Correlations among critical closing pressure, pulsatility index and cerebrovascular resistance (original) (raw)
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Cerebrovascular diseases (Basel, Switzerland), 2013
Ultrasound and the Doppler Effect were major achievements in physics and their application to medicine provided a number of advantages to investigate the vascular system. One should remember the work of Christian Andreas Doppler (1803-1853), an Austrian mathematician from Salzburg, who was concerned about colour variation of the stars and stated that color change throughout time was due to the relationship between the velocity of light and the speed of the moving stars. His work was confirmed on the ground with the celebrated experience of musicians playing a single note on a moving train while trained observers listened on the ground and verified the change in intensity when the train passed: the "Doppler effect" was certified. Doppler may not have even imagined the use of his ideas regarding ultrasounds and the wide range of applications thereafter. Medical applications in vascular medicine hit a milestone in the 1950's when the Japanese scientists Shigeo Satomura and Ziro Kaneko produced the first ultrasound device able to register Doppler shift in blood vessels: the "Doppler Rheograph". Since then, fast developments in technology have allowed a wide diffusion of a number of reliable devices along with the capability to depict and visualise vascular structures and, at the same time, to measure velocities of the blood flow. In 1980, another milestone occurred when Rune Aaslid introduced (1982) a device able to register Doppler signals through the intact skull. The use of ultrasounds in vascular medicine and in cerebral circulation in particular seems to have an endless field for pursuit. Continuous Doppler, pulsatile Doppler, transcranial colour coded Doppler, Doppler monitoring for diagnosis and also thrombolysis assisted ultrasound are some of their various modalities. Nowadays ultrasound has gained a definitive role in the investigation of all vascular patients. Affordability, reliability (in experienced hands), user friendly, repeatability, without contraindications are its main characteristics foreseeing a challenging and promising future.
Evaluation of cerebrovascular impedance and wave reflection in mouse by ultrasound
Journal of Cerebral Blood Flow & Metabolism, 2014
Genetic and surgical mouse models are commonly used to study cerebrovascular disease, but their size makes invasive hemodynamic testing technically challenging. The purpose of this study was to demonstrate a noninvasive measurement of cerebrovascular impedance and wave reflection in mice using high-frequency ultrasound in the left common carotid artery (LCCA), and to examine whether microvascular changes associated with hypercapnia could be detected with such an approach. Ten mice (C57BL/6J) were studied using a high-frequency ultrasound system (40 MHz). Lumen area and blood flow waveforms were obtained from the LCCA and used to calculate pulse-wave velocity, input impedance, and reflection amplitude and transit time under both normocapnic and hypercapnic (5% CO 2 ) ventilation. With hypercapnia, vascular resistance was observed to decrease by 87% ± 12%. Although the modulus of input impedance was unchanged with hypercapnia, a phase decrease indicative of increased total arterial compliance was observed at low harmonics together with an increased reflection coefficient in both the time (0.57 ± 0.08 versus 0.68 ± 0.08, P = 0.04) and frequency domains (0.62 ± 0.08 versus 0.73 ± 0.06, P = 0.02). Interestingly, the majority of LCCA blood flow was found to pass into the internal carotid artery (range = 76% to 90%, N = 3), suggesting that hemodynamic measurements in this vessel are a good metric for intracerebral reactivity in mouse.
