Description: Objective— Aortic reservoir pressure indices independently predict cardiovascular events and mortality. Despite this, there has never been a study in humans to determine whether the theoretical principles of the mathematically derived aortic reservoir pressure (RP derived ) and excess pressure (XP derived ) model have a real physiological basis. This study aimed to directly measure the aortic reservoir (AR direct ; by cyclic change in aortic volume) and determine its relationship with RP derived , XP derived , and aortic blood pressure (BP). Approach and Results— Ascending aortic BP and Doppler flow velocity were recorded via intra-arterial wire in 10 men (aged 62±12 years) during coronary artery bypass surgery. Simultaneous ascending aortic transesophageal echocardiography was used to measure AR direct . Published mathematical formulae were used to determine RP derived and XP derived . AR direct was strongly and linearly related to RP derived during systole ( r =0.988; P 〈0.001) and diastole ( r =0.985; P 〈0.001). Peak cross-correlation ( r =0.98) occurred at a phase lag of 0.004 s into the cardiac cycle, suggesting close temporal agreement between waveforms. The relationship between aortic BP and AR direct was qualitatively similar to the cyclic relationship between aortic BP and RP derived , with peak cross-correlations occurring at identical phase lags (AR direct versus aortic BP, r =0.96 at 0.06 s; RP derived versus aortic BP, r =0.98 at 0.06 s). Conclusions— RP derived is highly correlated with changes in proximal aortic volume, consistent with its physiological interpretation as corresponding to the instantaneous volume of blood stored in the aorta. Thus, aortic reservoir pressure should be considered in the interpretation of the central BP waveform.

Description: Exercise hypertension independently predicts cardiovascular mortality, although little is known about exercise central hemodynamics. This study aimed to determine the contribution of arterial wave travel and aortic reservoir characteristics to central blood pressure (BP) during exercise. We hypothesized that exercise central BP would be principally related to forward wave travel and aortic reservoir function. After routine diagnostic coronary angiography, invasive pressure and flow velocity were recorded in the ascending aorta via sensor-tipped intra-arterial wires in 10 participants (age, 55±10 years; 70% men) free of coronary artery disease with normal left ventricular function. Measures were recorded at baseline and during supine cycle ergometry. Using wave intensity analysis, dominant wave types throughout the cardiac cycle were identified (forward and backward, compression, and decompression), and aortic reservoir and excess pressure were calculated. Central systolic BP increased significantly with exercise (=19±12 mm Hg; P 〈0.001). This was associated with increases in systolic forward compression waves (=12 x 10 6 ±17 x 10 6 W·m –2 ·s –1 ; P =0.045) and forward decompression waves in late systole (=9 x 10 6 ±6 x 10 6 W·m –2 ·s –1 ; P 〈0.001). Despite significant augmentation in BP (=9±6 mm Hg; P =0.002), reflected waves did not increase in magnitude (=–1 x 10 6 ±3 x 10 6 W·m –2 ·s –1 ; P =0.2). Excess pressure rose significantly with exercise (=16±9 mm Hg; P 〈0.001), and reservoir pressure integral fell (=–5 x 10 5 ±5 x 10 5 Pa·s; P =0.010). Change in reflection coefficient negatively correlated with change in central systolic BP ( r =–0.68; P =0.03). We conclude that elevation of exercise central BP is principally because of increases in aortic forward traveling waves generated by left ventricular ejection. These findings have relevance to understanding central BP waveform morphology and pathophysiology of exercise hypertension.