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Biomedical subjects

J A Stevens

Publications and source records attributed to J A Stevens.

At least 19 recordsLinked to original sources
PubMed2007

Motor imagery of gait: a quantitative approach.

Motor imagery (MI) is widely used to study cognitive aspects of the neural control of action. Prior studies were mostly centred on hand and arm movements. Recently a few studies have used imagery tasks to explore the neurophysiology of human gait, but it remains unclear how to ascertain whether subjects actually perform imagery of gait as requested. Here we describe a new experimental protocol to quantify imagery of gait, by behaviourally distinguishing it from visual imagery (VI) processes and by showing its temporal correspondence with actual gait. Fourteen young healthy subjects performed two imagery tasks and an actual walking (AW) task. During both imagery tasks subjects were sitting on a chair and faced a computer screen that presented photographs of walking trajectories. During one task (MI), subjects had to imagine walking along the walking trajectory. During the other task (VI), subjects had to imagine seeing a disc moving along the walking trajectory. During the AW task, subjects had to physically walk along the same walking trajectory as presented on the photographs during the imagery tasks. We manipulated movement distance by changing the length of the walking trajectory, and movement difficulty by changing the width of the walking trajectory. Subjects reported onset and offset of both actual and imagined movements with a button press. The time between the two button presses was taken as the imagined or actual movement time (MT). MT increased with increasing path length and decreasing path width in all three tasks. Crucially, the effect of path width on MT was significantly stronger during MI and AW than during VI. The results demonstrate a high temporal correspondence between imagined and AW, suggesting that MI taps into similar cerebral resources as those used during actual gait. These results open the possibility of using this protocol for exploring neurophysiological correlates of gait control in humans.

Adult↗
PubMed2006

The costs of fatal and non-fatal falls among older adults.

OBJECTIVE: To estimate the incidence and direct medical costs for fatal and non-fatal fall injuries among US adults aged >or=65 years in 2000, for three treatment settings stratified by age, sex, body region, and type of injury. METHODS: Incidence data came from the 2000 National Vital Statistics System, 2001 National Electronic Injury Surveillance System-All Injury Program, 2000 Health Care Utilization Program National Inpatient Sample, and 1999 Medical Expenditure Panel Survey. Costs for fatal falls came from Incidence and economic burden of injuries in the United States; costs for non-fatal falls were based on claims from the 1998 and 1999 Medicare fee-for-service 5% Standard Analytical Files. A case crossover approach was used to compare the monthly costs before and after the fall. RESULTS: In 2000, there were almost 10 300 fatal and 2.6 million medically treated non-fatal fall related injuries. Direct medical costs totaled 0.2 billion dollars for fatal and 19 billion dollars for non-fatal injuries. Of the non-fatal injury costs, 63% (12 billion dollars ) were for hospitalizations, 21% (4 billion dollars) were for emergency department visits, and 16% (3 billion dollars) were for treatment in outpatient settings. Medical expenditures for women, who comprised 58% of the older adult population, were 2-3 times higher than for men for all medical treatment settings. Fractures accounted for just 35% of non-fatal injuries but 61% of costs. CONCLUSIONS: Fall related injuries among older adults, especially among older women, are associated with substantial economic costs. Implementing effective intervention strategies could appreciably decrease the incidence and healthcare costs of these injuries.

Accidental Falls↗
PubMed2005

Interference effects demonstrate distinct roles for visual and motor imagery during the mental representation of human action.

Four experiments were completed to characterize the utilization of visual imagery and motor imagery during the mental representation of human action. In Experiment 1, movement time functions for a motor imagery human locomotion task conformed to a speed-accuracy trade-off similar to Fitts' Law, whereas those for a visual imagery object motion task did not. However, modality-specific interference effects in Experiment 2 demonstrate visual and motor imagery as cooperative processes when the action represented is tied to visual coordinates in space. Biomechanic-specific motor interference effects found in Experiment 3 suggest one basis for separation of processing channels within motor imagery. Finally, in Experiment 4 representations of motor actions were found to be generated using only visual imagery under certain circumstances: namely, when the imaginer represented the motor action of another individual while placed at an opposing viewpoint. These results suggest that the modality of representation recruited to generate images of human action is dependent on the dynamic relationship between the individual, movement, and environment.

