Pulse wave analysis of the aortic pressure waveform in severe left ventricular systolic dysfunction

Hemodynamic Monitoring In The Cardiac Surgical Patient: Comparison of Three Arterial Catheters

OBJECTIVE

Systemic systolic (SAP) and mean (MAP) arterial pressure monitoring is the cornerstone in hemodynamic management of the cardiac surgical patient, and the radial artery is the most common site of catheter placement. The present study compared 3 different arterial line procedures. It is hypothesized that a 20-G 12.7- cm catheter inserted into the radial artery will be equal to a 20-G 12.7- cm angiocath placed in the brachial artery, and superior to a 20-G 5.00 cm angiocath placed in the radial artery.

DESIGN

A prospective randomized control study was performed.

SETTING

Single academic university hospital.

PARTICIPANTS

Adult patients ≥18 years old undergoing nonemergent cardiac surgery using cardiopulmonary bypass (CPB).

INTERVENTIONS

After approval by the Rhode Island Hospital institutional review board, a randomized prospective control study to evaluate 3 different peripheral intraarterial catheter systems was performed: (1) Radial Short (RS): 20-G 5- cm catheter; (2) Radial Long (RL): 20-G 12- cm catheter; and (3) Brachial Long (BL): 20-G 12- cm catheter.

MEASUREMENTS AND RESULTS

Gradients between central aortic and peripheral catheters (CA-P) were compared and analyzed before CPB and 2 and 10 minutes after separation from CPB. The placement of femoral arterial lines and administration of vasoactive medications were recorded. After exclusions, 67 BL, 61 RL, and 66 RS patients were compared. Before CPB, CA-P SAP and MAP gradients were not significant among the 3 groups. Two minutes after CPB, the CA-P SAP gradient was significant for the RS group (p = 0.005) and insignificant for BL (p = 0.47) and RL (p = 0.39). Two-group analysis revealed that CA-P SAP gradients are similar between BL and RL (p = 0.84), both of which were superior to RS (p = 0.02 and p = 0.04, respectively). At 10 minutes after CPB, the CA-P SAP gradient for RS remained significant (p = 0.004) and similar to the gradient at 2 minutes. The CA-P SAP gradients increased from 2 to 10 minutes for BL (p = 0.13) and RL (p = 0.06). Two minutes after CPB, the CA-P MAP gradients were significant for the BL (p = 0.003), RL (p < 0.0001), and RS (p < 0.0001) groups. Two-group analysis revealed that the CA-P MAP gradients were lower for the BL group compared with the RL (p = 0.054) and RS (p< 0.05) groups. Ten minutes after CPB, the CA-P MAP gradients in the RL and RS groups remained significant (p < 0.0001) and both greater than the BL group (p = 0.002). A femoral arterial line was placed more frequently in the RS group (8/66 = 12.1%) than in the RL group (3/61 = 4.9%) and the BL group (2/67 = 3.0%). Vasopressin was administered significantly more frequently in the RS group.

CONCLUSION

Regarding CA-P SAP gradients, the RL group performed equally to the BL group, both being superior to RS. Regarding CA-P MAP gradients, BL was superior to RL and RS. Clinically, femoral line placement and vasopressin administration were fewer for the BL and RL groups when compared with the RS group. This study demonstrated the benefits of a long (12.7 cm) 20- G angiocath placed in the radial artery.

Validation of a Suprasystolic Cuff System for Static and Dynamic Representation of the Central Pressure Waveform

BACKGROUND

Noninvasive pulse waveform analysis is valuable for central cardiovascular assessment, yet controversies persist over its validity in peripheral measurements. Our objective was to compare waveform features from a cuff system with suprasystolic blood pressure hold with an invasive aortic measurement.

METHODS AND RESULTS

This study analyzed data from 88 subjects undergoing concurrent aortic catheterization and brachial pulse waveform acquisition using a suprasystolic blood pressure cuff system. Oscillometric blood pressure (BP) was compared with invasive aortic systolic BP and diastolic BP. Association between cuff and catheter waveform features was performed on a set of 15 parameters inclusive of magnitudes, time intervals, pressure-time integrals, and slopes of the pulsations. The evaluation covered both static (subject-averaged values) and dynamic (breathing-induced fluctuations) behaviors. Peripheral BP values from the cuff device were higher than catheter values (systolic BP-residual, 6.5 mm Hg; diastolic BP-residual, 12.4 mm Hg). Physiological correction for pressure amplification in the arterial system improved systolic BP prediction (r2=0.83). Dynamic calibration generated noninvasive BP fluctuations that reflect those invasively measured (systolic BP Pearson R=0.73, P<0.001; diastolic BP Pearson R=0.53, P<0.001). Static and dynamic analyses revealed a set of parameters with strong associations between catheter and cuff (Pearson R>0.5, P<0.001), encompassing magnitudes, timings, and pressure-time integrals but not slope-based parameters.

CONCLUSIONS

This study demonstrated that the device and methods for peripheral waveform measurements presented here can be used for noninvasive estimation of central BP and a subset of aortic waveform features. These results serve as a benchmark for central cardiovascular assessment using suprasystolic BP cuff-based devices and contribute to preserving system dynamics in noninvasive measurements.

Novel Pulse Waveform Index by Ambulatory Blood Pressure Monitoring and Cardiac Function: A Pilot Study

Background

A simple ambulatory measure of cardiac function could be helpful for monitoring heart failure patients.

Objectives

The purpose of this paper was to determine whether a novel pulse waveform analysis using data obtained by our developed multisensor-ambulatory blood pressure monitoring (ABPM) device, the 'Sf/Am' ratio, is associated with echocardiographic left ventricular ejection fraction (LVEF).

Methods

Multisensor-ABPM was conducted twice at baseline in 20 heart failure (HF) patients with HF-reduced LVEF or HF-preserved LVEF (median age 66 years, male 65%) and over a 6- to 12-month follow-up after patient-tailored treatment. We assessed the changes in the pulse waveform index Sf/Am and LVEF that occurred between the baseline and follow-up. The Sf/Am consists of the area of the ejection part in the square forward wave (Sf) and the amplitude of the measured wave (Am). We divided the patients into the recovered (n = 11) and not-recovered (n = 9) groups defined by a ≥10% increase in LVEF.

Results

Although the ambulatory BP levels and variabilities did not change in either group, the Sf/Am increased significantly in the recovered group (baseline 21.4 ± 4.5; follow-up, 25.6 ± 3.7, P = 0.004). The not-recovered group showed no difference between the baseline and follow-up. The follow-up/baseline Sf/Am ratio was significantly associated with the LVEF ratio (r = 0.469, P = 0.037). The Sf/Am was significantly correlated with the LVEF in overall measurements (n = 40, r = 0.491, P = 0.001).

Conclusions

These results demonstrated that a novel noninvasive pulse waveform index, the Sf/Am measured by multisensor-ABPM is associated with LVEF. The Sf/Am may be useful for estimating cardiac function.

