Bilateral Functional Electrical Stimulation for the Treatment of Presbyphonia in a Sheep Model

OBJECTIVES

The aim of the study was to increase muscle volume and improve phonation characteristics of the aged ovine larynx by functional electrical stimulation (FES) using a minimally invasive surgical procedure.

METHODS

Stimulation electrodes were placed bilaterally near the terminal adduction branch of the recurrent laryngeal nerves (RLN). The electrodes were connected to battery powered pulse generators implanted subcutaneously at the neck region. Training patterns were programmed by an external programmer using a bidirectional radio frequency link. Training sessions were repeated automatically by the implant every other day for 1 week followed by every day for 8 weeks in the awake animal. Another group of animals were used as sham, with electrodes positioned but not connected to an implant. Outcome parameters included gene expression analysis, histological assessment of muscle fiber size, functional analysis, and volumetric measurements based on three-dimensional reconstructions of the entire thyroarytenoid muscle (TAM).

RESULTS

Increase in minimal muscle fiber diameter and an improvement in vocal efficiency were observed following FES, compared with sham animals.

CONCLUSION

This is the first study to demonstrate beneficial effects in the TAM of FES at molecular, histological, and functional levels. FES of the terminal branches of the RLN reversed the effects of age-related changes and improved vocal efficiency.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:848-854, 2024.

Adaptation of the transcriptional response to resistance exercise over 4 weeks of daily training

We present the time course of change in the muscle transcriptome 1 h after the last exercise bout of a daily resistance training program lasting 2, 10, 20, or 30 days. Daily exercise in rat tibialis anterior muscles (5 sets of 10 repetitions over 20 min) induced progressive muscle growth that approached a new stable state after 30 days. The acute transcriptional response changed along with progressive adaptation of the muscle phenotype. For example, expression of type 2B myosin was silenced. Time courses recently synthesized from human exercise studies do not demonstrate so clearly the interplay between the acute exercise response and the longer-term consequences of repeated exercise. We highlight classes of transcripts and transcription factors whose expression increases during the growth phase and declines again as the muscle adapts to a new daily pattern of activity and reduces its rate of growth. Myc appears to play a central role.

SpillOver stimulation: A novel hypertrophy model using co-contraction of the plantar-flexors to load the tibial anterior muscle in rats

The influence of loading on muscular hypertrophy has previously been studied in rodents by removal of synergistic muscles or various weight-lifting regimes. We present a novel model, evoking hypertrophy in the rat's tibialis anterior (TA) muscle by means of an implanted single channel electrical nerve stimulator. The amount of load experienced by the TA was measured in acute experiments in anaesthetized rats with contractions over a range of stimulation frequency and amplitude. A novel electrode configuration allowed us to elicit concentric, isometric and eccentric contractions within the same setup. This was achieved by 'SpillOver' stimulation in which we adjusted the amount of co-activation of the stronger antagonistic plantarflexors by increasing the stimulus above the level that caused full recruitment of the dorsiflexor muscles. The effect of loading on hypertrophy of the TA was tested in 3-4 week stimulation experiments in two groups of freely-moving rats, with a protocol that resembles typical resistance-training in humans. One group performed concentric contractions with no antagonistic co-contraction (unloaded, UNL, n = 5). In the other group the TA was loaded by simultaneous co-contraction of the antagonistically acting plantarflexors (SpillOver, n = 5). The wet mass of the stimulated TA increased in both groups; by 5.4 ± 5.5% for the UNL-group and 13.9 ± 2.9% for the SpillOver-group, with significantly greater increase in the SpillOver-group (p<0.05). Our results correlate well with values reported in literature, demonstrating that SpillOver-stimulation is a suitable model in which to study muscular hypertrophy. Even higher gains in muscle-mass may be possible by optimizing and adjusting the stimulation parameters according to the principles of progressive resistance training.

Functional Electrical Stimulation Leads to Increased Volume of the Aged Thyroarytenoid Muscle

Objectives/Hypothesis

To reverse sarcopenia and increase the volumes of atrophied laryngeal muscles by functional electrical stimulation (FES) using a minimal invasive surgical procedure in an aged ovine model.

Study Design

Prospective animal study.

Methods

A stimulation electrode was placed unilaterally near the terminal adduction branch of the recurrent laryngeal nerve (RLN) adjacent to the right cricothyroid joint. The electrode was connected to an implant located subcutaneously at the neck region. Predesigned training patterns were automatically delivered by a bidirectional radio frequency link using a programming device and were repeated automatically by the implant every other day over 11 weeks in the awake animal. Outcome parameters comprised volumetric measurements based on three‐dimensional reconstructions of the entire thyroarytenoid muscle (TAM), as well as gene expression analyses.

Results

We found significant increases of the volumes of the stimulated TAM of 11% and the TAM diameter at the midmembranous parts of the vocal folds of nearly 40%. Based on gene expression, we did not detect a shift of muscle fiber composition.

Conclusions

FES of the terminal branches of the RLN is a secure and effective way to reverse the effects of age‐related TAM atrophy and to increase volumes of atrophied muscles.

