Axial Blood Flow Research Articles

THERMOREGULATION IN THE HEART AND THE BIOPHYSICS OF CORONARY ARTERIAL FLOW

AbstractThe right and left coronary arteries are the principal sources of supply of oxygenated blood to the heart. Arising from the proximal rim of the ascending aorta, these arteries course along and over the surface of the organ, sending out branches that penetrate axial blood flow through arteries is governed or maintained by multifarious physical laws.The heart, an electrically stimulated muscular pump, squirts and receives circulating blood through its systolic and diastolic exertions. The non-stop life-long rapid action of the organ not just expends enormous energy but also generates considerable heat. While there are a number of factors that help the heart dissipate and reduce heat, a few other biophysical factors contribute hugely to maintain a thermostatic milieu.Circulation through vessels is maintained with a high degree of efficiency through combined actions of ejection systolic pressure, elasticity of the conducting arterial channels, and the proximo-distal decrease in diameters of arteries.This brief write-up discusses some of physics regulatng fluid flow dynamics and attempts to exemplify the significant role of 'centrifugal force' as a hitherto overlooked physical force in coronary haemodynamics. The application of biophysical postulates to cardiac cycle may help in furthering our understanding of coronary blood circulation and the multi-factorial influences on its functional integrity. It is inferenced that, the finding may have a number of applications and result in a better understanding of cardiac circulatory dynamics.

Optical microangiography of retina and choroid and measurement of total retinal blood flow in mice

We present a novel application of optical microangiography (OMAG) imaging technique for visualization of depth-resolved vascular network within retina and choroid as well as measurement of total retinal blood flow in mice. A fast speed spectral domain OCT imaging system at 820nm with a line scan rate of 140 kHz was developed to image the posterior segment of eyes in mice. By applying an OMAG algorithm to extract the moving blood flow signals out of the background tissue, we are able to provide true capillary level imaging of the retinal and choroidal vasculature. The microvascular patterns within different retinal layers are presented. An en face Doppler OCT approach [Srinivasan et al., Opt Express 18, 2477 (2010)] was adopted for retinal blood flow measurement. The flow is calculated by integrating the axial blood flow velocity over the vessel area measured in an en face plane without knowing the blood vessel angle. Total retinal blood flow can be measured from both retinal arteries and veins. The results indicate that OMAG has the potential for qualitative and quantitative evaluation of the microcirculation in posterior eye compartments in mouse models of retinopathy and neovascularization.

Editorial Comment: Correlate blood pressure, not blood flow, with atherosclerosis

Unsteady and three-dimensional simulation of blood flow in the human aortic arch. J Biomech Eng 2002;124:378–87. [15] Kilner PJ, Yang GZ, Mohiaddin RH, Firmin DN, Longmore DB. Helical and retrograde secondary flow patterns in the aortic arch studied by three-directional magnetic resonance velocity mapping. Circulation 1993;88(5 Pt 1):2235–47. [16] Batten JR, Nerem RM. Model study of flow in curved and planar arterial bifurcations. Cardiovasc Res 1982;16:178–86. [17] Matsumoto Y, Honda T, Hamada M, Toyama T, Matsuoka H, Hiwada K. Evaluation of short axial blood flow pattern in thoracic descending aorta by use of tagging cine magnetic resonance. Angiology 1994;45: 917–22. [18] Mercan H, Atalik K. Vortex formation in lid-driven arc-shape cavity flows at high Reynolds numbers. Eur J Mech B Fluids 2009;28:61–71. [19] Naruse T, Tanishita K. Large curvature effect on pulsatile entrance flow in a curved tube: model experiment simulating blood flow in an aortic arch. J Biomech Eng 1996;118:180–6. [20] Zabielski L, Mestel AJ. Helical flow around arterial bends for varying body mass. J Biomech Eng 2000;122:135–42. [21] Friedman M, Giddens D. Blood flow in major blood vessels—modeling and experiments. Ann Biomed Eng 2005;33:1710–3. [22] Gnasso A, Irace C, Carallo C, De Franceschi MS, Motti C, Mattioli PL et al. In vivo association between low wall shear stress and plaque in subjects with asymmetrical carotid atherosclerosis. Stroke 1997;28:993–8. [23] Slager CJ, Wentzel JJ, Gijsen FJH, Schuurbiers JCH, van der Wal AC, van der Steen AFW et al. The role of shear stress in the generation of rupture-prone vulnerable plaques. Nat Clin Pract Cardiovasc Med 2005;2: 401–7. [24] Dhawan SS, Avati Nanjundappa RP, Branch JR, Taylor WR, Quyyumi AA, Jo H et al. Shear stress and plaque development. Expert Rev Cardiovasc Ther 2010;8:545–56. [25] Hoi Y, Zhou YQ, Zhang X, Henkelman RM, Steinman DA. Correlation between local hemodynamics and lesion distribution in a novel aortic regurgitation murine model of atherosclerosis. Ann Biomed Eng 2011;39: 1414–22.

