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

Computerized Cuff Pressure Algometry as Guidance for Circumferential Tissue Compression for Wearable Soft Robotic Applications: A Systematic Review

In this article, we review the literature on quantitative sensory testing of deep somatic pain by means of computerized cuff pressure algometry (CPA) in search of pressure-related safety guidelines for wearable soft exoskeleton and robotics design. Most pressure-related safety thresholds to date are based on interface pressures and skin perfusion, although clinical research suggests the deep somatic tissues to be the most sensitive to excessive loading. With CPA, pain is induced in deeper layers of soft tissue at the limbs. The results indicate that circumferential compression leads to discomfort at ∼16-34 kPa, becomes painful at ∼20-27 kPa, and can become unbearable even below 40 kPa.

The International Classification of Functioning, Disability and Health provides a Model for Adaptive Seating Interventions for Children with Cerebral Palsy

Children with severe types of cerebral palsy use adaptive seating systems to encourage function and assist in delaying the development of deformity. These systems are often assessed for and provided by occupational therapists. However, there has been no unifying policy or theoretical basis on which these systems are provided and research evidence is lacking, with studies tending to be small and non-controlled.

The International Classification of Functioning, Disability and Health (World Health Organisation 2001a,b) aims to establish a common language for clinical practice as well as research, while bringing together the opposing social and medical models of health care delivery. This paper suggests that the ICF model is an ideal theoretical basis for adaptive seating system assessment and provision, given that these systems often conflict between the medical model of reducing or delaying impairment of body functions and structures and the social model of children and families accessing life and environmental situations through mobility and seating equipment.

The paper considers all the domains of the ICF with regard to the current literature. It concludes that using the model in the context of providing adaptive seating gives occupational therapists both a powerful tool for communicating with children and families as well as managers and a basis for evaluating practice.

Pressure mapping with textile sensors for compression therapy monitoring

Compression therapy is the cornerstone of treatment in the case of venous leg ulcers. The therapy outcome is strictly dependent on the pressure distribution produced by bandages along the lower limb length. To date, pressure monitoring has been carried out using sensors that present considerable drawbacks, such as single point instead of distributed sensing, no shape conformability, bulkiness and constraints on patient's movements. In this work, matrix textile sensing technologies were explored in terms of their ability to measure the sub-bandage pressure with a suitable temporal and spatial resolution. A multilayered textile matrix based on a piezoresistive sensing principle was developed, calibrated and tested with human subjects, with the aim of assessing real-time distributed pressure sensing at the skin/bandage interface. Experimental tests were carried out on three healthy volunteers, using two different bandage types, from among those most commonly used. Such tests allowed the trends of pressure distribution to be evaluated over time, both at rest and during daily life activities. Results revealed that the proposed device enables the dynamic assessment of compression mapping, with a suitable spatial and temporal resolution (20 mm and 10 Hz, respectively). In addition, the sensor is flexible and conformable, thus well accepted by the patient. Overall, this study demonstrates the adequacy of the proposed piezoresistive textile sensor for the real-time monitoring of bandage-based therapeutic treatments.

Prevention of pressure ulcer: interaction of body characteristics and different mattresses