Level of Evidence

NA Laryngoscope, 128:2852–2857, 2018

Monitoring of Fes-Induced Muscle Activity by Continuous Emg-Recording

Functional Electrical Stimulation (FES) requires information on the stimulated muscle for adjustment of the stimulation current, avoidance of muscle fatigue during the conditioning period and long term follow-up. Several applications of chronical FES are in clinical practice, but a system for direct registration of muscle activity under FES still does not exist. In six sheep the right Latissimus Dorsi Muscle (LDM) and Thoracodorsal Nerve were exposed. Stimulation electrodes were applied to each nerve and 3 EMG-applied sensing electrodes were placed into each LDM. The LDM tendon was connected to a force transducer. Burst stimulation was applied and the amplitude was increased from 0 to 4 mA in steps from burst to burst. EMG (M-wave) was amplified and recorded continuously via modified instrumentation amplifier, oscilloscope and tape recorder. Isometric muscle tension was recorded using force transducer, AID interface and PC. Continuous EMG-recording was performed in all cases. Simultaneous recording of muscle tension and EMG revealed a close correlation (lrl=0.95, p < 0.0001) between muscle strength and amplitude of the M-wave. Continuous recording of the EMG seems to be a reliable method for direct monitoring of the stimulated muscle. Three intramuscular electrodes can provide enough information to monitor FES induced muscle activity.

A novel miniature in-line load-cell to measure in-situ tensile forces in the tibialis anterior tendon of rats

Direct measurements of muscular forces usually require a substantial rearrangement of the biomechanical system. To circumvent this problem, various indirect techniques have been used in the past. We introduce a novel direct method, using a lightweight (~0.5 g) miniature (3 x 3 x 7 mm) in-line load-cell to measure tension in the tibialis anterior tendon of rats. A linear motor was used to produce force-profiles to assess linearity, step-response, hysteresis and frequency behavior under controlled conditions. Sensor responses to a series of rectangular force-pulses correlated linearly (R² = 0.999) within the range of 0–20 N. The maximal relative error at full scale (20 N) was 0.07% of the average measured signal. The standard deviation of the mean response to repeated 20 N force pulses was ± 0.04% of the mean response. The step-response of the load-cell showed the behavior of a PD2T2-element in control-engineering terminology. The maximal hysteretic error was 5.4% of the full-scale signal. Sinusoidal signals were attenuated maximally (-4 dB) at 200 Hz, within a measured range of 0.01–200 Hz. When measuring muscular forces this should be of minor concern as the fusion-frequency of muscles is generally much lower. The newly developed load-cell measured tensile forces of up to 20 N, without inelastic deformation of the sensor. It qualifies for various applications in which it is of interest directly to measure forces within a particular tendon causing only minimal disturbance to the biomechanical system.

In-situ measurements of tensile forces in the tibialis anterior tendon of the rat in concentric, isometric, and resisted co-contractions

Tensile-force transmitted by the tibialis anterior (TA) tendon of 11 anesthetized adult male Wistar rats (body-mass: 360.6 ± 66.3 g) was measured in-situ within the intact biomechanical system of the hind-limb using a novel miniature in-line load-cell. The aim was to demonstrate the dependence of the loading-profile experienced by the muscle, on stimulation-frequency and the resistance to shortening in a group of control-animals. Data from these acute-experiments shows the type of loading achievable by means of implantable electrical stimulators activating agonists or agonist/antagonist groups of muscles during programmed resistance-training in freely moving healthy subjects. Force-responses to electrical stimulation of the common peroneal nerve for single pulses and short bursts were measured in unloaded and isometric contractions. A less time-consuming approach to measure the force-frequency relationship was investigated by applying single bursts containing a series of escalating stimulus-frequencies. We also measured the range of loading attainable by programmed co-contraction of the TA-muscle with the plantar-flexor muscles for various combinations of stimulation-frequencies. The maximal average peak-force of single twitches was 179% higher for isometric than for unloaded twitches. Average maximal isometric tetanic-force per gramme muscle-mass was 16.5 ± 3.0 N g-1, which agrees well with other studies. The standard and time-saving approaches to measure the force-frequency relationship gave similar results. Plantar-flexor co-activation produced greatly increased tension in the TA-tendon, similar to isometric contractions. Our results suggest that unloaded contractions may not be adequate for studies of resistance-training. Plantar-flexor co-contractions produced considerably higher force-levels that may be better suited to investigate the physiology and cell-biology of resistance-training in rodents.

Correction: Reversing Age Related Changes of the Laryngeal Muscles by Chronic Electrostimulation of the Recurrent Laryngeal Nerve

[This corrects the article DOI: 10.1371/journal.pone.0167367.].

In Vitro Testing of an Implantable Wireless Telemetry System for Long-Term Electromyography Recordings in Large Animals

Multichannel bio-signal recording in undisturbed in vivo conditions is a frequent demand in experimental work for development of methodology and associated equipment for functional electrical stimulation (FES) application, limb prosthesis, and diagnostic tools in contemporary rehabilitation efforts. Intramuscular electromyogram (EMG) recordings can provide comprehensive insight in complex interactions of agonistic and antagonistic muscles during movement tasks and in contrast act as reliable control signals for both neuroprosthesis and mechanical prosthesis. We fabricated a fully implantable device, which is capable of recording electromyography signals from inside a body and transmit these signals wirelessly to an external receiver. The developed analog front end uses only two electrodes per channel, provides a gain of 60 dB, and incorporates a band pass filter with lower cut-off frequency of 4 Hz and upper cut-off frequency of 480 Hz. The bidirectional wireless data link, which operates in the 2.4 GHz Industrial, Scientific and Medical band, is designed for transmission distances of 10 m using an application data rate of 1 kSps for each of the two channels. Performed in vitro tests with the devices coated in epoxy resin and inserted into a phantom with tissue-equivalent characteristics confirmed the functionality of our concept and the measurement results are consistent with those from preceding simulations.

