Aortic Wave Research Articles

Effects of acute dietary nitrate supplementation on aortic wave reflection in young adults

Effects of acute dietary nitrate supplementation on aortic wave reflection in young adults

Effects of systemic niacin infusion on sympathetic activity, arterial stiffness and aortic wave reflection: A pilot study

Effects of systemic niacin infusion on sympathetic activity, arterial stiffness and aortic wave reflection: A pilot study

Beneficial effects of low-dose aspirin on aortic stiffness in hypertensive patients.

While treatment with low-dose aspirin has been established as a therapeutic tool for secondary prevention, the role of aspirin on primary prevention remains controversial. Aortic stiffness and wave reflections are independent predictors of cardiovascular events. The aim of the present study was to investigate the effect of low-dose aspirin on aortic stiffness and wave reflections in hypertensive patients. We studied 30 patients with grade I hypertension. Fifteen patients were treated with 160 mg of aspirin and 15 patients with placebo. Aortic stiffness and wave reflections were assessed by measuring carotid-femoral pulse wave velocity (PWV) and heart rate-adjusted augmentation index (AIx75), respectively. All measurements were conducted at baseline and 2 weeks after treatment. In the aspirin group, there was a significant reduction in PWV compared to the placebo group (from 8.9±1.5 to 8.5±1.6 m/s for the aspirin group vs from 8.6±1.4 to 8.7±1.6 m/s for the placebo group, net change: -0.5 m/s; p=0.02). AIx75 showed a marginal decrease (from 28.0±5.4 to 26.2±5.0% for the aspirin group vs from 31.2±9.7 to 30.6±9.2% for the placebo group, net change: -1.2%; p=0.06). In conclusion, a 2-week course of aspirin administration has a favorable effect on aortic stiffness and, to a lesser extent, on wave reflections in hypertensive patients. Whether the reduction in arterial stiffness is translated to fewer cardiovascular events needs to be confirmed by future prospective studies.

Intrinsic frequency for a systems approach to haemodynamic waveform analysis with clinical applications.

The reductionist approach has dominated the fields of biology and medicine for nearly a century. Here, we present a systems science approach to the analysis of physiological waveforms in the context of a specific case, cardiovascular physiology. Our goal in this study is to introduce a methodology that allows for novel insight into cardiovascular physiology and to show proof of concept for a new index for the evaluation of the cardiovascular system through pressure wave analysis. This methodology uses a modified version of sparse time-frequency representation (STFR) to extract two dominant frequencies we refer to as intrinsic frequencies (IFs; ω1 and ω2). The IFs are the dominant frequencies of the instantaneous frequency of the coupled heart + aorta system before the closure of the aortic valve and the decoupled aorta after valve closure. In this study, we extract the IFs from a series of aortic pressure waves obtained from both clinical data and a computational model. Our results demonstrate that at the heart rate at which the left ventricular pulsatile workload is minimized the two IFs are equal (ω1 = ω2). Extracted IFs from clinical data indicate that at young ages the total frequency variation (Δω = ω1 - ω2) is close to zero and that Δω increases with age or disease (e.g. heart failure and hypertension). While the focus of this paper is the cardiovascular system, this approach can easily be extended to other physiological systems or any biological signal.

Pulse wave analysis of the aortic pressure waveform in patients with vasovagal syncope.

Vascular reflex mechanisms contribute to vasovagal syncope. However, the alterations in central haemodynamics in patients with vasovagal syncope are unknown. 30 consecutive patients (36.5 ± 15 years, 14 females) with recurrent vasovagal syncope (VVS) and a positive tilt table test were compared to 39 age- and sex-matched controls (36.9 ± 16 years, 15 females) with a negative tilt table result and no history of syncope. Central aortic pressure parameters including augmentation index and central pulse pressure as markers of aortic stiffness were generated non-invasively by applanation tonometry of the radial artery and use of a validated mathematical transfer function. No difference in aortic augmentation index was observed between groups. (VVS 9 ± 2.6 vs. Control 11 ± 2.4, p = 0.8). However, in patients with vasovagal syncope the aortic pressure waveform significantly differed from healthy controls. A prolonged time to the peak of aortic pressure wave (aortic T2) was observed in patients with vasovagal syncope (226 ± 24 vs. 208 ± 21 ms, p = 0.001). Furthermore time to the first shoulder of the aortic pressure wave (aortic T1) was slightly shorter compared to healthy controls, but did not reach statistical significance (106 ± 22 vs. 110 ± 12 ms, p = 0.33). Patients with vasovagal syncope have an altered aortic pressure waveform at rest, but no signs of elevated aortic stiffness. The underlying mechanisms for these findings may potentially result from a complex imbalance of the autonomic nervous system with a continuous deregulation of the sympathetic and parasympathetic reflex arcs.

Sex differences in noninvasive estimates of left ventricular pressure energetics but not myocardial oxygen demand in young adults

BackgroundSex differences in arterial stiffness and wave reflections may lead to disproportionate increases in afterload and myocardial work in women. We examined sex differences in arterial stiffness, pressure from wave reflections, measures of left ventricular (LV) energetics and myocardial work. Methods99 Healthy adults participated in this study 84 were selected (42 females, 42 males) to be matched for potential confounders of central hemodynamic burden such as age, BMI, and mean arterial pressure. Aortic pressure waves were derived from the radial artery using a generalized transfer function. Pulse contour analysis and wave separation analysis were used to obtain: pulse wave velocity (PWV) as a measure of aortic stiffness, augmentation index (AIx) and reflection index (RIx) as measures of global wave reflections, LV pressure effort (ΔEw) as a measure of LV energy required to overcome wave reflections and the subendocardial viability ratio (SEVR) as a proxy of myocardial work. ResultsWomen exhibited higher ΔEw (p < 0.05), heart rate corrected AIx (p < 0.05) and RIx (p < 0.01), and lower PWV (p < 0.001) compared to men. Pressure from wave reflections (Pb) was significantly associated with ΔEw in women (r = 0.81, p < 0.001), but not in men (r = 0.14, p > 0.05). There were no sex differences for SEVR (p = 0.4). ConclusionWomen had higher pressure from wave reflections which was associated with greater LV pressure effort compared to men. Although women had increased LV pressure effort, proxies of myocardial perfusion and work were not affected.

Effects of Thoratec pulsatile ventricular assist device timing on the abdominal aortic wave intensity pattern.

Arterial waves are seen as possible independent mediators of cardiovascular risks, and the wave intensity analysis (WIA) has therefore been proposed as a method for patient selection for ventricular assist device (VAD) implantation. Interpreting measured wave intensity (WI) is challenging, and complexity is increased by the implantation of a VAD. The waves generated by the VAD interact with the waves generated by the native heart, and this interaction varies with changing VAD settings. Eight sheep were implanted with a pulsatile VAD (PVAD) through ventriculoaortic cannulation. The start of PVAD ejection was synchronized to the native R wave and delayed between 0 and 90% of the cardiac cycle in 10% steps or phase shifts (PS). Pressure and velocity signals were registered, with the use of a combined Doppler and pressure wire positioned in the abdominal aorta, and used to calculate the WI. Depending on the PS, different wave interference phenomena occurred. Maximum unloading of the left ventricle (LV) coincided with constructive interference and maximum blood flow pulsatility, and maximum loading of the LV coincided with destructive interference and minimum blood flow pulsatility. We believe that noninvasive WIA could potentially be used clinically to assess the mechanical load of the LV and to monitor the peripheral hemodynamics such as blood flow pulsatility and risk of intestinal bleeding.

Data-driven lossy tube-load modeling of arterial tree: in-human study.

