Key result
Lower body negative pressure significantly reduced cardiac output (Δ -1.2 L/min; P<0.01) and peak carotid blood velocity (Δ -6.30 cm/s; P=0.05), with complex hemodynamic changes visualized via vector projectile imaging.
Why the study?
Factors regulating complex blood flow patterns in the carotid bifurcation beyond arterial geometry are unknown, and whether physiological stressors alter these hemodynamics in vivo required evaluation using dynamic vector projectile imaging.
Does lower body negative pressure alter carotid bifurcation hemodynamics as measured by ultrasound vector projectile imaging in healthy adults?
Does lower body negative pressure alter carotid bifurcation hemodynamics as measured by ultrasound vector projectile imaging in healthy adults?
Ultrasound vector projectile imaging can effectively visualize and quantify complex hemodynamic changes in the carotid bifurcation during physiological stress in healthy humans.
LBNP may risk cerebral hypoperfusion in vulnerable patients; leaves open vector projectile imaging for carotid hemodynamics assessment.
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.
No takes yet. Share an insight, caveat, or question.
Au et al. (2019) studied Healthy adults (n=7). Lower body negative pressure (LBNP) vs. Baseline (before LBNP) was evaluated on Change in cardiac output and peak carotid blood velocity (Δ -1.2 L/min (-19%) for cardiac output, p=<0.01). Lower body negative pressure significantly reduced cardiac output (Δ -1.2 L/min; P<0.01) and peak carotid blood velocity (Δ -6.30 cm/s; P=0.05), with complex hemodynamic changes visualized via vector projectile imaging.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: