Valve origin of the aortic incisura

Personalized Pressure Conditions and Calibration for a Predictive Computational Model of Coronary and Myocardial Blood Flow

Predictive modeling of hyperemic coronary and myocardial blood flow (MBF) greatly supports diagnosis and prognostic stratification of patients suffering from coronary artery disease (CAD). In this work, we propose a novel strategy, using only readily available clinical data, to build personalized inlet conditions for coronary and MBF models and to achieve an effective calibration for their predictive application to real clinical cases. Experimental data are used to build personalized pressure waveforms at the aortic root, representative of the hyperemic state and adapted to surrogate the systolic contraction, to be used in computational fluid-dynamics analyses. Model calibration to simulate hyperemic flow is performed in a "blinded" way, not requiring any additional exam. Coronary and myocardial flow simulations are performed in eight patients with different clinical conditions to predict FFR and MBF. Realistic pressure waveforms are recovered for all the patients. Consistent pressure distribution, blood velocities in the large arteries, and distribution of MBF in the healthy myocardium are obtained. FFR results show great accuracy with a per-vessel sensitivity and specificity of 100% according to clinical threshold values. Mean MBF shows good agreement with values from stress-CTP, with lower values in patients with diagnosed perfusion defects. The proposed methodology allows us to quantitatively predict FFR and MBF, by the exclusive use of standard measures easily obtainable in a clinical context. This represents a fundamental step to avoid catheter-based exams and stress tests in CAD diagnosis.

The Dicrotic Notch: Mechanisms, Characteristics, and Clinical Correlations

PURPOSE OF REVIEW

The dicrotic notch (DN) has long been considered a marker of arterial stiffness and compliance. Herein, we explored the recent developments in vascular medicine research in an attempt to assess the DN utility in clinical cardiovascular medicine.

RECENT FINDINGS

Since its discovery, several studies have attempted to measure the changes in different parameters of the DN in physiological and pathological states. Despite the significance of their findings, the clinical role of the DN remained limited. This may have been related to the difficulty of measuring the DN via indwelling arterial catheters in the past. However, over the past two decades, several non-invasive methods have been developed, which may re-ignite interest in DN research. The DN may have broader applications in clinical cardiovascular medicine. Further research is needed to establish the accuracy of DN non-invasive measurement methods and compare its prognostic value to other circulatory parameters.

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.

Electrical Impedance Plethysmography Versus Tonometry To Measure the Pulse Wave Velocity in Peripheral Arteries in Young Healthy Volunteers: a Pilot Study

The leading cause of health loss and deaths worldwide are cardiovascular diseases. A predictor of cardiovascular diseases and events is the arterial stiffness. The pulse wave velocity (PWV) can be used to estimate arterial stiffness non-invasively. The tonometer is considered as the gold standard for measuring PWV. This approach requires manual probe fixation above the artery and depends on the skills of the operator. Electrical impedance plethysmography (IPG) is an interesting alternative using skin surface sensing electrodes, that is miniaturizable, cost-effective and allows measurement of deeper arteries. The aim of this pilot study was to explore if IPG can be a suitable technique to measure pulse wave velocity in legs as an alternative for the tonometer technique. The PWV was estimated by differences in the ECG-gated pulse arrival times (PAT) at the a. femoralis, a. popliteal, a. tibialis dorsalis and a. dorsalis pedis in nine healthy young adults using IPG and the SphygmoCor tonometer as a reference. The estimated PWV results from bioimpedance and the tonometer were fairly in agreement, and the beat-to-beat variability in PAT was similar. This pilot study indicates that the use of IPG may be a good alternative for estimating PWV in the legs.

