Cardiovascular modelling and ultrasound heart flow quantification : aortic flow and mitral regurgitation

Sammanfattning: The primary objective of this thesis was to model and simulate aortic flow and mitral regurgitation and to improve quantitative ultrasound measurements. The tools used were; theoretical analysis, computer simulation, model experiments, image analysis and clinical evaluation.The flow in the aorta is known to be influenced by both cardiac function and vascular characteristics. The influence of vascular characteristics were investigated in a three parameter windkessel model. Peak aortic velocity and acceleration were studied when these parameters were changed. The results indicate that aortic peak flow velocity is related to the compliance of the arterial system while the peak flow acceleration is inversely related to the characteristic impedance of the aorta and large vessels.To obtain a correct aortic flow velocity profile from a two dimensional colour flow echocardiographic investigation, a unit which incrementally delayed the ECG signal was designed and used to control the ultrasound scanning. By combining velocity data from incrementally delayed images in a software program, a time corrected profile was obtained.In order to determine regurgitant heart valve flow volume, the intensity of the ultrasound continuous wave signal has been suggested as a potential method. Measurements in a hydraulic model showed, however, that the intensity of the signal was, in addition to volume, also related to peak velocity, measuring angle and machine settings. Hence, conclusions drawn about regurgitant grade from the intensity signal require caution.Another method for determination of valve regurgitation is to study the laminar and nondisturbed flow in the region of acceleration proximal to the valve, normally the distance from orifice to the first aliased velocity. This was tested first in a steady flow model using colour M mode and colour 2D information, and later in a pulsatile flow model. Four different methods using velocity data from the entire reconstructed 2D velocity vector field were investigated. Model experiments and error calculation showed that flow was best determined by integrating velocities along hemi-spherical lines in two perpendicular planes within an angle of ±45° from the orifice centre line at a distance of approximately 1.2 to 1.4 times the orifice diameter, corresponding to velocities between 0.15 and 0.45 m/s. By combining 2D flow and spectral velocity data, regurgitant volume could be estimated for both circular, diagonal and crescent orifices to within + 15 to -11% from true volume.