Martin Ferguson-Pell

Pressure sore prevention for the wheelchair-bound spinal injury patient.

The concept of a wheelchair cushion fitting clinic for the prevention of pressure sores is reviewed in the light of recent estimates of the cost of pressure sores in the U.K. A method for measuring the pressure beneath the ischial tuberosities is discussed and techniques for measuring a patients habitual exercise frequency and seated posture are described. Results from the records of 600 spinal injury patients attending Rancho Los Amigos Hospital are reported and used to demonstrate the importance of low pressure beneath the ischial tuberosities as an indicator of wheelchair cushion suitability.

Spectral properties of electromyographic and mechanomyographic signals during isometric ramp and step contractions in biceps brachii

The purposes of this study were: (1) to apply wavelet and principal component analysis to quantify the spectral properties of the surface EMG and MMG signals from biceps brachii during isometric ramp and step muscle contractions when the motor units are recruited in an orderly manner, and (2) to compare the recruitment patterns of motor unit during isometric ramp and step muscle contractions. Twenty healthy participants (age = 34 ± 10.7 years) performed step and ramped isometric contractions. Surface EMG and MMG were recorded from biceps brachii. The EMGs and MMGs were decomposed into their intensities in time-frequency space using a wavelet technique. The EMG and MMG spectra were then compared using principal component analysis (PCA) and ANCOVA. Wavelet combined PCA offers a quantitative measure of the contribution of high and low frequency content within the EMG and MMG. The ANCOVA indicated that there was no significant difference in EMG total intensity, EMG(MPF), first and second principal component loading scores (PCI and PCII) between ramp and step contractions, whereas the MMG(MPF) and MMG PCI loading scores were significantly higher during ramp contractions than during step contractions. These findings suggested that EMG and MMG may offer complimentary information regarding the interactions between motor unit recruitment and firing rate that control muscle force production. In addition, our results support the hypothesis that different motor unit recruitment strategy was used by the muscle when contracting under different conditions.

Evidence supporting the use of two-hourly turning for pressure ulcer prevention.

Pressure relief is essential for pressure ulcer prevention. In order to accomplish complete pressure relief, changing position is traditionally taught in nursing education and employed in nursing practice. Although the interval for turning was not specified by Nightingale, ‘‘two-hourly turning’’ is routinely recommended in nursing textbooks and is widely accepted in clinical practice setting. Theorigin of the two-hourly turning regimen: who initiated this frequency of turningand any evidencebase to support the practice, still remains unclear. In this paper an attempt is made to explore the origin of the regimen of ‘‘two-hourly turning’’.

Tissue Shape and Deformation Versus Pressure as a Characterization of the Seating Interface

A review of pressure measurements as a characterization of the seating interface is presented along with a discussion of their limitations in evaluating potentially adverse conditions that may lead to pressure sore formation. A theoretical rationale is then developed for using tissue shape and deformation, in contrast to pressure, as a conceptualization of the seating interface. Previous studies that have investigated shape and deformation as a characterization of the seating interface, as well as those that have utilized shape measurement for cushion fabrication, are reviewed in light of the theoretical rationale presented. It is concluded that although the efficacy of tissue shape and deformation as a characterization of the seating interface has not been clinically proven, they provide a more direct measure of the net effect of external load, mechanical tissue properties, and boundary conditions (cushion effects) as compared to pressure measurements.

Monitoring the mobility of patients in bed

A method of detecting and logging movements made on Kings Fund hospital beds is described. The results of such mobility measurements indicate that during the first three nights after admission there is a progressive alteration in the number of movements made by elderly hospital patients. The group of patients clinically assessed as being at risk of developing pressure sores, or receiving sedatives, made a reduced number of movements.

Pressure changes under the ischial tuberosities of seated individuals during sacral nerve root stimulation

Neuromuscular stimulation via the sacral nerve roots is proposed for prevention of ischial pressure ulcers following a spinal cord injury (SCI). Acute effects of sacral functional magnetic stimulation (FMS) on seat interface pressure changes were investigated in five nondisabled volunteers. Similar effects were demonstrated with functional electrical stimulation in people with SCI who used a sacral anterior root stimulator implant. The results indicated that sacral nerve root stimulation, either by FMS or implanted electrical stimulation, induced gluteus maximus contraction and mild pelvic tilt sufficient for clinically significant reductions in ischial pressures during sitting.

Changes in surface electromyography signals and kinetics associated with progression of fatigue at two speeds during wheelchair propulsion.

The purpose of this study was to determine whether muscle balance is influenced by fatigue in a recordable way, toward creating novel defensive activity strategies for manual wheelchair users (MWUs). Wheelchair propulsion to a point of mild fatigue, level 15 on the Rating of Perceived Exertion scale, was investigated at two different speeds. Surface electromyographic (EMG) activity of 7 muscles was recorded on 14 nondisabled participants. Kinetic variables were measured using a SmartWheel. No significant effect was found of percentage endurance time on kinetic variables for the two propulsion speeds. Fatigue-related changes in the EMG spectra were identified as an increase of EMG intensity and a decrease of mean power frequency as a function of percent endurance time for the tested muscles under both fast and slow speed conditions. The greater increases in activity for propulsive muscles compared with recovery muscles during fast speed wheelchair propulsion indicated muscle imbalance associated with fatiguing wheelchair propulsion. This study shows how kinetic and EMG information might be used as feedback to MWUs to ensure that they conduct activity in ways that do not precipitate injury.

Thermodynamic rigid cushion loading indenter: A buttock-shaped temperature and humidity measurement system for cushioning surfaces under anatomical compression conditions

A method is described for measuring the heat and water vapor dissipation characteristics of wheelchair cushions and seating systems while under simulated loading conditions. Thermal interaction between the body and seating surfaces can result in elevated tissue temperature and moisture build-up, which may increase the risk of pressure ulcers associated with prolonged ischemia or due to macerative damage. Both the materials and geometry of commercial seating systems are thought to influence the body-support surface microclimate. A thermodynamic rigid cushion loading indenter (TRCLI) has been developed to simulate the thermal and loading conditions of the body on seating surfaces. Results are reported for 32 commercially available wheelchair cushions. The results differentiate the cushions into clusters of comparable properties that offer the potential for classification of support surfaces based on their heat and water vapor dissipation performance. This study has shown that deducing the heat and water vapor dissipation characteristics of a seating system from material physical properties is of limited value because of the influences of particular design features of combinations of materials. Testing of individual products with the use of the TRCLI can, however, reliably differentiate wheelchair cushions by their ability to dissipate heat and water vapor.

Spectral properties of electromyographic and mechanomyographic signals during dynamic concentric and eccentric contractions of the human biceps brachii muscle

The purpose of this study was to describe and examine the variations in recruitment patterns of motor units (MUs) in biceps brachii (BB) through a range of joint motion during dynamic eccentric and concentric contractions. Twelve healthy participants (6 females, 6 males, age=30±8.5 years) performed concentric and eccentric contractions with constant external loading at different levels. Surface electromyography (EMG) and mechanomyography (MMG) were recorded from BB. The EMGs and MMGs were decomposed into their intensities in time-frequency space using a wavelet technique. The EMG and MMG spectra were then compared using principal component analysis. Variations in total intensity, first principal component (PCI), and the angle θ formed by first component (PCI) and second component (PCII) loading scores were explained in terms of MU recruitment patterns and elbow angles. Elbow angle had a significant effect on dynamic concentric and eccentric contractions. The EMG total intensity was greater for concentric than for eccentric contractions in the present study. MMG total intensity, however, was lower during concentric than during eccentric contractions. In addition, there was no significant difference in θ between concentric and eccentric contractions for both EMG and MMG. Selective recruitment of fast MUs from BB muscle during eccentric muscle contractions was not found in the present study.

The Role of Wheelchair Seating Standards in Determining Clinical Practices and Funding Policy

The development of international standards for wheelchair seating offers practical benefits in the process of matching technical characteristics of assistive technologies to individual user needs. However, information provided in technical test reports must be treated with caution when aggregating technical characteristics to classify products or when implementing funding policy. This article suggests that clustering technical characteristics of seat cushions in isolation of clinical and other user requirements is not a viable way to establish product funding codes that are responsive to clinical need.