Measurement Of Pulsatile Blood Flow Research Articles

Computing pulsatile blood flow of coronary artery under incomplete boundary conditions

BackgroundAccurate measurement of pulsatile blood flow in the coronary arteries enables coronary wave intensity analysis, which can serve as an indicator for assessing coronary artery physiology and myocardial viability. Computational fluid dynamics (CFD) methods integrating coronary angiography images and fractional flow reserve (FFR) offer a novel approach for computing mean coronary blood flow. However, previous methods neglect the inertial effect of blood flow, which may have great impact on pulsatile blood flow calculation. To improve the accuracy of pulsatile blood flow calculation, a novel CFD based method considering the inertia term is proposed. MethodsA flow resistance model based on Pressure-Flow vs.Time curves is proposed to model the resistance of the epicardial artery. The parameters of the flow resistance model can be fitted from the simulated pulsating flow rates and pressure drops of a specific mode. Then, pulsating blood flow can be calculated by combining the incomplete pressure boundary conditions under pulsating conditions which are easily obtained in clinic. Through simulation experiments, the effectiveness of the proposed method is validated in idealized and reconstructed 3D model of coronary artery. The impacts of key parameters for generating the simulated pulsating flow rates and pressure drops on the accuracy of pulsatile blood flow calculation are also investigated. ResultsFor the idealized model, the previously proposed Pressure-Flow model has a significant leading effect on the computed blood flow waveform in the moderate model, and this leading effect disappears with the increase of the degree of stenosis. The improved model proposed in this paper has no leading effect, the root mean square error (RMSE) of the proposed model is low (the left coronary mode:≤0.0160, the right coronary mode:≤0.0065) for all simulated models, and the RMSE decreases with an increase of stenosis. The RMSE is consistently small (≤0.0217) as the key parameters of the proposed method vary in a large range. It is verified in the reconstructed model that the proposed model significantly reduces the RMSE of patients with moderate stenosis (the Pressure-Flow model:≤0.0683, the Pressure-Flow vs.Time model:≤0.0297), and the obtained blood flow waveform has a higher coincidence with the simulated reference waveform. ConclusionsThis paper confirms that ignoring the effect of inertia term can significantly affect the accuracy of calculating pulsatile blood flow in moderate stenosis lesions, and the new method proposed in this paper can significantly improves the accuracy of calculating pulsatile blood flow in moderate stenosis lesions. The proposed method provides a convenient clinical method for obtaining pressure-synchronized blood flow, which is expected to facilitate the application of waveform analysis in the diagnosis of coronary artery disease.

In Vivo Pulse Wave Measurement Through a Multimode Fiber Diffuse Speckle Analysis System

Continuous monitoring of in vivo pulsatile blood flow and pulse wave velocity (PWV) is important for clinical applications. These parameters are correlated with physiological parameters, such as blood pressure and elasticity of blood vessels. A multimode fiber diffuse speckle contrast analysis (MMF-DSCA) system was developed for fast measurement of in vivo pulsatile blood flow and pulse wave velocity. With MMF and CCD sensor, the diffuse speckle could be captured and processed with higher temporal resolution of 3 ms. We also induced for the first time an MMF-DSCA for evaluation of PWV, which allows estimation of the blood pressure continuously. To validate its performance, both phantom and in vivo experiments were conducted. The results demonstrate that MMF-DSCA could achieve fast pulsatile blood flow measurement with detailed information of the pulse wave profile and velocity. Taking the advantages of being simple and cost-effective, the flexible system can be easily adapted for continuous monitoring of vital biosigns, such as heart rate, pulse wave, and blood pressure.

Fast pulsatile blood flow measurement in deep tissue through a multimode detection fiber.

.Significance: Noninvasive in vivo fast pulsatile blood flow measurement in deep tissue is important because the blood flow waveform is correlated with physiological parameters, such as blood pressure and elasticity of blood vessels. Compromised blood flow may cause diseases, such as stroke, foot ulcer, and myocardial ischemia. There is great clinical demand for a portable and cost-effective device for noninvasive pulsatile blood flow measurement.Aim: A diffuse-optics-based method, diffuse speckle pulsatile flowmetry (DSPF), was developed for fast measurement () of deep tissue blood flow noninvasively. To validate its performance, both a phantom experiment and in vivo demonstration were conducted.Approach: Over the past two decades, single-mode fibers have been used as detection fibers in most diffuse-optics-based deep tissue blood flow measurement modalities. We used a multimode (MM) detection fiber with a core size of for diffused speckle pattern detection. A background intensity correction algorithm was implemented for speckle contrast calculation. The MM detection fiber helped to achieve a level of deep tissue blood flow measurement similar to that of conventional modalities, such as diffuse correlation spectroscopy and diffuse speckle contrast analysis, but it increases the measurement rate of blood flow to 300 Hz.Results: The design and implementation of the DSPF system were introduced. The theory of the background intensity correction for the diffused speckle pattern detected by the MM fiber was explained. A flow phantom was built for validation of the performance of the DSPF system. An in vivo cuff-induced occlusion experiment was performed to demonstrate the capability of the proposed DSPF system.Conclusions: An MM detection fiber can help to achieve fast () pulsatile blood flow measurement in the proposed DSPF method. The cost-effective device and the fiber-based flexible probe increase the usability of the DSPF system significantly.

