Effect of trabecular bone loss on cortical strain rate during impact in an in vitro model of avian femur

BACKGROUND: Osteoporotic hip fractures occur due to loss of cortical and trabecular bone mass and consequent degradation in whole bone strength. The direct cause of most fractures is a fall, and hence, characterizing the mechanical behavior of a whole osteopenic bone under impact is important. However, very little is known about the mechanical interactions between cortical and trabecular bone during impact, and it is specifically unclear to what extent epiphyseal trabecular bone contributes to impact resistance of whole bones. We hypothesized that trabecular bone serves as a structural support to the cortex during impact, and hence, loss of a critical mass of trabecular bone reduces internal constraining of the cortex, and, thereby, decreases the impact tolerance of the whole bone. METHODS: To test this hypothesis, we conducted cortical strain rate measurements in adult chicken's proximal femora subjected to a Charpy impact test, after removing different trabecular bone core masses to simulate different osteopenic severities. RESULTS: We found that removal of core trabecular bone decreased by ~10-fold the cortical strain rate at the side opposite to impact (p < 0.01), i.e. from 359,815 ± 1799 μm/m per second (mean ± standard error) for an intact (control) specimen down to 35,997 ± 180 μm/m per second where 67% of the total trabecular bone mass (~0.7 grams in adult chicken) were removed. After normalizing the strain rate by the initial weight of bone specimens, a sigmoid relation emerged between normalized strain rate and removed mass of trabecular bone, showing very little effect on the cortex strain rate if below 10% of the trabecular mass is removed, but most of the effect was already apparent for less than 30% trabecular bone loss. An analytical model of the experiments supported this behavior. CONCLUSION: We conclude that in our in vitro avian model, loss of over 10% of core trabecular bone substantially altered the deformation response of whole bone to impact, which supports the above hypothesis and indicates that integrity of trabecular bone is critical for resisting impact loads

EXECUTIVE FUNCTION SUBCOMPONENTS AND THEIR RELATIONS TO EVERYDAY FUNCTIONING IN HEALTHY OLDER ADULTS

Everyday functioning and its executive functioning cognitive correlates were investigated in healthy older adults (HOAs) using multiple methods of functional status. We were especially interested in the contributions of both process pure and traditional measures of the executive function subcomponents of switching, inhibition, and updating. Seventy HOAs (45 young-old and 25 old-old) and 70 younger adults completed executive function and neuropsychological tests. In addition to self- and informant questionnaires of functional abilities, HOAs completed two performance-based measures. An aging effect was found on all executive function measures. Old-old older adults and their informants did not report more functional difficulties, but demonstrated more difficulties on performance-based measures relative to young-old participants. For the HOAs, after controlling for age and education, the traditional, but not process pure, executive function measures explained a significant amount of variance in the informant-report and both performance-based measures. Updating measures differentially predicted performance-based measures, while switching was a unique predictor of informant-report and problem-solving measures. These findings highlight the importance of taking a fractionated approach to the study of executive functioning and functional status, and suggest that switching and updating abilities may contribute to age-related decline of everyday functioning in HOAs

Naturalistic assessment of executive function and everyday multitasking in healthy older adults

Everyday multitasking and its cognitive correlates were investigated in an older adult population using a naturalistic task, the Day Out Task. Fifty older adults and 50 younger adults prioritized, organized, initiated, and completed a number of subtasks in a campus apartment to prepare for a day out (e.g., gather ingredients for a recipe, collect change for a bus ride). Participants also completed tests assessing cognitive constructs important in multitasking. Compared to younger adults, the older adults took longer to complete the everyday tasks and more poorly sequenced the subtasks. Although they initiated, completed, and interweaved a similar number of subtasks, the older adults demonstrated poorer task quality and accuracy, completing more subtasks inefficiently. For the older adults, reduced prospective memory abilities were predictive of poorer task sequencing, while executive processes and prospective memory were predictive of inefficiently completed subtasks. The findings suggest that executive dysfunction and prospective memory difficulties may contribute to the age-related decline of everyday multitasking abilities in healthy older adults

Bridging the gap between the old and young?

