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Biomedical subjects

B Law

Publications and source records attributed to B Law.

At least 19 recordsLinked to original sources
PubMed2004

Intrabony course of the inferior alveolar nerve in the edentulous mandible.

The purpose of this study was to investigate the vertical positioning and intrabony branching patterns of the inferior alveolar nerve (IAN) in 39 edentulous human cadaveric mandibles by buccal microdissection. Dissected mandibles were classified on the basis of the height of the IAN within the body of the mandible and the branching pattern of the IAN. The IAN was located in the superior part of the body of the mandible in 30.7% (12/39) of cases, all of which showed a small posterior molar plexus of branches. In 69.2% (27/39) of cases the IAN was half-way or closer to the inferior border of the mandible. Of these latter cases, 41% demonstrated a small, posterior molar plexus of branches, 37% showed posterior and anterior plexuses, and 22% showed either no branches or a single trunk with a small number of single branches directed at the superior border of the mandible. These findings were rendered in 3D computer format for instructional purposes.

Aged↗
PubMed2003

Effects of population structure and admixture on exact tests for association between Loci.

The probability of multilocus genotype counts conditional on allelic counts and on allelic independence provides a test statistic for independence within and between loci. As the number of loci increases and each sampled genotype becomes unique, the conditional probability becomes a function of total heterozygosity. In that case, it does not address between-locus dependence directly but only indirectly through detection of the Wahlund effect. Moreover, the test will reject the hypothesis of allelic independence only for small values of heterozygosity. Low heterozygosity is expected for population subdivision but not for population admixture. The test may therefore be inappropriate for admixed populations. If individuals with parents in two different populations are always considered to belong to one of the populations, then heterozygosity is increased in that population and the exact test should not be used for sparse data sets from that population. If such a case is suspected, then alternative testing strategies are suggested.

Data Interpretation, Statistical↗
PubMed2001

Epidemiology of varicella zoster virus infection in Canada and the United Kingdom.

Many countries are currently studying the possibility of mass vaccination against varicella. The objective of this study was to provide a comprehensive picture of the pre-vaccine epidemiology of the varicella zoster virus (VZV) to aid in the design of immunization programs and to adequately measure the impact of vaccination. Population-based data including physician visit claims, sentinel surveillance and hospitalization data from Canada and the United Kingdom were analysed. The key epidemiological characteristics of varicella and zoster (age specific consultation rates, seasonality, force of infection, hospitalization rates and inpatient days) were compared. Results show that the overall epidemiology of varicella and zoster is remarkably similar between the two countries. The major difference being that, contrary to Canada, the epidemiology of varicella seems to be changing in the United Kingdom with an important decrease in the average age at infection that coincides with a significant increase in children attending preschool. Furthermore, differences exist in the seasonality between the United Kingdom and Canada, which seem to be primarily due to the school calendar. These results illustrate that school and preschool contact patterns play an important role in the dynamics of varicella. Finally, our results provide baseline estimates of varicella and zoster incidence and morbidity for VZV vaccine effectiveness and cost-effectiveness studies.

Adolescent↗
PubMed2001

Internal consistency, reproducibility, responsiveness, and construct validity of the Chinese (HK) version of the asthma quality of life questionnaire.

The purpose of this study was to test the acceptability, psychometric properties and construct validity of a Chinese translation of the Asthma Quality of Life Questionnaire (AQOL) and to determine whether it has any advantage over the Chinese (HK) version of the generic MOS SF-36 Health Survey that has been validated on Chinese in Hong Kong. Fifty-two patients with asthma were interviewed using the Chinese (HK) AQOL and the Chinese (HK) SF-36. Thirty-four of the 52 patients were interviewed a second time 6 months later using the same questionnaires. The Cronbach's alpha coefficients were above 0.7 for all four domains of the AQOL questionnaire. Significant correlations were found between the scores of each of the four domains of the Chinese (HK) AQOL and forced expiratory volume in 1 s (FEV1) (%predicted) during the initial visit and between changes in the mean scores of most of the domains of Chinese (HK) AQOL and changes in FEV1 between visits. The Chinese (HK) AQOL was found to be reproducible in those with stable asthma, and for those whose asthma severity changed between visits, there was significant change in one of the domains. It can detect differences in quality of life in asthma patients of varying severity. We conclude that the Chinese (HK) translation of the AQOL is reliable, valid, reproducible and discriminative and can be used to supplement generic instruments in evaluating the quality of life of patients with asthma.