A Study of reversal of diastolic blood flow in the middle cerebral artery using doppler ultrasound in the prognostication in sick neonates

Background: The cerebral circulation is maintained on the principle of brain uniqueness cerebral autoregulation. Many factors such as oxygen, carbon dioxide, and blood pressure play a major role in the smooth journey of cerebral circulation. There is no clear marker used to assess the impending mortality in sick neonates. The resistive index (RI) is a measure of pulsatile blood flow, reflecting the resistance to flow caused by microvascular bed. The RI of the cerebral vessels is used to know the amount of blood that is flowing in the brain. Increased cerebral blood flow reduces the RI and decreased flow increases the resistance and the brain stays between the two, and hence, the autoregulation is maintained. When the cerebral autoregulation is lost, the flow in the diastole reverses and helps in the prognostication. Objective and Design: A prospective cohort study was conducted between March 2017 and May 2018 catering to both inborn and outborn neonates at Manipal Hospital, Bengaluru, to determine the importance of reversal of diastolic flow of RI in the middle cerebral artery as a marker of mortality in sick neonates. Subjects and Interventions: We enrolled 22 sick neonates both term and preterm. Normal resistive indices in neonates were taken as 0.6–0.9. Method: The RI was manually assessed in the middle cerebral artery using pulsed-wave Doppler. The mean RI was calculated from the average peak systolic velocity and end-diastolic velocity of at least five sequential stable waveforms. The reversal of diastolic flow in the RI was determined by the retrograde flow of waveform during diastole. Univariate and multivariate analyses were performed to identify prognostic factors for the overall survival, which was depicted using Kaplan–Meier curve.P< 0.05 was considered statistically significant. Results: Neonates who had a reversal of diastolic flow had a poor mean survival of 1.3 h when compared to those patients who did not have a reversal of flow of 133.8 days (hazard ratio [HR] – 4.66; 95.% confidence interval [CI]: 1.250–16.96) which was statistically significant (P = 0.022). Furthermore, birth weight <1000 g had a mean survival of 29 days, whereas birth weight >2500 g had a mean survival of 104 days (HR – 0.96; 95% CI: 0.460–2.032) which also was statistically significant (P < 0.001). Conclusion: As determined by univariate and multivariate analyses, the reversal of diastolic flow in the cerebral artery can strongly be used as a surrogate marker for impending mortality in a sick neonate.

Influence of probe pressure on the pulsatile diffuse correlation spectroscopy blood flow signal on the forearm and forehead regions.

.In a pilot study of 11 healthy adults (24 to 39 years, all male), we characterize the influence of external probe pressure on optical diffuse correlation spectroscopy (DCS) measurements of pulsatile blood flow obtained on the forearm and forehead. For external probe pressure control, a hand inflatable air balloon is inserted between the tissue and an elastic strap. The air balloon is sequentially inflated to achieve a wide range of external probe pressures between 20 and 250 mmHg on the forearm and forehead, which are measured with a flexible pressure sensor underneath the probe. At each probe pressure, the pulsatility index (PI) of arteriole blood flow on the forehead and forearm is measured with DCS (2.1-cm source-detector separation). We observe a strong correlation between probe pressure and PI on the forearm (, ), but not on the forehead (, ). The forearm measurements demonstrate the sensitivity of the DCS PI to skeletal muscle tissue pressure, whereas the forehead measurements indicate that DCS PI measurements are not sensitive to scalp tissue pressure. Note, in contrast to pulsatility, the time-averaged DCS blood flow index on the forehead was significantly correlated with probe pressure (, ). This pilot data appears to support the initiation of more comprehensive clinical studies on DCS to detect trends in internal pressure in brain and skeletal muscle.

Highly parallel, interferometric diffusing wave spectroscopy for monitoring cerebral blood flow dynamics.

