Blood Velocity Measurements Research Articles

Measurement of hippocampal arteriolar diameter and blood velocity in awake head-fixed mice

Cerebral hypoperfusion is associated with neurodegeneration. However, the influence of disease on the microcirculation of specific brain regions is poorly understood. In the current study, we validated a technical approach that allows us to simultaneously image arteriolar diameter and blood velocity in the hippocampi of awake, head-fixed mice. The approach involved implanting a gradient-Index (GRIN) lens into the hippocampus and cementing it in place together with a steel head-fixation bar. Imaging was performed after 7-14 days recovery. On the day of imaging, we intravenously administered Alexa Fluor 633 hydrazide (1.25 mg/kg) to label arterioles, and after 90 minutes, secured the mice on a custom-built stage of a widefield fluorescence microscope. We measured blood velocity in parallel with vessel diameter by imaging fluorescent latex beads infused by tail vein cannulation. Vessel diameter and blood velocity were assessed in 14 vessels from 6 mice. Hypercapnia induces cerebral vasodilation and increases cerebral blood flow. In our experiments, inhalation of 10% CO 2 caused a 12.1 ± 6% (mean ± SEM) increase in vessel diameter and a significant (P<0.01, student’s t-test) increase in blood velocity from 1.09 ± 0.1 to 1.73 ± 0.2 cm/s (mean ± SEM). These data demonstrate the feasibility of this approach to assess microvascular function and perfusion in highly localized brain regions. NIH grant (HL142906) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A Method for High-Frequency Mechanical Scanning Ultrasonic Flow Imaging with Motion Compensation.

Mechanical scanning with a single transducer is an alternative method for high-frequency ultrasound imaging, which is simple in structure, convenient to implement, and low in cost. However, traditional mechanical scanning ultrasonic imaging introduces additional Doppler shift due to the movement of the transducer, which brings a challenge for blood velocity measurement. An improved mechanical scanning system for high-frequency ultrasonic color Doppler flow imaging is developed in this paper. The mechanical scanning system has a scanning stroke range of 15 mm, a maximum scanning speed of 168 mm/s, and an imaging depth of 20 mm. Since the mechanical scanning of the system is not in uniform motion, motion compensation was applied to achieve high-precision imaging both in B-mode and Doppler mode. The experiment results show that the system imaging resolution can reach about 140 μm in B-mode imaging, the relative velocity error is less than 5% in color Doppler flow imaging at different flow rates, and the CNR of power Doppler flow imaging of this system is greater than 15 dB. The proposed mechanical scanning imaging system can achieve high-resolution structure imaging and color flow imaging, which can provide more diagnostic information for the practical diagnosis and broaden the application range of mechanical scanning ultrasound imaging.

Ultrasound flow phantom for transcranial Doppler: An assessment of angular mismatch effect on blood velocity measurement in comparison to optical particle image velocimetry

Detecting abnormal blood flow is possible through transcranial Doppler (TCD) ultrasound by measuring blood velocity in cerebral arteries. Velocity measurements are at the highest precision when the direction of blood flow coincides with the ultrasound beam. However, because TCD is typically performed blindly (i.e., without a B-mode), a 0° interrogation angle is usually assumed. This leads to a common issue of angular mismatch. This study quantitatively shows the angular mismatch effects on the measured velocities using a TCD ultrasound flow phantom compared with the velocities measured by optical particle image velocimetry (PIV) as control. Resulting errors with and without ultrasound machine angular correction were also considered. An ultrasound phantom developed by combining polyvinyl alcohol hydrogel (PVA-H), quartz glass as a scatterer, and a gypsum plate as a skull bone was utilized to approximate the middle cerebral artery TCD measurement from the temporal window. The PVA-H and quartz glass compositions were controlled to achieve transparency and enable PIV velocity measurement. Then, TCD velocity measurement was conducted on several interrogation and mismatch angles. Comparison results revealed that without an ultrasound machine angle correction, all measurements yielded underestimation with 73.9% at the highest in the 80° interrogation window at the 130 mL/min flow. On the other hand, with the correction, the errors in almost all angles were comparatively lower; however, at 80° at the 124 mL/min flow, a maximum overestimation rate of 113.7% was found, showing a larger error magnitude. Therefore, we find that angular mismatch, especially in larger angles, leads to inaccurate velocity measurements in TCD. Our results suggest that despite angle correction, velocity errors may still occur when the interrogation angle changes.