Predictability of thermo-lesions using electrodes for deep brain stimulation - an in vitro study

Background

Typically, electrodes for Deep Brain Stimulation (DBS) are used for chronic stimulation. However, there are conditions where this therapy has to be discontinued. In such cases using the DBS electrodes as a tool for thermo-lesioning (coagulation) could be used for an alternative treatment. The aim of this study was to determine if it is possible to generate coagula with a predictable geometry and to define their dimensions as a function of power and time in an in vitro model (egg white at room temperature). Furthermore, we tested if repetitive (cumulative) coagulation has an impact on the overall form and size of the clot.

Findings

Coagulation-growth was achieved as a function of power and duration of coagulation; reproducible well-formed thermocoagulations could be achieved. When using two adjacent electrodes a power range between 1.25 Watt and 2.00 Watt resulted in homogenous ovoid coagula. After two minutes of coagulation the clots reached a maximum in size and further growth could not be achieved. It was also possible to increase the size of a preformed clot by repetitive coagulation either by increasing the power level or the duration of the coagulation process.

Conclusions

We could show that it is possible to obtain predictable coagula in-vitro when using DBS electrodes for thermocoagulation even though they have not been developed for that specific purpose. However, until in-vivo safety and efficacy of DBS electrodes for ablation purposes is properly assessed, only approved electrodes should be used for brain ablation.

Technical analysis of dual channel pulse generators used in deep brain stimulation; a safety evaluation

BACKGROUND

A sudden failure of implantable pulse generators (IPG) occurred in 15 out of 143 units during the last 4 years in our patients. This corresponds to a failure rate of 10.5%. In all cases, the connection between the causes of battery and electronic circuit was found defective in the destructive analysis. In order to better understand the failure causes we proceeded to an analysis of explanted IPGs which had reached their normal life span due to depletion of the battery.

METHOD

A functional test and an intensive destructive analysis were carried out in 14 units. The internal parts of the IPG were inspected by light and electron microscopy.

FINDINGS

Deformations of the connection between battery and electronic circuit could be found in 12 out of 14 IPGs. The epoxy bonds, which achieve the mechanical fixation between the two contact areas of the bond wires, were found separated in 86%. Additionally, in six out of 14 devices the bond wires were either found lifted or with cracks as a sign of material fatigue.

CONCLUSION

Based on these results we conclude that the IPGs of the affected series did have a technical weak spot. We presume that this issue appears systematically and not randomly or triggered by an unusual action of the patient.

Atrophy, but not necrosis, in rabbit skeletal muscle denervated for periods up to one year

Our understanding of the effects of long-term denervation on skeletal muscle is heavily influenced by an extensive literature based on the rat. We have studied physiological and morphological changes in an alternative model, the rabbit. In adult rabbits, tibialis anterior muscles were denervated unilaterally by selective section of motor branches of the common peroneal nerve and examined after 10, 36, or 51 wk. Denervation reduced muscle mass and cross-sectional area by 50-60% and tetanic force by 75%, with no apparent reduction in specific force (force per cross-sectional area of muscle fibers). The loss of mass was associated with atrophy of fast fibers and an increase in fibrous and adipose connective tissue; the diameter of slow fibers was preserved. Within fibers, electron microscopy revealed signs of ultrastructural disorganization of sarcomeres and tubular systems. This, rather than the observed transformation of fiber type from IIx to IIa, was probably responsible for the slow contractile speed of the muscles. The muscle groups denervated for 10, 36, or 51 wk showed no significant differences. At no stage was there any evidence of necrosis or regeneration, and the total number of fibers remained constant. These changes are in marked contrast to the necrotic degeneration and progressive decline in mass and force that have previously been found in long-term denervated rat muscles. The rabbit may be a better choice for a model of the effects of denervation in humans, at least up to 1 yr after lesion.

Kinematic evaluation in Parkinson's disease using a hand-held position transducer and computerized signal analysis

BACKGROUND

The objective of this work was to develop a device for quantification of akinesia in Parkinson's disease, for the use in home monitoring of PD patients, as a part of home telecare programs. For this purpose a simple movement task is to be preferred, and the measurement devices must be small, lightweight, and easy to use, so patients may perform the measurements unattended. Another intended application was optimisation of the electrode position during implantations of neuromodulation systems for treatment of Parkinson.

METHOD

A hand held transducer was used to measure the position of the thumb while the patient repeatedly flexed and extended the thumb. The position data was sampled and stored on a personal computer with a plug in converter card and software. Measurements were performed on 15 PD patients and 6 age-matched controls. Signal analysis procedures were developed in order to automatically derive numerical parameters that quantify the movement performance. In order to select the most relevant parameters, they were correlated to Unified Parkinson Disease Rating Scale (UPDRS) motor scores (Spearman's rank, single sided, p < 0.05).

FINDINGS

In reviews of the raw position signals the amplitude and frequency was found to be lower in patients than in controls. In patients the movement was frequently interrupted by short periods of hesitation. The calculated parameters of covered distance (correlation coefficient r = -0.63), hesitation (r = 0.64) and frequency (r = -0.6) were found to be most relevant, as they correlated best to the UPDRS hand pronation/supination score.

DISCUSSION

The equipment proved to be fast to setup and easy to use. The signal analysis methods provided meaningful numerical parameters for quantification of akinesia, represented in hand pronation/supination. These results suggest that the described methods may be useful for telemedicine and intraoperative use.