This study used a semantic differential scale to investigate the attitudes that students at Colorado State University hold toward older adults. The instrument evaluates specific attitudes held by college students. These attitudes are then compared to the level of interaction that students have had with older adults and the quality of that interaction. An initial investigation revealed that the level of interaction with older adults was positively correlated to a more positive attitude. This study aims to further investigate variables affecting this correlation, specifically quality of interaction versus quantity of interaction.College Honors

Naturalistic assessment of everyday functioning in individuals with mild cognitive impairment: the day-out task

The day-out task (DOT), a naturalistic task that requires multitasking in a real-world setting, was used to examine everyday functioning in individuals with mild cognitive impairment (MCI). Thirty-eight participants with MCI and 38 cognitively healthy older adult controls prioritized, organized, initiated, and completed a number of subtasks in a campus apartment to prepare for a day out (e.g., determine and gather change for bus, bring a magazine). Participants also completed tests assessing cognitive constructs important in multitasking (i.e., retrospective memory, prospective memory, planning). As compared with controls, the MCI group required more time to complete the DOT and demonstrated poorer task accuracy, performing more subtasks incompletely and inaccurately. Despite poorer DOT task accuracy, the MCI and control groups approached completion of the DOT in a similar manner. For the MCI group, retrospective memory was a unique predictor of the number of subtasks left incomplete and inaccurate, while prospective memory was a unique predictor of DOT sequencing. The DOT measures, but not the cognitive tests, were predictive of knowledgeable informant report of everyday functioning. THESE findings suggest that difficulty remembering and keeping track of multiple goals and subgoals may contribute to the poorer performance of individuals with MCI in complex everyday situations

Naturalistic assessment of everyday functioning in individuals with mild cognitive impairment: The day-out task.

OBJECTIVE: The Day Out Task (DOT), a naturalistic task that requires multitasking in a real-world setting, was used to examine everyday functioning in individuals with mild cognitive impairment (MCI). METHOD: Thirty-eight participants with MCI and 38 cognitively healthy older adult controls prioritized, organized, initiated and completed a number of subtasks in a campus apartment to prepare for a day out (e.g., determine and gather change for bus, bring a magazine). Participants also completed tests assessing cognitive constructs important in multitasking (i.e., retrospective memory, prospective memory, planning). RESULTS: Compared to controls, the MCI group required more time to complete the DOT and demonstrated poorer task accuracy, performing more subtasks incompletely and inaccurately. Despite poorer DOT task accuracy, the MCI and control groups approached completion of the DOT in a similar manner. For the MCI group, retrospective memory was a unique predictor of the number of subtasks left incomplete and inaccurate, while prospective memory was a unique predictor of DOT sequencing. The DOT measures, but not the cognitive tests, were predictive of knowledgeable informant report of everyday functioning. CONCLUSIONS: These findings suggest that difficulty remembering and keeping track of multiple goals and subgoals may contribute to the poorer performance of individuals with MCI in complex everyday situations

The night out task and scoring application: an ill-structured, open-ended clinic-based test representing cognitive capacities used in everyday situations.

OBJECTIVE: The night out task (NOT) was developed as a naturalistic, open-ended, multitasking measure that requires individuals to complete eight subtasks comparable to those encountered during real-world functioning (e.g., pack travel bag, prepare tea). We examined psychometric properties and administration feasibility of this direct observation measure within a clinic-like setting using a tablet-based coding application. METHOD: A sample of 148 community-dwelling older adults (82% cognitively healthy; 18% mild cognitive impairment) and 57 younger adults completed the NOT along with other neurocognitive tests and questionnaires. RESULTS: Inter-rater reliability across NOT primary (i.e., time, accuracy, efficiency) and process-related (e.g., error-types, self-corrections) variables was mostly excellent. NOT primary measures showed expected patterns of convergent and discriminant validity with measures of cognition, demographics, and well-being. External validity was established by the NOT ability to distinguish between age and diagnostic (cognitively healthy vs. mild cognitive impairment) groups. Demonstrating incremental validity, the NOT primary variables (execution time in particular) were predictive of self-reported functional abilities and completion quality of in-home everyday tasks over and earlier variables such as demographics, cognition, and mobility. CONCLUSIONS: These findings suggest that the NOT and its app interface, which allows for continuous logging of observations, are a feasible in-clinic measure to assess cognitive capacities important for real-world functioning. With further validation, the NOT may allow for earlier detection of functional difficulties. Understanding errors and strategies used during NOT performance could also have implications for individualized interventions