Force and pressure measurements at biomedical interfaces

The pressures arising at interfaces between living tissue and pressure applying parts are of increasing interest in medical and veterinary science. This interest arises primarily out of the need to control these pressures in order to ensure the safety and welfare of the subject while retaining the pressure applying device functionality. For instance, straps with windlass handles are used in emergency tourniquets used in medical pre-hospital and emergency settings to control blood loss. Tension bandages are used in the routine treatment of leg ulcers. Circumferential bands are integral to many harness parts essential for the use and control of horses. As with medical applications, bandaging is a major wound and rehabilitation treatment for animals. In all these applications, the key function of the device is control of some physiological (human) or behavioural aspect (animal) through pressure application. Despite the extensive use of pressure applicators in medical and veterinary practice, little is known about the actual pressures that arise at the interfaces between living tissue and the instruments and devices used to generate such pressures. Recent trends in emergency military ‘first-responder’ aid is providing the impetus for the development of new tourniquets which can be deployed easily and quickly by non-medical specialists (or self-applied). Similarly, concerns for the welfare of elite sports horses, particularly at major international competitions where very tight nosebands are used to restrict animal mouth action, has given rise to calls for control of the bands. However, it has proven impossible to enforce restrictions since there is no objective means of determining the actual noseband-tissue interface pressure and there is very little understanding of the interaction of circumferential bands and living tissue. In this work, novel biomedical interface pressure transducer (BIPT) technology is used along with a custom developed force dynamometers, in an experimental exploration of the actual pressures arising at tissue – pressure applicator interfaces in veterinary (bridle nosebands) and biomedical (emergency Junctional Tourniquet Effector (JTE)) application settings. In the case of bridle nosebands, clear evidence is provided for the occurrence of very significant pressure pulses and pressure gradients even for relatively mild use conditions. For JTEs, the preliminary experimental results indicate that blood loss (haemorrhage) in junctional arteries can be effectively controlled using mechanical effector heads but effector head placement is critical to attaining this control at pressures that are safe.