Ultrasound vector projectile imaging for detection of altered carotid bifurcation hemodynamics during reductions in cardiac output

Abstract

Purpose Complex blood flow is commonly observed in the carotid bifurcation, although the factors that regulate these patterns beyond arterial geometry are unknown. The emergence of high‐frame‐rate ultrasound vector flow imaging allows for noninvasive, time‐resolved analysis of complex hemodynamic behavior in humans, and it can potentially help researchers understand which physiological stressors can alter carotid bifurcation hemodynamics in vivo. Here, we seek to pursue the first use of vector projectile imaging (VPI), a dynamic form of vector flow imaging, to analyze the regulation of carotid bifurcation hemodynamics during experimental reductions in cardiac output induced via a physiological stressor called lower body negative pressure (LBNP). Methods Seven healthy adults (age: 27 ± 4 yr, 4 men) underwent LBNP at −45 mmHg to simulate a postural hemodynamic response in a controlled environment. Using a research‐grade, high‐frame‐rate ultrasound platform, vector flow estimation in each subject’s right carotid bifurcation was performed through a multi‐angle plane wave imaging (two transmission angles of 10° and −10°) formulation, and VPI cineloops were generated at a frame rate of 750 fps. Vector concentration was quantified by the resultant blood velocity vector angles within a region of interest; lower concentration indicated greater flow dispersion. Discrete concentration values during peak and late systole were compared across different segments of the carotid artery bifurcation before, and during, LBNP. Results Vector projectile imaging revealed that external and internal carotid arteries exhibited regional hemodynamic changes during LBNP, which acted to reduce both the subject’s cardiac output (Δ − 1.2 ± 0.5 L/min, −19%; P < 0.01) and peak carotid blood velocity (Δ − 6.30 ± 8.27 cm/s, −7%; P = 0.05). In these carotid artery branches, the vector concentration time trace before and during LBNP were observed to be different. The impact of LBNP on flow complexity in the two carotid artery branches showed variations between subjects. Conclusions Using VPI, intuitive visualization of complex hemodynamic changes can be obtained in healthy humans subjected to LBNP. This imaging tool has potential for further applications in vascular physiology to identify and quantify complex hemodynamic features in humans during different physiological stressor tests that regulate hemodynamics.

Going against the flow: are venous thromboembolism and impaired cerebral drainage critical risks for spaceflight?

“…Newer technologies, such as vector flow imaging, employ high-frame rate ultrasound which provides a more sensitive, angle-independent tool to quantify complex circulatory flows and could significantly improve both in-flight diagnostic and research specificity (27), as shown in the figure below. *insert Figure 1 here* What are the next steps?…”

“…Lower body negative pressure (LBNP) at low, and demonstrated safe, levels (i.e. <30 mmHg) may be a useful countermeasure to reintroduce caudal venous blood volume distribution thereby simulating the effects of gravitational stress including cerebral drainage patterns (6,7,19,27,28), but may in itself elevate risk of VT in the legs (29). A better understanding of risk factors, underpinning mechanisms, and actual prevalence of VT both in upper and lower part of the vasculature in space is needed to evaluate and determine best possible countermeasures including LBNP.…”

Contrast-Enhanced High-Frame-Rate Ultrasound Imaging of Flow Patterns in Cardiac Chambers and Deep Vessels

“…However, vector Doppler is limited in depth because of loss of lateral velocity accuracy as the depth of interest increases relative to the limited aperture size, reducing the angle between different directional Doppler acquisitions. Human blood flow imaging studies have been performed in the femoral artery (Au et al 2019) and the carotid artery (in two dimensions [Tortoli et al 2015;Saris et al 2019;Au et al 2020] and three dimensions [Correia et al 2016]). Vector Doppler has also been used in combination with ultrasound contrast agent microbubbles to image urinary flow dynamics (Ishii et al 2020).…”

Blood flow quantification in the aortoiliac arteries : from bench to bedside

“…Vector Doppler is not angledependent, is less operator-dependent and has been shown to be more accurate than conventional Doppler approaches, [71] including with complex blood flows. [72] Another Doppler-based technique is called Transverse Oscillation (TO) [73]. In this technique, only one US beam is used.…”

“…Still, the widespread application of these techniques in clinical practice is currently possible, and could improve the estimation of lesion severity [70]. Novel flow parameters can also be used to quantify flow-disturbing factors such as vector concentration or vector complexity, a measure of the multidirectionality of the flow field [32], [70], [72]. This could significantly improve the diagnosis and monitoring of patients with PAD.…”