A generalized canine transfer function accurately reconstructs central aortic pressure waveforms to enable enhanced pulse wave analysis

Routine preclinical blood pressure evaluation is an important risk assessment tool. Although proximal aortic pressure is most relevant for key target organs, abdominal aortic pressures are more commonly recorded. Pulse pressure amplification and waveform distortion in abdominal waveforms make it inappropriate for central hemodynamic analytical methods without the use of a mathematical transfer function. Clinical transfer functions have been developed to estimate ascending aortic waveforms from brachial or radial artery waveforms in humans, but no preclinical analogues exist. The aim of this study was to develop a canine-specific transfer function to reconstruct thoracic aortic pressure waveforms from abdominal aortic data to enable the application of central hemodynamic analytical methods. Simultaneous abdominal and thoracic blood pressures were recorded from seven conscious, male beagle dogs administered 3 well-characterized pharmacologic standards and animals were appointed to a training (n = 3) or validation (n = 4) group at baseline and during dosing. A generalized transfer function was developed from the training group data and evaluated for its ability to synthesize thoracic pressure waves in the training and validation groups. Select hemodynamic parameters were evaluated in measured and synthesized thoracic data. There was a high degree of correlation between measured and synthesized thoracic parameters (r2 = 0.74-0.99). There was no difference between indices computed from synthesized or actual thoracic waveforms at baseline or after administration of pharmacologic standards. This work demonstrates that a generalized preclinical transfer function can reproduce thoracic pressure waves across a range of hemodynamic responses thus enabling the application of central hemodynamic analytical methods.

A fast computational model for circulatory dynamics: effects of left ventricle-aorta coupling

The course of diseases such as hypertension, systolic heart failure and heart failure with a preserved ejection fraction is affected by interactions between the left ventricle (LV) and the vasculature. To study these interactions, a computationally efficient, biophysically based mathematical model for the circulatory system is presented. In a four-chamber model of the heart, the LV is represented by a previously described low-order, wall volume-preserving model that includes torsion and base-to-apex and circumferential wall shortening and lengthening, and the other chambers are represented using spherical geometries. Active and passive myocardial mechanics of all four chambers are included. The cardiac model is coupled with a wave propagation model for the aorta and a closed lumped-parameter circulation model. Parameters for the normal heart and aorta are determined by fitting to experimental data. Changes in the timing and magnitude of pulse wave reflections by the aorta are demonstrated with changes in compliance and taper of the aorta as seen in aging (decreased compliance, increased diameter and length), and resulting effects on LV pressure-volume loops and LV fiber stress and sarcomere shortening are predicted. Effects of aging of the aorta combined with reduced LV contractile force (failing heart) are examined. In the failing heart, changes in aortic properties with aging affect stroke volume and sarcomere shortening without appreciable augmentation of aortic pressure, and the reflected pressure wave contributes an increased proportion of aortic pressure.

The Role of the Vasculature in Heart Failure

The contribution of the vasculature in the development and progression of heart failure (HF) syndromes is poorly understood and often neglected. Incorporating both arterial and venous systems, the vasculature plays a significant role in the regulation of blood flow throughout the body in meeting its metabolic requirements. A deterioration or imbalance between the cardiac and vascular interaction can precipitate acute decompensated HF in both preserved and reduced ejection fraction phenotypes. This is characterised by the increasingly recognised concept of ventricular-arterial coupling: a well-balanced relationship between ventricular and vascular stiffness, which has major implications in HF. Often, the cause of decompensation is unknown, with international guidelines mainly centred on arrhythmia, infection, acute coronary syndrome and its mechanical complications as common causes of decompensation; the vascular component is often underrecognised. A better understanding of the vascular contribution in cardiovascular failure can improve risk stratification, earlier diagnosis and facilitate earlier optimal treatment. This review focuses on the role of the vasculature by integrating the concepts of ventricular-arterial coupling, arterial stiffness and venous return in a failing heart.

The central arterial stiffness parameters in decompensated versus compensated states of heart failure: a paired comparative cohort study

Background

Arterial stiffness is strongly linked to the pathogenesis of heart failure and the development of acute decompensation in patients with stable chronic heart failure. This study aimed to compare arterial stiffness indices in patients with heart failure with reduced ejection fraction (HFrEF) during the acute decompensated state, and three months later after hospital discharge during the compensated state.

Results

One hundred patients with acute decompensated HFrEF (NYHA class III and IV) and left ventricular ejection fraction ≤ 35% were included in the study. During the initial and follow-up visits, all patients underwent full medical history taking, clinical examination, transthoracic echocardiography, and non-invasive pulse wave analysis by the Mobil-O-Graph 24-h device for measurement of arterial stiffness. The mean age was 51.6 ± 6.1 years and 80% of the participants were males. There was a significant reduction of the central arterial stiffness indices in patients with HFrEF during the compensated state compared to the decompensated state. During the decompensated state, patients presented with NYHA FC IV (n = 64) showed higher AI (24.5 ± 10.0 vs. 16.8 ± 8.6, p < 0.001) and pulse wave velocity (9.2 ± 1.3 vs. 8.5 ± 1.2, p = 0.021) than patients with NYHA FC III, and despite the relatively smaller number of females, they showed higher stiffness indices than males.

Conclusions

Central arterial stiffness indices in patients with HFrEF were significantly lower in the compensated state than in the decompensated state. Patients with NYHA FC IV and female patients showed higher stiffness indices in their decompensated state of heart failure.

Scalability of cardiovascular intrinsic frequencies: Validations in preclinical models and non-invasive clinical studies

AIMS

Cardiovascular intrinsic frequencies (IFs) are associated with cardiovascular health and disease, separately capturing the systolic and diastolic information contained in a single (uncalibrated) arterial waveform. Previous clinical investigations related to IF have been restricted to studying chronic conditions, and hence its applicability for acute cardiovascular diseases has not been explored. Studies of cardiovascular complications such as acute myocardial infarction are difficult to perform in humans due to the high-risk and invasive nature of such procedures. Although they can be performed in preclinical (animal) models, the corresponding interpretation of IF measures and how they ultimately translate to humans is unknown. Hence, we studied the scalability of IF across species and sensor platforms.

MATERIALS AND METHODS

Scaled values of the two intrinsic frequencies ω1 and ω2 (corresponding to systolic and diastolic dynamics, respectively) were extracted from carotid waveforms acquired either non-invasively (via tonometry, Vivio or iPhone) in humans or invasively in rabbits and rats.

KEY FINDINGS

The scaled IF parameters for all species were found to fall within the same physiological ranges carrying similar statistical characteristics, even though body sizes and corresponding heart rates of the species were substantially different. Additionally, results demonstrated that all non-invasive sensor platforms were significantly correlated with each other for scaled IFs, suggesting that such analysis is device-agnostic and can be applied to upcoming wearable technologies.

SIGNIFICANCE

Ultimately, our results found that IFs are scalable across species, which is particularly valuable for the training of IF-based artificial intelligence systems using both preclinical and clinical data.

Establishment of a Modular Hemodynamic Simulator for Accurate In Vitro Simulation of Physiological and Pathological Pressure Waveforms in Native and Bioartificial Blood Vessels

Purpose

In vitro stimulation of native and bioartificial vessels in perfusable systems simulating natural mechanical environments of the human vasculature represents an emerging approach in cardiovascular research. Promising results have been achieved for applications in both regenerative medicine and etiopathogenetic investigations. However, accurate and reliable simulation of the wide variety of physiological and pathological pressure environments observed in different vessels still remains an unmet challenge.

