An integrated evaluation of compression devices with a focus on ambulatory monitoring of sub-bandage pressure and posture

This thesis describes an investigation on the performance of compression bandages and elastic stockings used in the treatment of venous ulcers. It examines the magnitude and distribution of pressures beneath these devices and the factors that influence the generation of compression. An electro-hydraulic interface pressure measuring device was specifically designed and developed to measure pressure beneath these compression devices. An integrated short term evaluation of the performance of twelve routinely used bandages and elastic stockings was carried out. Two techniques of bandaging and the effects of laundering on stockings were also examined. In vivo tests revealed that the majority of the compression devices failed to produce appropriate compression at the ankle and favourable pressure gradients over the leg. The tests also indicated that posture, technique of bandaging and the duration of use were important influencing factors. These factors have previously not been considered in the classification of bandages and stockings. Mechanical properties of the devices relevant to the generation of compression were also examined. In vitro tests on specimen materials showed non-linear and non-elastic load deformation behaviour and stress relaxation by all the devices. A subjective assessment based on the personal experiences of the bandager and the volunteer subjects yielded useful information on the compression devices. The findings of the integrated evaluation suggested a need for long term ambulatory monitoring of pressure and posture. A novel ambulatory pressure and posture monitoring device comprising a pressure transducer and sensor, a flexible goniometer and pocket sized data logger was developed. This device was used to the monitor sub-bandage pressure and posture on subjects in three controlled postures during activities of daily living. The long term performance of five commonly used compression bandages (Granuflex, Elastocrepe, Coban Wrap, Lestreflex and Low Tack) applied by the same physiotherapist, was investigated on a single subject. The Granuflex bandage was further investigated on nine subjects. With the exception of the Elastocrepe bandage, the pressures fell significantly over the first six hours after which the pressures progressively became independent of time. Superimposed on the decreasing trends were cyclic daily variations in pressure for all five bandages. The magnitude and gradient of sub-bandage pressures were influenced by posture. The Granuflex bandage produced the highest pressures with relatively small standard deviations after the first day. The Coban Wrap performed well in maintaining pressure with low standard deviations. The performances of the Low Tack and Lestreflex bandages were average while that of the Elastocrepe bandage was poor. The findings in this investigation warranted a more comprehensive study on venous ulcer patients. The ambulatory device was further miniaturised and the goniometer replaced with the activity sensor which measured posture unambiguously and was conducive for prolonged use on patients. A preliminary analysis of the data for three patient tests is reported in this thesis. The time course of the ambulatory sub-bandage pressure over the seven days had no discernible trend. Cyclic daily variations of pressure were observed and its association with the fall in pressure during periods of sleep were confirmed. The pressures generated during continuous ambulation varied considerably for each day, patient, bandage and site, and were influenced by posture. Favourable pressure gradients achieved during ambulation were generally low. The results indicate that the pressures in the lower section of the leg predominately dictates the profile of the pressure gradient. Analysis of daily activities revealed that the patients spent a majority of their time in the upright posture, often continuously during the hours of work. Further, the patients did not regularly spend time with their legs elevated. This lifestyle may have a direct bearing to venous ulceration. The preliminary analysis has highlighted the multiplicity and complexity of factors governing sub-bandage pressures during activities of daily living. The ambulatory pressure and posture monitoring device has proven to be a powerful investigative tool. This research has unveiled new long term characteristics of pressure generated by bandages and has also provided confirmation of many previous findings. The measurement of patient activity should provide additional information on venous ulceration and its reoccurrence. The investigation has confirmed the limitations of short term measurement of interface pressure beneath compression devices on non-ambulatory subjects. The knowledge acquired from this research should prove useful in the ongoing effort to improve compression therapy used in the treatment of venous ulcers.

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