Use of the Impella™ Microaxial Blood Pump for Ablation of Hemodynamically Unstable Ventricular Tachycardia

Ablation for ventricular tachycardia remains a challenge with suboptimal procedural success rates. One of the major causes of difficulty is precipitous hypotension when ventricular tachycardia is induced precluding even rapid mapping of the arrhythmia. We report the successful use of the Impella microcirculatory axial blood flow pump in 3 patients with hemodynamically unstable ventricular tachycardia that allowed successful completion of the procedure. In these 3 patients, there was no evidence of Impella-related valvular disturbance, iatrogenic ventricular arrhythmias, or interference with mapping and ablation catheter movement.

Concept and Anatomical Basis of Microdissected Tailoring Method for Free Flap Transfer

For a refined microsurgical reconstruction, it is desirable to adjust the flap to fit the three-dimensional details of the defect. Essentially, each vessel arborized in the subcutaneous adipose tissue supplies axial blood flow to an individual small area surrounding the vessel. Therefore, free alteration of the flap would be possible if the anatomy of these branches could be identified during surgery. The microdissected tailoring method is a new procedure for alteration of the flap, observing the branches of the perforator directly after microdissection. By means of this procedure, three flaps were transferred to complex tissue defects. In addition, among intraadipose branches of 59 perforators, 90 cases of three types of microdissected thin perforator flap transfer were measured to classify the anatomical variations relating to microdissected tailoring of the flap. All flap transfers were uneventful and no circulatory failure of the flaps was observed. Statistical analyses reveal that the intermuscular septum perforator branches at the deeper layer of the adipose tissue and then spreads more widely in the adipose layer than that of muscle perforator, regardless of the type of flap and the length of the intraadipose vessel. Microdissected tailoring of the flap provides the best solution for flap alteration in the reconstruction of a complex-shaped tissue defect. It represents a change in the concept of free flap transfer, because the flap is prepared according to the individual anatomy of the intraadipose vessel.

Estimating 2-D vector velocities using multidimensional spectrum analysis

Wilson (1991) presented an ultrasonic wideband estimator for axial blood flow velocity estimation through the use of the 2-D Fourier transform. It was shown how a single velocity component was concentrated along a line in the 2-D Fourier space, where the slope was given by the axial velocity. Later, it was shown that this approach could also be used for finding the lateral velocity component by also including a lateral sampling. A single velocity component would then be concentrated along a plane in the 3-D Fourier space, tilted according to the 2 velocity components. This paper presents 2 new velocity estimators for finding both the axial and lateral velocity components. The estimators essentially search for the plane in the 3- D Fourier space, where the integrated power spectrum is largest. The first uses the 3-D Fourier transform to find the power spectrum, while the second uses a minimum variance approach. Based on this plane, the axial and lateral velocity components are estimated. Several phantom measurements, for flow-to-depth angles of 60, 75, and 90 degrees, were performed. Multiple parallel lines were beamformed simultaneously, and 2 different receive apodization schemes were tried. The 2 estimators were then applied to the data. The axial velocity component was estimated with an average standard deviation below 2.8% of the peak velocity, while the average standard deviation of the lateral velocity estimates was between 2.0% and 16.4%. The 2 estimators were also tested on in vivo data from a transverse scan of the common carotid artery, showing the potential of the vector velocity estimation method under in vivo conditions.

