Dynamics of stability: the physiologic basis of functional health and frailty

Non-linear dynamical features of center of pressure extracted by recurrence quantification analysis in people with unilateral anterior cruciate ligament injury

Knowledge about the non-linear dynamical pattern of postural sway may provide important insights into the adaptability (flexibility) of human postural control in response to everyday stresses imposed on the body. A commonly used non-linear tool, i.e. recurrence quantification analysis, was chosen to investigate the effect of prior anterior cruciate ligament injury on the deterministic pattern of postural sway under different conditions of postural and cognitive difficulty. In double leg stance, as postural difficulty increased from open-eyes to closed-eyes and rigid-surface to foam-surface, the centre of pressure regularity (%determinism) increased as well. In comparison to healthy counterparts, subjects with prior anterior cruciate ligament injury produced more regularity when maintaining balance on their injured leg. Also, for both the double and single leg stance balance conditions, the performance of a secondary cognitive task (a backward digit span task) caused less center of pressure regularity than the single postural task, which suggests that both study populations required the same amount of cognitive involvement for maintaining balance. Center of pressure dynamic patterns exhibited by the anterior cruciate ligament deficient patients were more regular than those of the healthy controls indicating "complexity loss" and may be indicative of the reduced adaptability (flexibility) of a balance system to sudden perturbations.

Fatigue and motor redundancy: adaptive increase in finger force variance in multi-finger tasks

We studied the effects of fatigue of the index finger on indices of force variability in discrete and rhythmic accurate force production tasks performed by the index finger and by all four fingers pressing in parallel. An increase in the variance of the force produced by the fatigued index finger was expected. We hypothesized that the other fingers would also show increased variance of their forces, which would be accompanied by co-variation among the finger forces resulting in relatively preserved accuracy of performance. The subjects performed isometric tasks including maximal voluntary contraction (MVC) and accurate force production before and after a 1-min MVC fatiguing exercise by the index finger. During fatigue, there was a significant increase in the root mean square index of force variability during accurate force production by the index finger. In the four-finger tasks, the variance of the individual finger force increased for all four fingers, while the total force variance showed only a modest change. We quantified two components of variance in the space of hypothetical commands to fingers, finger modes. There was a large increase in the variance component that did not affect total force and a much smaller increase in the component that did. The results suggest an adaptive increase in force variance by nonfatigued elements as a strategy to attenuate effects of fatigue on accuracy of multi-element performance. These effects were unlikely to originate at the level of synchronization of motor units across muscle compartments but rather involved higher control levels.

Postural sway in low back pain: Effects of dual tasks

Recurrence quantification analysis (RQA), a nonlinear method of postural analysis, was used to explore the effects of dual-tasking on postural performance in people with nonspecific low back pain (LBP) compared with healthy participants. Postural performance was quantified by RQA % recurrence, % determinism, entropy and trend. People with nonspecific LBP (n=22) and unimpaired individuals (n=22) randomly performed quiet standing tasks with three levels of difficulty (rigid-surface eyes open, rigid-surface eyes closed and foam-surface eyes closed). These tasks were performed in isolation or concurrently with an easy or difficult cognitive task. Increasing postural difficulty was associated with higher % determinism, higher entropy and lower trend in anteroposterior (AP) and mediolateral (ML) directions in people with LBP and healthy participants. All RQA variables in the ML direction decreased as cognitive conditions became more difficult. Significant interactions between group and cognitive difficulty were shown for % recurrence, % determinism and trend in the AP direction. While healthy participants decreased % recurrence and trend by increasing the level of cognitive difficulty, the LBP patients did not. This preliminary study suggests that LBP may be one factor that modulates the posture-cognition interaction.

A frailty index to predict the mortality risk in a population of senior Mexican adults

BACKGROUND

Frailty in the elderly can be regarded as nonspecific vulnerability to adverse health outcomes, caused by multiple factors. The aim was to analyze the relationships between the frailty index, age and mortality in a two year follow up study of Mexican elderly.

METHODS

A frailty index was developed using 34 variables. To obtain the index, the mean of the total score for each individual was obtained. Survival analyses techniques were used to examine the risk ratios for the different levels of the frailty index. Kaplan-Meier estimates were obtained, adjusted for age and gender. Cox proportional hazards models were also built to obtain hazard ratio estimates.

RESULTS

A total of 4082 participants was analyzed. Participants had an average age of 73 years and 52.5% were women. On average, participants were followed-up for 710 days (standard deviation = 111 days) and 279 of them died. Mortality increased with the frailty index level, especially in those with levels between .21 to .65, reaching approximately 17% and 21%, respectively. Cox proportional hazards models showed that participants with frailty index levels associated to increased mortality (.21 and higher) represent 24.0% of those aged 65-69 years and 47.6% of those 85 and older.

CONCLUSION

The frailty index shows the properties found in the other studies, it allows stratifying older Mexican into several groups different by the degree of the risk of mortality, and therefore the frailty index can be used in assessing health of elderly.

The intersection of geriatrics and chronic kidney disease: frailty and disability among older adults with kidney disease

Older adults (aged >or=65 years) comprise the largest segment of the CKD population, and impaired kidney function is linked with unsuccessful aging. Individuals across the spectrum of kidney disease have clinical features of the frailty phenotype, suggesting that frailty is not confined to old age among vulnerable populations. This manifests as a high prevalence of impaired physical performance, emergent geriatric syndromes, disability, and risk of death. Considering the multiple system involvement underlying the symptoms and deficits seen in CKD, especially in the more severe stages, the concept of frailty is a highly useful tool to identify older adults with kidney disease who are on the trajectory of vulnerability leading to decline and death. Further work is needed to characterize the relationship between kidney disease and frailty and to identify opportunities to intervene.

Nonlinear analysis of ambulatory activity patterns in community-dwelling older adults

BACKGROUND

The natural ambulatory activity patterns of older adults are not well understood. User-worn monitors illuminate patterns of ambulatory activity and generate data suitable for analysis using measures derived from nonlinear dynamics.

METHODS

Ambulatory activity data were collected continuously from 157 community-dwelling older adults for 2 weeks. Participants were separated post hoc into groups based on the mean number of steps per day: highly active (steps > or = 10,000), moderately active (5,000 < or = steps < 10,000 steps), and inactive (steps <5,000 steps). Detrended fluctuation analysis (DFA), entropy rate (ER), and approximate entropy (ApEn) were used to examine the complexity of daily time series composed of 1-minute step count values. Coefficient of variation was used to examine time series variability. Between-group differences for each parameter were evaluated using analysis of variance.

