Meeting Abstract
24.6 Monday, Jan. 5 Direct visualization of hemolymph flow in the heart of a grasshopper LEE, W.-K.; SOCHA, J.J.*; Argonne National Laboratory; Virginia Tech jjsocha@vt.edu
Most insect circulatory systems are open, consisting solely of a muscular tube that runs from the abdomen to the anterior body. The heart system includes ostial valves, which can effect incurrent and excurrent flows, and fan-like muscles that originate at the body wall and insert serially along the heart. The combination of complex valving and muscle actuation can result in flow patterns that are not easily predicted from first principles; for instance, some insects are known to periodically reverse heart flow direction. Previous work on insect circulation has determined heartbeat patterns using indirect methods such as contact thermography or infrared light absorbance, but these methods only record bulk flow. Here, we used synchrotron x-ray phase contrast imaging combined with tracer particles to directly visualize intra-heart flow patterns in a grasshopper (Schistocerca americana). We used medical-grade microbubbles (~5 μm) and air bubbles (~10-40 μm) as flow markers, injected into the abdomens of grasshoppers, and recorded videos in real time using 25 keV x-rays. Analyses of x-ray videos reveal that: 1) Flow patterns were complex and time and location dependent, and some flows appear to exhibit a three-dimensional geometry; 2) At times there was no overall transport, but simply a back-and-forth oscillation of the hemolymph; 3) Respiratory structures (tracheae and/or air sacs) were compressed in patterns both synchronous or asynchronous to the local heartbeat; and 4) Maximum measured flows of were on the order of 1.0 cm/s with a Reynolds number of about 5. In addition, we observed possible vortices and incurrent flow through ostial openings. This work represents a new method of visualizing fluid flows in small (millimeter-to-centimeter scale) animals, and may have broad applications across fields, particularly involving developmental studies of vertebrate circulatory systems.
