[Evaluation of measurement systems for determining therapeutic effectiveness of anti-decubitus ulcer devices]

Comparison of three pressure monitors used to measure interface pressure under compression bandages

Background

Measuring the interface pressure produced by compression therapy devices is essential for research and clinical practice. New user-friendly measuring devices, such as Smart Sleeve Pressure Monitor (SSPM) and Juzo Pressure Monitor (JPM) allow longitudinal pressure measurement. However, their accuracy and agreement with well-established usage of the PicoPress (PP) are unknown. The aim of this study is to investigate measurement accuracy of PP, SSPM, and JPM.

Methods

The three devices were tested in 10 healthy volunteers by applying incrementally increasing pressure from 20 mm Hg to 50 mm Hg using a calibrated sphygmomanometer cuff. The linearity of the response and measurement accuracy were compared among the three devices. In a separate experiment, the three devices were compared by simultaneously recording the interface pressure under bandages immediately after bandaging and after 4 h of wearing the bandage.

Results

PP had the best performance with the reference of sphygmomanometer, while JPM had better linearity and accuracy than SSPM. The mean difference in the interface pressure under bandages was +13.36 mm Hg between SSPM and PP, and +0.50 mm Hg between JPM and PP. The 95% limits of agreement were −13.92 and +40.64 mm Hg, and −19.83 and +20.84 mm Hg, respectively.

Conclusions

JPM showed better agreement with both sphygmomanometer and PP compared to SSPM. JPM is a reasonable alternative for monitoring interface pressure continuously.

Wheelchair Tilt-in-Space and Recline Functions: Influence on Sitting Interface Pressure and Ischial Blood Flow in an Elderly Population

Pressure ulcers (PUs) result from localised injury to the skin and underlying tissue and usually occur over a bony prominence as a result of pressure, often in combination with shear forces. Both pressure magnitude and duration are thought to be key risk factors in the occurrence of PUs, thus exposing wheelchair-bound subjects to high risk of PU development. As a result, wheelchairs that incorporate tilt-in-space and recline functions are routinely prescribed to redistribute pressure away from their ischial tuberosities. The goal of this study was to analyse the role of full-body tilt and recline angles in governing sitting interface pressure and blood circulation parameters in elderly subjects and thereby investigate the efficacy of tilt-in-space wheelchairs for aiding pressure relief activity. Sitting interface pressure and ischial blood flow parameters were examined in 20 healthy elderly subjects while seated in a tilt-in-space and recline wheelchair. Five different angles of seat tilt (5°, 15°, 25°, 35°, and 45°) were assessed in combination with three different angles of backrest recline (5°, 15°, and 30°). The results of the study show that when compared to the upright reference posture, every position (except 15°T/5°R) resulted in a significant decrease in sitting interface pressure. Ischial blood flow also showed significant increases at four different positions (45°T/15°R, 15°T/30°R, 35°T/30°R, and 45°T/30°R) but only at larger tilt-in-space and recline angles. The results therefore suggest that small tilt-in-space and recline angles are indeed able to reduce sitting interface pressures, whereas changes in ischial blood flow only occur at larger angles. In the literature, cell deformation is thought to be dominant over tissue ischemia in the development of tissue necrosis and PUs. Therefore, together with our findings it can be concluded that frequently undertaking small adjustments in tilt-in-space and recline angle might be important for preventing cell deformation and any associated cell necrosis. Larger angles of tilt-in-space and recline seem to support blood flow returning to the tissues, which is likely to play a positive role in healing damaged tissue.

Comfort evaluation of a subject-specific seating interface formed by vibrating grains

Sitting is the most common posture for work in offices, and spinal cord injury (SCI) patients who are wheelchair dependent spend 10.6 h per day seated in wheelchairs. Thus, the comfort of subject-specific interfaces is increasingly important for the well-being of patients and office workers. This paper introduces a new method of forming a subject-specific interface, based on vibrating grains. Twenty subjects (10 females and 10 males) participated in the sitting test. Interface comfort was evaluated using the pressure distribution and subjective rating methods. Five seating interface types were compared. The results showed that compared with a flat interface, the interfaces formed by vibrating grains had a significantly reduced peak contact pressure (PeakCP) (by more than 58.03%), and that PeakCP was highly correlated with the comfort rating (R = -0.533) and discomfort rating(R = -0.603). This new method shows promise for guiding the future development of customized seating interfaces.

Seat pan and backrest pressure distribution while sitting in office chairs

Nowadays, an increasing amount of time is spent seated, especially in office environments, where sitting comfort and support are increasingly important due to the prevalence of musculoskeletal disorders. The aim of this study was to develop a methodology for chair-specific sensor mat calibration, to evaluate the interconnections between specific pressure parameters and to establish those that are most meaningful and significant in order to differentiate pressure distribution measures between office chairs. The shape of the exponential calibration function was highly influenced by the material properties and geometry of the office chairs, and therefore a chair-specific calibration proved to be essential. High correlations were observed between the eight analysed pressure parameters, whereby the pressure parameters could be reduced to a set of four and three parameters for the seat pan and the backrest respectively. In order to find significant differences between office chairs, gradient parameters should be analysed for the seat pan, whereas for the backrest almost all parameters are suitable.

