Limitations of a pulsed Doppler velocimeter for blood flow measurement in small vessels

1993 ◽  
Vol 75 (6) ◽  
pp. 2745-2754 ◽  
Author(s):  
A. W. Quail ◽  
D. B. Cottee ◽  
S. W. White
Keyword(s):  
Blood Flow ◽  
Doppler Shift ◽  
Volume Flow Rate ◽  
Volume Flow ◽  
Pulsed Doppler ◽  
Small Vessels ◽  
Flow Disturbances ◽  
Wide Range ◽  
Blood Flow Velocities ◽  
Flow Velocities

The performance of a new and simplified flow probe construction and the Iowa 545C-4 pulsed Doppler velocimeter was evaluated for measurement of blood flow over several months in small arteries of awake animals. Calibrations were performed over a wide range of intraluminal pressures and physiological flow velocities. Pressure-dependent differences in slope of the Doppler shift-volume flow relationship were detected in some probes. Signal strength was maintained at hematocrits > 10%. Distortion of pulsed Doppler signal peaks occurred in the conscious rabbit at peak aortic velocities, at which Reynold's number for turbulence was exceeded and the Doppler shift surpassed the Nyquist limit of 31.25 kHz for the velocimeter. Although the Doppler shift-volume flow relationship is linear at < 5 kHz, in some cases at higher Doppler shifts and blood flow velocities the relationship may become nonlinear, thus causing the volume flow rate to be underestimated by up to 38%. The cause of this phenomenon may be "aliasing" and/or the consequence of the range control capability of the velocimeter selectively sampling changing velocity profiles and flow disturbances in the central stream at higher velocities.

Reduction of the Clutter Component in Doppler Ultrasound Signals Based on Singular Value Decomposition: A Simulation Study

1997 ◽  
Vol 19 (1) ◽  
pp. 1-18 ◽  
Author(s):  
Léon A.F. Ledoux ◽  
Peter J. Brands ◽  
Arnold P.G. Hoeks
Keyword(s):  
Blood Flow ◽  
Singular Value Decomposition ◽  
Doppler Ultrasound ◽  
Singular Value ◽  
Pulsed Doppler ◽  
Rf Signals ◽  
Blood Flow Velocities ◽  
Value Decomposition ◽  
High Pass ◽  
Flow Velocities

In pulsed Doppler ultrasound systems, the ultrasound radiofrequency (RF) signals received can be employed to estimate noninvasively the time-dependent blood flow velocity distribution within an artery. The RF signals are composed of signals originating from clutter (e.g., vessel walls) and scatterers (e.g., red blood cells). The clutter, which is induced by stationary or slowly-moving structure interfaces, must be suppressed to get reliable estimates of the mean blood flow velocities. In conventional pulsed Doppler systems, this is achieved with a static temporal high-pass filter. The static cut-off frequency and the roll-off of these filters cause the clutter not always to be optimally suppressed. This paper introduces a clutter removal filter that is based on Singular Value Decomposition (SVD). Unlike conventional high-pass filters, which take into account only the information of the temporal direction, the SVD filter makes use of the information of the temporal and spatial directions. The advantage of this approach is that it does not matter where the clutter is located in the RF signal. The performance of the SVD filter is examined with computer-generated Doppler RF signals. The results are compared with those of a standard linear regression (SLR) filter. The performance of the SVD filter is good, especially if a large temporal window (i.e., approximately 100 RF signals) is applied, which improves the performance for low blood flow velocities. A major disadvantage of the SVD filter is its computational complexity, which increases considerably for larger temporal windows.

Patterns of Cerebral Blood Flow and Systemic Hemodynamics During Arithmetic Processing

2008 ◽  
Vol 22 (2) ◽  
pp. 81-90 ◽  
Author(s):  
Natalie Werner ◽  
Neval Kapan ◽  
Gustavo A. Reyes del Paso
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Time Course ◽  
Doppler Sonography ◽  
Transcranial Doppler Sonography ◽  
Systemic Hemodynamics ◽  
Heart Period ◽  
Blood Flow Velocities ◽  
Flow Velocities

The present study explored modulations in cerebral blood flow and systemic hemodynamics during the execution of a mental calculation task in 41 healthy subjects. Time course and lateralization of blood flow velocities in the medial cerebral arteries of both hemispheres were assessed using functional transcranial Doppler sonography. Indices of systemic hemodynamics were obtained using continuous blood pressure recordings. Doppler sonography revealed a biphasic left dominant rise in cerebral blood flow velocities during task execution. Systemic blood pressure increased, whereas heart period, heart period variability, and baroreflex sensitivity declined. Blood pressure and heart period proved predictive of the magnitude of the cerebral blood flow response, particularly of its initial component. Various physiological mechanisms may be assumed to be involved in cardiovascular adjustment to cognitive demands. While specific contributions of the sympathetic and parasympathetic systems may account for the observed pattern of systemic hemodynamics, flow metabolism coupling, fast neurogenic vasodilation, and cerebral autoregulation may be involved in mediating cerebral blood flow modulations. Furthermore, during conditions of high cardiovascular reactivity, systemic hemodynamic changes exert a marked influence on cerebral blood perfusion.

scholarly journals Effect of positioning from supine and left lateral positions to left lateral tilt on maternal blood flow velocities and waveforms in full-term parturients

Anaesthesia ◽  
2012 ◽  
Vol 67 (8) ◽  
pp. 936-936 ◽  
Author(s):  
P. Kundra ◽  
J. Velraj ◽  
U. Amirthalingam ◽  
S. Habeebullah ◽  
K. Yuvaraj ◽  
...  
Keyword(s):  
Blood Flow ◽  
Maternal Blood ◽  
Full Term ◽  
Lateral Tilt ◽  
Blood Flow Velocities ◽  
Flow Velocities
Sign in / Sign up

Export Citation Format

Share Document