TetraGrip - a four channel upper limb FES device for people with C5/C6 tetraplegia: device design and clinical outcome.

The TetraGrip is an inertial measurement unit-controlled surface upper limb FES device developed for improving hand functions of people with tetraplegia. The reliability of the control system and the repeatability and reproducibility of the device were assessed by analysing the results obtained when 14 able-bodied volunteers used the device. These volunteers were able to generate the control signals effectively once they had sufficient training. The two tetraplegic volunteers participated in a 12-week long clinical study (exercise, 4 weeks; functional tasks, 8 weeks), where they used the device to perform functional tasks. Outcome measures used were the grasp release test, the grip strength test, and the box and block test. Both tetraplegic volunteers showed improvement in performing the tasks specified in all outcome measures. The TetraGrip performed as intended when the able-bodied volunteers used it, and it improved the hand functions of both volunteers with tetraplegia. However, a larger clinical study is necessary to assess the performance of the device with a wider range of people with tetraplegia such as those with C5 complete/incomplete.

Upper limb functional electrical stimulation devices and their man-machine interfaces.

Functional Electrical Stimulation (FES) is a technique that uses electricity to activate the nerves of a muscle that is paralysed due to hemiplegia, multiple sclerosis, Parkinson's disease or spinal cord injury (SCI). FES has been widely used to restore upper limb functions in people with hemiplegia and C5-C7 tetraplegia and has improved their ability to perform their activities of daily living (ADL). At the time of writing, a detailed literature review of the existing upper limb FES devices and their man-machine interfaces (MMI) showed that only the NESS H200 was commercially available. However, the rigid arm splint doesn't fit everyone and prevents the use of a tenodesis grip. Hence, a robust and versatile upper limb FES device that can be used by a wider group of people is required.

Biomechanical approaches applied to the lower and upper limb for the measurement of spasticity: a systematic review of the literature.

PURPOSE: To review and characterise biomechanical approaches for the measurement of spasticity as one component of the upper motor neurone syndrome. METHOD: Systematic literature searches based on defined constructs and a four-step review process of approaches used or described to measure spasticity, its association with function or associated phenomena. Most approaches were limited to individual joints and therefore, to reflect this trend, references were grouped according to which body joint(s) were investigated or whether it addressed a functional activity. For each joint, references were further sub-divided into the types of measurement method described. RESULTS: A database of 335 references was established for the review process. The knee, ankle and elbow joints were the most popular, perhaps reflecting the assumption that they are mono-planar in movement and therefore simpler to assess. Seven measurement methods were identified: five involving passive movement (manual, controlled displacement, controlled torque, gravitational and tendon tap) and two involving active movement (voluntary and functional). Generally, the equipment described was in an experimental stage and there was a lack of information on system properties, such as accuracy or reliability. Patient testing was either by cohort or case studies. The review also conveyed the myriad of interpretations of the concept of spasticity. CONCLUSIONS: Though biomechanical approaches provide quantitative data, the review highlighted several limitations that have prevented them being established as an appropriate method for clinical application to measure spasticity.

The measurement of interface pressure and its role in soft tissue breakdown.

This paper describes the effect of applied pressure on soft tissue and its possible role in the development of pressure ulcers. It concentrates on the quantification of the applied pressure at the patient-support interface and the limitations and variability of current techniques, measurement systems and data presentation. It then describes the effects of interface pressures at the tissue and cellular level, and attempts that have been made to describe and model the tissue mechanics. Finally it sets a challenge to medical engineers to improve the present measurement systems and tissue models, thus increasing understanding, both clinically and at the cellular level, so that the incidence of pressure ulcers can be reduced.

Electrical stimulation of abdominal muscles for control of blood pressure and augmentation of cough in a C3/4 level tetraplegic.

