Reptiles may experience drastic growth rates, some species reaching an order of 10,000-fold of body mass increase during their lifespan. This massive increment in body mass may compromise blood flow, since the Poiseuille's equation indicates that resistance to flow increases with tube length. To circumvent this problem, reptiles increase their arterial pressure with body mass to maintain an adequate blood perfusion. The generation of higher pressures might be related to changes in heart morphology. For example, cardiomyocyte fiber orientation is an important indicator of cardiac function, and the ratio between compact to spongy myocardium is often related to cardiomyopathy and contractility in humans. Therefore, the evaluation of those morphological parameters is mandatory to comprehend how blood pressure scales with body mass in reptiles. With this proposal, we intend to investigate heart morphology of reptiles with and without intraventricular separation (crocodilians and chelonians, respectively), since the former presents mammalian-like pressure separation between systemic and pulmonary circuits, whereas the later exhibits equal systolic pressures for both circuits. In collaboration with Prof. Dane Crossley, from the University of North Texas, USA, we will obtain hearts from the American alligator, Alligator mississippiensis, and the common snapping turtle, Chelydra serpentina, from a large range of body masses (100g to 7000g), that will be scanned using state-of-the-art imaging techniques developed by Prof. Dr. Michael Pedersen, from the Comparative Medicine Lab from Aarhus University Hospital, Denmark, to track cardiomyocyte fibers arrangement. Images will also be used to measure variations in ventricular wall thickness and lumen radius; the combination of those parameters with the measurements of arterial pressures from A. mississippiensis and C. serpentina will allow us to estimate ventricular wall stress and tension. Pressure measurements from both A. mississipiensis and C. serpentina were recently obtained in a previous stage of the applicant's (Dr. Renato Filogonio) current post-doc project. Stroke volume and ejection fraction will be measured to understand how blood flow is affected by increased body masses. For that, we will use non-invasive functional magnetic resonance imaging (fMRI) in several species of crocodilians (Paleosuchus palpebrosus, Caiman latirostris, and Caiman crocodilus) and the freshwater turtle, Trachemys scripta, from animals ranging from 200g to 4000g. These species were made available by Prof. Dr. Tobias Wang, from the Section of Zoophysiology from Aarhus University, Denmark. Histological analysis of the heart will allow us to define the ratio between compact to spongy myocardium and determine how this trait affects cardiac output with increased body mass. This project will count with a broad collaboration from several research groups including those of Prof. Dr. Tobias Wang (Aarhus University, Denmark), Prof. Dr. Michael Pedersen (Aarhus University Hospital, Denmark), and Prof. Dr. Dane A. Crossley II (University of North Texas, USA). The results will be relevant to clarify important questions regarding the evolution of the cardiovascular system, but may also be pertinent to medical practitioners studying hemodynamic perturbations in congenital heart diseases.
News published in Agência FAPESP Newsletter about the scholarship: