Wandering: a significant problem among community-residing individuals with Alzheimer's disease

This study evaluated the frequency, predictors, and effects of wandering in a population-based sample of 193 individuals with Alzheimer's disease (AD). Although wandering occurred in subjects at all levels of cognitive impairment, analysis of variance indicated that for the group as a whole, greater frequency of wandering was associated with significantly more impairment in cognition, day-to-day functioning, and behavior. Caregiver distress also increased significantly with increased frequency of wandering. Logistic regression modeling identified functional impairment and disruptive behavior problems as the strongest independent predictors of wandering occurring within the past week. Cluster analysis revealed four characteristic groups of wanderers that represented a continuum of wandering frequency, each having a unique pattern of other behavioral disturbances. Based on this analysis, we recommend further evaluation and the development of possible treatment strategies that address the individual differences found among AD patients who wander.

The effect of lifelong exercise on psychomotor reaction time: a study of 38 pairs of male monozygotic twins

PURPOSE

The aim was to study the effect of lifetime physical activity on psychomotor speed.

METHODS

Foot and dominant hand visual simple and choice psychomotor reaction times were studied among monozygotic twins (38 pairs) aged 35-69, discordant for lifetime exercise histories.

RESULTS

There was a trend that some components of psychomotor reaction time were faster for frequent than for occasional exercisers, but the findings were not consistent for the hand and feet. After controlling for occupational physical activity, only choice decision time for the hand (26 ms, P < 0.01) and choice reaction time for the contralateral foot (51 ms, P < 0.05) both remained 7% faster. There was no trend for systematic differences in reaction times between twins engaged in regular exercise versus their siblings exercising infrequently.

CONCLUSIONS

Results suggest a somewhat smaller effect of exercise than reported in previous studies. Reaction time may be significantly affected only by vigorous, frequent exercise. Thus, health promotion through exercise may be unlikely to have notable effects on reaction time.

Determinants of paraspinal muscle cross-sectional area in male monozygotic twins

BACKGROUND AND PURPOSE

The purpose of this study was to investigate the general magnitude and relative contributions of anthropometric, lifestyle, and medical history factors and familial aggregation (combined effects of genes and early environment) as determinants of paraspinal muscle cross-sectional area (CSA).

SUBJECTS

The subjects were 65 pair of male monozygotic twins aged 35 to 65 years (mean = 49, SD = 8).

METHODS

Study methods included magnetic resonance imaging, percentage body fat determination, and a detailed interview.

RESULTS

Most of the anthropometric factors were associated with the CSAs. Familial aggregation was the strongest determinant, however, explaining 66% to 73% of the variance in the outcomes beyond what age alone predicted. Levels of occupational, sport, and leisure-time physical activities reported by the subjects had negligible effects.

CONCLUSION AND DISCUSSION

The CSAs of the paraspinal muscles were influenced more by some combination of genes and early environmental factors than by anthropometric factors and lifestyle choices in adulthood.

Determinants of psychomotor speed among 61 pairs of adult male monozygotic twins

BACKGROUND

Declining psychomotor speed is an indicator of the aging process, and it is influenced by genetics and environmental factors. The present study examined the relative effects of familial aggregation (reflecting a combination of genetics and early environmental influences), and occupational, lifestyle, and health factors on psychomotor speed.

METHODS

Hand and foot psychomotor speed was studied with 61 pairs of monozygotic male twins aged 35-67 years from the population-based Finnish Twin Cohort. The determinants of visual simple and choice reaction times were analyzed with multiple regression analysis.

RESULTS

Familial aggregation, reflecting genetic influences and shared environmental effects, explained in mean 47% of decision times, 31% of movement times, and 37% of response times (decision time and movement time combined). Age, cardiovascular morbidity, lifetime vigorous and frequent exercise participation, and mean lifetime daily hours sitting at work explained 0-19% of hand psychomotor speed and 0-10% of foot speed, depending on the outcome. The predicted increase in decision times due to the presence of cardiovascular morbidity was 11-35 ms. The predicted increase for hand and contralateral foot response times between ages 45 and 55 was 18-41 ms. Smaller effects were noted for each year of strenuous exercise and each hour/day of average lifetime sitting at work.

