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Biomedical subjects

R D D'Ambrosia

Publications and source records attributed to R D D'Ambrosia.

At least 19 recordsLinked to original sources
PubMed1998

Force feedback control of motor unit recruitment in isometric muscle.

The use of simple force feedback in an isometric muscle control system utilizing orderly recruitment of motor units is explored. Cat medial gastrocnemius motor units were stimulated with and without simple force feedback gain ranging from 0.7 to 0.9. Ramp, triangular, staircase, sinusoidal and bandwidth-limited pseudo-random input recruitment signals were used to study tracking accuracy through linear correlation in ramp and triangular signals, cross correlation in sinusoidal and random signals, and rise time and steady state error in staircase signals. Dramatic improvements were found in most tested tracking variables with the use of feedback; squared correlation coefficients increased from a mean of 0.93 to 0.99 for ramp signals and from 0.76 to 0.98 in triangular signals. Mean peak cross-correlations improved from 0.85 to 0.98 in random signals and from 0.93 to 0.98 for sinusoidal inputs, and mean time to peak cross-correlations decreased from 144 to 24 ms in random signals and from 156 to 25 ms in sine waves. Rise times in staircase signals decreased from a mean of 520 to 175 ms, and mean steady state error decreased from 12 to 3%. Significant effects of the triangle cycle time, sinusoidal frequency and staircase step were found on the performance of the muscle force control system. In addition, the possible effects of intrinsic feedback mechanisms on the control system were examined by repeating the closed loop part of the study but with the sciatic nerve cut proximally. The tracking results were essentially and statistically the same as in the closed loop condition. It was concluded that a simple feedback configuration provided superior tracking performance for a practical application in which orderly recruitment is used to control muscles; furthermore, it was concluded that this type of system would be virtually immune to external disturbances such as spasticity resulting from intact spinal neural feedback mechanisms found in paralyzed individuals.

Analysis of Variance↗
PubMed1998

Open-loop tracking performance of a limb joint controlled by random, periodic, and abrupt electrical stimulation inputs to the antagonist muscle pair.

The ability of the cat's ankle joint to track various input signals when controlled by electrically elicited motor unit recruitment, firing rate and antagonist muscle coactivation was examined. Pseudo-random, sinusoidal and staircase signals were used to control the soleus and tibialis anterior muscles isometrically and with a 250-g pendulum. Tracking was evaluated through cross correlation for pseudo-random and sinusoidal signals, and by rise time and steady-state error in step signals. Better tracking was obtained in isometric conditions than in load-moving conditions. Pseudo-random signals resulted in 250-ms delay between input and isometric torque output. For load-moving conditions, 340-ms and 400-ms delay in torque and angle were obtained. For sinusoids, delays decreased from 240 ms at 0.5 Hz, to 140 ms at 2 Hz in isometric conditions. Time delays for angle were between 300 and 400 ms, decreasing as frequency increased. Poor cross correlation was found for torque in load-moving conditions, because of pendulum nonlinear dynamics. Step size was not uniform in staircase trials, with steady-state errors between 9% and 39%, and rise times between 200 and 1000 ms. It is concluded that open-loop joint control results in poor tracking, presumably because it is devoid of feedback mechanisms.

Analysis of Variance↗
PubMed1997

Evaluation of antagonist coactivation strategies elicited from electrically stimulated muscles under load-moving conditions.

Muscle coactivation strategies that produce ankle dorsiflexion and plantar flexion were elicited by electrical stimulation of the tibialis anterior (TA) and soleus (SOL) muscles of the cat, and examined under several loading conditions. Four different load types were used: free-limb motion (no load), fly-wheel, and two pendulums, each with a different lever arm. Three types of coactivation strategies were considered. The first coactivation strategy consisted of antagonist activity that decreased as the agonist activity increased. The second strategy consisted of increasing antagonist activity with increasing agonist activity. And, in the third strategy, antagonist coactivation decreased at low force levels, then increased at high force levels. The three strategies were evaluated based on the joint angle's peak-to-peak movement and its ability to track a linear input command given by the correlation coefficient of the output signal versus linear input. Results showed that increasing antagonist activity resulted in decreasing peak-to-peak angle and a decreased signal tracking capability for each load condition. The latter, however, was not as obvious in the flywheel load (as compared with free-moving and pendulum conditions). A decreasing peak-to-peak torque for pendulum loads was also observed with increasing antagonist activity. In all loading conditions, maximal peak-to-peak angle and torque were present when a moderate degree of antagonist activity was engaged, and signal tracking capability improved with earlier engagement of the antagonist muscles. It is suggested that strategies using a combination of low-level coactivation, as described in the physiological literature and previous functional electrical stimulation (FES) studies, could satisfactorily address the issues of controllability and efficiency while maintaining long-term joint integrity.

Animals↗
PubMed1996

Evaluation of isometric antagonist coactivation strategies of electrically stimulated muscles.