A Novel Integrated Rotor of Axial Blood Flow Pump Designed With Computational Fluid Dynamics

Due to the smaller size, smaller artificial surface, and higher efficiency, axial blood pumps have been widely applied in clinic in recent years. However, because of its high rotor speed, axial flow pump always has a high risk for hemolysis, which the red blood cells devastated by the shearing of tip clearance flow. We reported a novel design with the integrated blade-shroud structure that was expected to solve this problem by abolishing the radial clearance between blade and casing designed with the techniques of computational fluid dynamics (CFD). However, the numerical simulation result of the newly designed structure showed an unexpected backflow (where flow velocity is reverse of the main flow direction) at the blade tip. In order to eliminate this backflow, four flow passes were attempted, and the expansion angles (which reflect the radial amplification of the flow pass, on the meridional section, and should be defined as the angle between the center line of the flow pass and the axial direction) of the blades of the integrated rotor are 0 degrees, 8 degrees, 15 degrees, and 20 degrees, respectively. In the CFD result, it could be easily found as the expansion angles increased, the backflow was restrained gradually, and was eliminated at last. After numerous "cut and try" circles, the pump model was finally optimized. The numerical simulation of this model also showed a stable hydraulic characteristic.

In vivoImaging of Oral Mucositis in an Animal Model Using Optical Coherence Tomography and Optical Doppler Tomography

To assess noninvasive optical coherence tomography (OCT) and optical Doppler tomography (ODT) for early detection and evaluation of chemotherapy-induced oral mucositis. Cheek pouches of 10 Syrian golden hamsters were imaged using OCT/ODT during development of chemotherapy-induced mucositis. I.p. injections of 5-fluorouracil and mechanical irritation induced oral lesions. At 2, 4, 7, and 11 days, one hamster was sacrificed and processed for histopathology. OCT images were visually examined; ODT results were semiquantified. Imaging data were compared with histologic findings. During the development of mucositis, OCT/ODT identified the following events: (a) change in epithelial thickness (beginning on day 2), (b) loss of surface keratinized layer continuity (beginning on day 4), (c) loss of epithelial (day 4 onwards) and submucosal integrity (day 7 onwards), (d) changes in axial blood flow velocity (increased on days 2 and 4; decreased on day 7), and (e) changes in blood vessel size (diameter doubled on day 2; quadrupled on day 4; unchanged on day 7). The semiquantitative imaging-based scoring system identified the severity of mucositis as defined by histopathology. The combination of imaging criteria used allowed for the detection of early, intermediate, and late mucositic changes. Imaging data gave higher scores compared with clinical scores early on, suggesting that the imaging-based diagnostic scoring was more sensitive to early mucositic change than the clinical scoring system. Once mucositis was established, imaging and clinical scores converged. OCT/ODT identified chemotherapy-induced oral changes before their clinical manifestation, and the proposed scoring system for oral mucositis was validated for the semiquantification of mucositic change.

Section 10: Surgical Approaches to the Treatment of Heart Failure

Section 10: Surgical Approaches to the Treatment of Heart Failure

Hemodynamic effects of intermittent pneumatic compression in patients with critical limb ischemia

Traditional teaching assumes that the distal arterial tree is maximally dilated in patients with critical limb ischemia (CLI). Endovascular or arterial bypass procedures are the commonly used interventions to increase distal perfusion. However, other forms of treatment such as spinal cord stimulation or intermittent pneumatic compression (IPC) have been shown to improve limb salvage rates. This prospective study was designed to determine if the use of IPC increases popliteal, gastrocnemial, collateral arterial, and skin blood flow in patients with CLI. Twenty limbs with CLI in 20 patients (mean age, 74 years) were evaluated with duplex ultrasound scans and laser Doppler fluxmetry in the semi-erect position before, during, and after IPC. One pneumatic cuff was applied on the foot and the other on the calf. The maximum inflation pressure was 120 mm Hg and was applied for 3 seconds at three cycles per minute. All patients had at least two-level disease by arteriography. Fourteen limbs were characterized as inoperable, and six were considered marginal for reconstruction. Flow volumes were measured in the popliteal, medial gastrocnemial, and a genicular collateral artery. Skin blood flux was measured on the dorsum of the foot at the same time. Significant flow increase during the application of IPC was found in all three arteries (18/20 limbs) compared with baseline values (P < .02). The highest change was seen in the popliteal, followed by the gastrocnemial and the collateral artery. After the cessation of IPC, the flow returned to baseline. This was attributed to the elevation of time average velocity, as the diameter of the arteries remained unchanged. The skin blood flux increased significantly as well (P < .03). In the two limbs without an increase in the arterial or skin blood flow, significant popliteal vein reflux was found. Both limbs were amputated shortly after. IPC increases axial, muscular, collateral, and skin blood flow in patients with CLI and may be beneficial to those who are not candidates for revascularization. Patients with significant venous reflux may not benefit from IPC. This supports the theory that one of the mechanisms by which IPC enhances flow is by increasing the arteriovenous pressure gradient.