CONCLUSIONS

Results indicate that cardiovascular status, age, strenuous exercise, and work play a role in psychomotor speed, but a rather minor one. In contrast, genetic and shared early environmental influences as revealed from familial aggregation were relatively strong, yet a major proportion of the variability in psychomotor speed remained unexplained.

Determinants of isokinetic and psychophysical lifting strength and static back muscle endurance: a study of male monozygotic twins

STUDY DESIGN

Retrospective cohort.

OBJECTIVES

To determine the relative contributions of anthropometric factors, physical activity, back and neck pain, overall health, and familial aggregation (the combined effects of genetics and childhood environment) to different measurements of adult back muscle function.

SUMMARY OF BACKGROUND DATA

Many methods of muscle testing are employed in the attempt to predict, prevent, treat, and rehabilitate low back pain. Poor correlations between the test results suggest that they are measuring different attributes and have different determinants.

METHODS

Muscle function tests, magnetic resonance images, and a detailed interview were obtained in 65 pairs of monozygotic male twins.

RESULTS

Familial aggregation was the strongest determinant of isokinetic and psychophysical lifting and static back endurance, explaining 56%, 32%, and 15% of the variances, respectively, beyond that which age alone predicted. Back pain and physical loading in work and leisure explained 2%, 0%, and 23% of the variances.

CONCLUSIONS

The combined effects of genetics and childhood environment play a dominant role in determining adult back muscle function. Physical loading at work and leisure, back and neck pain history, overall health, and anthropometric factors had a comparatively minor role, suggesting that the potential of interventions to increase and sustain back muscle function in healthy adults, measured through these tests, may be limited. The relative contributions of constitutional, behavioral, and environmental factors differ substantially in the three tests, and provide insights into what these commonly used tests actually reflect or measure. This knowledge can be used to guide more appropriate selection and interpretation of results of back muscle function tests.

Differences in hand and foot psychomotor speed among 18 pairs of monozygotic twins discordant for lifelong vehicular driving

The purpose of this study was to examine driving as a determinant of hand and foot psychomotor reaction times. Visual simple and choice hand and foot psychomotor reaction times were measured. The occupational driving contrast was determined by an interview reviewing every job held during each subject's lifetime. Comparison was made of psychomotor speed among 18 pairs of 39- to 62-year-old monozygotic male twins discordant for lifelong occupational driving. The mean discordance was the equivalent of 16 years of full-time driving. The twins who drove more tended to have slower hand simple and choice reaction times, although only the difference in hand-choice decision time was statistically significant (32 ms, P < 0.05). The drivers also had slower ipsilateral foot-choice decision times (21 ms, P < 0.01), but on average they had faster reaction times in 8 of the 12 ipsilateral and contralateral foot measurements. The slightly longer decision times could be related to some general harmful effects of driving, possibly whole-body vibration. Faster foot movement times of drivers may be affected by practice effects of rapid lower-extremity movements in driving.

Lifetime exercise and disk degeneration: an MRI study of monozygotic twins

Participation in some competitive sports has been shown to increase disk degeneration; however, the long-term effects of recreational physical activities are unclear. We investigated the effects of endurance exercise and power sports on disk degeneration in monozygotic male twins with contrasting lifetime exercise histories. The effects of endurance exercise were studied in 22 discordant twin pairs (mean lifetime frequencies of 3.9 vs 1.1 times/wk), and the effects of power sports were investigated in 12 discordant pairs (2,300 vs 200 h of weightlifting). The age range of the twins was from 35 to 69 yr. No differences in MRI findings between co-twins discordant for endurance exercise were found at any of the spinal regions. Subjects with more power sport involvement had greater disk degeneration in the T6-T12 region (P < 0.03), but similar findings were not present in the lumbar spine. Controlling for recalled back injuries, occupational loading, smoking, and driving did not significantly affect the results. No signs of beneficial or harmful effects of lifetime endurance exercise on disk degeneration were seen. Increased power sport participation was associated with slightly greater disk degeneration in the lower thoracic spine, but not in the lumbar spine.

