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- Barclay, Susan A, et al.
(författare)
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The shape of the proximal isovelocity surface area varies with regurgitant orifice size and distance from orifice : computer simulation and model experiments with color M-mode technique.
- 1993
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Ingår i: Journal of the American Society of Echocardiography. - 0894-7317 .- 1097-6795. ; 6:4, s. 433-445
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Tidskriftsartikel (refereegranskat)abstract
- The hemispheric proximal isovelocity surface area method for quantification of mitral regurgitant flow (i.e., Qc = 2 pi r2v), where 2 pi r2 is the surface area and v is the velocity at radius r, was investigated as distance from the orifice was increased. Computer simulations and steady flow model experiments were performed for orifices of 4, 6, and 8 mm. Flow rates derived from the centerline velocity and hemispheric assumption were compared with true flow rates. Proximal isovelocity surface area shape varied as distance from each orifice was increased and could only be approximated from the hemispheric equation when a certain distance was exceeded: > 7, > 10, and > 12 mm for the 4, 6, and 8 mm orifices, respectively. Prediction of relative error showed that the best radial zone at which to make measurements was 5 to 9, 6 to 14 and 7 to 17 mm for the 4, 6, and 8 mm orifices, respectively. Although effects of a nonhemispheric shape could be compensated for by use of a correction factor, a radius of 8 to 9 mm can be recommended without the use of a correction factor over all orifices studied if a deviation in calculated as compared with true flow of 15% is considered acceptable. These measurements therefore have implications for the technique in clinical practice.
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| 7. |
- Eidenvall, Lars, et al.
(författare)
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Two-dimensional color Doppler flow velocity profiles can be time corrected with an external ECG-delay device.
- 1992
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Ingår i: Journal of the American Society of Echocardiography. - 0894-7317 .- 1097-6795. ; 5:4, s. 405-413
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Tidskriftsartikel (refereegranskat)abstract
- Although two-dimensional ultrasound color flow imaging is often considered to be a real-time technique, the acquisition time for two-dimensional color images may be up to 200 msec. Time correction is therefore necessary to obtain correct flow velocity profiles. We have developed a time-correction method in which a specially designed unit detects the QRS complex from the patient and creates a trig pulse that is delayed incrementally in relation to the QRS complex. This trig pulse controls the acquisition of the ultrasound images. A number of consecutively delayed images, with known incremental delay between the sweeps, can thus be stored in the memory of the echocardiograph and transferred digitally to a computer. The time-corrected flow velocity profile is obtained by interpolation of data from the time-delayed profiles. The system was evaluated in a Doppler string phantom test. With this technique it is possible to study time-corrected flow velocity profiles without the need to alter existing ultrasound Doppler equipment.
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| 8. |
- Engvall, Jan, et al.
(författare)
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Coarctation of the aorta--a theoretical and experimental analysis of the effects of a centrally located arterial stenosis.
- 1991
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 29:3, s. 291-296
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Tidskriftsartikel (refereegranskat)abstract
- Aortic coarctation is a local constriction of the aorta that may severely affect haemodynamics. It is therefore important to quantify these effects. Using Bernoulli's equation and the momentum theorem, the pressure drop is described including the pressure recovery distal to the coarctation and the effects of collateral flow; both laminar and turbulent. Assuming the coarctation and collaterals to be stiff, a quadratic relationship between flow and pressure drop is expected for flow through the coarctation and for turbulent collateral flow. For laminar collateral flow, a linear relationship is expected. The coarctation flow was studied in a model consisting of a rigid tube with local constriction, connected to a flooded-level tank, containing a 36 per cent by weight solution of sucrose, with a viscosity equivalent to that of blood at body temperature. The pressure drop across the constriction showed a quadratic relationship to flow in agreement with theoretical expectations. Pressure recovery in this model was very slight (0-4 mm Hg). Nine patients with aortic coarctation were catheterised. Cardiac output and pressure drop across the coarctation were measured at rest and during supine cycle exercise at two different workloads. The relationship between mean pressure drop and cardiac output tended to be either 'parabolic' or, in some cases, approximately linear, suggesting that the flow situation in aortic coarctation can be quantified by expressions that either linearly or quadratically relate pressure and flow.
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