[Improved function of the hand in persons with tetraplegia using electric stimulation via implanted electrodes]. / Forbedret håndfunktion hos tetraplegikere ved elektrisk stimulering via implanterede elektroder.

Functional Electrical Stimulation (FES) is a controlled use of electrical stimulation of muscle contractions to obtain function. FES is utilised today in the treatment of spinal cord injured individuals for diaphragmatic pacing, bladder and bowel management, ejaculation, walking and hand function, as well as conditioning. We present The Freehand System, which consists of implanted electrodes to arm and hand muscles. This system has now been implanted in the first two Nordic tetraplegics. Candidates are tetraplegics with C5-6 lesions. After implantation it may take 6-8 months before the tetraplegic person can expect to use The Freehand System completely in daily life. The tetraplegic individual can choose between two grasps. The Freehand System can for some few very physically disabled tetraplegics be a good aid to increase their level of activities of daily living and independence. Continued development in the coming years may broaden the indications with benefit for more individuals.

[Dilator muscles of the pharynx and their implication in the sleep apnea syndrome of obstructive type. Review of the literature]. / Les muscles dilatateurs du pharynx et leur implication dans le syndrome d'apnée du sommeil de type obstructif. Revue de la littérature.

Pathophysiology of the obstructive sleep apnea syndrome shows three components: intra and peripharyngeal obstacles, excessive pharyngeal wall compliance and upper airway dilator muscle dysfunction. The intent of this paper is to provide an overview of the anatomy, histology, physiology and pathophysiology of the upper airway dilator muscles based on previously published articles. The upper airway dilator muscles can be separated in three different systems, main and accessory dilators, local and regional. They act in synergy. Their contraction occurs at the beginning of inspiration, thus maintaining opened the pharyngeal lumen through inspiration. Their action is modulated by several chemo or physical stimuli. In some apneic patients, these muscles demonstrate a dysfunction: hyperactivity during wakefulness, electromyogram wave amplitude reduced, delayed contraction during sleep and abnormal response to stimuli. This dysfunction might be due to neuromuscular histological abnormalities, a "fatigue" phenomenon or a central nervous command abnormality. Current explorations underlining an upper airway dilator muscle dysfunction will enable practitioners to decide which treatment is best and understand therapeutical failures; it will also help develop new therapeutical techniques such as functional electrical stimulation of the hypoglossal nerve/upper airway dilator muscles.

Regression-based indices of fatigue in paraplegics' electrically stimulated quadriceps.

We studied muscle fatigue in 19 paraplegic patients during an isometric sustained contraction. Both quadriceps (n = 38) were maximally stimulated for 126 s. We defined a nonlinear equation with four coefficients to fit the data and extract fatigue indices carrying information on the amount (asymptotic values, torque coordinate at the inflection point, total decrement from initial value) and the rate of torque decrease (maximum slope, time constant, time coordinate at the inflection point, time at which the torque reached 50% of initial value). Most of the indices reported in the literature provide information limited to the amount of torque decrease. Three of the coefficients we defined could be graphically estimated. The goodness of fit was very high (r2 = 0.993 +/- 0.001) but none of the indices provided information on both the amount and the rate of decrease. Major differences were encountered among the patients. Therefore, some of the computed indices varied to a great extent. We studied the curves exhibiting the same fatigue indices and defined a simple general fatigue index able to distinguish from muscles having different resistance to fatigue (asymptotic value x the time constant). This index is carrying both types of information and is expressed in relative torque x second (range from 1.81 to 22.82).

Surface action potentials related to torque output in paraplegics' electrically stimulated quadriceps muscle.

We recorded in 15 complete paraplegic patients the torque output and the surface action potentials (SAP) produced by the electrically stimulated quadriceps muscle during an isometric contraction lasting 126 s. We studied the evolution during the test of the peak to peak amplitude, the latency from the onset of stimulation, the rising time to peak, the peak to peak duration, the area of the recorded SAPs and we tried to relate those data to the torque production. Results were extremely different among patients but the general behaviour facing this test was comparable. After a short increase the mechanical output decreased and reached a plateau (range from 7.13 to 53.5% of initial value). The peak to peak amplitude first increased and then decreased, and was not related to the torque production. The latency, the rising time to peak and the peak to peak duration continuously increased to a maximum and then plateaued or slightly decreased after different courses of time. The latency from the onset of stimulation was less affected by the test than the rising time to peak and the peak to peak duration. Therefore, the nerve conduction velocity and the neuromuscular junction transmission did not vary to a great extent compared to the muscle fibre conduction velocity. The area of the rectified SAPs first increased and then decreased and was not related to the torque decrease.

Functional and histologic effects of a free nonvascularised muscle graft implanted into a reinnervated muscle after prolonged denervation.

