Abstract:In spite of cardiovascular system (CVS) response to posture changes have been widely studied, a number of mechanisms and their interplay in regulating central blood pressure and organs perfusion upon orthostatic stress are not yet clear. We propose a novel multiscale 1D-0D mathematical model of the human CVS to investigate the effects of passive (i.e., through head-up tilt without muscular intervention) posture changes. The model includes the main short-term regulation mechanisms and is carefully validated aga… Show more
“…Figure 1 f , g and top diagrams on all panels of figure 4 show how the separated components of pressure and flow waveforms are altered by orthostatic stress. Forward and backward pressure waves exhibit the same behaviour observed for the total (forward + backward) pressure signals after passive tilting to the standing posture [ 26 ], with both pressure components reduced in amplitude following global pulse pressure contraction ( figure 1 f , g ). Moving along the aortic-wise direction, figure 4 shows that both forward and backward pressure signals are progressively shifted upward to higher mean pressure levels because of the increasing hydrostatic contribution encountered while moving below the heart level: standing mean forward pressure +1.6 mmHg and mean backward pressure +2 mmHg at ascending aorta no.…”
Section: Resultsmentioning
confidence: 58%
“…The reason for this phase shifting lies in the raised heart rate with respect to the supine state (see table 1 ), altering the systolic–diastolic balance over the single heartbeat. Indeed, the higher heart rate encountered at standing posture leads to an increased systolic duration in contrast to a shortened diastole, resulting in the observed phase shifting of pressure and flow signals [ 26 ]. Figure 4 Forward (green) and backward (red) pressure ( P ) and wave intensity (WI) profiles—on top and bottom side of panels, respectively—obtained at different sites along the aorta for the supine (solid lines) and standing (dashed lines) positions.…”
Section: Resultsmentioning
confidence: 99%
“…Passive orthostatic stress experienced when tilting from the horizontal supine to the upright standing position triggers a number of cardiovascular responses [1,2]. In table 1, the response of the main haemodynamics parameters to posture change from 0∘ to 90∘ head-up is recalled (see [26] for more details). In the same table, we also specified which parameters are directly controlled by each short-term mechanism (baroreflex, cardiopulmonary reflex and cerebral autoregulation).…”
Section: Resultsmentioning
confidence: 99%
“…The CVS model accounts for the action of specific extravascular pressures onto given vascular districts: the intramyocardial pressure (IMP [28], figure 1c), the intrathoracic pressure (ITP [27], figure 1e, electronic supplementary material, equation (S8)) and the intracranial pressure (ICP [26], figure 1d). ITP and ICP depend on the body posture [26,27]. royalsocietypublishing.org/journal/rsos R. Soc.…”
Section: The Cardiovascular Modelmentioning
confidence: 99%
“…To explain the paradoxical results here Table 2. Standing versus supine wave velocity (c) computed along the arterial tree at sites specified by the numbers in the left column (refer to figure 1 and [26]). c values are reported as mean ± s.d.…”
Section: Mechanisms Of Wave Reflection and Pressure Reflection Coeffi...mentioning
Pressure-flow travelling waves are a key topic for understanding arterial haemodynamics. However, wave transmission and reflection processes induced by body posture changes have not been thoroughly explored yet. Current
in vivo
research has shown that the amount of wave reflection detected at a central level (ascending aorta, aortic arch) decreases during tilting to the upright position, despite the widely proved stiffening of the cardiovascular system. It is known that the arterial system is optimized when in the supine position, i.e. propagation of direct waves is enabled and reflected waves are trapped, protecting the heart; however, it is not known whether this is preserved with postural changes. To shed light on these aspects, we propose a multi-scale modelling approach to inquire into posture-induced arterial wave dynamics elicited by simulated head-up tilting. In spite of remarkable adaptation of the human vasculature following posture changes, our analysis shows that, upon tilting from supine to upright: (i) vessel lumens at arterial bifurcations remain well matched in the forward direction, (ii) wave reflection at central level is reduced due to the backward propagation of weakened pressure waves produced by cerebral autoregulation, and (iii) backward wave trapping is preserved.
