In-home physical frailty monitoring: relevance with respect to clinical tests.

BACKGROUND: Frailty detection and remote monitoring are of major importance for slowing down, and/or even stopping the frailty process in home-dwelling older people. Taking the Fried's criteria as a reference, this work aims to compare the results produced by a technological set (ARPEGE Pack) with those obtained by usual clinical tests, as well as to discuss the ability of the Pack to be used for long-run frailty remote monitoring. METHODS: 194 participants were given a number of geriatric tests and asked to make use of the ARPEGE technological tools as well as reference clinical tools to feed Fried's indicators. Spearman or Pearson's correlation coefficients were used to compare the ARPEGE results to the reference ones, depending on data statistical characteristics. RESULTS: Good correlations were obtained for measurements of weight (0.99), grip strength (0.89) and walking speed (0.79). Results are much less satisfactory for evaluation of physical activity and exhaustion (Spearman correlation coefficients 0.25 and 0.41, respectively). CONCLUSION: Correlations regarding weight, grip strength and walking speed confirm the validity of the data produced by the ARPEGE Pack to feed Fried's criteria. Assessing activity level and exhaustion from an abbreviated questionnaire is still questionable. However, for long-run monitoring other methods of evaluation can be explored. Beyond the quantitative results, the ARPEGE Pack has been proved to be acceptable and motivating in such a long-term frailty monitoring.

Fractal time series analysis of postural stability in elderly and control subjects.

BACKGROUND: The study of balance using stabilogram analysis is of particular interest in the study of falls. Although simple statistical parameters derived from the stabilogram have been shown to predict risk of falls, such measures offer little insight into the underlying control mechanisms responsible for degradation in balance. In contrast, fractal and non-linear time-series analysis of stabilograms, such as estimations of the Hurst exponent (H), may provide information related to the underlying motor control strategies governing postural stability. In order to be adapted for a home-based follow-up of balance, such methods need to be robust, regardless of the experimental protocol, while producing time-series that are as short as possible. The present study compares two methods of calculating H: Detrended Fluctuation Analysis (DFA) and Stabilogram Diffusion Analysis (SDA) for elderly and control subjects, as well as evaluating the effect of recording duration. METHODS: Centre of pressure signals were obtained from 90 young adult subjects and 10 elderly subjects. Data were sampled at 100 Hz for 30 s, including stepping onto and off the force plate. Estimations of H were made using sliding windows of 10, 5, and 2.5 s durations, with windows slid forward in 1-s increments. Multivariate analysis of variance was used to test for the effect of time, age and estimation method on the Hurst exponent, while the intra-class correlation coefficient (ICC) was used as a measure of reliability. RESULTS: Both SDA and DFA methods were able to identify differences in postural stability between control and elderly subjects for time series as short as 5 s, with ICC values as high as 0.75 for DFA. CONCLUSION: Both methods would be well-suited to non-invasive longitudinal assessment of balance. In addition, reliable estimations of H were obtained from time series as short as 5 s.

Identification of the period of stability in a balance test after stepping up using a simplified cumulative sum.

Falls are a major cause of death in older people. One method used to predict falls is analysis of Centre of Pressure (CoP) displacement, which provides a measure of balance quality. The Balance Quality Tester (BQT) is a device based on a commercial bathroom scale that calculates instantaneous values of vertical ground reaction force (Fz) as well as the CoP in both anteroposterior (AP) and mediolateral (ML) directions. The entire testing process needs to take no longer than 12 s to ensure subject compliance, making it vital that calculations related to balance are only calculated for the period when the subject is static. In the present study, a method is presented to detect the stabilization period after a subject has stepped onto the BQT. Four different phases of the test are identified (stepping-on, stabilization, balancing, stepping-off), ensuring that subjects are static when parameters from the balancing phase are calculated. The method, based on a simplified cumulative sum (CUSUM) algorithm, could detect the change between unstable and stable stance. The time taken to stabilize significantly affected the static balance variables of surface area and trajectory velocity, and was also related to Timed-up-and-Go performance. Such a finding suggests that the time to stabilize could be a worthwhile parameter to explore as a potential indicator of balance problems and fall risk in older people.

Motor unit conduction velocity distribution estimation from evoked motor responses.