RESULTS

All groups displayed patterns of fluctuating step count values containing complex temporal structure. DFA, ER, and ApEn parameter values increased monotonically and significantly with increasing activity level (p < .001). The variability of step count fluctuations did not differ among groups.

CONCLUSIONS

Highly active participants had more complex patterns of ambulatory activity than less active participants. The results supported the idea that, in addition to the volume of activity produced by an individual, patterns of ambulatory activity contain unique information that shows promise for offering insights into walking behavior associated with healthy aging.

Relationships of cardiac, pulmonary, and muscle reserves and frailty to exercise capacity in older women

BACKGROUND

A decline in exercise capacity (EC) is a characteristic of frailty. We hypothesized that decline is the effect of decrements in several physiological systems. We assessed whether the relationship of three main physiological systems-cardiac, pulmonary, and musculoskeletal-to EC is independent or interactive and whether their effect on EC varies with respect to frailty status.

METHODS

Observational study of 547 disabled women aged 65 years and older (Women's Health and Aging Study I) including 131 frail who participated in a test of EC. EC (seated step test), cardiac function (chronotropic index), pulmonary function (forced vital capacity, FVC), musculoskeletal function (quadriceps strength, QS), and frailty status were measured and interactive effects were modeled using linear regression and differentiation.

RESULTS

Each physiological system had a direct relationship with EC, which was lower in frail compared with nonfrail. The relationship between FVC and EC was positive and increased with increasing QS in nonfrail subjects. The effect of QS on EC was positive and increased with increasing FVC regardless of frailty. In subjects with low QS, frailty status was associated with lower EC and this effect became stronger with increasing FVC. Discussion Findings suggest but do not show that frailty status modifies the effects of physiological function in several systems on EC. Approaches to understanding emergent properties such as vulnerability to illness and death and clinical efforts to prevent and treat frailty should evaluate and possibly intervene on several physiological systems to be maximally effective.

Trajectories of dehydroepiandrosterone sulfate predict mortality in older adults: the cardiovascular health study

BACKGROUND

Dehydroepiandrosterone sulfate (DHEAS) has been proposed as an antiaging hormone, but its importance is unclear. Assessment of an individual's ability to maintain a DHEAS set point, through examination of multiple DHEAS levels over time, may provide insight into biologic aging.

METHODS

Using Cox proportional hazard models, we examined the relationship between DHEAS trajectory patterns and all-cause death in 950 individuals aged >or=65 years who were enrolled in the Cardiovascular Health Study and had DHEAS levels measured at three to six time points.

RESULTS

Overall, there was a slight decline in DHEAS levels over time (-0.013 microg/mL/y). Three trajectory components were examined: slope, variability, and baseline DHEAS. When examined individually, a steep decline or extreme variability in DHEAS levels was associated with higher mortality (p < .001 for each), whereas baseline DHEAS level was not. In adjusted models including all three components, steep decline (hazard ratio [HR] 1.75, confidence interval [CI] 1.32-2.33) and extreme variability (HR 1.89, CI 1.47-2.43) remained significant predictors of mortality, whereas baseline DHEAS level remained unpredictive of mortality (HR 0.97 per standard deviation, CI 0.88-1.07). The effect of trajectory pattern was more pronounced in men than in women. Individuals with both a steep decline and extreme variability in DHEAS levels had a significantly higher death rate than those with neither pattern (141 vs 48 deaths per 1,000 person-years, p < .001).

CONCLUSIONS

Our data show significant heterogeneity in the individual trajectories of DHEAS levels and suggest that these trajectories provide important biologic information about the rate of aging, whereas the DHEAS level itself does not.

Frailty and the degradation of complex balance dynamics during a dual-task protocol

BACKGROUND

Balance during quiet stance involves the complex interactions of multiple postural control systems, which may degrade with frailty. The complexity of center of pressure (COP) dynamics, as quantified using multiscale entropy (MSE), during quiet standing is lower in older adults, especially those with falls. We hypothesized that COP dynamics from frail elderly individuals demonstrate less complexity than those from nonfrail elderly controls; complexity decreases when performing a dual task; and postural complexity during quiet standing is independent of other conventional correlates of balance control, such as age and vision.

METHODS

We analyzed data from a population-based study of community-dwelling older adults. Frailty phenotype (nonfrail, prefrail, or frail) was determined for 550 participants (age 77.9 +/- 5.5 years). COP excursions were quantified for 10 trials of 30 seconds each. Participants concurrently performed a serial subtraction task in half of the trials. Complexity of balance dynamics was quantified using MSE. Root-mean-square sway amplitude was also computed.

RESULTS

Of the 550, 38% were prefrail and 9% were frail. Complexity of the COP dynamics in the anteroposterior direction was lower in prefrail (8.78 +/- 1.91 [mean +/- SD]) and frail (8.38 +/- 2.13) versus nonfrail (9.20 +/- 1.74) groups (p < .001). Complexity reduced by a comparable amount in all three groups while performing the subtraction task (p < .001). Quiet standing complexity was independently associated with frailty after adjusting for covariates related to balance while sway amplitude was not.

CONCLUSION

Cognitive distractions during standing may further compromise balance control in frail individuals, leading to an increased risk of falls.

Isometric handgrip exercise improves acute neurocardiac regulation

Isometric handgrip (IHG) training (>6 weeks) has been shown to reduce resting arterial blood pressure (ABP) and improve cardiac autonomic modulation. However, the effects of a single bout of IHG on acute neurocardiac regulation remain unknown. The purpose of this study was to examine the effect of IHG exercise on nonlinear heart rate dynamics and cardiac vagal activity. Nonlinear dynamics were assessed by sample entropy, detrended fluctuation analysis (alpha(1)), and correlation dimension techniques. The 4-second exercise test was used to calculate the cardiac vagal index (CVI), an indirect measure of cardiac vagal activity. In a randomized crossover design, 18 older (70 +/- 5 years of age) subjects completed IHG exercise (four 2-min isometric contractions at 30% MVC) and a time-matched control condition. Following a single bout of bilateral IHG, there was a small reduction in systolic blood pressure (125 +/- 2 to 122 +/- 1 mmHg, P < 0.01), in addition to, a significant decrease in alpha(1) (1.42 +/- 0.12 to 1.22 +/- 0.10, P < 0.05), an increase in sample entropy (1.28 +/- 0.03 to 1.40 +/- 0.05, P < 0.001), and an increase in the CVI (1.24 +/- 0.03 to 1.29 +/- 0.03, P < 0.01). These results suggest improvements in acute cardiac autonomic modulation following a single bout of IHG. This may be mechanistically linked to the observed reductions in ABP seen in previous IHG training studies. Alternatively, these acute effects may have clinical applications and require further investigation.

