Trunk Posture from Randomly Oriented Accelerometers.

This study systematically explored the potential of applying feedback control of functional neuromuscular stimulation (FNS) for stabilizing various erect and leaning standing postures after spinal cord injury (SCI). Perturbations ranging from 2 to 6% body weight were applied to two subjects with motor complete thoracic level SCI who were proficient at standing with implanted multichannel neural stimulators to activate the ankle, knee, hip and trunk muscles. The subjects stood with four different postures: erect, forward, forward-right and forward-left. Repeatable and controlled perturbations were applied in the forward, backward, rightward and leftward directions by linear actuators pulling on ropes attached to the subjects via a belt worn just above the waist. Upper extremity (UE) forces exerted on a stationary walker were measured with load cells attached to the handles. A feedback controller based on center of pressure (CoP) varied the stimulation levels to the otherwise paralyzed muscles so as to resist the effects of the perturbations. The effect of the feedback controller was compared to the case where only open-loop baseline stimulation was applied. This was done in terms of: (a) maximum resultant UE force exerted by the subjects on the walker, (b) maximum resultant CoP overshoot and (c) CoP root-mean-square deviation (RMSD). Feedback control resulted in significant reductions in the mean values of the majority of outcome values compared to baseline open-loop stimulation. Maximum resultant UE force was reduced by as much as 50% in one of the postures for one of the subjects. RMSD and maximum CoPs were reduced by as much as 75 and 70%, respectively, with feedback control. These results indicate that feedback control can be used to reject destabilizing disturbances in individuals with SCI using FNS not only for erect postures but also for leaning postures typically adopted during reaching while attempting various activities of daily living.

Independent sitting is a major milestone and is also a prerequisite for optimal performance of activities of daily living (ADLs). Development of sitting posture control is a dynamic process involving control of degrees of freedom of head and trunk. Traditionally, trunk has been modeled as a single unit (segment). However, recent studies have suggested that it is made up multiple spinal units, controlled by a combination of trunk muscles. During typical development, posture control of trunk is different for different trunk segments. This motor development of trunk control is a complex process due to constant interaction between the nervous system and environment. Any interruption in the normal processes would further complicate it, affecting the typical development of the child. Poor trunk control and respiratory complications are characteristic features among children, adolescents, and adults with neuromuscular disorders. Pediatric spinal cord injuries (SCIs) also pose a unique challenge compared to SCI in adults because of the continuous physical and cognitive development. Children with SCI exhibit deficits in trunk motor control, which impair their ability to sit or ambulate. These motor deficits can lead to compensatory changes in other segments of the body, which cause further deviations from typical postures. Trunk muscles have the dual function of supporting both, breathing and trunk posture. Therefore, in children with SCI, impairment of posture control will also affect respiratory functions. Depending on level and severity of the injury, can potentially lead to severe respiratory insufficiency. Symptoms of respiratory insufficiency are highly correlated with the level and severity of spinal lesions. Injury at higher cervical and thoracic cord levels causes paresis and paralysis of most of the respiratory muscles, which increase the workload of breathing. As a result, respiratory complications are the leading cause of death among children with SCI. Therefore, impairment of posture control following SCI also affects respiratory functions. Lack of appropriate tools to evaluate trunk motor control following SCI restricts the ability to understand its development and therefore it is a challenge to design treatments and strategies to slow down or prevent the progress of long-term effects of SCI in children. In this dissertation, we studied the postural control using a Segmental Assessment Trunk Control (SATCo) test and respiratory motor control using Respiratory Motor Control Assessment (RMCA) protocol in typically developing (TD) children and compared their results to age-matched children with SCI.

Using Mathematical Models and Advanced Control Systems Techniques to Enhance Neuroprosthesis Function

BackgroundThe pendulum test is a quantitative method used to assess knee extensor spasticity in humans with spinal cord injury (SCI). Yet, the clinical implementation of this method remains limited. The goal of our study was to develop an objective and portable system to assess knee extensor spasticity during the pendulum test using inertial measurement units (IMU).MethodsSpasticity was quantified by measuring the first swing angle (FSA) using a 3-dimensional optical tracking system (with external markers over the iliotibial band, lateral knee epicondyle, and lateral malleolus) and two wireless IMUs (positioned over the iliotibial band and mid-part of the lower leg) as well as a clinical exam (Modified Ashworth Scale, MAS).ResultsMeasurements were taken on separate days to assess test–retest reliability and device agreement in humans with and without SCI. We found no differences between FSA values obtained with the optical tracking system and the IMU-based system in control subjects and individuals with SCI. FSA values from the IMU-based system showed excellent agreement with the optical tracking system in individuals with SCI (ICC > 0.98) and good agreement in controls (ICC > 0.82), excellent test–retest reliability across days in SCI (ICC = 0.93) and good in controls (ICC = 0.87). Notably, FSA values measured by both systems showed a strong association with MAS scores (ρ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\uprho$$\\end{document} ~ −0.8) being decreased in individuals with SCI with higher MAS scores, reflecting the presence of spasticity.ConclusionsThese findings suggest that our new portable IMU-based system provides a robust and flexible alternative to a camera-based optical tracking system to quantify knee extensor spasticity following SCI.