Action potentials travel along the muscle fibers with a specific conduction velocity that depends on their structural and functional properties. Only the estimation of muscle conduction velocity distribution (MCVD) may be able to depict this propagation heterogeneity. Based on the method proposed by Cummins et al. (Electroenceph Clin Neurophysiol, 46:647-658, 1979) to estimate nerve conduction velocity distribution (NCVD), the present paper proposes a method that modifies the Cummins' approach to make it suitable for MCVD estimation from electrically evoked motor responses. The MCVD estimation algorithm was first assessed by means of simulated signals in order to control all signal features during the optimization process. Simulations showed that estimated distributions were very close to the true ones when taking into account the specificities of the muscle action potential, due to its generation and extinction (MSE divided by 5 on distribution standard deviation). This method was then applied to real signals. Elicited motor responses were recorded on the biceps brachii of healthy subjects either during repeated maximal stimulations at 20 Hz or during increasing intensity stimulations at 1 Hz. MCVD estimates were used to analyze fatigue and motor unit recruitment processes, respectively.

Modified bathroom scale and balance assessment: a comparison with clinical tests.

Frailty and detection of fall risk are major issues in preventive gerontology. A simple tool frequently used in daily life, a bathroom scale (balance quality tester: BQT), was modified to obtain information on the balance of 84 outpatients consulting at a geriatric clinic. The results computed from the BQT were compared to the values of three geriatric tests that are widely used either to detect a fall risk or frailty (timed get up and go: TUG; 10 m walking speed: WS; walking time: WT; one-leg stand: OS). The BQT calculates four parameters that are then scored and weighted, thus creating an overall indicator of balance quality. Raw data, partial scores and the global score were compared with the results of the three geriatric tests. The WT values had the highest correlation with BQT raw data (r = 0.55), while TUG (r = 0.53) and WS (r = 0.56) had the highest correlation with BQT partial scores. ROC curves for OS cut-off values (4 and 5 s) were produced, with the best results obtained for a 5 s cut-off, both with the partial scores combined using Fisher's combination (specificity 85 %: <0.11, sensitivity 85 %: >0.48), and with the empirical score (specificity 85 %: <7, sensitivity 85 %: >8). A BQT empirical score of less than seven can detect fall risk in a community dwelling population.

Balance quality assessment as an early indicator of physical frailty in older people.

Frailty is an increasingly common geriatric condition that results in an increased risk of adverse health outcomes such as falls. The most widely-used means of detecting frailty is the Fried phenotype, which includes several objective measures such as grip strength and gait velocity. One method of screening for falls is to measure balance, which can be done by a range of techniques including the assessment of the Centre of Pressure (CoP) during a balance assessment. The Balance Quality Tester (BQT) is a device based on a commercial bathroom scale that can evaluate balance quality. The BQT provides instantaneously the position of the CoP (stabilogram) in both anteroposterior (AP) and mediolateral (ML) directions and can estimate the vertical ground reaction force. The purpose of this study was to examine the relationship between balance quality assessment and physical frailty. Balance quality was compared to physical frailty in 186 older subjects. Rising rate (RR) was slower and trajectory velocity (TV) was higher in subjects classified as frail for both grip strength and gait velocity (p<;0.05). Balance assessment could be used in conjunction with functional tests of grip strength and gait velocity as a means of screening for frailty.

A segmentation approach to long duration surface EMG recordings.

The purpose of this study was to develop an automatic segmentation method in order to identify postural surface EMG segments in long-duration recordings. Surface EMG signals were collected from the cervical erector spinae (CES), erector spinae (ES), external oblique (EO), and tibialis anterior (TA) muscles of 11 subjects using a bipolar electrode configuration. Subjects remained seated in a car seat over the 150-min data-collection period. The modified dynamic cumulative sum (MDCS) algorithm was used to automatically segment the surface EMG signals. Signals were rejected by comparison with an exponential mathematical model of the spectrum of a surface EMG signal. The average power ratio computed between two successive retained segments was used to classify segments as postural or surface EMG. The presence of a negative slope of a regression line fitted to the median frequency values of postural surface EMG segments was taken as an indication of fatigue. Alpha level was set at 0.05. The overall classification error rate was 8%, and could be performed in 25 min for a 150-min signal using a custom-built software program written in C (Borland Software Corporation, CA, USA). This error rate could be enhanced by concentrating on the rejection method, which caused most of the misclassification (6%). Furthermore, the elimination of non-postural surface EMG segments by the use of a segmentation approach enabled muscular fatigue to be identified in signals that contained no evidence of fatigue when analysed using traditional methods.

