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Imaging and modeling the cardiovascular system
KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.ORCID iD: 0000-0002-9654-447X
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Understanding cardiac pumping function is crucial to guiding diagnosis, predicting outcomes of interventions, and designing medical devices that interact with the cardiovascular system.  Computer simulations of hemodynamics can show how the complex cardiovascular system is influenced by changes in single or multiple parameters and can be used to test clinical hypotheses. In addition, methods for the 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 cardiac model based on piston-like motions of the atrioventricular plane was developed. 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.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. , 96 p.
Series
TRITA-STH, 2016:9
Keyword [en]
Cardiac pumping, diastolic function, hemodynamics, modeling, simulation, arterial stiffness, ultrasound, shear wave elastography.
National Category
Other Medical Engineering
Research subject
Medical Technology
Identifiers
URN: urn:nbn:se:kth:diva-196538ISBN: 978-91-7729-192-3OAI: oai:DiVA.org:kth-196538DiVA: diva2:1046800
Public defence
2016-12-09, T2, Hälsovägen 11C, Huddinge, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2012-2800, 2012-2795VINNOVA, 2011-01365
Note

QC 20161115

Available from: 2016-11-15 Created: 2016-11-15 Last updated: 2016-11-15Bibliographically approved
List of papers
1. Modelling the heart with the atrioventricular plane as a piston unit
Open this publication in new window or tab >>Modelling the heart with the atrioventricular plane as a piston unit
2015 (English)In: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 37, no 1, 87-92 p.Article in journal (Refereed) Published
Abstract [en]

Medical imaging and clinical studies have proven that the heart pumps by means of minor outer volume changes and back-and-forth longitudinal movements in the atrioventricular (AV) region. The magnitude of AV-plane displacement has also shown to be a reliable index for diagnosis of heart failure. Despite this, AV-plane displacement is usually omitted from cardiovascular modelling. We present a lumped-parameter cardiac model in which the heart is described as a displacement pump with the AV plane functioning as a piston unit (AV piston). This unit is constructed of different upper and lower areas analogous with the difference in the atrial and ventricular cross-sections. The model output reproduces normal physiology, with a left ventricular pressure in the range of 8-130 mmHg, an atrial pressure of approximatly 9 mmHg, and an arterial pressure change between 75 mmHg and 130 mmHg. In addition, the model reproduces the direction of the main systolic and diastolic movements of the AV piston with realistic velocity magnitude (similar to 10 cm/s). Moreover, changes in the simulated systolic ventricular-contraction force influence diastolic filling, emphasizing the coupling between cardiac systolic and diastolic functions. The agreement between the simulation and normal physiology highlights the importance of myocardial longitudinal movements and of atrioventricular interactions in cardiac pumping.

Keyword
Atrioventricular interaction, Cardiac function, Cardiac pumping, Longitudinal function, Cardiac model, Bond graphs
National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:kth:diva-161634 (URN)10.1016/j.medengphy.2014.11.002 (DOI)000349585100011 ()25466260 (PubMedID)2-s2.0-84920913473 (ScopusID)
Note

QC 20150324

Available from: 2015-03-24 Created: 2015-03-13 Last updated: 2016-11-15Bibliographically approved
2. Hydraulic forces contribute to left ventricular diastolic filling
Open this publication in new window or tab >>Hydraulic forces contribute to left ventricular diastolic filling
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2016 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Myocardial active relaxation and restoring forces are known determinants of left ventricular (LV) diastolic function. We hypothesize the existence of an additional mechanism involved in LV filling, namely, a hydraulic force contributing to the longitudinal motion of the atrioventricular (AV) plane. A prerequisite for the presence of a net hydraulic force during diastole is that the atrial short-axis area (ASA) is smaller than the ventricular short-axis area (VSA). We aimed (a) to illustrate this mechanism in an analogous physical model, (b) to measure the ASA and VSA throughout the cardiac cycle in healthy volunteers using cardiovascular magnetic resonance imaging, and (c) to calculate the magnitude of the hydraulic force. The physical model illustrated that the anatomical difference between ASA and VSA provides the basis for generating a hydraulic force during diastole. In volunteers, VSA was greater than ASA during 75-100% of diastole. The hydraulic force was the same order of magnitude as the peak driving force of LV (1-3N vs 5-10N). Hydraulic forces are a consequence of left heart anatomy and aid LV diastolic filling. These findings suggest that the relationship between ASA and VSA, and the resulting hydraulic forces, should be considered when characterizing diastolic function and dysfunction. 

