Computer Simulation Studies of the Venous Circulation

Snyder, M. F.; Rideout, V. C.

doi:10.1109/tbme.1969.4502663

Cited by 115 publications

(54 citation statements)

References 9 publications

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“…This explanation of the immediate response to active and passive posture change implies that venous return and, consequently, cardiac output (CO) are not sufficiently reduced to induce a BP dip. Experimental studies, including measurements or estimations of CO during tilt (45, 51), indeed, report only a gradual decrease toward upright values, sometimes preceded by an initial increase.Several published models have been designed to simulate the cardiovascular response to passive tilt or active standing (1,21,22,28,29,32,44). The simulated BP response of a recent model, including a detailed circulation and reflex model (21), shows a major BP dip in the first 10 -20 s after HUT (20).…”

mentioning

confidence: 99%

Mathematical modeling of gravitational effects on the circulation: importance of the time course of venous pooling and blood volume changes in the lungs

Heusden

Gisolf

Stok

et al. 2006

American Journal of Physiology-Heart and Circulatory Physiology

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A dip in blood pressure (BP) in response to head-up tilt (HUT) or active standing might be due to rapid pooling in the veins below the heart (preload) or muscle activation-induced drop in systemic vascular resistance (afterload). We hypothesized that, in the cardiovascular response to passive HUT, where, in contrast to active standing, little BP dip is observed, features affecting the preload play a key role. We developed a baroreflex model combined with a lumped-parameter model of the circulation, including viscoelastic stress-relaxation of the systemic veins. Cardiac contraction is modeled using the varying-elastance concept. Gravity affects not only the systemic, but also the pulmonary, circulation. In accordance with the experimental results, model simulations do not show a BP dip on HUT; the tilt-back response is also realistic. If it is assumed that venous capacities are steady-state values, the introduction of stress-relaxation initially reduces venous pooling. The resulting time course of venous pooling is comparable to measured impedance changes. When venous pressure-volume dynamics are neglected, rapid (completed within 30 s) venous pooling leads to a drop in BP. The direct effect of gravity on the pulmonary circulation influences the BP response in the first ϳ5 s after HUT and tilt back. In conclusion, the initial BP response to HUT is mainly determined by the response of the venous system. The time course of lower body pooling is essential in understanding the response to passive HUT. baroreflex; cardiovascular system; modeling; tilt table A MODELING APPROACH to the study of the blood circulation and its response to postural changes can provide insight into the underlying physiology. Existing models approximate certain aspects of the circulation and its response to orthostatic stress, but the transients seen on passive head-up tilt (HUT) have proven difficult to capture.Transient response of the cardiovascular system to active standing and passive HUT has been the focus of various studies (3,34,45,47,51,59). The steady-state response to active standing and HUT is usually comparable, but there is a difference in the blood pressure (BP) and heart rate (HR) responses in the first 30 s (Fig. 1). On passive HUT, Rossberg and Martinez (34) found initial increases in HR comparable to the response to active standing. In later studies, however, a BP dip on active standing was reduced (3, 47) or absent (45,51,59) in passive HUT responses. The initial BP dip on standing is thought to be due to a decrease in peripheral resistance resulting from the active part of the maneuver (45). Sprangers et al. (45) point out two mechanisms: 1) the central (autonomic) command that accompanies active muscle contraction and 2) the displacement of large amounts of venous blood to the right atrium by the massive muscle action induced by active standing, eliciting a cardiopulmonary (CP) reflex effect on the systemic circulation. In passive tilt, if abrupt muscle contraction in response to sudden tilt maneuvers is avoided, perip...

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confidence: 99%

Mathematical modeling of gravitational effects on the circulation: importance of the time course of venous pooling and blood volume changes in the lungs

Heusden

Gisolf

Stok

et al. 2006

American Journal of Physiology-Heart and Circulatory Physiology

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“…19 but scaled to generate a nominal pressure of 6.0 mmHg in the neck veins (23). In addition, the valves present in neck veins (23) are characterized by a leaky valve representation similar to that employed by Snyder and Rideout (31). V ic includes component volumes such as blood, intracellular and extracellular fluid, and CSF.…”

Section: Cerebral Hemodynamicsmentioning

confidence: 99%

Cerebral autoregulation and gas exchange studied using a human cardiopulmonary model

