Backward Pressure Wave Research Articles

PP.37.01] TIME TO PEAK OF THE AORTIC FORWARD WAVE DETERMINES THE IMPACT OF AORTIC BACKWARD WAVE AND PULSE PRESSURES ON LEFT VENTRICULAR MASS

Objective: Although aortic backward waves and hence pulse pressure are well-recognised determinants of cardiovascular damage beyond brachial pressures, these effects are inconsistent across studies. We aimed to assess whether an extended time to peak of aortic forward wave (Ft) or early wave reflection time (Rt) increase the chances of backward wave pressures (Pb) and hence central aortic pulse pressure (PPc) modifying end-organ effects. Design and method: In 812 adult participants from a community sample we assessed aortic haemodynamics (SphygmoCor software and wave separation analysis) and left ventricular mass index (LVMI) (echocardiography). Results: An interaction between Ft and Pb was independently associated with aortic augmented pressure (Pa) (p < 0.02), PPc (p < 0.005), LVMI (p < 0.0001) and LV hypertrophy (LVH) (p = 0.001). The Ft-Pb interaction translated into a stepwise increase in the independent association between Pb and Pa or PPc across quartiles of Ft (p < 0.02 for comparison of slopes of relations). Furthermore, the Ft-Pb interaction translated into an increase in the independent association between PPc or Pb and LVMI (p < 0.0001 for comparison of slopes and strength of relations) or LVH (p < 0.01 for comparisons of Odds ratios), but not between forward wave pressures and LVMI or LVH across quartiles of Ft. A markedly better ability of Pb and PPc, but not forward wave pressures to detect LVH was noted in the highest as compared to the first three quartiles of Ft (p < 0.01). In contrast, Rt failed to influence the impact of Pb or PPc on LVMI. Conclusions: Time to peak of aortic forward wave, but not early wave reflection markedly influences the impact of aortic backward wave pressure and hence PP on LVMI and LVH in adults. Hence, the adverse effects of aortic backward wave and hence pulse pressures may be strongly determined by forward wave timing.

PP.15.05] HEMODYNAMICS DETERMINANTS OF THE SHORT-TERM BLOOD PRESSURE VARIABILITY ACCORDING TO THE WAVE TRANSMISSION AND RESERVOIR PRESSURE THEORIES

Objective: A high short-term blood pressure variability (BPV) can predict long-term cardiovascular mortality independently of 24-hour systolic blood pressure (24-h SBP). The present study aimed to investigate the hemodynamics determinants of BPV according to models of wave transmission and reservoir pressure. Design and method: A cohort of 624 normotensive and 633 untreated hypertensive Taiwanese participants (overall 669 men, aged 30–79 years) with complete base-line ambulatory blood pressure monitoring and hemodynamics study was drawn from a community-based survey. BPV was assessed by calculating the read-to-read average real variability of the 24-h diastolic blood pressure (ARVd). The wave transmission variables included carotid-femoral pulse wave velocity (cfPWV), amplitudes of the forward (Pf) and backward (Pb) pressure waves from the decomposed carotid pressure waveforms. The reservoir pressure variables included peak (PRP), amplitude (PRA), and integral (PRI), and excess pressure integral (XPRI) of the reservoir pressure model. Results: ARVd and 24-h SBP were significantly correlated with age, body mass index, and all wave-transmission and reservoir pressure variables. Based on the wave transmission model and multi-variable regression analysis, Pb, Pf, and cfPWV were significant independent determinants of ARVd (model r2 = 0.22) and 24-h SBP (model r2 = 0.535), when age, sex, body mass index, heart rate, and total peripheral resistance were accounted for. Based on the reservoir pressure model, the significant independent determinants were PRP and PRI for AVRd (model r2 = 0.22) and all 4 variables (PRP, PRA, PRI, and XPRI) for 24-h SBP (model r2 = 0.709). The model r2 for ARVd did not improve appreciably when 24-h SBP was also added to the models (model r2 = 0.224 and 0.231, for the wave transmission and reservoir pressure models, respectively). Conclusions: Unlike 24-h SBP, BPV is only partially influenced by the hemodynamics variables and is likely mainly determined by other non-hemodynamics factors.

