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Biomedical subjects

K L Chan

Publications and source records attributed to K L Chan.

At least 235 records · Page 13Linked to original sources
PubMed1971

Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City. 1. Distribution and density.

The distribution and density of Ae. aegypti and Ae. albopictus in Singapore were assessed from extensive larval surveys carried out from 1966 to 1968 to evaluate their respective roles in the epidemiology of dengue haemorrhagic fever and to study their ecology in the urban areas. Ten urban areas where the majority of dengue haemorrhagic fever cases occurred were surveyed.The results showed that both species were common in the city, with Ae. aegypti being the dominant species. The distribution of Ae. aegypti was more uniform and related to the prevailing housing types and conditions. Its premise index was highest in slum houses, intermediate in shop houses, and lowest in multistorey flats. Ae. albopictus, on the other hand, did not seem to be related to the prevailing housing type in its distribution but tended to be more widespread in areas with open spaces.The larval density index (the average number of larvae per housing unit) was higher for Ae. aegypti than for Ae. albopictus, in agreement with the relative densities shown by their premise indices. The larval density index correlated well with the premise index and correlated best with the infested-receptacle index. For practical purposes, the most suitable, convenient, and reliable measure of density of Ae. aegypti population seems to be the infested-receptacle index.An attempt was made to estimate the rate of dispersal of Ae. aegypti from a stable population to an adjacent area of multistorey flats. The rate of dispersal, estimated from the premise index and the larval density index, was approximately 2% per year of the "donor" population.

Aedes↗
PubMed1971

Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City. 2. Larval habitats.

Detailed information on the breeding habitats of Ae. aegypti and Ae. albopictus is necessary when planning programmes for their control. The larval habitats of the two species in 10 city areas were counted and classified according to type, frequency of occurrence, location, and function. Of all the breeding habitats recorded 95% were domestic containers. The most common Ae. aegypti breeding habitats were ant traps, earthenware jars, bowls, tanks, tin cans, and drums, ant traps being the most common indoors and earthenware jars the most common out doors. Breeding habitats for Ae. albopictus were commonly found in earthen ware jars, tin cans, ant traps, rubber tires, bowls, and drums; ant traps were the most common indoor habitat and tin cans were most common outdoors.The majority of Ae. aegypti breeding habitats were found indoors, while only half of all the Ae. albopictus breeding habitats were indoors. The indoor and outdoor distribution of breeding habitats of both species was not related to the type of housing in the area.The distribution of the type of breeding habitats, however, was related to the type of housing in the area. Ant traps were common to all areas, but water-storage containers and unused containers were common in slum-house and shop-house areas. Flats, however, had more containers used for keeping plants and flowers.The most common breeding habitats of Ae. aegypti and Ae. albopictus are discussed in relation to the habits of the people. It is concluded that control of the two species will depend largely on a change in such habits, either through public health education or by some form of law enforcement.

Aedes↗
PubMed1971

Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City. 3. Population fluctuations.

Fluctuations in the adult Ae. aegypti and Ae. albopictus populations and their relationship to rainfall were studied by weekly collections from a number of stations in the city. Aedes aegypti populations generally fluctuated with the rainfall, with multiple peaks, except in the middle of the year when there was no increase in rainfall at the time of the peak in population. It is suggested that other regulating factors, in addition to rainfall, also determine the fluctuations of this species. Aedes albopictus also fluctuated, with three peaks in a year, and these bore a close relationship to rainfall.In one area, both larvae and adults of Ae. albopictus were studied simultaneously. The larval populations were investigated by exposing tin cans in the field. The population peaks of larvae were found to precede those of adults by almost exactly 2 months. It is suggested that each adult population peak represents the cumulative effect of more than one generation of mosquitos.

Aedes↗
PubMed1971

Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City. 4. Competition between species.

There is a current belief stemming from statements made in the literature that Ae. aegypti is displacing Ae. albopictus in a number of cities of South-East Asia and in Calcutta, India. A critical review of these works showed that either the observations were inconclusive or the methods of collection were biased for one or the other species.Extensive surveys of the larval habitats of the two species in Singapore showed that the sharing of breeding habitats was uncommon in both urban and rural areas. In the laboratory, Ae. aegypti took a slightly shorter time to complete its development from egg-hatching to adult emergence.It is concluded that information available at present is insufficient to interpret the Ae. aegypti-Ae. albopictus population balance resulting from interspecific competition in Singapore. The pattern of distribution of the two species is unlikely to be the result of competitive displacement; it is, rather, probable that this pattern results from factors that favour the rapid increase and spread of one species over the other. It is suggested that Ae. aegypti in the city is favoured by rapid and extensive urbanization and by the higher fecundity and shorter life cycle of the species.

Aedes↗
PubMed1971

Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City. 5. Observations in relation to dengue haemorrhagic fever.

Dengue haemorrhagic fever in Singapore was a disease of the urban human population, with concentrations of cases occurring in areas of high population density. Mosquito surveys revealed that these areas also had high population densities of Ae. aegypti and Ae. albopictus.The disease occurred throughout the year but the incidence of cases appeared to follow a seasonal pattern. Observations from 1966 to 1968 showed that the number of cases increased in April, reached a peak in November, and, thereafter, decreased until the next increase in April of the following year. The epidemic curve generally agreed with the fluctuations of both Ae. aegypti and Ae. albopictus populations, although the latter species appeared to show a better correspondence with the incidence of cases.Six dengue viruses were isolated from the two Aedes species during 1966. One dengue type 2 virus was isolated from a pool of Ae. aegypti and 1 dengue type 1 virus and 4 dengue type 2 viruses were recovered from 5 pools of Ae. albopictus. These viruses were isolated from mosquitos collected during the period of increase in the incidence of cases and in 4 different areas of the city. The dengue virus infection rates per 1 000 mosquitos estimated in the present study were 0.51 for Ae. aegypti and 0.59 for Ae. albopictus.The data obtained in the present study suggest that both Ae. aegypti and Ae. albopictus are involved in the transmission of dengue haemorrhagic fever in Singapore.

Aedes↗
PubMedDate not supplied

Reference values for normal adult transesophageal echocardiographic measurements.

Normal transesophageal echocardiographic measurements have not been presented previously relative to the effects of age, sex, and body surface area. This comparison was obtained by measuring cardiac and aortic dimensions in 60 patients (20 to 75 years old; 33 women) with normal transesophageal echocardiograms. We found a variable and usually important relationship between body surface area and 11 of 20 structures measured. A gender effect was not significant after indexing for body surface area for all but one structure. Age correlated with the diameter of the aortic root, descending aorta, superior vena cava, and right pulmonary artery. Similar dimensions were noted for certain paired structures as the two atria, the mitral and tricuspid annuli, and the aortic root and right ventricular outflow tract. Although multiple factors underlie what is normal in a given individual, our reference values serve to facilitate recognition of cardiac and aortic disease.

Adult↗
PubMedDate not supplied

Dobutamine and dipyridamole stress echocardiography in patients with a low incidence of severe coronary artery disease.

The aim of this study was to determine the relative sensitivity, specificity, accuracy, and tolerance of dobutamine and dipyridamole stress echocardiography in patients with a lower likelihood of severe coronary artery disease. Previous comparative studies, which included patients with a history of myocardial infarction or a high incidence of coronary artery disease, showed both methods to have similar and acceptable diagnostic accuracy. To assess the role of these agents in evaluating patients with a lower likelihood of significant coronary artery disease, a lower-risk group was selected by excluding patients with known coronary artery disease, myocardial infarction, unstable angina, or strongly positive stress test results. Dobutamine and dipyridamole stress echocardiographic studies were performed in random order, before coronary angiography. Of the 46 patients enrolled (31 men and 15 women), 24 had atypical chest pain or none at all. Coronary angiography revealed no significant disease in 22 (48%), single-vessel disease in 11 (24%), and multivessel disease in only 13 patients (28%). Dobutamine and dipyridamole stress echocardiography were equally well tolerated, with identical accuracy (76%) that was maintained in patients with atypical symptoms. This confirms the usefulness of both dobutamine and dipyridamole stress echocardiography in evaluating patients with suspected coronary artery disease and extends this role to a lower-risk group for severe disease who often have atypical symptoms. The choice of which agent is used should reflect an institution's experience.

Cardiotonic Agents↗
PubMedDate not supplied

A prospective comparison of the multiplane probe with the biplane probe in structure visualization and Doppler examination during transesophageal echocardiography.

To compare the imaging capability of the multiplane probe with that of the biplane probe, 317 consecutive patients were randomized to undergo transesophageal echocardiography with either probe. Images of 24 cardiac structures and nine Doppler signals were graded prospectively on a three-grade system. Both multiplane and biplane probes provided excellent visualization of cardiac structures and Doppler signals, but the multiplane probe was significantly superior to the biplane probe. There were no differences in the number of attempts at esophageal intubation, the amount of sedation used, and the examination time. The number of complications was similar, although all failed intubations occurred with the multiplane probe.

Echocardiography↗
PubMedDate not supplied

Massive acute thrombosis of the descending thoracic aorta in heparin-associated thrombocytopenia and thrombosis.

Heparin-associated thrombocytopenia with thrombosis is a rare but serious complication in patients receiving heparin therapy. We report a case of a patient with this complication who had massive thrombosis within the descending thoracic aorta detected by transesophageal echocardiography. Our case suggests that a transesophageal echocardiographic examination can be useful in the early diagnosis of heparin-associated thrombocytopenia and thrombosis.

Acute Disease↗
PubMedDate not supplied

Complications of transesophageal echocardiography in ambulatory adult patients: analysis of 1500 consecutive examinations.

Transesophageal echocardiography is a new approach that can be used to image cardiac structures. It combines two existing technologies: cardiac ultrasound and endoscopy. To obtain a cardiac image, the transesophageal probe has to be positioned properly within the esophagus. The first 1500 consecutive transesophageal echocardiographic examinations in ambulatory adult patients from one center were analyzed to identify conditions associated with failed esophageal intubation and procedural complications. Esophageal intubation was not achieved in 11 patients (0.73%). The reasons for the failure of intubation were operator inexperience, hypersensitive pharynx despite topical anesthesia, and cervical spondylosis. Six of those patients also had a history of dysphagia. Procedural complications were identified in seven patients (0.47%). Tracheal intubation was present in four patients, with immediate development of stridor and incessant cough in two patients. Atrial fibrillation developed in two patients--one had atrial myxoma and one had mitral stenosis. Bronchospasm developed during the transesophageal examination in one patient who was receiving long-term treatment for bronchial asthma. We conclude that transesophageal echocardiography is feasible in most adult patients in the ambulatory setting and that the complication rate is very low. Proper patient selection and preparation are crucial to the successful performance of this procedure.

Adult↗