Lu¹,

Clark²,

Ghorbel³

et al. 2004

American Journal of Physiology-Heart and Circulatory Physiology

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. Cerebral autoregulation and gas exchange studied using a human cardiopulmonary model. Am J Physiol Heart Circ Physiol 286: H584-H601, 2004. First published August 28, 2003 10.1152/ajpheart.00594.2003.-The goal of this work is to study the cerebral autoregulation, brain gas exchange, and their interaction by means of a mathematical model. We have previously developed a model of the human cardiopulmonary (CP) system, which included the whole body circulatory system, lung and peripheral tissue gas exchange, and the central nervous system control of arterial pressure and ventilation. In this study, we added a more detailed description of cerebral circulation, cerebrospinal fluid (CSF) dynamics, brain gas exchange, and cerebral blood flow (CBF) autoregulation. Two CBF regulatory mechanisms are included: autoregulation and CO2 reactivity. Central chemoreceptor control of ventilation is also included. We first established nominal operating conditions for the cerebral model in an open-loop configuration using data generated by the CP model as inputs. The cerebral model was then integrated into the larger CP model to form a new integrated CP model, which was subsequently used to study cerebral hemodynamic and gas exchange responses to test protocols commonly used in the assessment of CBF autoregulation (e.g., carotid artery compression and the thigh-cuff deflation test). The model can closely mimic the experimental findings and provide biophysically based insights into the dynamics of cerebral autoregulation and brain tissue gas exchange as well as the mechanisms of their interaction during test protocols, which are aimed at assessing the degree of autoregulation. With further refinement, our CP model may be used on measured data associated with the clinical evaluation of the cerebral autoregulation and brain oxygenation in patients. physiological modeling; thigh-cuff test; carotid artery compression NORMAL CEREBRAL AUTOREGULATION provides a constant cerebral blood flow (CBF) over a wide range of cerebral perfusion pressures (CPP) (1, 25). Because this regulatory mechanism is complex, several investigators have found that mathematical models can help guide experimental design and provide explanations of experimental results (8, 14-16, 18, 32, 36). These models have largely been directed at developing mechanistic descriptions of cerebral autoregulation or the dynamics of intracranial systems. None have considered the effect of CO 2 on cerebral hemodynamics and autoregulation or described the gas exchange between cerebral vessels and brain tissue. Ursino et al. (37,39) and Czosnyka et al. (5) included CO 2 reactivity in their modeling studies of intracranial dynamics. However, their models did not include gas transport in brain tissue and thus can not simulate the impact of cerebral hemodynamic changes on brain tissue gas content.We recently presented a modeling study of human whole body gas exchange (20), in which our previous human cardiopulmonary (CP) model (19) was significantly extended to include descriptions of ...

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“…In a complex model, Beneken [49] used individual peripheral venous resistance values that produced an overall venous resistance of 0.08 PRU. However, the venous transmural pressure in parts of the dependent vasculature can reach levels at which the nonlinear nature of the venous pressure-volume relation becomes important [50]. In particular, the lower limb, splanchnic, and abdominal venous compartments show nonlinear pressure-volume relations.…”

Section: Governing Equationsmentioning

confidence: 99%

Mathematical Modeling of Cardiovascular System Dynamics Using a Lumped Parameter Method

Shim

Sah

Youn³

2004

Jpn.J.Physiol

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parameter models. We also discuss the nonlinear characteristics of the pressure-volume relationship in veins. Then the control pathways that participate in feedback mechanisms (baroreceptors and cardiopulmonary receptors) are described to explain the interaction between hemodynamics and autonomic nerve control in the circulation. Based on a set-point model, the computational aspects of reflex control are explained. Japanese Journal of Physiology Vol. 54, [545][546][547][548][549][550][551][552][553] 2004 REVIEW Abstract: This work reviews the main aspects of cardiovascular system dynamics with an emphasis on modeling hemodynamic characteristics by the use of a lumped parameter approach. The methodological and physiological aspects of the circulation dynamics are summarized with the help of existing mathematical models. The main characteristics of the hemodynamic elements, such as the heart and arterial and venous systems, are first described. Distributed models of an arterial network are introduced, and their characteristics are compared with those of lumped Key words: lumped parameter model, dynamics of the cardiovascular system, autonomic nerve control.

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Computer Simulation Studies of the Venous Circulation

Cited by 115 publications

References 9 publications

Mathematical modeling of gravitational effects on the circulation: importance of the time course of venous pooling and blood volume changes in the lungs

Mathematical modeling of gravitational effects on the circulation: importance of the time course of venous pooling and blood volume changes in the lungs

Cerebral autoregulation and gas exchange studied using a human cardiopulmonary model

Mathematical Modeling of Cardiovascular System Dynamics Using a Lumped Parameter Method

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