In this paper, we present and validate a data-driven method to lossy tube-load modeling of arterial tree in humans. In the proposed method, the lossy tube-load model is fitted to central aortic and peripheral blood pressure (BP) waves in the time domain. For this purpose, we employ a time-domain lossy tube-load model in which the wave propagation constant is formulated to two terms: one responsible for the alteration of wave amplitude and the other for the transport delay. Using the experimental BP data collected from 17 cardiac surgery patients, we showed that the time-domain lossy tube-load model is able to accurately represent the relation between central aortic versus upper-limb and lower-limb BP waves. In addition, the comparison of lossy versus lossless tube-load models revealed that (1) the former outperformed the latter in general with the root-mean-squared errors (RMSE) of 3.1 mm Hg versus 3.5 mm Hg, respectively (p-value &lt; 0.05), and (2) the efficacy of the former over the latter was more clearly observed in case the normalized difference in the mean central aortic versus peripheral BP was large; when the difference was &gt;5% of the underlying mean BP, lossy and lossless models showed the RMSE of 2.7 mm Hg and 3.7 mm Hg, respectively (p-value &lt; 0.05).

First in vivo application and evaluation of a novel method for non-invasive estimation of cardiac output

Surgical or critically ill patients often require continuous assessment of cardiac output (CO) for diagnostic purposes or for guiding therapeutic interventions. A new method of non-invasive CO estimation has been recently developed, which is based on pressure wave analysis. However, its validity has been examined only in silico. Aim of this study was to evaluate in vivo the reproducibility and accuracy of the “systolic volume balance” method (SVB). Twenty two subjects underwent 2-D transthoracic echocardiography for CO measurement (reference value of CO). The application of SVB method required aortic pressure wave analysis and estimation of total arterial compliance. Aortic pulses were derived by mathematical transformation of radial pressure waves recorded by applanation tonometry. Total compliance was estimated by the “pulse pressure” method. The agreement, association, variability, bias and precision between Doppler and SVB measures of CO were evaluated by intraclass correlation coefficient (ICC), mean difference, SD of differences, percentage error (PR) and Bland–Altman analysis. SVB yielded very reproducible CO estimates (ICC=0.84, mean difference 0.27±0.73L/min, PR=16.7%). SVB-derived CO was comparable with Doppler measurements, indicating a good agreement and accuracy (ICC=0.74, mean difference=−0.22±0.364L/min, PR≈15). The basic mathematical and physical principles of the SVB method provide highly reproducible and accurate estimates of CO compared with echocardiography.

The cardiac blood supply-workload balance in children.

It is well known that the reflected pressure wave in small children returns earlier than that in adolescent. The reason of early return of the reflected pressure wave in infancy is their height. The short distance between heart and reflection point makes the reflected pressure wave returning to the heart earlier. In adult, the early return (during systole) of the reflected pressure wave means disadvantage to cardiac blood supply-workload balance. The purpose of this study was to clarify whether the early return of the reflected pressure wave in small children impairs the cardiac blood supply-workload balance. This study enrolled 37 small left-to-right shunt patients with normal aortic circulation below 15years of age. The aortic pressure waveform was recorded using a pressure sensor mounted catheter, and augmentation index and subendocardial viability ratio were calculated. The age of patients was 6.1±3.2years. The augmentation index was 8.7±14.3% and the index had a negative correlation with patients' age (r=-0.6243, p<0.0001). The subendocardial viability ratio, which means the cardiac blood supply-workload balance, was 0.92±0.14 and the index had a positive relationship with patients' age (r=0.6435, p<0.0001). The cardiac blood supply-workload balance gradually improves from infancy to young adulthood. One of the causes of the unfavorable cardiac blood supply-workload balance in infancy would be the accelerated aortic pressure wave reflection due to their short height.

