P127 Spatial Variation of Reservoir Pressure in Children Assessed with High Fidelity Pressure Measurement in Five Aortic Locations

Objective To assess whether reservoir pressure (Pres) in young individuals with a compliant aorta is uniform throughout the aorta, as has recently been reported in older adults with cardiovascular disease (1). Methods High fidelity pressure was measured with a Verrata wire (Philips Volcano) in 5 aortic locations (ascending-to-abdominal) via pull-back in 11 children with a normal aorta (age 10.4 ± 4.9 years, mean ± SD). Pres was calculated using the ‘pressure-only’ approach (2), with exponential fitting over the whole of diastole (1) (WholeDia) or the period when pressure declined in an approximately exponential fashion (ExpDia). Results ExpDia produced a better fit than WholeDia (R2 = 0.99 ± 0.01 vs 0.91 ± 0.11, P < 0.001). P res amplitude (ΔP res ) in the ascending aorta from WholeDia fitting (12.0 ± 4.1 mmHg) was less than with ExpDia fitting (19.0 ± 5.2, P = 0.001). The zero-flow asymptotic pressure (P inf ) obtained from the fitting procedure was negative (non-physiological) in 76% (WholeDia) and 44% (ExpDia) of recordings, but fixing P inf to 37 mmHg (average of physiological values) had little effect on the resulting ΔP res . ΔP res varied by 5.7 ± 3.0 mmHg (WholeDia) and 7.3 ± 3.7 mmHg (ExpDia) between aortic locations (both P<0.001 compared with zero), corresponding to 44% ± 30% and 38% ± 17% of average ΔP res respectively. Maximum instantaneous spatial differences in P res amounted to a substantial percentage of ΔP res (45% ± 37% WholeDia; 24% ± 26% ExpDia) and were not reduced by time and/or pressure offsets to align P res foot. Conclusion In young individuals, P res was sensitive to the fitting period and often resulted in non-physiological P inf values. Regardless of calculation method or alignment, P res was not uniform along the aorta.