Functional morphology and patterns of blood flow in the heart of Python regius

Abstract

Brightness-modulated ultrasonography, continuous-wave Doppler, and pulsed-wave Doppler-echocardiography were used to analyze the functional morphology of the undisturbed heart of ball pythons. In particular, the action of the muscular ridge and the atrio-ventricular valves are key features to understand how patterns of blood flow emerge from structures directing blood into the various chambers of the heart. A step-by-step image analysis of echocardiographs shows that during ventricular diastole, the atrio-ventricular valves block the interventricular canals so that blood from the right atrium first fills the cavum venosum, and blood from the left atrium fills the cavum arteriosum. During diastole, blood from the cavum venosum crosses the muscular ridge into the cavum pulmonale. During middle to late systole the muscular ridge closes, thus prohibiting further blood flow into the cavum pulmonale. At the same time, the atrio-ventricular valves open the interventricular canal and allow blood from the cavum arteriosum to flow into the cavum venosum. In the late phase of ventricular systole, all blood from the cavum pulmonale is pressed into the pulmonary trunk; all blood from the cavum venosum is pressed into both aortas. Quantitative measures of blood flow volume showed that resting snakes bypass the pulmonary circulation and shunt about twice the blood volume into the systemic circulation as into the pulmonary circulation. When digesting, the oxygen demand of snakes increased tremendously. This is associated with shunting more blood into the pulmonary circulation. The results of this study allow the presentation of a detailed functional model of the python heart. They are also the basis for a functional hypothesis of how shunting is achieved. Further, it was shown that shunting is an active regulation process in response to changing demands of the organism (here, oxygen demand). Finally, the results of this study support earlier reports about a dual pressure circulation in Python regius.

Anatomy of the python heart

“…Shunts always lower the efficiency of oxygen transport, and it is the source of debate as to whether the reduced capacity for cardiac shunts in pythons may relate to their increased oxygen consumption during digestion or egg incubation (Wang and Hicks 2002;Wang et al 2003). Ultrasonography shows that the atrioventricular valves in pythons descend into the ventricle in diastole, so that the right atrio-ventricular valve lies on the vertical septum and thwarts the possibility of shunting during cardiac filling (Sklansky et al 2001;Starck 2009;Jensen et al 2010). This was supported experimentally by in situ perfused hearts .…”

“…In some snakes and turtles, shunts can, under some circumstances, approach 100%, which is then due to both wash-out and pressure shunts (Lillywhite and Donald 1989;Overgaard et al 2002). A recent study, however, concluded that shunts of up to 50% may take place in ball pythons (Starck 2009). Shunts always lower the efficiency of oxygen transport, and it is the source of debate as to whether the reduced capacity for cardiac shunts in pythons may relate to their increased oxygen consumption during digestion or egg incubation (Wang and Hicks 2002;Wang et al 2003).…”

“…Previous studies on the python heart have emphasized the large muscular ridge (e.g., Hopkinson and Pancoast 1837;Jacquart 1855), the differentiation into left and right sides of the ventricle (Acolat 1943;Webb et al 1971), the reduced size of the cavum venosum (Van Mierop and Kutsche 1985), as well as the dynamic actions of the atrioventricular valves (Sklansky et al 2001;Jensen et al 2010). Most studies on python hearts, however, have placed little emphasis on the differences from other snakes and reptiles (Pettigrew 1864;O'Donoghue 1918;Goodrich 1919;Leene and Vorstman 1930;Vorstman 1933;Meinertz 1952;Goodrich 1958;Kashyap 1959;Meinertz 1966b;Robb 1965;Webb et al 1974;Webb 1979;MacKinnon and Heatwole 1981;Van Mierop and Kutsche 1981;Poupa and Lindström 1983;Jacobson et al 1991;Young et al 1993;Young 1994;Young et al 1994;Farrell et al 1998;Rishniw and Carmel 1999;Snyder et al 1999;Rush et al 2001;Chetboul et al 2004;Schilliger et al 2005;Starck 2009). Thus, little is known about the structural configuration of the vertical septum and the bulbuslamelle (Webb et al 1971;Burggren and Johansen 1982;Wang et al , 2003Jensen et al 20...…”

“…Thus, all three septa contribute to the complex pressure separation in python hearts. Python hearts may grow up to 40% during the digestion of large meals (Andersen et al 2005), and may change the magnitude of cardiac shunts during digestion (Starck 2009). To understand these extraordinary phenomena, it is important to obtain a more detailed understanding of the ventricular anatomy of pythons.…”

Two-Dimensional and Doppler echocardiographic findings in healthy non-sedated red-eared slider terrapins (Trachemys scripta elegans)

“…Some authors have investigated normal ultrasound anatomy in some reptilian species such as Carpet Python (Morelia spilota variegata) (Sklansky et al 2001), Burmese Python (Python molurus bivittatus) (Snyder et al 1999) and the functional morphology and blood flow patterns in Ball Python (Python regius) (Starck 2009) and the alligator (Alligator Mississipiensis) (Malvin et al 1995). Nevertheless, to date just few echocardiographic studies in chelonian reptiles have been published.…”