Fitness Is Independently Associated with Central Hemodynamics in Metabolic Syndrome.

Fit individuals with metabolic syndrome (MetS) have lower mortality risk compared with less fit counterparts, despite the presence of obesity as a component of the syndrome. To understand the importance of fitness in treating this condition, we examined the association of fitness and fatness with central hemodynamic indices that are known independent predictors of cardiovascular events. Sixty-eight individuals with MetS participated in this cross-sectional study. Central hemodynamics is calculated from radial applanation tonometry and comprised aortic reservoir pressure, backward pressure wave (Pb), reflection magnitude (RM), and augmentation index at 75 bpm (AIx75). Cardiorespiratory fitness (CRF) and body fat percentage (BF%) were determined via indirect calorimetry during maximal exercise testing and dual-energy x-ray absorptiometry, respectively. CRF was inversely associated with aortic reservoir pressure (r = -0.29, P = 0.02), Pb (r = -0.42, P < 0.001), RM (r = -0.48, P < 0.001), and AIx75 (r = -0.65, P < 0.001). BF% was also correlated with AIx75 (r = 0.37, P < 0.05) and RM (r = 0.36, P < 0.005) but at a weaker association compared with CRF. Multiple regression analysis revealed CRF as a predictor of aortic reservoir pressure (β = -0.52, P = <0.01), Pb (β = -0.41, P < 0.03), and AIx75 (β = -0.45, P = 0.01), independent of BF% and other confounding factors. CRF predicts central hemodynamics independent of BF% and other confounding factors. This suggests that CRF improvement may be a higher priority when compared with fat loss for lowering the risk of cardiovascular mortality in MetS individuals.

Cardiac Diastolic Dysfunction is Associated With Aortic Wave Reflection, but Not Stiffness in a Predominantly Young-to-Middle-Aged Community Sample.

Whether the impact of backward wave pressures (Pbs) on left ventricular (LV) diastolic dysfunction (DD) antedates the effects of aortic stiffness is uncertain. We compared the relative contribution of various aortic hemodynamic parameters to preclinical DD in a predominantly young-to-middle-aged community-based sample. In 524 randomly selected participants of African ancestry (mean age = 46.8±18.4 years), we assessed central aortic pulse pressure (PPc), forward wave pressure (Pf), Pb, augmented pressure (Pa), the time-to-wave reflection (Rt), and aortic pulse wave velocity (PWV) using applanation tonometry (SphygmoCor software). LV mass index (LVMI), early to late transmitral velocity (E/A), and E/velocity of myocardial tissue lengthening (E/e') were determined using echocardiography. Independent of age, sex, mean arterial pressure, body mass index, diabetes mellitus and/or HbA1c > 6.1%, regular smoking, regular alcohol intake, treatment for hypertension, pulse rate, and LVMI; PPc (P < 0.002), Pb (P < 0.0005), Pa (P < 0.002), and Pf (P < 0.02), but not Rt or PWV were independently associated with E/e' (but not with E/A). With adjustments for confounders, PPc (P < 0.005), Pb (P < 0.002), and Pa (P < 0.001), but not Pf, Rt, or PWV were independently associated with E/e' ≥ 12 (moderate-to-severe DD, n = 69). The independent relations between PPc and E/e' or moderate-to-severe DD were not affected by adjustments for PWV, Pf, or Rt, but were abolished with adjustments for Pb. In a predominantly young-to-middle-aged community sample, the impact of Pbs on LV DD antedates the effects of aortic stiffness, the time-to-wave reflection, or Pfs.

Post-exercise effects on aortic wave reflection derived from wave separation analysis in young-to middle-aged pre-hypertensives and hypertensives.

Decreases in brachial blood pressure (BP) may occur for several hours following a bout of exercise. Although aortic backward waves predict cardiovascular damage independent of brachial BP, whether decreases in aortic backward waves also occur post-exercise in young-to-middle-aged hypertensives, the extent to which these changes exceed brachial BP changes, and the best method of identifying these changes is uncertain. We examined aortic function at baseline and 15-min post-exercise in 20 pre-hypertensive or hypertensive men and women (age 45±7years). Central aortic pressure, forward (Pf) and backward (Pb) wave pressures, the reflection index (RI) and augmentation pressure (AP) and index (AIx) were determined using applanation tonometry, and SphygmoCor software. Decreases in central aortic (p<0.001) but not brachial systolic BP and pulse pressure (PP) occurred post-exercise. In addition, decreases in post-exercise (baseline versus post-exercise) Pb (19±4 vs 13±3mm Hg p<0.0001), RI (72.9±22.1 vs 47.6±12.8%, p<0.0001), AIx (26.3±10.8 vs 7.8±11.6%, p<0.0001) and AP (9.9±3.9 vs 2.8±3.9mm Hg, p<0.0001), but not Pf, were noted. However, decreases in AIx were not correlated with decreases in Pb, and whilst decreases in aortic PP correlated with decreases in Pb (p<0.0001), no correlations were noted with decreases in AP or AIx. In young-to-middle-aged pre-hypertensive and hypertensive individuals, aortic backward waves decrease post-exercise; this change is not reflected in brachial BP measurements and is poorly indexed by measures of pressure augmentation.

Intrafamilial aggregation and heritability of tissue Doppler indexes of left ventricular diastolic function in a group of African descent

Although several indexes of left ventricular (LV) diastolic function show heritability, the genetic influence on the tissue Doppler index, E/eʹ (early transmitral velocity/velocity of myocardial tissue lengthening), an index of LV filling pressures in those of black African descent is currently unknown. Furthermore, whether any genetic influences on E/eʹ are through an impact of LV remodeling or aortic function is unknown. Intrafamilial aggregation and heritability (SAGE software) of E/eʹ (echocardiography) were assessed in 129 nuclear families (29 spouse pairs, 216 parent–child pairs, and 113 sibling–sibling pairs) from an urban developing community of black Africans, independent of LV mass index (LVMI), LV relative wall thickness (RWT), central aortic systolic pressure (SBPc), and backward wave pressures (Pb) (applanation tonometry, SphygmoCor software). Independent of confounders including LVMI and RWT, E/eʹ was correlated in parent–child (r = 0.23; P < .001) and sibling–sibling (r = 0.29; P < .005), but not in spouse (r = 0.13; P = .51) pairs. The relationships between parent–child (r = 0.22; P < .001) and sibling–sibling (r = 0.29; P < .005) pairs persisted with adjustments for SBPc. The relationships between parent–child (r = 0.22; P < .001) and sibling–sibling (r = 0.26; P < .01) pairs also persisted with adjustments for Pb. Independent of confounders including LVMI and RWT, E/eʹ showed significant heritability (h2 ± standard error of the mean [SEM] = 0.51 ± 0.11; P < .0001) which similarly persisted with adjustments for SBPc (h2 ± SEM = 0.50 ± 0.11; P < .0001) and Pb (h2 ± SEM = 0.49 ± 0.11; P < .0001). In conclusion, in a group of African ancestry, independent of LV remodeling and aortic function, E/eʹ shows significant intrafamilial aggregation and robust heritability. Hence, genetic factors may play an important role in determining moderate-to-severe LV diastolic dysfunction independent of cardiac remodeling or aortic function in groups of black African ancestry.

Coronary fluid mechanics in an ageing cardiovascular system

Coronary artery diseases are a leading cause of mortality and are increasingly prevalent with age. However, the large number of age-increasing co-morbidities make difficult to understand the impact of cardiovascular ageing alone on the coronary flow pattern. The present study aims to shed light on the effect of arterial and ventricular ageing on the coronary circulation, which is here studied by means of a validated mathematical model. Forward and backward pressure and flow waves are analysed, as well as their intensity. Results highlight a complex spatiotemporal coronary wave pattern, where intense waves originate from the aorta (particularly in systole) and from the deep myocardium, during both the isovolumic compression and the diastolic phase. The subendocardial viability ratio decreases with age, the total coronary flow is slightly reduced, and the left-ventricular work increases. Consequently, the left-ventricular work per unit of blood flow increases, thus limiting the cell oxygen availability abundance, and therefore increasing the risk of myocardial infarction. Our results highlight a physiological age-induced supply/demand unbalance, which can augment the risk of myocardial ischemia and can contribute to pave the way to other typical coronary pathological processes.

