Computer Simulations of Hemodynamic Effects of Different CPR Techniques

Cardiopulmonary resuscitation is a simple and effective medical treatment for patients with sudden cardiac arrest. Most researches on CPR are animal experiments and human trials. Because there are many confounding factors present in experiments,conflicting conclusions are often drawn. In this paper,we followed the line of theoretical research on CPR. Then,we adapted previous CPR models,simulated rive CPR techniques using the adapted model,and compared their hemodynamics in the same test system. Through the comparison,the simulation results agree quite well with experimental data. The simulation results show that when external counter pulsation is applied during CPR,it may improve the cardiac output and increase the diastolic aortic pressure. Yet,external counter pulsation is not widely used during CPR. We think that this experiment deserves further research. Given the benefits of models and simulations,our adapted model may be a useful tool in CPR research.     

Non-Invasive Hemodynamic Assessment of Aortic Coarctation: Validation with In Vivo Measurements

We propose a CFD-based approach for the non-invasive hemodynamic assessment of pre- and post-operative coarctation of aorta (CoA) patients. Under our approach, the pressure gradient across the coarctation is determined from computational modeling based on physiological principles, medical imaging data, and routine non-invasive clinical measurements. The main constituents of our approach are a reduced-order model for computing blood flow in patient-specific aortic geometries, a parameter estimation procedure for determining patient-specific boundary conditions and vessel wall parameters from non-invasive measurements, and a comprehensive pressure-drop formulation coupled with the overall reduced-order model. The proposed CFD-based algorithm is fully automatic, requiring no iterative tuning procedures for matching the computed results to observed patient data, and requires approximately 6–8 min of computation time on a standard personal computer (Intel Core2 Duo CPU, 3.06 GHz), thus making it feasible for use in a clinical setting. The initial validation studies for the pressure-drop computations have been performed on four patient datasets with native or recurrent coarctation, by comparing the results with the invasively measured peak pressure gradients recorded during routine cardiac catheterization procedure. The preliminary results are promising, with a mean absolute error of less than 2 mmHg in all the patients.     

Comparing Pre- and Post-operative Fontan Hemodynamic Simulations: Implications for the Reliability of Surgical Planning

Virtual modeling of cardiothoracic surgery is a new paradigm that allows for systematic exploration of various operative strategies and uses engineering principles to predict the optimal patient-specific plan. This study investigates the predictive accuracy of such methods for the surgical palliation of single ventricle heart defects. Computational fluid dynamics (CFD)-based surgical planning was used to model the Fontan procedure for four patients prior to surgery. The objective for each was to identify the operative strategy that best distributed hepatic blood flow to the pulmonary arteries. Post-operative magnetic resonance data were acquired to compare (via CFD) the post-operative hemodynamics with predictions. Despite variations in physiologic boundary conditions (e.g., cardiac output, venous flows) and the exact geometry of the surgical baffle, sufficient agreement was observed with respect to hepatic flow distribution (90% confidence interval??14?±?4.3% difference). There was also good agreement of flow-normalized energetic efficiency predictions (19?±?4.8% error). The hemodynamic outcomes of prospective patient-specific surgical planning of the Fontan procedure are described for the first time with good quantitative comparisons between preoperatively predicted and postoperative simulations. These results demonstrate that surgical planning can be a useful tool for single ventricle cardiothoracic surgery with the ability to deliver significant clinical impact.     