Treadmill walking with load carriage increases aortic pressure wave reflection

Introduction and objectivesThe study examined the effects of treadmill walking with load carriage on derived measures of central pressure and augmentation index in young healthy subjects. MethodologyFourteen male subjects (age 31.0 ± 1.0 years) volunteered in this study. Subjects walked 10 minutes on a treadmill at a speed of 5 km/h carrying no load during one session and a load of 10% of their body weight on both upper limbs in two water carboys with handle during the other session. Pulse wave analysis was performed at rest and immediately after exercise in the radial artery of the right upper limb by applanation tonometry. ResultsThe main result indicates that walking with load carriage sharply increased augmentation index at 75 bpm (−5.5 ± 2.2 to −1.4 ± 2.2% vs. −5.2 ± 2.8 to −5.5 ± 2.1%, p<0.05), and also induced twice as high increments in central pulse pressure (7.4 ± 1.5 vs. 3.1 ± 1.4 mmHg, p<0.05) and peripheral (20.5 ± 2.7 vs. 10.3 ± 2.5 mmHg, p<0.05) and central systolic pressure (14.7 ± 2.1 vs. 7.4 ± 2.0 mmHg, p<0.05). ConclusionsWalking with additional load of 10% of their body weight (aerobic exercise accompanied by upper limb isometric contraction) increases derived measures of central pressure and augmentation index, an index of wave reflection and arterial stiffness.

Treadmill walking with load carriage increases aortic pressure wave reflection

Introduction and objectivesThe study examined the effects of treadmill walking with load carriage on derived measures of central pressure and augmentation index in young healthy subjects. MethodologyFourteen male subjects (age 31.0 ± 1.0 years) volunteered in this study. Subjects walked 10 minutes on a treadmill at a speed of 5 km/h carrying no load during one session and a load of 10% of their body weight on both upper limbs in two water carboys with handle during the other session. Pulse wave analysis was performed at rest and immediately after exercise in the radial artery of the right upper limb by applanation tonometry. ResultsThe main result indicates that walking with load carriage sharply increased augmentation index at 75 bpm (−5.5 ± 2.2 to −1.4 ± 2.2% vs. −5.2 ± 2.8 to −5.5 ± 2.1%, p<0.05), and also induced twice as high increments in central pulse pressure (7.4 ± 1.5 vs. 3.1 ± 1.4 mmHg, p<0.05) and peripheral (20.5 ± 2.7 vs. 10.3 ± 2.5 mmHg, p<0.05) and central systolic pressure (14.7 ± 2.1 vs. 7.4 ± 2.0 mmHg, p<0.05). ConclusionsWalking with additional load of 10% of their body weight (aerobic exercise accompanied by upper limb isometric contraction) increases derived measures of central pressure and augmentation index, an index of wave reflection and arterial stiffness.

Aortic surgery is one of the risk factors for enhancement of pressure wave reflection in adult patients with congenital heart disease

Background: Excessive aortic pressure wave reflection is one of the risk factors of cardiovascular diseases. In some clinical course of congenital heart diseases, the elevated pressure wave reflection has been reported. The purpose of this study is to elucidate the risk factors of the enhanced pressure wave reflection in adult patients with congenital heart disease. Methods: We enrolled 99 adult (≥20years) patients with congenital heart disease. We measured their radial pressure augmentation index and examined the relationship between it and various clinical variables. Results: The radial pressure augmentation index was 77.1±19.1% and it had a significant correlation with the history of aorto-pulmonary shunt (t=4.194; p<0.0001), age (t=4.091; p<0.0001), height (t=−3.580; p=0.001) and the history of direct aortic surgery (t=2.253; p=0.027). Forty-four patients (44.4%) demonstrated high radial augmentation index (>1SD of age- and gender matched control) and the determinants of the elevated radial augmentation index were the history of aorto-pulmonary shunt (odds ratio, 21.32; 95% confidence interval, 5.47–83.14; p<0.0001) and the direct aortic surgery (4.18; 1.38–12.72; p=0.012). Conclusions: The history of aortic surgeries enhances aortic pressure wave reflection in adult patients with congenital heart disease. The enhanced aortic pressure wave reflection is one of the risk factors for cardiovascular diseases. Therefore, the adult patients with congenital heart disease after aortic surgeries should be carefully observed and tightly controlled concerning the risk factors for cardiovascular diseases.

Aortic Wave Reflections Are Associated With Anaerobic Power Production In Young Adults.

Aortic Wave Reflections Are Associated With Anaerobic Power Production In Young Adults.

