P6.19 PHYSIOLOGICAL CORRELATES OF AORTIC RESERVOIR AND EXCESS PRESSURE IN MAN

Abstract

Background: Central (aortic) blood pressure (BP) indices independently predict cardiovascular events and all-cause mortality, but the physiological mechanisms underlying aortic BP waveform morphology are subject to debate. The ‘aortic reservoir’ and ‘excess pressure’ are proposed as determinants of aortic BP, but this relationship has only been assessed using a mathematically-derived aortic reservoir-excess pressure model (ARderived and XPderived). This study aimed to directly measure the aortic reservoir (ARdirect; by cyclic change in aortic volume) and determine the relationship with ARderived and aortic BP. Methods: Ascending aortic BP and Doppler flow velocity were recorded via intra-arterial wire in 10 males (aged 62±12 years) during coronary artery bypass graft surgery. Simultaneous ascending aortic transesophageal echocardiography was used to measure ARdirect. Published mathematical formulae were used to determine ARderived and XPderived. A direct excess pressure (XPdirect) was calculated by subtracting ARdirect from aortic BP. Results: When normalised to the same scale (Figure A), ARdirect (solid line) was strongly and linearly related to ARderived (broken line) during systole (r=0.980, P<0.001, Figure B, point 1–2) and diastole (r=0.987, P<0.001 Figure B, point 2–3). The cyclic relationship between aortic BP and ARdirect was qualitatively and quantitatively (P>0.05) similar to the cyclic relationship between aortic BP and ARderived. Furthermore, XPdirect was linearly related to XPderived during systole (r=0.909, P<0.001) and diastole (r=0.663, P<0.001). Conclusion: Aortic reservoir and excess pressures are physiological phenomena highly related to mathematically-derived aortic reservoir, excess pressure and aortic BP.