Adolescent↗
PubMed2005

Gender differences for non-fatal unintentional fall related injuries among older adults.

OBJECTIVES: To quantify gender differences for non-fatal unintentional fall related injuries among US adults age 65 years and older treated in hospital emergency departments (EDs). METHODS: The authors analyzed data from a nationally representative sample of ED visits for January 2001 through December 2001, available through the National Electronic Injury Surveillance System All Injury Program (NEISS-AIP). For each initial ED visit, coders record one principal diagnosis (usually the most severe) and one primary part of the body affected. RESULTS: Based on 22,560 cases, an estimated 1.64 million older adults were treated in EDs for unintentional fall injuries. Of these, approximately 1.16 million, or 70.5%, were women. Fractures, contusions/abrasions, and lacerations accounted for more than three quarters of all injuries. Rates for injury diagnoses were generally higher among women, most notably for fractures which were 2.2 times higher than for men. For all parts of the body, women's injury rates exceeded those of men. Rate ratios were greatest for injuries of the leg/foot (2.3), arm/hand (2.0), and lower trunk (2.0). The hospitalization rate for women was 1.8 times that for men. CONCLUSIONS: Among older adults, non-fatal fall related injuries disproportionately affected women. Much is known about effective fall prevention strategies. We need to refine, promote, and implement these interventions. Additional research is needed to tailor interventions for different populations and to determine gender differences in the underlying causes and/or circumstances of falls. This information is vital for developing and implementing targeted fall prevention strategies.

Accidental Falls↗
PubMed2004

Recreational injuries among older Americans, 2001.

OBJECTIVE: To describe the epidemiology of non-fatal recreational injuries among older adults treated in United States emergency departments including national estimates of the number of injuries, types of recreational activities, and diagnoses. METHODS: Injury data were provided by the National Electronic Injury Surveillance System-All Injury Program (NEISS-AIP), a nationally representative subsample of 66 out of 100 NEISS hospitals. Potential cases were identified using the NEISS-AIP definition of a sport and recreation injury. The authors then reviewed the two line narrative to identify injuries related to participation in a sport or recreational activity among men and women more than 64 years old. RESULTS: In 2001, an estimated 62 164 (95% confidence interval 35 570 to 88 758) persons >/=65 years old were treated in emergency departments for injuries sustained while participating in sport or recreational activities. The overall injury rate was 177.3/100 000 population with higher rates for men (242.5/100 000) than for women (151.3/100 000). Exercising caused 30% of injuries among women and bicycling caused 17% of injuries among men. Twenty seven percent of all treated injuries were fractures and women (34%) were more likely than men (21%) to suffer fractures. CONCLUSIONS: Recreational activities were a frequent cause of injuries among older adults. Fractures were common. Many of these injuries are potentially preventable. As more persons engage in recreational activities, applying known injury prevention strategies will help to reduce the incidence of these injuries.

Age Distribution↗
PubMed2003

The formation of cluster elliptical galaxies as revealed by extensive star formation.

The most massive galaxies in the present-day Universe are found to lie in the centres of rich clusters. They have old, coeval stellar populations suggesting that the bulk of their stars must have formed at early epochs in spectacular starbursts, which should be luminous phenomena when observed at submillimetre wavelengths. The most popular model of galaxy formation predicts that these galaxies form in proto-clusters at high-density peaks in the early Universe. Such peaks are indicated by massive high-redshift radio galaxies. Here we report deep submillimetre mapping of seven high-redshift radio galaxies and their environments. These data confirm not only the presence of spatially extended regions of massive star-formation activity in the radio galaxies themselves, but also in companion objects previously undetected at any wavelength. The prevalence, orientation, and inferred masses of these submillimetre companion galaxies suggest that we are witnessing the synchronous formation of the most luminous elliptical galaxies found today at the centres of rich clusters of galaxies.