Effects of Exercise and Respiration on Hemodynamic Efficiency in CFD Simulations of the Total Cavopulmonary Connection

Congenital heart defects with a single functional ventricle, such as hypoplastic left heart syndrome and tricuspid atresia, require a staged surgical approach to separate the systemic and pulmonary circulations. Ultimately, the venous or pulmonary side of the heart is bypassed by directly connecting the vena cava to the pulmonary arteries with a modified t-shaped junction. The Fontan procedure (total cavopulmonary connection, TCPC) completes this process of separation. To date, computational fluid dynamics (CFD) simulations in this low pressure, passive flow, intrathoracic system have neglected the presumed important effects of respiration on physiology and higher “stress” states such as with exercise have never been considered. We hypothesize that incorporating effects of respiration and exercise would provide more realistic estimates of TCPC performance. Time-dependent, 3D blood flow simulations are performed by a custom finite element solver for two patient-specific Fontan models with a novel respiration model, developed to generate physiologic time-varying flow conditions. Blood flow features, pressure, and energy efficiency are analyzed at rest and with increasing flow rates to simulate exercise conditions. The simulations produce realistic pressure and flow data, comparable to that measured by catheterization and echocardiography, and demonstrate substantial increases in energy dissipation (i.e. decreased performance) with exercise and respiration due to increasing intensity of small scale vortices in the flow. As would be expected, these changes are highly dependent on patient-specific anatomy and Fontan geometry. We propose that respiration and exercise should be incorporated into TCPC CFD simulations to provide increasingly realistic evaluations of TCPC performance.     

Tuning to sound frequency in auditory field potentials

Neurons in auditory cortex are selective for the frequency content of acoustical stimuli. Classically, this response selectivity is studied at the single-neuron level. However, current research often employs functional imaging techniques to investigate the organization of auditory cortex. The signals underlying the imaging data arise from neural mass action and reflect the properties of populations of neurons. For example, the signal used for functional magnetic resonance imaging (fMRI-BOLD) was shown to correlate with the oscillatory activity quantified by local field potentials (LFPs). This raises the questions of how the frequency selectivity in neuronal population signals compares with the tuning of spiking responses. To address this, we quantified tuning properties of auditory-evoked potentials (AEP), different frequency bands of the LFP, analog multi-unit (AMUA), and spike-sorted single- and multiunit activity in auditory cortex. The AMUA showed a close correspondence in frequency tuning to the spike-sorted activity. In contrast, for the LFP, we found a clear dissociation of high- and low-frequency bands: there was a gradual increase of tuning-curve similarity, tuning specificity, and information about the stimulus with increasing LFP frequency. Although properties of the high-frequency LFP matched those of spiking activity, the lower-frequency bands differed considerably as did the AEP. These results demonstrate that electrophysiological population responses exhibit varying degrees of frequency tuning and suggest that those functional imaging methods that are related to high-frequency oscillatory activity should well reflect the neuronal processing of sound frequency.     

Hemodynamic modulation of monocytic cell adherence to vascular endothelium

Hemodynamic shear stress is hypothesized to contribute to the localization of atherosclerotic plaques to certain arterial sites. Monocyte recruitment to these sites is an early event in atherogenesis. To determine the possible mechanisms by which shear stress modulates monocyte adhesionin vivo, studies of human monocytic cell adherence to endothelium were conducted under different shear conditions in a parallel-plate flow chamber. The number of monocytes capable of developing firm adhesive contacts with endothelium decreased as shear stress-induced drag forces increased over the range of 0.5 to 30 dynes/cm². The number of adherent monocytic cells at a given shear stress was highly dependent on the activation state of the endothelium. To test the direct effect of shear stress on endothelial cell adhesivity, endothelial cells were presheared for 2 to 6 hr at 2, 10, or 30 dynes/cm², and monocytic cell adherence was quantified at 1 dyne/cm². Adherence increased 330% or 370% when endothelial cells were presheared for 2 hr at 2 or 10 dynes/cm², respectively, as compared to unsheared endothelium. In contrast, when endothelial cells were presheared at 30 dynes/cm², monocytic cell adherence at 1 dyne/cm² was not significantly different from unsheared controls. Increased monocytic cell adherence to presheared endothelium was via a vasuclar cell adhesion molecule 1 (VCAM-1)α₄β₁ mechanism, and enzyme-linked immunosorbent assay studies showed that preshearing at 2 dynes/cm² for 2 hr increased endothelial VCAM-1 expression by 38%. These data demonstrated that low levels of shear stress induce enthelial VCAM-1 expression and increase monocytic cell adherence via a VCAM-1/α₄β₁ mechanism. Thus, shear stress can modulate monocyte adherence to vascular endothelium through drag forces that affect the establishment and maintenance of adhesive bonds and by directly modulating the expression of endothelial VCAM-1. This dual effect of shear stress produces the most favorable conditions for adhesion at low-shear regions, where drag forces are low and induction of VCAM-1 is likely. The preferential adherence of monocytes to these regions may contribute to the localization of atherosclerotic plaques to low-shear regions of the arterial circulationin vivo.     