The performance of various coactivation strategies to control agonist-antagonist muscles in functional electrical stimulation (FES) applications was examined in a cat model using the tibialis anterior and soleus muscles to produce ankle isometric dorsiflexion and plantarflexion torques, respectively. Three types of coactivation strategies were implemented and tested. The first strategy was based on coactivation maps described in the literature as consisting of decreasing antagonistic activity as the input command to the agonist was increased. The second type of strategy was based on the physiologic coactivation data collected from normal subjects exhibiting joint stabilization during the full range of contractions. These strategies included scaled increasing antagonist activity and therefore joint stiffness with increasing agonist input command. A third strategy was devised which at low force levels mimicked the strategies described in the literature and at high force levels resembled strategies exhibited by normal subjects. The three strategies were evaluated based on their ability to track a linear or sinusoidal input command and their efficiency of torque transmission across the joint. Coactivation strategies using increasing antagonist activity resulted in decreased maximal joint torque and efficiency, decreased signal tracking capability for linear inputs, and increased harmonic distortion for sinusoidal inputs. Peak efficiency and tracking ability appeared when a moderate degree of antagonist activity was engaged near the neutral joint position. Signal tracking quality improved with earlier engagement of the antagonist muscles. Our results suggest that strategies combining low-level coactivation as described in the physiological literature and previous FES studies could satisfactorily address the issues of controllability, efficiency, and long-term joint integrity.

Animals↗
PubMed1996

Activity relationships of total hip arthroplasty in patients with osteonecrosis and osteoarthritis.

We compared the age adjusted results of all primary Osteonics total hip arthroplasties with osteonecrosis and osteoarthritis. The Harris index hip score was used for the analysis. Twenty-eight patients had osteoarthritis and 26 patients had osteonecrosis. The Harris hip score was used to compare the osteoarthritis and osteonecrosis gross. Patients with osteoarthritis gradually increased in Harris hip score, whereas osteonecrosis patients gradually decreased in Harris hip score over 60 months. However, after the patients were adjusted for age above and below 50 years, the trend for each group was similar despite the diagnosis. All patients below 50 years of age, regardless of diagnosis, gradually decreased in hip score over time. On the other hand, all patients over 50 had a gradual increase in hip score with time. The poor results seen in patients with osteonecrosis may be related more to age and activity level than to the primary diagnosis. We do not believe that the diagnosis of osteonecrosis plays as significant a role in the final outcome of a total hip arthroplasty as does the patient's age and, more importantly, activity level following hip arthroplasty.

Activities of Daily Living↗
PubMed1995

The dynamic response of the cat ankle joint during load-moving contractions.

The dynamic response of the cat's ankle joint during load-moving activation of the medial gastrocnemius was determined. Sinusoidal-input oscillations of ankle plantar flexion were performed by the muscle at frequencies ranging from 0.4 to 5 Hz against a 10-N load acting via a cable through a pulley with a 2 cm radius. This was followed by sinusoidal muscle length changes against the same load while excluding the joint. The frequency responses of the two conditions were compared and decomposed in terms of their relative phase and gain, and best-fit pole-zero models to yield the dynamic model of the joint isolated from the muscle properties. The muscle displacement transfer function M(j omega) was characterized as two sets of double poles at 2.1 and 3.2 Hz, with a pair of zeros at 0.92 and 20 Hz, and pure time delay of 8 mS. The joint model J(j omega) was obtained by adding a pole at 5 Hz and a zero at 13 Hz. It was concluded that the ankle joint acts as a lag system, introducing significant increase in the phase lag between stimulus input and mechanical output without affecting the frequency-dependent attenuation of gain. Average harmonic distortion was less than 5% in all cases. This particular finding reveals that, despite its inherently nonlinear mechanical characteristics, the joint introduces no degradation in the simplified linear behavior of the muscle-joint system. This model is useful in the design of systems employing electrical stimulation to restore movement to limbs paralyzed by spinal cord injury or stroke.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Electromyography and biomechanics of a dynamic knee brace for anterior cruciate ligament deficiency.

Twelve anterior cruciate ligament (ACL)-deficient subjects performed concentric isokinetic knee extensions at maximum effort both with and without the Bledsoe Pro Shifter knee brace. Electromyogram signals from the quadriceps, hamstrings, knee angle, and the extension force were recorded and evaluated to determine the effects of such dynamic bracing on muscle activity and joint stability. High activity, or asymptomatic, subjects (n = 5) experienced no change in muscle activity, but displayed a decrease in extension force throughout the active range of the brace. Low activity, or symptomatic, subjects (n = 7) exhibited increased quadriceps activity and decreased hamstrings activity, and displayed a minor increase in force in the mid-range (80 degrees to 40 degrees flexion). These results indicate that dynamic bracing prevents quadriceps inhibition in symptomatic subjects by exerting a posteriorly directed force to the superior tibia; thus, the brace compensates externally for the absence of the ACL.

Adult↗
PubMed1994

Comparison of isometric and load moving length-tension models of two bicompartmental muscles.