BSS-based filtering of physiological and ARFI-induced tissue and blood motion

Blind source separation (BSS) for adaptive filtering is presented in application to imaging both physiological and acoustic radiation force impulse (ARFI)-induced tissue and blood motion in the common carotid artery. The collected raw radiofrequency (RF) data includes vessel wall motion, blood flow and ARFI-induced motion. In the context of these complex motion patterns, the same BSS adaptive filtering method was employed for three diverse applications: 1. clutter filtering ensembles prior to blood velocity estimation, 2. extracting small axial velocity components from noisy velocity measurements given large flow angles and 3. reducing noise in measured ARFI-induced tissue displacement profiles to enhance differentiation of local tissue structures. The filter separated physiological vessel wall motion from axial blood flow and ARFI-induced motion; successful filter performance is demonstrated in velocity estimates, color flow images and ARFI displacement profiles. The results demonstrate the breadth of applications for BSS adaptive filtering in the clinical imaging environment. (E-mail: caterina.gallippi@duke.edu)

Three-dimensional blood flow analysis in a wide-necked internal carotid artery-ophthalmic artery aneurysm.

The aim of this study was to evaluate axial and secondary flow structures in a wide-necked internal carotid artery-ophthalmic artery aneurysm, one of the most common locations for endovascular coil placement. A clear acrylic aneurysm model was manufactured from a three-dimensional computerized tomography angiogram. Intraaneurysm blood flow analysis was conducted using an acrylic aneurysm model together with laser Doppler velocimetry and particle imaging velocimetry. The maximal axial blood flow velocities in the inflow and outflow zones at the aneurysm orifice were noted at the peak systolic phase, measuring 46.8 and 24.9% of that in the parent artery, respectively. The mean size of the inflow zone during one cardiac cycle was 44.3 +/- 9.8% (range 35.6-58.7%) the size of the axial section at the aneurysm orifice. In the lower and upper planes of the aneurysm dome, the mean size of inward and outward flow areas were 43.3 +/- 6.7% and 43.8 +/- 6.8% the size of the axial cross-sectional plane, respectively. The axial flow velocity structures were dynamically altered throughout the cardiac cycle, particularly at the aneurysm orifice. The fastest secondary flow at the opening was also noted at the peak systolic and early diastolic phases. Axial blood flow velocity was slower in the upper axial plane of the aneurysm dome than in the lower one. Conversely, the secondary flow component was faster in the upper plane. The side-wall aneurysm in this study did not demonstrate a simple flow pattern as was previously seen in ideally shaped experimental aneurysms in vitro and in vivo. The flow patterns of inflow and outflow zones were very difficult to predict based on the limited flow information provided on standard digital subtraction angiography, even in an aneurysm with a relatively simple dome shape.

Left ventricular assist device as bridge to heart transplantation--lessons learned with the MicroMed DeBakey axial blood flow pump.

