Biomedical subjects

S M Williams

Publications and source records attributed to S M Williams.

At least 73 records · Page 4Linked to original sources

PubMed2000

Coping style following acute stress in competitive sport.

The purpose of this study was to ascertain coping styles among competitive athletes in response to various acute stressors. Specifically, the authors used a 134-item survey to measure approach and avoidance coping styles, with task-focused and emotion-focused coping tendencies nested hierarchically as subdimensions under each. Australian and U.S. college-aged participants indicated the extent to which they used approach, avoidance, task-focused, and emotion-focused coping strategies (a 4-factor model) in response to selected acute stressors experienced during sport competition. The authors computed confirmatory factor analysis to test the theoretically driven model. The criterion loading of .30 and above for each of the factors reduced the survey to 65 items. Findings indicated stronger links between the 2 approach constructs of task- and emotion-focused coping than between the 2 avoidance constructs of those subdimensions. The goodness-of-fit indices for the 4-factor model were 0.58 and 0.57 for Australian and U.S. samples, respectively, and .71 overall. Concomitant low correlations between the 2 approach (0.18) and the 2 avoidance dimensions (0.43) reflected relatively high residuals between stressors. In general, psychometric analyses suggest that coping style may be more prevalent in some situations than others, lending partial support for the transactional model of coping.

Acute Disease↗

PubMed2000

Evaluation of waist circumference, waist-to-hip ratio, and the conicity index as screening tools for high trunk fat mass, as measured by dual-energy X-ray absorptiometry, in children aged 3-19 y.

BACKGROUND: A central fat pattern has adverse health implications in both children and adults. Because adiposity tracks from childhood into adulthood, the ability of simple anthropometric techniques to correctly measure truncal adiposity in childhood needs to be assessed. OBJECTIVES: We sought to assess the validity of waist circumference, waist-to-hip ratio (WHR), and the conicity index as indicators of trunk fat mass in children and adolescents. DESIGN: Trunk fat mass (kg) was measured with dual-energy X-ray absorptiometry in 278 girls and 302 boys aged 3-19 y. Receiver operating characteristic (ROC) curves and areas under the curves (AUCs) for the ROCs were calculated to compare the relative abilities of the anthropometric measures to correctly identify children with high trunk fat mass (z score for our study population of > or =1). RESULTS: The 80th percentile for waist circumference correctly identified 89% of girls and 87% of boys with high trunk fat mass (sensitivity) and 94% of girls and 92% of boys with low trunk fat mass (specificity). Waist circumference performed significantly better as an index of trunk fat mass than did WHR or the conicity index, as shown by the AUCs in girls and boys, respectively: waist circumference AUCs = 0.97 and 0.97, conicity index AUCs = 0.80 and 0.81, and WHR AUCs = 0.73 and 0.71. Our cutoffs for high trunk fat mass and high waist circumference are provided for both sexes for each year of age. CONCLUSION: Waist circumference provides a simple yet effective measure of truncal adiposity in children and adolescents.

Abdomen↗

PubMed2000

Ventilatory sensitivity to mild asphyxia: prone versus supine sleep position.

AIMS: To compare the effects of prone and supine sleep position on the main physiological responses to mild asphyxia: increase in ventilation and arousal. METHODS: Ventilatory and arousal responses to mild asphyxia (hypercapnia/hypoxia) were measured in 53 healthy infants at newborn and 3 months of age, during quiet sleep (QS) and active sleep (AS), and in supine and prone sleep positions. The asphyxial test mimicked face down rebreathing by slowly altering the inspired air: CO(2), maximum 5% and O(2), minimum 13.5%. The change in ventilation with inspired CO(2) was measured over 5-6 minutes of the test. The slope of a linear curve fit relating inspired CO(2) to the logarithm of ventilation was taken as a quantitative measure of ventilatory asphyxial sensitivity (VAS). Sleep state and arousal were determined by behavioural criteria. RESULTS: At 3 months of age, prone positioning in AS lowered VAS (0.184 prone v 0.269 supine, p = 0.050). At newborn age, sleep position had no effect on VAS. Infants aged 3 months were twice as likely to arouse to the test than newborns (p = 0.013). Placing infants prone as opposed to supine increased the chances of arousal 1.57-fold (p = 0.035). CONCLUSION: Our findings show 3 month old babies sleeping prone compared to supine have poorer ventilatory responses to mild asphyxia, particularly in AS, but the increased prevalence of arousal is a protective factor.

Arousal↗

PubMed2000

Combinations of variations in multiple genes are associated with hypertension.

The genetic analysis of hypertension has revealed complex and inconsistent results, making it difficult to draw clear conclusions regarding the impact of specific genes on blood pressure regulation in diverse human populations. Some of the confusion from previous studies is probably due to undetected gene-gene interactions. Instead of focusing on the effects of single genes on hypertension, we examined the effects of interactions of alleles at 4 candidate loci. Three of the loci are in the renin-angiotensin-system, angiotensinogen, ACE, and angiotensin II type 1 receptor, and they have been associated with hypertension in at least 1 previous study. The fourth locus studied is a previously undescribed locus, named FJ. In total, 7 polymorphic sites at these loci were analyzed for their association with hypertension in 51 normotensive and 126 hypertensive age-matched individuals. There were no significant differences between the 2 phenotypic classes with respect to either allele or genotype frequencies. However, when we tested for nonallelic associations (linkage disequilibrium), we found that of the 120 multilocus comparisons, 16 deviated significantly from random in the hypertensive class, but there were no significant deviations in the normotensive group. These findings suggest that genetic interactions between multiple loci rather than variants of a single gene underlie the genetic basis of hypertension in our study subjects. We hypothesize that such interactions may account for the inconsistent findings in previous studies because, unlike our study, prior studies almost always examined single-locus effects and did not consider the effects of variation at other potentially interacting loci.

Adolescent↗

PubMed2000

Factors affecting heart rate variability and heart rate responses to tilting in infants aged 1 and 3 months.

Heart rate variability (HRV) and heart rate (HR) responses following a 60 degree head-up tilt were measured in 60 infants at 1 and 3 mo of age to investigate the effects on these of age, sleep state, sleep position, and mother's smoking status. HRV was determined from Poincaré plots of 500 sequential RR intervals to measure overall variability derived from the SDRR of this plot, and instantaneous variability derived from the SDdeltaRR. HR responses to the tilt were measured as changes in RR interval length from rest to immediately following the tilt and again once a stable pattern was reached. SDRR and SDdeltaRR increased 20 and 40%, respectively, with age (p < 0.0001), SDRR was higher in active sleep (AS) than quiet sleep (QS, +72%, p < 0.0001) but both measures of variability (SDRR and SDdeltaRR) were lower in the prone position compared with supine (-18%, p < 0.0001). However, several findings were dependent on the basal RR interval, thus the age effect disappeared once RR interval was taken into account, sleep state remained an important factor and the lower variability when prone now became a difference of -3% (p = 0.034). The tilt generally provoked a reflex tachycardia followed by a bradycardia and settling to a stable HR level below, at, or above baseline within 30 s. The more unusual responses were no HR change, sustained tachycardia or sustained bradycardia (15% of total). These were more likely to occur in younger infants (p = 0.008) and in AS (p < 0.0001). No changes were seen in any of the cardiac indices related to maternal smoking status. The findings confirm several reports indicating that prone sleeping damps some physiologic responses. The data emphasize the need to consider basal heart rate, and sleep position as well as sleep state in autonomic function testing during infant sleep.

Female↗

PubMed2000

More broken bones: a 4-year double cohort study of young girls with and without distal forearm fractures.

Predictors of childhood fractures have not been investigated previously. This study was undertaken to determine whether a previous history of forearm fracture, low bone mineral density (BMD; both areal bone mineral density [aBMD, g/cm2] and volumetric bone mineral apparent density [BMAD, g/cm3]), or anthropometry, influence fracture risk in young girls. At baseline, two cohorts of girls, aged 3-15 years, were evaluated: 100 had recently broken a forearm (group 1) and 100 were fracture free (group 2). Four years later we restudied 170 of these girls (82 from group 1 and 88 from group 2). We now report the relationships of previous fracture history, baseline BMD (measured by dual-energy X-ray absorptiometry), baseline weight, and height to risk of new fracture. More new fractures occurred in group 1 (37 fractures in 24 girls) than in group 2 (8 fractures in 7 girls; p = 0.0007). The independent predictors for occurrence of a new fracture at any skeletal site in a multivariate model adjusting for age, weight, total body aBMD, and fracture history were previous fracture (hazard ratio [HR], 3.28; 95% CI, 1.41-7.64); age (HR per 1-year increase, 0.91; 95% CI, 0.84-0.99); total body aBMD (HR per 1 SD decrease, 1.92; 95% CI, 1.31-2.81); and body weight (HR per 1 SD increase, 1.49; 95% CI, 1.06-2.08). Girls with two risk factors together had substantially greater fracture risk: previous fracture and low spinal BMAD (HR, 9.4; 95% CI, 2.8-32.0), previous fracture and high body weight (HR, 10.2; 95% CI, 2.8-37.6), or previous fracture and low total body aBMD (HR, 13.0; 95% CI, 3.9-43.1). We conclude that previous forearm fracture, low total body aBMD, low spinal BMAD, and high body weight each increase risk of new fractures within 4 years in young girls. Interventions to reduce the risk of fractures, particularly forearm fractures, in girls warrant further study.