High-speed measurement of retinal arterial blood flow in the living human eye with adaptive optics ophthalmoscopy.

We present a technique to measure the rapid blood velocity in large retinal vessels with high spatiotemporal resolution. Red blood cell motion traces in the vessels were non-invasively imaged using an adaptive optics near-confocal scanning ophthalmoscope at a frame rate of 200 fps. We developed software to measure blood velocity automatically. We demonstrated the ability to measure the spatiotemporal profiles of the pulsatile blood flow with a maximum velocity of 95-156 mm/s in retinal arterioles with a diameter >100 µm. High-speed and high-resolution imaging increased the dynamic range, enhanced sensitivity, and improved the accuracy when studying retinal hemodynamics.

Effect of Localized Vibration Massage on Popliteal Blood Flow.

There is a broad scope of literature investigating whole-body vibration (WBV) effects on blood flow (BF). However, it is unclear how therapeutic localized vibrations alter BF. Low-frequency massage guns are advertised to enhance muscle recovery, which may be through BF changes; however, studies using these devices are lacking. Thus, the purpose of this study was to determine if popliteal artery BF increases from localized vibration to the calf. Twenty-six healthy, recreationally active university students (fourteen males, twelve females, mean age 22.3 years) participated. Each subject received eight therapeutic conditions randomized on different days with ultrasound blood flow measurements. The eight conditions combined either control, 30 Hz, 38 Hz, or 47 Hz for a duration of 5 or 10 min. BF measurements of mean blood velocity, arterial diameter, volume flow, and heart rate were measured. Using a cell means mixed model, we found that both control conditions resulted in decreased BF and that both 38 Hz and 47 Hz resulted in significant increases in volume flow and mean blood velocity, which remained elevated longer than the BF induced by 30 Hz. This study demonstrates localized vibrations at 38 Hz and 47 Hz significantly increase BF without affecting the heart rate and may support muscle recovery.

Cerebral blood flow and immediate and sustained executive function benefits following single bouts of passive and active exercise

Passive exercise occurs when an individual’s limbs are moved via an external force and is a modality that increases cerebral blood flow (CBF) and provides an immediate postexercise executive function (EF) benefit. To our knowledge, no work has examined for how long passive exercise benefits EF. Here, healthy young adults (N = 22; 7 female) used a cycle ergometer to complete three 20-min conditions: passive exercise (via mechanically driven flywheel), a traditional light intensity (37 W) “active” exercise condition (i.e., via volitional pedalling) and a non-exercise control condition. An estimate of CBF was obtained via transcranial Doppler ultrasound measurement of middle cerebral artery blood velocity (MCAv) and antisaccades (i.e., saccade mirror-symmetrical to a target) were completed prior to and immediately, 30- and 60-min following each condition to assess EF. Passive and active exercise increased MCAv; however, the increase was larger in the latter condition. In terms of antisaccades, passive and active exercise provided an immediate postexercise reaction time benefit. At the 30-min assessment, the benefit was observed for active but not passive exercise and neither produced a benefit at the 60-min assessment. Thus, passive exercise provided an evanescent EF “boost” and is a finding that may reflect a smaller cortical hemodynamic response.

Cerebrovascular Function in Migraine Patients during, their Interictal Period, Compared to Normal Healthy Controls

