Discussion
This pilot study explores the utility of SAM as a tool for characterisation of arterial stiffening in aortic biopsies. SAM has been used previously to study atherosclerosis1,2 and aneurysms3 in human aortas. However, to our knowledge there are no previous studies which have used SAM in relation to arterial stiffening in human tissue. Our previous work focussed on animal tissues5,8,10,12. Here, we examined the potential use of SAM for understanding human arterial stiffness. There was no correlation with PWV data, not surprising given the small numbers. Here, only localised regions in the medial layer of the aorta are examined by SAM, whereas the great clinical advantage of aortic PWV is its make-up from all parts of the aortic wall including the adventitia. It is highly likely that “classical” aortic PWV is a net effect of the mechanical properties of many components across the longitudinal, cylindrical and cross-sectional dimensions of the aortic wall. Hence PWV is providing a measurement at the whole organ level whereas SAM gives micro-detail for specific regions of the aortic wall. Acoustic wave speed ex-vivo here investigates the contributions of the different layers of the vessel separately. The wave speed measured with SAM is 1000 higher than “classical” aortic PWV, due to that fundamental difference. PWV is a measure of the rate at which pressure waves propagate along the vessel. In contrast, SAM measures the speed of sound in materials.