Frailty syndrome is associated with altered circulating redox balance and increased markers of oxidative stress

Frailty syndrome (FS) is a condition described in aging and characterized by physical vulnerability to stress and lack of physiological reserve. In this study we aim to define whether circulating oxidative stress correlates to frailty in terms of glutathione balance and oxidative protein damage. In 62 elderly outpatients, classified as frail patients according to Fried's criteria, evaluation of reduced glutathione (GSH), oxidized glutathione (GSSG), tumor necrosis factor-alpha, malonaldehyde-(MDA) and 4-hydroxy-2,3-nonenal-(HNE) protein plasma adducts were performed. A significant increase in the GSSG was observed in patients with FS when compared to non-frail. No difference was shown in the GSH amount, suggesting a glutathione oxidation more than impairment of the synthesis. TNF-alpha, MDA- and HNE-adducts, were significantly higher in FS as compared to non-frail patients. A logistic regression model correlating FS with redox balance showed a close relationship between glutathione ratio (OR=1.8, 95% CI=1.2-2.5) and MDA adducts (OR=2.8, 95% CI=1.6-4.7) to frailty. Our findings show an association between oxidative imbalance and Frailty Syndrome. GSSG/GSH ratio and plasma protein adducts strongly predict the frailty conditions and seem to be reliable and easily measurable markers in the context of the multidimensional analysis of elderly patients.

Associations of neutrophil and monocyte counts with frailty in community-dwelling disabled older women: results from the Women's Health and Aging Studies I

Frailty is an important geriatric syndrome that predicts disability and mortality. Substantial evidence suggests that inflammation marked by elevated IL-6 levels and total white blood cell (WBC) counts contribute to this syndrome. However, the relationships of WBC subpopulations, the important inflammatory and immune cells, with frailty have not been investigated. To address this important question, we conducted cross-sectional polytomous logistic regression analyses evaluating associations between baseline WBC differential counts and prevalent frailty (defined by the validated Fried's criteria) of 558 disabled women aged 65-101 years and 548 women aged 70-79 living in the community, both from the Women's Health and Aging Studies. The results showed that high neutrophil and monocyte counts were associated with frailty in disabled older women, albeit these associations did not reach statistical significance in women aged 70-79, adjusting for age, race, education, body mass index, smoking, and antibiotic use. In addition, the identified associations were independent of IL-6. No significant associations of lymphocyte, eosinophil, or basophil counts with frailty were observed. These findings provide initial insight into potential roles of neutrophils and monocytes in the pathogenesis of frailty and a basis for further investigation into their function and regulation in frail older women.

Practice and age-related loss of adaptability in sensorimotor performance

The purpose of the present investigation was to examine whether the ability to adapt to task constraints is influenced by short-term practice in older adults. Young (18-29 years old) and old (65-75 years old) adults produced force output to a constant force target and a 1-Hz sinusoidal force target by way of the index finger flexion. Participants completed each task 5 times per session for 5 concurrent sessions. The amount and structure of force variability was calculated using linear and nonlinear analyses. As expected, there was a decrease in the magnitude of variability (coefficient of variation) in both tasks and task-related change in the structure of force variability (approximate entropy) with training across groups. The authors found older adults to have a greater amount of variability than their younger counterparts in both tasks. Older adults also demonstrated an increase in the structure of force output in the constant task but a decrease in structure in the sinusoidal task. Age differences in the adaptability to task constraints persisted throughout practice. The authors propose that older adults' ability to adapt sensorimotor output to task demands is not a result of lack of familiarity with the task but that it is, instead, characteristic of the aging process.

Sleep disorders and their impacts on healthy, dependent, and frail older adults

BACKGROUND

Sleep disorders differ widely in the heterogeneous older adult population. Older adults can be classified into three groups based upon their overall level of disability: healthy, dependent, and frail. Frailty is an emerging concept that denotes older persons at increased risk for poor outcomes.

OBJECTIVE

The aim of this consensus review is to describe the sleep disorders observed in healthy and dependent older adults and to discuss the potential sleep disorders associated with frailty as well as their potential consequences on this weakened population.

METHODS

A review task force was created including neurologists, geriatricians, sleep specialists and geriatric psychiatrists to discuss age related sleep disorders depending on the three categories of older adults. All published studies on sleep in older adults on Ovid Medline were reviewed and 106 articles were selected for the purpose of this consensus.

RESULTS

Many healthy older adults have complains about their sleep such as waking not rested and too early, trouble falling asleep, daytime napping, and multiple nocturnal awakenings. Sleep architecture is modified by age with an increased percentage of time spent in stage one and a decreased percentage spent in stages three and four. Insomnia is frequent and its mechanisms include painful medical conditions, psychological distress, loss of physical activity and iatrogenic influences. Treatments are also involved in older adults' somnolence. The prevalence of primary sleep disorders such as restless legs syndrome, periodic limb movements and sleep disordered breathing increases with age. Potential outcomes relevant to these sleep disorders in old age include mortality, cardiovascular and neurobehavioral co-morbidities. Sleep in dependent older adults such as patients with Alzheimer Disease (AD) is disturbed. The sleep patterns observed in these patients are often similar to those observed in non-demented elderly but alterations are more severe. Nocturnal sleep disruption and daytime sleepiness are the main problems. They are the results of Sleep/wake circadian rhythm disorders, environmental, psychological and iatrogenic factors. They are worsened by other sleep disorders such as sleep disordered breathing. Sleep in frail older adults per se has not yet been formally studied but four axes of investigation should be considered: i) sleep architecture abnormalities, ii) insomnia iii) restless legs syndrome (RLS), iv) sleep disordered breathing.

