Impact of multilayered compression bandages on sub-bandage interface pressure: a model

Background

Multi-component medical compression bandages are widely used to treat venous leg ulcers. The sub-bandage interface pressures induced by individual components of the multi-component compression bandage systems are not always simply additive. Current models to explain compression bandage performance do not take account of the increase in leg circumference when each bandage is applied, and this may account for the difference between predicted and actual pressures.

Objective

To calculate the interface pressure when a multi-component compression bandage system is applied to a leg.

Method

Use thick wall cylinder theory to estimate the sub-bandage pressure over the leg when a multi-component compression bandage is applied to a leg.

Results

A mathematical model was developed based on thick cylinder theory to include bandage thickness in the calculation of the interface pressure in multi-component compression systems. In multi-component compression systems, the interface pressure corresponds to the sum of the pressures applied by individual bandage layers. However, the change in the limb diameter caused by additional bandage layers should be considered in the calculation. Adding the interface pressure produced by single components without considering the bandage thickness will result in an overestimate of the overall interface pressure produced by the multi-component compression systems. At the ankle (circumference 25 cm) this error can be 19.2% or even more in the case of four components bandaging systems.

Conclusion

Bandage thickness should be considered when calculating the pressure applied using multi-component compression systems.

Detection of volatile organic compounds using porphyrin derivatives

Seven different porphyrin compounds have been investigated as colorimetric gas sensors for a wide range of volatile organic compounds. The porphyrins examined were the free base and Mg, Sn, Zn, Au, Co, and Mn derivatives of 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine. Chloroform solutions of these materials were prepared and changes in their absorption spectra induced by exposure to various organic compounds measured. The porphyrins that showed strong responses in solution were selected, and Langmuir-Blodgett films were prepared and exposed to the corresponding analytes. This was done to determine whether they are useful materials for solid state thin film colorimetric vapor sensors. Porphyrins that readily coordinate extra ligands are shown to be suitable materials for colorimetric volatile organic compound detectors. However, porphyrins that already have bound axial ligands when synthesized only show a sensor response to those analytes that can substitute these axial ligands. The Co porphyrin displays a considerably larger response than the other porphyrins investigated which is attributed to a switch between Co(II) and Co(III) resulting in a large spectral change.

Impact of variation in limb shape on sub-bandage interface pressure

BACKGROUND

Sub-bandage interface pressure generated by medical compression bandages (MCB) and hosiery changes in mobile patients as they move due to the change in the limb size. However, the amount of variation in the interface pressure is dependent on the stiffness of the compression material. Researchers have proposed several indices to describe this change in interface pressure, including the static stiffness index (SSI) and the dynamic stiffness index (DSI). These indices can also be used to classify compression products.

OBJECTIVES

To explore the different proposed indices to describe the stiffness of a compression material and compare it to the engineering stress-strain modulus which is used for the same purpose; To estimate theoretically the change in the interface pressure which is caused by the change in the limb shape as a consequence of calf muscle activity and the associated transient variation in limb dimensions.

METHOD

Use Chord modulus to classify compression material; Use thin and thick cylinder wall theory to estimate the variation in the interface pressure due to changes in the limb shape secondary to muscle contraction; Use tensile test devices to obtain the Chord modulus for two different MCB at two different dynamic ranges.

RESULTS

Chord modulus (E) describes the change in tension in a dynamic situation, and this is labelled as stiffness in the bandaging literature; Chord modulus, with the help of a mathematical model that was developed based on thick wall cylinder theory, can be used to predict the change in sub-bandage interface pressure caused by the change in limb shape secondary to calf muscle activity; Chord modulus can be used to classify bandages and describe how they will behave when they are applied to a leg.

CONCLUSION

The dynamic pressure can be predicted using a simple mathematical model using Chord modulus, which can be calculated in vitro using standard tensile testing equipment. In addition, Chord modulus can be used to classify compression bandages and hosiery.

Clinical outcomes and fusion success associated with the use of BoneSave in spinal surgery

BACKGROUND

Achieving spinal fusion is the guiding principle behind surgical treatment for a range of spinal pathologies, often requiring a substantial amount of bone-graft. Iliac crest autograft represents the gold standard although associated morbidities and limited graft material have led to the development of alternatives. BoneSave (Stryker, UK), a porous tricalcium phosphate-hydroxyapatite ceramic, is one such alternative, employed in spinal fusion over the past few years. Very little research exists into the clinical outcomes associated with its use.

METHODS

Clinical data was collected retrospectively from the case notes of 45 patients who underwent posterolateral inter-transverse spinal fusion involving the application of BoneSave between June 2003 and January 2005. Latest follow-up information was collected via a postal questionnaire (average follow-up of 46 months). Validated outcome instruments employed included the Short Form 36 and Oswestry Disability Index. In addition visual analogue scales for pain, patient global impression of change, work status, persisting symptoms and patient satisfaction data were collected. Radiological evaluation of fusion was carried out from the most recent spinal radiographs available for each patient.

RESULTS

Qualitative post-operative data was available in 96%, with a questionnaire response rate of 68.4%. Radiographical evaluation was possible in 67%. Significant post-operative improvements were seen across all outcome measures in the large majority of cases. Successful fusion was achieved in 56.7% of cases.

CONCLUSIONS

The clinical outcomes associated with the use of BoneSave in spinal fusion are comparable to those available in the literature for more conventional techniques. The fusion rate was not significantly lower.