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Article ; Online: Age and sex-dependent sensitivity analysis of a common carotid artery model.

Schäfer, Friederike / Sturdy, Jacob / Hellevik, Leif Rune

Biomechanics and modeling in mechanobiology

2024

Abstract: The common carotid artery (CCA) is an accessible and informative site for assessing cardiovascular function which makes it a prime candidate for clinically relevant computational modelling. The interpretation of supplemental information possible through ... ...

Abstract	The common carotid artery (CCA) is an accessible and informative site for assessing cardiovascular function which makes it a prime candidate for clinically relevant computational modelling. The interpretation of supplemental information possible through modelling is encumbered by measurement uncertainty and population variability in model parameters. The distribution of model parameters likely depends on the specific sub-population of interest and delineation based on sex, age or health status may correspond to distinct ranges of typical parameter values. To assess this impact in a 1D-CCA-model, we delineated specific sub-populations based on age, sex and health status and carried out uncertainty quantification and sensitivity analysis for each sub-population. We performed a structured literature review to characterize sub-population-specific variabilities for eight model parameters without consideration of health status; variations for a healthy sub-populations were based on previously established references values. The variabilities of diameter and distensibility found in the literature review differed from those previously established in a healthy population. Model diameter change and pulse pressure were most sensitive to variations in distensibility, while pressure was most sensitive to resistance in the Windkessel model for all groups. Uncertainties were lower when variabilities were based on a healthy sub-population; however, the qualitative distribution of sensitivity indices was largely similar between the healthy and general population. Average sensitivity of the pressure waveform showed a moderate dependence on age with decreasing sensitivity to distal resistance and increasing sensitivity to distensibility and diameter. The female population was less sensitive to variations in diameter but more sensitive to distensibility coefficient than the male population. Overall, as hypothesized input variabilities differed between sub-populations and resulted in distinct uncertainties and sensitivities of the 1D-CCA-model outputs, particularly over age for the pressure waveform and between males and females for pulse pressure.
Language	English
Publishing date	2024-02-19
Publishing country	Germany
Document type	Journal Article
ZDB-ID	2093052-5
ISSN	1617-7940 ; 1617-7959
ISSN (online)	1617-7940
ISSN	1617-7959
DOI	10.1007/s10237-023-01808-0
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Article ; Online: Monitoring variability in parameter estimates for lumped parameter models of the systemic circulation using longitudinal hemodynamic measurements.

Bjørdalsbakke, Nikolai L / Sturdy, Jacob / Ingeström, Emma M L / Hellevik, Leif R

Biomedical engineering online

2023 Volume 22, Issue 1, Page(s) 34

Abstract: Background: Physics-based cardiovascular models are only recently being considered for disease diagnosis or prognosis in clinical settings. These models depend on parameters representing the physical and physiological properties of the modeled system. ... ...

Abstract	Background: Physics-based cardiovascular models are only recently being considered for disease diagnosis or prognosis in clinical settings. These models depend on parameters representing the physical and physiological properties of the modeled system. Personalizing these parameters may give insight into the specific state of the individual and etiology of disease. We applied a relatively fast model optimization scheme based on common local optimization methods to two model formulations of the left ventricle and systemic circulation. One closed-loop model and one open-loop model were applied. Intermittently collected hemodynamic data from an exercise motivation study were used to personalize these models for data from 25 participants. The hemodynamic data were collected for each participant at the start, middle and end of the trial. We constructed two data sets for the participants, both consisting of systolic and diastolic brachial pressure, stroke volume, and left-ventricular outflow tract velocity traces paired with either the finger arterial pressure waveform or the carotid pressure waveform. Results: We examined the feasibility of separating parameter estimates for the individual from population estimates by assessing the variability of estimates using the interquartile range. We found that the estimated parameter values were similar for the two model formulations, but that the systemic arterial compliance was significantly different ([Formula: see text]) depending on choice of pressure waveform. The estimates of systemic arterial compliance were on average higher when using the finger artery pressure waveform as compared to the carotid waveform. Conclusions: We found that for the majority of participants, the variability of parameter estimates for a given participant on any measurement day was lower than the variability both across all measurement days combined for one participant, and for the population. This indicates that it is possible to identify individuals from the population, and that we can distinguish different measurement days for the individual participant by parameter values using the presented optimization method.
MeSH term(s)	Humans ; Hemodynamics ; Arteries/physiology ; Blood Pressure/physiology ; Heart ; Models, Biological ; Models, Cardiovascular
Language	English
Publishing date	2023-04-13
Publishing country	England
Document type	Journal Article
ZDB-ID	2084374-4
ISSN	1475-925X ; 1475-925X
ISSN (online)	1475-925X
ISSN	1475-925X
DOI	10.1186/s12938-023-01086-y
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Article ; Online: Effects of arterial wall models and measurement uncertainties on cardiovascular model predictions.