Coronary fluid mechanics in an ageing cardiovascular system

Coronary artery diseases are a leading cause of mortality and are increasingly prevalent with age. However, the large number of age-increasing co-morbidities make difficult to understand the impact of cardiovascular ageing alone on the coronary flow pattern. The present study aims to shed light on the effect of arterial and ventricular ageing on the coronary circulation, which is here studied by means of a validated mathematical model. Forward and backward pressure and flow waves are analysed, as well as their intensity. Results highlight a complex spatiotemporal coronary wave pattern, where intense waves originate from the aorta (particularly in systole) and from the deep myocardium, during both the isovolumic compression and the diastolic phase. The subendocardial viability ratio decreases with age, the total coronary flow is slightly reduced, and the left-ventricular work increases. Consequently, the left-ventricular work per unit of blood flow increases, thus limiting the cell oxygen availability abundance, and therefore increasing the risk of myocardial infarction. Our results highlight a physiological age-induced supply/demand unbalance, which can augment the risk of myocardial ischemia and can contribute to pave the way to other typical coronary pathological processes.

Brachial Pressure Control Fails to Account for Most Distending Pressure-Independent, Age-Related Aortic Hemodynamic Changes in Adults.

Although several characteristics of aortic function, which are largely determined by age, predict outcomes beyond brachial blood pressure (BP), the extent to which brachial BP control accounts for age-related variations in aortic function is uncertain. We aimed to determine the extent to which brachial BP control in the general population (systolic/diastolic BP < 140/90 mm Hg) accounts for age-related aortic hemodynamic changes across the adult lifespan. Central aortic pulse pressure (PPc), backward wave pressure (Pb), pulse wave velocity (PWV), and PP amplification (PPamp) (applanation tonometry and SphygmoCor software) were determined in 1,185 participants from a community sample (age >16 years; 36.4% uncontrolled BP). With adjustments for distending pressure (mean arterial pressure, MAP), no increases in PPc, Pb, or PWV and decreases in PPamp were noted in those with an uncontrolled brachial BP younger than 50 years. In those older than 50 years with an uncontrolled brachial BP, MAP-adjusted aortic hemodynamic variables were only modestly different to those with a controlled brachial BP (PPc, 46±14 vs. 42±15 mm Hg, P < 0.02, Pb, 23±8 vs. 21±8 mm Hg, PWV, 8.42±3.21 vs. 8.19±3.37 m/second, PPamp, 1.21±0.17 vs. 1.21±0.14). Nonetheless, with adjustments for MAP, marked age-related increases in PPc, Pb, and PWV and decreases in PPamp were noted in those with uncontrolled and controlled brachial BP across the adult lifespan (P < 0.0001). Brachial BP control in the general population fails to account for most distending pressure-independent, age-related changes in aortic hemodynamics across the adult lifespan.

Wave Separation, Wave Intensity, the Reservoir-Wave Concept, and the Instantaneous Wave-Free Ratio: Presumptions and Principles.