Implantable device for long-term electrical stimulation of denervated muscles in rabbits

Although denervating injuries produce severe atrophic changes in mammalian skeletal muscle, a degree of functional restoration can be achieved through an intensive regime of electrical stimulation. An implantable stimulator was developed so that the long-term effects of different stimulation protocols could be compared in rabbits. The device, which is powered by two lithium thionyl chloride batteries, is small enough to be implanted in the peritoneal cavity. All stimulation parameters can be specified over a wide range, with a high degree of resolution; in addition, up to 16 periods of training (10-180 min) and rest (1-42 h) can be set in advance. The microcontroller-based device is programmed through a bidirectional radiofrequency link. Settings are entered via a user-friendly computer interface and annotated to create an individual study protocol for each animal. The stimulator has been reliable and stable in use. Proven technology and rigorous quality control has enabled 55 units to be implanted to date, for periods of up to 36 weeks, with only two device failures (at 15 and 29 weeks). Changes in the excitability of denervated skeletal muscles could be followed within individual animals. Chronaxie increased from 3.24 +/- 0.54 ms to 15.57 +/- 0.85 ms (n = 55, p < 0.0001) per phase in the 2 weeks following denervation.

Functional electrical stimulation-induced surface muscle stiffness captured by computer-controlled tonometry

A new tonometric test system to assess surface stiffness over relaxed and activated calf muscles was developed. The mechanical arrangement consists of a skin indentor driven by a torque motor (galvo-drive) that is rigidly connected to an ankle dynamometer. The indentation depth is measured by a displacement transducer. Software routines for cyclic indentation (recording of stiffness curves), static indentation (sensing of twitch responses), and vibration (skin resonance) were implemented. A visual interface is used to capture surface stiffness during target contractions and during controlled relaxation. For functional electrical stimulation (FES) applications, the software includes a pulse train synthesizer to generate arbitrary stimulation test patterns. The system's performance was tested in FES and voluntary contraction procedures.

The Vienna functional electrical stimulation system for restoration of walking functions in spastic paraplegia

An eight-channel stimulation system, currently intended for stimulation of lower extremities, was developed and is introduced. The major development goals were easy handling, modularity to make the system easily adaptable for other functional electrical stimulation (FES) applications, and a wide stimulation parameter range for application-specific parameter optimization. For paraplegic stepping, the system worn by the patient consists of 2 four-channel stimulation modules, a central unit holding the battery and circuitry for power management and communication control, a wireless remote control unit, and a palmtop computer as the main control and input device. A software package for Microsoft Windows supports the design and optimization of stimulation sequences in the rehabilitation center. First tests with patients familiar with FES showed smoother movements during stepping and acceptable good handling. In combination with the PC software, the required stimulation sequences could be created in a very short time.

Functional and biological test of a 20 channel implantable stimulator in sheep in view of functional electrical stimulation walking for spinal cord injured persons

A newly developed implantable stimulator with 20 output channels, mainly intended for the stimulation of lower extremities in paraplegics, was implanted in 6 sheep over a time period of 26 weeks. Five epineural electrodes each were used to contact various nerves at different locations to elicit hip and knee extension and flexion and to make carrousel and selective stimulation possible. Different electrode application strategies in view of paraplegic standing and walking were investigated. Additional implanted electrodes allowed M-wave monitoring for selectivity investigations in 3 sheep. Stimulator, electrode leads, and electrodes proved to be reliable. Selective stimulation with electrodes placed on the trunk of the sciatic nerve could be demonstrated but with bad reproducibility. Histological investigation of the tissues surrounding electrodes and leads showed the expected stable foreign body response. Strong hip and knee extension could be gained in all cases while only weak flexion forces could be elicited in most cases. Muscle biopsies showed that daily stimulation for 8 h at threshold level caused an increase in muscle Type I fibers and a decrease in Type IIc fibers. Implants and electrodes fulfill the most important functional and biological criteria for their clinical application for paraplegic walking. The intention to provide selective flexion functions via epineural stimulation could not be demonstrated sufficiently in this animal model.

Basic design and construction of the Vienna FES implants: existing solutions and prospects for new generations of implants

We can distinguish 3 generations of FES implants for activation of neural structures: 1. RF-powered implants with antenna displacement dependent stimulation amplitude; 2. RF-powered implants with stabilised stimulation amplitude; and 3. battery powered implants. In Vienna an 8-channel version of the second generation type has been applied clinically to mobilisation of paraplegics and phrenic pacing. A 20-channel implant of the second generation type for mobilisation of paraplegics and an 8-channel implant of the third generation type for cardiac assist have been tested in animal studies. A device of completely new design for direct stimulation of denervated muscles is being tested in animal studies. There is a limited choice of technologically suitable biocompatible and bioresistant materials for implants. The physical design has to be anatomically shaped without corners or edges. Electrical conductors carrying direct current (D.C.) have to be placed inside a hermetic metal case. The established sealing materials, silicone rubber and epoxy resin, do not provide hermeticity and should only embed DC-free components. For electrical connections outside the hermetic metal case welding is preferable to soldering; conductive adhesives should be avoided. It is advisable to use a hydrophobic oxide ceramic core for telemetry antenna coils embedded in sealing polymer. Cleaning of all components before sealing in resin is of the utmost importance as well as avoidance of rapid temperature changes during the curing process.

