Biomedical subjects

Shauna Dudley-Javoroski

Publications and source records attributed to Shauna Dudley-Javoroski.

10 recordsLinked to original sources

PubMed2006

Feedback-controlled stimulation enhances human paralyzed muscle performance.

Chronically paralyzed muscle requires extensive training before it can deliver a therapeutic dose of repetitive stress to the musculoskeletal system. Neuromuscular electrical stimulation, under feedback control, may subvert the effects of fatigue, yielding more rapid and extensive adaptations to training. The purposes of this investigation were to 1) compare the effectiveness of torque feedback-controlled (FDBCK) electrical stimulation with classic open-loop constant-frequency (CONST) stimulation, and 2) ascertain which of three stimulation strategies best maintains soleus torque during repetitive stimulation. When torque declined by 10%, the FDBCK protocol modulated the base stimulation frequency in three ways: by a fixed increase, by a paired pulse (doublet) at the beginning of the stimulation train, and by a fixed decrease. The stimulation strategy that most effectively restored torque continued for successive contractions. This process repeated each time torque declined by 10%. In fresh muscle, FDBCK stimulation offered minimal advantage in maintaining peak torque or mean torque over CONST stimulation. As long-duration fatigue developed in subsequent bouts, FDBCK stimulation became most effective ( approximately 40% higher final normalized torque than CONST). The high-frequency strategy was selected approximately 90% of the time, supporting that excitation-contraction coupling compromise and not neuromuscular transmission failure contributed to fatigue of paralyzed muscle. Ideal stimulation strategies may vary according to the site of fatigue; this stimulation approach offered the advantage of online modulation of stimulation strategies in response to fatigue conditions. Based on stress-adaptation principles, FDBCK-controlled stimulation may enhance training effects in chronically paralyzed muscle.

Adaptation, Physiological↗

PubMed2006

Postfatigue potentiation of the paralyzed soleus muscle: evidence for adaptation with long-term electrical stimulation training.

Understanding the torque output behavior of paralyzed muscle has important implications for the use of functional neuromuscular electrical stimulation systems. Postfatigue potentiation is an augmentation of peak muscle torque during repetitive activation after a fatigue protocol. The purposes of this study were 1) to quantify postfatigue potentiation in the acutely and chronically paralyzed soleus and 2) to determine the effect of long-term soleus electrical stimulation training on the potentiation characteristics of recently paralyzed soleus muscle. Five subjects with chronic paralysis (>2 yr) demonstrated significant postfatigue potentiation during a repetitive soleus activation protocol that induced low-frequency fatigue. Ten subjects with acute paralysis (<6 mo) demonstrated no torque potentiation in response to repetitive stimulation. Seven of these acute subjects completed 2 yr of home-based isometric soleus electrical stimulation training of one limb (compliance = 83%; 8,300 contractions/wk). With the early implementation of electrically stimulated training, potentiation characteristics of trained soleus muscles were preserved as in the acute postinjury state. In contrast, untrained limbs showed marked postfatigue potentiation at 2 yr after spinal cord injury (SCI). A single acute SCI subject who was followed longitudinally developed potentiation characteristics very similar to the untrained limbs of the training subjects. The results of the present investigation support that postfatigue potentiation is a characteristic of fast-fatigable muscle and can be prevented by timely neuromuscular electrical stimulation training. Potentiation is an important consideration in the design of functional electrical stimulation control systems for people with SCI.

Adaptation, Physiological↗

PubMed2006

Electrically induced muscle contractions influence bone density decline after spinal cord injury.

STUDY DESIGN: Longitudinal repeated-measures; within-subject control. OBJECTIVE: We examined the extent to which an isometric plantar flexion training protocol attenuates bone loss longitudinally after SCI. SUMMARY OF BACKGROUND DATA: After spinal cord injury (SCI), bone mineral density (BMD) of paralyzed extremities rapidly declines, likely because of loss of mechanical loading of bone via muscle contractions. METHODS: Six individuals with complete paralysis began a 3-year unilateral plantar flexor muscle activation program within 4.5 months after SCI. The opposite limb served as a control. Compliance with recommended dose was > 80%. Tibia compressive force was > 140% of body weight. RESULTS: Bilateral hip and untrained tibia BMD declined significantly over the course of the training. Lumbar spine BMD showed minimal change. Percent decline in BMD (from the baseline condition) for the trained tibia (approximately 10%) was significantly less than the untrained tibia (approximately 25%) (P < 0.05). Trained limb percent decline in BMD remained steady over the first 1.5 years of the study (P < 0.05). CONCLUSIONS: Compressive loads of approximately 1 to 2 times body weight, induced by muscle contractions, partially prevent the loss of BMD after SCI. Future studies should establish dose-response curves for attenuation of bone loss after SCI.

Adult↗

PubMed2006

Assessment of physical function and secondary complications after complete spinal cord injury.

PURPOSE: Two physical function questions on the widely used SF-12 Health Related Quality of Life questionnaire appear less than optimal for people with complete spinal cord injury (SCI). Physical function questions typically receive the lowest score unless the individual is ambulatory. Additionally, the influence of secondary complications of SCI on quality of life is largely unknown. The purposes of this report are: (1) to determine whether two SF-12 physical function follow-up questions provide increased information in subjects with complete SCI; and (2) to describe the secondary complications of SCI in this group. METHOD: Ten subjects with complete SCI completed two survey instruments (the SF-12 and a Secondary Complications survey) every 3 months. The SF-12 included two physical function follow-up questions designed to improve the sensitivity and appropriateness of the SF-12 for a population with complete SCI. RESULTS: The SF-12 follow-up questions revealed differences in physical function that did not appear with the original SF-12 items. With the new questions, subject scores approximated population normative values. The most common secondary complications (back pain, shoulder pain, leg spasms, leg joint stiffness, and difficulty coughing) were the most likely to be rated as moderately or greatly bothersome. CONCLUSION: We advocate the use of follow-up questions for the SF-12 in complete SCI populations that are not ambulating to better discriminate changes in physical function. Secondly, we advocate further investigations to better understand the incidence and the severity of secondary complications after SCI.

Adolescent↗

PubMed2006

Musculoskeletal plasticity after acute spinal cord injury: effects of long-term neuromuscular electrical stimulation training.

Maintaining the physiologic integrity of paralyzed limbs may be critical for those with spinal cord injury (SCI) to be viable candidates for a future cure. No long-term intervention has been tested to attempt to prevent the severe musculoskeletal deterioration that occurs after SCI. The purposes of this study were to determine whether a long-term neuromuscular electrical stimulation training program can preserve the physiological properties of the plantar flexor muscles (peak torque, fatigue index, torque-time integral, and contractile speed) as well as influence distal tibia trabecular bone mineral density (BMD). Subjects began unilateral plantar flexion electrical stimulation training within 6 wk after SCI while the untrained leg served as a control. Mean compliance for the 2-yr training program was 83%. Mean estimated compressive loads delivered to the tibia were approximately 1-1.5 times body weight. The training protocol yielded significant trained versus untrained limb differences for torque (+24%), torque-time integral (+27%), fatigue index (+50%), torque rise time (+45%), and between-twitch fusion (+15%). These between-limb differences were even greater when measured at the end of a repetitive stimulation protocol (125 contractions). Peripheral quantitative computed tomography revealed 31% higher distal tibia trabecular BMD in trained limbs than in untrained limbs. The intervention used in this study was sufficient to limit many of the deleterious muscular and skeletal adaptations that normally occur after SCI. Importantly, this method of load delivery was feasible and may serve as the basis for an intervention to preserve the musculoskeletal properties of individuals with SCI.

Adult↗

PubMed2006

Predictive model of muscle fatigue after spinal cord injury in humans.

The fatigability of paralyzed muscle limits its ability to deliver physiological loads to paralyzed extremities during repetitive electrical stimulation. The purposes of this study were to determine the reliability of measuring paralyzed muscle fatigue and to develop a model to predict the temporal changes in muscle fatigue that occur after spinal cord injury (SCI). Thirty-four subjects underwent soleus fatigue testing with a modified Burke electrical stimulation fatigue protocol. The between-day reliability of this protocol was high (intraclass correlation, 0.96). We fit the fatigue index (FI) data to a quadratic-linear segmental polynomial model. FI declined rapidly (0.3854 per year) for the first 1.7 years, and more slowly (0.01 per year) thereafter. The rapid decline of FI immediately after SCI implies that a "window of opportunity" exists for the clinician if the goal is to prevent these changes. Understanding the timing of change in muscle endurance properties (and, therefore, load-generating capacity) after SCI may assist clinicians when developing therapeutic interventions to maintain musculoskeletal integrity.

Adolescent↗

PubMed2006

Peripheral quantitative computed tomography: measurement sensitivity in persons with and without spinal cord injury.

