[The role of synergetics in biofluid mechanics: added theoretical foundation for explaining central aspects of biology, athermoma development and thrombosis].
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Arteriosclerosis↗
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Mean blood pressure and velocity for calculation of ventricular systolic work.
In physiology, the mean arterial pressure is defined as an average pressure during one or several cardiac cycles. When calculus is not used, the mean pressure is approximately calculated as the diastolic pressure plus one third of the pulse pressure. In this article it is demonstrated that, when ventricular systolic work is concerned, the above definition of mean pressure must be replaced by a weighted average during the ejection phase of the systole. This gives a formula, by which a much higher estimate of the mean pressure is obtained.
Blood Flow Velocity↗
Hemodynamic consequences of replacing the aorta by vascular grafts simulated in a mathematical model.
OBJECTIVE: Replacing parts of the aorta by a noncompliant vascular prosthesis results in marked alterations of the aortic input impedance and influences arterial hemodynamics. We propose a mathematical model of circulation able to predict hemodynamic changes after simulation of vascular grafting. METHODS: Using a mathematical 128-branch model of the human arterial system a digitized aortic flow wave was chosen as the input signal to this system. After determination of the modules of elasticity of native vascular tissue and customary prostheses in technical experiments, replacement of any part of the aorta with a prosthesis was simulated by increasing the elasticity in the parts desired. RESULTS: During control conditions, the model displayed a physiologic distribution of flow and pressure waves throughout the arterial system. Simulated replacement of the aorta resulted in an increase of pressure amplitude and a partial loss of the aortic "Windkessel" function. Calculation of the aortic input impedance showed an increase of the characteristic impedance, while the peripheral resistance remained unaltered. CONCLUSION: This mathematical model of the arterial circulation proves to be useful to simulate hemodynamic changes after implantation of vascular grafts. The results of the model analysis are consistent with previous work done in experimental setups.
Aorta↗
Simple and Patlak models for myocardial blood flow measurements with nitrogen-13-ammonia and PET in humans.
UNLABELLED: The Simple and Patlak models for estimating myocardial blood flow with 13N-ammonia have become attractive for clinical applications with PET because of their simplicity and ease of implementation. However, these models are sensitive to factors such as the data acquisition times and data integration times, which can cause errors in the estimation of myocardial blood flow, as demonstrated in this study. Limiting the application of these models to specific conditions can minimize the errors. METHODS: Dynamic PET images of the uptake of 13N-ammonia in the heart were obtained in seven humans under rest and dipyridamole stress. Myocardial blood flow was estimated using the Simple and Patlak models for different data acquisition times and data integration times. Blood flow values were compared to flow values computed with the two-compartment model as a reference. RESULTS: Blood flow values calculated with the Simple and Patlak models during the first 2 min of data acquisition were closely correlated to the two-compartment model values. Longer acquisition times resulted in significant underestimation of blood flow for the Simple model. Long integration times of greater than 60 sec also resulted in significant underestimation of blood flow for both models. CONCLUSION: The Simple and Patlak models produce estimates of myocardial blood flow that are well correlated with the two-compartment model estimated blood flows for the integration time of 60 sec from 60 to 120 sec postinjection. Because of the errors associated with longer data acquisition times and longer integration times, use of these models should be limited to a well-documented data acquisition paradigm.
Ammonia↗
A mathematical model for the heterogeneity of myocardial perfusion using nitrogen-13-ammonia.
UNLABELLED: Heterogeneity of left ventricular myocardial perfusion is an important clinical characteristic. Different aspects of this heterogeneity were analyzed. METHODS: The coefficient of variation (v), characterizing heterogeneity, was modeled as a function of the number of segments (n), characterizing spatial resolution of the measurement, using two independent pairs of mutually dependent parameters: the first pair describes v as a power function of n, and the second pair adds a correction for n small. n was varied by joining equal numbers of neighboring segments. Local similarity of the perfusion was characterized by the correlation between the perfusions of neighboring segments. Genesis of the perfusion distribution was modeled by repeated asymmetric subdivision of the perfusion into a volume among two equal subvolumes. These analyses were applied to study the differences between 16 syndrome X patients and 16 age- and sex-matched healthy volunteers using 13N-ammonia parametric PET perfusion data with a spatial resolution of 480 segments. RESULTS: The heterogeneity of patients is higher for the whole range of spatial resolutions considered (2 < or = n < or = 480; for n = 480, v = 0.22 +/- 0.03 and 0.18 +/- 0.02; p < 0.005). This is because the first pair of parameters differs between patients and volunteers (p < 0.005), whereas the second pair does not (p > 0.1). For both groups of subjects there is a significant positive local correlation for distances up to 30 segments. This correlation is a formal description of the patchy nature of the perfusion distribution. CONCLUSION: When comparing values of v, these should be based on the same value of n. The model makes it possible to calculate v for all values of n < or = 480. Mean perfusion together with the two pairs of parameters are necessary and sufficient to describe all aspects of the perfusion distribution. For n small, heterogeneity estimation is less reliable. Patients have a higher heterogeneity because their perfusion distribution is more asymmetrical from the third to the seventh generation of subdivision (8 < or = n < or = 128). Therefore, a spatial resolution of n > or = 128 is recommended for parametric imaging of perfusion with PET. Patients have only a very slightly more patchy distribution than volunteers. The differences in perfusion between areas with low perfusion and areas with high perfusion is larger in patients.
