Leg general muscle moment and power patterns in able-bodied subjects during recumbent cycle ergometry with ankle immobilization

Rehabilitation of persons with pareses commonly uses recumbent pedalling and a rigid pedal boot that fixes the ankle joint from moving. This study was performed to provide general muscle moments (GMM) and joint power data from able-bodied subjects performing recumbent cycling at two workloads. Twenty-six able-bodied subjects pedalled a stationary recumbent tricycle at 60 rpm during passive cycling and at two workloads (low 15 W and high 40 W per leg) while leg kinematics and pedal forces were recorded. GMM and power were calculated using inverse dynamic equations. During the high workload, the hip and knee muscles produced extensor/flexor moments throughout the extensions/flexions phases of the joints. For low workload, a prolonged (crank angle 0-258°) hip extension moment and a shortened range (350-150°) of knee extension moment were observed compared to the corresponding extension phases of each joint. The knee and hip joints generated approximately equal power. At the high workload the hip and knee extensors generated increased power in the propulsion phase. For the first time, this study provides GMM and power patterns for able-bodied subjects performing recumbent cycling with an immobilized ankle. The patterns showed greater similarities to upright cycling with a free ankle, than previously supposed.

Spinal and cortical activity-dependent plasticity following learning of complex arm movements in humans

Activity-dependent plasticity is a fundamental requirement for human motor learning, which takes place at several stages of the motor system and involves various mechanisms in neuronal circuitry. Here, we investigate parameters of cortical and spinal excitability before and immediately after a single session of locomotion-like arm training (LMT) or sequential visuo-motor learning (VMT). Both training paradigms focused especially on mainly activating the flexor carpi radialis muscle (FCR). The activity-dependent change in the excitability of FCR-associated neurons was investigated using standard transcranial magnetic stimulation, including analysis of motor-evoked potentials (MEP) amplitude, short-interval intracortical inhibition and intracortical facilitation (ICF). Furthermore, spinal plasticity was also assessed by means of homosynaptic FCR H-reflex depression (HD). LMT decreased HD and ICF. In contrast, VMT had no significant effect on cortical and spinal parameters. There was a nonsignificant tendency of an increase in MEP amplitudes after both interventions. This implies that human locomotor-related learning involves spinal mechanisms. Despite the decreasing importance of quadrupedal coordination in the course of evolution, these changes in transsynaptic plasticity may reflect a persisting locomotor memory-encoding function in the spinal circuitry of the human upper extremities. Evaluating FCR HD might be helpful for the evaluation and development of locomotor rehabilitation strategies.

[Functional magnetic stimulation as a supposedly 'painless' option for movement induction in plegics]

BACKGROUND

It is known in the rehabilitation of central pareses that functional electrical stimulation (FES) of the muscles can induce movement and accomplish training in patients. The main limitations of this method are that patients with preserved sensation experience pain and the reflexes triggered by FES. Therefore the application of the largely "painless" magnetic stimulation (FMS) of the muscles would be a potential alternative in the rehabilitation of patients with partially preserved sensation. As the generation of high force and power levels is considered to be an essential requirement of effective rehabilitation strategies, we have shown in previous work that FMS with large surface magnetic coils fitted to the thigh can generate about 2.5 times higher isometric forces in patients with preserved sensation, than can FES.

OBJECTIVES

The goal of the present pilot study was to prove that the mechanical power generated by functional magnetic stimulation is superior to that produced by electrical stimulation too.

METHODS

We have measured the mechanical torque, the power, the accomplished work and the kinematics in 4 healthy control subjects, who performed pedalling propelled by FMS and FES until complete muscular exhaustion, using a cycling test-bed under isotonic conditions (constant resistance).

RESULTS

We have proved that the generated work, mean power, cadence and smoothness of pedalling essentially depend on peak torque and power. Furthermore, we found evidence that smoother pedalling could be achieved using magnetic, compared to electrical stimulation because of the higher peak torques that were generated by FMS.

CONCLUSION

This study supports the concept that peripheral magnetic stimulation is an appropriate rehabilitation method for patients with central pareses and preserved sensory apparatus because FMS is less painful than electrical stimulation.

Force-pain relationship in functional magnetic and electrical stimulation of subjects with paresis and preserved sensation

OBJECTIVE

Using "painless" magnetic stimulation (FMS) to support the cycling of paretic subjects with preserved sensation is possible and potentially superior to electrical stimulation (FES). We investigated the dependence of the torque and the pain evoked by FMS and FES on stimulation conditions in order to optimize magnetic stimulation.