Absorptiometry, Photon↗

PubMed2000

Evaluating frequency proximity in stream segregation.

Consecutive sounds of similar structure that are close in frequency or pitch are more likely to be perceived as part of the same sequence than those at greater frequency separations. The principle of grouping into such perceptual sequences, or auditory streams, is known as frequency proximity. However, the metric by which one frequency difference is judged to be greater or less than another in complex auditory scenes is not yet known. Two experiments explored the metric for frequency proximity. We presented repeating three-tone stimulus patterns at a rate where they are normally heard as two streams, one containing the highest tone and one containing the lowest. The middle tone joined one stream or the other depending on its frequency. Subjects reported the perceived allocation of the variable tone by responding on a 5-point scale. The frequency at which either of these two percepts was equally probable was found to be lower than a logarithmic midpoint or the midpoints on a cochlear map or the Mel scale; that is, it was unlike metrics arrived at by direct comparisons of tones. Further, the midpoint for high and low tones presented synchronously was lower than that for the same tones presented sequentially, demonstrating that in addition to a proximity factor, some additional factor or factors must operate differently when the lower and upper fixed tones are, or are not, presented simultaneously.

Adolescent↗

PubMed2000

Prevalence of overweight and obesity in bipolar patients.

BACKGROUND: Patients who receive pharmacologic treatment for bipolar illness frequently gain weight. This study evaluated the prevalence of overweight and obesity in an unselected group of bipolar patients and matched reference subjects. METHOD: The prevalence of overweight, obesity, and central adiposity was evaluated in 89 euthymic bipolar (DSM-IV) patients and 445 reference subjects, matched for age and sex, using a cross-sectional study design. RESULTS: Female patients were more often overweight and obese than female reference subjects (chi2 = 9.18, df = 2, p = .01). The frequency of overweight was similar in male patients and male reference subjects, but male patients were more likely to be obese. Patients were more centrally obese than the general population in women (chi2 = 32.21, df = 1, p = <.001) and in men (chi2= 8.81, df = 1, p = .003). Patients treated with antipsychotic drugs were more obese than patients not receiving these drugs (chi2= 4.7, df = 1, p = .03). CONCLUSION: Body fat is more centrally distributed in pharmacologically treated bipolar patients than in matched population controls. Obesity is more prevalent in patients than in the general population. Obesity prevalence is clearly related to the administration of antipsychotic drugs.

Adipose Tissue↗

PubMed1999

Maps of central visual space in ferret V1 and V2 lack matching inputs from the two eyes.

In the visual cortex, the representation of central visual space is supplied by matching geniculate inputs that are driven exclusively by one eye or the other. In layer 4 of early visual areas (V1 in primates and V1 and V2 in cat), these inputs form a nearly uniform array of small ocular dominance domains, while preserving overall topographic order within the cortical map. In ferret, however, ocular dominance domains in different regions of the visual cortex are strikingly irregular in size and shape. The exceptionally large size of domains in some regions implies a departure from the usual visuotopic matching of inputs from the two eyes. Using optical-imaging, electrophysiological, and anatomical techniques, we show that this regional variation is attributable to exclusively monocular maps of the central portions of the ipsilateral visual field in V1 and the contralateral visual field in V2. In addition, we document a complex interdigitation of V1 and V2 that entails a discontinuity in the mapping of visual space and fragmentation of V2 into isolated cortical territories. We suggest that both the monocularity of these cortical maps and the visuotopic discontinuity along the V1-V2 border derive from asymmetries in the crossed and uncrossed retinal pathways.

Animals↗

PubMed1999

Water fluoridation and the sudden infant death syndrome.