Preparation of a skeletal muscle ventricle in sheep: severe damage to the Latissimus dorsi muscle due to mobilization before preconditioning

As part of a study examining the use of a skeletal muscle ventricle for cardiac assistance in sheep, a new concept of muscle preconditioning was put into practice. We aimed to produce a latissimus dorsi muscle (LDM) capable of performing chronic work immediately after the construction of a skeletal muscle ventricle. The left LDM was detached from the thoracic wall, divided longitudinally and reattached in situ to achieve vascular delay. The right LDM was left unaffected. Thereafter, preconditioning of both LDM was started according to the clinically approved stimulation protocol for cardiomyoplasty. Preconditioning of the unaffected right LDM in situ resulted in a complete muscle fiber transformation with no signs of degeneration or necrosis. Mobilization of the left LDM before preconditioning led to a distinct damage of the muscle. During conditioning, the increase in burst duration from 2 to 3 impulses in sheep A and from 3 to 5 impulses in sheep B resulted in a homogenous degeneration of the muscle fibers of the left LDM. Histomorphological analysis showed a dramatic increase in the percent perimysial and endomysial connective tissue. The applied concept of muscle prefabrication proved to be a failure. Muscle splitting and mobilization followed by vascular delay and in situ conditioning as a concept of muscle prefabrication should be strictly avoided.

[EMG monitoring in functional electrostimulation]

When using functional electrical stimulation (FES), correct adjustment of stimulation parameters, and monitoring of the stimulated muscle is mandatory if tissue damage is to be avoided. Although several FES systems are already in regular use, a method for direct muscle monitoring is still lacking. This paper investigates the suitability of the electromyogram (EMG) for such a purpose. In six sheep, the right latissimus dorsi muscle (LDM) and the associated thoracodorsal nerve were exposed. Stimulation was effected via electrodes placed on the nerve. Three electrodes were placed in the LDM for EMG recording, and the tendon was connected to a force transducer for isometric force measurement. Stimulation was applied for one second (burst), followed by a three-second pause. The stimulation current was increased in 0.2 mA steps, starting at 0 mA and ending at 4 mA. Throughout the investigation, the EMG signal was monitored with an oscilloscope. In addition, the EMG signal and the force transducer signal were recorded for subsequent analysis. An analysis of the data of all six sheep revealed an almost linear relationship between muscle force and m-wave amplitude (magnitude of r = 0.95, p < 0.001). M-wave monitoring during EMG recording with three intramuscular electrodes is a reliable method of monitoring FES-induced muscle activity, but the absolute force cannot be measured.

Long-term electromyogram recording from the posterior cricoarytenoid muscle as a potential biological trigger for phrenic pacing: results of an animal study

Diaphragm pacing has been used to restore respiration in approximately 1,000 patients worldwide suffering from high quadriplegia or from central alveolar hypoventilation syndrome. Compared with conventional mechanical ventilation, electrophrenic respiration (EPR) reduces the risk of pulmonary infections and increases the mobility of patients. Voluntary activation of the pacemaker during speech would improve patients' quality of life and allow application of EPR in a more physiological way. An animal study was performed to investigate the electromyogram (EMG) of the posterior cricoarytenoid (PCA) muscle and the movement of the glottis via impedance measurement (electroglottography) with the aim to examine reproducibility and stability of the recordings from the PCA muscle as a potential biological trigger for a phrenic pacemaker. The EMG of the PCA muscle was recorded via implanted electrodes for a 200 day period. The EMG signal proved stable for that period, artifacts caused by movements can be suppressed, and swallowing can be detected. In contrast, impedance measurement to detect movement of the glottis proved not useful. Based on the results of this study, the use of the PCA EMG as a biological trigger for a phrenic pacemaker has to be considered a realistic option.

MYOSTIM-FES to prevent muscle atrophy in microgravity and bed rest: preliminary report

Long-term flights in microgravity cause atrophy and morphological changes of skeletal muscles. Training with mechanical devices is insufficient regarding the required time to exercise and space for devices. The objective of this project is to develop a passive training method based on functional electrostimulation (FES) to preserve muscle mass and fiber composition with minimal impairment to the cosmonaut. For a pilot experiment on the MIR space station, a suitable 8 channel FES device was developed. It consists of electrode trousers that carry surface electrodes and cables, 2 interconnected 4 channel stimulators, and a laptop personal computer (PC) for stimulator programming and processing compliance data. An automatic extensive training of 4 muscle groups of the lower extremities is performed for 6 h/day, with 1 s on and 2 s off tetanic contractions at 20-30% of maximum tetanic muscle force. The synchronous activation of antagonists of the thigh and lower leg prevents uncoordinated movements.

Dynamic force responses in electrically stimulated triceps surae muscles: effects of fatigue and temperature

To elicit dynamic force responses (unfused tetani) in isometric triceps surae muscles, low frequency electrical stimulation ranging from 12.5 to 30.0 Hz was applied. The fusing frequency (FF) and the relative dynamic force amplitude (DF) at the 20% and 40% maximum voluntary contraction (MVC) levels were calculated as parameters to determine effects of muscle fatigue (n = 6) and local muscle cooling. In the fatigued muscle (15 min plantar flexion at a 20% MVC level), the FF and DF increased when the fatigue was induced by voluntary contraction (FF increased from 19.6 to 22.5 Hz at 20% MVC) and also when induced by electrical stimulation (FF increased from 19.2 to 23.3 Hz). Cooling of the muscles showed an inverse effect on both parameters, indicating contractile slowing. The responsible physiological mechanisms as well as practical applications, using low frequency stimulation to monitor degenerative changes in muscles, are discussed.