Evaluation of driver discomfort during long-duration car driving.

The evolution of indices of fatigue, discomfort, and performance of subjects seated for long duration (150 min) in car seats were studied (n=11). Four experimental configurations were used: with and without vibration for two seats (U, uncomfortable; C, comfortable). Surface electromyography (SEMG) data were recorded bilaterally from cervical erector spinae and external oblique muscles. Discomfort increased significantly during the trial, regardless of the experimental condition (p<0.05). Performance was significantly worse for seat U with vibration (p<0.05). The median frequency of SEMG signals did not change between experimental conditions or across time. It would appear that, either the level of discomfort experienced was insufficient to change either performance or SEMG measures, or that the large parameter estimation variance of the SEMG signals might have masked any underlying spectral change. Further refinement of the SEMG signal processing methodology may be necessary to be able to detect fatigue of postural muscles.

Estimation of grip force using the Grip-ball dynamometer.

The Grip-ball is an innovative device that has been designed to measure grip strength. The Grip-ball consists of an airtight ball that contains a pressure sensor and Bluetooth communication system. The Grip-ball can be inflated to different initial pressures, with data available continuously in real time. The aim of this study was to build a model to predict the force applied to the Grip-ball dynamometer based only on the pressure measured by the Grip-ball and its initial pressure. Forces ranging from 2 to 70 kg were applied to a hybrid version of the device for 10 different initial pressures, ranging from atmospheric pressure of 100 kPa through to 190 kPa. A model was constructed to predict applied force, with force as a function of the initial pressure and the pressure measured. The error of the model was calculated as 1.29 kg across all initial pressures and forces applied. The results of the study are comparable with the errors observed for the gold standard in grip force measurement, the Jamar dynamometer. The best results for force prediction were obtained over the range in which frailty is typically detected. The Grip-ball will now be tested using a large population in order to establish clinical norms.

Development of a monitoring system for physical frailty in independent elderly.

Frailty is of increasing concern due to the associated decrease in independence of elderly who suffer from the condition. An innovative system was designed in order to objectively quantify the level of frailty based on a series of remote tests, each of which used objects similar to those found in peoples' homes. A modified ball, known as the Grip-ball was used to evaluate maximal grip force and exhaustion during an entirely remote assessment. A smartphone equipped with a tri-axial accelerometer was used to estimate gait velocity and physical activity level. Finally, a bathroom scale was used to assess involuntary weight loss. The smart phone processes all of the data generated, before it is transferred to a remote server where the user, their entourage, and any medical professionals with authorization can access the data. This innovative system could enable the onset of frailty to be detected early, thus giving sufficient time for a targeted intervention program to be implemented, thereby increasing independence for elderly users.

Design and validation of the Grip-ball for measurement of hand grip strength.

The Grip-ball is a new dynamometer used to evaluate grip strength, as well as for use in home-based rehabilitation of the hand and forearm. The Grip-ball consists of pressure and temperature sensors and an electronic wireless communication system contained in an airtight ball. That can be inflated to different pressures. The device has advantages over standard dynamometers in that it looks like a simple ball, and can wirelessly communicate via Bluetooth to any compatible receiver, thus have potential to be used for clinical assessment and rehabilitation in a remote setting. The reliability and reproducibility of the device were assessed for the pressure sensor itself, as well as the relationship between the force applied and the pressure measured by the Grip-ball. The initial validation was performed using the pressure sensor without the ball in order to confirm the accuracy of the sensor used. A second validation study was conducted using the Grip-ball rather than just its sensor to examine the relationship between the pressure measured inside the ball and force applied. The results showed that there is a very good correlation (r=0.997, p<0.05) between the pressure measured by the Grip-ball sensor and that measured by a Vigorimeter, thus confirming the reliability of the sensor used in the Grip-ball. A quadratic regression equation was calculated in order to predict the force applied based on the pressure measured inside the ball, and the initial pressure to which the ball was inflated (R(2)=0.97, standard error 10.9N). Such a finding compares favourably with the variability inherent in Jamar recordings, thus indicating that the Grip-ball could be used to assess grip force. An industrial version of the Grip-ball, which is currently under development, will be able to be used for the entire range of grip force in the population.

Reliability and validity of the Grip-Ball dynamometer for grip-strength measurement.