Characterization of a pressure measuring system for the evaluation of medical devices

The purpose of this study is to evaluate the possible use of four “FSA” thin and flexible resistive pressure mapping systems, designed by Vista Medical (Winnipeg, Manitoba, Canada), for the measurement of interface pressure exerted by lumbar belts onto the trunk. These sensors were originally designed for the measurement of low pressure applied by medical devices on the skin. Two types of tests were performed: standard metrology tests such as linearity, hysteresis, repeatability, reproducibility and drift, and specific tests for this application such as curvature, surface condition and mapping system superposition. The linear regression coefficient is between 0.86 and 0.98; hysteresis is between 6.29% and 9.41%. Measurements are repeatable. The location, time and operator, measurement surface condition and mapping system superposition have a statistically significant influence on the results. A stable measure is verified over the period defined in the calibration procedure, but unacceptable drift is observed afterward. The measurement stays suitable on a curved surface for an applied pressure above 50 mmHg. To conclude, the sensor has acceptable linearity, hysteresis and repeatability. Calibration must be adapted to avoid drift. Moreover, when comparing different measurements with this sensor, the location, the time, the operator and the measurement surface condition should not change; the mapping system must not be superimposed.

Center-of-Pressure Movements During Equine-Assisted Activities

We compared anteroposterior and mediolateral range of motion and velocity of the center of pressure (COP) on the horse’s back between riders without disabilities and riders with cerebral palsy. An electronic pressure mat was used to track COP movements beneath the saddle in 4 riders without disabilities and 4 riders with cerebral palsy. Comparisons between rider groups were made using the Mann–Whitney test (p < .05). The two rider groups differed significantly in anteroposterior range of COP motion, mediolateral range of COP motion, and mediolateral COP velocity. Anteroposterior COP velocity did not differ between groups. The results suggest that measurements of COP range of motion and velocity are potentially useful for monitoring changes in balance as an indicator of core stability during equine-assisted activities.

Usability of normal force distribution measurements to evaluate asymmetrical loading of the back of the horse and different rider positions on a standing horse

Pressure measurement devices in equine sports have primarily focused on tack (saddle pads and saddle fitting methods). However, saddle pressure devices may also be useful in evaluating the interaction and distribution of normal forces between the horse and rider, including rider position and riding technique. This study examined the validity, reliability, repeatability and possibilities of using a saddle pressure device to evaluate rider position. All measurements were performed using a standing horse. Validity was tested by calculating the correlation coefficient between measured normal force and the weight of the rider. Repeatability was tested by calculating intra-class correlation coefficients. The use of normal force measurements to evaluate horse-rider interaction was tested by adding a known weight to saddle or rider and collecting measurements with the rider sitting in four different positions. The device was found to be valid and reliable for force measurements when the measurement device was not replaced. The system could be used to determine the expected differences with added weight and in different rider positions. The normal force distribution measurement device proved to be a valid and reliable tool for studying the interaction between a rider and a static horse provided it is positioned carefully and consistently relative to both the horse and the saddle.

Association between objective and subjective measurements of comfort and discomfort in hand tools

In the current study, the relationship between objective measurements and subjective experienced comfort and discomfort in using handsaws was examined. Twelve carpenters evaluated five different handsaws. Objective measures of contact pressure (average pressure, pressure area and pressure-time (P-t) integral) in static and dynamic conditions, muscle activity (electromyography) of five muscles of the upper extremity, and productivity were obtained during a sawing task. Subjective comfort and discomfort were assessed using the comfort questionnaire for hand tools and a scale for local perceived discomfort (LPD). We did not find any relationship between muscle activity and comfort or discomfort. The P-t integral during the static measurement (beta=-0.24, p<0.01) was the best predictor of comfort and the pressure area during static measurement was the best predictor of LPD (beta=0.45, p<0.01). Additionally, productivity was highly correlated to comfort (beta=0.31, p<0.01) and discomfort (beta=-0.49, p<0.01).

Evaluation of antidecubitus mattresses

Pressure sores are a current problem in hospitals and care of the elderly, leading to protracted hospital stays and a high care burden. The trauma for the patients is severe, and the cost of pressure sore prevention and treatment, is considerable. Antidecubitus mattresses are used for prevention and in treatment, but they also contribute to the cost of treating pressure sores. The problem highlighted in the review is that the mattresses' effectiveness in preventing and treating pressure sores has not been sufficiently evaluated. When antidecubitus mattresses are evaluated, it is often only with regard to aspects of the interface pressure and the mattresses' ability to redistribute the pressure. The review points out the important observation that, to be able to evaluate the efficacy of the antidecubitus mattress, the mattress's effect on tissue viability needs to be studied. The parameters that ought to be considered when evaluating a support surface are: interface pressure, pressure and blood flow distribution, temperature and humidity in the skin-support surface interface. The authors propose that the effect on tissue viability of external loading can be assessed by simultaneous measurement of the interface pressure and tissue perfusion.

Auflagedruckmessung in der Dekubitusbehandlung

BACKGROUND

Pressure relief is an important factor to determine the quality of anti-decubitus devices. Many studies have been carried out to measure the interface pressure, but because the results differed markedly, we made a study to assess the measurement devices.

METHODS

The systems FSA, a device for internal use in the Lück company, the X-Sensor and an invasive subcutaneous pressure measurement over the os-sacrum (COACH: piezoelectric probe, MIPM) were tested on 20 healthy volunteers (average age 27 years, average BMI 21.8).

RESULTS

The values of interface measurement showed obvious deviations from subcutaneous pressure in two cases (FSA +1.8%, Lück -33%, X-Sensor +65%) and some results showed extreme variations (FSA +18 mmHg, Lück -21 mmHg, X-Sensor +27 mmHg).

CONCLUSIONS

The interface pressure measurement (with a few volunteers) is not suitable for a correct assessment of anti-decubitus devices. Furthermore, the use of this method is not necessary to monitor pressure relief in intensive care patients. These systems can, however be useful in the training of nursing staff.