Battery-powered miniature implant for electrical nerve stimulation

The range of application of implantable stimulators in functional electrical stimulation (FES) for therapeutic purposes and for the restoration of lost or damaged functions has steadily grown within the last 20 years. Each time a clinically used method is improved, a new field of FES application explored or basic research conducted, animal experiments are needed to check and evaluate the findings and results. It is precisely for this use that the stimulation system described in this paper was developed. The battery-powered single-channel stimulator can be used for the excitation of motor and sensory nerves with monophasic or biphasic impulses. All parameters and functions are programmable via the bidirectional telemetry circuit. Implant programming is achieved by a laptop computer, supported by a graphical user interface, instead of by a specially designed programmer. The maximum settings of the stimulation parameters are: frequency 100 Hz, monophasic pulse duration 0.8 ms, biphasic pulse duration 1.6 ms, stimulation current 3 mA. The implant volume was reduced to 2 cm3 (length 23 mm, width 13 mm, height 7.5 mm), lowering the weight to 3.6 g. Due to this small volume the implant can be used in small animals. The power supply via battery obviates the need for transcutaneous tunneling or permanent external high-frequency senders and facilitates the keeping of the animals.

Battery-powered implantable nerve stimulator for chronic activation of two skeletal muscles using multichannel techniques

Chronic activation of skeletal muscle is used clinically in representative numbers for diaphragm pacing to restore breathing and for dynamic graciloplasty to achieve fecal continence. The 3 different stimulation techniques currently used for electrophrenic respiration (EPR) all apply high frequency powered implants. It was our goal to make these stimulation methods applicable for EPR by a battery-powered nerve stimulator that would maximize the patient's freedom of movement. Additionally, the system should allow the implementation of multichannel techniques and alternating stimulation of 2 skeletal muscles as a further improvement in graciloplasty. Generally, the developed implantable nerve stimulator can be used for simultaneous and alternating activation of 2 skeletal muscles. Stimulation of the motor nerve is achieved by either single channel or multichannel methods. Carousel stimulation and sequential stimulation can be used for graciloplasty as well as for EPR. For EPR we calculated an operating time of the implant battery of 4.1 years based on the clinically used stimulation parameters with carousel stimulation. The multichannel pulse generator is hermetically sealed in a titanium case sized 65 x 17 mm (diameter x height) and weighs 88 g.

Personal computer supported eight channel surface stimulator for paraplegic walking: first results

Today functional electrical stimulation (FES) is used among other treatments to restore hand and arm function, to restore mobility of the lower extremities, for phrenic pacing, and in cardiomyoplasty. Common to all FES applications is that they require careful setup of stimulation parameters. To improve these tasks, personal computer (PC) based software for stimulation parameter evaluation and data acquisition was written. First, the described software was used to mobilize paraplegic patients in conjunction with an 12C bus controlled 8 channel surface stimulator. Electrodes were placed on each leg on the m. quadriceps and m. gluteus for hip and knee extension and the peroneal nerve to elicit flexion reflex. The fourth channel was used to correspond to subjects' individual needs. The stimulation patterns for standing up, walking, and sitting down easily could be set up and optimized by adjusting up to 128 stimulation parameters in a task-specific way.

Multifunctional implantable nerve stimulator for cardiac assistance by skeletal muscle

Different methods are used, clinically and experimentally, to assist severely impaired heart function by means of skeletal muscle. The efficiency of these methods is restricted by skeletal muscle losing strength after transpositioning and during conditioning and not being sufficiently resistant to fatigue. This is mainly due to the nonphysiological activation of the nerves by electrical stimulation. We have developed a battery operated, ECG triggered multichannel implant that is capable of implementing various advanced stimulation techniques. The stimulator can activate 2 skeletal muscles via the motor nerves. It allows for application of multichannel stimulation methods, i.e., carousel stimulation and sequential stimulation, as well as the programming of optimized pulse trains. Synchronization delay and burst duration can be automatically and dynamically adapted to the heart rate. The multichannel stimulator is hermetically sealed in a titanium case. Its calculated life span on the basis of the integrated battery is 3-5 years, depending on the programmed stimulation parameters. The implant dimensions are 65 x 17 mm (diameter x height), and it weighs 93 g. The implant has been tested in vitro as well as in vivo.

[Modular PC-based data acquisition and processing system for biological signals]

The data acquisition system described here is designed for biomedical research and permits the recording of up to eight biological signals simultaneously. A personal computer using the Windows 95 operating system is employed for data monitoring, data processing and analysis during experiments. The system has been designed for reliability, economy, flexibility and ease of handling, with the aim of achieving universal application. To avoid interface incompatibility, problems with transfer protocols and the data formats of commercially available products, analog signals are used for further processing. The individual input channels are electrically isolated from one another and the PC to avoid ground loops, and for reasons of safety. An isolated voltage supply is available for pre-amplifiers and bridges. A bandwidth of 0-5 kHz and the maximum sampling rate of 12.5 kHz suffice to pick up higher frequency signals such as EMG and ENG. The modular software and hardware concepts permit the use of almost any desktop or laptop PC as a central processing unit. The PC handless documentation, data acquisition, data analysis and the preparation of publications. If needed, further analytical functions can be added in modular form. Finally, the option of saving data in the ASCII format permits processing of results with such standard software packages as Excel, Access, Matlab and Origin.

Experimental development of an electrically stimulated biological skeletal muscle ventricle for chronic aortic counterpulsation

OBJECTIVE

The chronic shortage of donor organs for cardiac transplantation and the high costs for mechanical assist devices demand the development of alternative cardiac assist devices for the treatment of severe heart failure. Cardiac assistance by stimulated skeletal muscles is currently investigated as such a possible alternative. The goal of the presented study was to construct a newly designed biological skeletal muscle ventricle and to evaluate its possible hemodynamic efficacy in an acute sheep model.

