Aqueous flow limitation in uniform collapsible tubes: multiple flow-limited flow-rates at the same pressure drop and upstream transmural pressure
Proc. ASME Summer Bioengineering Conference, 50, ASME, (2001)Abstract
Large-amplitude oscillation in collapsible tubes is often but not necessarily associated with flow-rate limitation1,2. Flow limitation can arise through either of two mechanisms, one based on viscous head
loss and the other on wavespeed3. The transition between the two appears to be seamless, so that flow limitation can occur at any flowrate. In contrast, the self-excited oscillations which are often
associated with flow limitation require fluid inertia for their maintenance, and are accordingly seen only above a Reynolds number based on uncollapsed tube diameter of a few hundred. The question of
the minimum Reynolds number is of importance in numerical modelling, where stability or validity may be lost as the Reynolds number increases. Clinically, undesirable oscillations can also occur in the inferior vena cava if heart-lung bypass pumping is turned up too high4. Until now, the lowest Reynolds number for published oscillations was about 300, for an extremely diaphanous tube5. We have re-investigated this question, using ordinary latex Penrose tubes.