The length-tension relations of two bicompartmental muscles, including parallel and pennated fibers, were experimentally determined for isometric and load moving contractions. Comparison of the isometric and constant mass load length-tension curves obtained from the same preparations demonstrated significant reductions in force, a shift of the optimal length and increased elongation range for shortening contractions under constant mass load. Pennated muscle demonstrated a larger reduction in force and greater shift in the optimal length relative to the changes in a muscle with parallel fibers. A bicompartmental model was fitted to the experimental data to provide quantitative insight to the changes described above, and for use in mathematical models of other bicompartmental muscles, and for design of optimal electrical stimulation system for restoration of function in spinal cord injury patients.

Animals↗
PubMed1990

Energy consumption in paraplegic ambulation using the reciprocating gait orthosis and electric stimulation of the thigh muscles.

The energy consumption of six thoracic paraplegic persons ambulating in the reciprocating gait orthosis (RGO) with and without functional electric stimulation (FES) of their thigh muscles was determined as a function of walking speed. Plots of Kcal/kg-min and Kcal/kg-m vs walking speed in the RGO and RGO & FES were experimentally determined in this study and compared with the energy cost of walking in the long leg brace (LLB), the hip guidance orthosis (HGO), and an FES walking aid from data available in the literature. The RGO powered with electric stimulation of the thigh muscles required the lowest energy expenditure in Kcal/kg-m across the full range of walking speeds. The RGO, HGO, LLB, and FES walking orthoses ranked second, third, fourth, and fifth respectively. The lowest energy costs in Kcal/kg-min were associated with the RGO & FES, followed by the RGO, HGO, LLB, and FES for walking speeds below .28m/sec. At walking speeds higher than .28m/sec the HGO demonstrates lower energy cost followed by the RGO & FES, RGO, FES, and LLB. At the end of a 30-m walk, patients using the RGO & FES had a mean heart rate (HR) which was 12 beats/min less than the mean HR when using the RGO without FES, 31 beats/min less than the HR when using the LLB, and 42 beats/min less than the HR when using FES only. It was concluded that the FES-powered RGO combines the advantages of a passive mechanical orthosis with those of FES to provide substantial improvements in energy cost which may provide paraplegic persons with a mode of independent ambulation superior to the wheelchair.

Adult↗
PubMed1989

Stabilization of sacroiliac joint disruption with threaded compression rods.

Eleven cases of sacroiliac dislocation and/or fracture (Malgaigne pattern) were successfully reduced and stabilized using two threaded compression rods. The mean follow-up period was 26.1 months (range, seven to 45 months). None of the implants failed and there was no subsequent displacement. Two patients had mild residual lower back pain, and one was treated with implant removal without subsequent relief of pain. One patient, in whom the operation was done 110 days after dislocation, had extension of an incomplete preoperative peroneal nerve palsy. After anterior pelvic ring stabilization has been performed, two threaded 3/16-inch diameter rods are driven from the normal posterior iliac wing superficial to the sacrum and through the reduced opposite iliac wing. Compression is obtained with washers and nuts. This procedure can be performed safely and effectively, providing stable fixation and allowing early mobilization to help lessen or prevent the complications associated with prolonged bed rest.

Adolescent↗
PubMed1988

Complex femur fractures: treatment with the Wagner external fixation device or the Grosse-Kempf interlocking nail.

One hundred complex femur fractures were treated with the Grosse-Kempf interlocking nail and 35 were treated with the Wagner external fixation device. Retrospectively, we analyzed the results in the two groups to determine specific indications for the future use of these nails. The Grosse-Kempf nail, although a technically demanding procedure, achieved excellent overall end results in comminuted closed fractures, and in Type I, Type II, and some Type III open fractures after appropriate wound care. We found that the Wagner apparatus was a simple, easy device for obtaining initial fracture stabilization in contaminated Type III-B and Type III-C open fractures. It does, however, require substantial postoperative care; four cases required secondary intramedullary fixation. We found a high infection rate with secondary reamed intramedullary nailing after initial stabilization with the external fixator.

Adolescent↗
PubMed1988

A case report of malignant mesenchymoma with discussion of musculoskeletal tumor staging: the Enneking system.

A 54-year-old black man presented with a soft-tissue sarcoma of the left anterior thigh. Surgical staging studies and initial biopsy results identified the lesion as a grade IIB pleomorphic liposarcoma. After radical hip disarticulation, follow up pathologic studies of the disarticulated limb showed the tumor to be confined to the anterior compartment of the left thigh without extracompartmental extension. The post-excisional surgical pathology report identified at least four different malignant mesenchymal elements: liposarcoma, myosarcoma, chondrosarcoma, and extraosseous osteogenic sarcoma. The sarcoma was therefore reclassified as a malignant mesenchymoma. The fact that the tumor was found to be intracompartmental at the time of surgery changed the staging of the tumor to stage IIA. A radical surgical margin, as recommended by Enneking, remained the treatment of choice. Three months postoperatively, the patient had chest pain and dyspnea. Chest films revealed multiple pulmonary nodules and the patient died of pneumonia 3 months later.

Femur↗