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Biomedical subjects

M T Chan

Publications and source records attributed to M T Chan.

34 records · Page 2Linked to original sources
PubMed1996

Minimum alveolar concentration of halothane and enflurane are decreased in early pregnancy.

BACKGROUND: Minimum alveolar concentration (MAC) of isoflurane is decreased in early pregnancy but it is not known whether this occurs to the same extent with other inhalational anesthetics. The MAC of halothane and enflurane were compared in pregnant women undergoing elective termination of pregnancy and in nonpregnant women. METHODS: We studied 16 pregnant women scheduled for termination of pregnancy at 8 to 13 weeks gestation and 16 non-pregnant patients undergoing laparoscopic sterilization. Eight patients in each group received halothane and the others received enflurane. After inhalational induction of anesthesia and tracheal intubation, MAC was determined in each patient by observing the motor response to a 10-s, 50-Hz, 80-mA transcutaneous electric tetanic stimulus to the ulnar nerve at varying concentrations of either halothane or enflurane. The end-tidal concentration of inhalational anesthetic was kept constant for at least 15 min before each stimulus and the concentration was varied ultimately in steps of 0.05 vol% (halothane) or 0.10 vol% (enflurane) until a sequence of three alternate responses (move, not move, move) or (not move, move, not move) was obtained. Minimum alveolar concentration for each person was taken as the mean of the two concentrations just permitting and just preventing movement, and MAC for the group was the median of individual MAC values. Confidence intervals were calculated for the percentage decrease in MAC for pregnant women compared with nonpregnant women. RESULTS: The median (range) MAC of halothane, 0.58 vol% (0.53 to 0.58), and enflurane, 1.15 vol% (0.95-1.25), in the pregnant women were less than those in the nonpregnant women, 0.75 vol% (0.70 to 0.78), P = 0.0005 and 1.65 vol% (1.45 to 1.75), P = 0.0007, respectively. The percentage decrease (95% CI) in MAC for pregnant women was 27% (20 to 27%) for halothane and 30% (24 to 36%) for enflurane. CONCLUSIONS: The MAC of halothane and enflurane were reduced by a similar degree in pregnant women at 8 to 13 weeks gestation compared with nonpregnant women.

Adolescent↗
PubMed1995

Postpartum changes in the minimum alveolar concentration of isoflurane.

BACKGROUND: Minimum alveolar concentration (MAC) is decreased in pregnancy, but it is not known how quickly after delivery MAC returns to normal. We measured the MAC of isoflurane in a group of women undergoing elective tubal ligation after delivery. METHODS: After delivery, 20 patients underwent inhalational induction of anesthesia with isoflurane and tracheal intubation. MAC was determined in each patient by observing the response to a 10-s, 50-Hz, 80-mA transcutaneous tetanic electric stimulus to the ulnar nerve at various concentrations of isoflurane. The end-tidal concentration of isoflurane was kept constant for at least 10 min before each stimulus, and the concentration of isoflurane was ultimately varied in steps of 0.05 vol% until we obtained a sequence of three alternate responses: move-not move-move or not move-move-not move. The MAC for each subject was taken as the mean of the two concentrations just permitting and just preventing movement. A venous blood sample was taken immediately before induction of anesthesia for measurement of progesterone concentration. MAC was compared with time after delivery and plasma progesterone concentrations by Kendall's rank correlation. RESULTS: There was a positive correlation between MAC and the time after delivery (P < 0.001). The median MAC of isoflurane was 0.775 vol% (range 0.675-0.775 vol%) in five women 24-36 h postpartum. MAC was more variable, 0.825 vol% (0.675-0.975 vol%) in nine women 36-72 h postpartum, whereas six patients more than 72 h postpartum had a MAC of 1.125 vol% (1.025-1.175 vol%). The correlation between MAC and plasma progesterone concentration was almost statistically significant (P = 0.060). CONCLUSIONS: The MAC of isoflurane was reduced in women 24-36 h postpartum and gradually increased to normal values by 72 h postpartum.

