An Interface Pressure Sensor for Routine Clinical Use

Interface pressure measurements in leg ulcer management

Interface pressure measurements are undertaken in health care as a useful tool to assist in understanding the pressures that exist between the skin surface and another surface. Pressure monitors are utilized to measure pressures under compression bandages and pressure garments and in determining pressures between patients and support surfaces such as pressure-reducing mattresses and cushions. This literature review identified that many studies using these measurements are inadequately described, and that there are many variables such as the effect of time, posture and temperature associated with such measurements that may lead to misinterpretation of results. Studies utilizing interface pressure measurements should be interpreted with caution and measurement techniques could be improved.

Seat pressure measurement technologies: considerations for their evaluation

Interface pressure measurement has generated interest in the automotive industry as a technique which could be used in the prediction of driver discomfort for various car seat designs, and provide designers and manufacturers with rapid information early on in the design process. It is therefore essential that the data obtained are of the highest quality, relevant and have some quantitative meaning. Exploratory experimental work carried out with the commercially available Talley Pressure Monitor is outlined. This led to a better understanding of the strengths and weaknesses of this system and the re-design of the sensor matrix. Such evaluation, in the context of the actual experimental environment, is considered essential.

Pressure differences of elastic compression stockings at the ankle region

BACKGROUND

Elastic compression stockings are widely used medical devices for the prevention of edema and treatment of venous diseases. Many beneficial effects have been described in the past. The exact amount of pressure underneath elastic compression stockings at different areas of the leg remains controversial.

OBJECTIVE

To examine the pressure at the skin underneath class II elastic compression stockings at different places around the ankle at the B level.

METHODS

Patients with known venous insufficiency and regularly using class II elastic therapeutic compression stockings (25-35 mm Hg) for venous diseases were included. All subjects were wearing completely new stockings at the time of the study. Measurements were performed with an electropneumatic interface pressure measuring device (Oxford Pressure Monitor MK II) with inflatable small sensoring cells. Six sensors were placed around the smallest circumference at the ankle (B-area). The highest and lowest recordings as well as the means were evaluated.

RESULTS

The mean pressure of class II elastic stockings measured around the ankle was 24.7 mm Hg (SD, 8.4). The lowest pressures were found at the medial site (18.3 mm Hg; 74% of the mean), and the highest at the pretibial zone (33.9 mm Hg, 137%).

CONCLUSIONS

The pressure exerted by pressure class II elastic compression stockings a the medial site just above the ankle (B area) is too low to have influence and improve the venous insufficiency. For phlebology this is the target area. It might be a reason for the high recurrence rate of venous ulcers even if patients wear stockings. Also, the mean pressure of class II stockings was found to be below the normal levels of its pressure class (25-35 mm Hg according to the European CEN classification). The results advocate the use of pressure class III elastic compression stocking more often and the use of pelottes or foam pads.

Accuracy of interface pressure measurement systems

Interface pressure measurement is needed to assess beds designed to prevent pressure sores, so it is therefore important to establish the accuracy of interface pressure measuring systems. In this study, the Talley SA500 pressure evaluator (with 28 mm and 100 mm sensor pads), the DIPE (with 100 mm sensor pad), and a water-filled bladder system (with 0.1 ml and 0.3 ml water) were assessed. Measurement errors were evaluated using a loading system with pressures up to 7.4 kPa (55 mm Hg) in steps of 0.9 kPa (6.9 mm Hg). All systems tested over-measured interface pressure, the error being approximately linearly proportional to the loading pressure. The repeatability for a given system was approximately constant. The mean error (+/- SD) (%) and repeatability (kPa) for the systems were: 28 mm Talley 12 +/- 1%, +/- 0.07 kPa; 100 mm Talley 15 +/- 1%, +/- 0.07 kPa; DIPE 27 +/- 3%, +/- 0.12 kPa; 0.1 ml water bladder 17 +/- 1%, +/- 0.13 kPa; 0.3 ml water bladder 26 +/- 3%, +/- 0.07 kPa. Different interfaces affected accuracy markedly, and repeatability was affected when an inhomogeneous interface was used. The study shows that the errors associated with interface pressure measurement systems can be substantial, and can vary from one system to another.

The effectiveness of a pressure clinic in preventing pressure sores

The role of a pressure clinic in reducing the incidence of pressure sores is described. Interface pressures are routinely measured to ensure that appropriate cushioning is provided. In patients most at risk, thermography is also valuable to ensure that the blood flow to the skin is not compromised. The implementation of such a clinic has proved successful and has resulted in a reduction of over 50% both in the incidence of sores and in the admission rate due to sores, when compared with studies from other spinal units.

Choosing a wheelchair cushion

A preliminary survey of twelve cushions on the standard 8L chair suggests that sheepskin and ministry cushions compare favourably with commercial cushions in respect to pressure and displacement characteristics. Ripple and water cushions were best.