Turbulence Intensity Measured in the Center of Canine Ascending Aorta with a Hot-Film Anemometer

Abstract

The turbulence intensity near the central axis of the canine ascending aorta was measured with a hot-film anemometer. The cardiac output and the heart rate were controlled arbitrarily by the use of an extracorporeal circulation called open-loop method and of an atrial pacing. Drugs other than anesthetics were not used.
Blood flow velocity waveforms showed high-frequency fluctuations appearing near at the peak systolic velocity and persisting all the way through the deceleration phase of systole. These fluctuations were regarded as turbulence.
We designed a computer method for separating the turbulence from the physiological changes of the blood flow velocity. The mean turbulence intensity was defined as the square root of the time integral of the ensemble average square of the turbulence velocity; the integration interval was the whole deceleration phase of the ensemble average blood flow velocity. The relative mean turbulence intensity was defined as the ratio of the mean turbulence intensity to the time mean sectional average velocity in the aorta. It was constant in most animals regardless of the changes in fluid mechanical parameters. In some animals, however, the relative mean turbulence intensity was dependent upon the peak Reynolds number. The relative mean turbulence intensity positively correlated with the frequency parameter, but the correlation was not so strong. The amplitude ratio (ratio of the peak velocity to the mean velocity) failed to make its role clear in the turbulence phenomena in the present experiments.