Many practical problems in the field of engineering become so complex that they may be effectively solved only with the aid of a computer. An effective solution depends on the use of an efficient algorithm. Plotting root locus diagrams is such a problem. This thesis presents such an algorithm. Root locus design of feedback control systems is a very powerful tool. Stability of systems under the influence of variables can be easily determined from the root locus diagram. For even moderately complex systems of the type found in practical applications, determination of the locus is extremely difficult if accuracy is required. The difficulty lies in the classical method of graphically determining the location of points on the locus by trial and error. Such a method cannot be efficiently applied to a computer program. The text presents an original algorithm for plotting the root locus of a general system. The algorithm is derived using the combined methods of complex variable algebra and numerical analysis. For each abscissa desired a polynomial is generated. The real roots of this polynomial are the ordinate values for points on the root locus. Root finding methods from numerical analysis enable the solution of the problem to be one of convergent iteration rather than trial and error. Among the material presented is a computer program for solution of the general problem, an example of a completely analytic solution, and a table of solutions for more simple systems. The program inputs are the coefficients of the open loop transfer function and the range and increments of the real axis which are to be swept. The output lists the real and imaginary components of all solution points at each increment of the sweep. Also listed are the magnitude and angle components of the solution point and the value of system gain for which this is a solution. For less complex problems, the method can be applied analytically. This may result in an explicit relation between the real and imaginary components of all solution points or even in a single expression which can be analyzed using the methods of analytic geometry. As with any advance in the theory of problem solving, the ideas presented in the thesis are best applied in conjunction with previous solution methods. Specifically, an idea of the approximate location of the root locus can be obtained using sketching rules which are well known. The method presented

Muscle atrophy is a major sequela occurring after spinal cord injury (SCI) that results from disuse. Additionally, other secondary complications of SCI (e.g., alterations in muscle blood flow) may contribute to muscle loss. PURPOSE: To determine the time course of muscle blood flow changes in relation to muscle atrophy in a rodent severe contusion SCI model. METHODS: Sixty-three 4-months-old (skeletally-mature) male Sprague-Dawley rats received SHAM surgery (T9 laminectomy) or severe (250 kdyne) contusion SCI using a computer-guided impactor. At 1-, 2-, and 4-weeks (wk) post-surgery, an intravenous catheter was implanted into the tail vein of SHAM and SCI animals. Colored microspheres (15μm diameter) were then infused into the circulation, allowing for the measurement of regional blood flow (ml/min/g tissue mass). Subsequently, the animals were euthanized and the mass of the dissected right and left soleus, gastrocnemius, and plantaris were taken. Concentrations of the colored microspheres within each muscle were determined via spectrophotometry, following chemical digestion of the muscle. Muscle blood flow calculations were then averaged across the contralateral hindlimbs for the aforementioned muscles. SCI vs SHAM comparisons were made at each time point using independent samples t-tests and Pearson’s correlation coefficients. RESULTS: SCI animals exhibited 23-41% lower soleus mass, 17-27% lower gastrocnemius mass, and 16-29% lower plantaris mass vs SHAM, at all time points (p<0.001). Soleus and gastrocnemius blood flow (corrected for tissue mass, ml/min/g) was 51% lower (p<0.001) and 25% lower (p<0.05) after SCI, respectfully, at 1-wk only. Additionally, a positive relationship between soleus mass and blood flow (corrected for mass) was identified at 1-wk (r= 0.687, p<0.01). No significant alterations in plantaris blood flow were identified at any time point. CONCLUSION: Hindlimb muscle atrophy and reduced muscle blood flow occurred within 1-wk of severe contusion SCI. Thereafter, muscle blood renormalized in comparison with SHAM animals. Further research is needed to determine whether the reductions in muscle blood flow occurring after SCI contribute to muscle loss and/or whether prevention of blood flow deficits preserves muscle mass.

