Abstract-Wave reflections affect the proximal aortic pressure and flow waves and play a role in systolic hypertension. A measure of wave reflection, receiving much attention, is the augmentation index (AI), the ratio of the secondary rise in pressure and pulse pressure. AI can be limiting, because it depends not only on the magnitude of wave reflection but also on wave shapes and timing of incident and reflected waves. More accurate measures are obtainable after separation of pressure in its forward (P f ) and reflected (P b ) components. However, this calculation requires measurement of aortic flow. We explore the possibility of replacing the unknown flow by a triangular wave, with duration equal to ejection time, and peak flow at the inflection point of pressure (F tIP ) and, for a second analysis, at 30% of ejection time (F t30 ). Wave form analysis gave forward and backward pressure waves. Reflection magnitude (RM) and reflection index (RI) were defined as RMϭP b /P f and RIϭP b /(P f ϩP b ), respectively. Healthy subjects, including interventions such as exercise and Valsalva maneuvers, and patients with ischemic heart disease and failure were analyzed. RMs and RIs using F tIP and F t30 were compared with those using measured flow (F m Key Words: aorta Ⅲ blood flow Ⅲ blood flow velocity Ⅲ blood pressure Ⅲ pulse A ortic pressure, and especially pulse pressure (PP), is now recognized as an important indicator of cardiovascular risk 1-4 and can guide pharmaceutical treatment. 5,6 Wave reflections affect the pressure and flow wave in the proximal aorta, 7 and their contribution depends on their magnitude (determined by the periphery and the large arteries) and time of return (mainly determined by the large, conduit arteries). When the reflected wave arrives in systole, it augments pressure, leading to increased systolic and PP. This augmentation is greater when the heart is hypertrophied. 8 In heart failure, wave reflections affect the flow wave negatively, thereby reducing stroke volume and cardiac output. 8 -10 One way to estimate the amount of reflection is by waveform analysis in which aortic pressure is separated into its forward and backward components. 7,11,12 The ratio of the magnitudes of the backward (reflected) wave and the forward (incident) wave, the reflection magnitude (RM), allows for the estimation of the amount of reflection, but this waveform analysis requires measurement of both pressure and flow waves. A method that requires the measurement of pressure only is computation of the augmentation index (AI). 13,14 AI gives reproducible results 15,16 and is in use in clinical settings. [17][18][19][20] However, AI is determined by both the magnitude and timing of the reflected wave. This is evident from Figure 1A. In this figure, the original pressure wave is separated into its forward and backward components and then reassembled for different delays of the same backward wave. AI is clearly influenced by the time of return of the reflected wave. Figure 1B gives 2 examples in w...

Reconstruction of BAP from FinAP as implemented in the Finometer reduces the pressure differences, with an individual RTF calibration to well within AAMI requirements.

Reconstruction of intrabrachial artery pressure from finger artery pressure with waveform filtering and level correction reduces the pressure differences substantially, with diastolic and mean within Association for the Advancement of Medical Instrumentation requirements. After one supine return-to-flow calibration, all pressure differences meet the requirements. Return-to-flow calibration should not be repeated in sitting position.

We investigated the quantitative contribution of all local conduit arterial, blood, and distal load properties to the pressure transfer function from brachial artery to aorta. The model was based on anatomical data, Young's modulus, wall viscosity, blood viscosity, and blood density. A three-element windkessel represented the distal arterial tree. Sensitivity analysis was performed in terms of frequency and magnitude of the peak of the transfer function and in terms of systolic, diastolic, and pulse pressure in the aorta. The root mean square error (RMSE) described the accuracy in wave-shape prediction. The percent change of these variables for a 25% alteration of each of the model parameters was calculated. Vessel length and diameter are found to be the most important parameters determining pressure transfer. Systolic and diastolic pressure changed Ͻ3% and RMSE Ͻ1.8 mmHg for a 25% change in vessel length and diameter. To investigate how arterial tapering influences the pressure transfer, a single uniform lossless tube was modeled. This simplification introduced only small errors in systolic and diastolic pressures (1% and 0%, respectively), and wave shape was less well described (RMSE, ϳ2.1 mmHg). Local (arm) vasodilation affects the transfer function little, because it has limited effect on the reflection coefficient. Since vessel length and diameter translate into travel time, this parameter can describe the transfer accurately. We suggest that with a, preferably, noninvasively measured travel time, an accurate individualized description of pressure transfer can be obtained. blood pressure; transfer function; personalization; brachial artery; aorta AORTIC PRESSURE appears a better indicator of cardiovascular morbidity and mortality than peripheral, e.g., brachial or radial, pressure (5,15,16,37,38). Also, ascending aortic pressure defines the systolic load on the heart through ventricular wall stress. Effects of therapy are preferably studied using aortic pressure (19). However, whereas peripheral pressures can be obtained noninvasively, measurement of aortic pressure requires invasive techniques. Transfer functions that calculate aortic pressure from peripheral pressure circumvent this invasive measurement and provide an opportunity to noninvasively obtain this cardiovascular information.Several approaches have been taken to arrive at transfer functions. Chen et al. (4) and Fetics et al. (7) used a special mathematical transformation to obtain a transfer function from human data, and the averaged transfer function of a group of patients was used as "standard" transfer. Karamanoglu et al.(18) used a segmented model of the arterial tree to derive the transfer function. Gizdulich et al. (9, 10) proposed a method to obtain brachial pressure from finger pressure by fitting a second order filter to averaged data. Stergiopulos et al. (27) showed that splitting the brachial pressure in its backward and forward waves and by shifting these waves with respect to each other over the travel time between aorta and brach...

Central aortic pressure gives better insight into ventriculo-arterial coupling and better prognosis of cardiovascular complications than peripheral pressures. Therefore transfer functions (TF), reconstructing aortic pressure from peripheral pressures, are of great interest. Generalized TFs (GTF) give useful results, especially in larger study populations, but detailed information on aortic pressure might be improved by individualization of the TF. We found earlier that the time delay, representing the travel time of the pressure wave between measurement site and aorta is the main determinant of the TF. Therefore, we hypothesized that the TF might be individualized (ITF) using this time delay. In a group of 50 patients at rest, aged 28-66 yr (43 men), undergoing diagnostic angiography, ascending aortic pressure was 119 +/- 20/70 +/- 9 mmHg (systolic/diastolic). Brachial pressure, almost simultaneously measured using catheter pullback, was 131 +/- 18/67 +/- 9 mmHg. We obtained brachial-to-aorta ITFs using time delays optimized for the individual and a GTF using averaged delay. With the use of ITFs, reconstructed aortic pressure was 121 +/- 19/69 +/- 9 mmHg and the root mean square error (RMSE), as measure of difference in wave shape, was 4.1 +/- 2.0 mmHg. With the use of the GTF, reconstructed pressure was 122 +/- 19/69 +/- 9 mmHg and RMSE 4.4 +/- 2.0 mmHg. The augmentation index (AI) of the measured aortic pressure was 26 +/- 13%, and with ITF and GTF the AIs were 28 +/- 12% and 30 +/- 11%, respectively. Details of the wave shape were reproduced slightly better with ITF but not significantly, thus individualization of pressure transfer is not effective in resting patients.