“…Figure 1 f , g and top diagrams on all panels of figure 4 show how the separated components of pressure and flow waveforms are altered by orthostatic stress. Forward and backward pressure waves exhibit the same behaviour observed for the total (forward + backward) pressure signals after passive tilting to the standing posture [ 26 ], with both pressure components reduced in amplitude following global pulse pressure contraction ( figure 1 f , g ). Moving along the aortic-wise direction, figure 4 shows that both forward and backward pressure signals are progressively shifted upward to higher mean pressure levels because of the increasing hydrostatic contribution encountered while moving below the heart level: standing mean forward pressure +1.6 mmHg and mean backward pressure +2 mmHg at ascending aorta no.…”
Section: Resultsmentioning
confidence: 58%
“…The reason for this phase shifting lies in the raised heart rate with respect to the supine state (see table 1 ), altering the systolic–diastolic balance over the single heartbeat. Indeed, the higher heart rate encountered at standing posture leads to an increased systolic duration in contrast to a shortened diastole, resulting in the observed phase shifting of pressure and flow signals [ 26 ]. Figure 4 Forward (green) and backward (red) pressure ( P ) and wave intensity (WI) profiles—on top and bottom side of panels, respectively—obtained at different sites along the aorta for the supine (solid lines) and standing (dashed lines) positions.…”
Section: Resultsmentioning
confidence: 99%
“…Passive orthostatic stress experienced when tilting from the horizontal supine to the upright standing position triggers a number of cardiovascular responses [1,2]. In table 1, the response of the main haemodynamics parameters to posture change from 0∘ to 90∘ head-up is recalled (see [26] for more details). In the same table, we also specified which parameters are directly controlled by each short-term mechanism (baroreflex, cardiopulmonary reflex and cerebral autoregulation).…”
Section: Resultsmentioning
confidence: 99%
“…The CVS model accounts for the action of specific extravascular pressures onto given vascular districts: the intramyocardial pressure (IMP [28], figure 1c), the intrathoracic pressure (ITP [27], figure 1e, electronic supplementary material, equation (S8)) and the intracranial pressure (ICP [26], figure 1d). ITP and ICP depend on the body posture [26,27]. royalsocietypublishing.org/journal/rsos R. Soc.…”
Section: The Cardiovascular Modelmentioning
confidence: 99%
“…To explain the paradoxical results here Table 2. Standing versus supine wave velocity (c) computed along the arterial tree at sites specified by the numbers in the left column (refer to figure 1 and [26]). c values are reported as mean ± s.d.…”
Section: Mechanisms Of Wave Reflection and Pressure Reflection Coeffi...mentioning
Pressure-flow travelling waves are a key topic for understanding arterial haemodynamics. However, wave transmission and reflection processes induced by body posture changes have not been thoroughly explored yet. Current
in vivo
research has shown that the amount of wave reflection detected at a central level (ascending aorta, aortic arch) decreases during tilting to the upright position, despite the widely proved stiffening of the cardiovascular system. It is known that the arterial system is optimized when in the supine position, i.e. propagation of direct waves is enabled and reflected waves are trapped, protecting the heart; however, it is not known whether this is preserved with postural changes. To shed light on these aspects, we propose a multi-scale modelling approach to inquire into posture-induced arterial wave dynamics elicited by simulated head-up tilting. In spite of remarkable adaptation of the human vasculature following posture changes, our analysis shows that, upon tilting from supine to upright: (i) vessel lumens at arterial bifurcations remain well matched in the forward direction, (ii) wave reflection at central level is reduced due to the backward propagation of weakened pressure waves produced by cerebral autoregulation, and (iii) backward wave trapping is preserved.
Low‐dimensional (1D or 0D) models can describe the whole human blood circulation, for example, 1D distributed parameter model for the arterial network and 0D concentrated models for the heart or other organs. This paper presents a combined 1D‐0D solver, called first_blood, that solves the governing equations of fluid dynamics to model low‐dimensional hemodynamic effects. An extended method of characteristics is applied here to solve the momentum, and mass conservation equations and the viscoelastic wall model equation, mimicking the material properties of arterial walls. The heart and the peripheral lumped models are solved with a general zero‐dimensional (0D) nonlinear solver. The model topology can be modular, that is, first_blood can solve any 1D‐0D hemodynamic model. To demonstrate the applicability of first_blood, the human arterial system, the heart and the peripherals are modelled using the solver. The simulation time of a heartbeat takes around 2 s, that is, first_blood requires only twice the real‐time for the simulation using an average PC, which highlights the computational efficiency. The source code is available on GitHub, that is, it is open source. The model parameters are based on the literature suggestions and on the validation of output data to obtain physiologically relevant results.
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