Spinal cord injury (SCI) is a debilitating condition affecting an estimated 1,275,000 Americans at a cost of over 40 billion dollars each year. The main causes of SCI are automobile accidents, falls, other accidents, and violence such as gunshot or stab wounds. Depending on the precise location and severity of the insult, patients experience a range of motor, sensory, and autonomic impairments resulting either from disruption of ascending and descending axonal tracts or damage to the local neuronal circuitry at the injury site. Although much effort has been dedicated to the development of treatments and cures for this condition, to date, there is no effective way to reinstate motor, sensory, or autonomic functions. The burgeoning field of stem cell research has offered exciting new possibilities for the treatment of SCI, but little success has been realized in the limited clinical trials that have been performed thus far. The following chapter will review the cellular consequences of SCI, the efforts made to counteract these consequences by non-stem cell approaches, the stem cell-based strategies currently being investigated in preclinical studies, and the current state of clinical stem cell trials on patients suffering from SCI.

The model of NCS (Networked Control Systems) with state observer is presented when the network-induced random time-varying delays are bounded and the upper bound of which is longer than one sampling period. Thus we established a discrete-time jump system model with Markov delay. Based on this, this paper gave also initial feasible solution of interior-point algorithm to design stabilizing controllers by the optimization method. This paper generalizes previous results on delay-less state observer systems. Theoretical analysis and simulation on a cart and inverted pendulum with random time delay show that feedback control based state observer can make the system stable.

Optimal causal control of a wave energy converter in a random sea

A cross-sectional study evaluating BMD at the hip and tibia, and SOS at the radius and mid-tibia in individuals with spinal cord injury (SCI) and a subgroup of non-SCI individuals. To investigate the speed of sound (SOS) in bone in relation to bone mineral density (BMD). Kinesiology Department, McMaster University, Ontario, Canada. In 14 individuals with SCI and 10 non-SCI individuals, proximal femur and tibia BMD were measured using dual energy X-ray absorptiometry, and radius and tibia SOS were measured with an ultrasonometer. T-scores were calculated using healthy reference databases. Inter-relationships between measurement techniques were determined using Pearson's correlation coefficients. P-values less than 0.05 were considered statistically significant. : The average ages of the SCI and non-SCI groups were 33+/-9 and 27+/-6 years, respectively. Lesion level ranged from C4 to T12 and average time postinjury was 12 years, with a range of 1.6-25 years. Using the WHO criteria for osteoporosis, nine of 14 SCI subjects were osteoporotic at the hip, with the remainder in the osteopenic range. Tibia SOS T-scores were in the osteoporotic range for one subject with SCI, and two were in the osteopenic range. Among non-SCI individuals, one male had a tibia SOS T-score of -1.4, all others were within the normal range. Hip BMD and tibia SOS were significantly correlated (r=0.46, P<0.01). Hip BMD and tibia BMD were more strongly correlated (r=0.80, P<0.0005). Tibia BMD was not significantly correlated with SOS at the tibia (r=0.35, P=0.09). Radius SOS T-scores were positive and not significantly correlated with any lower limb variable. Lower-limb bone mass is reduced in spinal cord-injured individuals, but SOS at the mid-tibia is not. It remains to be determined whether ultrasound measurements can predict fracture in the SCI population.

Prognostic, retrospective case series. OBJECTIVE.: This study is part of a larger investigation to develop and validate a standardized and reliable method to evaluate and classify the neurologic consequence of spinal cord injury (SCI) in children. Such an instrument may also find use in the evaluation of patients with concomitant brain injury and/or cognitive impairment. We examined the relationship between the International Standards for Neurologic Classification of Spinal Cord Injury (ISCSCI) examination and magnetic resonance imaging (MRI) findings in a pediatric SCI population. Recently, the reliability of the ISCSCI in young children with SCI who are unable to cognitively engage in the examination has been called into question. This has important implications as appropriate classification of these patients is necessary for prognostication, follow-up care, and appropriate placement into clinical trials. Our longitudinal pediatric SCI database was reviewed for children with chronic SCI (>6 months), ISCSCI examinations performed by experienced testers, and adequate MRIs of the spine. ISCSCI results were correlated with MRI findings. Twenty-six subjects were identified. Overall, good to excellent relationships between ISCSCI neurologic level (NL) and MRI level of injury were found [Kendall tau correlation coefficient 0.90 (P < 0.001)]. The ISCSCI NL was on an average, two-thirds of a vertebral level cephalad to the center of the lesion on MRI. One child with MRI evidence of cord disruption tested incomplete at ISCSCI examination. The ISCSCI examination was found to have good to excellent relationships with MRI level in children with chronic SCI. Our results suggest MRI may be a useful adjunct for the determination of NL in children unable to participate with the examination. Our results also suggest caution in using the ISCSCI for the determination of completeness in young children. Further research into new methods (e.g., diffusion tensor imaging) to determine completeness of injury is warranted.

