Dr Graham Webb

Impairments in dynamic balance have a detrimental effect to older patient groups at risk of falls.  Gait initiation (GI) is a transitional movement that older patients can often struggle with and centre of pressure (COP) excursions using force plates have been used to measure GI performance.  The NintendoÒ Wii Balance Board (WBB) offers a more clinically viable method of COP excursion measurement.  Ten older patients attending a strength and balance class, and ten young healthy adults performed three trials of GI after 10s of steady standing from a standardised foot position (shoulder width) and walk 3m to pick up an object. Trials were conducted on a weekly basis for 4 weeks. Averaged WBB COP excursions (distance) and path time (between GI-onset and first toe-off) were used for analysis. The WBB exhibited excellent COP medio-lateral and antero-posterior excursion reliability [ICC3,1 = 0.866 and 0.895 respectively] and fair reliability for COP path length [ICC3,1 = 0.517].  Healthy subjects presented with larger excursions in both planes and shorter COP path length than older patients [p= <0.03]. The WBB is a clinically viable tool in measuring the COP changes of GI and it could therefore provide therapists with a supplementary measurement in the clinical setting when documenting changes in balance.  However, limitations in the accuracy and precision of the WBB in dynamic transition tasks need to be established before it can be used in clinical practice.

Following discharge amputees do not always receive regular reviews by physiotherapists, and may adopt a variety of habitual gait patterns that can lead to back pain. The increase in transverse rotation of the pelvis in trans-femoral amputees, as produced by circumduction, is a contributing factor to lower back pain (Morgenroth et al., 2010). Real-time biofeedback of kinematic data to amputees may help address inappropriate habitual gait patterns. Recently there has been renewed interest in the application of biofeedback for gait re-education (Lunenburger et al. 2007). Such feedback could also help therapists convey information to patients regarding kinematic alterations during hands-on physiotherapy in a rehabilitation gym.

Approximately 5000 new referrals are received every year in the UK for limb amputations [1]. Lower back pain is reported in as high as 52 - 94% of lower limb amputees, from [2]. Following discharge patients do not receive regular reviews by physiotherapists and often adopt a variety of habitual gait patterns that can lead to back pain. Circumduction is a one such pattern which is thought to contribute to lower back pain. It involves a wider than normal lateral arc of the prosthesis during swing to prevent the foot striking the floor [3]. This results in an asymmetrical movement of the pelvis and lumbar spine. An increase in transverse rotation of the pelvis in trans-femoral amputees is a contributing factor to lower back pain [4]....

There has been renewed interest in the application of biofeedback for gait and posture re-education. Electrical stimulation is one means of presenting feedback stimuli to patients and has been used with amputees to provide knowledge of gait event timing through implanted and surface stimulation of discrete anatomical regions [1, 2].

Electrotactile displays (ETD) use an array of electrodes to present information through transcutaneous electrical stimulation, thus providing spatial resolution for information coding. ETDs have found various uses. For example Vuillerme has developed a device to present information about ankle orientation to the tongue [3].

Technology is improving the design of artificial legs but their users need more sophisticated control systems to walk naturally. The latest engineering techniques are key to helping amputees re-learn to walk naturally.

Biofeedback is a real-time training technique that involves measuring a physiological function and conveying information back to the patient, to help them learn to adjust their performance. Biofeedback is used successfully in many areas of neuromuscular rehabilitation and sports training. Lower limb amputees particularly present a need for augmented feedback. Following amputation the proprioceptive pathways required to regulate gait are impaired. During physiotherapy patients have a limited view of their body, and the physiotherapist may not be best physically placed to witness gait changes. Outside the clinic patients often adopt poor walking patterns, such as circumduction and abduction, which can lead to lower back pain and a reduced quality of life.

This work focused on the development of a biofeedback training system to assist in the reduction of habitual circumduction and abduction gait patterns seen in trans-femoral amputees. Guided by a review of the literature, a training system was developed that uses electro-tactile sensory stimulation to provide feedback of the patient’s thigh motion whilst they walk on a treadmill.

A greater understanding of the psychophysical response to electro-tactile stimulation was required in order to present discernible information in a safe and comfortable manner. Thirteen healthy subjects were therefore recruited into a study that found thresholds of perception and discomfort to stimulation around the thigh. The study also found that subjects were able to discriminate the location of stationary stimuli and the speed and direction of moving stimuli whilst laying supine, flexing and extending the leg, and walking on a treadmill. By correctly identifying the numbered electrode locations they demonstrated an ability to perceive spatially coded information presented to the thigh using electrical stimulation.

A camera-based motion capture system was incorporated into the completed biofeedback system, and software was written to capture kinematic data in real-time. To enable the calculation of feedback stimuli, a 3-dimensional biomechanical model was constructed and the patient’s hip joint angles were compared to a joint angle reference database. Kinematic event detection made it possible to deliver the electro-tactile stimuli in relation to the users gait.

Four amputees tested the biofeedback system and reported positively on the experience. The subjects did not walk with a circumduction gait, so it was not possible to assess the therapeutic effects of the system. However they were able to perceive and understand the feedback stimuli, relate the information to their movement, and in some cases make positive changes to their gait. Sensation threshold levels and the ability to discriminate stimuli were also found in the amputee group to be comparable with the non-amputees.

This work has potential to become integrated into prosthetic components, and can be adapted for use with a broader range of patient groups with upper and lower limb movement disorders. The analysis software has potential to be further developed to provide real-time interpretation of gait patterns.

There has been ongoing concern that prolonged use of MP3 players can lead to noise-induced hearing loss. Acoustic exposure is the product of intensity and duration of exposure. Previous work has utilised measurements of maximum headphone output and output during listening tests to determine acoustic intensity; whilst duration of use is currently assessed with questionnaires and interviews. The subjective nature of these latter methods has led to a wide variation in figures for device use, restricting the scope of media player risk assessment. A need was therefore identified for an improved method of acquiring data of users’ listening habits. This need was addressed with the design of a new data-logging device that discretely measures voltage output from the media player, whilst in use. A calibration method is proposed to implement the headphone transfer function into the data-logger, to relate output voltage to exposed pressure. It is proposed that the headphone transfer function is measured using an acoustic manikin, representative of the population of interest. The real ear measurement is put forward as an appropriate tool for validating results gained using this approach. A data-logger was designed and a proof of concept has been demonstrated in a software program written for this purpose. The proposed method has the advantages that an objective measurement can be made of the user’s natural listening habits, over a long period of time, with a resolution comparable to personal acoustic dosimetry. A number of practical steps are required to further this work before data can be collected. A software graphic equaliser was used to implement the transfer function, but the chosen filter topology gave an unsatisfactory response, an investigation is required for further work. The device requires migration to hardware and the experimental calibration and validation of the system are also required. The worldwide population of MP3 player users is in the region of hundreds of millions of people. The relationship between user and device is becoming closer and portable music technology is becoming ubiquitous, permitting extended listening durations. There is therefore a strong need to continue this field of research, to increase understanding of the risks of this aspect of recreational noise.