Ammonia↗
A mathematical high time resolution model of the arterial system under extracorporeal circulation.
OBJECTIVE: The purpose of the following study was to establish a computer-generated model of the hemodynamic effects of pulsatile extracorporal perfusion describing flow and pressure parameters in the body for any given input flow patterns. METHODS: The human arterial tree was delineated according to a 128-branch model encompassing bifurcations and linear physical properties of the arterial walls. The distribution of flow and pressure waves was calculated based on a refined 3-element windkessel model. Autoregulatory mechanisms of brain and kidneys were implemented. RESULTS: By providing a simulated, "pump-generated" flow curve as the input signal to the system, the model was able to create and display flow and pressure curves at a high time resolution in each part of the systemic circulation including reflection phenomena throughout any observation period chosen. The hemodynamic effects of different pump-flow patterns, age, variations in hematocrit, hypothermia and occlusion of arterial branches, like the renal artery, could be simulated. CONCLUSION: In an attempt to get closer to a mathematically based regulation of heart-lung machines, this model of computer generated extracorporeal circulation provides an initial step. Ongoing research is required for implementation of metabolic conditions and continuous approximation of the model of the real physiologic or pathologic situation.
Arteries↗
[Separating elastic, flow and velocity work and work of smooth musculature of the peripheral arterial pulse of the human].
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Blood Flow Velocity↗
Reduction of coronary flow in the native circulation after bypass. Observations in a hydraulic model of the cardiovascular system.
The effects of aorta-coronary bypass upon flow in the native coronary artery were investigated in a hydraulic model of the cardiovascular system. An aorta-coronary bypass with a diameter identical to the coronary artery was used, since a graft diameter-to-coronary diameter ratio of one has been described as optimal. Stenoses of increasing severity were created in the simulated coronary artery. Aorta-coronary bypass eliminated the pressure gradients across the stenotic coronary segments. This caused a 50% reduction of flow in the normal or mildly stenotic native coronary artery. A higher percentage reduction of flow occurred in the bypassed artery when it was severely stenotic. Such a reduction of flow in patients may accelerate the atherosclerotic-thrombotic process and contribute to the high prevalence of occlusion of natural vessels following bypass. This disadvantageous hydraulic circumstance should be considered, particularly when bypass of mildly stenotic vessels is contemplated.
Blood Pressure↗
Multiscale modeling of the cardiovascular system: application to the study of pulmonary and coronary perfusions in the univentricular circulation.
The objective of this study is to compare the coronary and pulmonary blood flow dynamics resulting from two configurations of systemic-to-pulmonary artery shunts currently utilized during the Norwood procedure: the central (CS) and modified Blalock Taussig (MBTS) shunts. A lumped parameter model of the neonatal cardiovascular circulation and detailed 3-D models of the shunt based on the finite volume method were constructed. Shunt sizes of 3, 3.5 and 4 mm were considered. A multiscale approach was adopted to prescribe appropriate and realistic boundary conditions for the 3-D models of the Norwood circulation. Results showed that the average shunt flow rate is higher for the CS option than for the MBTS and that pulmonary flow increases with shunt size for both options. Cardiac output is higher for the CS option for all shunt sizes. Flow distribution between the left and the right pulmonary arteries is not completely balanced, although for the CS option the discrepancy is low (50-51% of the pulmonary flow to the right lung) while for the MBTS it is more pronounced with larger shunt sizes (51-54% to the left lung). The CS option favors perfusion to the right lung while the MBTS favors the left. In the CS option, a smaller percentage of aortic flow is distributed to the coronary circulation, while that percentage rises for the MBTS. These findings may have important implications for coronary blood flow and ventricular function.
