0368 : Aortic impedance in older subjects: MR and applanation tonometry study by wave intensity analysis

Abstract

Central pressure waveform can be decomposed into pressure transmission and reflection waves. Zc, characteristic impedance of aorta can be measured through the recording of pulse pressure and aortic flow signals and reflects structural and functional properties of elastic central and peripheral muscular arteries. This study proposes a novel method using wave intensity analysis to assess reflected waves by decomposition of magnetic resonance imaging central aortic flow and central aortic pressure waveform measured by tonometry in 30 older subjects allowing to obtain the aortic characteristic impedance in the time domain and reflection index (IR) and reflection magnitude (MR). Elderly patients were mean aged of 75.25±5.85 years (14 female, 16 male). Mean Zc value was 424.34±94.41 DSC for the whole aging population. We found a strong negative association between Zc and LVET (r=–0.53, p=0.004). We found also a trend of negative association between Zc and aortic diameter, at the aortic root, (r=–0.36, p=0.05), and pressure augmentation (r=–0.36, p=0.06), and also with Aix (r = –0.32, p=0.09). Zc was positively associated with PPA (r = 0.41, p=0.02), and also strongly with HR (r= 0.54, p=0.003). Association between RM and IR were positively significant with aorta length measure by MRI, respectively (r=0.41, p=0.03) for RM and (r=0.42, p=0.03) for IR. RM associated positively with thoracic aorta length (r2 = 0.15, p=0.04) after adjustment to age and height, IR also associated positively with thoracic aorta length (r2 = 0.16, p=0.04) after adjustment to age and height. This automatic signal treatment of aortic flow and pulse pressure waveform is a good method for assessment of wave reflections in older subjects allowing obtaining reflection magnitude. Aortic characteristic impedance is inversely correlated to left ventricular ejection time and aortic diameter as new insights suggest.