Simulating re-reflections of arterial pressure waves at the aortic valve using difference equations

Re-reflections of arterial pressure waves at the aortic valve and their influence on aortic wave shape are only poorly understood so far. Therefore, the aim of this work is to establish a model enabling the simulation of re-reflection and to test its properties. A mathematical difference equation model is used for the simulations. In this model, the aortic blood pressure is split into its forward and backward components which are calculated separately. The respective equations include reflection percentages representing reflections throughout the arterial system and a reflection coefficient at the aortic valve. While the distal reflections are fixed, different scenarios for the reflection coefficient at the valve are simulated. The results show that the model is capable to provide physiological pressure curves only if re-reflections are assumed to be present during the whole cardiac cycle. The sensitivity analysis on the reflection coefficient at the aortic valve shows various effects of re-reflections on the modelled blood pressure curve. Higher levels of the reflection coefficient lead to higher systolic and diastolic pressure values. The augmentation index is notably influenced by the systolic level of the reflection coefficient. This difference equation model gives an adequate possibility to simulate aortic pressure incorporating re-reflections at the site of the aortic valve. Since a strong dependence of the aortic pressure wave on the choice of the reflection coefficient have been found, this indicates that re-reflections should be incorporated into models of wave transmission. Furthermore, re-reflections may also be considered in methods of arterial pulse wave analysis.

In vivo laser Doppler holography of the human retina

The eye offers a unique opportunity for the non-invasive exploration of cardiovascular diseases. Optical angiography in the retina requires sensitive measurements, which hinders conventional full-field laser Doppler imaging schemes. To overcome this limitation, we used digital holography to perform laser Doppler perfusion imaging of human retina with near-infrared light. Two imaging channels with a slow and a fast CMOS camera were used simultaneously for real-time narrowband measurements, and offline wideband measurements, respectively. The beat frequency spectrum of optical interferograms recorded with the fast (up to 75 kHz) CMOS camera was analyzed by short-time Fourier transformation. Power Doppler images drawn from the Doppler power spectrum density qualitatively revealed blood flow in retinal vessels over 512 × 512 pixels covering 2.4 × 2.4 mm² on the retina with a temporal resolution down to 1.6 ms. The sensitivity to lateral motion as well as the requirements in terms of sampling frequency are discussed.

Hemodynamics of multiple versus single 50 percent coronary arterial stenoses

The purpose of this study was to compare coronary blood flow in the presence of multiple fixed coronary arterial stenoses with that in the presence of a single stenosis of equivalent length and diameter. The study was performed using an in vitro pulse duplicating system. The aortic root section consisted of an acrylic mold of the root of the aorta of a calf. The coronary system was designed to produce coronary flow with physiological magnitudes and phasic patterns. Aortic and left ventricular pressures as well as the reduction in pressure across the coronary test section containing the stenotic segments were measured with catheter-tip micromanometers. Coronary flow was measured with a cannulating electromagnetic flow transducer. The fluid viscosity was 0.04 poise. Studies were performed sequentially with one 2 mm long arterial segment with a stenosis of 50 percent of luminal diameter, two such stenotic segments and three such stenotic segments in series. A single 4 mm long, 50 percent diameter stenotic segment and a 6 mm long, 50 percent diameter stenotic segment were also studied. The heart rate was 71 beats/min, stroke volume 80 ml and aortic pressure 140/75 mm Hg. A single 2 mm long, 50 percent stenotic segment caused a 6 percent reduction of coronary flow; three such stenoses in series caused a 19 percent reduction of coronary flow. In contrast, a single 6 mm long, 50 percent diameter stenotic segment caused only an 8 percent reduction of coronary flow. The results suggest that in a maximally dilated coronary bed, a greater reduction of coronary flow would occur in the presence of multiple short stenoses than in the presence of a single stenosis of equivalent length and diameter.

Hemodynamic determinants of the frequency and amplitude of a musical murmur produced by a regurgitant mitral bioprosthetic valve