Ultrasound Med Biol 2009 Stapleton
The presence of axillary artery aneurysm and/or thrombus in overhead throwing athletes has been linked, theoretically, with the finding of compression by the humeral head induced by a diagnostic arm maneuver. However, whether this intermittent compression is incidental or of pathological significance has yet to be determined. Flow-mediated vasodilation (FMD), intima-media thickness (IMT) and maximum vasodilatory capacity were measured locally (3rd portion of the axillary artery) and downstream (brachial artery) in individuals previously tested for inducible axillary artery compression (compressor group [COMP]: n 5 8, mean (SD) age: 23 (4) y; ''noncompressor'' control group [NONCOMP]: n 5 8, 26 (4) y). A high-resolution ultrasound machine recorded arterial diameter and blood flow velocity. A rapid inflation/deflation pneumatic cuff placed distal to the site of measurement induced reactive hyperemia. Custom-designed wall tracking software with synchronized Doppler waveform analysis detected changes in arterial diameter, blood flow velocity and shear rate from baseline to 3 min after cuff deflation. Glyceryl trinitrate and/or ischemic hand grip exercises were administered to induce maximum vasodilation. No significant differences in FMD, IMT or maximum vasodilator capacity were observed between groups at the axillary artery. However, the downstream brachial FMD response was significantly diminished in the COMP group (6.38 [3.28]%) compared with the NONCOMP group (10.38 [2.74]%; p 5 0.006) despite a comparable shear rate between groups (COMP: 81.92 (44.55) s 21 ; NONCOMP: 83.18 (40.02) s 21 ; p 5 0.961). Pooled data revealed a significant negative relationship (r 5 20.52, p 5 0.038) between the FMD response and degree of arterial compression. These results suggest a chronic change in downstream vascular function in individuals demonstrating clinically significant inducible axillary artery compression. (
2021
Supplemental material, sj-pdf-1-inc-10.1177_17511437211010032 for FUSIC HD. Comprehensive haemodynamic assessment with ultrasound by Ashley Miller, Marcus Peck, Tom Clark, Hannah Conway, Segun Olusanya, Nick Fletcher, Nick Coleman, Prashant Parulekar, Jonathan Aron, Justin Kirk-Bayley, Jonathan Nicholas Wilkinson, Adrian Wong, Jennie Stephens, Antonio Rubino, Ben Attwood, Andrew Walden, Andrew Breen, Manprit Waraich, Catherine Nix and Simon Hayward in Journal of the Intensive Care Society
Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine, 2012
Ultrasound has various biological effects in the human body. The effects of continuous monitoring with ultrasound (sonolysis) on vasodilatation of the radial artery were described recently. We wanted to ascertain whether similar changes in the blood flow velocity during sonolysis could also be detected in the middle cerebral artery. Fifteen healthy volunteers (6 male and 9 female; age range, 23-68 years; mean ± SD, 47.1 ± 15.1 years) were subjected to 1 hour of middle cerebral artery sonolysis using a diagnostic transcranial probe with a 2-MHz Doppler frequency and measurement of the blood flow velocity at 2-minute intervals. During a second session, a flow curve was recorded for 10 seconds at 2-minute intervals. The peak systolic velocity, end-diastolic velocity, mean flow velocity, pulsatility index, and resistive index were recorded during both measurements. Irregular changes in the measured blood flow parameters were recorded during both sessions. Changes in particular hemodynam...
Assessment of Endothelial Function Using Ultrasound
Applied Aspects of Ultrasonography in Humans, 2012
Parameter Recommendations Subject preparation Fast overnight prior to testing, and avoid exercise during the preceding 24 hrs. Refrain from taking drugs with known vascular effects. Rest supine for 20 mins in a quiet, temperature controlled room at 21 o C. Test conducted with subjects in the supine position. Artery segment of interest must remain at or below heart level. Women should be tested during the early follicular phase of the ovarian cycle (i.e., day 7-14 of the ovarian cycle). For successive tests, subjects should report at the same time of day to reduce error associated with circadian variation. Probe selection A higher frequency probe (12MHz) should be used for superficial arteries (e.g., brachial, radial or posterior tibialis). A lower frequency probe (7.5MHz) should be used for deeper arteries (e.g., common femoral). The same transducer should be used for all subjects in a given study. Probe placement Mark anatomical placement for studies with repeated measurements. Use a probe holding device to maintain image focus. Ultrasound Settings Standardize ultrasound global (acoustic output, gain, dynamic range, gamma, rejection) and probe-dependent (zoom factor, edge enhancement, frame averaging, target frame rate) settings. Artery Artery selection should be made based on the population of interest, e.g., lower limb arteries should be measured in patients with SCI. Diameters (general) Extend across the entire imaging plane to minimize skewing prior to focusing. Use automated or semi-automated image analysis software. Use mean or end-diastolic diameters. Baseline diameters Collect prior to cuff inflation. Subject should hold breath during measurement. Collect and average 3 * 10 sec measurements. Peak diameters Capture diameters continuously to ensure true peak diameter. Blood velocity The beam-vessel angle must be <60°. Measure continuously. Time-averaged maximum velocities are more accurate and reproducible than time-averaged mean velocities. Shear Stimulus Shear rate is a suitable substitute for shear stress. Diameters and velocities must be captured continuously to estimate shear. Shear rates should be presented as an integral, we recommend 40 secs postischemia. Attention should be paid to secondary flow phenomena, e.g., turbulence and velocity acceleration. Analysis Present FMD in absolute (mm) and relative (%) terms. The shear rate stimuli should be presented for each research setting. Do not normalize FMD to shear rate as ratio or using ANCOVA. HLM can be used to statistically account for shear rate in the evaluation of FMD.