Pressure mapping of medical compression bandages used for venous leg ulcer treatment (2010)

Chronic leg ulcers affect 1% of the adult population in the developed countries. The majority of leg ulcers are due to venous disease. The impact of venous ulcers on the quality of life is significant, and it costs the NHS £300 − 600m annually. Medical compression bandages (MCBs) are the cornerstone in the treatment of chronic venous ulcers. MCBs should be applied with a pressure gradient reducing from the ankle to the knee. Visual inspection of bandages in situ for the amount of extension and overlap in the MCBs is normally what nurses use in day by day clinical practice to control the pressure they apply to patients’ legs. Interface pressure produced by a bandage is proportional to the tension which, in turn, is proportional to the extension of the bandage, and pressure is inversely proportional to the limb radius. Experts in the field believe that applying MCBs with a constant extension will enable users to achieve the required gradient pressure profile, as the circumference of the leg increases from the ankle towards the mid-calf. Despite the many studies published investigating the effectiveness of different MCBs, very little work has been done to understand the underpinning physics of how MCBs apply pressure to the leg. In addition, although many types of pressure measurement systems have been developed and used by various researchers, most of these devices have not been systematically tested for their performance and measurement reliability. In this thesis, the physics behind compression therapy is investigated and modeled using mathematical equations, some of which are validated experimentally. Analytical results suggest that ignoring MCBs thickness when computing the interface pressure will have a negligible effect on the accuracy of the pressure calculation produced by singlelayer MCBs. However, MCBs thickness should be considered in computing the interface pressure produced by multi-layer MCBs. Moreover, a model developed by other researchers to explain the impact of the pressure sensor’s physical dimensions on the interface pressure is tested experimentally. Results suggest that the model is not sufficient to estimate the amount of perturbation in the pressure, and a better model is needed. Furthermore, the thesis outlines experiments conducted to study MCBs and obtain polynomial expressions to describe the MCBs tension-elongation curves. The polynomial expressions are used in conjunction with mathematical models to compute the interface pressure induced by MCBs. In addition, the thesis demonstrates how the information obtained from these experiments is used in line with a mathematical model to classify compression bandages and simulate the impact of limb shape change secondary to calf muscle activity on the interface pressure. Moreover, the thesis reports on the evaluation of various types of resistive-based flexible pressure sensors. It illustrates that FlexiForce outperforms other resistive-based flexible sensors in static evaluation for sensitivity to low pressures, nonlinearity, repeatability, hysteresis and drift. However, the typical accuracy of FlexiForce sensor is found to be ±12% full scale, where full scale in this case is 120mmHg. The accuracy error is further reduced to approximately ±6% full scale by arranging the sensors in arrays and using averaging techniques. Arrays of FlexiForce sensors are used then to map the interface pressure under MCBs applied to different mediums. The pressure maps obtained by FlexiForce sensors are compared with the maps obtained using microelectromechanical systems (MEMS) force sensors and PicoPress transducer, a commercial medical pressure transducer used currently to study the pressure induced under MCBs. Furthermore, the measured pressures in all these cases are compared with the pressures computed theoretically from the bandage extension. Results show low levels of agreement or, in some cases, no agreement between the measured and computed pressures, which lead to question the reliability of using extension as a feedback method to control the interface pressure applied by MCBs. Additionally, in spite of some deficiencies in the performance of FlexiForce sensors, the thesis demonstrates that they could be used to obtain pressure maps for qualitative purposes. This, in some cases, is found to provide more reliable pressure readings than commercial sensors like PicoPress. Generally, current medical pressure transducers are thick; thus, they tend to overestimate the pressure applied by compression bandages significantly. The thesis details the assessment of pressure-mapping bandage prototypes and the associated tests carried out to evaluate their performance. Preliminary results suggest that the pressure-mapping bandage prototypes cannot be used to have accurate measurements. Nevertheless, they can provide the user with qualitative information about the pressure profile in terms of pressure levels and gradient. Finally, the thesis presents the usage of a pressure-mapping leg for training purposes for student nurses. This involved studying student nurses’ bandaging techniques and pinpointing their main bandaging technique pitfalls. Compared with experienced nurses, fewer of the student nurses applied MCBs with reverse pressure gradient.