Wave separation analysis and wave intensity analysis (WIA) use (aortic) pressure and flow to separate them in their forward and backward (reflected) waves. While wave separation analysis uses measured pressure and flow, WIA uses their derivatives. Because differentiation emphasizes rapid changes, WIA suppresses slow (diastolic) fluctuations of the waves and renders diastole a seemingly wave-free period. However, integration of the WIA-obtained forward and backward waves is equal to the wave separation analysis-obtained waves. Both the methods thus give similar results including backward waves spanning systole and diastole. Nevertheless, this seemingly wave-free period in diastole formed the basis of both the reservoir-wave concept and the Instantaneous wave-Free Ratio of (iFR) pressure and flow. The reservoir-wave concept introduces a reservoir pressure, Pres, (Frank Windkessel) as a wave-less phenomenon. Because this Windkessel model falls short in systole an excess pressure, Pexc, is introduced, which is assumed to have wave properties. The reservoir-wave concept, however, is internally inconsistent. The presumed wave-less Pres equals twice the backward pressure wave and travels, arriving later in the distal aorta. Hence, in contrast, Pexc is minimally affected by wave reflections. Taken together, Pres seems to behave as a wave, rather than Pexc. The iFR is also not without flaws, as easily demonstrated when applied to the aorta. The ratio of diastolic aortic pressure and flow implies division by zero giving nonsensical results. In conclusion, presumptions based on WIA have led to misconceptions that violate physical principles, and reservoir-wave concept and iFR should be abandoned.

7A.07

Objective: Obesity causes an increased blood pressure (BP). This effect may be diminished in communities of African descent. However, the impact of obesity on ambulatory or aortic BP, which are enhanced in groups of African ancestry, has not been assessed. We aimed to determine the extent to which obesity is related to variations in office, ambulatory and aortic BP in a community sample of African ancestry with a high prevalence of obesity. Design and method: In 1167 randomly selected participants of black South African ancestry >16 years of age (42.5% obese and 45.1% with abdominal obesity), we determined the impact of adiposity indexes on age-related increases in office, ambulatory (n = 767) and aortic (n = 1141) BP. Aortic BP was determined using radial applanation tonometry and SphygmoCor software. Results: Age was strongly related to all BP values and indexes of metabolic abnormalities (p < 0.0001). Independent of age, adiposity indexes were associated with insulin resistance, HDL cholesterol, glucose and triglyceride concentrations (p < 0.0001 for all). However, across the adult lifespan neither office, 24-hour, day, night, nor aortic BP were increased in participants with an increased waist circumference (WC), or body mass index (BMI)(> = 30 kg/m2) as compared to participants with a normal WC or BMI. Independent of age, WC accounted for only 0 to 1.02% of the variation in office, 24-hour or aortic BP and translated into only a 0.38 to 1.40 mm Hg increase in office or 24-hour systolic or diastolic BP for every 15.9 to 16.6 cm (1 SD) increase in WC. Neither WC (Odds ratio = 1.12, CI = 0.78 to 1.61, p = 0.54) nor BMI (Odds ratio = 1.11, CI = 0.78 to 1.58. p = 0.55) were associated with hypertension (38.5%) diagnosed according to 24-hour BP thresholds or the presence of treatment. Independent of age, adiposity indexes were not positively associated with factors that account for age-related increases in BP (aortic pulse wave velocity, and aortic forward and backward wave pressures). Conclusions: Although obesity and hypertension are prevalent in black African communities and obesity independently associates with metabolic abnormalities, obesity plays little role in the pathogenesis of hypertension in these communities.

Intrafamilial Aggregation and Heritability of Aortic Reflected (Backward) Waves Derived From Wave Separation Analysis.

Although aortic wave reflection may be inherited, the extent to which indexes of wave reflection derived from wave separation analysis (reflected (backward) wave index (RI) and pressure (Pb)) show intrafamilial aggregation and heritability is uncertain. We therefore aimed to determine the intrafamilial aggregation and heritability of RI and Pb and compare these with indexes of pressure augmentation. Aortic Pb, RI, augmented pressure (Pa), and augmentation index (AIx) were determined using radial applanation tonometry and SphygmoCor software in 1,152 participants of 315 families (111 father-mother, 705 parent-child, and 301 sibling-sibling pairs) from an urban developing community of black Africans. Heritability estimates were determined from Statistical Analysis for Genetic Epidemiology software. With appropriate adjustments, significant correlations were noted between parent-child pairs for Pb and Pa (P < 0.05 for all), but not for RI (P = 0.50) or AIx (P = 0.90) and between sib-sib pairs for Pb and Pa (P < 0.05), but not for RI (P = 0.54) or AIx (P = 0.14). No correlations for indexes of wave reflection were noted between fathers and mothers (P > 0.57). After adjustments, Pb (h2 = 0.24±0.07) and Pa (h2 = 0.23±0.07) (P < 0.001 for both) but not RI (h2 = 0.04±0.06, P = 0.27) or AIx (h2 = 0.10±0.07, P = 0.07) showed significant heritability. Aortic reflected (backward) waves derived from either wave separation (Pb) or pulse wave analysis (Pa) show a similar degree of intrafamilial aggregation and heritability, but the use of RI or AIx may underestimate reflected wave effects.