Eck, V G / Sturdy, J / Hellevik, L R

Journal of biomechanics

2017 Volume 50, Page(s) 188–194

Abstract: We developed a methodology to assess and compare the prediction quality of cardiovascular models for patient-specific simulations calibrated with uncertainty-hampered measurements. The methodology was applied in a one-dimensional blood flow model to ... ...

Abstract	We developed a methodology to assess and compare the prediction quality of cardiovascular models for patient-specific simulations calibrated with uncertainty-hampered measurements. The methodology was applied in a one-dimensional blood flow model to estimate the impact of measurement uncertainty in wall model parameters on the predictions of pressure and flow in an arterial network. We assessed the prediction quality of three wall models that have been widely used in one-dimensional blood flow simulations. A 37-artery network, previously used in one experimental and several simulation studies, was adapted to patient-specific conditions with a set of three clinically measurable inputs: carotid-femoral wave speed, mean arterial pressure and area in the brachial artery. We quantified the uncertainty of the predicted pressure and flow waves in eight locations in the network and assessed the sensitivity of the model prediction with respect to the measurements of wave speed, pressure and cross-sectional area. Furthermore, we developed novel time-averaged sensitivity indices to assess the contribution of model parameters to the uncertainty of time-varying quantities (e.g., pressure and flow). The results from our patient-specific network model demonstrated that our novel indices allowed for a more accurate sensitivity analysis of time-varying quantities compared to conventional Sobol sensitivity indices.
MeSH term(s)	Aorta ; Arterial Pressure ; Brachial Artery/physiology ; Hemodynamics ; Humans ; Models, Cardiovascular ; Patient-Specific Modeling ; Uncertainty
Language	English
Publishing date	2017-01-04
Publishing country	United States
Document type	Journal Article
ZDB-ID	218076-5
ISSN	1873-2380 ; 0021-9290
ISSN (online)	1873-2380
ISSN	0021-9290
DOI	10.1016/j.jbiomech.2016.11.042
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Article ; Online: The levels of disclosure relating to mine closure obligations by platinum mining companies

Sturdy, Joline / Cronjé, Christo J

South African journal of economic and management sciences Vol. 20, No. 1 , p. 1-8

2017 Volume 20, Issue 1, Page(s) 1–8

Author's details	Joline Sturdy, Christo J. Cronje
Keywords	content analysis ; disclosure framework ; environmental disclosure ; global reporting initiative ; international integrated reporting framework ; mine closure obligation ; platinum and precious metal sub-sector ; provision for decommissioning ; rehabilitation
Language	English
Size	Online-Ressource
Publishing place	Pretoria
Document type	Article ; Online
ZDB-ID	2628615-4
DOI	10.4102/sajems.v20i1.1556
Database	ECONomics Information System

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Article ; Online: Modeling the differentiation of A- and C-type baroreceptor firing patterns.

Sturdy, Jacob / Ottesen, Johnny T / Olufsen, Mette S

Journal of computational neuroscience

2017 Volume 42, Issue 1, Page(s) 11–30

Abstract: The baroreceptor neurons serve as the primary transducers of blood pressure for the autonomic nervous system and are thus critical in enabling the body to respond effectively to changes in blood pressure. These neurons can be separated into two types (A ... ...

Abstract	The baroreceptor neurons serve as the primary transducers of blood pressure for the autonomic nervous system and are thus critical in enabling the body to respond effectively to changes in blood pressure. These neurons can be separated into two types (A and C) based on the myelination of their axons and their distinct firing patterns elicited in response to specific pressure stimuli. This study has developed a comprehensive model of the afferent baroreceptor discharge built on physiological knowledge of arterial wall mechanics, firing rate responses to controlled pressure stimuli, and ion channel dynamics within the baroreceptor neurons. With this model, we were able to predict firing rates observed in previously published experiments in both A- and C-type neurons. These results were obtained by adjusting model parameters determining the maximal ion-channel conductances. The observed variation in the model parameters are hypothesized to correspond to physiological differences between A- and C-type neurons. In agreement with published experimental observations, our simulations suggest that a twofold lower potassium conductance in C-type neurons is responsible for the observed sustained basal firing, where as a tenfold higher mechanosensitive conductance is responsible for the greater firing rate observed in A-type neurons. A better understanding of the difference between the two neuron types can potentially be used to gain more insight about pathophysiology and treatment of diseases related to baroreflex function, e.g. in patients with autonomic failure, a syndrome that is difficult to diagnose in terms of its pathophysiology.
Language	English
Publishing date	2017-02
Publishing country	United States
Document type	Journal Article
ZDB-ID	1230659-9
ISSN	1573-6873 ; 0929-5313
ISSN (online)	1573-6873
ISSN	0929-5313
DOI	10.1007/s10827-016-0624-6
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Article ; Online: Effect of side branch flow upon physiological indices in coronary artery disease.

Gosling, Rebecca C / Sturdy, Jacob / Morris, Paul D / Fossan, Fredrik Eikeland / Hellevik, Leif Rune / Lawford, Patricia / Hose, D Rodney / Gunn, Julian

Journal of biomechanics

2020 Volume 103, Page(s) 109698

Abstract: Recent efforts have demonstrated the ability of computational models to predict fractional flow reserve from coronary artery imaging without the need for invasive instrumentation. However, these models include only larger coronary arteries as smaller ... ...

Abstract	Recent efforts have demonstrated the ability of computational models to predict fractional flow reserve from coronary artery imaging without the need for invasive instrumentation. However, these models include only larger coronary arteries as smaller side branches cannot be resolved and are therefore neglected. The goal of this study was to evaluate the impact of neglecting the flow to these side branches when computing angiography-derived fractional flow reserve (vFFR) and indices of volumetric coronary artery blood flow. To compensate for the flow to side branches, a leakage function based upon vessel taper (Murray's Law) was added to a previously developed computational model of coronary blood flow. The augmented model with a leakage function (1D
MeSH term(s)	Aged ; Computer Simulation ; Coronary Angiography ; Coronary Artery Disease/physiopathology ; Coronary Vessels/diagnostic imaging ; Coronary Vessels/physiopathology ; Female ; Fractional Flow Reserve, Myocardial ; Hemodynamics ; Humans ; Male ; Middle Aged ; Models, Cardiovascular ; Predictive Value of Tests
Language	English
Publishing date	2020-02-26
Publishing country	United States
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	218076-5
ISSN	1873-2380 ; 0021-9290
ISSN (online)	1873-2380
ISSN	0021-9290
DOI	10.1016/j.jbiomech.2020.109698
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Book ; Online: Redrawing the Boundaries

Sturdy, J. V. M / Knight, Jonathan

The Date of Early Christian Literature

(BibleWorld)

2014

Abstract: Was the New Testament written in the early first century CE or at a much later date? Sturdy's work was conceived as a reply to John Robinson's Reading the New Testament, which dated the New Testament material very early. Sturdy argued that the Pauline ... ...

Series title	BibleWorld
Abstract	Was the New Testament written in the early first century CE or at a much later date? Sturdy's work was conceived as a reply to John Robinson's Reading the New Testament, which dated the New Testament material very early. Sturdy argued that the Pauline letters are in places interpolated, Colossians, Ephesians and the Pastorals are pseudonymous, and that Luke and Acts are not by the same author. He believed that Matthew was the last Synoptic Gospel to be written, with John assigned to the period 140 CE. Redrawing the Boundaries offers a radical approach to New Testament Studies that stands in a
Language	English
Size	Online-Ressource (179 p)
Publisher	Taylor and Francis
Publishing place	Hoboken
Document type	Book ; Online
Note	Description based upon print version of record
ISBN	9781845533014 ; 1845533011
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Article ; Online: Head stabilization measurements as a potential evaluation tool for comparison of persons with TBI and vestibular dysfunction with healthy controls.

Sessoms, Pinata H / Gottshall, Kim R / Sturdy, Jordan / Viirre, Erik

Military medicine

2015 Volume 180, Issue 3 Suppl, Page(s) 135–142

Abstract: A large percentage of persons with traumatic brain injury incur some type of vestibular dysfunction requiring vestibular physical therapy. These injuries may affect the natural ability to stabilize the head while walking. A simple method of utilizing ... ...

Abstract	A large percentage of persons with traumatic brain injury incur some type of vestibular dysfunction requiring vestibular physical therapy. These injuries may affect the natural ability to stabilize the head while walking. A simple method of utilizing motion capture equipment to measure head movement while walking was used to assess improvements in head stabilization of persons undergoing computerized vestibular physical therapy and virtual reality training for treatment of their vestibular problems. Movement data from the head and sacrum during gait were obtained over several visits and then analyzed to determine improved oscillatory head movement relative to the sacrum. The data suggest that, over time with treatment, head stabilization improves and moves toward a pattern similar to that of a healthy control population. This simple analysis of measuring head stability could be transferred to smaller, portable systems that are easily utilized to measure head stability during gait for use in gait assessment and physical therapy training.
MeSH term(s)	Adult ; Brain Injuries/complications ; Brain Injuries/diagnosis ; Brain Injuries/physiopathology ; Female ; Gait/physiology ; Humans ; Male ; Postural Balance/physiology ; Vestibular Diseases/diagnosis ; Vestibular Diseases/etiology ; Vestibular Diseases/physiopathology ; Walking/physiology ; Young Adult
Language	English
Publishing date	2015-03
Publishing country	United States
Document type	Comparative Study ; Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	391061-1
ISSN	1930-613X ; 0026-4075
ISSN (online)	1930-613X
ISSN	0026-4075
DOI	10.7205/MILMED-D-14-00386
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Book ; Online: Modeling the differentiation of A- and C-type baroreceptor firing patterns

Sturdy, Jacob / Ottesen, Johnny T / Olufsen, Mette S

2016

Abstract	The baroreceptor neurons serve as the primary transducers of blood pressure for the autonomic nervous system and are thus critical in enabling the body to respond effectively to changes in blood pressure. These neurons can be separated into two types (A and C) based on the myelination of their axons and their distinct firing patterns elicited in response to specific pressure stimuli. This study has developed a comprehensive model of the afferent baroreceptor discharge built on physiological knowledge of arterial wall mechanics, firing rate responses to controlled pressure stimuli, and ion channel dynamics within the baroreceptor neurons. With this model, we were able to predict firing rates observed in previously published experiments in both A- and C-type neurons. These results were obtained by adjusting model parameters determining the maximal ion-channel conductances. The observed variation in the model parameters are hypothesized to correspond to physiological differences between A- and C-type neurons. In agreement with published experimental observations, our simulations suggest that a twofold lower potassium conductance in C-type neurons is responsible for the observed sustained basal firing, whereas a tenfold higher mechanosensitive conductance is responsible for the greater firing rate observed in A-type neurons. A better understanding of the difference between the two neuron types can potentially be used to gain more insight into the underlying pathophysiology facilitating development of targeted interventions improving baroreflex function in diseased individuals, e.g. in patients with autonomic failure, a syndrome that is difficult to diagnose in terms of its pathophysiology. Comment: Keywords: Baroreflex model, mechanosensitivity, A- and C-type afferent baroreceptors, biophysical model, computational model
Keywords	Quantitative Biology - Neurons and Cognition ; Quantitative Biology - Quantitative Methods
Subject code	590
Publishing date	2016-09-07
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Uncertainty Quantification and Sensitivity Analysis for Computational FFR Estimation in Stable Coronary Artery Disease.

Fossan, Fredrik E / Sturdy, Jacob / Müller, Lucas O / Strand, Andreas / Bråten, Anders T / Jørgensen, Arve / Wiseth, Rune / Hellevik, Leif R

Cardiovascular engineering and technology

2018 Volume 9, Issue 4, Page(s) 597–622

Abstract: Purpose: The main objectives of this study are to validate a reduced-order model for the estimation of the fractional flow reserve (FFR) index based on blood flow simulations that incorporate clinical imaging and patient-specific characteristics, and to ...

Abstract	Purpose: The main objectives of this study are to validate a reduced-order model for the estimation of the fractional flow reserve (FFR) index based on blood flow simulations that incorporate clinical imaging and patient-specific characteristics, and to assess the uncertainty of FFR predictions with respect to input data on a per patient basis. Methods: We consider 13 patients with symptoms of stable coronary artery disease for which 24 invasive FFR measurements are available. We perform an extensive sensitivity analysis on the parameters related to the construction of a reduced-order (hybrid 1D-0D) model for FFR predictions. Next we define an optimal setting by comparing reduced-order model predictions with solutions based on the 3D incompressible Navier-Stokes equations. Finally, we characterize prediction uncertainty with respect to input data and identify the most influential inputs by means of sensitivity analysis. Results: Agreement between FFR computed by the reduced-order model and by the full 3D model was satisfactory, with a bias ([Formula: see text]) of [Formula: see text] at the 24 measured locations. Moreover, the uncertainty related to the factor by which peripheral resistance is reduced from baseline to hyperemic conditions proved to be the most influential parameter for FFR predictions, whereas uncertainty in stenosis geometry had greater effect in cases with low FFR. Conclusion: Model errors related to solving a simplified reduced-order model rather than a full 3D problem were small compared with uncertainty related to input data. Improved measurement of coronary blood flow has the potential to reduce uncertainty in computational FFR predictions significantly.
MeSH term(s)	Aged ; Blood Flow Velocity ; Cardiac Catheterization/methods ; Computed Tomography Angiography ; Coronary Angiography/methods ; Coronary Artery Disease/diagnosis ; Coronary Artery Disease/physiopathology ; Coronary Stenosis/diagnosis ; Coronary Stenosis/physiopathology ; Coronary Vessels/diagnostic imaging ; Coronary Vessels/physiopathology ; Female ; Fractional Flow Reserve, Myocardial ; Humans ; Male ; Middle Aged ; Models, Cardiovascular ; Patient-Specific Modeling ; Predictive Value of Tests ; Prognosis ; Reproducibility of Results ; Uncertainty
Language	English
Publishing date	2018-10-31
Publishing country	United States
Document type	Comparative Study ; Journal Article ; Research Support, Non-U.S. Gov't ; Validation Studies
ZDB-ID	2543111-0
ISSN	1869-4098 ; 1869-408X
ISSN (online)	1869-4098
ISSN	1869-408X
DOI	10.1007/s13239-018-00388-w
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