Methods

We established a modular hemodynamic simulator (MHS) with interchangeable and modifiable components suitable for the perfusion of native porcine—(i.e. the aorta, brachial and radial arteries and the inferior vena cava) and bioartificial fibrin-based vessels with anatomical site specific pressure curves. Additionally, different pathological pressure waveforms associated with cardiovascular diseases including hyper- and hypotension, tachy- and bradycardia, aortic valve stenosis and insufficiency, heart failure, obstructive cardiomyopathy and arterial stiffening were simulated. Pressure curves, cyclic distension and shear stress were measured for each vessel and compared to ideal clinical pressure waveforms.

Results

The pressure waveforms obtained in the MHS showed high similarity to the ideal anatomical site specific pressure curves of different vessel types. Moreover, the system facilitated accurate emulation of physiological and different pathological pressure conditions in small diameter fibrin-based vessels.

Conclusion

The MHS serves as a variable in vitro platform for accurate emulation of physiological and pathological pressure environments in biological probes. Potential applications of the system include bioartificial vessel maturation in cardiovascular tissue engineering approaches as well as etiopathogenetic investigations of various cardiovascular pathologies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13239-021-00577-0.

Lower-body dynamic exercise reduces wave reflection in healthy young adults

NEW FINDINGS

What is the central question of this study? There is a paradoxical reduction in augmentation index during lower-body dynamic (LBD) exercise in the face of an increase in central pressure. To determine causality, the amplitudes of forward and backward pressure waves were assessed separately using wave separation analysis. What is the main finding and its importance? Reflection magnitude decreased during LBD exercise in healthy young adults and was attributable to an increased forward pressure wave amplitude and decreased backward pressure wave amplitude. This vasoactive response might limit the adverse effects of wave reflection during LBD exercise, optimizing ventricular-arterial interactions.

ABSTRACT

Acute lower-body dynamic (LBD) exercise decreases surrogate measures of wave reflection, such as the augmentation index. However, the augmentation index is influenced by the combined effects of wave reflection timing, magnitude and other confounding factors external to wave reflection, which make it difficult to discern the origin of changes in surrogate measures. The relative contributions of forward (Pf) and backward (Pb) pressure wave amplitudes to central pressure can be determined by wave separation analysis. Reflection magnitude (RM = Pb/Pf) and the timing of apparent wave reflection return can also be determined. We tested the hypothesis that acute LBD exercise decreases RM and reflected wave transit time (RWTT). Applanation tonometry was used to record radial artery pressure waveforms in 25 adults (24 ± 4 years of age) at baseline and during light-, moderate- and vigorous-intensity exercise. Wave separation analysis was conducted offline using a personalized physiological flow wave to determine Pf, Pb, RM and RWTT. The RM decreased during all intensities of exercise compared with baseline (all P < 0.001; baseline, 43 ± 5%; light, 33 ± 6%; moderate, 23 ± 7%; vigorous, 17 ± 5%). The reduction in RM was attributable to the combined effect of increased Pf and decreased Pb during exercise. The RWTT decreased during all intensities of exercise compared with baseline (all P < 0.04; baseline, 156 ± 17 ms; light, 144 ± 15 ms; moderate, 129 ± 16 ms; vigorous, 121 ± 17 ms). Lastly, in a stepwise multilinear regression, Pf, but not Pb and RWTT, contributed to increased central pulse pressure during LBD exercise. These data show that wave reflection decreased and that central pulse pressure is most influenced by Pf during LBD exercise.

Synthetic photoplethysmography (PPG) of the radial artery through parallelized Monte Carlo and its correlation to body mass index (BMI)

Cardiovascular disease is one of the leading causes of death in the United States and obesity significantly increases the risk of cardiovascular disease. The measurement of blood pressure (BP) is critical in monitoring and managing cardiovascular disease hence new wearable devices are being developed to make BP more accessible to physicians and patients. Several wearables utilize photoplethysmography from the wrist vasculature to derive BP assessment although many of these devices are still at the experimental stage. With the ultimate goal of supporting instrument development, we have developed a model of the photoplethysmographic waveform derived from the radial artery at the volar surface of the wrist. To do so we have utilized the relation between vessel biomechanics through Finite Element Method and Monte Carlo light transport model. The model shows similar features to that seen in PPG waveform captured using an off the shelf device. We observe the influence of body mass index on the PPG signal. A degradation the PPG signal of up to 40% in AC to DC signal ratio was thus observed.

The Mediterranean Diet Benefit on Cardiovascular Hemodynamics and Erectile Function in Chronic Heart Failure Male Patients by Decoding Central and Peripheral Vessel Rheology

BACKGROUND

Mediterranean diet was evaluated on erectile performance and cardiovascular hemodynamics, in chronic heart failure patients.

METHODS

150 male stable heart failure patients were enrolled in the study (62 ± 10 years, New York Heart Association (NYHA) classes I-II, ejection fraction ≤40%). A detailed echocardiographic evaluation including estimation of the global longitudinal strain of the left ventricle and the systolic tissue doppler velocity of the tricuspid annulus was performed. Erectile dysfunction severity was assessed by the Sexual Health Inventory for Men-5 (SHIM-5) score. Adherence to the Mediterranean diet was evaluated by the MedDietScore.

RESULTS

The SHIM-5 score was positively correlated with the MedDietScore (p = 0.006) and augmentation index (p = 0.031) and inversely correlated with age (p = 0.002). MedDietScore was negatively associated with intima-media-thickness (p < 0.001) and serum prolactin levels (p = 0.05). Multi-adjusted analysis revealed that the inverse relation of SHIM-5 and prolactin levels remained significant only among patients with low adherence to the Mediterranean diet (p = 0.012).

CONCLUSION

Consumption of Mediterranean diet benefits cardiovascular hemodynamics, while suppressing serum prolactin levels. Such physiology may enhance erectile ability independently of the of the left ventricle ejection fraction.

Predicting Parameters for Successful Weaning from Veno-Arterial Extracorporeal Membrane Oxygenation in Cardiogenic Shock

Aims

Percutaneous veno‐arterial extracorporeal membrane oxygenation (VA‐ECMO) is utilized for patients with cardiogenic shock or cardiac arrest. However, the procedure protocol for weaning from VA‐ECMO has not been well established. The present study aimed to determine the usefulness of echocardiographic and pulmonary artery catheter parameters for predicting successful weaning from VA‐ECMO in patients with refractory cardiogenic shock.

Methods and results

We retrospectively studied 50 patients who were hospitalized and supported by VA‐ECMO for >48 h between January 2013 and March 2017. Patients successfully weaned from VA‐ECMO without reintroduction of VA‐ECMO or left ventricular assist device implantation were defined as 30 day survivors. Echocardiographic and pulmonary artery catheter parameters were evaluated when ECMO flow was limited to a maximum of 1.5–2.0 L/min. Twenty‐four patients were successfully weaned from VA‐ECMO, whereas 26 were not. Fractional shortening, corrected left ventricular ejection time (LVETc, defined as LVET divided by the square root of heart rate), left ventricular outflow tract velocity time integral, and LVETc divided by pulmonary artery wedge pressure (PAWP) were significantly larger in the 30 day survivor groups. Multivariable analysis revealed LVETc∕PAWP as a significant independent predictor of successful weaning (LVETc∕PAWP, odds ratio 0.82, 95% confidence interval 0.71–0.94, P = 0.005). Receiver operating characteristic curve analysis revealed 15.9 as the optimal LVETc∕PAWP for predicting successful weaning (area under the curve 0.82).