Journal Article↗
PubMed2002

Motor vehicle and fall related deaths among older Americans 1990-98: sex, race, and ethnic disparities.

OBJECTIVES: To examine differences in motor vehicle and fall related death rates among older adults by sex, race, and ethnicity. METHODS: Annual mortality tapes for 1990-98 provided demographic data including race and ethnicity, date, and cause of death. Trend analyses were conducted using Poisson regression. RESULTS: From 1990-98, overall motor vehicle related death rates remained stable while death rates from unintentional falls increased. Motor vehicle and fall related death rates were higher among men. Motor vehicle related death rates were higher among people of color while fall related death rates were higher among whites. Among whites, fall death rates increased significantly during the study period, with an annual relative increase of 3.6% for men and 3.2% for women. CONCLUSIONS: The risk of death from motor vehicle and fall related injuries among older adults differed by sex, race and ethnicity, results obscured by simple age and sex specific death rates. This study found important patterns and disparities in these death rates by race and ethnicity useful for identifying high risk groups and guiding prevention strategies.

Accidental Falls↗
PubMed2001

Submillimeter evidence for the coeval growth of massive black holes and galaxy bulges.

The correlation, found in nearby galaxies, between black hole mass and stellar bulge mass implies that the formation of these two components must be related. Here we report submillimeter photometry of eight x-ray-absorbed active galactic nuclei that have luminosities and redshifts characteristic of the sources that produce the bulk of the accretion luminosity in the universe. The four sources with the highest redshifts are detected at 850 micrometers, with flux densities between 5.9 and 10.1 millijanskies, and hence are ultraluminous infrared galaxies. If the emission is from dust heated by starbursts, then the majority of stars in spheroids were formed at the same time as their central black holes built up most of their mass by accretion. This would account for the observed demography of massive black holes in the local universe. The skewed rate of submillimeter detection with redshift is consistent with a high redshift epoch of star formation in radio-quiet active galactic nuclei, similar to that seen in radio galaxies.

Journal Article↗
PubMed2001

The public health perspective in health promotion and disability prevention for older adults: the role of the Centers for Disease Control and Prevention.

As the United States federal public health agency, the role of the Centers for Disease Control and Prevention (CDC) in health promotion and disability prevention with older adults encompasses research, surveillance and program activities in aging. This article characterizes the objectives and context of prevention in later life and summarizes CDCs functions, collaborative partnerships with public health agencies and other organizations, and range of activities in older adult health. As a major focus of these efforts, chronic disease risk reduction is examined through CDC's efforts in the area of physical activity; a longitudinal investigation of osteoarthritis in an older biracial rural population; and chronic illness self-management programs as a prototype for secondary prevention. Other CDC activities highlighted include addressing the burden of vaccine-preventable diseases through CDC-funded programs to improve immunization coverage in older adults, and falls prevention interventions and resources. Future directions in aging at CDC are also outlined.

Accidental Falls↗
PubMed2000

Reducing falls and resulting hip fractures among older women.