CONCLUSION

Our knowledge in the field of sleep disorders in older adults has increased in recent years, yet some groups within this heterogeneous population, such as frail older adults, remain to be more thoroughly studied and characterized.

Frailty: defining and measuring of a concept

Older, more vulnerable individuals are increasingly often described in the literature as being frail. Because frailty is often perceived as being undesirable and associated with high health risks, it is important to establish how we can predict, recognize, and treat frailty. Frailty is predisposed by advancing age in combination with physiological deterioration, especially a loss of muscle mass and bone density. Although the symptoms of frailty are diverse, the most common symptoms are a deterioration of activities of daily living (ADL), mobility, nutritional status, cognition, and endurance. The consequences of frailty are institutionalization, morbidity, and mortality. The main determinants of frailty are limitations in ADL, weight loss, diminished mobility or patterns of activity, lowered serum cholesterol level, and sensitivity to change. There is no gold standard for the measurement of frailty, and often studies use a combination of instruments. Although a couple of multidimensional instruments have been developed to measure frailty in its totality, the reliability and validity of these instruments have yet to be established. Successful interventions against frailty include increasing muscle strength through training and individualized recommendations made on the basis of an extensive geriatric assessment.

Frailty and impaired cardiac autonomic control: new insights from principal components aggregation of traditional heart rate variability indices

BACKGROUND

Age-related deterioration in homeostatic regulatory mechanisms leads to decreased complexity in their output. For example, the degradation of cardiac autonomic control results in loss of complexity in the heart rate signal. Frailty is a state of critically impaired homeostasis that results in heightened vulnerability to stressors. We propose a new measure of heart rate variability (HRV) to capture the impairment in cardiac autonomic control associated with frailty.

METHODS

Traditional time and frequency domain indices of HRV were obtained from 2-hour ambulatory electrocardiograms (ECGs) of 276 women (65-101 years old) in the Women's Health and Aging Study-I. Principal components analysis was conducted on the correlation matrix of HRV indices. Frailty was defined using a validated instrument. Regression models were used to evaluate associations of HRV measures with age, frailty, and 5-year mortality.

RESULTS

The first two principal components (PCs), PC1 and PC2, explained 90% of the variance in HRV indices. PC1 is the mean of log-transformed HRV indices. PC2 is a linear combination of log-transformed indices, with positive weights for very low frequency (VLF), low frequency (LF), and standard deviation of N-N intervals (SDNN), and negative weights for high frequency (HF), root-mean-squared differences of successive N-N intervals (RMSSD), and proportion of all N-N intervals that are larger than 50 ms (pNN50). Decreases in SDNN, VLF, LF, and LF/HF were associated with an increased risk of frailty. PC2 was more strongly associated with age (beta = -.23, p < .001) and frailty (beta = -.73, p < 10(-5)) than were the individual HRV indices and LF/HF. PC2 was also the best predictor of 5-year mortality (beta = -.60, p < 10(-6)).

CONCLUSIONS

Cardiac autonomic control, as reflected by HRV, is impaired in frailty. A new measure derived from PC aggregation of traditional HRV indices provides a compact summary of this impairment.

Physiological complexity underlying heart rate dynamics and frailty status in community-dwelling older women

OBJECTIVES

To assess whether less physiological complexity underlying regulation of heart rate dynamics, as indicated by lower approximate entropy for heart rate (ApEn(HR)), is associated with frailty. For supporting validity, relationships between frailty and traditional linear indices of heart rate variability (HRV) were also assessed.

DESIGN

Cross-sectional.

SETTING

Women's Health and Aging Study I, a community-based observational study, 1992 to 1995.

PARTICIPANTS

Subset of 389 community-dwelling women aged years and older with moderate to severe disability with ApEn(HR) data (convenience sampling).

MEASUREMENTS

Electrocardiographic Holter recordings obtained over 2- to 3-hour periods were processed for ApEn(HR) and HRV measures. ApEn(HR) is a nonlinear statistic that quantifies the regularity of heart rate fluctuations over time. Lower ApEn(HR) is characteristic of heart rate time series containing a high proportion of repetitive patterns. Frailty was defined according to validated phenotype criteria.

RESULTS

Median ApEn(HR) was lower in frail than in nonfrail subjects (P=.02). Lower ApEn(HR) (top quartile) was associated with lower likelihood of frailty than higher ApEn(HR) (bottom three quartiles) (odds ratio=0.47, 95% confidence interval=0.26-0.86), even after adjustment for major confounders. Frailty was consistently associated with lower HRV as assessed using time- and frequency-domain indices.

CONCLUSION

This study supports the notion that less physiological complexity marks frailty and provides an empirical basis to the concept of frailty as a syndrome of homeostatic impairment. Future research will determine whether noninvasive measures of physiological complexity underlying heart rate dynamics might be useful for screening and monitoring of clinical vulnerability in older adults.

Complexity of force output during static exercise in individuals with Down syndrome

Force variability is greater in individuals with Down syndrome (DS) compared with persons without DS and is similar to that seen with normal aging. The purpose of this study was to examine the structure (in both time and frequency domains) of force output variability in persons with DS to determine whether deficits in force control are similar between individuals with DS and older adults. An isometric handgrip task at a constant force (30% of maximal voluntary contraction) was completed by individuals with DS (n = 29, age 26 yr), and healthy young (n = 26, age 27 yr) and older (n = 33, age 70 yr) individuals. Mean, standard deviation (SD), and coefficient of variation (CV) were used to analyze the magnitude of force output variability. Spectral analysis and approximate entropy (ApEn) were used to analyze the structure of force output variability. Mean force output for DS was lower than in young controls (P < 0.05) but no different from old controls. Individuals with DS had greater SD and CV than young and old controls (P < 0.05). The DS group had a significantly greater proportion of spectral power within the 0-to 4-Hz bandwidth than the young and older controls (P < 0.05). The DS group had significantly lower ApEn values than the young controls (P < 0.05), but there were no differences in ApEn between the DS group and the old controls (P > 0.05). In conclusion, young persons with DS demonstrate enhanced temporal structure and greater amplitude of low-frequency oscillations in the force output signal than age-matched non-DS peers. Interestingly, young persons with DS and older persons without DS have similar time-dependent structure of force output variability. This would suggest a possible link between premature aging and less complex force output in persons with DS.