Conclusions

The present findings indicate that LVETc∕PAWP is a potential predictor of successful weaning from VA‐ECMO.

Simultaneous influence of sex and age on blood pressure difference between supine and sitting body positions

OBJECTIVES

Doctors' offices and outpatient departments typically measure blood pressure (BP) with the patient in a sitting position, whereas inpatient departments also use the supine position. As sex and age influence the autonomic function associated with BP regulation our study compared BP measurements in supine and sitting positions for men and women of different ages.

METHODS

We included 91 men and 118 women (≥18 years) without severe diseases. Hypertension was not an exclusion criterion because it is common in older persons. Mean left brachial BP and heart rate were determined by a digital sphygmomanometer in supine position as well as in sitting position before and after hand force measurement.

RESULTS

In a supine position women had slightly lower diastolic BP values than men. After sitting up, the diastolic BP increased in nearly all subjects. This increase was greater in women older than 50 years than for aged-matched men. In contrast to diastolic BP the systolic BP increased after sitting up in only two thirds of the subjects. Especially in women younger than 50 years the systolic BP often did not increase but decreased in response to postural change. The pulse pressure was mostly reduced after sitting up. This reduction was more pronounced in women than men independent of age and physical effort (i.e. hand force measurement). The sitting position also caused an increased heart rate, which was independent of sex and age.

CONCLUSION

Postural changes in the systolic and diastolic BP simultaneously depend on sex and age that needs to be considered for BP measurements in supine and sitting body positions.

Dynamic Modulation of Device-Arterial Coupling to Determine Cardiac Output and Vascular Resistance

Clinical adoption of mechanical circulatory support for shock is rapidly expanding. Achieving optimal therapeutic benefit requires metrics of state to guide titration and weaning of support. Using the transvalvular positioning of a percutaneous ventricular assist device (pVAD), device:heart interactions are leveraged to determine cardiac output (CO) and systemic vascular resistance (SVR) near-continuously without disrupting therapeutic function. An automated algorithm rapidly alternates between device support levels to dynamically modulate physiological response. Employing a two-element lumped parameter model of the vasculature, SVR and CO are quantified directly from measurements obtained by the pVAD without external calibration or invasive catheters. The approach was validated in an acute porcine model across a range of cardiac (CO = 3-10.6 L/min) and vascular (SVR = 501-1897 dyn s/cm⁵) states. Cardiac output calculations closely correlated (r = 0.82) to measurements obtained by the pulmonary artery catheter-based thermodilution method with a mean bias of 0.109 L/min and limits of agreement from - 1.67 to 1.89 L/min. SVR was also closely correlated (r = 0.86) to traditional catheter-based measurements with a mean bias of 62.1 dyn s/cm⁵ and limits of agreement from - 260 to 384 dyn s/cm⁵. Use of diagnostics integrated into therapeutic device function enables the potential for optimizing support to improve outcomes for cardiogenic shock.

Novel heat shock protein 90 inhibitor improves cardiac recovery in a rodent model of donation after circulatory death

OBJECTIVE

Organ donation after circulatory death (DCD) is a potential solution for the shortage of suitable organs for transplant. Heart transplantation using DCD donors is not frequently performed due to the potential myocardial damage following warm ischemia. Heat shock protein (HSP) 90 has recently been investigated as a novel target to reduce ischemia/reperfusion injury. The objective of this study is to evaluate an innovative HSP90 inhibitor (HSP90i) as a cardioprotective agent in a model of DCD heart.

METHODS

A DCD protocol was initiated in anesthetized Lewis rats by discontinuation of ventilation and confirmation of circulatory death by invasive monitoring. Following 15 minutes of warm ischemia, cardioplegia was perfused for 5 minutes at physiological pressure. DCD hearts were mounted on a Langendorff ex vivo heart perfusion system for reconditioning and functional assessment (60 minutes). HSP90i (0.01 μmol/L) or vehicle was perfused in the cardioplegia and during the first 10 minutes of ex vivo heart perfusion reperfusion. Following assessment, pro-survival pathway signaling was evaluated by western blot or polymerase chain reaction.

RESULTS

Treatment with HSP90i preserved left ventricular contractility (maximum + dP/dt, 2385 ± 249 vs 1745 ± 150 mm Hg/s), relaxation (minimum -dP/dt, -1437 ± 97 vs 1125 ± 85 mm Hg/s), and developed pressure (60.7 ± 5.6 vs 43.9 ± 4.0 mm Hg), when compared with control DCD hearts (All P = .001). Treatment abrogates ischemic injury as demonstrated by a significant reduction of infarct size (2,3,5-triphenyl-tetrazolium chloride staining) of 7 ± 3% versus 19 ± 4% (P = .03), troponin T release, and mRNA expression of Bax/Bcl-2 (P < .05).

CONCLUSIONS

The cardioprotective effects of HSP90i when used following circulatory death might improve transplant organ availability by expanding the use of DCD hearts.

The Role of Arterial Stiffness and Central Hemodynamics in Heart Failure

Whereas traditional understanding of left ventricular afterload was focused on a steady-state circulation model with continuous pressures and flow, a more realistic concept is emerging, taking the pulsatile nature of the heart and the arterial system into account. The most simple measure of pulsatility is brachial pulse pressure, representing the pulsatility fluctuating around the mean blood pressure level. Brachial pulse pressure is widely available, fundamentally associated with the development and treatment of heart failure (HF), but its analysis is often confounded in patients with established HF. The next step of analysis consists of arterial stiffness, central (rather than brachial) pressures, and of wave reflections. The latter are closely related to left ventricular late systolic afterload, ventricular remodeling, diastolic dysfunction, exercise capacity, and, in the long term, the risk of new-onset HF. Wave reflection may also evolve as a suitable therapeutic target for HF with preserved and reduced ejection fraction. A full understanding of ventricular-arterial coupling, however, requires dedicated analysis of time-resolved pressure and flow signals. This review provides a summary of current understanding of pulsatile hemodynamics in HF.

Pulsatile arterial haemodynamics in heart failure

Due to the cyclic function of the human heart, pressure and flow in the circulation are pulsatile rather than continuous. Addressing pulsatile haemodynamics starts with the most convenient measurement, brachial pulse pressure, which is widely available, related to development and treatment of heart failure (HF), but often confounded in patients with established HF. The next level of analysis consists of central (rather than brachial) pressures and, more importantly, of wave reflections. The latter are closely related to left ventricular late systolic afterload, ventricular remodelling, diastolic dysfunction, exercise capacity, and, in the long-term, the risk of new-onset HF. Wave reflection may also represent a suitable therapeutic target. Treatments for HF with preserved and reduced ejection fraction, based on a reduction of wave reflection, are emerging. A full understanding of ventricular-arterial coupling, however, requires dedicated analysis of time-resolved pressure and flow signals, which can be readily accomplished with contemporary non-invasive imaging and modelling techniques. This review provides a summary of our current understanding of pulsatile haemodynamics in HF.