METHODS

Torque and pain induced by quadriceps stimulation in 13 subjects with paresis and preserved sensation (due to multiple sclerosis) were compared under the conditions: (1) small vs large stimulated surfaces of the thigh, (2) varying contraction velocities of the muscle (isometric vs 15 and 30 rpm isokinetic speed), (3) FMS vs FES modalities, and (4) varying magnetic coil locations.

RESULTS

Torque and pain significantly depended on the amount of surface and location of stimulation during FMS, on the stimulation modality, and on the muscle contraction velocity during FES and FMS. FMS with a saddle-shaped coil produced more torque (p<0.05) than any other stimulation modality, even at 30 rpm velocity.

CONCLUSIONS

To support leg cycling of subjects with preserved sensation, the application of FMS stimulation with a large-surface saddle-shaped coil and the focusing of stimulation on the lateral-frontal surface of the thigh produces greater torque and less pain than FES.

SIGNIFICANCE

Optimized magnetic stimulation is a superior alternative to electrical stimulation in the rehabilitation of subjects with preserved sensation.

FES-propelled cycling of SCI subjects with highly spastic leg musculature

BACKGROUND

The presence of spasms precludes the use of artificial electrical activation of the muscles to restore mobility. The prospect of using an electrical stimulus that produces motor activation without causing unwanted reflex activation in patients with high levels of spasticity is an appealing one.

OBJECTIVE

The purpose of the study was to determine the efficacy of modulated middle frequency alternating current (MFAC) muscle stimulation compared to the conventional method of standard low frequency rectangular pulse (LFRP) stimulation used in cycling of persons with spinal cord injury (SCI) and pronounced spasticity.

METHODS

To evaluate cycling-relevant differences between stimulation modes, 13 subjects with SCI (ASIA-A), 11 of them with strong spasticity, underwent isometric and cycling measurements using both 20 Hz LFRP and 4 KHz modulated with 50 Hz MFAC. The isometric long-lasting reflex torque response in the quadriceps and hamstrings muscles, and the dynamic work during 1000 sec of ergometric cycling as well as the number of involuntary stops caused by hyperreflexia were recorded.

RESULTS

The long-lasting reflex torque response was significantly lower when using MFAC than with LFRP stimulation. During MFAC stimulation work generated was on average 374% higher (p = 0.002) and the number of involuntary stops was on average 32% lower (p < 0.001) than during standard LFRP stimulation-propelled cycling.

CONCLUSION

These findings suggest that MFAC-stimulated cycling of strongly spastic SCI subjects is more effective in terms of generated isometric torque and power than stimulation with LFRP. Thus, more health benefits, e.g., cardiovascular and muscular training and spasticity-decreasing effects, can be expected faster using MFAC instead of LFRP in stimulation-propelled cycling.

Functional electrical stimulation assisted cycling of patients with subacute stroke: kinetic and kinematic analysis

BACKGROUND

Cycling is a safe and functionally effective exercise for patients with early post-stroke and poor balance. Such exercise is considered even more effective when functional electrical stimulation is added. Our principal aim was to determine the biomechanically quantifiable parameters of cycling that can be improved in patients with subacute hemiparesis by incorporating functional electrical stimulation. These parameters were defined as objective goals that can be achieved in clinical applications. A secondary aim was to determine whether they could be used to identify subjects who would benefit from such therapy.

METHODS

Using a tricycle testbed, we tested 39 subacute (mean 10.9 weeks post-stroke (SD 5.9)), hemiplegic subjects. During isometric measurements we recorded volitional and electrically evoked crank torques, the latter at maximal tolerable intensity. During ergometric measurements, volitional pedaling was alternated with combined pedaling (volitional supported by stimulation), performed at 30-s intervals. Power, smoothness, and symmetry of cycling were evaluated.

FINDINGS

Twenty-six percent of the subjects significantly improved the smoothness of their cycling with functional electrical stimulation. Only 8% and 10% significantly increased their power and symmetry, respectively. The improvement in smoothness significantly correlated with the capability of the individual to generate electrical torque (Spearman's rank correlation coefficient=0.66 at P=0.001).