Conceptualizing compensatory responses: implications for treatment and research

Many scientists approach the discovery and application of knowledge of physiological processes from a reductionistic paradigm. A reductionistic approach focuses on treating one or a few key disease-related variables but overlooks the interaction of systems and their dependency on one another to produce homeostasis. The purposes of this article are to examine the current paradigm underlying treatment and its effect on patient outcome and to present an alternative perspective for understanding the body's compensatory responses and their implications for treatment and research. Chaos theory and nonlinear methods are presented as possible ways to conceptualize and explore the complex integration of physiological patterns in response to disease, aging, and treatment.

Upregulated ex vivo expression of stress-responsive inflammatory pathway genes by LPS-challenged CD14(+) monocytes in frail older adults

Frailty has been increasingly recognized as an important clinical syndrome in old age. The frailty syndrome is characterized by chronic inflammation, decreased functional and physiologic reserve, and increased vulnerability to stressors, leading to disability and mortality. However, molecular mechanisms that contribute to inflammation activation and regulation in frail older adults have not been investigated. To begin to address this, we conducted a pathway-specific gene array analysis of 367 inflammatory pathway genes by lipopolysaccharide (LPS)-challenged CD14(+) monocytes from 32 community-dwelling frail and age-, race-, and sex-paired nonfrail older adults (mean age 83 years, range 72-94). The results showed that ex vivo LPS-challenge induced average 2.0-fold or higher upregulated expression of 116 genes in frail participants and 85 genes in paired nonfrail controls. In addition, frail participants had 2-fold or higher upregulation in LPS-induced expression of 7 stress-responsive genes than nonfrail controls with validation by quantitative real time RT-PCR. These findings suggest upregulated expression of specific stress-responsive genes in monocyte-mediated inflammatory pathway in the syndrome of frailty with potential mechanistic and interventional implications.

Stimulus-response paradigm for characterizing the loss of resilience in homeostatic regulation associated with frailty

Frailty is a state of health signified by an increased vulnerability to adverse health outcomes in the face of stressors (e.g. infection). There is emerging consensus that research on both the theory and measurement of frailty must focus on the dynamic interactions within and across systems underlying the frailty syndrome. In this paper, we propose a dynamical systems modeling approach, based on the stimulus-response experimental paradigm, to propel future advances in the study of frailty. Our proposal is novel in that it provides a quantitative framework to operationalize and test the core notion underlying frailty that it signifies a loss of resilience in homeostatic regulation. The proposed framework offers many important benefits, including (a) insights into whether and how homeostatic regulation differs between frail and non-frail older adults, (b) identification of critical regulatory systems, if they exist, that could function as sentinel systems for screening and early detection of frailty, (c) establishment of the value of provocative tests that can provide maximal information on the integrity of systems identified in (b), and (d) evaluation and unification of diverse empirical descriptions of frailty by providing a mathematical framework anchored in quantifying the loss of resilience, an essential property of frailty.

Dynamic models for the study of frailty

Frailty can be viewed as resulting from the degradation of multiple interacting physiologic systems that are normally responsible for healthy adaptation to the daily demands of life. Mathematical models that can quantify alterations in the dynamics of physiologic systems and their interactions may help characterize the syndrome of frailty and enable investigators to test interventions to prevent its onset. One theoretical mathematical model reported by Varadhan et al. in this issue of the Journal represents one type of regulatory process that may become altered in frail individuals-the stimulus-response mechanism [Varadhan, R., Seplaki, C.S., Xue, Q.L., Bandeen-Roche, K., Fried, L.P. Stimulus-response paradigm for characterizing the loss of resilience in homeostatic regulation associated with frailty. Mech. Ageing Dev., this issue]. This model focuses on the timing of recovery from a single stimulus, rather than the full array of responses that might be altered in a complex dynamical system. Therefore, alternative models are needed to describe the wide variety of behaviors of physiologic systems over time and how they change with the onset of frailty. One such model, based on a simple signaling network composed of a lattice of nodes and the bi-directional connections between them, can reproduce the complex, fractal-like nature of healthy physiological processes. This model can be used to demonstrate how the degradation of signaling pathways within a physiologic system can result in the loss of complex dynamics that characterizes frailty.

What limits for acute care in the elderly?

PURPOSE OF REVIEW

This review aims to address the important question of the increasing life expectancy and the aging population in the healthcare system today. We try to give some elements that will help the reflection about the ethical stakes balancing the necessity of care in the increasing number of elderly patients and the limited resources available, in the special context of acute care.

RECENT FINDINGS

There is growing evidence that the chronological age itself is not a reliable marker of bad prognosis or of mortality. The new concept of frailty may better correlate with the aging process of the elderly. The frailty index is an integrative approach considering the multiple factors impacting on the aging individual. Applied in the practical arena, it might become a useful tool for clinicians.

SUMMARY

Aging implies many biological modifications at molecular, cellular, organic levels as well as of the behavior. Some aspects of these processes and their consequences on health are described. The frailty concept is detailed, and its potential interest explained. We conclude that the measurement of aging phenomenon, including the frailty index, may help us to better assess the true health and the required therapeutics of elderly patients.

Motor entropy in response to task demands and environmental information

This experiment tested the hypothesis that human motor adaptation can be represented as the conservation of entropy across the task, organism, and environment. Healthy young individuals generated a submaximal isometric force with the index finger of their dominant hand. Subjects performed this task under different task demands (error tolerance) and environmental information (feedback frequency) conditions. In order to extend previous findings, we employ the use of approximate entropy (ApEn) to capture the temporal aspects of the variability in the isometric force and to create links to other studies of time-series in human behavior. We showed that ApEn of the force time-series, made conditional upon satisfying the task demands, decreased as the task demands were increased and the environmental information reduced. There was a compensatory interaction between task and environment on the force dynamics that could be represented by a quadratic surface, capturing 92% of the total variance. Our results show that when faced with a reduced likelihood of achieving the task goal (increased task entropy) and an environment that provides little information (increased environmental entropy), the subjects employed similar force production strategies over time, resulting in a more regular pattern.

