells from which the virus immunogen was grown. However, the mechanism of protection is unclear. We report here the analysis of sera from these protected monkeys and demonstrate that there is positive correlation of protection with antibody response to the HLA class I molecule.

Animals↗
PubMed1992

Xamoterol in hypertrophic cardiomyopathy: effects on diastolic function and heart rate.

The aims of this study were to determine the effects of the partial beta 1-adrenergic agonist, xamoterol, on diastolic function and ambulatory heart rate in hypertrophic cardiomyopathy. Eleven patients with non-obstructive hypertrophic cardiomyopathy were studied with cross-sectional and Doppler echocardiography and 24-h Holter monitoring before and after a single intravenous dose of xamoterol. Resting heart rate (mean +/- SD) increased from 76 +/- 16 before, to 83 +/- 15 beats/min 15 min after xamoterol, p = 0.03. In the 4-h period after xamoterol, maximum heart rate was reduced (127 +/- 21 to 112 +/- 19, p = 0.01) and minimum heart increased (60 +/- 16 to 67 +/- 17, p = 0.04) compared to the same 4-h period of the previous day. There were no significant changes in cross-sectional or Doppler echocardiographic measurements of left ventricular function following xamoterol. Xamoterol stabilises the heart rate in hypertrophic cardiomyopathy. The absence of a significant effect on Doppler measurements does not preclude a beneficial effect on diastolic function. This initial study suggests that xamoterol should be further investigated as a new medical therapy for hypertrophic cardiomyopathy.

Adolescent↗
PubMed1992

Investigation of a hemodynamic basis for syncope in hypertrophic cardiomyopathy. Use of a head-up tilt test.

BACKGROUND: Syncope and sudden death in hypertrophic cardiomyopathy may have a hemodynamic basis. The presence of a small ventricular cavity with high intracavity pressures may activate left ventricular baroreceptors and cause reflex hypotension as described in other populations with syncope. METHODS AND RESULTS: To investigate this potential mechanism of syncope in hypertrophic cardiomyopathy, we studied 17 patients with a history of syncope (syncopal), 19 without syncope (nonsyncopal), and nine normal control subjects by using a head-up tilt test. Head-up tilt at 60 degrees for 45 minutes was followed by 10-minute tilts during incremental doses of isoprenaline. Heart rate, blood pressure, and two-dimensional and Doppler echocardiography were monitored throughout. On tilting, hypertrophic cardiomyopathy patients showed a decline in mean arterial pressure of -5 +/- 6 mm Hg (p less than 0.001) compared with no change in control subjects (0.2 +/- 6 mm Hg, p = 0.9). Left ventricular outflow tract velocity decreased on tilting in control subjects (-8 +/- 6 cm/sec, p = 0.004) but increased in the syncopal and nonsyncopal patients (20 +/- 50 cm/sec, p = 0.05). Reflex hypotension with or without bradycardia, associated with syncope or presyncope, was induced in seven syncopal patients, two nonsyncopal patients, and two control subjects (p = 0.05). The early response to tilt in these subjects was characterized by maintenance of blood pressure but a greater increase in left ventricular fractional shortening than in the other subjects (10 +/- 8% versus 1 +/- 1%, p = 0.002). The onset of hypotension was associated with a trend toward further decreases in left ventricular diameters, outflow tract velocity, and transmitral flow velocities. In the remaining patients who had a negative test, transient hypotension (systolic pressure less than 100 mm Hg) occurred in seven syncopal patients and three nonsyncopal patients compared with none of the control subjects (p = 0.01). In total, hypotension was demonstrated in 82% of syncopal patients compared with 26% of nonsyncopal patients and 22% of control subjects (p = 0.001). CONCLUSIONS: Patients with hypertrophic cardiomyopathy and a history of syncope frequently display hypotension during head-up tilt. In some cases, sudden hypotension occurs and is usually associated with bradycardia and a reduced cavity size, findings compatible with activation of a ventricular baroreflex. In other cases, transient hypotension occurs and could be explained by an impairment of baroreceptor function. These mechanisms may contribute to the occurrence of syncope in daily life.