Background: Migraine is a debilitating neurovascular disorder which primarily impacts the working age population. The aim of the study was to determine if transient hemodynamic alterations during each migraine attack translates into cerebrovascular alterations, during migraineurs interictal period. A secondary hypothesis was to determine if there was any relationship between vascular hemodynamics and either the severity or frequency of migraine attacks.Methods: We recruited 29 volunteers: 13 migraineurs (mean age 28±8.8 years; 12 female and 1 male) and 16 age-matched controls (mean age 26.6±6.9; 9 female and 7 male). Volunteers were classified as migraine sufferer or not (control group). All individuals underwent a detailed ophthalmic examination by a qualified optometrist and a Migraine Disability Assessment. Cerebral blood velocity measurements for the Middle Cerebral Artery (MCA) and Vertebral Artery (VA) were obtained using Colour Doppler Imaging using the Hitachi Aloka Noblus ultrasound system. The investigators were blind to the migraine diagnosis.Results: During their interictal period migraineurs appear to have no significant difference in any hemodynamic parameter, for either their MCA and VA, when compared to normal healthy controls. Neither was a significant relationship between Migraine Disability Assessment Scores and any vascular parameter reported.Conclusion: This study found nil cerebrovascular alterations which could be measured in migraineurs compared to normal healthy controls, during their interictal period.

Neuro-vascular coupling and heart rate variability in patients with type II diabetes at different stages of diabetic retinopathy.

There is evidence that diabetes is accompanied by a break-down of functional hyperemia, an intrinsic mechanism of neural tissues to adapt blood flow to changing metabolic demands. However, to what extent functional hyperemia is altered in different stages of diabetic retinopathy (DR) in patients with type II diabetes is largely unknown. The current study set out to investigate flicker-induced retinal blood flow changes in patients with type II diabetes at different stages of DR. A total of 76 subjects were included in the present parallel-group study, of which 56 had diabetes with either no DR or different stages of non-proliferative DR (n = 29 no DR, 12 mild DR, 15 moderate to severe DR). In addition, 20 healthy subjects were included as controls. Retinal blood flow was assessed before and during visual stimulation using a combined measurement of retinal vessel calibers and blood velocity by the means of Doppler optical coherence tomography (OCT). To measure systemic autonomic nervous system function, heart rate variability (HRV) was assessed using a short-term orthostatic challenge test. In healthy controls, retinal blood flow increased by 40.4 ± 27.2% during flicker stimulation. Flicker responses in patients with DR were significantly decreased depending on the stage of the disease (no DR 37.7 ± 26.0%, mild DR 26.2 ± 28.2%, moderate to severe DR 22.3 ± 13.9%; p = 0.035, ANOVA). When assessing systemic autonomous neural function using HRV, normalized low frequency (LF) spectral power showed a significantly different response to the orthostatic maneuver in diabetic patients compared to healthy controls (p < 0.001). Our study indicates that flicker induced hyperemia is reduced in patients with DR compared to healthy subjects. Further, this impairment is more pronounced with increasing severity of DR. Further studies are needed to elucidate mechanisms behind the reduced hyperemic response in patients with type II diabetes. [https://clinicaltrials.gov/], identifier [NCT03 552562].

Large-depth three-photon fluorescence microscopy imaging of cortical microvasculature on nonhuman primates with bright AIE probe In vivo

Multiphoton microscopy has been a powerful tool in brain research, three-photon fluorescence microscopy is increasingly becoming an emerging technique for neurological research of the cortex in depth. Nonhuman primates play important roles in the study of brain science because of their neural and vascular similarity to humans. However, there are few research results of three-photon fluorescence microscopy on the brain of nonhuman primates due to the lack of optimized imaging systems and excellent fluorescent probes. Here we introduced a bright aggregation-induced emission (AIE) probe with excellent three-photon fluorescence efficiency as well as facile synthesis process and we validated its biocompatibility in the macaque monkey. We achieved a large-depth vascular imaging of approximately 1 mm in the cerebral cortex of macaque monkey with our lab-modified three-photon fluorescence microscopy system and the AIE probe. Functional measurement of blood velocity in deep cortex capillaries was also performed. Furthermore, the comparison of cortical deep vascular structure parameters across species was presented on the monkey and mouse cortex. This work is the first in vivo three-photon fluorescence microscopic imaging research on the macaque monkey cortex reaching the imaging depth of ∼1 mm with the bright AIE probe. The results demonstrate the potential of three-photon microscopy as primate-compatible method for imaging fine vascular networks and will advance our understanding of vascular function in normal and disease in humans.