Relationship between muscle sympathetic nerve activity and aortic wave reflection characteristics in aerobic and resistance athletes (1172.1)

Recent reports have indicated that resistance exercise training performed absent an aerobic exercise program may increase arterial stiffness. Our purpose was to compare the augmentation index (AIx) and left ventricular wasted pressure energy (LVEW) as markers of arterial stiffness and ventricular‐vascular coupling efficiency in young aerobic (AT) and resistance (RT) trained athletes. We also investigated the relationship between muscle sympathetic nerve activity (MSNA) and AIx to determine if sympathetic outflow could explain any observed differences in arterial stiffness.Methods: MSNA (via microneurography of the peroneal nerve) was measured in 15 male subjects (8 RT, 7 AT). Aortic pressure waveforms were synthesized using applanation tonometry of the radial artery to derive AIx and LVEW values.Results: RT subjects had greater AIx (12 ± 3 vs. ‐7 ± 2; P&lt;0.01), LVEW (429 ± 111 vs. ‐360 ± 77; P&lt;0.01) and MSNA burst incidence (109 ± 23 vs. 31 ± 5; P&lt;0.01) than AT subjects. MSNA burst incidence was also significantly related to AIx in all subjects (R2=0.61; P&lt;0.01).Conclusions: A positive association was found between MSNA and AIx in young males. Furthermore, a history of RT is associated with increased arterial stiffness and elevated sympathetic outflow.

The effect of lower body weight support on arterial wave reflection in healthy adults

Body weight support (WS) during treadmill exercise is used to rehabilitate orthopedic/neurological patients. WS lowers musculoskeletal strain and load. It compresses the lower body and increases intrathoracic volume. We studied short-term effects of WS on wave reflection indices using applanation tonometry during progressive WS of 25%, 50%, and 75% of body weight in 25 healthy men. WS decreased mean heart rate from 79 to 69 beats/min (P < .001). Peripheral and central mean arterial, systolic, and pulse pressures (PP) remained unchanged. There was a trend toward lower peripheral and central diastolic pressure. PP amplification ratio decreased significantly (P = .005). Reflected wave characteristics: Augmented pressure and index increased in a stepwise manner with WS (both P < .001). Both ejection duration and systolic duration of the reflected pressure wave (Ätr) increased progressively (both P < .001). The round-trip travel time (Δtp) was unchanged. Left ventricular workload and oxygen demand: Left ventricular wasted pressure energy increased (P < .001), and the subendocardial viability ratio decreased (P = .005), whereas the tension time index remained unchanged. In normal men, WS acutely decreases the PP amplification ratio, increases the amplitude and duration of the reflected aortic pressure wave, and increases measures of wasted left ventricular pressure energy and oxygen demand.

Patients with refractory angina have increased aortic wave reflection and wasted left ventricular pressure energy

BackgroundEarly return of reflected blood pressure (BP) waves from the lower body augments central systolic BP and increases systolic pressure-time index (SPTI) and wasted left ventricular (LV) pressure energy, which increase afterload and myocardial oxygen (MVO2) demand. Accordingly, we sought to determine wave reflection characteristics and diastolic timing in a group of patients with chronic stable angina resistant to anti-anginal therapy. MethodsRadial artery BP waveforms were recorded non-invasively by applanation tonometry in 36 patients with refractory angina (RA) and a reference control (CON) group of 36 successfully treated hypertensive patients without angina matched for age, gender, height, BMI, and mean BP. Pulse wave analysis (PWA) of the ascending aortic BP waveform was used to determine central hemodynamics, diastolic timing, wave reflection characteristics and wasted LV pressure energy (LVEw). ResultsCompared to the CON group, RA patients had higher central aortic augmented BP, augmentation index (Alx) and reflected pressure wave systolic duration (SDR). These modifications in wave reflection characteristics were associated with an increase in SPTI and LVEw and a decrease in pulse BP amplification and the diastolic pressure time fraction. ConclusionsRA patients have changes in systolic wave reflections and diastolic timing that increase LV afterload, MVO2 demand and wasted LV energy and reduce coronary artery perfusion. These alterations in cardiovascular function contribute to an undesirable mismatch in the MVO2 supply/demand ratio that favors ischemia and angina pectoris and may precipitate future adverse cardiovascular events.