Clinical assessment of a non-invasive wearable MEMS pressure sensor array for monitoring of arterial pulse waveform, heart rate and detection of atrial fibrillation

There is an unmet clinical need for a low cost and easy to use wearable devices for continuous cardiovascular health monitoring. A flexible and wearable wristband, based on microelectromechanical sensor (MEMS) elements array was developed to support this need. The performance of the device in cardiovascular monitoring was investigated by (i) comparing the arterial pressure waveform recordings to the gold standard, invasive catheter recording (n = 18), (ii) analyzing the ability to detect irregularities of the rhythm (n = 7), and (iii) measuring the heartrate monitoring accuracy (n = 31). Arterial waveforms carry important physiological information and the comparison study revealed that the recordings made with the wearable device and with the gold standard device resulted in almost identical (r = 0.9–0.99) pulse waveforms. The device can measure the heart rhythm and possible irregularities in it. A clustering analysis demonstrates a perfect classification accuracy between atrial fibrillation (AF) and sinus rhythm. The heartrate monitoring study showed near perfect beat-to-beat accuracy (sensitivity = 99.1%, precision = 100%) on healthy subjects. In contrast, beat-to-beat detection from coronary artery disease patients was challenging, but the averaged heartrate was extracted successfully (95% CI: −1.2 to 1.1 bpm). In conclusion, the results indicate that the device could be useful in remote monitoring of cardiovascular diseases and personalized medicine.

High-performance transparent pressure sensors based on sea-urchin shaped metal nanoparticles and polyurethane microdome arrays for real-time monitoring

An ultra-sensitive and transparent piezoresistive pressure sensor based on a sea-urchin shaped metal nanoparticle (SSNP)-polyurethane (PU) composite with microdome arrays is successfully fabricated for the first time. The piezoresistive pressure sensor with microdome arrays was prepared using a nanoimprinting process based on an intermediate polymer substrate (IPS) replica mold. It showed a superior sensitivity (71.37 kPa^-1) and a high optical transmittance (77.7% at 550 nm) due to the effective quantum tunneling effect even at small concentrations of conductive SSNP filler (6 mg mL^-1). The high-performance characteristics of the piezoresistive pressure sensor are attributed to the geometric effects of the microdome structure, especially the stress concentration at small contact spots and the deformation of the contact area. The piezoresistive pressure sensor with microdome arrays also exhibited a fast response/relaxation time (30 ms), ultra-low pressure detection (4 Pa), and excellent long-term stability under harsh conditions. In addition, the effectiveness of the piezoresistive pressure sensors in various sensing applications including sensing mapping, human arterial pulse monitoring, and the detection of muscle movement is also successfully demonstrated. It is anticipated that this novel transparent pressure sensor based on a SSNP-PU composite with microdome arrays will be a key component in the development of integrated transparent sensing applications.

Pulse wave reflection responses to bench press with and without practical blood flow restriction

Resistance exercise is recommended to increase muscular strength but may also increase pulse wave reflection. The effect of resistance exercise combined with practical blood flow restriction (pBFR) on pulse wave reflection is unknown. The purpose of this study was to evaluate the differences in pulse wave reflection characteristics between bench press with pBFR and traditional high-load bench press in resistance-trained men. Sixteen resistance-trained men participated in the study. Pulse wave reflection characteristics were assessed before and after low-load bench press with pBFR (LL-pBFR), traditional high-load bench press (HL), and a control (CON). A repeated-measures ANOVA was used to evaluate differences in pulse wave reflection characteristics among the conditions across time. There were significant (p ≤ 0.05) interactions for heart rate, augmentation index, augmentation index normalized at 75 bpm, augmentation pressure, time-tension index, and wasted left ventricular energy such that they were increased after LL-pBFR and HL compared with rest and CON, with no differences between LL-pBFR and HL. Aortic pulse pressure (p < 0.001) was elevated only after LL-pBFR compared with rest. In addition, there was a significant (p ≤ 0.05) interaction for aortic diastolic blood pressure (BP) such that it was decreased after LL-pBFR compared with rest and CON but not HL. The subendocardial viability ratio and diastolic pressure-time index were significantly different between LL-pBFR and HL compared with rest and CON. There were no significant interactions for brachial systolic or diastolic BP, aortic systolic BP, or time of the reflected wave. In conclusion, acute bench press resistance exercise significantly altered pulse wave reflection characteristics without differences between LL-pBFR and HL.

The effects of facemasks on airway inflammation and endothelial dysfunction in healthy young adults: a double-blind, randomized, controlled crossover study

Background

Facemasks are increasingly worn during air pollution episodes in China, but their protective effects are poorly understood. We aimed to evaluate the filtration efficiencies of N95 facemasks and the cardiopulmonary benefits associated with wearing facemasks during episodes of pollution.

Results

We measured the filtration efficiencies of particles in ambient air of six types of N95 facemasks with a manikin headform. The most effective one was used in a double-blind, randomized, controlled crossover study, involving 15 healthy young adults, conducted during 2 days of severe pollution in Beijing, China. Subjects were asked to walk along a busy-traffic road for 2 h wearing authentic or sham N95 facemasks. Clinical tests were performed four times to determine changes in the levels of biomarkers of airway inflammation, endothelial dysfunction, and oxidative stress within 24 h after exposure.

The facemasks removed 48–75% of number concentrations of ambient air particles between 5.6 and 560 nm in diameter. After adjustments for multiple comparison, the exhaled nitric oxide level and the levels of interleukin-1α, interleukin-1β, and interleukin-6 in exhaled breath condensate increased significantly in all subjects; however, the increases in those wearing authentic facemasks were statistically significantly lower than in the sham group. No significant between-group difference was evident in the urinary creatinine-corrected malondialdehyde level. In arterial stiffness indicators, the ejection duration of subjects wearing authentic facemasks was higher after exposure compared to the sham group; no significant between-group difference was found in augmentation pressure or the augmentation index.

Conclusions

In young healthy adults, N95 facemasks partially reduced acute particle-associated airway inflammation, but neither systemic oxidative stress nor endothelial dysfunction improved significantly. The clinical significance of these findings long-term remains to be determined.

Trial registration

The trial registration number (TRN) for this study is ChiCTR1800016099, which was retrospectively registered on May 11, 2018.

Electronic supplementary material

The online version of this article (10.1186/s12989-018-0266-0) contains supplementary material, which is available to authorized users.

Intrinsic Frequency Analysis and Fast Algorithms

Intrinsic Frequency (IF) has recently been introduced as an ample signal processing method for analyzing carotid and aortic pulse pressure tracings. The IF method has also been introduced as an effective approach for the analysis of cardiovascular system dynamics. The physiological significance, convergence and accuracy of the IF algorithm has been established in prior works. In this paper, we show that the IF method could be derived by appropriate mathematical approximations from the Navier-Stokes and elasticity equations. We further introduce a fast algorithm for the IF method based on the mathematical analysis of this method. In particular, we demonstrate that the IF algorithm can be made faster, by a factor or more than 100 times, using a proper set of initial guesses based on the topology of the problem, fast analytical solution at each point iteration, and substituting the brute force algorithm with a pattern search method. Statistically, we observe that the algorithm presented in this article complies well with its brute-force counterpart. Furthermore, we will show that on a real dataset, the fast IF method can draw correlations between the extracted intrinsic frequency features and the infusion of certain drugs.

What's Next for Acute Heart Failure Research?