In-vivo blood velocity measurement by multiple tpg encoding and maximum likelihood spectral estimation

The purpose of this paper is to show the application of the multiple velocity encoding (MVEnc) and the maximum likelihood velocity estimation (MLVEst) methods to the measurement of velocity of blood in the popliteal artery of a live human knee in presence of stationary tissue (spins). These methods were developed before by the author of this paper. Blood velocity images of the same popliteal artery were obtained in order to compare them with the ones obtained using other methods. Additionally, they can be used to obtain true angiographic images of any vessel.

Mechanisms Determining VO2peak During Single Leg Knee‐Extension Exercise in Heart Failure with Preserved Ejection Fraction Patients: Peripheral vs. Central Phenotypes

BackgroundHeart failure with preserved ejection fraction (HFpEF) is characterized by exercise intolerance, including a reduced maximal aerobic capacity that affects all aspects of daily living. The mechanisms responsible for the decreased exercise tolerance in HFpEF are incompletely understood. Our research group has characterized two unique HFpEF phenotypes based on cardiac output reserve relative to exercise metabolic work: those with either a “central” (Type A) or “peripheral” (Type B) limitation to exercise. We sought to investigate the peripheral limitations to exercise in these 2 phenotypes using single‐leg knee extension (SLKE) exercise, a modality that reduces the central limitations to exercise. Specifically, we tested the hypothesis that patients with the Type B phenotype would have lower leg VO2peak secondary to insufficient oxygen extraction (i.e., lower ∆a‐vO2diff) when compared to patients with the Type A phenotype.MethodsWe studied 20 HFpEF patients with either the Type A (n = 8; 68 ± 2yr; 5F) or Type B (n = 12; 70 ± 2yr; 7F) phenotype. Participants performed an incremental SLKE peak exercise test on a custom ergometer. Leg blood flow (LBF) was measured at the common femoral artery using duplex Doppler ultrasound. Average LBF (ml/min) at each workload was determined from measured blood velocity and vessel diameter. a‐vO2diff was calculated from hemoglobin and venous oxygen saturation directly from a femoral venous catheter, and arterial oxygen saturation via pulse oximetry. Leg VO2 (ml/min) was determined as the product of LBF and a‐vO2diff. All data are presented as mean ± SEM.ResultsParticipants with the Type A “central” phenotype reached a peak exercise workload of 20 ± 4 W and those with the Type B “peripheral” phenotype reached 15 ± 2 W (p = 0.18). Leg VO2peak was not different between the two phenotypes (Type A: 215 ± 23; Type B: 253 ± 34 ml/min; p = 0.42). The peak increase in LBF was ~ 50% greater in Type B (+1940 ± 243 ml/min) than Type A (+1309 ± 161 ml/min) patients, though this response was more variable (p = 0.07). Additionally, the ∆a‐vO2diff from rest to peak exercise was significantly lower in those with the Type B phenotype (Type A: +7.17 ± 0.87; Type B: +4.63 ± 0.46 ml O2/dl blood; p = 0.01). Finally, the ∆LBF/∆VO2 slope was lower in patients with the Type A phenotype (Type A: 6.78 ± 0.55; Type B: 8.72 ± 0.43; p = 0.01).ConclusionContrary to our hypothesis, there was no difference in leg VO2peak between phenotypes. Patients with Type B HFpEF had greater limitations in skeletal muscle oxygen extraction during exercise as evidenced by their diminished ability to increase a‐vO2diff during incremental SLKE, similar to the observed a‐vO2diff extraction impairments during whole body exercise. Importantly, by phenotyping HFpEF patients based on their limitations to exercise, we may be able to better individualize treatment strategies to improve exercise tolerance.

