Tubular hearts are widespread in animals. Many of these hearts – simple tubes of muscle that contract to drive flow within the tube – are also “valveless” with the direction of the flow determined only by the muscular contractions.
We use a host of techniques to study the role of accessory structures (such as the pericardium, or outer layer that surrounds the muscular tube), pumping mechanism (peristalsis, dynamic suction pumping) and evolution of these structures.
The valveless, tubular hearts of tunicates are an excellent model for these studies. This is the contraction of the heart of Ciona savignyi, a solitary tunicate:
We use in vivo micro-injection techniques to introduce fluorescent dyes, fluorescent microbeads, and contrast agents to quantify fluid flow and circulatory system morphology of individual tunicates. Example injection with fluorescein dye:
Injection with fluorescent microbeads allows us to quantify flow within the circulatory system with micro particle image velocimetry (µPIV), which produces 2D velocity vector fields:
In a collaboration with Dr. Laura Miller (Mathematics, Univ. of North Carolina at Chapel Hill), we also use computational simulations to investigate the role of accessory structures and pumping mechanism in ways that cannot be accomplished through experiments alone. Simulation below is pumping by a flexible heart using the immersed boundary method to study the role of the pericardium (code by Laura Miller).
L.D. Waldrop, L.A. Miller. 2015. Large Amplitude Short Wave Peristalsis and Its Implications for Transport. Biomechanics and Modeling in Mechanobiology 15(3): 629-642. Full text.
A. Baird, L.D. Waldrop, L.A. Miller. 2015. Neuromechanical pumping: boundary flexibility and traveling depolarization waves drive flow within valveless, tubular hearts. Japan Journal of Industrial and Applied Mathematics 32(3): 829–846. Full text.
L.D. Waldrop, L.A. Miller. 2015. The role of the pericardium in the valveless, tubular heart of the tunicate, Ciona savignyi. Journal of Experimental Biology 218(17): 2753–2763. Full text.