Fractal scaling properties of heart rate dynamics following resistance exercise training

With aging and disease, there is a breakdown of the natural fractal-like organization of heart rate (HR). Fractal-like correlation properties of HR can be assessed with detrended fluctuation analysis (DFA). A short-time scaling exponent (αs) value of 1 is associated with healthy HR dynamics, whereas values that deviate away from 1, in either direction, indicate fractal collapse. The purpose of this study was to examine the effect of resistance exercise training (RT) on fractal correlation properties of HR dynamics. Resting ECG was collected at baseline, following a 4-wk time control period and 6 wk of RT (3 days per wk) in 34 men (23 ± 1 years of age). Fractal properties of HR were assessed with DFA. There was no change in αsfollowing either the time control period or RT (1.01 ± 0.06 to 0.98 ± 0.06 to 0.93 ± 0.04, P > 0.05). Given the potential bidirectional nature of fractal collapse, subjects were retrospectively separated into two groups (higher αsand lower αs) on the basis of the initial αsby using cluster analysis. An interaction was detected for αsfollowing RT ( P < 0.05). There was no change in αsin either group following the time control, but αsincreased following RT in the lower αsgroup ( n = 18; 0.73 ± 0.04 to 0.69 ± 0.04 to 0.88 ± 0.04) and αsdecreased following RT in the higher αsgroup ( n = 16; 1.20 ± 0.04 to 1.24 ± 0.04 to 0.98 ± 0.04). In conclusion, RT improves fractal properties of HR dynamics.

Effects of an attention demanding task on dynamic stability during treadmill walking

Background

People exhibit increased difficulty balancing when they perform secondary attention-distracting tasks while walking. However, a previous study by Grabiner and Troy (J. Neuroengineering Rehabil., 2005) found that young healthy subjects performing a concurrent Stroop task while walking on a motorized treadmill exhibited decreased step width variability. However, measures of variability do not directly quantify how a system responds to perturbations. This study re-analyzed data from Grabiner and Troy 2005 to determine if performing the concurrent Stroop task directly affected the dynamic stability of walking in these same subjects.

Methods

Thirteen healthy volunteers walked on a motorized treadmill at their self-selected constant speed for 10 minutes both while performing the Stroop test and during undisturbed walking. This Stroop test consisted of projecting images of the name of one color, printed in text of a different color, onto a wall and asking subjects to verbally identify the color of the text. Three-dimensional motions of a marker attached to the base of the neck (C5/T1) were recorded. Marker velocities were calculated over 3 equal intervals of 200 sec each in each direction. Mean variability was calculated for each time series as the average standard deviation across all strides. Both "local" and "orbital" dynamic stability were quantified for each time series using previously established methods. These measures directly quantify how quickly small perturbations grow or decay, either continuously in real time (local) or discretely from one cycle to the next (orbital). Differences between Stroop and Control trials were evaluated using a 2-factor repeated measures ANOVA.

Results

Mean variability of trunk movements was significantly reduced during the Stroop tests compared to normal walking. Conversely, local and orbital stability results were mixed: some measures showed slight increases, while others showed slight decreases. In many cases, different subjects responded differently to the Stroop test. While some of our comparisons reached statistical significance, many did not. In general, measures of variability and dynamic stability reflected different properties of walking dynamics, consistent with previous findings.

Conclusion

These findings demonstrate that the decreased movement variability associated with the Stroop task did not translate to greater dynamic stability.

T-lymphocytes expressing CC chemokine receptor-5 are increased in frail older adults

OBJECTIVES

To evaluate the frequencies of T-lymphocytes expressing CC chemokine receptor-5 (CCR5(+) T-cells) and their relationship with frailty in older adults.

DESIGN

Case-control study with an age-, race-, and sex-matched design.

SETTING

General Clinical Research Center.

PARTICIPANTS

Community-dwelling adults aged 72 and older from Baltimore, Maryland.

METHODS

Frailty was determined using five validated criteria: weakness, slow walking speed, fatigue, low physical activity, and weight loss. Those meeting three or more of these five criteria were defined as frail and those with none as nonfrail. Complete blood counts were performed to obtain peripheral lymphocyte counts using an automated (Coulter) counter. Peripheral blood was collected for surface immunofluorescent staining of CCR5 and other T-cell markers.

RESULTS

Twenty-six frail and matched nonfrail participants (mean age+/-standard deviation 83.8+/-5.3, range 72-94) completed the study. Frail participants had higher CCR5(+), CCR5(+)CD8(+), and CCR5(+)CD45RO(-) T-cell counts than matched nonfrail controls (349+/-160/mm(3) vs 194+/-168/mm(3), P=.02; 208+/-98/mm(3) vs 105+/-62/mm(3), P=.02; and 189+/-149/mm(3) vs 52+/-36/mm(3), P=.01; respectively). Furthermore, there was a trend toward graded increase in these T-cell counts across the frailty scores in frail participants (e.g., CCR5(+)CD8(+) counts of 123+/-52/mm(3), 248+/-115/mm(3), and 360+/-215/mm(3) for those with frailty scores of 3, 4, and 5, respectively).

CONCLUSION

These initial results suggest an expansion of the CCR5(+) T-cell subpopulation in frailty. They provide a basis for further characterization of CCR5(+) T-cells and their role in frailty, with potential therapeutic implications.

Does androgen-deprivation therapy accelerate the development of frailty in older men with prostate cancer?: a conceptual review

The majority of men with prostate cancer are aged > or =65 years. Men, as they age, are more likely to suffer from impaired physical function. The standard treatment for recurrent prostate cancer is androgen-deprivation therapy (ADT). Well-established toxicities from ADT include lean weight loss or sarcopenia, muscle weakness, fatigue, and reduced activity levels. Frailty is a term from geriatrics that describes older individuals with limited physiologic reserve who are at significant risk for adverse outcomes, including falls, disability, hospitalization, and death. An increasingly accepted definition of frailty is a syndrome in which > or =3 of the following are present: unintentional (lean) weight loss > or =10 pounds in the past year, weakness (measured by grip strength), slow walking speed, self-reported exhaustion, and low physical activity. This clinical syndrome overlaps closely with the known toxicities of ADT. In addition, alterations in the inflammatory system, neuroendocrine system, and energy production are associated with this syndrome, as evidenced by biomarkers such as C-reactive protein, interleukin-6, and tumor necrosis factor-alpha. For this article, the authors reviewed the evidence for the effect of ADT on each of the 5 frailty components plus the identified biomarkers, and the evidence indicates that ADT may accelerate the development of frailty in vulnerable older men with prostate cancer. Given the association of frailty with important clinical outcomes such as hospitalization and death, this potential consequence of ADT should be considered carefully when initiating therapy in older patients with recurrent prostate cancer.