Adolescent↗
PubMed2001

Long-term persistence of antibodies induced by vaccination and safety follow-up, with the first combined vaccine against hepatitis A and B in children and adults.

It is important to monitor the long-term persistence of antibodies induced by vaccination. Four cohorts were followed for their long-term immunity after vaccination with a combined hepatitis A and B vaccine (Twinrix; SmithKline Beecham Biologicals, Rixsenart, Belgium). Two cohorts of adults (ages 17-60 years), one of 1-6-year-olds, and one of 6-15-year-olds were vaccinated following a 0, 1, and 6-month schedule. Follow-up data until month 72 (adults) and month 60 (children) are available. At month 72, antibody to hepatitis A virus (anti-HAV) seropositivity (S+) was 100% for both adult cohorts (n = 40 and n = 47) and 95% and 89% of the vaccinees were seroprotected against hepatitis B virus (HBV), respectively. The geometric mean titres (GMTs; mIU/ml) for anti-HAV were 977 and 542 and the GMTs for the antibody to hepatitis B surface antigen (anti-HBs) were 322 and 90. For 1-6-year-olds at month 60 (n = 39), anti-HAV S+ was 100% with a GMT of 479 and 97% were protected against HBV with a GMT of 195. At month 60 for the 6-15-year-olds (n = 42), anti-HAV S+ was 100% with a GMT of 990 and 95% were protected against HBV with a GMT of 263. There have been no safety issues during the follow-up. In the past 5 years, a postmarketing surveillance system was available. Using this system, all spontaneous adverse events are collected and archived. Although infrequent, the most commonly reported adverse events after more than 13 million doses were allergic-type reactions followed by fever and injection site reactions. The combined hepatitis A and B vaccine is safe and is well tolerated. Immunity provided by the vaccine remains high in adults and children with comparable results to those obtained with monovalent vaccines.

Adolescent↗
PubMed2000

Factors to consider in the development of generic bioanalytical high-performance liquid chromatographic-mass spectrometric methods to support drug discovery.

Mass spectrometric detection is gradually replacing ultraviolet (UV) as the method of choice in bioanalysis, especially in the area of early drug discovery where high sensitivity and rapid sample throughput is required and where samples are frequently pooled or "cocktailed" prior to dosing or analysis. The change from UV to MS detection requires a significant change in approach since the use of MS poses a number of unexpected problems and limitations which relate to instrument design and the ionisation process. Whilst electrospray ionisation (ESI) allows the analyst to focus on the analyte of interest it is non-selective and blind to background effects which can in certain instances alter the response of the compound of interest, leading to inaccurate data. In addition, when analysing compound mixtures, a number of precautions need to be taken since adduct formation in the MS source, the highly ESI responsive nature of formulating agents and the effect of the isotopic distribution in organic drug molecules can all lead to the production of compromised data. Whilst many of these problems can be minimised or avoided this often results in a complex and inflexible analysis system. Ultimately the analyst has to assess the degree of risk involved and take actions which reflect the use the data.

Chromatography, High Pressure Liquid↗
PubMed2000

Analysis of varicella vaccine breakthrough rates: implications for the effectiveness of immunisation programmes.