Quantification of Wave Reflection Using Peripheral Blood Pressure Waveforms

This paper presents a novel minimally invasive method for quantifying blood pressure (BP) wave reflection in the arterial tree. In this method, two peripheral BP waveforms are analyzed to obtain an estimate of central aortic BP waveform, which is used together with a peripheral BP waveform to compute forward and backward pressure waves. These forward and backward waves are then used to quantify the strength of wave reflection in the arterial tree. Two unique strengths of the proposed method are that 1) it replaces highly invasive central aortic BP and flow waveforms required in many existing methods by less invasive peripheral BP waveforms, and 2) it does not require estimation of characteristic impedance. The feasibility of the proposed method was examined in an experimental swine subject under a wide range of physiologic states and in 13 cardiac surgery patients. In the swine subject, the method was comparable to the reference method based on central aortic BP and flow. In cardiac surgery patients, the method was able to estimate forward and backward pressure waves in the absence of any central aortic waveforms: on the average, the root-mean-squared error between actual versus computed forward and backward pressure waves was less than 5 mmHg, and the error between actual versus computed reflection index was less than 0.03.

Do backward pressure waves arise from “reflections” or from a “reservoir”?

Do backward pressure waves arise from “reflections” or from a “reservoir”?

Wave reflections, arterial stiffness, and orthostatic hypotension.

The effect of wave reflections on blood pressure change associated with posture remains unclear. We therefore applied a wave separation technique to investigate the relations of the backward pressure wave amplitude with orthostatic pressure changes and orthostatic hypotension (OH). We analyzed data from 613 subjects who had participated in our hemodynamic studies. Measurements of brachial systolic (SBP) and diastolic blood pressures (DBP), carotid-femoral pulse wave velocity (cf-PWV), and backward pressure wave amplitude from a decomposed carotid pressure wave (Pb) were obtained at supine position. SBP and DBP were measured again 3 minutes after standing. OH was defined as a fall of ≥20 mm Hg in SBP and/or ≥10 mm Hg in DBP. Subjects with OH (n = 100) were characterized with significantly higher supine SBP and DBP and significantly lower standing SBP and DBP when compared with subjects without OH. Subjects with OH were also characterized with significantly higher cf-PWV and Pb. cf-PWV and Pb separately were significantly associated with the orthostatic SBP change in univariable and multivariable analyses. Also, cf-PWV and Pb separately were significant predictors of OH in univariable and multivariable analyses. cf-PWV predicted OH in the younger but less so in the older subgroup, whereas Pb demonstrated similar prediction in both subgroups. In a final multivariable model, both cf-PWV and Pb were significant independent predictors of OH. Wave reflections are an independent determinant of orthostatic SBP change and OH in both younger and older subjects.

Anatomy of arterial systems reveals that the major function of the heart is not to emit waves associated with the axial blood motion