We analysed the effect of different body features on contact area, interface pressure and pressure distribution of three different mattresses. Thirty-eight volunteers (age ranged from 17 to 73 years, 23 females) were asked to lie on three different mattresses in a random order: I, standard hospital foam mattresses; II, higher specification foam mattresses (Viscorelax Sure® ); III, constant low pressure devices (CareMedx® , AirSystems). Measurements were performed in supine position and in a 90° left- and right-sided position, respectively, using a full-body mat (pressure mapping device Xsensor X2-Modell). Outcome variables were contact area (CA) in cm(2) , mean interface pressure (IP) in mmHg and pressure distribution (PD) estimated as rate of low pressures between 5 and 33 mmHg on each mattress in percent. Mean CA was lowest in the standard hospital foam mattresses and increased in the higher specification foam mattresses and was highest in the constant low pressure device (supine position: 491 ± 86 cm(2) , 615 ± 95 cm(2) , 685 ± 116 cm(2) ). Mean IP was highest in the standard hospital foam mattresses and lower but similar in the higher specification foam mattresses and the constant low pressure devices (supine position: 22·3 ± 1·5 mmHg, 17·6 ± 1·7 mmHg, 17·6 ± 2·2 mmHg). Models were estimated for CA, IP and PD including the independent variables height, weight and waist-to-hip-ratio (WHR). They show that body morphology seems to play a minor role for CA, IP and PD, but very thin and tall patients and very small and obese people might benefit from different mattresses. Our data show that CA increases with increasing specification of mattresses. Higher specification foam mattresses and constant low pressure devices show similar IP, but constant low pressure devices show a wider pressure distribution. Body morphology should be considered to optimise prevention for single patients.

Longitudinal study evaluating a seating system using a sacral pad and kneeblock for children with cerebral palsy

PURPOSE

Adaptive seating systems using sacral pads and kneeblocks are commonly used throughout the UK with children with complex motor disorders to improve their posture and stability in sitting. We sought to evaluate how effective these systems are for a group of children with cerebral palsy.

METHOD

A six-visit trial was performed to examine whether this combination controls pelvic and hip positioning. Twenty-three children with cerebral palsy aged 7 - 14 years participated (11 females and 12 males). The kneeblocks (active intervention) were removed for a period in the middle of the trial. Force exerted through the kneeblock, pressure exerted on the sacral pad and postural alignment was measured for change.

RESULTS

Statistically significant differences before and after kneeblock removal were found for force at the kneeblock, but no difference was found in pressure at the sacral pad. No statistically significant correlations between force and pressure or posture were found.

CONCLUSION

The results indicate that seating systems using a sacral pad and kneeblock may not improve overall posture but may improve hip position in children with cerebral palsy.

Interface pressure measurements: Visual interpretation of pressure maps with MS clients

PURPOSE

Pressure mapping systems provide useful information for pressure care assessment. Healthcare professionals tend to rely upon their colour-coded pressure maps to assist clinical decision-making, based on ranking these from best to worst pressure distribution. The current study investigated whether such ranking is an appropriate method of assessment when compared to use of the numerical output of average and maximum pressure values (mmHg), yielded by the system.

METHOD

This community-based correlational study involved 27 multiple sclerosis clients (15 wheelchair users; 12 non-wheelchair users). Pressure maps were recorded on each participant's current seating surface and on six pressure reducing cushions, using the Force Sensing Array pressure mapping system. Outcome measures included (1) rank order of pressure maps based on visual interpretation by two occupational therapists, (2) average pressure (mmHg) and (3) maximum pressure (mmHg). Visual ranking of the colour-coded pressure maps was correlated with average and maximum pressure values for each map.

RESULTS

Correlations between visual ranking of maps and maximum pressures were high for six out of seven surfaces (p < 0.05) for non-wheelchair users; however, they were much less between average pressures and visual interpretation for the same cohort. Similarly, correlations between visual ranking of maps and average pressures for wheelchair users was minimal and was only noted as being high (p < 0.05) on two surfaces when considering maximum pressures and visual interpretation.

CONCLUSIONS

This study contests the usefulness of the visual ranking of pressure maps in interpreting interface pressures with MS clients, especially with wheelchair users. Visual interpretation of pressure maps by clinicians may be useful in eliminating inappropriate support surfaces from a selection, or those that display easily identifiable 'extremes' of pressure values. Clinicians need to incorporate and interpret the numerical data as well as pressure maps when conducting their assessment and making provision.

Study of skin-fabric interactions of relevance to decubitus: friction and contact-pressure measurements

BACKGROUND/PURPOSE

Prolonged pressure as well as friction and shear forces at the skin-textile interface are decisive physical parameters in the development of decubitus. The present article describes the contact phenomena at the skin-textile interface and the development of a purpose-built textile friction analyser (TFA) for the tribological assessment of skin-fabric interactions, in connection with decubitus prevention.