METHODS

A total of 14 adult sheep were used for acute experiments. The entire thoracic aorta including the aortic root was excised from a donor sheep. An aorto-pericardial pouch conduit (APPC) was created by enlarging the aortic circumference in its middle section with two strips of pericardium. This biological conduit was anastomosed in parallel to the descending aorta of a recipient sheep, using the aortic root as an inflow valve to the conduit. Stimulation electrodes were applicated to the thoracodorsal nerve and the latissimus dorsi muscle was detached from the trunk and wrapped around the pouch. ECG-triggered functional electrical stimulation was applied during cardiac diastole to simulate aortic counterpulsation. Stimulation was performed during various hemodynamic conditions.

RESULTS

A standardised surgical procedure suitable for long term studies was established during six experiments. An APPC, with 70-80 mm filling volume, was found to be of optimal size. In another eight experiments, hemodynamic measurements were performed. Under stable hemodynamic conditions the stimulation of the biological skeletal muscle ventricle induced a significant increase of mean arterial pressure by 14% and mean diastolic pressure by 26%. During pharmacologically induced periods of cardiac failure, the stimulation of the APPC increased mean arterial pressure by 13% and mean diastolic pressure by 19%. In all eight experiments, the diastolic peak pressure reached supra-systolic values during stimulation.

CONCLUSIONS

The results demonstrate the hemodynamic efficacy of this newly designed biological skeletal muscle ventricle as an aortic counterpulsation device. Chronic experiments using a preconditioned fatigue-resistant muscle will further help to evaluate its possible clinical significance.

Computer aided adjustment of the phrenic pacemaker: automatic functions, documentation, and quality control

Electrical stimulation of the phrenic nerves of patients with complete ventilatory insufficiency with the Vienna respiratory pacemaker has been in clinical use since 1983. During the adjustment of stimulation parameters with this device, the following problems have occurred: for some measurements like the recruitment curve, series of complete inspiration cycles have to be stimulated, which causes the danger of muscle fatigue for unconditioned patients. The documentation is completed predominantly by hand, taking time and increasing the possibility of error. As a first step to solve these problems, we developed a new stimulation and measurement system. It consists of a PC with data acquisition hardware, the necessary sensors, and amplifier circuitry. The implanted stimulator is controlled via the parallel interface. The new system offers some advantages: computer control shortens the time for measurement and documentation, and the stress on the patient and the risk of error is reduced; synchronized measurement makes it possible to use single stimulation pulses instead of bursts and ramps to reduce diaphragm fatigue; digital signal processing improves measurement results and reproducibility; and help functions and self tests are provided, together with a graphical user interface. We used sensors for air flow, diaphragm EMG, and acceleration, on up to 8 channels simultaneously. Combined sample rates of up to 100 kS/s were possible. The system could be adapted for other uses involving functional electrical stimulation with our implantable nerve stimulators. Using this equipment saves a lot of effort, and the adjustment process can be focused on improved stimulation results and better performance for the patient. Current research is studying implementation of automatic functions like acquisition of stimulation thresholds. This could result in a predominantly automated adjustment of the phrenic pacemaker and even in a closed-loop controlled system in the future.

Useful applications and limits of battery powered implants in functional electrical stimulations

Battery powered stimulation implants have been well-known for a long time as heart pacemakers. In the last few years, fully implantable stimulators have been used in the field of functional electrical stimulation (FES) for applications like dynamic cardiomyoplasty and electro-stimulated graciloplasty for fecal incontinence. The error rate of battery powered implants is significantly smaller than that for conventional stimulator systems, and the quality of life for the patients is increased because the need for an external power and control unit is eliminated. The use of battery powered implants is limited by the complexity of the stimulation control strategies and the battery capacity. Therefore, applications like the stimulation of lower extremities for walking, cochlea stimulation, or direct muscle stimulation cannot be supported. The improvement of implantable batteries, microcontrollers, and ultralow power products is ongoing. In the future, battery powered implants will also meet the requirements of complex applications. Systems for restoration of hand and breathing functions after spinal cord injury can be the next field of use for battery powered implants. For these purposes, we developed a battery powered multichannel implant with a sufficient life span for phrenic pacing. The problems during development and the limits of this system are described in this paper.

Vienna phrenic pacemaker--experience with diaphragm pacing in children

Eight children, five boys and three girls, aging from 2 to 13 years (M = 9 +/- 3) were treated with the "Vienna phrenic pacemaker". Indication for implantation was central alveolar hypoventilation syndrome (CAH) in one case and total ventilatory insufficiency due to high cervical cord or brain stem lesion (SCI) in seven cases. Four electrodes were applied to each phrenic nerve via sternotomy. Both hemidiaphragms were paced synchronously with increasing duty cycles to condition the diaphragms for continuous electrophrenic respiration (EPR). EPR could be performed successfully in all children but one. Four children could achieve chronical EPR, one is in conditioning period. Two patients could not be discharged from hospital due to parental neglect and died after two and three years of intermittent stimulation. Six children could be discharged from hospital, two of them died after one and four years of chronic pacing. In one case tracheotomy could be closed definitively. Ventilatory insufficiency due to CAH and SCI can be treated even in children with diaphragm pacing, provided the indication for implantation, containing medical and social aspects, was made correctly. Diaphragm pacing probably will not lengthen life of severely injured children but it can increase the quality of their life and therefore should be preferred to positive pressure mechanical ventilation.