OBJECTIVES: Evaluation of a FES (Functional Electrical Stimulation) device for the relief of postural hypertension and augmentation of cough in a C3 ventilator-dependent tetraplegic. STUDY DESIGN: A single case study. SETTING: A supra regional spinal unit in the UK. METHOD: A dual channel stimulator was designed that allowed selection and initiation of two predetermined stimulation intensities using a chin controlled joystick. Two sets of 70 mm diameter electrodes were placed either side of the abdomen. Approximately 80 mA, 300 micros, 40 Hz was required for assisted cough while about 40 mA was required for maintenance of blood pressure. After eating, the lower level stimulus is self-administered every 3 to 5 min gradually increasing the time between groups of burst to once every hour after 90 min. RESULTS: Following eating, a blood pressure of 60/45 mmHg was recorded. After five 1 s bursts of stimulation in quick repetition, this was increased to 133/92 mmHg. After 2 min blood pressure had fallen to 124/86 mmHg and to 93/66 after a further 4 min. The electrical stimulation was then repeated, returning the blood pressure to the previous higher level. Measurement of peak expiratory flow showed an increase from 275 l/min for an unassisted cough to 425 l/min when using the device. CONCLUSION: The device is used every day. The user is now independent in coughing function and no longer requires suction or manual assistance. Maintenance of blood pressure has significantly improved his quality of life.

Clinical use of the Odstock dropped foot stimulator: its effect on the speed and effort of walking.

OBJECTIVE: To assess the clinical effectiveness of the Odstock dropped foot stimulator by analysis of its effect on physiological cost index (PCI) and speed of walking. This functional electrical stimulation (FES) device stimulates the common peroneal nerve during the swing phase of gait. DESIGN: A retrospective study of patients who had used the device for 4 1/2 months. SUBJECTS: One hundred fifty-one patients with a dropped foot resulting from an upper motor neuron lesion. SETTING: A medical physics and biomedical engineering department of a district general hospital specializing in the clinical application of FES and a neurophysiotherapy department at a separate hospital. MAIN OUTCOME MEASURES: Changes in walking speed and effort of walking, as measured by PCI over a 10-meter course. RESULTS: There was a 92.7% compliance with treatment. Stroke patients showed a mean increase in walking speed of 27% (p<.01) and reduction in PCI of 31% (p<.01) with stimulation, and changes of 14% (p<.01) and 19% (p<.01), respectively, while not using the stimulator. Multiple sclerosis patients gained similar orthotic benefit but no "carry-over." CONCLUSIONS: The measured differences in walking with and without stimulation were statistically significant in the stroke and multiple sclerosis groups. In this study use of the stimulator improved walking. Those with stroke demonstrated a short-term "carry-over" effect.

Patients' perceptions of the Odstock Dropped Foot Stimulator (ODFS).

OBJECTIVE: To determine the perceived benefit, pattern and problems of use of the Odstock Dropped Foot Stimulator (ODFS) and the users' opinion of the service provided. DESIGN: Questionnaire sent in a single mailshot to current and past users of the ODFS. Returns were sent anonymously. SETTING: Outpatient-based clinical service. SUBJECTS: One hundred and sixty-eight current and 123 past users with diagnoses of stroke (CVA), multiple sclerosis (MS), incomplete spinal cord injury (SCI), traumatic brain injury (TBI) and cerebral palsy (CP). INTERVENTION: Functional electrical stimulation (FES) to correct dropped foot in subjects with an upper motor neuron lesion, using the ODFS. MAIN OUTCOME MEASURES: Purpose-designed questionnaire. RESULTS: Return rate 64% current users (mean duration of use 19.5 months) and 43% past users (mean duration of use 10.7 months). Principal reason cited for using equipment was a reduction in the effort of walking. Principal reasons identified for discontinuing were an improvement in mobility, electrode positioning difficulties and deteriorating mobility. There were some problems with reliability of equipment. Level of service provided was thought to be good. CONCLUSION: The ODFS was perceived by the users to be of considerable benefit. A comprehensive clinical follow-up service is essential to achieve the maximum continuing benefit from FES-based orthoses.

The effects of common peroneal stimulation on the effort and speed of walking: a randomized controlled trial with chronic hemiplegic patients.