INTERPRETATION

The smoothness of cycling was the most sensitive parameter improved by functional electrical stimulation. This improvement depended on the amount of torque evoked, and the torque achieved, in turn, correlated with the tolerated intensity of stimulation.

Fahrradfahren Querschnittgel�hmter mittels funktioneller Elektrostimulation

Cycling using functional electrical stimulation offers paraplegics the possibility of muscle and cardiovascular training as well as the chance for independent locomotion. To investigate whether this method might be suitable for a large group of paraplegics, the first German feasibility study of functional electrical stimulation (FES) cycling with seven paraplegic patients was started at the beginning of 2003. Even at the beginning of the study, and without training, these patients were able to drive distances of 0.5-1.6 km. To stimulate cardiovascular adaptation processes in the case of FES ergometer training or to cover useful distances in the case of FES cycling, a minimum amount of generated mechanical output power is required, which as a rule cannot be achieved yet. In this study, we point out two particular aspects of FES cycling, which impair power output: prolonged fatigue mode and viscous joint friction of the paraplegic FES cyclist. We discuss current possibilities for increasing output power and endurance.

[The electrical stimulation bicycle: a neuroprosthesis for the everyday use of paraplegic patients]

Until recently, few patients with complete paraplegia could walk or stand with the help of functional electrical stimulation (FES) of the leg muscles regularly at home. In comparison, FES cycling with an adapted tricycle is easy to put into practice because the legs remain connected to the pedals and through the use of a tricycle or stationary bicycle, the balancing problems of the patient recedes into the background. In the first German feasibility studies for paraplegic cycling, eleven completely paraplegic patients have been tested so far. The goal is to make FES cycling a daily activity in the lives of as many patients as possible.

18F-FDG PET studies in patients with extratemporal and temporal epilepsy: evaluation of an observer-independent analysis

The aim of this study was to evaluate an observer-independent analysis of 18F-fluorodeoxyglucose (FDG) PET studies in patients with temporal or extratemporal epilepsy.

METHODS

Twenty-seven patients with temporal epilepsy and 22 patients with extratemporal epilepsy were included in the study. All patients with temporal epilepsy and 7 patients with extratemporal epilepsy underwent surgical treatment. In patients who showed significant postoperative improvement (temporal, n = 23; extratemporal, n = 6), the epileptogenic focus was assumed to be located in the area of surgical resection. In extratemporal epilepsy patients who did not undergo surgery, the focus localization was determined using a combination of semiology, ictal and interictal electroencephalography, [99mTc]ethyl cysteinate dimer SPECT, MRI and [11C]flumazenil PET. Visual analysis was performed by two experienced and two less experienced blinded observers using sagittal, axial and coronal images. In the automated analysis after anatomic standardization and generation of three-dimensional stereotactic surface projections (SSPs), a pixelwise comparison of 18F-FDG uptake with an age-matched reference database (n = 20) was performed, resulting in z score images. Pixels with the maximum deviation were detected, summarized and attached to one of 20 predefined surface regions of interest. For comparison with 18F-FDG PET and MR images, three-dimensional overlay images were generated.

RESULTS

In patients with temporal epilepsy, the sensitivity was comparable for visual and observer-independent analysis (three-dimensional SSP 86%, experienced observers 86%-90%, less experienced observers 77%-86%). In patients with extratemporal epilepsy, three-dimensional SSP showed a significantly higher sensitivity in detecting the epileptogenic focus (67%) than did visual analysis (experienced 33%-38%, each less experienced 19%). In temporal lobe epilepsy, there was moderate to good agreement between the localization found with three-dimensional SSP and the different observers. In patients with extratemporal epilepsy, there was a high interobserver variability and only a weak agreement between the localization found with three-dimensional SSP and the different observers. Although three-dimensional SSP detected multiple lesions more often than visual analysis, the determination of the highest deviation from the reference database allowed the identification of the epileptogenic focus with a higher accuracy than subjective criteria, especially in extratemporal epilepsy.

CONCLUSION

Three-dimensional SSP increases sensitivity and reduces observer variability of the analysis of 18F-FDG PET images in patients with extratemporal epilepsy and is, therefore, a useful tool in the evaluation of this patient group. The benefit of this analytical approach in patients with temporal epilepsy is less apparent.