The objective of this study was to quantify key parameters describing varicella zoster virus (VZV) vaccine efficacy. To do so a mathematical model was developed to represent breakthrough cases as a function of time after vaccination in vaccine efficacy trials. Efficacy parameter sets were identified by fitting the predicted annual number of breakthrough infections with that observed in three clinical trials chosen to represent the plausible range of vaccine efficacy. Results suggest that varicella vaccination seems to result in a high proportion of individuals who are initially totally protected (97% for the base-case). However, individuals lose full protection relatively rapidly (3% per year for the base-case). Once total protection has waned individuals have a high probability of developing a breakthrough infection if exposed to varicella (73% of the probability in unvaccinated susceptibles for the base-case). Results also highlight that vaccine efficacy parameters should be estimated concurrently to take into account dependencies between parameters.

Child, Preschool↗
PubMed2000

Re-evaluation of anion-exchange HPLC for the analysis of acidic compounds.

A number of weak and strong anion-exchange HPLC phases have been evaluated for the analysis of acidic drugs and related compounds. Using eluents with high organic content, reasonable chromatography could be obtained and widely differing compounds easily separated in isocratic mode. Retention was related to solute pKa and concentration of ammonium acetate in the eluent. All the phases showed an unexplained loss in retention with repeated use, although with one material; nucleosil SAX, this was low (15%) and considered acceptable. This material was also shown to be relatively stable under typical bioanalytical conditions.

Acetates↗
PubMed2000

Modelling the impact of immunization on the epidemiology of varicella zoster virus.

The objective of this study was to develop and apply a dynamic mathematical model of VZV transmission to predict the effect of different vaccination strategies on the age-specific incidence and outcome of infection. To do so a deterministic realistic age-structured model (RAS) was used which takes account of the increased potential for transmission within school aged groups. Various vaccine efficacy scenarios, vaccine coverages and vaccination strategies were investigated and a sensitivity analysis of varicella incidence predictions to important parameters was performed. The model predicts that the overall (natural and breakthrough) incidence and morbidity of varicella would likely be reduced by mass vaccination of 12-month-old children. Furthermore, adding a catch-up campaign in the first year for 1-11 year olds seems to be the most effective strategy to reduce both varicella incidence and morbidity (in the short and long term), though with the possible detrimental effect of increasing the incidence of zoster.

Adolescent↗
PubMed2000

The Immunization Monitoring Program Active (IMPACT) prospective five year study of Canadian children hospitalized for chickenpox or an associated complication.

BACKGROUND: Varicella vaccine was approved for use in Canada in 1998. A major goal of universal varicella vaccine programs is to reduce severe infection and associated complications. Baseline data are essential against which to judge the effectiveness of routine childhood immunization. OBJECTIVE: To describe morbidity and mortality among children hospitalized for chickenpox. Methods. From January 1, 1991, to March 31, 1996, chickenpox admissions to 11 pediatric referral centers were actively identified. Patient and illness characteristics were compared for 3 subgroups defined by prior health: healthy; unhealthy but immunocompetent; immunocompromised. RESULTS: Of 861 cases 488 (56.7%) were healthy, 75(8.7%) were unhealthy and 298 (34.6%) were immunocompromised. The immunocompromised children differed from healthy/unhealthy cases in mean age (6.4 vs. 4.0/4.6 years, respectively, P < 0.0001); median interval from rash onset to admission (2 vs. 5/5 days, P < 0.0001); complication rate (20% vs. 90%/79%; P = 0.001); and rate of acyclovir therapy (98% vs. 24%/39%; P = 0.001). Unhealthy vs. healthy cases had a higher frequency (P < 0.01) of intensive care (13.3% vs. 4.7%), ventilation (9.3% vs. 2.0%) and death (4% vs. 0.2%). CONCLUSION: These data provide a baseline for morbidity/mortality resulting from chickenpox before varicella vaccine use in Canada.

Adolescent↗
PubMed1999

Reduced cortisol potentiates the exercise-induced increase in corticotropin to a greater extent in trained compared with untrained men.