OBJECTIVE: To measure the effect of the Odstock Dropped Foot Stimulator (ODFS), a common peroneal stimulator, on the effort and speed of walking. DESIGN: A randomized controlled trial. SUBJECTS: Hemiplegic patients who had suffered a single stroke at least six months prior to the start of the trial whose walking was impaired by a drop-foot. INTERVENTIONS: The treatment, functional electrical stimulation (FES) group, used the stimulator and received a course of physiotherapy; the control group received physiotherapy alone. MAIN OUTCOME MEASURES: Changes in walking speed measured over 10 m and the effort of walking measured by physiological cost index (PCI). RESULTS: Thirty-two subjects completed the trial, 16 in the FES group and 16 in the control group. Mean increase in walking speed between the beginning and end of the trial was 20.5% in the FES group (when the stimulator was used), and 5.2% in the control group. Improvement was also measured in PCI with a reduction of 24.9% in the FES group (when the stimulator was used) and 1% in the control group. No improvement in these parameters was measured in the FES group when the stimulator was not used. CONCLUSION: Walking was statistically significantly improved when the ODFS was worn but no 'carry-over' was measured. Physiotherapy alone, in this group of subjects with established stroke, did not improve walking.

Limb blood flow, cardiac output and quadriceps muscle bulk following spinal cord injury and the effect of training for the Odstock functional electrical stimulation standing system.

As part of the assessment of the Odstock functional electrical stimulation (FES) standing system for mid to low thoracic lesion spinal cord injured (SCI) subjects, cardiac output, high blood flow and quadriceps muscle thickness were measured before and following an electrical stimulation muscle retraining programme. The same parameters were also measured in a group of uninjured subjects and in SCI subjects. It was found that there was no difference in cardiac output between the groups. However thigh blood flow was found to be around 65% of normal values in the spinally injured group. This returned to normal values following the retraining programme. The quadriceps muscle wasted to approximately 50% of its original thickness in the first 3 weeks following spinal cord injury. The retraining programme increased the muscle thickness to near normal values.

Development of a wheelchair-mounted folding standing frame.

Functional electrical stimulation (FES) is capable of providing standing function to certain mid-thoracic paraplegics following spinal injury. To be of use in the community such systems require the provision of a mechanical support attached to the user's wheelchair so that it is available for use at all times. The design specification was such that the frame should fit a wide range of wheelchairs, not increase the external dimensions of the wheelchair, be easily removed to enable transfers, provide a safe, stable support once erect and be quick and simple both to erect and to fold away. Although primarily designed for use as part of the FES standing system, the frame is also applicable for patients with a number of other chronic neurological or arthritic conditions. As such the specification has been extended so that the design is suitable for users with tremor or reduced upper limb function.

Practical low cost stand/sit system for mid-thoracic paraplegics.

The use of functional electrical stimulation (FES) to enable paraplegics to stand is not new or indeed difficult to undertake under laboratory conditions. However, there are substantial problems to overcome before such systems can be used routinely by patients without professional supervision. The overriding consideration has to be one of safety, i.e. the system must be 'fail safe'. Secondly, the system must be quick and easy to use in a wide variety of locations, otherwise it will not provide any increase in function. Finally, it must be inexpensive enough to be available to a large number of paraplegics. The primary aim of our work was to provide such a system to enable mid-thoracic lesion paraplegics to stand wherever they wish. This involved the development of a microprocessor-based stimulator to enable the stimulating envelope to be individually tailored to a given patient's requirements and the provision of closed loop control to minimize fatigue. A folding standing frame was also designed which replaces the arm rests on a standard wheelchair. Using this system, the user is able to stand within 30 s of stopping and can remain standing for up to 10 min. Cosmetic calipers (knee-ankle-foot orthoses) are also being used for paraplegics who require to stand for longer periods. It is hoped that such a system will provide stable standing for a large number of paraplegics at a unit cost of approximately 750 pound.

Measurement of pulsatile limb and finger blood flow by electrical impedance plethysmography: criteria for the diagnosis of abnormal flow.