The association of trunk muscle cross-sectional area and magnetic resonance image parameters with isokinetic and psychophysical lifting strength and static back muscle endurance in men

The relationship between trunk muscle morphology as measured on transverse magnetic resonance images and isokinetic lifting, psychophysical lifting, and static back muscle endurance testing was examined in 110 men, ages 35-67 years (mean, 48 years), who had been chosen based on their exposure to a wide variety of occupational and leisure-time physical activities. The computed T2-relaxation times and the T2-weighted and proton density-weighted signal intensities of the erector spinae, quadratus lumborum, and psoas major muscles had almost no association with any of the strength tests. The cross-sectional areas of the muscles had good correlations with isokinetic lifting strength (r = 0.46-0.53). They did not correlate well with psychophysical lifting and static back muscle endurance. Other characteristics or neurological or psychological factors may have more influence on those tests.

Isokinetic and psychophysical lifting strength, static back muscle endurance, and magnetic resonance imaging of the paraspinal muscles as predictors of low back pain in men

Magnetic resonance imaging was used to determine the cross-sectional areas and the T2-weighted and proton density-weighted signal intensities of the paraspinal muscles in a group of 128 men, aged 35-63, who had varied histories of occupational and leisure-time physical activities. These measures, and the isokinetic lifting, psychophysical lifting, and static back muscle endurance tests were examined as predictors of low back pain over 12 months of follow-up, in the 43 men who reported no low back pain in the year preceding testing. None of the imaging measures or the muscle function tests was useful as a predictor of future low back pain. Associations with the frequency of low back pain before testing were investigated in the larger group. Smaller total cross-sectional area of the paraspinal muscles and greater signal intensities had weak but significant correlations with more frequent low back pain in the previous year, possibly due to muscle atrophy.

Differences in psychomotor reaction time in male monozygotic twins discordant for lifetime cigarette smoking

The effects of long-term cigarette smoking on psychomotor reaction time were investigated among 8 pairs of monozygotic male twins highly discordant for lifetime smoking (means 32.4 versus 0.6 pack-years). The men had no diagnosed cardiovascular disease or other major diseases, musculoskeletal complaints, or vision problems that might interfere with reaction time testing. The twins had similar education, work, and exercise histories; alcohol and coffee consumption and exposure to solvents were examined as possible confounds. Direct comparison of cotwins also controlled for age, genetics, and possible early environmental factors. Simple and choice reaction time were measured in the dominant hand and in both feet. The decision-time component of total reaction time was of primary interest. On average, long-term smokers had slower decision times than their nonsmoking twins; however, the differences were small (5 to 14%) and were not statistically significant for four of the six decision-time measures, perhaps due to the lack of power with only eight twin pairs. Further study may confirm our evidence suggesting that long-term cigarette smoking impedes reaction time, a key measure of function of the central nervous system.

1995 Volvo Award in clinical sciences. Determinants of lumbar disc degeneration. A study relating lifetime exposures and magnetic resonance imaging findings in identical twins

STUDY DESIGN

Retrospective cohort.

OBJECTIVES

To investigate the effects of lifetime exposure to commonly suspected risk factors on disc degeneration using magnetic resonance imaging, and to estimate the effects of these suspected risk factors relative to age and familial aggregation, reflecting genetic and shared environmental influences.

SUMMARY OF BACKGROUND DATA

Structural and biochemical changes associated with disc degeneration are suspected as the underlying conditions of many back-related symptoms. Little is known about the determinants of disc degeneration.

METHODS

Based on lifetime discordance in suspected environmental risk factors for disc degeneration, 115 male identical twin pairs were selected. An in-depth interview was conducted of occupational and leisure time physical loading, driving, and smoking. Disc degeneration was evaluated using observational and digital magnetic resonance imaging assessment methods.