Hemodynamic response to emotional memory recall with eye movement

Previous studies on rapid eye movement sleep have demonstrated the effect of eye movement on emotional memory. However, the brain mechanism involved in the influence of the eye movement on the emotional recall remains unclear. We investigated the prefrontal response during an emotional memory recall with and without eye movement. Ten healthy volunteers were recruited. The changes in concentration of oxygenated hemoglobin ([oxy-Hb]) in the prefrontal cortex were examined using near-infrared spectroscopy (NIRS) during a task that involved emotional recall with and without eye movement. Six participants demonstrated a significant increase in [oxy-Hb] during emotional recall, and the level of increase was reduced through repeated emotional recall with eye movement. The results suggest that eye movement is associated with a reduction in the hemodynamic response to emotional memory recall.     

Tuning compliance of nanoscale polyelectrolyte multilayers to modulate cell adhesion

It is well known that mechanical stimuli induce cellular responses ranging from morphological reorganization to mineral secretion, and that mechanical stimulation through modulation of the mechanical properties of cell substrata affects cell function in vitro and in vivo. However, there are few approaches by which the mechanical compliance of the substrata to which cells adhere and grow can be determined quantitatively and varied independent of substrata chemical composition. General methods by which mechanical state can be quantified and modulated at the cell population level are critical to understanding and engineering materials that promote and maintain cell phenotype for applications such as vascular tissue constructs. Here, we apply contact mechanics of nanoindentation to measure the mechanical compliance of weak polyelectrolyte multilayers (PEMs) of nanoscale thickness, and explore the effects of this tunable compliance for cell substrata applications. We show that the nominal elastic moduli E(s) of these substrata depend directly on the pH at which the PEMs are assembled, and can be varied over several orders of magnitude for given polycation/polyanion pairs. Further, we demonstrate that the attachment and proliferation of human microvascular endothelial cells (MVECs) can be regulated through independent changes in the compliance and terminal polyion layer of these PEM substrata. These data indicate that substrate mechanical compliance is a strong determinant of cell fate, and that PEMs of nanoscale thickness provide a valuable tool to vary the external mechanical environment of cells independently of chemical stimuli.     

Physiological responses to fire fighting activities

Summary Eight professional fire fighters participated in six fire fighting scenarios at a training facility. Data on heart rate (HR), rectal temperature (T_re), and skin temperatures at the chest and thigh were collected using a portable data acquisition system. Average HR ranged from 122 to 151 beats · min⁻¹ during the six scenarios. Detailed analyses indicated that HR and T_re increases are related to both the physical and environmental stresses of the various activities carried out. The most demanding activity, that of building search and victim rescue, resulted in an average HR of 153 beats · min⁻¹ and T_re rise of 1.3‡ C, while the least demanding activity, that of the crew captain who directs the fire fighting, resulted in an average HR of only 122 beats · min⁻¹ and a T_re rise of only 0.3‡ C. This study shows that fire fighting is strenuous work for those directly entering a building and performing related duties, but that the physical demands of other activities are considerably less. The results further suggest that heat strain injuries in fire fighters could perhaps be reduced by rotating duties frequently with other crew members performing less stressful work.