Each year over one million patients with acute heart failure (AHF) present to a United States emergency department (ED). The vast majority are hospitalized for further management. The length of stay and high postdischarge event rate in this cohort have changed little over the past decade. Therapeutic trials have failed to yield substantive improvement in postdischarge outcomes; subsequently, AHF care has changed little in the past 40 years. Prior research studies have been fragmented as either "inpatient" or "ED-based." Recognizing the challenges in identification and enrollment of ED patients with AHF, and the lack of robust evidence to guide management, an AHF clinical trials network was developed. This network has demonstrated, through organized collaboration between cardiology and emergency medicine, that many of the hurdles in AHF research can be overcome. The development of a network that supports the collaboration of acute care and HF researchers, combined with the availability of federally funded infrastructure, will facilitate more efficient conduct of both explanatory and pragmatic trials in AHF. Yet many important questions remain, and in this document our group of emergency medicine and cardiology investigators have identified four high-priority research areas.

Wave intensity of aortic root pressure as diagnostic marker of left ventricular systolic dysfunction

Background

Systolic left ventricular function strongly influences the blood pressure waveform. Therefore, pressure-derived parameters might potentially be used as non-invasive, diagnostic markers of left ventricular impairment. The aim of this study was to investigate the performance of pressure-based parameters in combination with electrocardiography (ECG) for the detection of left ventricular systolic dysfunction defined as severely reduced ejection fraction (EF).

Methods and results

Two populations, each comprising patients with reduced EF and pressure-matched controls, were included for the main analysis (51/102 patients) and model testing (44/88 patients). Central pressure was derived from radial readings and used to compute blood flow. Subsequently, pulse wave analysis and wave intensity analysis were performed and the ratio of the two peaks of forward intensity (SDR) was calculated as a novel index of ventricular function. SDR was significantly decreased in the reduced EF group (2.5 vs. 4.4, P<0.001), as was central pulse pressure, augmentation index and ejection duration (ED), while the QRS-duration was prolonged. SDR and ED were independent predictors of ventricular impairment and when combined with QRS in a simple decision tree, a reduced EF could be detected with a sensitivity of 92% and a specificity of 80%. The independent power of ED, SDR and QRS to predict reduced EF was furthermore confirmed in the test population.

Conclusion

The detection or indication of reduced ejection fraction from pressure-derived parameters seems feasible. These parameters could help to improve the quality of cardiovascular risk stratification or might be used in screening strategies in the general population.

In-vitro investigation of the hemodynamic responses of the cerebral, coronary and renal circulations with a rotary blood pump installed in the descending aorta

This study investigates the hemodynamic responses of the cardiovascular system when a rotary blood pump is operating in the descending aorta, with a focus on the cerebral, coronary and renal autoregulation, using our in-house cardiovascular emulator. Several improvements have been made from our previous studies. A novel coronary system was developed to replicate the native coronary perfusion. Three pinch valves actuated by stepper motors were used to simulate the regional autoregulation systems of the native cerebral, coronary and renal circulations. A rotary pump was installed in the descending aorta, in series with the heart, and the hemodynamic responses of the cardiovascular system were investigated with a focus on cerebral, coronary and renal circulation over a wide range of pump rotor speeds. Experiments were performed twice, once with the autoregulation systems active and once with the autoregulation systems inactive, to reflect that there will be some impairment of autoregulatory systems in a patient with heart failure. It was shown that by increasing the rotor speed to 3000 rpm, the cardiac output was improved from 2.9 to 4.1 L/min as a result of an afterload reduction induced by the pressure drop upstream of the pump. The magnitudes of changes in perfusion in the cerebral, coronary and renal circulations were recorded with regional autoregulation systems active and inactive.

Clinical and Research Considerations for Patients With Hypertensive Acute Heart Failure: A Consensus Statement from the Society for Academic Emergency Medicine and the Heart Failure Society of America Acute Heart Failure Working Group

Management approaches for patients in the emergency department (ED) who present with acute heart failure (AHF) have largely focused on intravenous diuretics. Yet, the primary pathophysiologic derangement underlying AHF in many patients is not solely volume overload. Patients with hypertensive AHF (H-AHF) represent a clinical phenotype with distinct pathophysiologic mechanisms that result in elevated ventricular filling pressures. To optimize treatment response and minimize adverse events in this subgroup, we propose that clinical management be tailored to a conceptual model of disease that is based on these mechanisms. This consensus statement reviews the relevant pathophysiology, clinical characteristics, approach to therapy, and considerations for clinical trials in ED patients with H-AHF.

In-vitro investigation of cerebral-perfusion effects of a rotary blood pump installed in the descending aorta

This study describes use of a cardiovascular simulator to replicate the hemodynamic responses of the cerebrovascular system with a mechanical circulatory support device operating in the descending aorta. To do so, a cerebral autoregulation unit was developed which replicates the dilation and constriction of the native cerebrovascular resistance system and thereby regulates the cerebral flow rate within defined limits. The efficacy of the replicated autoregulation mechanism was investigated by introducing a number of step alterations in mean aortic pressure and monitoring the cerebral flow. The steady responses of the cerebral flow to changes in mean aortic pressure were in good agreement with clinical data. Next, a rotary pump, modeling a mechanical circulatory support device, was installed in the descending aorta and the hemodynamic responses of the cerebral system were investigated over a wide range of pump operating conditions. Insertion of a mechanical circulatory support device in the descending aorta presented an improved cardiac output as a result of afterload reduction. It was observed that the primary drop in cerebral flow, caused by the pump in the descending aorta, was compensated over the course of five seconds due to a gradual decrease in cerebrovascular resistance. The experimental results suggest that the implantation of a mechanical circulatory support device in the descending aorta, a less invasive procedure than typical mechanical circulatory support implantation, will not have an adverse effect on the cognitive function, provided that the cerebral autoregulation is largely unimpaired.

Association of aortic stiffness and wave reflections with coronary flow reserve in women without obstructive coronary artery disease: An ancillary study from the National Heart, Lung, and Blood Institute-sponsored Women's Ischemia Syndrome Evaluation (WISE)

BACKGROUND

Increased aortic stiffness and reduced coronary flow reserve (CFR) independently predict adverse outcomes. But information about relationships between arterial properties and CFR in subjects without obstructive coronary artery disease (CAD) is limited.

METHODS

CFR was measured (Doppler flow wire and intracoronary adenosine) in 50 women (age 53 ± 11 years) with symptoms and signs of myocardial ischemia without obstructive CAD. Aortic pulse wave velocity (aPWV), a measure of aortic stiffness, was obtained via catheter pullback; radial artery pressure waves were measured by applanation tonometry and central aortic pressure synthesized.

RESULTS

Overall, CFR (mean 2.61 ± 0.47) was significantly correlated with aPWV (r = -0.51), pulse wave amplification (r = 0.45), augmented pressure (r = -0.48), augmentation index (AIx, r = -0.44), aortic systolic pressure (r = -0.49), left ventricular wasted energy (LVEw, r = -0.47) (all P < .001), systolic pressure time index (r = -0.37, P < .008), and rate pressure product (r = -0.29, P < .04). In the multiple regression model including aPWV, CFR was still significantly correlated with aPWV (P < .008) and aortic systolic pressure (P < .01). No other measures contributed significant additional information. Women with CFR ≤2.5 versus those with CFR >2.5 had greater aPWV (894 ± 117 vs 747 ± 93 cm/s, P < .001), augmented pressure (14 ± 4.9 vs 11 ± 4.1 mmHg, P < .008), AIx (32 ± 6.6 vs 27 ± 6.6%, P < .003), LVEw (30 ± 12 vs 21 ± 10 dyne-s/cm(2) × 10(2), P < .02) and reduced pulse pressure amplification (1.20 ± .07 vs 1.26 ± .10, P < .008) and pressure wave travel time (133 ± 7.3 vs 138 ± 6.9 milliseconds, P < .04).