National Category
Medical and Health Sciences
Research subject
Medical Technology
Identifiers
urn:nbn:se:kth:diva-196532 (URN)
Note

QC 20161115

Available from: 2016-11-15 Created: 2016-11-15 Last updated: 2016-11-15Bibliographically approved
3. Contribution of the Arterial System and the Heart to Blood Pressure during Normal Aging: A Simulation Study
Open this publication in new window or tab >>Contribution of the Arterial System and the Heart to Blood Pressure during Normal Aging: A Simulation Study
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2016 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 6, e0157493Article in journal (Refereed) Published
Abstract [en]

During aging, systolic blood pressure continuously increases over time, whereas diastolic pressure first increases and then slightly decreases after middle age. These pressure changes are usually explained by changes of the arterial system alone (increase in arterial stiffness and vascular resistance). However, we hypothesise that the heart contributes to the age-related blood pressure progression as well. In the present study we quantified the blood pressure changes in normal aging by using a Windkessel model for the arterial system and the time-varying elastance model for the heart, and compared the simulation results with data from the Framingham Heart Study. Parameters representing arterial changes (resistance and stiffness) during aging were based on literature values, whereas parameters representing cardiac changes were computed through physiological rules (compensated hypertrophy and preservation of end-diastolic volume). When taking into account arterial changes only, the systolic and diastolic pressure did not agree well with the population data. Between 20 and 80 years, systolic pressure increased from 100 to 122 mmHg, and diastolic pressure decreased from 76 to 55 mmHg. When taking cardiac adaptations into account as well, systolic and diastolic pressure increased from 100 to 151 mmHg and decreased from 76 to 69 mmHg, respectively. Our results show that not only the arterial system, but also the heart, contributes to the changes in blood pressure during aging. The changes in arterial properties initiate a systolic pressure increase, which in turn initiates a cardiac remodelling process that further augments systolic pressure and mitigates the decrease in diastolic pressure.

National Category
Medical Image Processing
Identifiers
urn:nbn:se:kth:diva-189802 (URN)10.1371/journal.pone.0157493 (DOI)000378393600007 ()27341106 (PubMedID)2-s2.0-84976491042 (ScopusID)
Funder
Swedish Research Council, 2012-2800
Note

QC 20160720

Available from: 2016-07-20 Created: 2016-07-15 Last updated: 2016-11-15Bibliographically approved
4. ARTERIAL STIFFNESS ESTIMATION BY SHEAR WAVE ELASTOGRAPHY: VALIDATION IN PHANTOMS WITH MECHANICAL TESTING
Open this publication in new window or tab >>ARTERIAL STIFFNESS ESTIMATION BY SHEAR WAVE ELASTOGRAPHY: VALIDATION IN PHANTOMS WITH MECHANICAL TESTING
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2016 (English)In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 42, no 1, 308-321 p.Article in journal (Refereed) Published
Abstract [en]

Arterial stiffness is an independent risk factor found to correlate with a wide range of cardiovascular diseases. It has been suggested that shear wave elastography (SWE) can be used to quantitatively measure local arterial shear modulus, but an accuracy assessment of the technique for arterial applications has not yet been performed. In this study, the influence of confined geometry on shear modulus estimation, by both group and phase velocity analysis, was assessed, and the accuracy of SWE in comparison with mechanical testing was measured in nine pressurized arterial phantoms. The results indicated that group velocity with an infinite medium assumption estimated shear modulus values incorrectly in comparison with mechanical testing in arterial phantoms (6.7 +/- 0.0 kPa from group velocity and 30.5 +/- 0.4 kPa from mechanical testing). To the contrary, SWE measurements based on phase velocity analysis (30.6 +/- 3.2 kPa) were in good agreement with mechanical testing, with a relative error between the two techniques of 8.8 +/- 6.0% in the shear modulus range evaluated (40-100 kPa). SWE by phase velocity analysis was validated to accurately measure stiffness in arterial phantoms.

Keyword
Accuracy, Arterial phantom, Arterial stiffness, Group velocity, Lamb waves, Mechanical testing, Phase velocity, Poly(vinyl alcohol), Shear modulus, Shear wave elastography
National Category
Medical Image Processing
Identifiers
urn:nbn:se:kth:diva-181377 (URN)10.1016/j.ultrasmedbio.2015.08.012 (DOI)000367733800032 ()26454623 (PubMedID)2-s2.0-84957007046 (ScopusID)
Funder
VINNOVA, 2011-01365Swedish Research Council, 2012-2795
Note

QC 20160203

Available from: 2016-02-03 Created: 2016-02-01 Last updated: 2016-11-15Bibliographically approved

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