Children with cerebral palsy exhibit greater and more regular postural sway than typically developing children

Following recent advances in the analysis of centre-of-pressure (COP) recordings, we examined the structure of COP trajectories in ten children (nine in the analyses) with cerebral palsy (CP) and nine typically developing (TD) children while standing quietly with eyes open (EO) and eyes closed (EC) and with concurrent visual COP feedback (FB). In particular, we quantified COP trajectories in terms of both the amount and regularity of sway. We hypothesised that: (1) compared to TD children, CP children exhibit a greater amount of sway and more regular sway and (2) concurrent visual feedback (creating an external functional context for postural control, inducing a more external focus of attention) decreases both the amount of sway and sway regularity in TD and CP children alike, while closing the eyes has opposite effects. The data were largely in agreement with both hypotheses. Compared to TD children, the amount of sway tended to be larger in CP children, while sway was more regular. Furthermore, the presence of concurrent visual feedback resulted in less regular sway compared to the EO and EC conditions. This effect was less pronounced in the CP group where posturograms were most regular in the EO condition rather than in the EC condition, as in the control group. Nonetheless, we concluded that CP children might benefit from therapies involving postural tasks with an external functional context for postural control.

Dinâmica não-linear e exercício físico: conceitos e aplicações

Médicos, fisiologistas, bioquímicos, psicólogos e até profissionais envolvidos com exercício físico estão recentemente aumentando seus interesses pela dinâmica não-linear, uma teoria científica desenvolvida principalmente por matemáticos, que é genericamente conhecida por Teoria da Complexidade. Embora poucos trabalhos em Educação Física e Esporte utilizem esse paradigma para solucionar seus problemas, nota-se um crescente interesse por esse mesmo enfoque, principalmente em relação aos efeitos do exercício físico sobre mudanças na variabilidade e complexidade de séries temporais fisiológicas. Geralmente, tais mudanças se revelam na forma de queda em seu comportamento temporal, denotando diminuição na complexidade do organismo ou de componentes envolvidos especificamente na sua regulação. De acordo com a Teoria da Complexidade, por enfatizar interações não-lineares existentes em sistemas biológicos, verifica-se que não é importante apenas a elevação (supercompensação) de componentes do organismo com a prática de exercícios físicos, mas também aqueles que atrofiam (descompensação) paralelamente, porque podem contribuir para a ocorrência de perda de sincronia na funcionalidade desses sistemas. Assim, em oposição à ênfase que se dá no treinamento físico à repetição monótona de atividade física intensa e voltada para efeitos específicos positivos, que invariavelmente leva à simplificação do organismo, recomenda-se maior variação qualitativa e quantitativa nos exercícios praticados. O objetivo é preservar sua complexidade natural ou impedir que ocorra diminuição rápida com o envelhecimento. A presente revisão tem por objetivo, além de descrever a possível perda de complexidade com o treinamento físico, discutir alguns conceitos da Teoria da Complexidade de modo introdutório, com particular ênfase em tópicos envolvendo saúde e desempenho físico.

Are visual feedback delays responsible for aging-related increases in force variability?

The current investigation examined if age-related differences in the control of isometric force production are related to an increase in visual motor processing time. Young and old adults produced isometric force production to a visually displayed target while visual feedback delay was manipulated over a broad range (50 to 3200 ms). The force output of the oldest age group was more variable across the range of delays, but only demonstrated enhanced time dependent structure at short delays. It is concluded that age differences in visual motor processing time contribute to decrements in both the feedback and feedforward control of force output.

A practical approach to geriatric assessment in oncology

More than half of new cancers are diagnosed in elderly patients, but data from randomized clinical trials do not represent the elderly population. Comprehensive geriatric assessment (CGA) can contribute valuable information to oncologists for risk stratification of elderly cancer patients. Functional impairments, frailty markers, cognitive impairments, and physical disabilities increase the risk for adverse outcomes during cancer treatment. Evidence is accumulating that selected elderly cancer patients benefit from CGA and geriatric interventions. However, perceived barriers to CGA include time, familiarity, cost, and lack of a well-defined procedure to interpret and apply the information. We present a model for rapid selection of elderly who would benefit from CGA using screening tools such as the Vulnerable Elders-13 Survey. We also define important geriatric functional risk factors, including mobility limitation, frailty, and dementia, and demonstrate how brief screening tests can make use of data realistically available to clinical oncologists to determine a stage of aging. Summary tables and a decision tree demonstrate how these data can be compiled to determine the risk for toxicities and to anticipate ancillary support needs.

Factors contributing to frailty: literature review

AIM

This paper presents a review of theoretical and research literature in order to identify the factors contributing to frailty.

BACKGROUND

Frailty is a multifaceted gerontological concept that lacks a clear definition, but may result from an identifiable homogeneous cluster of bio-psycho-social-spiritual factors.

METHOD

A total of 134 articles were identified through a search of the MEDLINE (1966 to July 2004), CINAHL (1982 to July 2004), PsychInfo (1985 to July 2004) and Ageline (1995 to July 2004) databases. Each article was reviewed to determine its fit with inclusion/exclusion criteria. Seven research and 11 theoretical articles were retained and further reviewed for methodological quality using a validity tool.

FINDINGS

Seventeen different definitions of frailty were identified. Regardless of the differing definitions, common contributing factors could be identified. Physical, cognitive/psychological, nutritional and social factors, as well as ageing and disease, were evident in both the theoretical and research literature.

CONCLUSIONS

Although there is strong agreement that a relationship exists between a cluster of factors and frailty, designation of the factors as contributors or outcomes of frailty differs. Without a clear explanatory theory of the path from contributors to frailty to outcomes, research will continue to produce confusing results. A theoretical framework that includes bio-psycho-social-spiritual factors as contributors to frailty is recommended as the most useful framework for gerontological nursing.

Cardiolocomotor coupling in young and elderly people

BACKGROUND

Walking is a complex act that requires the coordination of locomotor, cardiovascular, and autonomic systems. Aging affects each of these systems and may alter physiological mechanisms regulating the interactions between them.

