Peripheral Augmentation Index Defines the Relationship Between Central and Peripheral Pulse Pressure

Abstract

Abstract-Peripheral systolic blood pressure is amplified above central aortic systolic pressure, but the late systolic shoulder of the peripheral pulse may approximate central systolic pressure. Because late systolic pressure also determines the peripheral augmentation index, a measure of pressure wave reflection within the systemic circulation, this implies a direct relationship between amplification and augmentation. We compared the late systolic shoulder of the peripheral pressure waveform with estimates of central systolic pressure obtained using a transfer function in 391 subjects undergoing diagnostic coronary angiography and/or elective angioplasty (30% with insignificant coronary artery disease). In a subset (nϭ12) Key Words: aorta Ⅲ augmentation index Ⅲ central blood pressure Ⅲ pulse pressure Ⅲ pulse wave analysis P ropagation of the pressure pulse from the left ventricle to the systemic circulation is accompanied by reflections from sites of impedance mismatch. These reflections result in backward traveling pressure waves, which augment pressure at the aortic root, this being quantified by the aortic or "central" augmentation index (AI; cAI; Figure 1). 1-3 At the same time, pulse pressure propagation and reflection within the upper limb results in peripheral amplification of the pressure pulse, so that peripheral systolic pressure (pSBP) measured at the brachial artery, radial artery, or digital artery exceeds central systolic blood pressure (cSBP) at the aortic root. 1,4 Because of the slow rate of change of pressure during diastole, diastolic blood pressure (DBP) is similar at central and peripheral sites (as is mean arterial pressure), 5 but central pulse pressure (cPP) differs from peripheral pulse pressure (pPP). The potential importance of cSBP and cPP was demonstrated in the Conduit Artery Function Evaluation Study, where the difference in outcome between hypertensive regimes was explained by differing central but not peripheral blood pressures, and cPP was predictive of overall outcome. 6 Augmentation of central arterial pressure and peripheral amplification have been regarded as largely unrelated phenomena, with the former being determined by characteristics of wave propagation in the aorta and by reflections from the head and lower body and the latter by reflections from the upper limb. However, cAI is closely related to the peripheral AI (pAI), a measurement taken direct from the late systolic shoulder (pSBP 2 ) of the peripheral arterial waveform (Figure 1), which, in turn, may approximate cSBP. 7 This implies a direct relationship between amplification and augmentation. The purpose of this study was to investigate how closely pSBP 2 equates to cSBP and to define the relationship between AI and cSBP. We first investigated the relationship between pSBP 2 and cSBP estimated noninvasively using a transfer function. We then examined the relationship of pSBP 2 to cSBP measured invasively at the time of cardiac catheterization. The relationship between central and peripheral pressure is critica...

Comparison of two measuring instruments, B-pro and SphygmoCor system as reference, to evaluate central systolic blood pressure and radial augmentation index

“…These authors also found a positive correlation (r¼0.82, Po0.001) between CAIx estimated with SphygmoCor and rAIx estimated with HEM-9010AI, similar to that seen in our study with SphygmoCor (r¼0.86, Po0.01) but greater than that found between CAIx estimated with SphygmoCor, and rAIx estimated with B-Pro (r¼0.46, Po0.01). The rAIx values reported by both Kohara et al 14 (0.69±16.3 in males and 0.81±16.1 in females) and Munir et al 13 (0.79 ± 11.8) are lower than those obtained in our study. However, considering that the correlation of our data using SphygmoCor coincides with the results of other authors 13,14 and is in disagreement with the estimation of rAIx using B-Pro, it would seem necessary to revise the methodology used by this device in estimating this parameter.…”

“…12 The increases in central blood pressure, mean blood pressure and rAIx were estimated as well. rAIx was calculated from the radial wave pulse as follows: (second peak SBP (SBP2)ÀDBP)/(first peak SBPÀDBP)Â100, 13 as seen in Figure 1. Intra-observer reliability evaluated in 20 subjects before the study began, using the intraclass correlation coefficient, showed values of 0.971 (95%CI: 0.923-0.989) for CASP and 0.952 (95%CI: 0.871-0.982) for rAIx.…”

“…rAIx in turn was calculated from the radial wave pulse as follows: (second peak SBP (SBP2)ÀDBP)/(first peak SBPÀDBP)Â100. 13 Using the SphygmoCor (PWV), and with the patient in the supine position, the pulse wave of the carotid and femoral arteries was analyzed, estimating the delay with respect to the electrocardiogram wave and calculating the PWV. Distance measurements were taken with a measuring tape from the sternal notch to the carotid and femoral arteries at the sensor location.…”

“…The morphology of the radial pulse can also be used to estimate the peripheral or radial augmentation index (rAIx), as a parameter assessing vascular structure and function. 13,14 However, few studies have been made of the relationships with other arterial stiffness parameters, or of comparisons between different methods that estimate this same parameter.…”

Impact of passive vibration on pressure pulse wave characteristics

“…As the changes in P2 and AIx were correlated and Tr was unaffected after PV, our data suggest that the post-vibration AIx response could be mainly driven by a reduction in vascular smooth muscle tone in the legs. 30,31 The aortic pressure pulse wave is a composite of an early forward wave (P1) and a reflected wave traveling from the periphery back to the aorta (P2). 6 In cardiac patients with increased AIx, aortic SBP is determined by P2 whereas peripheral SBP is more dependent on P1.…”