Cardiomyopathy, Hypertrophic↗
PubMed1992

Long-term efficacy of percutaneous transluminal coronary angioplasty.

Percutaneous transluminal coronary angioplasty (PTCA) is a well-accepted procedure used in therapy for coronary artery stenosis. It is a delicate procedure depending upon the operator's experience and technique. Major efforts have been directed toward improving such performance. This is a report of our growing experience accumulated over the last eight years. From July 1983 to December 1990, 893 cases of coronary artery disease with a total of 1111 procedures received PTCA in this hospital. The success rate in dilatation increased year by year; to peak in 1990 (94%). PTCA was performed in 447 cases of single vessel disease; 310 cases of double vessels disease; and 136 cases of triple vessels disease. Dilated coronary artery lesions included left anterior descending artery, 637 (64%), right coronary artery, 198 (20%), and left circumflex artery 157 (16%). More than one procedure was undertaken in 178 patients, and about 20% patients had repeated PTCA. Major complications such as acute myocardial infarction developed in 3.0%. One point one percent had emergency surgery and the mortality rate was 1.8%. The majority of cases were followed up and appeared well after successful angioplasty. In conclusion, PTCA is an valuable procedure for treatment of critical coronary artery stenosis, with acceptable complications.

Adult↗
PubMed1991

Adrenergic hypersensitivity after beta-blocker withdrawal in hypertrophic cardiomyopathy.

Withdrawal of beta-blocker therapy has been associated with the development of adrenergic hypersensitivity and adverse clinical effects in patients with coronary artery disease and hypertension. The aim of this study was to establish the occurrence and clinical significance of adrenergic hypersensitivity after abrupt withdrawal of long-term beta blockade in hypertrophic cardiomyopathy. Beta-adrenergic sensitivity was measured using the isoprenaline chronotropic dose25. Symptom assessment chronotropic dose25 calculation, bicycle exercise, echocardiography and Holter monitoring were performed while the patient received beta-blocker therapy and repeated on days 2, 4, 6, 8 (acute withdrawal period) and on day 21 after abrupt withdrawal. The study was terminated after 7 patients had been studied because all patients experienced a marked deterioration in symptoms and several clinical events had occurred. The chronotropic dose25 (mean +/- standard deviation) demonstrated beta 1-adrenergic hypersensitivity with a minimal value of 1.6 +/- 0.8 micrograms during the acute withdrawal period compared with 3.8 +/- 1.7 micrograms on day 21 (p = 0.003). Heart rates during rest and exercise showed an overshoot increase during the acute withdrawal period. The maximal 24-hour ventricular ectopic count was higher during the acute withdrawal period than during day 21 (p = 0.04). Of 3 patients with inducible outflow tract gradients, 2 developed resting gradients greater than 30 mm Hg during the acute withdrawal period. There was an increase in peak late filling velocity of mitral inflow after beta-blocker withdrawal. In conclusion, transient beta-adrenergic hypersensitivity occurs after beta-blocker withdrawal in hypertrophic cardiomyopathy and is associated with significant physiologic changes and adverse clinical consequences.

Adult↗
PubMed1991

Inhibition of nitric oxide generation affects the induction of diabetes by streptozocin in mice.

The experiments reported here indicate that nitric oxide may play an important role in vivo in chemically-induced diabetes mellitus in mice. CBA mice treated with repeated low doses of streptozocin developed sustained hyperglycemia. This was significantly reduced by injections of L-NG-monomethyl-arginine (L-NMMA), a specific inhibitor of the synthesis of nitric oxide, but not affected by the inactive enantiomer, D-NMMA. Histologically the pancreata of animals treated with streptozocin and injected with L-NMMA showed little or no cellular infiltration and significantly lower degrees of islet cell destruction compared to mice treated with streptozocin alone, suggesting that nitric oxide may also be involved in the development of insulitis.