Light-scattering methods are widely used in soft matter physics and biomedical optics to probe dynamics in turbid media, such as diffusion in colloids or blood flow in biological tissue. These methods typically rely on fluctuations of coherent light intensity, and therefore cannot accommodate more than a few modes per detector. This limitation has hindered efforts to measure deep tissue blood flow with high speed, since weak diffuse light fluxes, together with low single-mode fiber throughput, result in low photon count rates. To solve this, we introduce multimode fiber (MMF) interferometry to the field of diffuse optics. In doing so, we transform a standard complementary metal-oxide-semiconductor (CMOS) camera into a sensitive detector array for weak light fluxes that probe deep in biological tissue. Specifically, we build a novel CMOS-based, multimode interferometric diffusing wave spectroscopy (iDWS) system and show that it can measure ∼20 speckles simultaneously near the shot noise limit, acting essentially as ∼20 independent photon-counting channels. We develop a matrix formalism, based on MMF mode field solutions and detector geometry, to predict both coherence and speckle number in iDWS. After validation in liquid phantoms, we demonstrate iDWS pulsatile blood flow measurements at 2.5 cm source-detector separation in the adult human brain in vivo. By achieving highly sensitive and parallel measurements of coherent light fluctuations with a CMOS camera, this work promises to enhance performance and reduce cost of diffuse optical instruments.

Relationship Between ‘Immediate’ Resistive Index Measurement After Renal Transplantation and Renal Allograft Outcomes

BackgroundThe arterial resistive index, also referred to as the resistive index (RI) or Pourcelot Index, is a measure of pulsatile blood flow. Previous studies have demonstrated the usefulness of the RI as a predictor of allograft outcomes based on RI measurement in the later stages after transplantation. However, there is little evidence of the predictive value of “immediate” RI measurement within 24 hours after transplantation. MethodsWe performed a retrospective cohort study of 305 adult renal transplants carried out between 2003 and 2013. The associations between immediate RI measurement (within 24 hours after transplantation) and donor, recipient, and surgical factors were analyzed. In addition, the correlations between immediate RI measurement and renal allograft outcomes, including delayed graft function (DGF) and transplant failure (TF), also were evaluated. ResultsFrom a cohort of 305 patients, 52 were excluded on the basis of on confounding factors. Of the remaining 253 patients, the mean age was 48.4 years, 57.5% were male, and approximately one-third had diabetes. Two hundred twenty-six patients had an RI < 0.8, whereas only 27 had an RI ≥ 0.8. Significant associations were found between elevated RI (≥0.8) and both DGF (odds ratio = 3.22, P = .006) and TF (odds ratio = 3.54, P = .008). ConclusionsImmediate RI measurement after renal transplantation is a strong predictor of both DGF and TF.

Measurement of real pulsatile blood flow using X-ray PIV technique with CO2 microbubbles.

Synchrotron X-ray imaging technique has been used to investigate biofluid flows in a non-destructive manner. This study aims to investigate the feasibility of the X-ray PIV technique with CO2 microbubbles as flow tracer for measurement of pulsatile blood flows under in vivo conditions. The traceability of CO2 microbubbles in a pulsatile flow was demonstrated through in vitro experiment. A rat extracorporeal bypass loop was used by connecting a tube between the abdominal aorta and jugular vein of a rat to obtain hemodynamic information of actual pulsatile blood flows without changing the hemorheological properties. The decrease in image contrast of the surrounding tissue was also investigated for in vivo applications of the proposed technique. This technique could be used to accurately measure whole velocity field information of real pulsatile blood flows and has strong potential for hemodynamic diagnosis of cardiovascular diseases.

Renal resistive index can predict response to furosemide in septic patients with oliguria

Oliguria is common in septic patients and is frequently therapeutically addressed with loop diuretics; that is, furosemide. Diuretic treatment in shock and hypovolemia is not rational, but can be tried in oliguric patients with normovolemia or hypervolemia and without hypotension. In such patients it still does not always increase dieresis and can also be harmful. The resistive index is a measure of pulsatile blood flow that reflects the resistance to blood flow caused by the microvascular bed distal to the site of measurement. It can reflect functional status of the tissue distal to the point of measurement. We investigated whether measuring the renal resistive index (RI) could be helpful in determining which patients will respond to furosemide treatment.

Measurement of blood flow rates in the lower extremities with use of a nuclear magnetic resonance based instrument

Direct, noninvasive measurement of pulsatile blood flow to the human extremity is now possible by means of a flow measurement instrument that is based on the principles of nuclear magnetic resonance. The instrument uses a physically independent calibration module as a primary calibration standard. Volumetric calibration of this module indicates that it is precise and accurate over the range of 0 to 100 ml/min. The calibration module is used, in turn, to calibrate an electromagnetic flow sensor that is incorporated into the instrumentation. The calibration module and the electromagnetic sensor were found to be linearly related over the range of 5 to 100 ml/min, with a regression correlation coefficient of 0.996. The calibrated electromagnetic flow sensor is used as a secondary standard for calibration of the nuclear magnetic resonance sensor. Blood flow measurements, obtained by use of this method, agree closely with those obtained by plethysmographic methods. They differ from the plethysmographic results in that magnetic resonance flows will distinguish between the at-rest blood flow in the normal extremity and the flows seen in the extremity (also at rest) with claudication. Based on the results obtained from studying a limited number of limbs with a high degree of ischemia, the method will not distinguish the limb with ischemia from the limb with claudication. Limitations of the method and refinements required to make the method clinically useful are discussed.