CONCLUSIONS

Among symptomatic women without obstructive CAD, CFR was inversely related to aortic systolic pressure and indices of aortic stiffness. These changes in arterial properties increase left ventricular afterload requiring the ventricle to generate additional, but wasted, energy that increases indices of myocardial oxygen demand, reduces CFR and increases vulnerability to ischemia.

American Society of Hypertension position paper: central blood pressure waveforms in health and disease

A number of devices are available which noninvasively estimate central aortic blood pressure using a variety of approaches such as tonometry or oscillometry. In this position paper, we discuss how the central pressure waveform is generated and measured, how central pressure waveforms appear in health and disease, the predictive value of central blood pressure measurements, the effects of interventions on waveforms, and areas of future need in this field of clinical and research endeavor.

Wearable Sensing of In-Ear Pressure for Heart Rate Monitoring with a Piezoelectric Sensor

In this study, we developed a novel heart rate (HR) monitoring approach in which we measure the pressure variance of the surface of the ear canal. A scissor-shaped apparatus equipped with a piezoelectric film sensor and a hardware circuit module was designed for high wearability and to obtain stable measurement. In the proposed device, the film sensor converts in-ear pulse waves (EPW) into electrical current, and the circuit module enhances the EPW and suppresses noise. A real-time algorithm embedded in the circuit module performs morphological conversions to make the EPW more distinct and knowledge-based rules are used to detect EPW peaks. In a clinical experiment conducted using a reference electrocardiogram (ECG) device, EPW and ECG were concurrently recorded from 58 healthy subjects. The EPW intervals between successive peaks and their corresponding ECG intervals were then compared to each other. Promising results were obtained from the samples, specifically, a sensitivity of 97.25%, positive predictive value of 97.17%, and mean absolute difference of 0.62. Thus, highly accurate HR was obtained from in-ear pressure variance. Consequently, we believe that our proposed approach could be used to monitor vital signs and also utilized in diverse applications in the near future.

Duration of Diabetes Predicts Aortic Pulse Wave Velocity and Vascular Events in Alström Syndrome

CONTEXT

Alström syndrome is characterized by increased risk of cardiovascular disease from childhood.

OBJECTIVE

To explore the association between risk factors for cardiovascular disease, aortic pulse wave velocity, and vascular events in Alström syndrome.

DESIGN

Cross-sectional analyses with 5-year follow-up.

SETTING

The UK NHS nationally commissioned specialist clinics for Alström syndrome.

PATIENTS

Thirty-one Alström patients undertook vascular risk assessment, cardiac studies, and aortic pulse wave velocity measurement. Subsequent clinical outcomes were recorded.

INTERVENTIONS

Insulin resistance was treated with lifestyle intervention and metformin, and diabetes with the addition of glitazones, glucagon-like peptide 1 agonists, and/or insulin. Thyroid and T deficiencies were corrected. Dyslipidemia was treated with statins and nicotinic acid derivatives. Cardiomyopathy was treated with standard therapy as required.

MAIN OUTCOME MEASURES

The associations of age, gender, and risk factors for cardiovascular disease with aortic pulse wave velocity were assessed and correlated with the effects of reduction in left ventricular function. Vascular events were monitored for 5 years.

RESULTS

Aortic pulse wave velocity was positively associated with the duration of diabetes (P = .001) and inversely with left ventricular ejection fraction (P = .036). Five of the cohort with cardiovascular events had higher aortic pulse wave velocity (P = .0247), and all had long duration of diabetes.

CONCLUSIONS

Duration of diabetes predicted aortic pulse wave velocity in Alström syndrome, which in turn predicted cardiovascular events. This offers hope of secondary prevention because type 2 diabetes can be delayed or reversed by lifestyle interventions.

Intrinsic Frequency and the Single Wave Biopsy: Implications for Insulin Resistance

Insulin resistance is the hallmark of classical type II diabetes. In addition, insulin resistance plays a central role in metabolic syndrome, which astonishingly affects 1 out of 3 adults in North America. The insulin resistance state can precede the manifestation of diabetes and hypertension by years. Insulin resistance is correlated with a low-grade inflammatory condition, thought to be induced by obesity as well as other conditions. Currently, the methods to measure and monitor insulin resistance, such as the homeostatic model assessment and the euglycemic insulin clamp, can be impractical, expensive, and invasive. Abundant evidence exists that relates increased pulse pressure, pulse wave velocity (PWV), and vascular dysfunction with insulin resistance. We introduce a potential method of assessing insulin resistance that relies on a novel signal-processing algorithm, the intrinsic frequency method (IFM). The method requires a single pulse pressure wave, thus the term " wave biopsy."

Determinants and covariates of central pressures and wave reflections in systolic heart failure

BACKGROUND

In general, higher blood pressure levels and increased central pulsatility are indicators for increased cardiovascular risk. However, in systolic heart failure (SHF), this relationship is reversed. Therefore, the aim of this work is to compare pulsatile hemodynamics between patients with SHF and controls and to clarify the relationships between measures of cardiac and arterial function in the two groups.

METHODS

We used parameters derived from angiography, echocardiography, as well as from pulse wave analysis (PWA) and wave separation analysis (WSA) based on non-invasively assessed pressure and flow waves to quantify cardiac function, aortic stiffness and arterial wave reflection in 61 patients with highly reduced (rEF) and 122 matched control-patients with normal ejection fraction (nEF).

RESULTS

Invasively measured pulse wave velocity was comparable between the groups (8.6/8.05 m/s rEF/nEF, P = 0.24), whereas all measures derived by PWA and WSA were significantly decreased (augmentation index: 18.1/24.8 rEF/nEF, P < 0.01; reflection magnitude: 56.3/62.1 rEF/nEF, P < 0.01). However, these differences could be explained by the shortened ejection duration (ED) in rEF (ED: 269/308 ms rEF/nEF, P < 0.01; AIx: 22.2/22.8 rEF/nEF, P = 0.7; RM: 59.3/60.6 rEF/nEF, P = 0.47 after adjustment for ED). Ventricular function was positively associated with central pulse pressures in SHF in contrast to no or even a slightly negative association in controls.

CONCLUSIONS

The results suggest that the decreased measures of pulsatile function may be caused by impaired systolic function and altered interplay of left ventricle and vascular system rather than by a real reduction of wave reflections or aortic stiffness in SHF.

Eardrum-inspired active sensors for self-powered cardiovascular system characterization and throat-attached anti-interference voice recognition

The first bionic membrane sensor based on triboelectrification is reported for self-powered physiological and behavioral measurements such as local internal body pressures for non-invasive human health assessment. The sensor can also be for self-powered anti-interference throat voice recording and recognition, as well as high-accuracy multimodal biometric authentication, thus potentially expanding the scope of applications in self-powered wearable medical/health monitoring, interactive input/control devices as well as accurate, reliable, and less intrusive biometric authentication systems.

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.

