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Biomedical subjects

A S Douglas

Publications and source records attributed to A S Douglas.

At least 19 recordsLinked to original sources
PubMed2002

The actuation of a biomimetic poly(vinyl alcohol)poly(acrylic acid) gel.

Active polymer gels expand and contract in response to certain environmental stimuli, such as the application of an electric field or a change in the pH level of the surroundings. This ability to achieve large, reversible deformations with no external mechanical loading has generated much interest in the use of these gels as biomimetic actuators and "artificial muscles". In previous work, a thermodynamically consistent finite-elastic constitutive model has been developed to describe the mechanical and actuation behaviours of active polymer gels. The mechanical properties were characterized by a free-energy function, and the model uses an evolving internal variable to describe the actuation state. In this work, an evolution law for the internal variable is determined from free actuation experiments on a poly(vinyl alcohol)poly(acrylic acid) (PVAPAA) gel. The complete finite-elastic/evolution law constitutive model is then used to predict the response of the PVA-PAA gel to isotonic and isometric loading and actuation. The model is shown to give relatively good agreement with experimental results.

Acrylic Resins↗
PubMed2001

Modeling tongue surface contours from Cine-MRI images.

This study demonstrated that a simple mechanical model of global tongue movement in parallel sagittal planes could be used to quantify tongue motion during speech. The goal was to represent simply the differences in 2D tongue surface shapes and positions during speech movements and in subphonemic speech events such as coarticulation and left-to-right asymmetries. The study used tagged Magnetic Resonance Images to capture motion of the tongue during speech. Measurements were made in three sagittal planes (left, midline, right) during movement from consonants (/k/, /s/) to vowels (/i/, /a/, /u/). MR image-sequences were collected during the C-to-V movement. The image-sequence had seven time-phases (frames), each 56 ms in duration. A global model was used to represent the surface motion. The motions were decomposed into translation, rotation, homogeneous stretch, and in-plane shear. The largest C-to-V shape deformation was from /k/ to /a/. It was composed primarily of vertical compression, horizontal expansion, and downward translation. Coarticulatory effects included a trade-off in which tongue shape accommodation was used to reduce the distance traveled between the C and V. Left-to-right motion asymmetries may have increased rate of motion by reducing the amount of mass to be moved.

Adult↗
PubMed2001

Modeling the motion of the internal tongue from tagged cine-MRI images.

A new technique, tagged Cine-Magnetic Resonance Imaging (tMRI), was used to develop a mechanical model that represented local, homogeneous, internal tongue deformation during speech. The goal was to infer muscle activity within the tongue from tissue deformations seen on tMRI. Measurements were made in three sagittal slices (left, middle, right) during production of the syllable /ka/. Each slice was superimposed with a grid of tag lines, and the approximately 40 tag line intersections were tracked at 7 time-phases during the syllable. A local model, similar to a finite element analysis, represented planar stretch and shear between the consonant and vowel at 110 probed locations within the tongue. Principal strains were calculated at these locations and revealed internal compression and extension patterns from which inferences could be drawn about the activities of the Verticalis, Hyoglossus, and Superior Longitudinal muscles, among others.

Adult↗
PubMed1999

Changing incidence of Achilles tendon rupture in Scotland: a 15-year study.

OBJECTIVE: To determine the incidence of Achilles tendon rupture in Scotland from 1980 to 1995. DESIGN: Retrospective analysis of prospectively collected data. SETTING: Data were obtained from the National Health Service Information and Statistics Division and analyzed in terms of age- and gender-specific incidence rates and time trends by age group. PARTICIPANTS: A total of 4,201 patients with Achilles tendon ruptures occurring during the study period. MAIN OUTCOME MEASURES: Calculation of incidence and of seasonality. RESULTS: The overall incidence of Achilles tendon rupture increased from 4.7/100,000 in 1981 to 6/100,000 in 1994, with a peak in 1986. In men, the incidence rose from 6.3/100,000 to 7.3/100,000. In women, the increase in incidence was more pronounced, from 3/100,000 to 4.7/100,000. In men, peak incidence rate occurred in the 30- to 39-year age group, whereas in women, the peak age-specific incidence occurred in those aged 80 years and older, with a steady increase after age 60. There was no evidence of a seasonality effect in the rate of occurrence of Achilles tendon rupture. A bimodal distribution of age at time of Achilles tendon rupture was noted. CONCLUSION: There was a significant increase in the incidence of Achilles tendon rupture during the period from 1980 to 1995. This reflects the increased incidence of the injury noted in other Northern European countries.

Achilles Tendon↗
PubMed1999

Seasonality, but not prevalence of sudden infant death syndrome varies by region in mainland Britain.