Animals↗
PubMed1991

Effects of a meal on hemodynamic function at rest and during exercise in patients with hypertrophic cardiomyopathy.

Many patients with hypertrophic cardiomyopathy experience postprandial exacerbation of their symptoms. The vasodilation associated with eating may be deleterious in hypertrophic cardiomyopathy, especially during exercise. To examine the hemodynamic effects of a meal in hypertrophic cardiomyopathy, 11 patients were studied with invasive hemodynamic monitoring during exercise testing in the fasting state and 45 min after a 740 kcal (3,100 J) meal. The meal induced a decrease in systemic vascular resistance index at rest (mean +/- SD, -17 +/- 14%), increases in mean right atrial (31 +/- 21%), mean pulmonary artery (14 +/- 14%) and mean pulmonary capillary wedge (17 +/- 14%) pressures and an increase in cardiac index (18 +/- 10%) due to an increased heart rate without any significant change in stroke volume. During postprandial exercise, heart rate, rate-pressure product, cardiac index and cardiac filling pressures were higher than during fasting exercise and one patient had a decrease in exercise blood pressure compared with the fasting test. Five patients with postprandial exacerbation of symptoms in everyday life had a lesser increase in systemic arterial pressure and stroke volume during both exercise tests and a smaller increase in cardiac index after the meal than did the six patients without postprandial symptom exacerbation, suggesting more severe cardiac disease. It is concluded that patients with hypertrophic cardiomyopathy have an abnormal hemodynamic response to food, in which stroke volume fails to increase and pulmonary capillary wedge and pulmonary artery pressures increase. These adverse changes persist during postprandial exercise and may predispose to exertional collapse in certain patients.

Adult↗
PubMed1991

A comparison of T cell responses to glycoprotein B (gB-1) of herpes simplex virus type 1 and its non-glycosylated precursor protein, pgB-1.

The ability of non-glycosylated precursor glycoprotein B (pgB) to induce T cell responses in herpes simplex virus (HSV) infected mice was compared with fully glycosylated glycoprotein B (gB) and with whole virus. pgB was as effective as gB in priming for virus- and glycoprotein-specific T cells. pgB could also re-stimulate virus or glycoprotein primed cells in vitro as efficiently as gB. In addition, priming with pgB protected mice against a lethal challenge with HSV type 1 (HSV-1) and could induce the early in vivo production of IL-2 and IL-3 in infected mice. In all of these responses, pgB was as effective as gB. Thus, the carbohydrate side chains on gB do not appear to be necessary for T cell recognition of this protein.

Animals↗
PubMed1990

Effect of preload change on resting and exercise cardiac performance in hypertrophic cardiomyopathy.

The purpose of this study was to investigate the hemodynamic responses, at rest and on exercise, of patients with hypertrophic cardiomyopathy to changes in circulating volume. After Swan-Ganz and radial arterial cannulation, 13 patients with hypertrophic cardiomyopathy performed maximal exercise tests after diuretic (frusemide 20 mg intravenously) and after fluid loading (0.9% saline at 10 ml/kg body weight intravenously) on different days. At rest, right atrial and pulmonary capillary wedge pressures increased with volume loading and decreased with a diuretic. There were no significant changes in the resting, supine cardiac or stroke indexes but in the upright position, the cardiac index and stroke index were higher after volume loading (2.5 +/- 0.7 vs 2.2 +/- 0.5 liters/min/m2, p less than 0.05; 33 +/- 11 vs 27 +/- 9 ml/m2, p less than 0.005, respectively). Although the right atrial, pulmonary arterial and pulmonary capillary wedge pressures were higher during exercise after volume loading, there were no significant differences in exercise heart rate, systemic blood pressure, cardiac index, stroke index, systemic vascular resistance index or overall exercise capacity compared to exercise after diuresis. The data show that the cardiac index and stroke index, at supine rest and during upright exercise, were not influenced by the preload changes induced in these patients with hypertrophic cardiomyopathy. The results suggest that these patients are operating on the plateau of left ventricular Frank-Starling function (filling pressure/output) curve.

Adult↗