Blood Flow Velocity↗
A model of the cardiovascular regulation as a diagnostic tool in acute myocardial infarction.
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Diagnosis, Computer-Assisted↗
Anger inhibition, cardiovascular recovery, and vagal function: a model of the link between hostility and cardiovascular disease.
A model of the association between hostility and cardiovascular disease (CVD) is proposed based upon anger inhibition, slow cardiovascular recovery, and low parasympathetic activity (vagal tone). This model is opposed to the more conventional model that emphasizes anger expression, cardiovascular reactivity, and high sympathetic tone. We argue that in social reality, incidences of anger inhibition outnumber incidences of anger expression to a great extent, irrespective of preferred expression style. Moreover, slow cardiovascular recovery, rather than high reactivity, may be the mechanism underlying the CVD risk associated with anger inhibition. Both anger inhibition and slow cardiovascular recovery are associated with a persistently low vagal tone. Thus, the anger inhibition/vagal inhibition model seems more consistent with the actual nature of anger in daily life and with the known cardiovascular control mechanisms. The model may better account for the chronic pathophysiological state that is believed to lead to CVD. Importantly, an experimental inhibition/recovery paradigm might also allow to test potential behavioral and cognitive accelerators of cardiovascular recovery. As an example of an important socially-mediated health risk that may be elucidated using the anger inhibition/vagal inhibition model, we discuss Black-White differences that have been found in CVD.
Adaptation, Psychological↗
Computer analysis of external counterpulsation by use of a nonlinear mathematical model of the cardiovascular system.
A pressure system externally applied to the limbs of a patient has been proven effective in assisting circulation in animal and clinical studies. In this study a nonlinear mathematical model of the cardiovascular system is utilized to determine the effectiveness of high-frequency components in the external pressure waveform. The development of the model, the method of analysis, and the results acquired with the model are presented in this report, demonstrating its suitability for the study of external counterpulsation.
Animals↗
[Non-invasive study of cardiovascular function using models of biological age].
In a group of 67 healthy persons (18-60 yrs, mean 37 yrs, male 32, female 35) 77 parameters were investigated (9 physical, 6 biochemical, 3 from ECG, 14 polygraphic, 45 echocardiographic), in 38, ones a significant correlation (Pearson's) with age was found. Biological age or functional cardiovas. age (BA), was calculated using the following formulas: 1.BA = .23BMI- +.11mBP-.43PTT +29.58CO/LVET-.4vPWT-.16FS +15.27h/r, r = 0.980. 2.BA1 = .22mBP +.8AoR-.4vPWT-.19FS +.04iMLV, r = 0.968. BMI--body mass index, mBP--mean blood pressure in Torr, PTT--pulse transmission time (CARi-AII in FCG) in ms, CO/LVET--duration between C-O points in apexcardiogram in ms/left ventricular ejection time (CARu-CARi in carotidogram) in ms ratio, vPWT--velocity of posterior wall thickness of left ventricle in mm.s-1, FS--fractional shortening in %, h/r--2(enddiastolic posterior wall thickness of left ventricle in mm)/enddiastolic diameter of left ventricle in mm ratio, AoR--diameter of the aortic root (mm), iMVL--index of massa of the left ventricle. No significant correlation between heart rate and tests using in formula was found. We found "normal biological age" or cardiovascular function in all groups. But the significant differences between men and women in relative biological age (ca 12% using formula 1, 19% using formula 2, both p < 0.001) were found. (Tab. 3, Ref. 23.)
Adolescent↗
Multivariate autoregressive modeling of autonomic cardiovascular control in neonatal lamb.
The neonatal cardiovascular control system is a complicated interactive system which is under vigorous development at birth. From the measurement point of view the cardiovascular control is a closed-loop system. However, it can be examined on a beat-by-beat basis by analyzing circulatory-controlled variables with advanced signal analysis techniques. This paper proposes to use a multivariate autoregressive modeling technique in the analysis of several simultaneous physiological signals in order to examine interactions and inherent properties in the system. With the proposed multivariate autoregressive modeling technique, a signal is modeled as a linear combination of its own past and the past values of the other simultaneous signals plus a predictive error term of the model. The interactions in the system after the model identification are analyzed in frequency domain utilizing power spectrum estimates of the signals and signal contributions. The applicability of the proposed method was examined by a three-variable model between heart rate, blood pressure and respiration in the study of autonomic cardiovascular control in a chronic neonatal lamb model, in which the cardiovascular status was changed by using a beta-adrenergic autonomic nervous blockade. The study showed that the multivariate autoregressive modeling technique is a feasible technique in studying complicated interactions within the cardiovascular control system.