The purpose of this study was to assess the hemodynamic determinant of the amplitude and frequency of a musical murmur produced by a regurgitant degenerated bioprosthetic valve in the mitral position. The prosthetic valve, obtained at surgery, was studied in the mitral position of an in vitro pulse duplicating system. In vitro, the valve produced a musical murmur that was caused by flutter of a flail leaflet. When the peak pressure difference between the left ventricle and left atrium was increased from 95 to 150 mm Hg, the fundamental frequency of the musical murmur increased from 91 to 187 hertz and the amplitude increased from 2,080 to 11,420 dynes/cm2. The fundamental frequency of the musical murmur was linearly related to the peak systolic pressure difference between the left ventricle and the left atrium (correlation coefficient [r] = 0.99). Similarly, the fundamental frequency of the musical murmur was linearly related to the magnitude of regurgitant flow across the valve (r = 0.99); and the regurgitant flow as expected was linearly related to the systolic pressure difference between the left ventricle and left atrium. The amplitude of the musical murmur was also related to both the peak systolic pressure difference between the left ventricle and left atrium (r = 0.99) and the magnitude of regurgitant flow (r = 0.99). These results indicate that the magnitude of regurgitant flow, determined by the systolic pressure difference between the left ventricle and left atrium, was a determinant of both the amplitude and the frequency of the musical murmur.

Mechanism of a musical systolic murmur caused by a degenerated porcine bioprosthetic valve

The cause of a musical (cooing) murmur produced by a degenerated bioprosthetic valve in the mitral position was investigated. Spectral analysis of the murmur recorded at the chest wall at the site of the maximum palpable impulse showed virtually all sound in a narrow frequency band around the dominant frequency of 158 hertz. The same valve, surgically removed and mounted in the mitral position in a pulse duplicating system, produced an audible musical murmur detected by a phonocatheter in the atrial chamber. Nearly all of the sound-pressure occurred in a narrow band of frequency around 145 hertz. High speed motion pictures (500 frames/s) showed systolic flutter of a flail leaflet. The frequency of this leaflet flutter was 142 hertz. Hot film anemometry showed minimal turbulence, all located near the margin of the regurgitant leaflet. The intensity of the murmur was unrelated to the intensity of turbulence. A second degenerated bioprosthetic valve that produced in vivo a typical blowing holosystolic mitral regurgitant murmur produced in vitro a murmur with a broad range of frequencies (20 to 500 hertz). With this valve, the intensity of the murmur was related to the intensity of the turbulence. Motion pictures showed no leaflet flutter. Flutter of an insufficient valve leaflet causing uniform and periodic high frequency fluctuating pressures therefore appeared to be the cause of the musical quality of the systolic murmur in a degenerated bioprosthetic valve.

Mechanism of early systolic closure of the aortic valve in discrete membranous subaortic stenosis

The mechanism of the apparent early closure of the aortic valve in patients with discrete membranous subaortic stenosis was studied. Discrete membranous subaortic stenosis was simulated in vitro to assess the fluid dynamic characteristics in the region of the aortic valve that may be responsible for the early closure. In the presence of a simulated fixed membranous subaortic obstruction, early systolic closure of the aortic valve was observed on high-speed motion pictures. Opening and early closure of the valve involved only one of the three aortic leaflets. Closure of the open leaflet was associated with the development of a pronounced pressure drop across the open leaflet caused by a large decrease of pressure in the main stream of flow relative to the pressure in the sinus of Valsalva. The pressure decrease in the main stream of flow resulted from a loss of pressure energy caused by an increase in the kinetic energy of the fluid caused by turbulence. Early systolic closure of the aortic valve in discrete membranous subaortic stenosis, therefore, results from the development of a pressure drop across the open leaflet caused by fluid dynamic factors related to the development of turbulent blood flow distal to the subvalvular obstruction.

Effect of turbulent blood flow on systolic pressure contour in the ventricles and great vessels: significance related to anacrotic and bisferious pulses

The effect of turbulent blood flow on the contour of systolic pressure in the left and right ventricles and great vessels was investigated in 64 patients undergoing diagnostic cardiac catheterization. Intracardiac pressure and sound were recorded using a catheter-tip micromanometer. Measurements were made in normal subjects and patients with a variety of disorders including aortic stenosis, hypertrophic obstructive cardiomyopathy, coarctation of the aorta and atrial septal defect. Observations showed a consistent association of the intracardiac murmur, which is indicative of turbulence, with a transient reduction of the centrally recorded systolic pressure. The resultant abnormal systolic pressure contour can be explained on the basis of fluid dynamic considerations related to turbulence.

Use of the systolic time intervals in clinical pharmacology

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