Cross-sectional validation study. The performance of previously published physical activity (PA) intensity cutoff thresholds based on proprietary ActiGraph counts for manual wheelchair users (MWUs) with spinal cord injury (SCI) was initially evaluated using an out-of-sample dataset of 60 individuals with SCI. Two types of PA intensity classification models based on raw accelerometer signals were developed and evaluated. Research institutions in Pittsburgh PA, Birmingham AL, and Bronx NY. Data were collected from 60 MWUs with SCI who followed a structured activity protocol while wearing an ActiGraph activity monitor on their dominant wrist and portable metabolic cart which measured criterion PA intensity. Data was used to assess published models as well as develop and assess custom models using recall, specificity, precision, as well as normalized Mathew's correlation coefficient (nMCC). All the models performed well for predicting sedentary vs non-sedentary activity, yielding an nMCC of 0.87-0.90. However, all models demonstrated inadequate performance for predicting moderate to vigorous PA (MVPA) with an nMCC of 0.76-0.82. The mean absolute deviation (MAD) cutoff threshold yielded the best performance for predicting sedentary vs non-sedentary PA and may be used for tracking daily sedentary activity. None of the models displayed strong performance for MVPA vs non-MVPA. Future studies should investigate combining physiological measures with accelerometry to yield better prediction accuracies for MVPA.

The purpose of this study was to determine the main factors that influence physical work capacity (PWC) in wheelchair-dependent paraplegics with spinal cord injury (SCI) using multivariate analysis. Thirty-two male paraplegics with SCI (PSCI) performed a submaximal arm exercise test on an arm-cranking ergometer to determine their PWC (oxygen uptake: ml x kg(-1) x min(-1)) at a heart rate of 150 beats x min(-1) (PWC150). Hayashi's Quantification first type was applied to analyze the effects on PWC150 of six factors: age, smoking, level of physical activity, occupation, level of SCI and period since SCI. This analysis revealed high partial correlation coefficients between PWC150 and the level of SCI (0.651) and physical activity level (0.583) compared to other factors. In addition, the multiple correlation coefficient for six factors in predicting PWC150 was 0.726. These results indicate that the level of SCI and physical activity are the most important factors in determining PWC in wheelchair-dependent male PSCI.

Human balance control system allows people to independently perform acts of daily living and to avoid falls that can cause injuries and hospitalization. Aging or various pathologies may cause disorders in the balance system and result in wide variety of problems and generally decreased quality of life. Researchers and health professionals therefore strive to develop effective methods and instruments for prompt diagnosis and rehabilitation of balance disorders. A common approach used to detect balance problems in scientific studies and clinical applications is to analyze various parameters of postural stability gathered during quiet stance. This paper presents an experimental setting for postural stability evaluation composed of two independent systems. A commercial force platform (Ecowalk) and a sensor node with multiple inertial and magnetic sensors are combined to simultaneously measure trunk orientation and center-of-pressure (COP) during quiet stance. A preliminary study with 8 healthy subjects was conducted in order to test the system functionality. Trunk orientation and COP were measured in four different conditions for every subject as they tried to maintain steady upright position. The area of trunk sway trajectory and COP variability were calculated from orientation and force platform measurements. The goal of this study was to explore whether use of the created experimental setting can provide a measure of two different biomechanical properties related to the balance control system during quiet stance trials. The initial results are promising as they have shown consistency in both variables during trials in different conditions, but further measurements with more subjects are needed for stronger conclusions.Keywordshuman balance controlpostural stability evaluationbiomechanicscenter-of-pressuretrunk orientation

Approaches to the analysis and design of feedback control systems in which measurement quantization is present are discussed. The author regards a quantized measurement of a real number simply as a partial observation of that number and not as a straightforward approximation with associated error. As a consequence, the results have an information theoretic component that is absent from earlier research, the majority of which deals with measurement quantization by means of signal-plus-noise models and least-squares theory. It is possible to compute an upper bound on the asymptotic accuracy (measured as a mutual information) with which the current state of a linear system can be specified given a long record of quantized measurements. In deriving this upper bound, it is shown how input to the system can be used as information-gathering tools, and an observer-like construction for systems with quantized outputs is obtained. The results have some interesting system theoretic ramifications, and they form the foundation for a theory of observability for state-space systems with piecewise constant output. This theory differs from the usual one in several significant ways, and the utility of its attendant formalism is demonstrated by some simple examples. >