Adult↗
PubMed1995

Massive lingual swelling following palatoplasty. An unusual cause of upper airway obstruction.

We report a case of upper airway obstruction as a result of delayed massive lingual swelling following routine cleft palate repair in an otherwise healthy 12-month-old girl. We believe that ischaemia and venous congestion were the causes of macroglossia, after prolonged use of the Digman Dott tongue retractor. In any difficult and lengthy repair, we recommend the prophylactic insertion of a nasopharyngeal airway under direct vision by the surgeons after surgery to prevent potential upper airway obstruction.

Acute Disease↗
PubMed1994

Novel gene expression system for plant cells based on induction of alpha-amylase promoter by carbohydrate starvation.

The 5' regulatory region and putative signal sequence of a rice alpha-amylase gene, alpha Amy8, was fused to a bacterial gene encoding beta-glucuronidase (GUS) and introduced into rice, tobacco, and potato via Agrobacterium-mediated transformation systems. Expression of this chimeric gene in suspension cells of transgenic plants was suppressed by the presence of sucrose in the medium and induced by its absence. Induction or suppression of GUS expression in transgenic rice could be reversed by the deprivation or replenishment, respectively, of sucrose in the medium. The expressed GUS fusion protein was translocated to the endoplasmic reticulum, modified by glycosylation, and secreted into the culture medium of transgenic cells. In the presence of a glycosylation inhibitor, tunicamycin, the enzymatically active form of GUS was assembled in the endoplasmic reticulum. The yield of GUS secreted by transgenic cells was estimated to be as high as 40% of total secreted proteins. The reversible induction of the alpha-amylase promoter in culture cells by sugar level in the medium provides an excellent inducible expression system for basic research in plant science. Combination of the alpha-amylase promoter and signal sequence also offers a novel approach for large scale production of low cost, easily purified, secreted recombinant proteins.

Amino Acid Sequence↗
PubMed1994

Decreased minimum alveolar concentration of isoflurane in pregnant humans.

BACKGROUND: Minimum alveolar concentration (MAC) is decreased in pregnant animals, but this change has not been demonstrated in humans, probably because of ethical considerations. It is less problematic to determine MAC in pregnant women undergoing termination of pregnancy, however, and therefore we compared the MAC of isoflurane in these women with the MAC in matched nonpregnant women. METHODS: Patients underwent inhalational induction of anesthesia with isoflurane and tracheal intubation. MAC was determined in each patient by testing the response to a 10-s, 50-Hz, 80-mA transcutaneous tetanic electrical stimulus to the ulnar nerve at varying concentrations of isoflurane. The end-tidal concentration of isoflurane was kept constant for 10 min before each stimulus and the concentration of isoflurane ultimately varied in steps of 0.05% until we obtained a sequence of three alternate responses (move, not move, move) or (not move, move, not move). MAC for each patient was taken as the mean of the two concentrations just permitting and just preventing movement. MAC for the group was taken as the median of the individual MAC values. A blood sample was taken immediately before induction of anesthesia for measurement of progesterone concentrations. Data were compared between groups by the Mann-Whitney test. RESULTS: The median (range) MAC for isoflurane in the pregnant group, 0.775% (0.675-0.825), was less than that in the nonpregnant group, 1.075% (1.025-1.175) (P < 0.001). The median (range) plasma progesterone concentration in the pregnant group, 63.4 (0.8-106) nM, was greater than that in the nonpregnant group, 8.4 (0.7-66) nM (P < 0.02). CONCLUSIONS: The MAC of isoflurane was reduced by 28% in pregnant women at 8-12 weeks' gestation compared with that of nonpregnant controls.

Anesthesia, Inhalation↗
PubMed1994

Drug overdosage and other poisoning in Hong Kong--the Prince of Wales Hospital (Shatin) experience.