Middle Cerebral Artery Pulsatility Index is Elevated in Chronic Kidney Disease

IntroductionCKD patients exhibit an increased risk of cerebrovascular disease such as stroke, transient ischemic attacks, and cerebral small vessel disease. One mechanism that may contribute to this risk is increased cerebrovascular stiffness and augmented pulsatility of blood flow into the cerebral microcirculation. Middle cerebral artery pulsatility index (MCA PI) provides an indirect measure of cerebrovascular stiffness and can be measured with transcranial Doppler (TCD) ultrasonography. Prior work suggests that MCA PI is elevated in CKD patients following stroke, but it remains unclear if MCA PI is elevated in CKD patients without a history of cerebrovascular disease. Moreover, whether MCA PI correlates with central (aortic) arterial stiffness in CKD remains unknown. We hypothesized that MCA PI would be elevated in CKD patients stages III‐IV compared to controls without CKD matched for age, race, sex, diabetes and hypertension. Furthermore, we hypothesized that MCA PI would correlate with central arterial stiffness and estimated glomerular filtration rate (eGFR) in CKD.Methods13 CKD participants stages III‐IV (mean eGFR=38±3 ml/min/1.73m2) and 10 controls without CKD (age=60±2y) underwent measurement of middle cerebral artery blood velocity via TCD during 5 minutes of seated rest. MCA PI was averaged over the 5 minute period and calculated as MCA PI = (peak systolic blood velocity – diastolic blood velocity)/(mean blood velocity). In CKD, central arterial stiffness was measured via carotid‐femoral pulse wave velocity (cfPWV) after 5 minutes of supine rest. MCA PI was compared between CKD vs CON via 2‐tailed, independent sample T‐tests and the relationships between MCA PI, cfPWV, and eGFR CKD were examined via linear regression.ResultsMCA PI was elevated in CKD compared to CON (0.91±0.06 vs 0.73±.04, P=0.04) and was associated with cfPWV (R=0.72, P=0.01). However, we observed no relationship between MCA PI and eGFR in CKD (P=0.83).DiscussionIn support of our hypothesis, MCA was elevated in CKD compared to controls and was associated with central arterial stiffness. These findings suggest that cerebrovascular stiffness is elevated in CKD patients without a history of cerebrovascular disease, and that MCA PI correlates with central arterial stiffness in CKD. Increases in cerebrovascular stiffness and subsequent flow pulsatility may comprise one mechanism of cerebrovascular disease risk in CKD. Future work should clarify the relationship between MCA PI and severity of renal disease in a larger cohort, and examine the prognostic value of MCA PI as a predictor of future cerebrovascular disease burden in CKD.

Study on the radial sectional velocity distribution and wall shear stress associated with carotid artery stenosis

Atherosclerosis is an important cause of cardiovascular disease. The wall shear stress (WSS) is one of the key factors of plaque formation and dislodgement. Currently, WSS estimation is based on the measurement of the blood velocity gradient. However, due to the lack of flow field measurements in carotid stenosis vessels, the two distribution forms (parabolic and non-parabolic) commonly considered in numerical simulations could cause WSS estimates to differ by more than 40%, which could seriously affect the accuracy of mechanical analysis. This study applied three-dimensional (3D) printing technology to create an experimental model of real-structure carotid arteries. Microparticle image velocimetry was adopted to comprehensively measure blood velocity field data at the stenosis location, providing experimental validation of numerical simulation (Fluent; finite volume method) results. Then, the flow field was simulated at a normal human heart rate (45–120 beats per minute). The radial sectional velocity exhibited a plateau-like distribution with a similar velocity in the central region (more than 65% of the total channel width). This study provides an accurate understanding of the WSS at the carotid stenosis location and proposes a reliable method for the study of flow fields under various blood flow conditions.

Measurement of Blood Velocity With Laser Scanning Microscopy: Modeling and Comparison of Line-Scan Image-Processing Algorithms.

Laser scanning microscopy is widely used to measure blood hemodynamics with line-scans in physiological and pathological vessels. With scans of broken lines, i.e., lines made of several segments with different orientations, it also allows simultaneous monitoring of vessel diameter dynamics or the activity of specific cells. Analysis of red blood cell (RBC) velocity from line-scans requires specific image-processing algorithms, as angle measurements, Line-Scanning Particle Image Velocimetry (LSPIV) or Fourier transformation of line-scan images. The conditions under which these image-processing algorithms give accurate measurements have not been fully characterized although the accuracy of measurements vary according to specific experimental parameters: the vessel type, the RBC velocity, the scanning parameters, and the image signal to noise ratio. Here, we developed mathematical models for the three previously mentioned line-scan image-processing algorithms. Our models predict the experimental conditions in which RBC velocity measurements are accurate. We illustrate the case of different vessel types and give the parameter space available for each of them. Last, we developed a software generating artificial line-scan images and used it to validate our models.

