The intravenous membrane oxygenator (IMO) incorporates a centrally positioned balloon surrounded by hollow microporous fibers. Previous studies using this configuration have demonstrated that rhythmic pulsation of the balloon enhances gas exchange, presumably by three dimensional convective mixing. This study sought to characterize vessel wall vibrations imparted by intra vena caval balloon pumping. An in vitro flow loop incorporating a current IMO prototype was used for these measurements. The IMO prototype was inserted in a modeled vena cava on which ultrasonic dimension transducers were mounted on the outer surface. The flow loop was operated at physiologic flow rates. The balloon was activated, and dynamic vessel diameter measurements were recorded as the pumping frequency was varied from 40 to 120 beats per minute (bpm). A Fast Fourier Transform algorithm generated a frequency spectrum at each bpm and for two different balloon configurations; a single balloon versus a tripartite arrangement, the authors' results demonstrate that the mean amplitude of vena caval oscillations varied with bpm, and that this variation followed the trends in oxygen transfer rates. This suggests that the motion of the vessel wall may contribute to convective mixing of blood. In addition, this work demonstrated significant differences in the frequency spectra associated with our two balloon configurations.
|Published - Jul 1994
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