The CrossTalk articles by Tyberg et al. (2013) and Westerhof & Westerhof (2013) and the comments about the forward and backward pressure waves in the arterial system reveal that most researchers depict the left ventricle as a wave emitter, and all the wave models arise from the axial momentum equation or the Navier–Stokes equations applied to the blood. These models not only have difficulty in defining the reflection sites, they also cannot explain many physiological observations such as that the heart rate is inversely proportional to the size of the animal (Milnor, 1989), that the large arterial vessels have a high distensibility and are subjected to substantial longitudinal stretching in vivo, and that the organs of most mammals have similar structures and connect perpendicularly to the aorta at similar relative positions. Anatomical designs are important elements in the mechanism of blood delivery and therefore a realistic haemodynamic model should be able to provide insight into the underlying physiological effects. Recently, taking those physiological observations into account, we integrated some haemodynamic theories (Lin Wang et al. 2004a,b2004a, 2008) to construct a multi-rank distributed-cyclic-hydraulic-press (DCHP) model (Lin Wang & Wang, 2013) to describe the ventricular–arterial system and provided a quantitative method for exploring its overall behaviour. We proposed that the transportation of blood from the heart to the peripheral arterioles is via hydraulic devices of four different ranks. Since pressure is a continuous parameter, instead of taking the branching points or the side-openings as the reflection sites for waves, we treated them as sites for offering both hydraulic pressure forces and blood flow to the connecting lower rank systems. In this model, the left ventricle is depicted as the hydraulic pressure supplier of the first rank. As the blood is ejected from the left ventricle, it encounters the arch of the aorta, changes its axial velocity dramatically in both magnitude and direction. According to Newton's second law, as the blood changes its momentum, it exerts a force on the arterial wall. Thus, the periodic burst of blood from the left ventricle provides a pulsatile force to the main aorta. This pulsatile force will cause the aorta to conduct a distributed radial oscillatory motion which can be represented and measured either by the distributed radius pulse of the artery R(z,t) or the accompanying pressure pulse P(z,t). The gradient of the pulse pressure also induces an inevitable axial oscillatory motion Q(z,t) of the blood. However, this is not the purpose of the ventricular output. Skalak et al. (1966) and Milnor (1989) reported that most of the energy supplied by the left ventricle is dissipated in the friction of viscous flow, while almost all of the amount of work done in distending the arteries is returned later in each cycle of the heart beat because of the relatively small viscous behaviour of the vascular wall. Along large arteries, there is little attenuation of the pressure pulse; hence the ventricular energy input is mainly delivered via the radial pulsatile motion. To reduce energy dissipation, the axial flow in the large arteries should be as small as possible. The 180 deg bend near the arch of the aorta greatly reduces its axial kinetic energy; the ends of the ulnar artery and the radial artery join together as a loop at the palmar arch. Similarly, the deep plantar artery unites with the termination of the lateral plantar artery to complete the plantar arch (Marieb & Hoehn, 2009). At these arches, the head-on collision between blood approaching from opposite directions eliminates their axial momentum and helps to distribute blood more uniformly to all of the perpendicularly attached side-branches. These arterial structures have the effect of reducing the kinetic energy associated with the axial flow Q to only a few per cent of the energy associated the pressure P. The flow Q is a vector parameter, and is more posture dependent compared with the scalar parameter P; hence downgrading the role of Q in large arteries may also give mammals more freedom to change their postures. Two important concepts are utilized in the multi-rank DCHP model (Lin Wang & Wang, 2013). First, the pressure pulse is not governed by the axial momentum equation or the Navier-Stokes equations, but by the radial momentum equations for the blood and the arterial wall or the low dissipated PR wave equation (Lin Wang et al. 2004b). Second, resonant behaviours between the heart and the main aorta (Lin Wang et al. 2004a, 2008), or between the aorta and different organs (Lin Wang et al. 1991) are plausible. Here we share our model in the expectation that it can be used for physiological and pathological studies of arterial systems in the future.

Reservoir and excess pressures predict cardiovascular events in high-risk patients

BackgroundAnalysis of the arterial pressure curve plays an increasing role in cardiovascular risk stratification. Measures of wave reflection and aortic stiffness have been identified as independent predictors of risk. Their determination is usually based on wave propagation models of the circulation. Another modeling approach relies on modified Windkessel models, where pressure curves can be divided into reservoir and excess pressure. Little is known of their prognostic value. Methods and resultsThe aim of this study is to evaluate the predictive value of parameters gained from reservoir theory applied to aortic pressure curves in a cohort of high-risk patients. Furthermore the relation of these parameters to those from wave separation analysis is investigated.Central pressure curves from 674 patients with preserved ejection fraction, measured by radial tonometry and a validated transfer function, were analyzed. A high correlation between the amplitudes of backward traveling pressure waves and reservoir pressures was found (R=0.97). Various parameters calculated from the reservoir and excess pressure waveforms predicted cardiovascular events in univariate Cox proportional hazards modeling. In a multivariate model including several other risk factors such as brachial blood pressure, the amplitude of reservoir pressure remained a significant predictor (HR=1.37 per SD, p=0.016). ConclusionsBased on very different models, parameters from reservoir theory and wave separation analysis are closely related and can predict cardiovascular events to a similar extent. Although Windkessel models cannot describe all of the physiological properties of the arterial system, they can be useful to analyze its behavior and to predict cardiovascular events.