Mitral valve surgery combined with coronary bypass grafting: multivariate analysis of factors predicting early and late results

Total of 123 patients (mean age: 63.8 +/- 7.3 years, (male/female 65/35 percent) underwent mitral valve surgery combined with coronary artery bypass grafting during a seven year period. Preoperatively 12% of them belonged to NYHA functional class II, 54% to class III, 29% to class IV and 3% was operated under emergency conditions. The mitral valve lesion was most frequently either ischaemic (45%) or rheumatic (33%) in origin. Left ventricle function was moderately decreased in 18% and severely damaged in 3% of the patients as documented by preoperative ventriculography. Coronary surgery was performed in all cases with an average number of distal anastomosis of 2.2 +/- 1.1 per patient. The hospital mortality was 13%. Risk factors for early and late mortality were determined by univariate and multivariate analysis. Advanced preoperative functional class and decreased left ventricular function or ischaemic etiology were identified as significant risk factors for early mortality. The patients were followed for an average of 33 +/- 25 months. The majority of them experienced significant functional improvement postoperatively with 69% belonging to NYHA class I or II. The late survival for the 107 hospital survivors was 94.7% at one year, and 84.7% at five years, respectively. Late survival was independently determined by preoperative functional class or previous myocardial infarction. Freedom from ischemic and valve related complications at five years was 95% and 71.2% respectively. 58.2% of the hospital survivors were in functional class I or II and free of any valve related or ischemic complications at the end of the fifth follow up year.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic and mitral valve replacement with the Carpentier-Edwards pericardial bioprosthesis: mid-term clinical results

Between May 1st 1985 and December 31st 1992, 283 Carpentier-Edwards pericardial valves were implanted in 260 patients in the aortic (n = 196), mitral (n = 41) and both aortic and mitral (n = 23) positions at the Gasthuisberg University Hospital in Leuven, Belgium. Patients undergoing tricuspid valve replacement or mixed replacement with another type of prosthesis were excluded from this study. The mean age was 70 +/- 7 years, there were 121 males and 139 females. The mean follow up was 40.55 months, the total follow up experience 10543 months (878.6 patients years). Hospital mortality was 10.4%, and was not significantly related to the position of the valve: 17.3% +/- 7.88% (n = 23) for double valve replacement, 10.2% +/- 2.16% (n = 196) for aortic valve replacement and 7.3% +/- 4.06% (n = 41) for mitral valve replacement. Hospital mortality was 14.1% +/- 3.27% for those with and 7.48% +/- 2.5% for those without concomitant coronary surgery (p = NS). Survival at 92 months was 63% +/- 6% and was not significantly related to the position of the valve. Not a single patient needed to be reoperated because of primary tissue failure. We conclude that the mid-term durability of this valve is excellent and consider the Carpentier-Edwards pericardial valve as the stented bioprosthesis of choice both in the aortic and mitral positions for the elderly. Because of the older age of our study population and the medium term length of follow up, we were unable to draw any conclusions concerning the incidence of calcific degeneration of this valve.

Fatty acid peptide derivatives as model compounds to protect elastin against degradation by elastases

Peptide sequences which fit the extended binding sites of porcine pancreatic elastase and human leukocyte elastase were covalently coupled to oleic acid. These compounds behave as competitive inhibitors towards both elastases. The coupling of fatty acid moiety to the peptide greatly decreases its inhibitor constant (Ki) vs human leukocyte elastase (Ki for Oleoyl(Ala)2ProValine: 3.0 (10(-6)M). It is less active on porcine pancreatic elastase (Ki for Oleoyl(Ala)2ProAlanine: 3.8 10(-4)M). The modifications of the carboxylic end group of the peptide to an aldehyde further greatly enhanced the inhibition capacity of the compound towards leukocyte elastase (Ki for Oleoyl(Ala)2ProAlaninal: 0.7 microM). Oleoyl peptide derivatives were seen to bind in a saturable fashion to purified insoluble elastin, and decreased the susceptibility of the macromolecule to hydrolysis by both pancreatic and leukocyte elastases. As stoichiometric quantities of elastase (vs inhibitor) could not desorb 3H-oleoyl(Ala)2Pro-Val bound to insoluble elastin, it is postulated that oleoyl peptide derivatives may act as bifunctional agents. This contention was further strengthened by the comparison of the adsorption curves of elastase to untreated insoluble elastin and elastin saturated with oleoyl peptide derivatives respectively. It was shown finally that Oleoyl(Ala)2Pro-Valine was also capable of inhibiting elastases in their adsorbed form to insoluble elastin.