RESULTS

Heavier lifetime occupational and leisure physical loading was associated with greater disc degeneration in the upper lumbar levels (P = 0.055 - 0.001), whereas sedentary work was associated with lesser degeneration (P = 0.006). These univariate associations did not reach statistical significance in the lower lumbar region. In multivariate analyses of the upper lumbar levels, the mean job code explained 7% of the variability in observational disc degeneration scores; the addition of age explained 16%, and familial aggregation improved the model such that 77% of the variability was explained. In the lower lumbar levels, leisure time physical loading entered the multivariate model, explaining 2% of the variability. Adding age explained 9%, and familial aggregation raised the variability in disc degeneration scores explained to 43%.

CONCLUSIONS

The present study findings suggest that disc degeneration may be explained primarily by genetic influences and by unidentified factors, which may include complex, unpredictable interactions. The particular environmental factors studied, which have been among those most widely suspected of accelerating disc degeneration, had very modest effects.

Similarities in degenerative findings on magnetic resonance images of the lumbar spines of identical twins

Although the etiology of most degenerative changes in the lumbar spine is unclear, genetic factors may play an important role. To investigate this link, we reviewed magnetic resonance images of the lumbar spines of identical twins to assess the degree of similarities in degenerative findings in the discs. Observers who were blinded to twinship evaluated sagittal T1-weighted and T2-weighted magnetic resonance images of the lumbar spines of forty male identical twins (twenty pairs) with respect to changes in the end plates, desiccation of the discs, bulging or herniated discs, and decrease in the height of the disc space. Similarities between co-twins were significantly greater than would be expected by chance. Whereas smoking status and age explained 0 to 15 per cent of the variability in the various degenerative findings in the discs, 26 to 72 per cent of the variability was explained with the addition of a variable representing co-twin status. These findings are compatible with a marked genetic influence and warrant further investigation.

Correlations of isokinetic and psychophysical back lift and static back extensor endurance tests in men

Isokinetic lift, psychophysical lift, and static back endurance tests are among the most widely used measurements of muscle function for determining risk for, and recovery from, back problems. After determining test repeatability we examined the degree of association between these test measures in 100 men selected to represent a variety of occupations and lifestyles. Isokinetic lifting had low correlations with test results for psychophysical lifting (r = 0.28) and static back endurance (r = 0.24). Static back endurance and psychophysical lift test results were not at all correlated (r = 0.03). RELEVANCE--:Muscle function measurements for back problems are sometimes arbitrarily selected due to health practioners' beliefs and preferences or practical reasons such as the availability of equipment. Yet little is known about the associations of these tests with one another or with anthropometric factors. The data presented in this study document that isokinetic lift, psychophysical lift, and static back endurance tests appear to measure very different aspects of muscle function, and comparing studies using these different test methods should be approached with these low inter-test correlations in mind.

Changes in occupational physical loading during the lifetimes of Finnish men

OBJECTIVES

The aims of this study were to compare summary measures for occupational physical loading based on different periods of work history and to describe how loading exposures change with age and vary by age group.

METHODS

Detailed work histories reported by 232 men, aged 35-69 years, were used to compare loading in the current, longest, and heaviest jobs and a lifetime measure and to graph changes in loading over time.

RESULTS

The longest job was the best surrogate for lifetime loading (correlation coefficient 0.90). The heaviest work tended to occur in the men's teens and early twenties. For older men, the current or longest job was a poor substitute for the job with the heaviest loading (correlation coefficients 0.24, 0.28). There appeared to be both a cohort and a period effect for sedentary work, lifting and time spent in twisted or bent positions, but not for driving.

CONCLUSIONS

If the true risk for back problems is not limited to current activities, exposure misclassification may occur in many studies.

Comparison of foot and hand reaction times among men: a methodologic study using simple and multiple-choice repeated measurements

The primary study goal was to compare visual simple and choice reaction times of the hand and foot to assess validity of measurements for evaluating subjects' ability to perform rapid, controlled movements. First, we examined the repeatability (N = 34) for four different data-sampling methods from a series of 12 trials within sessions and between two test sessions. Simple and choice reaction times with the preferred hand and both feet were then compared among 153 healthy male volunteers aged 35 to 67 years. Pearson correlations for hand and ipsilateral and contralateral foot reaction times on simple and choice tasks (.53 to .80, p < .001) showed that psychomotor foot reaction time is a valid method for study of neuromuscular control of lower extremities.

