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- Wulff, John, et al.
(author)
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Flow characteristics of the Hemopump : an experimental in vitro study.
- 1997
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In: Annals of Thoracic Surgery. - 0003-4975 .- 1552-6259. ; 63:1, s. 162-166
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Journal article (peer-reviewed)abstract
- BACKGROUND: The Hemopump (DLP/Medtronic) has been in clinical use for about 7 years. There is still no adequate way of determining actual output from the three available pump systems in the clinical situation. If the pump is completely stopped during weaning from the device, there is a possibility of back-leakage through the pump, endangering the patient from regurgitation into the left ventricle. It can also make it more difficult to judge the recovery of heart function because of a volume load of the left ventricle. The aim of this study was to evaluate in a standardized, experimental in vitro model the output from three different-sized Hemopump catheters at various pressure levels and to quantify the back-flow through the pumps.METHODS: The Hemopump models were tested in an in vitro study regarding total outflow at various speeds at three pressure levels. The back-flow through the pumps was also measured with the pumps at a complete stop.RESULTS: The outflow from the Hemopumps ranged from 0.4 to 4.5 L/min, depending on which pump and speed were used. Variations in total output, depending on speed and various pressure settings, could be up to 0.4 L/min. Back-flow through the pump into the left ventricle may be as great as 1.6 L/min.CONCLUSIONS: The flow outputs from the different Hemopump models were reproducible over time and were closely related to the resistance of the model. The Hemopump, if not running, can induce substantial regurgitation through the pump into the left ventricle.
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- Bolger, A F, et al.
(author)
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Understanding continuous-wave Doppler signal intensity as a measure of regurgitant severity.
- 1997
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In: Journal of the American Society of Echocardiography. - 0894-7317 .- 1097-6795. ; 10:6, s. 613-622
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Journal article (peer-reviewed)abstract
- Continuous-wave Doppler signal intensity is commonly expected to reflect the severity of mitral regurgitation. Physical principles predict that alignment of the imaging beam, flow velocity, and turbulence can also be important or even dominant determinants of continuous-wave Doppler signal intensity. The reliability of tracking regurgitant severity with continuous-wave Doppler signal intensity was assessed in vitro with varying volume, velocity, turbulence, and beam alignment. The conditions wherein continuous-wave Doppler signal intensity increased with regurgitant volume were specific but poorly predictable combinations of orifice size, flow volume, and perfect beam alignment. Under other conditions flow velocity and turbulence effects dominated, and continuous-wave Doppler signal intensity did not reflect changing regurgitant volume. Continuous-wave Doppler signal intensity-based impressions of regurgitant severity may be unreliable and even misleading under some circumstances.
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- Brandt, Einar, et al.
(author)
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Segmentation of echo cardiographic image sequences using spatio-temporal information
- 1999
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In: Medical Image Computing and Computer-Assisted Intervention – MICCAI’99. - Berlin : Springer. - 354066503X ; , s. 410-419
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Book chapter (peer-reviewed)abstract
- This paper describes a new method for improving border detection in image sequences by including both spatial and temporal information. The method is based on three dimensional quadrature filters for estimating local orientation. A simplification that gives a significant reduction in computational demand is also presented. The border detection framework is combined with a segmentation algorithm based on active contours or ’snakes’, implemented using a new optimization relaxation that can be solved to optimality using dynamical programming. The aim of the study was to compare segmentation performance using gradient based border detection and the proposed border detection algorithm using spatio-temporal information. Evaluation is performed both on a phantom and in-vivo data from five echocardiographic short axis image sequences. It could be concluded that when temporal information was included weak and incomplete boundaries could be found where gradient based border detection failed. Otherwise there was no significant difference in performance between the new proposed method and gradient based border detection.
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