METHODS

Interface pressure distributions were recorded in the pelvic and femoral regions between supine persons and a foam mattress. Fabrics made of various natural and synthetic yarns were investigated using the TFA. A vertical load of 7.7 kPa was applied to the swatches, simulating high interface pressures at the skin-fabric interface and clinical conditions of bedridden persons. Fabrics were rubbed in reciprocating motions against a validated skin-simulating material to determine static as well as dynamic friction coefficients (COFs).

RESULTS

Maximum contact pressures ranged from 5.2 to 7.7 kPa (39-58 mmHg) and exceeded the capillary closure pressure (32 mmHg) in all investigated bedding positions. For both COFs, a factor of 2.5 was found between the samples with the lowest and highest values. Our results were in a similar range to COFs found in measurements on human skin in vivo. The results showed that our test method can detect differences of 0.01 in friction coefficients.

CONCLUSION

TFA measurements allow the objective and reliable study of the tribology of the skin-textile biointerface and will be used to develop medical textiles with improved performance and greater efficacy for decubitus prevention.

Measurement of Lower Leg Compression In Vivo: Recommendations for the Performance of Measurements of Interface Pressure and Stiffness

BACKGROUND

Interface pressure and stiffness characterizing the elastic properties of the material are the parameters determining the dosage of compression treatment and should therefore be measured in future clinical trials.

OBJECTIVE

To provide some recommendations regarding the use of suitable methods for this indication.

METHOD

This article was formulated based on the results of an international consensus meeting between a group of medical experts and representatives from the industry held in January 2005 in Vienna, Austria.

RESULTS

Proposals are made concerning methods for measuring the interface pressure and for assessing the stiffness of a compression device in an individual patient.

CONCLUSIONS

In vivo measurement of interface pressure is encouraged when clinical and experimental outcomes of compression treatment are to be evaluated.

Interface pressure measurement during surgery: a comparison of four operating table surfaces

OBJECTIVE

To compare the pressure-reducing and pressure-redistributing characteristics of four operating room (OR) table mattresses using interface pressure measurements, in two positions adopted for surgical procedures.

METHOD

Support surfaces were randomly assigned to 80 patients. These were: an overlay pad filled with fibres (the standard OR mattress), a custom-made viscoelastic polyurethane foam mattress, an inflatable mattress with air-filled cells and a fluid mattress. An XSENSOR full-body pressure-mapping pad was used to record interface pressures of 40 patients in the supine position and 40 patients in the lithotomy position. Measurements were analysed for peak pressure, peak pressure index, total contact surface area and the occurrence of a significant increase in interface pressure during the surgical procedure.

RESULTS

The highest interface pressures were measured on the standard mattress, in both the supine and lithotomy position. Overall, the fluid mattress showed the best pressure-reducing and pressure-redistributing capacities.

CONCLUSION

As long as no reference values are available for interface pressures under which no pressure-related damage will occur, clinical testing of OR table surfaces is still necessary.

Managing and promoting change: implementing the Leg Club model

Patient knowledge of their disease may increase concordance to compression therapy. The Lindsay Leg Club model (Lindsay, 2004) empowers the community nursing team to truly get to know their communities and deliver local, high-quality, evidence-based care for patients with leg ulcers and leg related problems. The author's experience of opening a Leg Club has lead to changes in clinical practice: re-evaluation of the use of long stretch bandages in favour of short stretch; replacing conventional compression bandage systems with two piece graduated compression hosiery; increased patient concordance post healing with increased use of compression hosiery; the introduction of toe bandaging and appropriate long-term management for those patients with lymphoedema; and developing the role of the nursing auxiliary in leg ulcer care.