SCOPE OF THE PROBLEM: Fall-related injuries are the leading cause of injury deaths and disabilities among older adults (i.e., persons aged > or = 65 years). The most serious fall injury is hip fracture; one half of all older adults hospitalized for hip fracture never regain their former level of function. In 1996, a total of 340,000 hospitalizations for hip fracture occurred among persons aged > or = 65 years, and 80% of these admissions occurred among women. From 1988 to 1996, hip fracture hospitalization rates for women aged > or = 65 years increased 23%. ETIOLOGIC OR RISK FACTORS: Risk factors for falls include increasing age, muscle weakness, functional limitations, environmental hazards, use of psychoactive medications, and a history of falls. Age is also a risk factor for hip fracture. Women aged > or = 85 years are nearly eight times more likely than women aged 65-74 years to be hospitalized for hip fracture. White women aged > or = 65 years are at higher risk for hip fracture than black women. Other riskfactors for hip fracture include lack of physical activity, osteoporosis, low body mass index, and a previous hip fracture. RECOMMENDATIONS FOR PREVENTION: Because approximately 95% of hip fractures result from falls, minimizing fall risk is a practical approach to reducing these serious injuries. Research demonstrates that effective fall prevention strategies require a multifaceted approach with both behavioral and environmental components. Important elements include education and skill building to increase knowledge about fall risk factors, exercise to improve strength and balance, home modifications to reduce fall hazards, and medication assessment to minimize side effects (e.g., dizziness and grogginess). PROGRAM AND RESEARCH NEEDS: Coordination needs to be improved among the diverse Federal, state, and local organizations that conduct fall prevention activities. The effectiveness of existing fall prevention programs among specific groups of women (e.g., those aged > or = 85 years or living with functional limitations) needs careful evaluation. New primary fall prevention approaches are needed (e.g., characterizing footwear that promotes stability), as well as secondary prevention strategies (e.g., protective hip pads) that can prevent injuries when falls occur. Finally, efforts are needed to increase collaboration among national experts from various disciplines, to reach consensus regarding priority research areas and program issues, and to work toward long-term strategies for reducing falls and fall-related injuries among older adults. CONCLUSION: Persons aged > or = 65 years constitute the fastest-growing segment of the U.S. population. Without effective intervention strategies, the number of hip fractures will increase as the U.S. population ages. Fall prevention programs have reduced falls and fall-related injuries among high-risk populations using multifaceted approaches that include education, exercise, environmental modifications, and medication review. These programs need to be evaluated among older adults aged > or = 65 years who are living independently in the community. In addition, secondary prevention strategies are needed to prevent hip fractures when falls occur. Effective public health strategies need to be implemented to promote behavioral changes, improve current interventions, and develop new fall prevention strategies to reduce future morbidity and mortality associated with hip fractures among older adults.

Accident Prevention↗
PubMed2000

New aspects of motion perception: selective neural encoding of apparent human movements.

Perception of apparent motion operates somewhat differently for objects and human figures. Depending on the interstimulus interval, the latter d may give rise to either perception of a direct path (i.e. biologically impossible) or indirect path (i.e. biologically possible). Here, PET was used to investigate whether a change in brain activity accompanies this perceptual shift. We found neural encoding of apparent motion to be a function of the intrinsic properties of the stimulus presented (object vs human) as well as the kind of human movement path perceived (biomechanically possible vs impossible). Motor and parietal cortex were only involved for possible motion which suggests that these regions are selectively activated to process actions which conform to the capabilities of the observer.

Adult↗
PubMed1999

Surveillance for injuries and violence among older adults.