Observer variability in the assessment of disc degeneration on magnetic resonance images of the lumbar and thoracic spine

STUDY DESIGN

Intraobserver and interobserver reproducibility study.

OBJECTIVE

This study investigates the variability in the interpretation of degenerative disc findings using magnetic resonance imaging.

SUMMARY OF BACKGROUND DATA

Magnetic resonance imaging has been used for years in clinical diagnostics, primarily to investigate disc herniation and spinal stenosis. Less attention has been paid to other disc findings and their assessment reliability.

METHODS

Three independent readers evaluated magnetic resonance images of the lumbar and the lower and middle thoracic spines of 122 subjects by grading 12 aspects of the intervertebral discs and adjacent endplates using written definitions and example images. Images of 20 subjects were reevaluated for the assessment of intraobserver agreement.

RESULTS

Agreement was highest in the lower lumbar and poorest in the middle thoracic spine. Intraobserver agreement was generally fair to excellent for almost all variables in the lumbar and lower thoracic spine (most intraclass correlation and kappa coefficients for these regions were above 0.70). Interobserver agreement was notably lower than intraobserver agreement, except for osteophytes and endplate defects in some regions.

CONCLUSIONS

Intraobserver agreement in the evaluation of disc degeneration was at an acceptable level, in general, in the lumbar and lower thoracic spine. However, assessments were substantially more variable between readers, which limits comparisons of evaluations between different readers.

Magnetic resonance imaging findings and their relationships in the thoracic and lumbar spine. Insights into the etiopathogenesis of spinal degeneration

STUDY DESIGN

Descriptive epidemiologic study about magnetic resonance imaging findings in the spine.

OBJECTIVES

To describe the prevalence of magnetic resonance imaging findings in a general population at spinal levels T6-S1, and to examine the relationships of these findings within each spinal level and between levels.

SUMMARY OF BACKGROUND DATA

The prevalence of specific findings and the associations between findings and spinal levels can provide general insights into the etiopathogenesis of spinal degeneration.

METHODS

Subjects consisted of 232 men from a population sample (mean age 49.3 years). Signal intensity, disc bulging, disc herniation, and endplate irregularities were among 11 findings assessed from magnetic resonance images.

RESULTS

The disc signal intensities were assessed to be lowest in the lumbar and middle thoracic regions. Disc bulging and disc height narrowing were most common in the lower levels of both the thoracic and lumbar regions. All magnetic resonance imaging findings except herniations and endplate irregularities were clearly associated with age. Osteophytes were most highly associated with disc bulging in levels T6-L3, and with endplate irregularities in the lower lumbar levels. Disc herniations were not consistently associated with any other findings. The disc levels that most highly correlated are grouped as follows: T6-T10, T10-L4, and L4-S1.

CONCLUSIONS

With the exception of endplate irregularities and herniations, the magnetic resonance imaging findings appeared to be associated with the same pathogenic process. The interaction of mechanical factors and spinal structures varies between spinal levels, and the degeneration common in the lower parts of the thoracic and lumbar spine could be an outcome of vulnerability for torsional forces. Some gross guidelines for grouping findings can be drawn from disc level correlations.

The Australian Schools Health and Fitness Survey. Physical fitness related to blood pressure but not lipoproteins

BACKGROUND

Recent research indicates that levels of conventional coronary heart disease risk factors in children are related to the premature development of atheroma. It is therefore important to determine how risk factors might be modified on a population scale in children.