Striated muscle atrophy and degeneration, which increase with the delay of denervation, represent two of the main causes for poor recovery following delayed nerve repair. The present study, using a rat model, tests the hypothesis that an adjunction of small, free, nonvascularised muscle grafts of contralateral healthy triceps into a chronically denervated triceps improves muscle regeneration and recovery following sciatic nerve repair delayed for 3 months. Our experiments seem to show a relative increase in mechanical properties in animals in which free muscle graft into the triceps was performed 3 weeks following nerve repair. The improvement of the regenerative process of muscles which have suffered a long period of denervation should be considered as an additional therapeutic procedure in the case of late nerve repair.

Compound motor action potentials and mechanical failure during sustained contractions by electrical stimulation in paraplegic patients.

In nine paraplegic patients we recorded the torque output and compound motor action potentials (CMAPs) produced by the quadriceps muscle during an isometric contraction elicited by electrical stimulation. The torque, the peak to peak amplitude, the latency, the peak to peak duration and the total surface of the rectified CMAPs were computed over a period of 126 s. After a brief increase the mechanical output rapidly decreased and reached a stable minimum level by the end of 126 s. The final torque output values ranged from 7.1 to 54% of initial values. This torque decrease was related neither to length of time between injury and testing, nor to the thoracic level of the spinal cord injury. The peak to peak amplitude of the CMAPs changed over the course of stimulation. It was noted to increase over a period of time after which it decreased to a minimum level. The latency from the onset of stimulation to the onset of the CMAP varied to a relatively small extent compared to the peak to peak duration. Therefore, the conduction velocity along the muscle fibres appeared to be more affected by the test than by the conduction velocity along the nerve fibres and the transmission across the neuromuscular junction. The mechanisms involved in the changes in CMAPs and the change in torque output over the time course of stimulation are discussed.

Determination of fatigue in the electrically stimulated quadriceps muscle and relative effect of ischaemia.

The creation of muscle fatigue using surface electrical stimulation represents a highly reproducible phenomenon in spinal cord injured patients. The torque output was recorded as a function of time. The fatigue curves recorded over 110s exhibited three main parts: first, a plateau of short duration, followed by a more or less steep slope and then a second plateau which was maintained for a long time. This phenomenon was fitted using an exponential equation which had been developed and four parameters introduced that outlined to the muscle behaviour. A set of fatigue indices was defined to characterize the asymptotic value, the slope, the coordinates of the inflexion point, the time constant and the vertical amplitude of the curve recorded. Two populations were studied; a group of 11 thoracic level of injury paraplegic patients and a group of 10 able-bodied control subjects. The computed coefficients of determination, r2, were of very high values (0.99). Therefore, fatigue indices gave reliable information. Torque output did not differ between the two populations until 25 s had elapsed, but from 30 s onwards it was markedly lower in paraplegics. The residual torque output was 21.1 +/- 10.6% in the paraplegic group while it was 58.5 +/- 8.9% in the control group. The effect of blood supply in the production of fatigue was also studied by repeating the same tests using a tourniquet at the groin level. The residual torque became 14.7 +/- 2.3% in the paraplegic group and 42.9 +/- 6.3% in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Length-tension relationship of the posterior deltoid to triceps transfer in C6 tetraplegic patients.

We assessed the length-tension relationship of the posterior deltoid to triceps transfer in 8 tetraplegics (n = 11 transfers) and compared the results to the length-tension relationship of the normal triceps measured in a check sample composed of 9 able bodied, right handed women. We designed a device to lock the arm and forearm and used a force transducer to assess the torque output isometrically. The muscle was tested at 6 different lengths (130, 110, 90, 70, 45 and 0 degree of elbow flexion) with the shoulder abducted at 90 degrees. As expected, the transfer behaved differently from the normal triceps. The mean maximum torque recorded was 7.8 Nm in patients while it was 27 Nm in the check sample. When compared, the absolute values (ie values expressed with a dimension of torque) were significantly different between groups (0.00001 < p < 0.002). The expression of this relation (ie the relative values expressed as percentage of maximum values) revealed significant statistical differences (p < 0.002) at 90 and 70 degrees of elbow flexion; the peak torque was recorded at 130 degrees in patients while it was recorded at 110 degrees in the check sample, with a plateau between 110 degrees and 70 degrees. On the other hand, if the length-tension relationship was fairly similar among subjects of the check sample, it exhibited tremendous differences among patients; it seemed that initial tension given by the surgeon represented a variable difficult to control without a device dedicated to that task.

Effects of functional electrical stimulation (FES) on evoked muscular output in paraplegic quadriceps muscle.

In order to assess the effects of FES on muscle output, chronic electrical stimulation of the quadriceps muscle was applied for half an hour twice a day for 2 months, in 10 thoracic level traumatic paraplegic patients. Results concerning torque (at 6 different muscle lengths) and fatigue were measured using a strain gauge transducer in isometric condition, and compared with the findings in 15 paraplegic patients who had not received electrical stimulation, and with 10 able bodied subjects with normal motor functions. With training, muscle strength was very significantly improved whilst fatigue resistance remained at a low level. The peak torque was not found to be of the same muscle length when comparing paraplegics and control subjects; it seemed to demonstrate that length-tension relationship of the muscular actuator was changing when it was electrically activated. Moreover, the force recorded in paraplegics remained markedly lower than in able bodied people.