Impact of impaired cerebral blood flow autoregulation on electroencephalogram signals in adults undergoing propofol anaesthesia: a pilot study.

Cerebral autoregulation actively maintains cerebral blood flow over a range of MAPs. During general anaesthesia, this mechanism may not compensate for reductions in MAP leading to brain hypoperfusion. Cerebral autoregulation can be assessed using the mean flow index derived from Doppler measurements of average blood velocity in the middle cerebral artery, but this is impractical for routine monitoring within the operating room. Here, we investigate the possibility of using the EEG as a proxy measure for a loss of cerebral autoregulation, determined by the mean flow index. Thirty-six patients (57.5 [44.25; 66.5] yr; 38.9% women, non-emergency neuroradiology surgery) anaesthetised using propofol were prospectively studied. Continuous recordings of MAP, average blood velocity in the middle cerebral artery, EEG, and regional cerebral oxygen saturation were made. Poor cerebral autoregulation was defined as a mean flow index greater than 0.3. Eighteen patients had preserved cerebral autoregulation, and 18 had altered cerebral autoregulation. The two groups had similar ages, MAPs, and average blood velocities in the middle cerebral artery. Patients with altered cerebral autoregulation exhibited a significantly slower alpha peak frequency (9.4 [9.0, 9.9] Hz vs 10.5 [10.1, 10.9] Hz, P<0.001), which persisted after adjusting for age, norepinephrine infusion rate, and ASA class (odds ratio=0.038 [confidence interval, 0.004, 0.409]; P=0.007). In this pilot study, we found that loss of cerebral autoregulation was associated with a slower alpha peak frequency, independent of age. This work suggests that impaired cerebral autoregulation could be monitored in the operating room using the existing EEG setup. NCT03769142.

EVA: Fully automatic hemodynamics assessment system for the bulbar conjunctival microvascular network

Background and objectiveConjunctival microcirculation has been used to quantitatively assess microvascular changes due to systemic disorders. The space between red blood cell clusters in conjunctival microvessels is essential for assessing hemodynamics. However, it causes discontinuities in vessel image segmentation and increases the difficulty of automatically measuring blood velocity. In this study, we developed an EVA system based on deep learning to maintain vessel segmentation continuity and automatically measure blood velocity. MethodsThe EVA system sequentially performs image registration, vessel segmentation, diameter measurement, and blood velocity measurement on conjunctival images. A U-Net model optimized with a connectivity-preserving loss function was used to solve the problem of discontinuities in vessel segmentation. Then, an automatic measurement algorithm based on line segment detection was proposed to obtain accurate blood velocity. Finally, the EVA system assessed hemodynamic parameters based on the measured blood velocity in each vessel segment. ResultsThe EVA system was validated for 23 videos of conjunctival microcirculation captured using functional slit-lamp microscopy. The U-Net model produced the longest average vessel segment length, 158.03 ± 181.87 µm, followed by the adaptive threshold method and Frangi filtering, which produced lengths of 120.05 ± 151.47 µm and 99.94 ± 138.12 µm, respectively. The proposed method and one based on cross-correlation were validated to measure blood velocity for a dataset consisting of 30 vessel segments. Bland-Altman analysis showed that compared with the cross-correlation method (bias: 0.36, SD: 0.32), the results of the proposed method were more consistent with a manual measurement-based gold standard (bias: -0.04, SD: 0.14). ConclusionsThe proposed EVA system provides an automatic and reliable solution for quantitative assessment of hemodynamics in conjunctival microvascular images, and potentially can be applied to hypoglossal microcirculation images.

Validity of transcranial Doppler ultrasonography-determined dynamic cerebral autoregulation estimated using transfer function analysis.

Transcranial Doppler ultrasonography (TCD) is used widely to evaluate dynamic cerebral autoregulation (dCA). However, the validity of TCD-determined dCA remains unknown because TCD is only capable of measuring blood velocity and thus only provides an index as opposed to true blood flow. To test the validity of TCD-determined dCA, in nine healthy subjects, dCA was evaluated by transfer function analysis (TFA) using cerebral blood flow (CBF) or TCD-measured cerebral blood velocity during a perturbation that induces reductions in TCD-determined dCA, lower body negative pressure (LBNP) at two different stages: LBNP - 15mmHg and - 50mmHg. Internal carotid artery blood flow (ICA Q) was assessed as an index of CBF using duplex Doppler ultrasound. The TFA low frequency (LF) normalized gain (ngain) calculated using ICA Q increased during LBNP at - 50mmHg (LBNP50) from rest (P = 0.005) and LBNP at - 15mmHg (LBNP15) (P = 0.015), indicating an impaired dCA. These responses were the same as those obtained using TCD-measured cerebral blood velocity (from rest and LBNP15; P = 0.001 and P = 0.015). In addition, the ICA Q-determined TFA LF ngain from rest to LBNP50 was significantly correlated with TCD-determined TFA LF ngain (r = 0.460, P = 0.016) despite a low intraclass correlation coefficient. Moreover, in the Bland-Altman analysis, the difference in the TFA LF ngains determined by blood flow and velocity was within the margin of error, indicating that the two measurement methods can be interpreted as equivalent. These findings suggest that TCD-determined dCA can be representative of actual dCA evaluated with CBF.

Dual-beam delay-encoded all fiber Doppler optical coherence tomography for in vivo measurement of retinal blood flow

In this paper, we propose and demonstrate a dual-beam delay-encoded Doppler spectral domain optical coherence tomography (OCT) system for in vivo measurement of absolute retinal blood velocity and flow with arbitrary orientation. The incident beam is split by a beam displacer into two probe beams of the single-spectrometer spectral domain OCT system with orthogonal polarization states and an optical path length delay. We validate our approach with a phantom and in vivo experiments of human retinal blood flow, respectively.

Abstract 10665: Pulse Wave Velocity Measured at End-Diastole Underestimates Aortic Stiffness

Introduction: Aortic stiffness (AS) is assessed using pulse wave velocity (= distance (D) between two aortic sites / foot-to-foot transit time of pressure or velocity pulse (ffPTT) between the sites ) which is considered as “gold standard”. But, PWV varies with cyclic pressure in the normal aorta and PWV measured at end-diastole underestimates AS. This underestimation is greatest when aorta is the stiffest. Hypothesis: We hypothesize that PWV measured at diastole is lower than that measured at systole and that PWV should be measured over the entire cardiac cycle for better representation of AS. Methods: We measured pressures invasively with a dual sensor catheter (0.46 mm dia) at two descending aortic sites (25 mm apart) in normal rats. We measured blood velocities noninvasively with two Doppler probes placed at aortic arch and abdominal aorta. The pressure and blood velocity signals were acquired simultaneously (at baseline &amp; post-esmolol admin). From the two pressure signals we measured PWVsp (at dicrotic notch; end-systolic fiducial marker) and PWVdp (at end-diastole; foot fiducial marker). PWVd (end-diastole; foot) was measured from the two blood velocity signals. Results &amp; Conclusions: We plotted the PWV versus blood pressure. We found that the slope of aPWVsp &gt; the slope of aPWVdp indicating that PWV varies with blood pressure within the cardiac cycle. We also found that slope of aPWVd &lt; aPWVdp because, D used to calculate PWVdp is fixed at 25mm, whereas D used to calculate aPWVd was estimated as the distance between Doppler probe tips on the surface of the skin (aortic arch curvature was not accounted for). In conclusion, a more representative AS can be assessed through 1. PWV measurement at systole &amp; diastole within the cardiac cycle of a noninvasively measured vessel wall motion (a pressure signal surrogate) where the systolic and diastolic fiducial points can be identified, and 2. use of two aortic sites on the straight part of the descending aorta for better estimating of D.

TCT-256 A Novel Thermoconvection-Equipped Microcatheter (PhysioCath) for Coronary Blood Velocity and Pressure Measurement: Preliminary Experience

TCT-256 A Novel Thermoconvection-Equipped Microcatheter (PhysioCath) for Coronary Blood Velocity and Pressure Measurement: Preliminary Experience