PROBLEM/CONDITION: Injuries and violence are major causes of disability and death among adults aged > or =65 years in the United States. Injuries impair older adults' quality of life and result in billions of dollars in health-care expenditures each year. REPORTING PERIOD: This report reviews 1987-1996 data regarding fall-related deaths, 1988-1996 data on hospitalizations for hip fracture, 1990-1997 data regarding motor vehicle-related injuries, 1990-1996 data on suicides, and 1987-1996 data on homicides. DESCRIPTION OF SYSTEMS: Data on fall-related deaths, suicides, and homicides are from the National Center for Health Statistics annual mortality data tapes for 1987-1996. Homicide data are supplemented with information from the Federal Bureau of Investigation's Supplemental Homicide Reports for 1987-1996. Data on hospitalizations for hip fracture are from the 1988-1996 National Hospital Discharge Surveys. Information regarding motor vehicle-related injuries for 1990-1997 is from the National Highway Traffic Safety Administration's Fatality Analysis Reporting System and General Estimates System. RESULTS: Rates of fall-related deaths for older adults increased sharply with advancing age and were consistently higher among men in all age categories. Men were 22% more likely than women to sustain fatal falls. A trend of increasing rates of fall-related deaths was observed from 1987 through 1996 in the United States, although rates were consistently lower for women throughout this period. Rates of hospitalizations for hip fracture differed by age and were higher for white women than for other groups. Rates increased with advancing age for both sexes but were consistently higher for women in all age categories. U.S. hospitalization rates for hip fracture increased for women from 1988 through 1996 while the rates for men remained stable. Rates of motor vehicle-related injuries increased slightly from 1990 through 1997, and marked variations in state-specific death rates were observed; in most states, older men had death rates approximately twice those for older women. Although suicide rates remain higher among older adults than among any other age group, rates of suicide among adults aged > or =65 years decreased 16% during the study period. Suicide rates among older adults varied by sex and age group. Homicide rates declined 36% among older adults. Homicide rates were highest for black men, followed by black women and white men; the homicide risk for blacks relative to whites decreased from 4.8 to 3.9 per 100,000 persons, indicating that the gap between rates for blacks and whites is closing. Half of the older homicide victims were killed by someone they knew. INTERPRETATION: The increase in rates of fall-related deaths and hip fracture hospitalizations from 1988 through 1996 might reflect a change in the proportion of adults aged > or =85 years compared with those aged 65-84 years - a change that results, in part, from reduced mortality from cardiovascular and other chronic diseases. Fall-related death rates might be higher among older men because they often have a higher prevalence of comorbid conditions than women of similar age. Racial differences in hospitalization rates might have some underlying biologic basis; the prevalence of osteoporosis, a condition that contributes to reduced bone mass and increased bone fragility, is greatest among older white women. Compared with whites aged > or =65 years, blacks of comparable ages have greater bone mass and are less likely to sustain fall-related hip fractures. Additional studies are needed to determine why rates of motor vehicle-related injury have increased slightly among older adults and why these rates vary by state. Declining rates of suicide among older adults might be related to changes in the effect or type of risk factors traditionally observed in this age group. Research is needed to identify reasons for variations in suicide rates among older persons. Homicides among olde

Accidental Falls↗
PubMed1999

Sceptical medicine.

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Academic Medical Centers↗
PubMed1998

Client perceptions of a rural-based cardiac rehabilitation program: a grounded theory approach.

A grounded theory approach was used in an attempt to generate theory about client perceptions and experiences of a cardiac rehabilitation program conducted in a rural community. A series of interviews was conducted with a selection of people who had experienced a life-threatening cardiac event. The cohort was divided into two groups: those who attended a cardiac rehabilitation program and those who did not. The findings, though not generalisable, allowed the generation of a number of theories (which may come to be the genesis of future research) regarding the differences in the physiological, psychological, sociological and vocational well-being between the groups. The findings also suggested that location of the program, the times it was conducted, and the communication skills of significant healthcare workers who recruited participants were important factors affecting attendance.

Aged↗
PubMed1997

The short-term natural history of irritable bowel syndrome: a time-series analysis.

Although researchers have studied irritable bowel syndrome (IBS), including its physiological and psychological characteristics and treatments' effectiveness, basic descriptive information about IBS has been limited to lists of symptoms and explanations of what IBS is not. The purpose of the present study is to describe how core IBS symptoms vary over time. Twenty-five subjects (17 females, 8 males), who were not receiving treatment for IBS, rated the severity of their IBS symptoms daily for 8 weeks. Four symptoms' (abdominal pain, abdominal tenderness, constipation and diarrhea) ratings were slimmed to create a primary IBS symptom score. The data were detrended, then a time-series analysis was performed. Many subjects' IBS severity was predictable over more than one day, and symptoms tended to occur in clusters rather than randomly. Anxiety and depression were slightly to moderately correlated with IBS variables, but virtually all of these correlations were nonsignificant.

Adult↗