A Bio-Inspired Approach for the Reduction of Left Ventricular Workload

Previous studies have demonstrated the existence of optimization criteria in the design and development of mammalians cardiovascular systems. Similarities in mammalian arterial wave reflection suggest there are certain design criteria for the optimization of arterial wave dynamics. Inspired by these natural optimization criteria, we investigated the feasibility of optimizing the aortic waves by modifying wave reflection sites. A hydraulic model that has physical and dynamical properties similar to a human aorta and left ventricle was used for a series of in-vitro experiments. The results indicate that placing an artificial reflection site (a ring) at a specific location along the aorta may create a constructive wave dynamic that could reduce LV pulsatile workload. This simple bio-inspired approach may have important implications for the future of treatment strategies for diseased aorta.

Structural and Functional Arterial Parameters, Immunovirological Control and Vitamin D in HIV-Infected Patients

Objective: HIV-infected patients still experience higher Cardiovascular (CV) mortality rates, even if an adequate viral suppression is achieved. In addition, vitamin D insufficiency, a common condition in HIV-infected patients, is increasingly associated with CV risk. We therefore aim to investigate relationships between immunological parameters, antiretroviral therapy, plasma vitamin D and arterial parameters, including aortic stiffness and wave reflections, in HIV-infected patients who achieved viral suppression but possibly remain at increased CV risk. Methods: We conducted a cross-sectional study including 178 middle-aged HIV-infected patients. HIV infection was controlled in a large number of participants, representative of a real-world setting. In addition to carotid Intima Media Thickness (IMT), central hemodynamic parameters involved aortic Pulse Wave Velocity (PWV), carotid Augmentation index (AIx) and Pulse Pressure Amplification (PPA) measured noninvasively using applanation tonometry. Results: Aortic PWV was slightly but unsignificantly higher than the theoretical values obtained in general population according to age and blood pressure, and was independent of HIV-related parameters. In univariate and multivariate analyses, carotid AIx was positively correlated with current CD4 T-cell count and PPA was positively correlated with vitamin D, independently of other confounders. No HIV-related parameters or vitamin D entered the multivariate analysis of carotid IMT / plaque. Conclusion: In our chronically treated population, HIV infection was not associated with increased aortic stiffness but with a positive correlation between current CD4 T-cell count and degree of AIx, suggesting that patients with higher CD4 T-cell count may have higher wave reflections. The positive correlation between vitamin D and PPA suggests that vitamin D deficiency may be independently associated with altered central hemodynamics in well controlled HIV-infected patients. These findings should be confirmed in prospective studies.

Numerical validation of a suprasystolic brachial cuff-based method for estimating aortic pressure

Central aortic pressures are better predictors of cardiovascular events than peripheral pressures. However, central aortic blood pressures cannot be measured noninvasively; for this reason, estimating aortic pressures from noninvasive measurements of peripheral pressures has been the subject of numerous studies. In the present study, a novel method was proposed to noninvasively estimate aortic pressures from the oscillometric wave of a suprasystolic brachial cuff. The errors of estimation were evaluated in relation to various cardiovascular properties using an integrated cardiovascular-cuff model. Obtained results demonstrated that the estimation errors are affected mainly by aortic stiffness. The estimation errors for aortic systolic pressure, diastolic pressure, pulse pressure and wave shape under the assumed cardiovascular conditions were 5.84 ± 1.58 mmHg, -0.28 ± 0.41 mmHg, 6.12 ± 1.42 mmHg and 1.72 ± 0.57 mmHg, respectively, all of which fell within the error ranges established by existing devices. Since the method is easy to be automated and bases the estimation fully on patient-specific information, its clinical application is promising, although further clinical studies are awaited to validate the method in vivo.