Filling of a model left ventricle studied by colour M mode Doppler

It has been proposed that the early diastolic flow pattern inside the left ventricle reflects ventricular diastolic function. The flow pattern often divides into two phases towards the apex. The aim of this study was to examine the hydrodynamic nature of this phenomenon.

A rubber balloon representing the ventricle was connected to a reservoir representing the atrium, both filled with anticoagulated blood. Rigid "mitral" orifices 20 mm long and 15-40 mm in diameter were used. Surrounding the ventricle was a water filled chamber to which suction could be applied. The colour M mode Doppler sample beam coincided with the ventricular long axis. Colour M mode measures velocity at multiple sites along the beam simultaneously. The timing and magnitude of the velocities were analysed digitally. The filling was also qualitatively studied by ultrasonic two dimensional sector scanning.

At the start of the filling, blood moved simultaneously at all levels, behaving as a fluid column. This was denoted "phase I". A flow wave then propagated from the mitral orifice towards the apex, called "phase II". This was found to represent a ring vortex, with blood velocities twice its propagation velocity [ratio 2.1(SEM 0.016)]. The ratio between the velocity time integrals of phase II and phase I decreased progressively from 51(15) to 0.41(0.14) when mitral orifice diameter was increased in 5 mm steps from 15 mm to 40 mm (p < 0.001). The propagation velocity correlated strongly with peak transmitral blood velocity, r = 0.95, p < 0.001. The flow patterns resembled patterns recorded in patients.

The two phases of the filling pattern represented the motion of a blood column and the propagation of a ring vortex, respectively. Mitral orifice size determined which phase dominated the flow pattern.