Biomedical subjects
Publications and source records attributed to P K Yen.
Southern Chinese girls aged 11 years and 9 months to 12 years and 3 months in Hong Kong have a mean menarcheal age of 11.50 years (standard deviation of 0.47) using the recollection method. Highly significant differences are found when compared to the 12-year-old girls in Hong Kong studied in the past decades. Therefore, a secular trend of earlier menarcheal age is demonstrated.
Southern Chinese girls aged 11 years 9 months to 12 years 3 months in Hong Kong have a mean skeletal age of 12.57 years assessed from the left hand and wrist radiographs by the Greulich and Pyle Atlas Method. Significant secular trend of earlier skeletal maturation was demonstrated with p less than or equal to 0.001. Such difference was contributed by improved socio-economic, nutritional and socio-hygienic conditions during the past decades.
Five patients were treated for corrections of problems in the primary dentition. Anterior and posterior crossbite, deep overbite malocclusion, and overbite malocclusion were treated with simple removable orthodontic appliances. Early orthodontic treatment for these patients helped resolve any functional problems that could interfere with later growth and development, such as health and function of the TMJ complex.
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Intense adherence accompanied by cytotoxicity, which initially occurred at 4 h of interaction was observed when the microfilariae of Breinlia macropi were introduced to cultures of quokka peritoneal macrophages previously sensitized in 20% immune serum. No significant difference in the adherence or cytotoxic effects was observed among macrophages from normal, microfilaraemic and amicrofilaraemic quokkas. However, the serum component mediating these effects was found only in microfilaraemic and seropositive amicrofilaraemic quokkas. This mediator was heat-labile and its mediation of the adherence and cytotoxic effects was independent of complement. Because of its apparent dissociation from IgG and its heat lability, the possibility that the mediator resides in the previously-described reaginic antibody of the quokkas was discussed.
Video recordings and ultrastructural studies have revealed an intricate sequence of antibody-mediated cytotoxic activity by quokka peritoneal macrophages on Breinlia macropi microfilariae. The microfilaricidal activity was effected by at least two types of macrophages measuring 17 micrometers and 8 micrometers in diameter respectively. The relatively large macrophages were responsible for trapping, encircling and eventually degrading the highly motile microfilariae in a sequence of events in which the participating macrophages may interdigitate. The smaller macrophages adhered transiently to a number of adjacent sites on the surface of a trapped microfilaria, resulting in a series of damaged spots. This activity of the small macrophages was interpreted as responsible for killing the microfilaria. Thus the microfilaricidal activity was interpreted to be accomplished by the co-operative functions of the relatively large and small macrophages.
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Growth of the bone structures of the nasal septum was studied in two young Macaca fascicularis (human age, 8 to 9 years) that received serial injections of lead acetate as a maker. The nasal septum in these monkeys is a thin, fragile, but morphologically complex, structure. A number of adjustment sites to the lengthening of the midface were observed, namely, at the cranial surface, at the junction of the bulbous perpendicular plate of the vomer and the nasal septum, and at the inferior junction of the vomer and palate. No apparent growth site was present at the interface of the septal cartilage with the vomer. Results suggest that the nasal septum in Macaca fascicularis adapts to growth changes in the midface.
Infective larvae of Wuchereria, Brugia, Breinlia, Dirofilaria and Setaria species from an experimental vector, Aedes togoi, are compared. The distinctive bubble-like caudal papillae of Wuchereria bancrofti are readily distinguishable from the protuberant ones of Brugia spp; the 'ear-like' papillae of Breinlia are distinct from the 'knob-like' ones of Dirofilaria or the 'thorn-like' terminal papilla of Setaria.
The dynamics of the transmission of subperiodic Brugia malayi in a typical endemic area in Malaysia was studied over a period of 4 years. Mass chemotherapeutic control with diethylcarbamazine citrate was found to be inefficient, new cases being detected even after the fifth treatment cycle of 6 mg/kg X 6 days per cycle. This is in marked contrast to the situation in periodic b. malayi areas where mass treatment efficiently controlled the infection. The disparity in results in these two areas is attributed to zoonotic transmission of subperiodic B. malayi from non-human primates where a mean infection rate of 76.3% was found.
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Filarial infections in 447 cats and 68 dogs from six endemic areas of human filariasis in Peninsular Malaysia were studied as part of the study on the zoonotic transmission of subperiodic Brugia malayi infection. 20.6% of cats and 57.4% of dogs had filarial infections. Cats were infected with subperiodic B. malayi, B. pahangi, Dirofilaria repens and D. immitis. Dogs were infected with B. pahangi and D. immitis. 6.9% of the cats had subperiodic B. malayi infection. The zoonotic implications of these infections and their impact on the filariasis control programme in Peninsular Malaysia were discussed.
Remodeling of the trabeculae in cancellous bone was studied in young monkeys that received multiple weekly injections of lead acetate as a marker. Resorption of old bone and deposition of new bone were demonstrated. The rate of deposition of new bone varied at different sites of the same trabeculae and also at different time intervals of the same site. The total formation time of new bone to fill the trabecular space was estimated.
Histochemical demonstration of acid phosphatase activity in microfilariae gives sufficiently characteristic and consistent results for the differentiation of even closely related species. No difference could be detected among nocturnally periodic, nocturnally subperiodic and diurnally subperiodic Brugia malayi, but they could readily be distinguished from B. pahangi. Similarly, Dirofilaria repens could be readily distinguished from D. immitis and B. booliati from B. sergenti. The enzyme distribution pattern of a Malaysian rural strain of Wuchereria bancrofti was different from those of other regions.
Remodeling of the osteons or Haversian canal system in compact bone was studied in young monkeys that received serial injections of lead acetate as an intravital strain. The successive stages of the formation of an osteon have been demonstrated. The rate of the filling of the lamellar bone decelerated as the lumen of the Haversian canal decreased. The total formation time of individual osteons was estimated.
Four daily doses of ASA were administered by mouth to young growing monkeys which received six injections of lead acetate every seven days as an intravital stain to indicate sites of bone and dentin mineralization. Microscopic evaluation of the inhibitory effects on membranous bone growth and dentin apposition was made. Four doses of ASA at 325 mg/kg inhibited membranous bone growth as well as the remodeling of the Haversian canal systems for about 16-18 days, with incomplete recovery during the experimental period. No comparable effect on dentinogenesis was observed. This preliminary study indicates that four doses of ASA at this level caused a toxic effect directly on membranous bone growth but not on dentin apposition.
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