METHODS

We examined the effects of healthy aging on cardiac-locomotor coupling using treadmill walking at incremental speeds from 0.8 mph to normal walking speed in 12 healthy young (29.0 +/- 5.0 years) and 9 healthy elderly persons (70.3 +/- 5.1 years). interbeat (R-R) intervals, step intervals, maximum foot pressure (MFP) and normalized maximum force, blood pressure (BP), and blood flow velocity (BFV) in the middle cerebral artery were continuously measured.

RESULTS

Step intervals and R-R intervals decreased, and MFP and BFV increased with walking speed in both groups; systolic BP increased (p <.0001) in the old group. In elderly, but not in young participants, step intervals and R-R intervals were coupled (R(2) = 0.84, p <.0001), and MFP was correlated with systolic BP (R(2) = 0.51, p <.02).

CONCLUSION

Cardiolocomotor coupling that becomes manifest with aging may optimize cardiovascular responses during walking. In elderly people, forces generated during the gait cycle may be transmitted to arterial pressure and thus synchronize the central cardiovascular network with the stepping rhythm.

Optimal movement variability: a new theoretical perspective for neurologic physical therapy

Variability is a natural and important feature of human movement. Using existing theoretical frameworks as a foundation, we propose a new model to explain movement variability as it relates to motor learning and health. We contend that mature motor skills and healthy states are associated with an optimal amount of movement variability. This variability also has form and is characterized by a chaotic structure. Less than optimal movement variability characterizes biological systems that are overly rigid and unchanging, whereas greater than optimal variability characterizes systems that are noisy and unstable. Both situations characterize systems that are less adaptable to perturbations, such as those associated with abnormal motor development or unhealthy states. From our perspective, the goal of neurologic physical therapy should be to foster the development of this optimal amount of movement variability by incorporating a rich repertoire of movement strategies. The development of such a repertoire can be enhanced by incorporating a multitude of experiences within the therapeutic milieu. Promoting complex variation in human movement allows either motor development or the recovery of function after injury not to be hard coded, but determined instead by the active engagement of the individual within their environment. Measurement tools derived from nonlinear dynamics that characterize the complexity of movement variability provide useful means of testing these propositions. To illustrate, we present 2 clinical case studies, one pediatric and one adult, where we applied our theoretical framework to measuring change in postural control.

Discrete bandwidth visual feedback increases structure of output as compared to continuous visual feedback in isometric force control tasks

BACKGROUND

Performance variability measures provide a partial picture of force control ability. Nonlinear analyses can reveal important information related to the randomness and complexity of the data, providing a more complete picture of the physiological process.

METHODS

We investigated the effects of visual feedback on the structure and performance of the force output from isometric force control tasks. Twelve young volunteers completed isometric force control tasks using two types of visual feedback: discrete bandwidth (+/-4% maximal voluntary contraction) and continuous line matching. We determined force signal variability (standard deviation), self-similarity (fractal dimension), and complexity (approximate entropy). Analyses of variance (feedback x muscle group x force level) were conducted and P values less than 0.05 were considered significant.

FINDINGS

The force signal in discrete bandwidth feedback, compared to continuous line matching, had significantly a higher standard deviation (P=.000): 2.18 Nm (SD 1.98) vs. 0.99 Nm (SD 0.91); lower fractal dimension (P=.000): 1.07 (SD 0.04) vs. 1.16 (SD 0.04); and lower approximate entropy (P=.000): 0.12 (SD 0.07) vs. 0.26 (SD 0.09).

INTERPRETATION

The greater self-similarity (lower fractal dimension) and greater regularity (lower approximate entropy) of the discrete bandwidth, compared to the continuous line matching, may indicate a process that required more kinesthetic (intrinsic) feedback to modulate force. Clinicians may choose to employ visual feedback paradigms that target the use of intrinsic feedback during rehabilitation. Discrete bandwidth feedback may be useful for delineating impairments in motor skill and measuring outcomes of intervention programs.

Tiredness in daily activities: a subjective measure for the identification of frailty among non-disabled community-living older adults

The objective of this study was to determine whether the responses to questions about tiredness in daily activities is an early subjective sign of frailty indicating older community-living adults at increased risk for disability and mortality. Tiredness in daily activities as measured by the Mob-T Scale, maximal power in sustained work, and comorbid diseases were assessed together with sociodemographic variables in a sample of 705 non-disabled, 70-year old men and women surveyed in 1984. Vital status of members was determined prospectively over the next 15 years. Onset of disability was measured at 5-, 10-, and 15-year follow-up. Onset of disability among non-disabled 70-year old men and women was strongly related to tiredness in daily activities at 5- and 10-year follow-up. Scores on the Mob-T Scale were significantly associated with mortality during the aggregate 15-year follow-up period. Multiple stepwise regression analyses not only indicated that tiredness in daily activities is a strong independent predictor of both disability and mortality, but also that tiredness mediates the effects of comorbidity and maximal power in sustained work on disability/mortality. Self-reported tiredness in daily activities is suggested as a basis for identifying vulnerable frail subsets of older adults requiring targeted strategies for prevention.

Are age-related increases in force variability due to decrements in strength?

The purpose of this investigation was to examine the relationship between strength and the magnitude and time sequential structure of force variability. Young and old adults produced isometric force via index finger abduction to a visually presented target corresponding to a constant force level of 5 or 25% maximal voluntary contraction (MVC). Cluster analysis was used to divide subjects into groups based on age and strength. The variability of older adults was greater and showed more time dependent structure than their younger counterparts. The force output of weaker subjects was also more variable and had a stronger sequential structure. Indeed, when MVC was controlled for there was no significant age effect on force variability. The relationship between strength and variability remained significant, however, when chronological age was controlled for. The findings revealed that the established age-related changes in force variability are more fundamentally due to the association between strength and force variability and provide a further challenge to using chronological age as a marker of the biological aging process in studies of motor control.

Aging-related temporal constraints to stability and instability in postural control

In this study, we review the evidence that older adults tend to have both a shorter time to lose stability in the maintenance of standing posture and the functionally related but inverse problem of needing more time to reacquire stability in transitioning to a postural state. These age-related time limitations to processes of stability are hypothesized to enhance the probability of falling with aging and the problems that can occur in the transition between activities, such as sitting to standing and standing to walking. The potential role of fitness and health variables in mediating the temporal constraints on the acquisition and loss of postural stability in aging is discussed.