AIMS: To determine whether exposure to fluoridated water supplies prenatally or postnatally at the time of death increases the risk of sudden infant death syndrome (SIDS). METHODS: A nationwide, case-control study, with infant's water fluoridation status determined from census area unit information for mother's usual address at the time of the infant's birth, infant's usual address at the time of death / nominated sleep and address where infant died / was at nominated sleep. SIDS risk associated with fluoride exposure postnatally was assessed according to method of infant feeding (breast or reconstituted formula), for the two days prior to infant's death / nominated sleep. RESULTS: Infants exposed to fluoridated water supplies during pregnancy were not at increased risk for SIDS, adjusted odds ratio (OR) 1.19 (95% confidence interval (CI) 0.82, 1.74). For breast-fed infants at the time of death / nominated sleep, fluoridated water exposure was not associated with an increased risk for SIDS, adjusted OR 1.09 (95% CI 0.66, 1.79). Similarly, 'fluoridated' formula feeding, when compared with 'unfluoridated' formula feeding, showed no increased risk of SIDS, adjusted OR 1.25 (95% CI 0.73, 2.13). There was no evidence of an interaction between fluoridation and infant feeding for the last two days (chi2 = 0.171, df = 1, p = 0.68). CONCLUSION: Exposure to a fluoridated water supply prenatally or postnatally at the time of death did not affect the relative risk for SIDS.

Analysis of Variance↗

PubMed1999

An empirical basis for Mach bands.

Mach bands, the illusory brightness maxima and minima perceived at the initiation and termination of luminance gradients, respectively, are generally considered a direct perceptual manifestation of lateral inhibitory interactions among retinal or other lower order visual neurons. Here we examine an alternative explanation, namely that Mach bands arise as a consequence of real-world luminance gradients. In this first of two companion papers, we analyze the natural sources of luminance gradients, demonstrating that real-world gradients arising from curved surfaces are ordinarily adorned by photometric highlights and lowlights in the position of the illusory bands. The prevalence of such gradients provides an empirical basis for the generation of this perceptual phenomenon.

Animals↗

PubMed1999

Mach bands as empirically derived associations.

If Mach bands arise as an empirical consequence of real-world luminance profiles, several predictions follow. First, the appearance of Mach bands should accord with the appearance of naturally occurring highlights and lowlights. Second, altering the slope of an ambiguous luminance gradient so that it corresponds more closely to gradients that are typically adorned with luminance maxima and minima in the position of Mach bands should enhance the illusion. Third, altering a luminance gradient so that it corresponds more closely to gradients that normally lack luminance maxima and minima in the position of Mach bands should diminish the salience of the illusion. Fourth, the perception of Mach bands elicited by the same luminance gradient should be changed by contextual cues that indicate whether the gradient is more or less likely to signify a curved or a flat surface. Because each of these predictions is met, we conclude that Mach bands arise because the association elicited by the stimulus (the percept) incorporates these features as a result of past experience.

Computer Simulation↗

PubMed1999

Colosalpingeal fistula: a rare complication of colonic diverticular disease.

Diverticular disease is a common condition in Western countries. The formation of inflammatory fistulae, usually from sigmoid colon to bladder or vagina, can be a feature of complicated cases of the disorder and is normally an indication for surgical intervention. We present a case of colosalpingeal fistulation occurring secondary to diverticulitis, a complication which, to our knowledge, has not been previously reported in the radiological literature. As in this instance, the initial clinical presentation of this problem can often be non-specific, with localising symptoms occurring later. In our case, barium enema examination allowed good demonstration of the fistulous communication before the more specific symptoms were clinically apparent.

Aged↗

PubMed1999

A comparison of the use, effectiveness and safety of bezafibrate, gemfibrozil and simvastatin in normal clinical practice using the New Zealand Intensive Medicines Monitoring Programme (IMMP).

AIMS: Because of the importance of treating dyslipidaemia in the prevention of ischaemic heart disease and because patient selection criteria and outcomes in clinical trials do not necessarily reflect what happens in normal clinical practice, we compared outcomes from bezafibrate, gemfibrozil and simvastatin therapy under conditions of normal use. METHODS: A random sample of 200 patients was selected from the New Zealand Intensive Medicines Monitoring Programme's (IMMP) patient cohorts for each drug. Questionnaires sent to prescribers requested information on indications, risk factors for ischaemic heart disease, lipid profiles with changes during treatment and reasons for stopping therapy. RESULTS: 80% of prescribers replied and 83% of these contained useful information. The three groups were similar for age, sex and geographical region, but significantly more patients on bezafibrate had diabetes and/or hypertension than those on gemfibrozil or simvastatin. After treatment and taking the initial measure into account, the changes in serum lipid values were consistent with those generally observed, but with gemfibrozil being significantly less effective than expected. More patients (15.8%S) stopped gemfibrozil because of an inadequate response compared with bezafibrate (5.4%) and simvastatin (1.6%). Gemfibrozil treatment was also withdrawn significantly more frequently due to a possible adverse reaction compared with the other two drugs. CONCLUSIONS: In normal clinical practice in New Zealand gemfibrozil appears less effective and more frequently causes adverse effects leading to withdrawal of treatment than either bezafibrate or simvastatin.