Measurement of blood flow rates in the lower extremities with use of a nuclear magnetic resonance based instrument

Direct, noninvasive measurement of pulsatile blood flow to the human extremity is now possible by means of a flow measurement instrument that is based on the principles of nuclear magnetic resonance. The instrument uses a physically independent calibration module as a primary calibration standard. Volumetric calibration of this module indicates that it is precise and accurate over the range of 0 to 100 ml/min. The calibration module is used, in turn, to calibrate an electromagnetic flow sensor that is incorporated into the instrumentation. The calibration module and the electromagnetic sensor were found to be linearly related over the range of 5 to 100 ml/min, with a regression correlation coefficient of 0.996. The calibrated electromagnetic flow sensor is used as a secondary standard for calibration of the nuclear magnetic resonance sensor. Blood flow measurements, obtained by use of this method, agree closely with those obtained by plethysmographic methods. They differ from the plethysmographic results in that magnetic resonance flows will distinguish between the at-rest blood flow in the normal extremity and the flows seen in the extremity (also at rest) with claudication. Based on the results obtained from studying a limited number of limbs with a high degree of ischemia, the method will not distinguish the limb with ischemia from the limb with claudication. Limitations of the method and refinements required to make the method clinically useful are discussed.

Pulsatile flow simulator for comparison of cardiac output measurements by electromagnetic flow meter and thermodilution.

This study examined a pulsatile flow simulator for the purpose of evaluating two measurement devices, an extracorporeal flow probe with an electromagnetic flow meter and several thermodilution catheters. We measured the performance of these devices in a range of low to high flows. Using either saline or blood as a perfusate, we obtained different results with these fluids (p less than 0.001). Each catheter behaved in a linear manner, although variation occurred among the catheters with both saline (minimum slope 1.090, maximum slope 1.190) and blood (minimum slope 1.107, maximum slope 1.154). An increase in rate and stroke volumes of the simulator did not demonstrate an identifiable trend in error. The thermodilution catheters were most accurate at 5.0 L/min irrespective of rate, stroke volume, or perfusate used. In contrast, the electromagnetic flow meter accurately represented flows across the wide range of outputs examined (2.4 to 10.7 L/min). (Slope with saline 1.091, slope with blood 1.080) Throughout the range of flow, the flow meter gave a calibration line 5% higher with blood than with saline. The results indicate that accurate measurement of pulsatile blood flow can be achieved in vitro with an electromagnetic flow meter using saline as a perfusate, provided a correction factor is determined and applied to convert values for saline to accurate values for blood.

Laser Doppler velocimetry measurement of pulsatile blood flow in capillary tubes

Laser Doppler velocimetry (LDV) is a technique which can be applied to determine the maximum velocity, V max, of red blood cells (RBCs) in retinal arteries. Under conditions of constant flow, the flow rate can be accurately derived from V max and the vessel diameter through the assumption of a parabolic velocity profile. Our in vitro study of pulsatile flow evaluated the validity of integrating the instantaneous LDV-measured V max over the flow cycle to derive a mean flow rate. Measurements were made on suspensions of polystyrene spheres in water and RBCs in physiological saline perfusing glass capillary tubes (70–200 μm diameter) at velocities in the range of retinal artery blood velocities. The LDV-determined flow rate differed from an independently measured flow rate by less than 1% for the spheres and by less than 12% for the RBCs. Whether the velocity profile of blood remains parabolic at every phase of the flow cycle, as is the case for the spheres in water, cannot be concluded from this study.

Theoretical analysis of the CW doppler ultrasonic flowmeter.

The widespread application of ultrasonic techniques for the measurement of pulsatile blood flow has been hampered by the lack of a detailed theoretical understanding of the Doppler ultrasonic flowmeter. A general model for the Doppler flowmeter based upon stochastic considerations of the scattering of ultrasound by blood is introduced in this paper. The model characterizes the back- scattered ultrasound as a Gaussian random process and the expression for the autocovariance function is derived. For the CW Doppler flowmeter, the power spectral density function is computed, and its significance is emphasized: measurement of blood flow velocity corresponds to estimation of the average frequency of the Doppler power spectrum.

A new ultrasonic flowmeter for intravascular application.

An instrument for the measurement of pulsatile blood flow has been developed. The device uses a small probe suitable for intravascular insertion, and the method of measurement employs a combination of ultrasonic pulse techniques and phase detection.

The Measurement of Pulsatile Blood Flow by the Computed Pressure Gradient Technique

The Measurement of Pulsatile Blood Flow by the Computed Pressure Gradient Technique