Tissue-interface pressures on three different support-surfaces for trauma patients

The purpose of this study was to evaluate and compare tissue-interface pressures on three different support-surfaces for trauma patients. The support-surfaces were a semi soft overlay mattress, a vacuum mattress and a spine board. Tissue-interface pressures were measured in a standardised way between the scapulae, the sacrum, the heels and the different support-surfaces in 20 healthy volunteers. Appreciation of comfort of the support-surface was assessed using a 10-point visual analog scale. High and potentially ischaemic interface pressures were found on all three support-surfaces, with the highest pressures (exceeding 170 mmHg) measured on the spine board. The spine board got the worst comfort score. It was also noted that no support was given to the normal lumbar lordosis by the spine board. There is a need for new support-surfaces for trauma patients, which reduce interface pressures and are comfortable.

Impact of Sitting Time on Seat-Interface Pressure and on Pressure Mapping With Multiple Sclerosis Patients

OBJECTIVE

To examine changes in seat-interface pressure with multiple sclerosis (MS) patients.

DESIGN

Case series.

SETTING

Multiple Sclerosis Society's Resource Centre and community.

PARTICIPANTS

Convenience sample of 15 MS wheelchair users and 12 MS non-wheelchair users.

INTERVENTION

Interface pressure was measured for 8 minutes using the Force Sensing Array pressure mapping system.

MAIN OUTCOME MEASURES

Number of activated sensors, standard deviation, average and maximum pressures.

RESULTS

With the wheelchair users, significant decreases were found in the standard deviation and average and maximum pressures during 0 to 2 minutes of sitting ( P <.01). Average pressure was the only parameter to show a significant decrease in the non-wheelchair users ( P <.01) during 0 to 2 minutes. Significant increases were found in all output parameters during 2 to 4 minutes with both groups ( P <.05). Non-wheelchair users showed no significant changes in the output parameters after 4 minutes, but wheelchair users showed significant continued increases in the output parameters from 4 to 8 minutes ( P <.05).

CONCLUSIONS

Because no significant changes in interface pressure occurred after 4 minutes of sitting with the non-wheelchair users, 4 minutes may be a reasonable sitting time before interface pressure is recorded with this group. Significant changes in interface pressure continued up to 8 minutes with the wheelchair users, therefore 8 minutes or beyond may be a reasonable sitting time before recording with this group.

An investigation of the impact of the Force Sensing Array pressure mapping system on the clinical judgement of occupational therapists

OBJECTIVES

To examine the impact of pressure mapping technology on the clinical decisions of occupational therapists and to examine the role of the Braden Scale in assisting with the selection of pressure-reducing cushions.

DESIGN

Case studies.

SETTING

Community.

SUBJECTS

Forty clients.

INTERVENTIONS

Clients were pressure mapped on their current seating surface and on four pre-selected cushions by the principal researcher. An occupational therapist completed the Braden Scale and a decision tree to assist in recommending a suitable pressure-reducing cushion.

MAIN OUTCOME MEASURES

Interface pressure maps, Braden Scale, and the cushion recommended, using a decision tree to guide clinical judgement.

RESULTS

Thirty per cent (12) of the 40 cushions recommended were changed when the pressure maps from the Force Sensing Array (FSA) system were viewed. In 70% (26) of cases, the maps supported the cushion recommended. In 25% (10) of the cases, the maps showed that the client's current seating surface was unsuitable. After viewing the pressure maps, a surface other than the client's current surface was recommended in 47% (19) of the cases. There was a lack of agreement between the risk level of the clients as identified by the Braden Scale score, and the risk level of the clients as identified by the occupational therapist using a decision tree and the FSA maps.

CONCLUSION

Pressure mapping technology has a positive impact on clinical decisions regarding the provision of pressure-reducing cushions. Future research should examine the predictive validity of this technology. The Braden Scale may underpredict the risk level of the clients.

The role of pressure-redistributing equipment in the prevention and management of pressure ulcers

In response to a focus on education and research in pressure ulcer prevention, this paper reviews the evolution of pressure-redistributing mattresses and explores the effectiveness of interface pressure measurement in mattress development.