Bezafibrate↗

PubMed1999

Laboratory-scale inactivation of African swine fever virus and swine vesicular disease virus in pig slurry.

Two methods were evaluated for the inactivation of African swine fever (ASV) and swine vesicular disease (SVD) viruses in pig slurry: chemical treatment and heat treatment. The addition of NaOH or Ca(OH)2 at different concentration/time combinations at 4 degrees C and 22 degrees C was examined, as was virus stability at different temperature/time combinations. ASF virus (ASFV) was less resistant to both methods than SVD virus (SVDV). In slurry from one source, ASFV was inactivated at 65 degrees C within 1 min, whereas SVDV required at least 2 min at 65 degrees C. However, it was found that thermal inactivation depended on the characteristics of the slurry used. Addition of 1% (w/v) of NaOH or Ca(OH)2 caused the inactivation of ASFV within 150 s at 4 degrees C; 0.5% (w/v) NaOH or Ca(OH)2 required 30 min for inactivation. NaOH or Ca(OH)2 (1% (w/v)) was not effective against SVDV at 22 degrees C after 30 min, and 1.5% (w/v) NaOH or Ca(OH)2 caused inactivation of SVDV at both 4 degrees C and 22 degrees C. At higher chemical concentrations or temperatures, ASFV and SVDV inactivation was faster in slurry than in buffered medium.

African Swine Fever Virus↗

PubMed1999

Recovery and assay of African swine fever and swine vesicular disease viruses from pig slurry.

Assaying samples for infectious virus is more difficult when the sample is toxic to cells used in the assay, e.g. with samples of infected pig slurry. Various techniques were compared for the recovery of African swine fever virus (ASFV) and swine vesicular disease virus (SVDV) in pig slurry. Extraction with Freon led to 80-100% recovery of SVDV added to pig slurry. The assay sensitivity enabled undiluted, centrifuged sample to be put directly onto monolayers of IB-RS2 cells, allowing a minimum detection level of 100.7 pfu ml-1. ASFV was difficult to recover intact, and the best technique allowed a recovery of 60% with a minimum detectable level of 101.8 HAD50 ml-1, due to toxicity to the cells at low sample dilutions. Extraction with the addition of an equal volume of ox serum to inoculated slurry was best at recovering ASFV. Poor recoveries with the other techniques may have been due to the inactivation of the virus while in the slurry rather than as a result of the inability of the method to extract ASFV.

African Swine Fever Virus↗

PubMed1999

Pilot scale thermal treatment of pig slurry for the inactivation of animal virus pathogens.

This paper describes a pilot scale treatment plant that has been designed and built for the thermal inactivation in pig slurry of two viruses that infect pigs--African swine fever virus (ASFV) and swine vesicular disease virus (SVDV). The plant treats pig slurry continuously at a rate of up to 100 litres/hour and functions by heating the slurry, maintaining at least 99.99% of the slurry at the required temperature for a minimum period of 5 minutes, and then recovering the heat to raise the temperature of the incoming slurry. Results obtained indicated that SVDV was inactivated in pig slurry to below detectable levels with an alkaline pH (pH 7.5 to 8, as is usually the case) at a temperature of between 50 and 55 degrees C. In acidified slurry (pH 6.4), inactivation occurred between 55 and 60 degrees C. The difference in inactivation temperatures was probably due to the presence of free ammonia in the unacidified slurry. ASFV was inactivated by operating the plant at a temperature of 53 degrees C at a pH of 8.

African Swine Fever↗

PubMed1999

Seasonal differences in risk factors for sudden infant death syndrome. The New Zealand Cot Death Study Group.

The aim of this study was to explore whether the risk of sudden infant death syndrome (SIDS) associated with prone sleeping position and other risk factors varies with season. The study was a large nation-wide case-control study, which compared 485 cases with 1800 controls. Parents of 393 (81.0%) cases and 1591 (88.4%) controls were interviewed. Obstetric records were also examined. Infants dying in winter were older and had lower birthweights than those dying in summer. The increased risk of SIDS associated with prone sleeping position was greater in winter than in summer. In contrast, the increased risk of SIDS associated with excess thermal insulation and bed sharing was less in winter than in summer. Prone sleeping position accounts for about half of the difference between the mortality rate in summer and that in winter. This suggests that some factor related to season modifies the effect of prone sleeping position.

Age Distribution↗