METHODS AND RESULTS

In 1985, the Australian Schools Health and Fitness Survey was conducted on a representative sample of Australian schoolchildren aged 7 to 15 years. In children aged 9, 12, and 15, data on plasma cholesterol, triglycerides, and high-density lipoprotein cholesterol were obtained along with measurements of blood pressure, fitness, and body fatness. From an original sample of 2400 in these three age categories 1919 underwent the full set of measurements. Univariate analysis of these data revealed a strong association between body fatness and plasma lipids. There was no significant association between fitness (measured as physical work capacity at a heart rate of 170 beats per minute per kilogram of lean body mass) and plasma lipids, but a significant negative association was found for fitness and systolic blood pressure (r = -.12, P < .001). Multiple regression analysis revealed that the association of fitness with systolic blood pressure was only partly accounted for by the confounding effect of lower body fatness in fitter children.

CONCLUSIONS

These data collected on a representative sample of children under standardized conditions confirm a previous finding of a link between fitness and blood pressure in schoolchildren and also support a growing consensus that fitness is only weakly linked to plasma lipids and lipoproteins in children and adolescents.

Factors potentiating the risk of sudden infant death syndrome associated with the prone position

BACKGROUND

In several studies the sudden infant death syndrome (SIDS) has been significantly associated with sleeping in the prone position. It is not known how the prone position increases the risk of SIDS.

METHODS

We analyzed data from a case-control study (58 infants with SIDS and 120 control infants) and a prospective cohort study (22 infants with SIDS and 213 control infants) in Tasmania. Interactions were examined in matched analyses with a multiplicative model of interaction.

RESULTS

In the case-control study, SIDS was significantly associated with sleeping in the prone position, as compared with other positions (unadjusted odds ratio, 4.5; 95 percent confidence interval, 2.1 to 9.6). The strength of this association was increased among infants who slept on natural-fiber mattresses (P = 0.05), infants who were swaddled (P = 0.09), infants who slept in heated rooms (P = 0.006), and infants who had had a recent illness (P = 0.02). These variables had no significant effect on infants who did not sleep in the prone position. A history of recent illness was significantly associated with SIDS among infants who slept prone (odds ratio, 5.7; 95 percent confidence interval, 1.8 to 19) but not among infants who slept in other positions (odds ratio, 0.83). In the cohort study, the risk of SIDS was greater among infants who slept prone on natural-fiber mattresses (odds ratio, 6.6; 95 percent confidence interval, 1.3 to 33) than among infants who slept prone on other types of mattresses (odds ratio, 1.8).

CONCLUSIONS

When infants sleep prone, the elevated risk of SIDS is increased by each of four factors: the use of natural-fiber mattresses, swaddling, recent illness, and the use of heating in bedrooms.

A comparison of prospective and retrospective responses on sudden infant death syndrome by case and control mothers

Based on information from two studies of sudden infant death syndrome (SIDS) from 1988-1991 in Tasmania, Australia, prospective and retrospective maternal responses to an identical set of questions were compared for 27 cases and 25 controls. There was good agreement on demographic factors, maternal obstetric history, parental smoking, and infant feeding practices. Reported changes in sleep habits were slightly greater for cases, and further work is needed to determine if this reflects recall bias or real changes during early infant life. Case mother reports regarding family history of disease and infant bedding were more discrepant, suggesting recall bias and supporting prospective collection of this information.

Thermal environment and sudden infant death syndrome: case-control study

OBJECTIVE

To compare the thermal environment of infants who died of the sudden infant death syndrome with that of age matched control infants.

DESIGN

Case-control study. Infants who died were matched with two controls, one for age and one for age and birth weight. Thermal measurements were conducted at the death scene for cases and at the scene of last sleep for control infants, who were visited unexpectedly within four weeks of the index infant's death on a day of similar climatic conditions. A follow up questionnaire was administered to parents of cases and controls.

SETTING

The geographical area served by the professional Tasmanian state ambulance service, which includes 94% of the Tasmanian population.

SUBJECTS

41 infants died of the sudden infant death syndrome at home; thermal observations at death scene were available for 28 (68%), parental questionnaire data were available for 40 (96%). 38 controls matched for age and 41 matched for age and birth weight.