This study aimed to investigate whether seasonal variation in day length contributed to winter/summer variation in sudden infant death syndrome (SIDS) at different latitudes in mainland Britain. Over 11 yrs 13,973 deaths were studied. Using appropriate analytic techniques a sine curve was fitted to monthly rates with the amplitude indicating magnitude of seasonal change. The rate of SIDS per 1,000 live births was the same (1.73) in the north as in the south. The amplitude was a quarter less in the north (41.3%) than in the south (54.2%) (p<0.001). While annual rates did not differ, the within year distribution did. The findings for seasonality of SIDS births were similar (amplitudes: north 213%, south 32.3%). Correlations were made between SIDS amplitude and individual environmental factors, particularly temperature and day length. These complex issues, while reported briefly, do not allow firm conclusions. In the north the winter day length is shorter, sunshine hours are less and temperature is lower, but the winter increment in SIDS is less. The extent of seasonal variation of sudden infant death syndrome is greater in the south as compared with the colder, darker north but this has no effect on sudden infant death syndrome rates. Changing photoperiod by latitude, amongst other environmental influences, may hold clues to the aetiology of sudden infant death syndrome.

Humans↗
PubMed1998

Seasonality of sudden infant death syndrome (SIDS) by age at death.

Seasonality of sudden infant death syndrome (SIDS) is a well-established epidemiological finding. The purpose of the study was to determine whether this feature varied significantly with age at death. In total, 13990 cases of SIDS in Scotland, England and Wales during 1982-1992 were studied by age group at death. Seasonality was established by fitting a sinusoidal curve and for each set of monthly data the peak position in the year and its magnitude were determined. Weighted regression revealed significant differences in peak position and amplitude of seasonal variation between those dying at < or = 4 months and those aged > or = 5 months at death. Those infants in the younger age group were more likely to die earlier in the winter months and had a smaller variation in seasonality. The peak (acrophase) months were January for < or = 4 months and February for > or = 5 months at death. Weighted regressions of peak position and amplitude on age at death had p-values of <0.001 and <0.01, respectively. A log linear model relating SIDS incidence to month of birth, month of death and age was able to explain some of these findings. The findings support the hypothesis that in SIDS there may be more than one infant cohort, each of which passes through a vulnerable developmental window at different ages.

Age Factors↗
PubMed1998

Does vitamin D deficiency account for ethnic differences in tuberculosis seasonality in the UK?

OBJECTIVES: Notifications of tuberculosis in England and Wales are reported to peak in the summer season. The purpose of this study was to confirm that finding and to determine to what extent patients of Indian Subcontinent (ISC) ethnic origin contributed to the seasonality. The clinical presentation of the disease is presumed to occur some months following reactivation of the endogenous latent focus of tuberculosis infection. There arises the possibility of vitamin D deficiency producing immunological inadequacy at the end of winter and beginning of spring. PATIENTS AND METHODS: Monthly (or 4-weekly) aggregated data over 7 years were collected from the three countries of mainland Britain, England, Wales, Scotland and from the city of Birmingham in England. The notifications from Birmingham were divided into those of ISC ethnic origin and 'whites'. The presence or absence of seasonality was determined by fitting a sinusoidal curve by the technique called 'cosinor analysis'. In this method amplitude gives a measure of the extent of the seasonal variation. RESULTS: The summer peak of clinical diagnosis was confirmed in the UK series from England, Wales and Scotland. In England and Wales without Scotland a larger seasonal variation was present. Scotland, with a lower proportion of population of ISC ethnic origin, was examined separately and the results in Scotland alone failed to confirm seasonality. In the data from Birmingham, seasonality was confirmed with a greater amplitude, particularly in those over 60 years of age. The finding was influenced by those of ISC ethnic origin, seasonality not being present in the 'white' population. CONCLUSION: The results from Birmingham are very striking, but there were almost three times as many patients in the ISC ethnic group as in indigenous 'white' patients. A series with larger numbers of 'white' patients would be necessary to confirm the absence of seasonality in the 'white' population. The discussion reviews the evidence that vitamin D may have an important hormonal role in immunological defence in the prevention of tuberculosis.

Causality↗
PubMed1998

Seasonality of sudden infant death syndrome in mainland Britain and Ireland 1985-95.

By the end of 1995 four years had passed since the dramatic fall in the incidence of sudden infant death syndrome (SIDS), following the "back to sleep" campaign. This time lag permitted a more definitive epidemiological reassessment than had been possible before. The extent of seasonal variation from 1992-5 fell by about half, occurring mainly as a single step down in 1992. The fall was relatively greater in winter than in summer. Before 1992 the extent of seasonal variation (amplitude) was greater in those age > or = 5 months compared with those aged < or = 4 months. Since 1992 the falls in incidence and amplitude have been greater in the younger group, suggesting that SIDS deaths in younger and older babies may have different causes.

