Aortic Reservoir Pressure Corresponds to Cyclic Changes in Aortic Volume

Abstract

C entral (aortic) blood pressure (BP) waveform indices independently predict cardiovascular events and all-cause mortality, 1 but the physiological mechanisms to explain the waveform morphology remain disputed. The well-established wave reflection theory ascribes transmission of discrete forward and backward (incident and reflected) waves as the principal contributory factor underlying the shape of the central BP waveform.2 However, while providing a plausible description of central BP morphology, recent studies have concluded that the influence of discrete reflected waves on central BP may be less than originally conceived, and this is probably because of wave dispersion along the aorta and entrapment of reflected waves in the periphery. 3,4 Indeed, augmentation of central BP may be largely attributable to forward wave propagation (as a result of left ventricular [LV] ejection) and proximal aortic reservoir function. [5][6][7][8][9] Importantly, wave separation theory obscures the pressure buffering role of the highly elastic proximal aorta (ie, the aortic reservoir), and a failure to consider this function may lead to incorrect interpretations of the physiology underlying central BP waveform morphology.The reservoir-excess pressure concept is an alternate method proposed to explain the underlying physiology of the aortic BP waveform. This method has been used invasively to study changes in aortic BP associated with both aging and exercise. 6,8 Moreover, indices derived from this model were recently shown to predict cardiovascular events (fatal and nonfatal) and procedures independent from brachial BP and other conventional cardiovascular risk parameters (eg, age, sex, cholesterol, smoking, diabetes mellitus), including Framingham risk score, in an analysis of the Conduit Artery Function Evaluation study. 10 In accounting for the reservoir function of the aorta, 7,11 the reservoir-excess pressure model is founded on the basis that aortic BP can be separated into © 2014 American Heart Association, Inc.

Impact of leg blood flow restriction during walking on central arterial hemodynamics

“…Contrary to our hypothesis, wave separation analysis revealed that the reflected wave was not enhanced by the BFR during walking. In this regard, recent reports indicate that the reflected wave emanates around the proximal aorta (6) and that wave reflection from the periphery does not appear to influence the rise of aortic systolic BP during leg cycling exercise (6,20,21). Leg BFR-induced elevation of aortic systolic BP might be supported by these notions but not by the traditional wave theory.…”

“…However, the present findings are not consistent with this arterial wave reflection theory. The observed increases in central BP can be explained by changes in IWA and RWA acting through impeded outflow (impaired diastolic discharge) (6,20,21). Exercise-induced change in aortic PP was correlated with corresponding changes in IWA and RWA, and changes in IWA were entered into the multiple regressional model as a significant independent determinant of the exercise-induced change in aortic BP.…”

Practical Suitability of a Stand-Alone Oscillometric Central Blood Pressure Monitor: A Review of the Microlife WatchBP Office Central

“…Although the wave reflection theory may provide a plausible description of CBP morphology, recent studies indicate that the influence of wave reflection on CBP may be less than initially assumed due to wave dispersion along the aorta and entrapment of reflected waves in the periphery. Accumulating evidence has shown that the reservoir function has a significant contribution to the augmentation of CBP [40]. The aortic reservoir represents the buffering role of the highly elastic proximal aorta, and the reservoir pressure is the minimum hydraulic force needed for the ventricle to generate the blood flow.…”

“…This leads to augmented BP and results in left ventricular hypertrophy due to the increased myocardial load. The reservoir pressure is highly correlated with changes in proximal aortic volume, and parameters from the reservoir wave can predict cardiovascular events and correlates with left ventricular mass [40,41,42]. The excess pressure integral is the difference between the measured BP waveform and reservoir pressure, and is a measure of the extra work needed by the left ventricle.…”

Central pressure should be used in clinical practice

“…12,13 In the latter population there was an improvement of the c statistic with the inclusion of aortic excess pressure into predictor models for CV events already containing conventional Framingham risk factors (including brachial BP). 13 This novel marker, representing excess left ventricular (LV) work, has been validated in humans, 14 and can be produced from pressure waveforms (oscillometric cuff or tonometry) without using a generalised transfer function, and is a promising area for future study.…”