Non-invasive wave reflection quantification in patients with reduced ejection fraction

The non-invasive quantification of arterial wave reflection is an increasingly important concept in cardiovascular research. It is commonly based on pulse wave analysis (PWA) of aortic pressure. Alternatively, wave separation analysis (WSA) considering both aortic pressure and flow waveforms can be applied. Necessary estimates of aortic flow can be measured by Doppler ultrasound or provided by mathematical models. However, this approach has not been investigated intensively up to now in subjects developing systolic heart failure characterized by highly reduced ejection fraction (EF). We used non-invasively generated aortic pressure waveforms and Doppler flow measurements to derive wave reflection parameters in 61 patients with highly reduced and 122 patients with normal EF. Additionally we compared these readings with estimates from three different flow models known from literature (triangular, averaged, Windkessel). After correction for confounding factors, all parameters of wave reflection (PWA and WSA) were comparable for patients with reduced and normal EF. Wave separations assessed with the Windkessel based model were similar to those derived from Doppler flow in both groups. The averaged waveform performed poorer in reduced than in normal EF, whereas triangular flow represented a better approximation for reduced EF. Overall, the non-invasive assessment of WSA parameters based on mathematical models compared to ultrasound seems feasible in patients with reduced EF.

Arterial wave reflections and ventricular-vascular interaction in patients with left ventricular systolic dysfunction

Central aortic pressure waveform (AoPW) is the summation of a forward-traveling wave generated by the left ventricle and a backward-traveling wave caused by the reflection of the forward wave. The aim of this study was to evaluate the effect of ventricular-vascular coupling on the morphology of AoPW in chronic heart failure patients with different degrees of left ventricular systolic dysfunction (LVSD) using pulse wave analysis (PWA). PWA of AoPW and left ventricular (LV) function were evaluated by applanation tonometry in 26 control subjects, in 12 patients with left ventricular ejection fraction (LVEF) ≤ 30%, and in 14 patients with LVEF > 30%. Augmentation pressure, augmentation index, wasted energy, and ejection duration were lower in patients with LVEF ≤ 30% than in those with LVEF > 30% and in control subjects. Furthermore, augmentation index showed an inverse correlation with Doppler mitral E-wave amplitude (r = -0.40; P = 0.04) and E/A ratio (r = -0.42; P = 0.03) and a direct correlation with deceleration time of mitral E-waves (r = 0.39; P = 0.04). In patients with severe LVSD (LVEF ≤ 30%), aortic wave reflections negatively interfere with LV function and induce a shortening of ejection duration. In contrast, AoPW is similar in patients with moderate LVSD (LVEF > 30%) and in control subjects.

Arterial stiffness, central pressures, and incident hospitalized heart failure in the chronic renal insufficiency cohort study

BACKGROUND

Chronic kidney disease is associated with an increased risk of heart failure (HF). We aimed to evaluate the role of large artery stiffness, brachial, and central blood pressure as predictors of incident hospitalized HF in the Chronic Renal Insufficiency Cohort (CRIC), a multiethnic, multicenter prospective observational study of patients with chronic kidney disease.

METHODS AND RESULTS

We studied 2602 participants who were free of HF at baseline. Carotid-femoral pulse wave velocity (CF-PWV; the gold standard index of large artery stiffness), brachial, and central pressures (estimated via radial tonometry and a generalized transfer function) were assessed at baseline. Participants were prospectively followed up to assess the development of new-onset hospitalized HF. During 3.5 years of follow-up, 154 participants had a first hospital admission for HF. CF-PWV was a significant independent predictor of incident hospitalized HF. When compared with the lowest tertile, the hazard ratios among subjects in the middle and top CF-PWV tertiles were 2.33 (95% confidence interval, 1.37-3.97; P=0.002) and 5.24 (95% confidence interval, 3.22-8.53; P<0.0001), respectively. After adjustment for multiple confounders, the hazard ratios for the middle and top CF-PWV tertiles were 1.95 (95% confidence interval, 0.92-4.13; P=0.079) and 3.01 (95% confidence interval, 1.45-6.26; P=0.003), respectively. Brachial systolic and pulse pressure were also independently associated with incident hospitalized HF, whereas central pressures were less consistently associated with this end point. The association between CF-PWV and incident HF persisted after adjustment for systolic blood pressure.

CONCLUSIONS

Large artery stiffness is an independent predictor of incident HF in chronic kidney disease, an association with strong biological plausibility given the known effects of large artery stiffening of left ventricular pulsatile load.

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.

U-shaped relationship of left ventricular ejection time index and all-cause mortality

BACKGROUND

Previous studies have suggested that systolic and diastolic heart failure is associated with alterations of left ventricular ejection time index (LVETI). We sought to examine the relation of LVETI to mortality in an elderly population.

METHODS

We prospectively enrolled 852 patients undergoing cardiac catheterization for suspected coronary artery disease (CAD) in 2001 and 2002. LVETI was measured noninvasively using radial applantation tonometry and pulse waveform analysis. Mortality data were assessed by telephone interviews with general practitioners, hospital records, and the national mortality register.

RESULTS

The mean age was 64.8 years, 60.7% of subjects were men, 70.1% of subjects had significant CAD, and 28.6% of subjects had impaired systolic function. After a mean follow-up of 8.2 ± 2.3 years, 183 deaths occurred. At baseline, LVETI was significantly associated with age, systolic and diastolic blood pressure, pulse pressure, and N-terminal probrain natriuretic peptide. A shorter LVETI was significantly and independently associated with impaired systolic function. Kaplan-Meier analysis revealed that both prolonged and shortened ejection time index (1st and 3rd tertile LVETI) were associated with a decreased survival probability (P <0.05, log-rank-test) compared with normal LVETI (2nd tertile). In multivariable Cox regression analysis, the hazard ratios for all-cause mortality were 1.66 for 1st tertile LVETI (P = 0.01) and 1.75 for 3rd tertile LVETI (P = 0.006). The effect of a shortened LVETI on mortality was partly due to the effect of impaired systolic function on ejection duration.

CONCLUSIONS

We observed a U-shaped relation between ejection duration and all-cause mortality.

In vitro comparison of two different mechanical circulatory support devices installed in series and in parallel

This study investigates the novel approach of placing a ventricular assist pump in the descending aorta in series configuration with the heart and compares it with the two traditional approaches of left-ventricle-to-ascending-aorta (LV-AA) and left-ventricle-to-descending-aorta (LV-DA) placement in parallel with the heart. Experiments were conducted by using the in-house simulator of the cardiovascular blood-flow loop (SCVL). The results indicate that the use of the LV-AA in-parallel configuration leads to a significant improvement in the systemic and pulmonic flow as the level of continuous flow is increased; however, this approach is considered highly invasive. The use of the LV-DA in-parallel configuration leads to an improvement in the systemic and pulmonic flow at lower levels of continuous flow but at higher levels of pump support leads to retrograde flow. In both in-parallel configurations, increasing the level of pump continuous flow leads to a decrease in pulsatility to a certain extent. The results of placing the pump in the descending aorta in series configuration show that the pressure drop upstream of the pump facilitates cardiac output as a result of afterload reduction. In addition, the pressure rise downstream of the pump may assist with renal perfusion. However, at the same time, the pressure drop generated at the proximal part of the descending aorta induces a slight drop in carotid perfusion, which would be autoregulated by the brain in a native cardiovascular system. The pulse wave analysis shows that placing the pump in the descending aorta leads to improved pulsatility in comparison with the traditional in-parallel configurations.