Grip-strength measurement is a key element in the evaluation of numerous conditions including frailty. An innovative grip-strength evaluation tool, the Grip-Ball has been developed for remote assessment of grip-strength. The Grip-Ball is an airtight ball that can be inflated to different pressures, thus varying the stiffness of the ball and the grip-strength dynamics. Three different initial pressures of 100, 125, and 150 kPa were evaluated in respect to reliability and validity, when compared to the Jamar. Reliability was very high, with ICC values of 0.95, 0.98, and 0.99 for 100, 125, and 150 kPa, respectively. The new device was highly correlated with the force measured using the Jamar for all initial pressures (r= 0.88, 0.93, and 0.93 for 100, 125, and 150 kPa, respectively). The possibility of varying the initial pressure would enable the Grip-Ball to be used for standard grip-strength testing and rehabilitation, while still maintaining high reliability and validity.

Analysis of fatigue and tremor during sustained maximal grip contractions using Hilbert-Huang Transformation.

The objective of this study was to evaluate muscle fatigue and tremor during a Sustained Maximal Grip Contraction (SMGC) using the Hilbert-Huang Transformation (HHT). Thirty-nine healthy subjects volunteered for the study and performed a 25-s SMGC. Fatigue parameters such as the relative force output (RFO) were calculated from the residual of SMGC after applying Empirical Mode Decomposition (EMD). Using the energy spectrum of the Intrinsic Mode Functions (IMF) obtained using HHT, isometric force tremor was identified from the 4 to 12 Hz region in IMF3 and IMF4. Data were analysed for five consecutive 5-s epochs to identify changes in fatigue and tremor over time. The HHT method was able to identify a greater resistance to fatigue in women compared to men (p≤0.05) and in non-dominant hands compared to dominant hands (p≤0.05). Consistent with the results for fatigue, women had less tremor than men (p≤0.05), while non-dominant hands trembled less than did dominant hands (p≤0.05). Higher levels of tremor were observed for non-fatigue-resistant subjects for both 10-15 s and 15-20 s epochs (p≤0.05). The HHT is an appropriate method to identify both fatigue and tremor during SMGC. It would be of interest to apply this method to the study the elderly or patients with neuromuscular disorders.

Construct validity of a modified bathroom scale that can measure balance in elderly people.

OBJECTIVES: To investigate the construct validity of a bathroom scale measuring balance in elderly people. DESIGN: Cross-sectional study. SETTING: Participants were recruited via nursing homes and an organization that provides exercise classes for community-dwelling elderly people. PARTICIPANTS: Nursing home patients were compared with active community-dwelling elderly people. Eligibility criteria for both groups were: aged 65 years or older and being able to step onto a bathroom scale independently. MEASUREMENTS: The balance measurement of the bathroom scale was compared with the following three clinical balance measurements: Performance Oriented Mobility Assessment (POMA), Timed Up and Go (TUG), and Four Test Balance Scale (FTBS). An independent samples t-test was performed to determine whether nursing home patients scored lower on these four balance tests compared with community-dwelling elderly people. Correlations were calculated between the bathroom scale balance scores and those of the clinical balance tests for nursing home patients and community-dwelling elderly people separately. RESULTS: Forty-seven nursing home patients with a mean age of 81 years (SD 6.40) and 54 community-dwelling elderly people with a mean age of 76 years (SD 5.06) participated in the study. The results showed that nursing home patients had significantly lower scores on all four balance tests compared with community-dwelling elderly people. Correlations between the bathroom scale scores and the POMA, TUG, and FTBS in nursing home patients were all significant: .49, -.60, and .63, respectively. These correlations were not significant in active community-dwelling elderly people, -.04, -.42, and .33, respectively. Linear regression analyses showed that the correlations for the bathroom scale and POMA, bathroom scale and TUG, and bathroom scale and FTBS did not differ statistically between nursing home patients and community-dwelling elderly people. CONCLUSION: These results suggest that the modified bathroom scale is useful for measuring balance in elderly people. However, the added value of this assessment method for clinical practice remains to be demonstrated.

Longitudinal evaluation of balance quality using a modified bathroom scale: usability and acceptability.

We adapted a commercial bathroom scale in order to acquire the raw data from the weight sensors and then to send them to a server via a mobile phone. We investigated the usability and acceptability of the device in a long-term experiment with 22 elderly users that produced more than 5000 weight recordings. Four basic variables were extracted from the vertical force measurements and the stabilogram. The technology was accepted unreservedly, presumably because it did not differ from devices usually encountered in the home. The quantitative results showed a high variability of day-to-day measurement, which was countered by taking a moving average. A balance index was able to identify changes in balance over time. The preliminary results appear promising.