OBJECTIVES: To determine (1) the error attributable to external tibia-length measurements by using peripheral quantitative computed tomography (pQCT) and (2) the effect these errors have on scan location and tibia trabecular bone mineral density (BMD) after spinal cord injury (SCI). DESIGN: Blinded comparison and criterion standard in matched cohorts. SETTING: Primary care university hospital. PARTICIPANTS: Eight able-bodied subjects underwent tibia length measurement. A separate cohort of 7 men with SCI and 7 able-bodied age-matched male controls underwent pQCT analysis. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The projected worst-case tibia-length-measurement error translated into a pQCT slice placement error of +/-3 mm. We collected pQCT slices at the distal 4% tibia site, 3 mm proximal and 3 mm distal to that site, and then quantified BMD error attributable to slice placement. RESULTS: Absolute BMD error was greater for able-bodied than for SCI subjects (5.87 mg/cm(3) vs 4.5 mg/cm(3)). However, the percentage error in BMD was larger for SCI than able-bodied subjects (4.56% vs 2.23%). CONCLUSIONS: During cross-sectional studies of various populations, BMD differences up to 5% may be attributable to variation in limb-length-measurement error.

Adult↗

PubMed2005

Monitoring standing wheelchair use after spinal cord injury: a case report.

PURPOSE: An important issue in spinal cord injury (SCI) research is whether standing can yield positive health benefits. However, quantifying dose of standing and establishing subject compliance with a standing protocol is difficult. This case report describes a method to monitor dose of standing outside the laboratory, describes the standing patterns of one subject, and describes this subject's satisfaction with the standing protocol. METHOD: A man with T-10 complete paraplegia agreed to have his commercially available standing wheelchair instrumented with a custom-designed logging device for a 2-year period. The micro-controller-based logger, under custom software control, was mounted to the standing wheelchair. The logger recorded date, duration, angle of standing, and start/stop times. RESULTS: The client exceeded a suggested minimum dosage of standing per month (130.4% of goal), choosing to stand for short bouts (mean = 11.57 min) at an average angle of 61 degrees, on an average 3.86 days per calendar week. He was generally very satisfied with the standing device and provided subjective reports of improved spasticity and bowel motility. CONCLUSION: This case report describes a standing and surveillance system that allow quantification of standing dose. Future controlled studies are needed to evaluate whether standing can be beneficially affect secondary complications after SCI.

Adult↗

PubMed2005

Bone mineral density after spinal cord injury: a reliable method for knee measurement.

OBJECTIVES: To test the interrater reliability of a standardized method to analyze knee bone mineral density (BMD) using dual-energy x-ray absorptiometry (DXA); to compare spine, hip, and knee BMD of people with spinal cord injury (SCI) with able-bodied controls; and to determine the relation between hip BMD and knee BMD in SCI and able-bodied subjects. DESIGN: Criterion standard and masked comparison. SETTING: Primary care university hospital. PARTICIPANTS: A convenience sample of 11 subjects with complete SCI was age and sex matched with 11 able-bodied control subjects. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Four raters analyzed regions of interest according to operational definitions recently developed to standardize the analysis of BMD of the knee. Subjects with chronic SCI and matched controls underwent conventional DXA scans of the spine and hips and "less conventional" scans of the distal femurs and proximal tibias. The relation between hip and knee BMD was analyzed. RESULTS: The knee measurements were highly reliable (femur intraclass correlation coefficient model 2,1 [ICC(2,1)]=.98; tibia ICC(2,1)=.89). Subjects with SCI had lower BMD values than controls at all hip and knee sites (P<.05). Lumbar spine BMD did not differ between groups. Hip BMD was moderately predictive of distal femur BMD (R2=.67), but less correlated with the proximal tibia (R2=.38). CONCLUSIONS: Knee BMD can be reliably analyzed using DXA with this protocol. Subjects with SCI have diminished knee and hip BMD. Low hip BMD is associated with low distal femur BMD.

Absorptiometry, Photon↗

PubMed2003

Musculoskeletal deterioration and hemicorporectomy after spinal cord injury.

BACKGROUND AND PURPOSE: The long-term management following an hemicorporectomy (HCP) is not well documented in the scientific literature. The purpose of this case report is to describe the 25-year history of a man with a spinal cord injury who experienced severe musculoskeletal deterioration and hemicorporectomy. CASE DESCRIPTION: The client sustained T10 complete paraplegia at age 18 years, developed severe decubitus ulcers, and required an HCP as a life-saving measure 13 years later. The authors describe the chronology of several rehabilitation and prosthetic strategies and speculate on factors that may have contributed to their successes and failures. OUTCOMES: The client survived 12 years after the HCP and returned to independent mobility, self-care, and schooling despite complications with continued skin breakdown. Over the 12 years following discharge from the hospital after the spinal cord injury, he spent 749 days in the hospital. During the 12 years he lived after discharge from the hospital following the HCP, he was hospitalized 190 days. DISCUSSION: The authors discuss factors contributing to the client's musculoskeletal deterioration including chronic wounds, postural deviations, and incomplete adherence to pressure-relief recommendations and raise considerations for physical therapists who treat patients after HCP.

Adult↗