The relationship between intracardiovascular smoke-like echo and erythrocyte rouleaux formation

Intravascular smoke-like echo always appears in regions of stasis, but the exact mechanism of its production is unclear. We investigated its appearance in relation to erythrocyte rouleaux formation. To study this relationship we performed a series of in vitro and animal experiments. In the in vitro study, we observed an erythrocyte suspension by ultrasonography and found it to be echo-free. Under the microscope, red blood cells were observed in a dispersed state. If an equal amount of lymphocyte separation solution was added to the suspension, smoke-like echo appeared, and red blood cells were seen in a rouleaux pattern. In animal (mongrel dogs) experiments, under physiologic conditions with normal blood flow velocity, all cardiac cavities and the inferior vena cava were echo-free. When stasis was induced experimentally in the inferior vena cava, red blood cells aggregated to form rouleaux and smoke-like echo appeared. On resumption of normal blood flow, the rouleaux dispersed to form erythrocytes again. The mechanism of production of intracardiovascular smoke-like echo is closely related to the formation of erythrocyte rouleaux. When rouleaux are formed, they become larger and appear nearer or larger than the ultrasonic wavelength. Thus reflections are produced and smoke-like echo appears.