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Valve Closure (valve + closure)

Distribution by Scientific Domains

Medical Sciences	100%

Selected Abstracts

Aortic Valve Closure: Relation to Tissue Velocities by Doppler and Speckle Tracking in Patients with Infarction and at High Heart Rates

ECHOCARDIOGRAPHY, Issue 4 2010
Ph.D., Svein A. Aase M.Sc.
Aim: To resolve the event in tissue Doppler (TDI)- and speckle tracking-based velocity/time curves that most accurately represent aortic valve closure (AVC) in infarcted ventricles and at high heart rates. Methods: We studied the timing of AVC in 13 patients with myocardial infarction and in 8 patients at peak dobutamine stress echo. An acquisition setup for recording alternating B-mode and TDI image frames was used to achieve the same frame rate in both cases (mean 136.7 frames per second [FPS] for infarcted ventricles, mean 136.9 FPS for high heart rates). The reference method was visual assessment of AVC in the high frame rate narrow sector B-mode images of the aortic valve. Results: The initial negative velocities after ejection in the velocity/time curves occurred before AVC, 44.9 ± 21.0 msec before the reference in the high heart rate material, and 25.2 ± 15.2 msec before the reference in the infarction material. Using this time point as a marker for AVC may cause inaccuracies when estimating end-systolic strain. A more accurate but still a practical marker for AVC was the time point of zero crossing after the initial negative velocities after ejection, 5.4 ± 15.3 msec before the reference in high heart rates and 8.2 ± 12.9 msec after the reference in the infarction material. Conclusion: The suggested marker of AVC at high heart rate and in infarcted ventricles was the time point of zero crossing after the initial negative velocities after ejection in velocity/time curves. (Echocardiography 2010;27:363-369) [source]

How should we estimate driving pressure to measure interrupter resistance in children?

PEDIATRIC PULMONOLOGY, Issue 9 2007
MB ChB, P. Seddon BSc
Abstract Interrupter resistance (Rint) is a widely used measure of airway caliber, but concerns remain about repeatability and sensitivity. Some Rint variability may derive from the linear back-extrapolation algorithm (LBE 30/70) usually used to estimate driving pressure. To investigate whether other methods of estimating driving pressure could improve repeatability and sensitivity, we studied 39 children with asthma. Two measurements of Rint,each the median of 10 interruptions,were made 5 min apart, and 14 children had a third measurement after bronchodilator (RintBD). Mouth pressure transients were analyzed using several algorithms, to compare the magnitude, repeatability, and sensitivity to bronchodilator change of Rint values yielded. Algorithms taking driving pressure from later in the transient, predictably, yielded higher values of Rint than those which back-extrapolated to time of valve closure. Algorithms which did not rely on back-extrapolation, including mean oscillation pressure (MOP) and mean plateau pressure (MP 30/70) had better repeatability. Sensitivity to detect change, calculated as ratio of bronchodilator response to repeatability coefficient (,Rint/CR), was also better for non-extrapolating algorithms: MP 30/70 1.67, LBE 30/70 1.28 (P,=,0.0004). Measuring Rint using techniques other than conventional back-extrapolation may give more consistent and clinically useful results, and these approaches merit further exploration. Pediatr Pulmonol. 2007; 42:757,763. © 2007 Wiley-Liss, Inc. [source]

Laser Doppler Velocimetry and Flow Visualization Studies in the Regurgitant Leakage Flow Region of Three Mechanical Mitral Valves

ARTIFICIAL ORGANS, Issue 4 2001
Richard S. Meyer
Abstract: Streak line flow visualization and laser Doppler velocimetry (LDV) were conducted in the regurgitant leakage flow region of 3 mechanical heart valve types: CarboMedics, Medtronic Hall, and St. Jude Medical. Streak line flow visualization identified regions of high regurgitant flow, and LDV measurements were focused on those locations. Maximum regurgitant flow velocities after valve closure ranged from 0.7 to 2.6 m/s, and maximum Reynolds shear stress after valve closure ranged from 450 to 3,600 dyne/cm2. These data indicate that leakage flows can generate turbulent jets with elevated Reynolds stresses even in bileaflet valves. [source]