Age Factors↗
PubMed1997

Month of birth as an independent variable in the sudden infant death syndrome.

Well-known epidemiological features of sudden infant death syndrome (SIDS) are age at death and the increased numbers in winter. There are more SIDS deaths in late autumn/early winter and there is a seasonal rhythm of births with a peak in late summer and early autumn. The data set was 14033 SIDS deaths from Scotland, England and Wales over the 11 years 1982-92. Using log-linear models, which accounted for age at death and month of death, birth month was found to be a statistically significant risk factor for SIDS independent of age at death and winter environment (P < 0.001). Although winter season had the largest effect (relative risk 2.7 in January compared with August), the independent effect of birth month was of clinical as well as statistical significance with a relative risk for August births of 1.37 compared with those born in April. The analysis of each birth month cohort revealed a change in age distribution with infants born in early winter (December) dying at a younger age (mean 108 days) than those born in midsummer (June) (mean 146 days). Although winter season and age are the most influential factors, the substantial effect of month of birth requires explanation and points to as yet unidentified environmental influences during pregnancy.

Age Distribution↗
PubMed1997

Circannual rhythm of measles subsequent to immunisation.

This is an epidemiological study of biennial and annual rhythms of measles in England and Wales between 1959-1994 highlighting changes following immunisation. The study describes annual rhythms starting in autumn (Week 41) and the statistical method tests the fit of a sine curve to annual data. Before immunisation the previously established biennial rhythm was seen: the two years differed in magnitude of seasonal variation, position of the peak, "visibility of school holidays" and peak breadth. After immunisation (1968) these biennial features tended to disappear, one annual rhythm becoming the predominant feature. By the late eighties adjacent years had very similar sine curve fits. About 1990 (89-91) the fit of the sine curve was no longer significant, was of low amplitude and numbers were at an all time low. In 1992 significant annual variation returned, numbers rose and magnitude of seasonal variation increased. At this time a new epidemic was being predicted on other evidence and this renewed sine curve fit may be an additional warning signal. A possible influence of normal birth rhythm on numbers of susceptibles is described.

Child↗
PubMed1997

Seasonality and other epidemiological features of haemolytic uraemic syndrome and E. coli O157 isolates in Scotland.

The main objective was to determine whether there was seasonality in presentation of haemolytic uraemic syndrome (HUS) in children and adults, and compare this with the reporting of E. coli O157. The data came from Scotland, examining admissions during 1980-95 and E. coli isolates 1984-95. Seasonality was sought by fitting a sine curve to monthly or four-weekly data throughout the year. Seasonality was present for HUS and E. coli isolates in patients under 15 years of age but not in those above that age. The highest point of the sine curve was in July/August but there was a high plateau from June to September. The timing was similar to other diarrhoeal disease. This is an epidemiological study, the purpose being to clarify the seasonal features of HUS. E. coli infection is an important food hazard and a sound knowledge of the epidemiology, could lead to optimal control. The Scottish geographic distribution is illustrated.

Adolescent↗
PubMed1997

Seasonal changes in psychological well-being in an elderly population.

BACKGROUND: Little is known about seasonal fluctuations in psychological well-being among elderly people. METHOD: Over a period of 21 months, 1466 elderly people completed the General Health Questionnaire and the Leeds Scales for Depression and Anxiety. Scores during the winter months (December to February) were compared with those during other months of the year. RESULTS: Scores on all scales were significantly higher during the winter months, but there was no difference in rates of caseness. Unlike younger populations, elderly women did not exhibit greater seasonality in well-being than did elderly men. CONCLUSIONS: Elderly people exhibit a small seasonal fluctuation in psychological well-being, which is probably of little clinical importance, and there is no gender difference. The findings support the contention that seasonal mood changes are most pronounced among females of reproductive age.

Age Factors↗
PubMed1996

Seasonality and the sudden infant death syndrome during 1987-9 and 1991-3 in Australia and Britain.

OBJECTIVE: To determine whether seasonality of the sudden infant death syndrome persists now that rates have fallen, mostly after widespread adoption of the "face upwards" sleeping position. DESIGN: Monthly data on the sudden infant death syndrome during 1987-9 were compared for seasonality with those of 1991-3; rates were studied as deaths per 1000 live births. SETTING: Australia and Britain (England, Wales, and Scotland). SUBJECTS: Infants under 1 year dying of the syndrome (2401 for Australia and 6630 for Britain). MAIN OUTCOME MEASURE: Extent of seasonal variation (amplitude) was established by cosinor analysis; amplitudes for the earlier and later years were compared. RESULTS: The rate fell in every month, and, though it did so relatively more in winter than summer, seasonality remained a distinctive feature. In the comparison of amplitudes the ratio between the earlier and later years was 1.4 in both Australia and Britain. Some differences between the hemispheres were noted. CONCLUSIONS: Seasonality of the sudden infant death syndrome remains to be explained and continues to be an important aetiological lead. Studies from other countries are needed.

Australia↗
PubMed1996

Seasonal differences in biochemical parameters of bone remodelling.

AIMS: To compare bone remodelling parameters in late autumn and early spring in 20 post-menopausal women. METHODS: The parameters measured were serum osteocalcin and its apparent degree of carboxylation (measured by hydroxyapatite binding), total and bone specific alkaline phosphatase and urinary bone resorption markers, (pyridinoline and deoxypyridinoline). RESULTS: Serum osteocalcin concentrations were lower in autumn than in spring but the degree of carboxylation was similar. Total and bone specific alkaline phosphatase activities in serum were higher in autumn than in spring. These results support previous observations. However, notable and previously unreported changes in urinary bone resorption markers were observed. Pyridinoline concentrations were lower and deoxypyridinoline higher in autumn compared with spring. The ratio of pyridinoline:deoxypyridinoline was therefore very different between the seasons. CONCLUSIONS: The results clearly demonstrate that seasonal changes in these variables of bone remodelling must be taken into consideration when designing, reporting or analysing studies of bone metabolism in vivo.

Aged↗
PubMed1996

Seasonality of tuberculosis: the reverse of other respiratory diseases in the UK.

BACKGROUND: In Western societies there is a winter peak in mortality, largely accounted for by respiratory and cardiovascular deaths. In view of the known seasonal variation in vitamin D, and of the postulated link between tuberculosis and vitamin D deficiency, a study was undertaken to examine whether the presentation of tuberculosis had the same seasonal rhythm as other pulmonary infections. METHODS: Using cosinor analysis the presence or absence of seasonality was determined for 57,313 tuberculosis notifications for England and Wales. OPCS data in four weekly notifications over a 10 year period (1983-92) were examined as two quinquential sets (1983-7 and 1988-92). These were compared with two groups of acute respiratory illness: 138,992 notifications to OPCS of pneumonia deaths for 1988-92 and all admissions to Scottish hospitals with respiratory disease (252,163 cases) during 1980-4. RESULTS: Analysis of notifications of tuberculosis revealed a summer peak with an amplitude of 10%. This pattern differs markedly from other respiratory disorders in which a winter peak and summer trough is observed. CONCLUSIONS: The unusual seasonality of tuberculosis is currently unexplained. One possibility is that low post-winter trough levels of vitamin D (which are known to affect macrophage function and cell mediated immunity) might result in impaired cellular immunity leading, after a latent period, to reactivation of dormant mycobacterial infection.

Humans↗
PubMed1996

Seasonal variation in sudden infant death syndrome and bronchiolitis--a common mechanism?

The purpose of this study was to compare epidemiologic features of sudden infant death syndrome (SIDS) and bronchiolitis and to apply statistical examination in order to examine the hypothesis that similar mechanisms could be at work in both conditions. The setting was Scotland from 1982 through 1990. We compared 1,211 deaths from SIDS with 10,058 hospital admissions for bronchiolitis in infancy. The comparisons included age, sex ratio, and seasonality. The sex ratios were similar (SIDS [M:F]:1.61:1; bronchiolitis: 1.63:1), but age distribution was different (chi 2 = 104.6, p < 0.001). When monthly rates throughout the year were compared using correlation of residuals from average season variation and by autocorrelation of residual series, no significant relationships were found between the two conditions (r2 = 0.0004). Once the seasonal pattern common to both conditions was accounted for, SIDS was not autocorrelated between months whereas bronchiolitis exhibited a high level of autocorrelation indicating an epidemic pattern for the latter but not for the former. While a common seasonal variation may indicate some shared etiologic factors associated with winter season, the two conditions do not appear to be closely related. The hypothesis that a common host susceptibility is at work is not supported. Further investigations of seasonal influences are warranted.

Age Distribution↗
PubMed1996

Seasonality of birth in sudden infant death syndrome.

The objective was to clarify the optimal birth month for avoidance of SIDS and the seasonal characteristic of each birth-month cohort. The statistical method was cosinor analysis, and this established seasonality of SIDS death and births, the extent of this seasonality (amplitude) and the position of the peak (acrophase). There is a lowering of risk, by one third, amongst babies born in February-May compared to those born in August-November. The seasonal variation of death was twice as great for birth in September as compared with those in April. Those born in May-June lived on average six weeks longer than those born in November-April. Advice on subsequent pregnancy delivery date should be given to families who have already experienced SIDS. For those born in autumn there may be two components-the first a genetic or intrauterine component independent of month of birth, and the second an independent effect of interaction with winter environment.

Cohort Studies↗