From 1988 to 1991, 732 patients (91.1% Chinese) were admitted to four general medical wards at the Prince of Wales Hospital in Hong Kong with acute poisoning. The patients were predominantly female (68.9%) and relatively young (86.3% below the age of 40). Further analysis of 655 patients indicates that the vast majority of patients (96%) were admitted after self-poisoning with drugs or chemicals while 4% of cases were due to accidental poisoning. The main agents used by the former group included hypnotics/sedatives (33.1%), household products (15.7%), and analgesics (13.7%). There were nine deaths (1.4%). When compared to other Western countries, two important variations in the pattern of acute poisoning were seen. A substantial proportion of drugs ingested by our patients were not precisely identified. 'Dettol', a household product, was commonly used for self-poisoning in Hong Kong. Territory-wide studies of longer duration are needed to provide the physicians in Hong Kong with much needed information on the incidence and the pattern of acute poisoning.

Adolescent↗
PubMed1993

Agrobacterium-mediated production of transgenic rice plants expressing a chimeric alpha-amylase promoter/beta-glucuronidase gene.

We have successfully transferred and expressed a reporter gene driven by an alpha-amylase promoter in a japonica type of rice (Oryza sativa L. cv. Tainung 62) using the Agrobacterium-mediated gene transfer system. Immature rice embryos (10-12 days after anthesis) were infected with an Agrobacterium strain carrying a plasmid containing chimeric genes of beta-glucuronidase (uidA) and neomycin phosphotransferase (nptII). Co-incubation of potato suspension culture (PSC) with the Agrobacterium inoculum significantly improved the transformation efficiency of rice. The uidA and nptII genes, which are under the control of promoters of a rice alpha-amylase gene (alpha Amy8) and Agrobacterium nopaline synthase gene (nos), respectively, were both expressed in G418-resistant calli and transgenic plants. Integration of foreign genes into the genomes of transgenic plants was confirmed by Southern blot analysis. Histochemical localization of GUS activity in one transgenic plant (R0) revealed that the rice alpha-amylase promoter functions in all cell types of the mature leaves, stems, sheaths and roots, but not in the very young leaves. This transgenic plant grew more slowly and produced less seeds than the wild-type plant, but its R1 and R2 progenies grew normally and produced as much seeds as the wild-type plant. Inheritance of foreign genes to the progenies was also confirmed by Southern blot analysis. These data demonstrate successful gene transfer and sexual inheritance of the chimeric genes.

Agrobacterium tumefaciens↗
PubMed1993

Disease profiles in Chinese in Hong Kong: an analysis of the primary diagnoses in 561 acute hospital medical admissions.

Little is known about the disease profiles in Chinese living in an urbanized community like Hong Kong. Accordingly, the discharge summaries of 561 acute hospital medical admissions were reviewed and the primary diagnoses (the main reason for admission or the most important clinical problem) were coded according to the International Classification of Diseases. Our data indicate that cardiovascular diseases are the most important cause of acute medical admissions and mortality and that gastrointestinal hemorrhage is very common amongst the Chinese in Hong Kong.

Adult↗
PubMed1984

Assessment of erythrocyte deformability by constant flow filtration technique: analysis of factors influencing the initial pressure.

When filtering red blood cells (RBC) resuspended into buffer at constant flow, the pressure-time curve is dependent on erythrocyte deformability (E.D) and also on the plugging of pores by RBC or leukocytes (WBC). To understand the influence of these 3 factors, we used an apparatus with: 1) a constant flow syringe (Bioblock) (1.56 ml/mn); 2) a pressure transducer (Statham P23 ID); 3) a recorder (Gould); 4) a 5 micron polycarbonate filter (Nuclepore) housed in a lucite block according to USAMI & al. (1). Resuspensions of RBC from 4 to 14% haematocrit with 0 to 600 WBC/mm3 were investigated. Results indicate that: 1/ The first inflexion point of the pressure-time curve (initial pressure leading to calculation of beta) is related to the RBC's deformability; 2/beta is (in our experimental conditions) dependent on the WBC number; 3/beta seems very sensitive to deformability changes as shown by rapid increases induced by osmolarity changes.

Erythrocytes↗