RESULTS

Cases had more excess thermal insulation for their given room temperature (2.3 togs) than matched controls (0.6 togs) (p = 0.009). For every excess thermal insulation unit (tog) the relative risk of the sudden infant death syndrome was 1.26 (95% confidence interval 1.05 to 1.52). The average thermal bedding value calculated from parental recall was similar to that observed by attendant ambulance officers (mean difference = 0.4 tog, p = 0.39). Cases were more likely to have been found prone (odds ratio 4.58; 1.48 to 14.11). Prone sleeping position was not a confounder or effect modifier of the relation between excess thermal insulation and the syndrome.

CONCLUSIONS

Overheating and the prone sleeping position are independently associated with an increased risk of the sudden infant death syndrome. Further work on infant thermal balance and sudden infant death is required and guidelines for appropriate infant thermal care need to be developed.

Characteristics of the infant thermal environment in the control population of a case-control study of SIDS

This report examines the thermal environment during last sleep of a control population to investigate how the thermal environment of the infant's bedroom varies by season, external temperature and by certain maternal and infant characteristics. Two age-matched control infants were chosen for each case, one of which was also matched on birthweight. The home visits were not pre-arranged and were matched on climatic conditions, time of year and time period of day for the index case. The initial response rate for controls (n = 108) was 86%. Although there was a large amount of variation in the infant thermal environment, thermal insulation correlated with room temperature (r = -0.44, P = 0.0001) and external temperature (r = -0.30, P = 0.002). The thermal environment of the infant, as defined by excess thermal insulation for room temperature, did not vary by indoor or outdoor temperature, but higher average values were observed in teenage mothers (mean difference = 2.7 tog [95% Cl = 0.3, 5.2]), infants who slept in an adult bed (mean difference = 2.6 tog [-0.1, 5.4]) and infants with an illness (mean difference = 0.8 tog [-0.3, 1.9]). There was a tendency for the thermal environment of infants to be higher and more variable during winter, supporting previous hypotheses that paradoxical overheating may occur in some infants during winter. Further work is required to provide a set of recommendations on the optimal thermal conditions for post-neonatal infants.

Prone sleeping position and SIDS: evidence from recent case-control and cohort studies in Tasmania

The most recent data from the cohort and case-control studies of SIDS and prone position recently reported from Tasmania are reviewed. The cohort analysis was based on 4103 infants born between 1 January 1988 and 1 December 1990 assessed as being at high risk at birth, of whom 29 later died of SIDS. A matched analysis which controlled for infant birthweight and maternal age indicated that prone sleeping position was associated with an increased risk of SIDS (OR 3.92, 95% Cl [1.37-11.24]). The case-control study was based on all (n = 55) Tasmanian SIDS death from October 1989 to April 1991 and matched live controls. The unadjusted odds ratio for prone position and SIDS was 5.04 (95% Cl [2.29-11.11]). The population attributable risk percentage, based on the high risk cohort data, was 0.38 (95% Cl [0.35-0.41]), suggesting that a significant reduction in SIDS incidence might occur if the prevalence of the prone sleeping position in the infant population were reduced. Other factors which may be important for the development of any public health interventions to reduce SIDS based on these findings are discussed.

Prospective cohort study of prone sleeping position and sudden infant death syndrome

Studies of the link between prone sleeping position and sudden infant death syndrome have been criticised on grounds of recall bias and for not taking into account possible confounding effects. To avoid recall bias and to allow measurement of important biological factors a prospective cohort study of the cause of sudden infant death syndrome (SIDS) is being conducted. The infants included are those at high risk of the syndrome as assessed by a perinatal score. Of the 3110 members of the cohort born between January, 1988, and end of March, 1990, 23 infants later died of SIDS. Sleep position information was available for 15 of these. Matched analysis to control for the confounding effects of infant birthweight and maternal age indicated that prone sleeping position was associated with an increased risk of SIDS (OR 4.47 95% Cl [1.30-15.43]). The findings are strengthened by the results of a concurrent retrospective case-control study of 42 SIDS cases in which the prone position was also associated with an increased risk of SIDS (unadjusted OR 3.45 [1.59-7.49]).