Predicting maximal grip strength using hand circumference.

The objective of this study was to analyze the correlations between anthropometric data and maximal grip strength (MGS) in order to establish a simple model to predict "normal" MGS. Randomized bilateral measurement of MGS was performed on a homogeneous population of 100 subjects. MGS was measured according to a standardized protocol with three dynamometers (Jamar, Myogrip and Martin Vigorimeter) for both dominant and non-dominant sides. Several anthropometric data were also measured: height; weight; hand, wrist and forearm circumference; hand and palm length. Among these data, hand circumference had the strongest correlation with MGS for all three dynamometers and for both hands (0.789 and 0.782 for Jamar; 0.829 and 0.824 for Myogrip; 0.663 and 0.730 for Vigorimeter). In addition, the only anthropometric variable systematically selected by a stepwise multiple linear regression analysis was also hand circumference. Based on this parameter alone, a predictive regression model presented good results (r(2) = 0.624 for Jamar; r(2) = 0.683 for Myogrip and r(2) = 0.473 for Vigorimeter; all adjusted r(2)). Moreover a single equation was predictive of MGS for both men and women and for both non-dominant and dominant hands. "Normal" MGS can be predicted using hand circumference alone.

Classification of elderly as fallers and non-fallers using Centre of Pressure velocity.

Falls are a leading cause of death in the elderly. One of the most common methods of predicting falls is to evaluate balance using force plate measurement of the Centre of Pressure (COP) displacement. This signal, known as a stabilogram, can be decomposed into movement in anteroposterior (AP) and mediolateral (ML) directions. It has been suggested that studying the velocity of COP displacement could lead to new insights into fall risk. The aim of this study was to attempt to classify elderly fallers and non-fallers, as well as control subjects based on COP velocity measurements. Three groups of 10 subjects (controls, elderly fallers, and elderly non-fallers) were compared. Discriminant function analysis was able to correctly classify 90% of the subjects based only on COP velocity measurements. Further work is needed to determine whether this parameter might be of use in longitudinal measurement of fall risk in home-dwelling elderly.

Domo-Grip: functional evaluation and rehabilitation using grip force.

Grip force measurement is routinely used to identify pathologies, evaluate muscular function, and as part of rehabilitation. Grip force has also been shown to be a good indicator of the capacity of elderly to live independently owing to its strong relationship with clinical tests such as the Index of Activities of Daily Living. An autonomous, communicant grip-force measurement device is presented in this paper in order to perform grip-force evaluation at home. The Domo-Grip system consists of the Grip-Ball, the Grip-Box, and Grip-Soft. The Grip-Ball measures the pressure resulting from grip force, the Grip-Box serves as the communication hub, while Grip-Soft is an interactive software suite. The Domo-Grip system can be used as part of a home-based rehabilitation, and also for functional evaluation as part of an assessment of the capacity of elderly to live autonomously.

Nonlinear chaotic component extraction for postural stability analysis.

This paper proposes a nonlinear analysis of the human postural steadiness system. The analyzed signal is the displacement of the centre of pressure (COP) collected from a force plate used for measuring postural sway. Instead of analyzing the classical nonlinear parameters on the whole signal, the proposed method consists of analyzing the nonlinear dynamics of the intrinsic mode functions (IMF) of the COP signal. Based on the computation of the IMFs Lyapunov exponents, it is shown that pre-processing the COP signal with the Empirical Mode Decomposition allows an efficient extraction of its chaotic component.

Biomechanical analysis of older adults stepping up: a method of evaluating balance.

The aim of this study was to analyze differences in biomechanical parameters between elderly and control participants when stepping up, to evaluate control of balance. Eleven control and 14 elderly participants performed a step from an initial static posture onto a 7-cm-high force plate. For the spontaneous-velocity condition, elderly participants performed a slower progression velocity than control participants. Elderly participants spent proportionally more time in stance phase, with a corresponding decrease in swing phase, than the control participants, irrespective of movement velocity. In contrast, at spontaneous velocity the parameters related to ground-reaction force (GRF) showed that anteroposterior and mediolateral forces at toe-off of the support limb and the slope of vertical force during weight transfer were significantly smaller for the elderly than for control participants. These GRF parameters depended on the stepping-up velocity. The elderly develop a spatiotemporal strategy and reduced movement velocity to control support balance.