Imaging and modeling the cardiovascular system

Understanding cardiac pumping function is crucial to guiding diagnosis, predicting outcomes of interventions, and designing medical devices that interact with the cardiovascular system. In turn, better diagnostics and treatment of cardiovascular function would improve the prognosis of cardiovascular diseases, which account for 31% of all global deaths. The heart and the vascular system are strongly coupled, and changes in arterial properties that occur with age and in the presence of pathologies have a significant impact on cardiac function. Because of the complexity of the cardiovascular system and the diversity of disease processes, it is not always possible to understand the role played by each part of the system in the final outcome. Computer simulations of hemodynamics can show how the system is influenced by changes in single or multiple cardiovascular parameters and can be used to test clinically relevant hypotheses. In addition, methods for the detection and quantification of important markers such as elevated arterial stiffness would help reduce the morbidity and mortality related to cardiovascular disease. The general aim of this thesis work was to improve understanding of cardiovascular physiology and develop new methods for assisting clinicians during diagnosis and follow-up of treatment in cardiovascular disease. Both computer simulations and medical imaging were used to reach this goal.

In the first study, a new cardiac model based on piston-like motions of the atrioventricular plane was developed in order to deepen the understanding of the forces responsible for filling and emptying of the cardiac chambers. In the second study, the presence of the anatomical basis needed to generate hydraulic forces during diastole was assessed in heathy volunteers. In the third study, a previously validated lumped-parameter model was used to quantify the contribution of arterial and cardiac changes to blood pressure during aging. In the fourth study, in-house software that measures arterial stiffness by ultrasound shear wave elastography (SWE) was developed and validated against mechanical testing.

The studies showed that longitudinal movements of the atrioventricular plane can well explain cardiac pumping and that the macroscopic geometry of the heart enables the generation of hydraulic forces that aid ventricular filling. Additionally, simulations showed that structural changes in both the heart and the arterial system contribute to the progression of blood pressure with age. Finally, the SWE technique was validated to accurately measure stiffness in arterial phantoms. Future ex vivo and in vivo studies are needed to determine the technique’s sensitivity and applicability to clinical measurements.

List of scientific papers

I. Modeling the heart with the atrioventricular plane as a piston unit. E. Maksuti, A. Bjällmark, M. Broomé. Medical Engineering & Physics. vol. 37, p. 87–92, 2015.
https://doi.org/10.1016/j.medengphy.2014.11.002

II. Hydraulic forces contribute to left ventricular diastolic filling. E. Maksuti, M. Carlsson, H. Arheden. S.J. Kovács, M. Broomé, M. Ugander. [Manuscript]

III. Contribution of the arterial system and the heart to blood pressure during normal aging – a simulation study. E. Maksuti, N. Westerhof, B. Westerhof, M. Broomé, N. Stergiopulos. PLoS ONE. 11(6):e0157493, 2016.
https://doi.org/10.1371/journal.pone.0157493

IV. Arterial stiffness estimation by shear wave elastography: validation in phantoms with mechanical testing. E. Maksuti, E. Widman, D. Larsson, M. W. Urban, M. Larsson, A. Bjällmark. Ultrasound in Medicine & Biology. vol. 42, p. 309–321, 2016.
https://doi.org/10.1016/j.ultrasmedbio.2015.08.012