The MicroMed DeBakey left ventricular assist device (LVAD) axial blood flow pump was used as bridge to heart transplantation (HTx) in patients with terminal heart failure. The aim was to evaluate this novel mechanical circulatory support system in regard to overall outcome. Prospective study in 15 HTx candidates (mean age 40+/-7 years) with terminal heart failure and maximal medical treatment due to ischemic cardiomyopathy (CMP, n=5), dilated CMP (n=3), restrictive CMP (n=2), unclassified CMP (n=1), metabolic CMP (n=1), valvular CMP (n=1) and congenital CMP (n=2). All patients were implanted with a MicroMed DeBakey LVAD. A rescue procedure was necessary in eight critical patients, while seven underwent elective LVAD implantation. Procedures were performed via median sternotomy, in normotherm femoro-femoral CPB (mean duration 59+/-1 min). Oral Marcoumar (INR 2.0-3.0) and Aspirin (100 mg daily) were started as soon as possible. Patients were discharged into a specialized rehabilitation clinic from which it was possible to release them home after a few weeks. Successful implantation and discharge from ICU (mean stay 10+/-7 days) was possible in 11 patients. Seven were transplanted (mean support 50.7 days) and one is awaiting HTx (support >310 days) in the comfort of his home (NYHA I). Survival was 100% among the transplanted patients. Of the seven elective implants, five, and of the eight rescue procedures three patients underwent successful HTx. Four patients died early, while three patients died late on pump support due to intracranial hemorrhage (n=2, 73 and 76 days) and chest infection (n=1, 124 days). All survivors were discharged from hospital, with significant decrease in NYHA class (mean 3.8-2.4 (n=11)). Treadmill testing showed increased exercise tolerance, from 35 to 71W (n=4). Plasma BNP values (mean 950-162 ng/l (n=4)) and pulmonary resistance (mean 316-194.5 dyne s/cm(5) (n=3)) decreased significantly during LVAD support. The MicroMed DeBakey LVAD is simple to implant; outpatient treatment is safe and efficient. Patients' condition and pulmonary resistances normalize within 6 weeks, making previously considered inoperable patients amenable for HTx. HTx can be performed in low-risk situation, allowing better donor-recipient matching and improving overall outcome.

Decorrelation-based blood flow velocity estimation: effect of spread of flow velocity, linear flow velocity gradients, and parabolic flow.

In recent years, a new method to measure transverse blood flow, based on the decorrelation of the radio frequency (RF) signals has been developed. In this paper, we investigated the influence of nonuniform flow on the velocity estimation. The decorrelation characteristics of transverse blood flow using an intravascular ultrasound (IVUS) array catheter are studied by means of computer modeling. Blood was simulated as a collection of randomly located point scatterers; moving this scattering medium transversally across the acoustical beam represented flow. First-order statistics were evaluated, and the signal-to-noise ratio from the signals were measured. The correlation coefficient method was used to present the results. Three velocity profiles were simulated: random spread of blood-flow velocity, linear blood-flow velocity gradient, and parabolic blood-flow. Radio frequency and envelope signals were used to calculate the decorrelation pattern. The results were compared to the mean decorrelation pattern for plug blood-flow. The RF signals decorrelation patterns were in good agreement with those obtained for plug blood flow. Envelope decorrelation patterns show a close agreement with the one for plug blood flow. For axial blood flow, there is a discrepancy between decorrelation patterns. The results presented here suggest that the decorrelation properties of an IVUS array catheter for measuring quantitative transverse blood flow probably will not be affected by different transverse blood-flow conditions.

Behavior of free jejunal flaps after early disruption of blood supply

We describe three free jejunal flaps that lost their axial blood supply in the early postoperative period—two flaps on the 7th day and the third on the 17th day. At 7 days, reestablishment of axial blood flow was essential to flap survival, whereas after 17 days, vascularization from the recipient bed was adequate to maintain viability. Based on these observations, a conservative approach to flap salvage for cases with pedicle disruption at 17 days or later is recommended.

Fractal fluctuations in transcranial Doppler signals

Cerebral blood flow (CBF) velocity measured using transcranial Doppler ultrasonography (TCD) is not strictly constant, but has both a systematic and random component. This behavior may indicate that the axial blood flow in the middle cerebral artery is a chaotic process. Herein we use the relative dispersion, the ratio of the standard deviation to the mean, to show by systematically aggregating the data that the correlation in the beat-to-beat CBF time series is a modulated inverse power law. This scaling of the CBF time series indicates the existence of long-time memory in the underlying control process. We argue herein that the control system has allometric properties that enable it to maintain a relatively constant brain perfusion.