The range of pulsatile arm and finger blood flow, measured by electrical impedance plethysmography, has been investigated in a hospital ward. The range of absolute blood flows, in ml min-1, was found to be too wide to be used as a standard for identifying single blood flow readings as being abnormal. A blood flow ratio was calculated by dividing the blood flow in the right forearm or middle finger by the blood flow in the left forearm or middle finger. This ratio was found to have a clearly defined range. A blood flow in a unilaterally injured or otherwise abnormal arm or finger was considered to be significantly altered if the blood flow ratio fell outside the previously defined normal range. The diagnosis of significantly altered arm and finger blood flow from abnormalities in the blood flow ratio was tested in a series of experiments, in which artificial changes in upper limb flow were created by high elevation of the right hand. The ratio was measured in 11 patients with unilateral upper limb injuries and in 3 patients who required an urgent assessment of the upper limb circulation. Abnormalities in the ratio were identified in 12 out of 18 subjects after high elevation of the hand and in 8 out of the 14 patients.

Measurement of cardiac output by electrical impedance plethysmography.

There are many potential applications for cardiac output measurement in clinical and experimental medicine. The most commonly used techniques are invasive procedures, requiring cardiac or arterial catheterization, a disadvantage that has restricted their wider application. Impedance plethysmography has been developed as a non-invasive, beat-by-beat method of cardiac output measurement, which provides an estimate of stroke volume from changes in the electrical impedance of the thorax during cardiac systole. The values for cardiac output obtained by this technique have been extensively compared with values obtained by other methods, both in experimental animals and in the human subject. In the majority of studies high correlation coefficients have been obtained, although impedance plethysmography has tended to give higher absolute values than most other methods. Values for cardiac output obtained by impedance plethysmography are best assessed by comparison with a series of normal values obtained by this technique, rather than with values obtained by other methods. We discuss the results of an investigation of normal cardiac output by impedance plethysmography; theoretical objections to impedance cardiography are considered, and various methods of determining the specific resistivity of blood are reviewed.

Non-invasive measurement of limb and digit blood flow.

There are many clinical applications for non-invasive measurements of limb and digit blood flow, but often plethysmographs are inconvenient to use. Most experimental work has been carried out on patients with vascular disease. The variation of blood flow with various environmental and physiological factors has been investigated. Little information is available on the effects of injury or surgical trauma on blood flow in limbs. Plethysmographic methods measure arterial flow or pulse volume by several techniques including volumetric displacement, electrical impedance, gravimetry and the mercury in rubber strain gauge. Calorimetric, Doppler and isotope clearance techniques have also been applied to the measurement of blood flow in digits. None of these methods fulfils all the criteria for the requirements of an ideal device and some are too complicated, uncomfortable or cumbersome for widespread use. The results from different techniques are compared and the reasons for variability are discussed. Possible mechanisms for the effects of trauma on limb blood flow are suggested. Experimental comparisons of different plethysmographs are described and the requirements for future development of these devices are defined.

A simple method of measuring the electrical resistance of the skin.

A simple device has been developed to measure skin resistance. Normal values have been established and the effect of changing measurement parameters has been investigated. Peripheral nerve blocks have also been applied and their effect upon the skin resistance reported.

Measurement of limb blood flow by electrical impedance plethysmography.

Limb blood flow has been measured in 72 individuals by the noninvasive technique of electrical impedance plethysmography. Venous occlusion was not used. Blood flow was measured in 230 limbs in which 195 limbs were either in normal individuals or the clinically normal limbs of patients (normal limbs). Thirty-five limbs were clinically abnormal. Measurements on limbs with clinical abnormalities showed that blood flow values often fell within the limits of the normal range. However 3 cases of known vascular injury and 2 cases studied after hand surgery under tourniquet showed lowered blood flow values by comparison with the unaffected limb. A simultaneously recorded range of cardiac output and stroke volume measurements gave similar results to those obtained in a previous, unconnected study.

An adaptive control system for a complete hand/arm prosthesis.

A complete hand/arm prosthesis is proposed in which the user has only supervisory control, the details of grip force, joint angles etc. being controlled automatically. By such a system it is possible in principle to control an eleven-degree of freedom prosthesis (four in the hand and seven in the arm) with only four inputs being provided by the patient. Thus increasing the flexibility of the system without putting too much strain on the patient.