We examined the effect of acute exercise and reduced cortisol on pituitary and adrenal responsiveness and the impact of reduced plasma cortisol on maximal oxygen consumption (VO2max) in eight trained (T) and eight untrained (UT) males. Subjects completed two graded maximal exercise tests (GXT), each preceded by either overnight metyrapone (MET) or placebo (PLA) administration. Blood samples were collected before and after GXT. With PLA, resting corticotropin (ACTH) levels were higher in T versus UT men; however, cortisol and 11-deoxycortisol were similar between groups. Following GXT on PLA, cortisol was unchanged but 11-deoxycortisol increased in both groups; however, ACTH increased only in UT men. For both groups, cortisol, 11-deoxycortisol, and ACTH were different post-GXT with MET versus PLA. Furthermore, following GXT with MET, the ACTH response was greater in T versus UT subjects. VO2max was not altered by MET in either group. We conclude that (1) at rest, only ACTH levels differed between T and UT men; (2) individually, the GXT and MET provide a similar ACTH response in UT but not in T subjects; (3) when GXT and MET are superimposed, they provide a stronger stimulus to pituitary and adrenal reserve than either test alone; (4) the combination of MET and GXT elicits a greater ACTH response in T compared with UT men; and (5) an acute reduction in plasma cortisol does not alter VO2max.

Adrenocorticotropic Hormone↗
PubMed1999

Safety and immunogenicity of Haemophilus influenzae-tetanus toxoid conjugate vaccine given separately or in combination with a three-component acellular pertussis vaccine combined with diphtheria and tetanus toxoids and inactivated poliovirus vaccine for the first four doses.

The purpose of this randomized, controlled trial was to assess the safety and immunogenicity of a three-component acellular pertussis vaccine combined with diphtheria and tetanus toxoids and inactivated poliovirus vaccine given either separately or combined as a single injection with a Haemophilus influenzae type b-tetanus toxoid conjugate vaccine. A total of 180 infants were immunized at 2, 4, and 6 months of age; 129 were given a booster dose at 16-19 months of age. Vaccine-associated adverse events were similar whether the vaccines were combined as a single injection or given separately. There were no differences in levels of antibodies to Bordetella pertussis antigens (pertussis toxoid, filamentous hemagglutinin, and pertactin), diphtheria toxoid, or the three poliovirus types. The tetanus antitoxin level after the primary three-dose series was higher in recipients of the combined vaccine (2.37 IU/mL) than in recipients of the separate injections (1.32 IU/mL; two-sided P = .0001). In contrast, combined vaccine recipients had lower levels of antibody to H. influenzae type b polysaccharide after the third dose (1.57 microg/mL) than did those given separate injections (3.22 microg/mL; two-sided P = .0026). The antibody levels were not significantly different before or 1 month after the booster dose (32.9 microg/mL vs. 47.8 microg/mL, respectively; two-sided P = .07). We conclude that the vaccines were immunogenic and well tolerated. Despite lower levels of antibody to the H. influenzae type b polysaccharide after the primary three-dose series, mixing of the vaccines in a single syringe likely induced immunologic priming, as suggested by the high antibody levels after the booster dose.

Antibodies, Bacterial↗
PubMed1999

Epidemiological features of pertussis in hospitalized patients in Canada, 1991-1997: report of the Immunization Monitoring Program--Active (IMPACT).

To assess the morbidity associated with the continued high levels of pertussis, we studied all children <2 years of age who were admitted to the 11 Immunization Monitoring Program--Active (IMPACT) centers, which constitute 85% of Canada's tertiary care pediatric beds. In the 7 years preceding implementation of acellular pertussis vaccine, a total of 1,082 pertussis cases were reported, of which 49.1% were culture-confirmed. The median age of the patients was 12.4 weeks; 78.9% of cases were in children <6 months of age. Complications of pertussis were common: pneumonia was reported in 9.4% of cases, new seizures in 2.3%, and encephalopathy in 0.5%. There were 10 deaths (0.9%), all in children < or =6 months of age. Duration of hospitalization was longer (9.3 days vs. 4.9 days; P = .001) and intensive care was required more frequently (19.2% vs. 4.9%; P = .001) in infants under <6 months of age than in those > or =6 months. Pertussis continues to cause significant morbidity and occasional mortality in Canada, particularly in young infants.

Canada↗