White Coat Hypertension Is More Risky Than Prehypertension

Arterial aging may link cardiovascular risk to white coat hypertension (WCH). The aims of the present study were to investigate the role of arterial aging in the white coat effect, defined as the difference between office and 24-hour ambulatory systolic blood pressures, and to compare WCH with prehypertension (PH) with respect to target organ damage and long-term cardiovascular mortality. A total of 1257 never-been-treated volunteer subjects from a community-based survey were studied. WCH and PH were defined by office and 24-hour ambulatory blood pressures. Left ventricular mass index, carotid intima-media thickness, estimated glomerular filtration rate, carotid-femoral pulse wave velocity, carotid augmentation index, amplitude of the reflection pressure wave, and 15-year cardiovascular mortality were determined. Subjects with WCH were significantly older and had greater body mass index, blood pressure values, intima-media thickness, carotid-femoral pulse wave velocity, augmentation index, amplitude of the backward pressure wave, and a lower estimated glomerular filtration rate than PH. Amplitude of the backward pressure wave was the most important independent correlate of the white coat effect in multivariate analysis (model r 2 =0.451; partial r 2 /model r 2 =90.5%). WCH had significantly greater cardiovascular mortality than PH (hazard ratio, 2.94; 95% confidence interval, 1.09–7.91), after accounting for age, sex, body mass index, smoking, fasting plasma glucose, and total cholesterol/high-density lipoprotein-cholesterol ratio. Further adjustment of the model for amplitude of the backward pressure wave eliminated the statistical significance of the WCH effect. In conclusion, the white coat effect is mainly caused by arterial aging. WCH carries higher risk for cardiovascular mortality than PH, probably via enhanced wave reflections that accompany arterial aging.

Self-Reported Sitting Time Is Associated With Higher Pressure From Wave Reflections Independent of Physical Activity Levels in Healthy Young Adults

Time spent in sedentary pursuits such as sitting (SIT) is associated with an increased risk of cardiovascular disease independent of physical activity (PA). The purpose of this study was to examine the associations of PA and SIT with central hemodynamic burden in young adults. Aortic pressure waveforms were obtained using radial applanation tonometry and a generalized transfer function in 70 young healthy men (n = 41) and women (n = 29) (mean age = 23±1 years; body mass index = 24±1kg/m(2)). A wave separation technique that uses a physiologic pseudoaortic flow waveform was used to derive incident/forward wave pressure (Pf) and reflected/backward wave pressure (Pb). Levels of PA (metabolic equivalent, minutes per week) and SIT (sitting time per day) were obtained by self-report using the International Physical Activity Questionnaire. A negative correlation existed between PA and Pf (r = -0.30; P < 0.05) and Pb (r = -0.36; P < 0.05). A positive correlation existed between SIT and Pf (r = 0.39; P < 0.05) and Pb (r = 0.44; P < 0.05). According to results from multiple regression, after adjusting for potential confounders (age, sex, height, heart rate, mean pressure) and PA, associations between SIT and Pf (P < 0.05) and SIT and Pb (P < 0.05) remained. SIT is associated with higher forward wave pressure and backward wave pressure, 2 novel hemodynamic correlates of cardiovascular disease risk and target organ damage, in young apparently healthy men and women. This association is independent of PA.

CrossTalk proposal: Forward and backward pressure waves in the arterial system do represent reality

CrossTalk proposal: Forward and backward pressure waves in the arterial system do represent reality