EUROPEAN  TISSUE  REPAIR  SOCIETY

The Wound Healing Research Unit (WHRU) based within the University of Wales College of Medicine, Cardiff is an internationally recognised centre for excellence in wound healing research, education and practice and earlier this year the achievements of the WHRU were recognised by the award of Centre of Excellence Status by the Welsh Development Agency. While the WHRU has forged many working partnerships with research centres and commercial organisations, one of the strongest links is with a local academic institution, the University of Glamorgan. In particular a vibrant collaboration has developed over the last decade with the Medical Electronics and Signal Processing Research Unit (MESPRU) within the School of Electronics. The School of Electronics is, itself, a recognised Centre of Excellence in Electronic Product Engineering. This partnership, led by Professors Keith Harding (WHRU) and Bob Williams (University of Glamorgan) has focused upon the quantification of physical and physiological parameters associated with wounds and their healing.

The central philosophy of the group is to identify practical, yet clinically relevant measurements that will help clinicians predict either wound development or the likely progress of a wound given a particular intervention. On a daily basis the research group is comprised of WHRU technical and clinical staff, with biological and electronic engineering input from the School of Electronics. The success of the group can be clearly seen through consideration of its publication record where one single aspect of the group's activity - the assessment of lower limb compression - generated seventeen publications, fourteen abstracts or letters and forty-eight presentations between 1998 and 2000.

Current research interests of the Physical Measurement Group
The core activities of the Physical Measurement Group span eight areas:

• How do compression bandages and stockings assist venous leg ulcer healing?
• The assessment of shear forces under compression bandages and upon patient support surfaces
• The evaluation of beds, mattresses and cushions using contact pressure measurements
• The assessment of colour and texture within wounds
• The effect of local heating upon wound healing
• The use of thermal imaging to assess wounds and soft tissues
• Quantification of MRI scans through wounds and their surrounding tissues
• The assessment of local blood flow in and around wounds.

The role of compression bandages and stockings
Evaluation of the physical effects of compression bandages and stockings remains a key activity for the Physical Measurement Group. This work began in the mid 1990s and has worked to characterise the forces, both perpendicular and parallel to the lower limb applied by various bandage types. Figure 1 illustrates the strain gauge transducer used within this work, which provides repeatable and precise (+/- 2mmHg over a 0-100mmHg operating range) measurements of the compression applied by bandages and stockings to the lower limb. This work has been reported upon several occasions during ETRS meetings and within the pages of Wound Repair and Regeneration. The measurement system was first developed and used to compare bandages applied to rigid cylinders - in this way the group worked to exclude the natural heterogeneity encountered through differences in limb size and tissue characteristics. This laboratory system (Figure 2) has now been used to explore why pressure measurements may diverge from the predictions offered through use of the Laplace equation and its derivatives. We have more recently, explored the effects of different bandage application techniques upon the generated levels of compression. Over the next months, the system will be moved from the moved in the laboratory with a series of volunteer studies planned to explore the changes in compression that occur during locomotion.

Figure 1. Strain gauge transducer used to access the
forces applied by compression bandages and stockings.

While the main focus during our work on compression bandages has been the characterisation of the extent of compression, physiological effects cannot be ignored. Earlier work upon skin temperature changes under compression bandages suggested that the changes in skin temperature observed under the bandage may be due to more than simple thermal insulation with a corresponding fall in the skin temperature of the other, non bandaged limb. At the Brussels 2000 meeting of the ETRS we presented the early stages of a new approach to characterising blood flow under intact compression bandages. In this approach, an area of the bandage is soaked in ultrasound coupling gel and blood flow recorded using a Laser Doppler Flux single-point probe. This approach is under refinement and has now been used with success upon the lower limb and using Laser Doppler Imaging to map regional changes in flow.

Figure 2. The initial test-rig showing rigid cylinders of different dimensions used to mimic the application of compresion bandages to different sized limbs.

The evaluation of beds, mattresses and cushions
This is a relatively new area of interest to the Physical Measurement Group but builds upon the experience of Dr Michael Clark, who provides day-to-day leadership for all of the Group's activities. The evaluation of beds, mattresses and other support surfaces using laboratory measures of contact (interface) pressure has been seriously compromised by over optimistic marketing claims by manufacturers. Recently several research groups have attempted to return the area to a sound scientific footing, an initiative underpinned by the current ISO Working Group developing standards for pressure-redistributing cushions, and by the EPUAP Working Group on Contact Pressure Measurement. The Physical Measurement Group undertake contact pressure measurement using the Talley Medical Oxford Pressure Monitor Mark II, while shear component characterisation is undertaken using paired strain gauge transducers, where one of the pair is effectively isolated from shear forces. Much of this work is undertaken on volunteer subjects and the relevance of such measurements can be debated. It is clear that whether one uses physical indenters or human subjects, do the relative differences between the contact pressures measured upon different surfaces mirror differences between the effectiveness and efficacy of the same surfaces? This is perhaps the fundamental question, which if resolved would clearly indicate the value of laboratory measures as proxies for clinical outcome when considering pressure ulcer development and healing.

Conclusion
The collaboration between the Wound Healing Research Unit and the School of Electronics at the University of Glamorgan has resulted in an active research group that has been highly productive. The core activities and interests of the Physical Measurement Group have been outlined, with more detailed discussion upon two of the research strands we follow. We would welcome both developing and strengthening contacts with other ETRS members - if there are areas of common interest perhaps new collaborations and projects may flow from this brief introduction to the Physical Measurement Group!

Michael Clark