[Circulatory support by an electrically stimulated muscle flap. Experimental experiences]

Functional electrical stimulation of the latissimus dorsi muscle flap for circulatory assistance extends the traditional concept of using this flap for reconstructive procedures into the field of cardiac surgery. It requires a transformed muscle which is able to contract for long periods of time without fatigue. Two main groups of experiments have been carried out in sheep. In six sheep the latissimus dorsi muscle (MLD) was transformed into a fatigue-resistant muscle by the means of multichannel stimulation of the supplying motor nerve. After that, stimulation of MLD at a frequency of 70 contractions per minute could be performed continuously without significant muscle fatigue. The loss of maximal force caused by the conditioning procedure was about one third of the initial force. In a second series of acute experiments the MLD was used for cardiomyoplasty. The muscle was divided into two parts which were wrapped around the heart in two different forms. The resting tension of the muscle was preserved. EKG-synchronous stimulation resulted in an increase in left ventricular pressure between 12 and 53%. The increase in arterial pressure was between 10,6 and 58%.

Monitoring of FES-induced muscle activity by continuous EMG-recording

Functional Electrical Stimulation (FES) requires information on the stimulated muscle for adjustment of the stimulation current, avoidance of muscle fatigue during the conditioning period and long term follow-up. Several applications of chronical FES are in clinical practice, but a system for direct registration of muscle activity under FES still does not exist. In six sheep the right Latissimus Dorsi Muscle (LDM) and Thoracodorsal Nerve were exposed. Stimulation electrodes were applied to each nerve and 3 EMG-applied sensing electrodes were placed into each LDM. The LDM tendon was connected to a force transducer. Burst stimulation was applied and the amplitude was increased from 0 to 4 mA in steps from burst to burst. EMG (M-wave) was amplified and recorded continuously via modified instrumentation amplifier, oscilloscope and tape recorder. Isometric muscle tension was recorded using force transducer, A/D interface and PC. Continuous EMG-recording was performed in all cases. Simultaneous recording of muscle tension and EMG revealed a close correlation (IrI=0.95, p < 0.0001) between the muscle strength and amplitude of the M-wave. Continuous recording of the EMG seems to be a reliable method for direct monitoring of the stimulated muscle. Three intramuscular electrodes can provide enough information to monitor FES induced muscle activity.

Multichannel stimulation of phrenic nerves by epineural electrodes. Clinical experience and future developments

Between 1983 and 1992, 23 patients with complete ventilatory insufficiency of differing etiologies were treated with an eight channel implant (Medimplant Inc., Vienna) for fatigue free stimulation of both phrenic nerves. Data for 15 patients with high spinal cord lesions (ages: 9-51 years) are summarized: 1) level of lesion: C0, 3 patients; C1/C2, 4; C2/C3, 8; 2) time between incident and implantation: 3-14 months; 3) diaphragm training: 1-22 months; 4) chronic pacing: 5-83 months; 5) tracheostomy closed: 7 patients; 6) living permanently at home: 13 patients; 7) respiratory rate per minute: 12-17; 8) duration of inspiration: 1.0-1.3 sec; 9) tidal volume: 7-20 ml/kg body weight; 10) volume per minute: 121-198 ml/kg body weight; 11) pH: 7.39-7.42; 12) pCO2: 22.9-38.6 mmHg; 13) pO2: 81.2-104.5 mmHg; and 14) died by December 1992, 4 patients. All currently available implants for phrenic pacing need an external power supply and radio control. The authors have developed and tested the first fully implantable device. Features of this implant include an electronic circuit based on the microcontroller MC68HC705C8; surface mounted technology (SMD); eight channels; constant current source adjustable to 5 mA in 256 steps, impulse duration: 100-1000 musec, stimulation frequency: 1-33 Hz; and minimum lifetime: 3 years. The implant is programmed via bidirectional radio transmission using an IBM compatible computer. The dimensions, including battery, eight electrode connectors, and antenna, are 67 x 48 x 13 mm. The implant weights 58 g. This new device may improve patients' safety and quality of life in the near future.

First experimental application of multichannel stimulation devices for cardiomyoplasty

The effect of long-term application of epineural electrodes to nerves was investigated in rat experiments. Neural damage reached a maximum of 6% shortly after implantation and decreased to 3% after 1 year. Impedance and threshold of epineural electrode were investigated in sheep experiments for up to 12 months. The mean impedance was in the range of 1 kohm, while the threshold less than 1 mA. The reduction in fatigue produced by multichannel stimulation was demonstrated by sequential isometric contractions of rectus muscles in sheep. The decrease in force was only 10% after 60 minutes of multichannel stimulation as compared to a reduction of 50% for single channel stimulation. Studies of cardiomyoplasty with single channel stimulation confirmed results reported by other investigators. In acute experiments with sheep, we demonstrated fiber-selective stimulation which led to isolated contraction of the left or right distal part or the right proximal part of the latissimus dorsi muscle. Potential advantages in the application of implantable multichannel stimulation devices as compared to single channel stimulation for cardiomyoplasty include: (1) fatigue-free stimulation at submaximal force level; (2) selection of hemodynamically effective electrode combinations; (3) potential for consecutive activation of muscle fiber groups, thereby allowing better simulation of the physiological contraction of the heart muscle; (4) redundancy of electrodes in case of technical failure or dislocation; and (5) stimulation of more than one muscle, if necessary.