Animals↗
[Application of power band graph method to the modeling and simulation of cardiovascular system].
This paper presents a computer simulation model of the cardiovascular circulation system, which describes the blood flow dynamic law in the cardiovascular system by the state equation. The model can be used in physiological study and computer-aided medical education. In this paper, the Power Band Graph (PBG) modeling method is used to realize modeling of the human circulation system and conduct a simulation study on a simplified physiological system model. The results demonstrate that the PBG method, as an understandable and unity modeling method, is quite effective and practicable and can be used widely in the field of physiological system simulation.
Computer Simulation↗
Simulation of hemodynamic responses to the valsalva maneuver: an integrative computational model of the cardiovascular system and the autonomic nervous system.
The Valsalva maneuver is a frequently used physiological test in evaluating the cardiovascular autonomic functions in human. Although a large pool of experimental data has provided substantial insights into different aspects of the mechanisms underlying the cardiovascular regulations during the Valsalva maneuver, so far a complete comprehension of these mechanisms and the interactions among them is unavailable. In the present study, a computational model of the cardiovascular system (CVS) and its interaction with the autonomic nervous system (ANS) was developed for the purpose of quantifying the individual roles of the CVS and the ANS in the hemodynamic regulations during the Valsalva maneuver. A detailed computational compartmental parameter model of the global CVS, a system of mathematical equations representing the autonomic nervous reflex regulatory functions, and an empirical cerebral autoregulation (CA) model formed the main body of the present model. Based on simulations of the Valsalva maneuvers at several typical postures, it was demonstrated that hemodynamic responses to the maneuver were not only determined by the ANS-mediated cardiovascular regulations, but also significantly affected by the postural-change-induced hemodynamic alterations preceding the maneuver. Moreover, the large-magnitude overshoot in cerebral perfusion immediately after the Valsalva maneuver was found to result from a combined effect of the circulatory autonomic functions, the CA, and the cerebral venous blood pressure.
Afferent Pathways↗
The cost-effectiveness of drug treatments for primary prevention of cardiovascular disease: a modelling study.
BACKGROUND: Efficient prevention policies need to be informed by knowledge of the cost-effectiveness of preventive treatments. This paper calculates the cost-effectiveness of aspirin, antihypertensive treatments and statins for prevention of cardiovascular disease. DESIGN: The investigation is a modelling study. METHODS: Ten-year cardiovascular risks and treatment eligibility were determined for each individual in a population of 5603 obtained from the Health Survey of England. Using published costs and evidence of effectiveness the cost-effectiveness of treating each eligible individual was determined over a 10-year time horizon. The marginal cost-effectiveness of additional antihypertensive drugs and increasing doses of statins were determined and a sensitivity analysis was carried out. RESULTS: Of the 5603 individuals 27.5% (95% confidence interval, 26.3-28.7%) were eligible for at least one treatment: the majority of these were eligible for all three. Cost per cardiovascular disease event prevented is strongly determined by pretreatment cardiovascular disease risk. In three-quarters of patients eligible for all three treatments, the lowest cost per event prevented was with aspirin and in the remainder with two-drug antihypertensive treatment. The marginal costs per event prevented were highest with the addition of a fourth antihypertensive drug and statins. These findings depend on the use of low-cost antihypertensives but are otherwise robust to a wide range of assumptions. CONCLUSIONS: Modelling the cost-effectiveness of treatments to prevent cardiovascular disease is feasible and provides valuable information. Cost-effectiveness analysis argues for more widespread use of aspirin and two-drug antihypertensive treatment and against the use of four-drug antihypertensive treatment or statins.
Adult↗
Interpreting open- and closed-loop transfer relations between cardiorespiratory parameters: lessons learned from a computer model of beat-to-beat cardiovascular regulation.
A computer model of cardiovascular control has been developed based on the response characteristics of cardiovascular control components derived from experiments in animals and humans. Results from the model were compared to those obtained experimentally in humans, and the similarities and differences were used to identify both the strengths and inadequacies of the concepts used to form the model. Findings were confirmatory of some concepts but contrary to some which are firmly held in the literature, indicating that understanding the complexity of cardiovascular control probably requires a combination of experiments and computer models which integrate multiple systems and allow for determination of sufficiency and necessity.
Computer Simulation↗