Verification and clinical demonstration of the echo Doppler series effect and vortex shed distance

We evaluated observable flow patterns beyond an obstruction in a flow model and documented, by echo Doppler examination, the clinical incidence and significance of these flow patterns in children with congenital cardiac disease. The flow model consisted of a constant-pressure reservoir that allowed flow to pass through an obstruction and then into an observation chamber. Carbon particles were injected into the system to allow visualization of flow and to act as ultrasound reflectors. Flow at rates from 0.6-1.2 l/min passed through interchangeable round, triangular and elliptical obstructing orifices. Flow formed a jet at the obstructing orifice. Downstream, the jet remained intact for a distance before dispersing into numerous vortices. These vortices swirled and moved in multiple directions, but generally downstream, until damping occurred and laminar flow reorganized. Mean vortex shed distance was 13 mm (range 12-15 mm). The mean length of the postjet flow disturbance in out model was 42 mm (range 40-46 mm). The length of these flow effects did not appear to depend significantly upon the flow rate or obstructive orifice geometry for flows and orifices that we investigated. Only visually detectable flow disturbances caused frequency dispersion that were detectable by echo Doppler. These same flow patterns were investigated by echo Doppler examination in 47 children with pulmonary stenosis, aortic stenosis and arterial and ventricular septal defects. A flow disturbance was detected in 77% of patients in downstream chambers or great vessels that were in series with the chamber or great vessel that would be expected to contain the flow disturbance. We called the extension of the flow disturbance downstream the 'series effect'. Nine patients (19%) demonstrated displacement of the first detection of the flow disturbance beyond the primary site of the abnormality, and such displacement was probably due to a long vortex shed distance. This study indicates that flow abnormalities created by cardiac defects are frequently characterized by the series effect and vortex shed distance, both of which may cause confusion regarding the site of the defect.