Kombinierte Erfassung von axialem und transversalem Blutfluß mit einem 50MHz-Ultraschall-B-Bild-System für die Dermatologie

High frequency broadband ultrasound in the range from 50 to 150 MHz allows high resolution and nonivasive imaging as well as functional diagnostics of the skin in dermatology [2]. Besides morphologic imaging, functional diagnostics is of great interest, especially concerning qualitative and quantitative detection of blood flow in the microcirculatory system of the skin. Special requirements mainly related to small vessel diameters and low flow velocities determine the design of an imaging system and the development of appropriate methods for echo signal processing. In this paper a method for the combined estimation of (with respect to the direction of sound propagation) axial and transversal blood flow and, therefore, for the estimation of the true velocity is presented. Special emphasis is put on high spatial and high velocity resolution. Results obtained using simulation data as well as flow phantom measurements are presented.

Discussion

Background. We have previously presented a method for performing coronary artery bypass graft operation on the beating heart without cardiopulmonary bypass (CPB). This method has now been explored. Method. Thirty-two patients were prospectively randomized. The study group was operated on using an axial blood flow pump (Hemopump; HP) as circulatory support. Operations were performed on the beating heart. The control group was operated on using CPB, aortic cross-clamping, and cardioplegic arrest. Results. All patients went through the procedure without major complications, and were discharged from the hospital. No statistical differences were observed between the groups for time on support (HP, 60.5 minutes; CPB, 70.5 minutes) or total operating time (HP, 178 minutes; CPB, 162 minutes). The number of grafts was greater in the CPB group (HP, 1.8; range, 1 to 3; CPB, 2.5; range, 1 to 4; p = 0.03). Statistical differences were found for intraoperative bleeding (HP mean, 312 mL; CPB mean, 582 mL; p = 0.0003) and myocardial trauma as measured by postoperative troponin-T values (HP, 0.23 μg/L; CPB, 1.17 μg/L; p = 0.004). Conclusions. Hemopump-supported coronary artery bypass graft operation has been shown to be a safe and feasible procedure with the potential benefits of reduced operative bleeding and myocardial damage without prolonging intraoperative support or total operating time.

Beating heart coronary surgery supported by an axial blood flow pump

Background. We have previously presented a method for performing coronary artery bypass graft operation on the beating heart without cardiopulmonary bypass (CPB). This method has now been explored. Method. Thirty-two patients were prospectively randomized. The study group was operated on using an axial blood flow pump (Hemopump; HP) as circulatory support. Operations were performed on the beating heart. The control group was operated on using CPB, aortic cross-clamping, and cardioplegic arrest. Results. All patients went through the procedure without major complications, and were discharged from the hospital. No statistical differences were observed between the groups for time on support (HP, 60.5 minutes; CPB, 70.5 minutes) or total operating time (HP, 178 minutes; CPB, 162 minutes). The number of grafts was greater in the CPB group (HP, 1.8; range, 1 to 3; CPB, 2.5; range, 1 to 4; p = 0.03). Statistical differences were found for intraoperative bleeding (HP mean, 312 mL; CPB mean, 582 mL; p = 0.0003) and myocardial trauma as measured by postoperative troponin-T values (HP, 0.23 μg/L; CPB, 1.17 μg/L; p = 0.004). Conclusions. Hemopump-supported coronary artery bypass graft operation has been shown to be a safe and feasible procedure with the potential benefits of reduced operative bleeding and myocardial damage without prolonging intraoperative support or total operating time.

Modeling the temporal fluctuations of the cerebral blood flow velocity waveforms using surrogate data testing

The objective of this study is to find out which mathematical model best explains the temporal fluctuations of the axial blood flow velocity waveforms in the basal arteries of the brain. Blood flow velocity time series were sampled by transcranial Doppler (TCD) examination of the middle cerebral arteries in 10 healthy volunteers. A recently developed mathematical test (surrogate data analysis) was used to examine whether the spectral Doppler maximum waveform is consistent with some; prespecified model (null hypothesis). We tested four different null hypotheses. 1. Uncorrelated white noise. 2. Linearly filtered noise. 3. Linearly filtered noise with a static nonlinear amplitude transformation. 4. Noisy nonlinear limit cycle. All null hypotheses except the last one could be rejected. We conclude that the TCo waveforms are best described as a nonlinear limit cycle with some percentage of noisel either dynamical and/or observationall which is uncorrelated from one single oscillation to the next. These results are a strong argument to perform nonlinear analysis in future TCD studies in order to obtain a better understanding of the cerebral hemodynamics. [Neural Res 1998; 20: 381–390]