Introduction: Percutaneous Transluminal Coronary Angioplasty (PTCA) has been proven to be an effective treatment for coronary heart disease, yet within six months restenosis occurs in up to 45% of patients (Bestehorn 1998). Although brachytherapy and drug eluting stents are showing promising results, it is important to improve the success of PTCA and to understand the effect of the angioplasty balloon on the artery wall.
Methods: Pressure-volume (PV) curves show the balloon inflation volume and the change in balloon pressure, and were used in this research to assess the value of such data in determining the mechanical characteristics of arteries, which were modelled in the laboratory by mock arteries, allowing their properties to be measured independently. Eight silicone rubber mock arteries with varying wall thickness but equal inner diameter were used for the assessment of wall properties (tube compliance, elastic modulus). Tube compliance and elastic modulus were determined using 9 pairs of balloon catheters of different shape, size and manufacturer. Each balloon was inserted into all of the 8 test tubes and the pressure-volume relationships were recorded. This was repeated 4 times. After subtracting the influence of the measurement system, compliance and elastic modulus were determined from the characterising 'slope' of the pressure-volume curve. Due to the significant influences of different mechanical and dimensional properties of each individual balloon catheter, the measured tube compliances needed to be corrected for each balloon type. The correction values were determined by direct measurement on the mock arteries.
Results: Balloon compliance normalized over length was in the range of 0.09 to 0.32 (µl/bar)/mm, with a measurement SD between 0.005 and 0.04 (µl/bar)/mm. After subtracting the system compliance, the tube compliances using all balloon catheters and determined for the 3 most distinctive test tubes were 7.1, 5.2 and 3.6 (µl/bar)/mm with standard deviations of 2.11, 1.69 and 1.04 (µl/bar)/mm respectively. The average accuracy relative to the mean compliance improved from 35% (uncorrected) to 12% (corrected) for all balloon catheters used.
Conclusion: In conclusion, measurement of mechanical wall properties from pressure-volume curves can be determined with a range of different PTCA balloon catheters, provided the values obtained are corrected for the influence of the different balloon properties. The correction factor for each balloon can be found using reference tubes with known compliances.
Olbrich T, Murray A. Determining mechanical properties of coronary arteries using a range of different angioplasty balloon catheters. Proceedings of the World Congress on Medical Physics and Biomedical Engineering, 2003.
Professor Alan Murray, Freeman Unit, Newcastle upon Tyne. Tel: +44 (0)191-223-1370.
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