Ventricular Pressure Waveforms Research Articles

Relationship Between the Right Ventricular Pressure Waveform and the Vasodilator Response of Pulmonary Artery Pressure in Pulmonary Artery Hypertension

Background and Objectives:This study was performed to discern whether the vasodilatory response of pulmonary artery pressure could be predicted by the right ventricular (RV) pressure waveforms, and therefore, from continuous wave Doppler signals of tricuspid regurgitant jet (CWTR). Subjects and Methods:Twelve patients with pulmonary hypertension who underwent cardiac catheterization were enrolled. Nitroprusside was infused at a dose of 0.5 μg/kg/min, with the dosage being increased by 0.5 μg/kg/min every 5 minutes to a maximum of 4 μg/kg/min. Cardiac output (CO), pulmonary vascular resistance (PVR), peak systolic RV pressure (Pp), RV pressure at the inflection point (Pi), ΔP (Pp-Pi) and CWTR were obtained before and at the end of the nitroprusside infusion. A positive response to the vasodilator was defined when there was ≥20% change in the mean pulmonary artery pressure at the end of the nitroprusside infusion. Results:Eight patients did not show a positive response (Group 1) while four patients did (Group 2). Mean decrements in Pp following the nitroprusside test were 4.1±7.7 mmHg in group 1 and 27.8±5.6 mmHg in group 2. There were no significant differences between groups 1 and 2 in baseline CO, PVR or Pp. However group 1 had a significantly higher ΔP than group 2 (29.0± 10.5 mmHg vs. 13.3±3.0 mmHg, p<0.05). In the configuration analysis of CWTR, the slope between the inflection point and peak velocity was linear in group 1, while there was an indentation in group 2. Conclusion:Patients with a small difference between Pp and Pi tend to be reactive to a vasodilator and this tendency can be predicted from the configuration of CWTR. (Korean Circulation J 2003;33 (11):1011-1017)

Characteristics of transient blood flow in MHVs with different maximum opening angles using fluid-structure interaction method

A numerical analysis has been performed to investigate the characteristics of two-dimensional transient blood flows interacting with the leaflet motion in a bileaflet mechanical heart valve with different maximum opening angles, located in the aortic position. Here, for one cycle of heartbeat the analysis has been carried out in the light of fluid-structure interaction since the blood flow and the leaflet motion are coupled with each other. Blood has been assumed to be a Newtonian and non-Newtonian fluid, where the Carreau model has been used for the simulation of non-Newtonian fluid. Physiologic ventricular and aortic pressure waveforms have been used as flow boundary conditions at the ventricle and the aorta. A finite volume computational fluid dynamics code and a finite element structure dynamics code have been used concurrently to solve the flow and the structure equations, respectively, where the two equations are strongly coupled. Flow fields, leaflet behavior, and shear stresses with time have been obtained. Also the discharge and the regurgitation flow rates have been calculated. The maximum shear stress, an important issue for valve hemodynamic analysis, has been found in the vicinity of the contact point where a leaflet contacts with housing in the final stage of the closing phase.

Analysis of blood flow interacted with leaflets in MHV in view of fluid-structure interaction

Interaction of blood flow and leaflet behavior in a bileaflet mechanical heart valve was investigated using computational analysis. Blood flows of a Newtonian fluid and a non-Newtonian fluid with Carreau model were modeled as pulsatile, laminar, and incompressible. A finite volume computational fluid dynamics code and a finite element structure dynamics code were used concurrently to solve the flow and structure equations, respectively, where the two equations were strongly coupled. Physiologic ventricular and aortic pressure waveforms were used as flow boundary conditions. Flow fields, leaflet behaviors, and shear stresses with time were obtained for Newtonian and non-Newtonian fluid cases. At the fully opened phase three jets through the leaflets were found and large vortices were present in the sinus area. At the very final stage of the closing phase, the angular velocity of the leaflet was enormously large. Large shear stress was found on leaflet tips and in the orifice region between two leaflets at the final stage of closing phase. This method using fluid-structure interaction turned out to be a useful tool to analyze the different designs of existing and future bileaflet valves.

Computerized left ventricular pressure-volume relationships (pV-loops) using disposable angiographic tip transducer pigtail catheters.

Left ventricular pressure-volume relationships expressed as pV loops could yield important hemodynamic information in the cardiac catheterization laboratory. Many clinical situations might benefit from a quantitative assessment of left ventricular function. Potential applications of pV loops include the assessment of vasoactive and inotropic drugs, balloon valvuloplasty, coronary angioplasty, and surgical treatment of valvular heart disease. For many years the clinical use of pV loops has been hindered by logistical difficulties. The ability to merge on-line concurrent digital imaging data for computation of left ventricular volume and digital left ventricular pressure wave forms obtained from high fidelity tip-transducer angiocatheters has allowed us to develop a technique which can generate pV loops during cardiac catheterization procedures. The method offers an automated measurement of left ventricular volume independent of edge detection or an interactive technique for tracing endocardial borders by a trained operator. Illustrative case studies are included to demonstrate the potential of the method during ventricular angiographic procedures. Implementation and computational time requirements of the method are discussed. The concept and the value of pV loop generation to study left ventricular performance has been known for many years. Combining digital imaging and digital physiologic data obtained with disposable tip-transducer angiocatheters with modern networking technology, the technique can more easily be applied to catheterization procedures and could enhance invasive hemodynamic assessment of left ventricular function.

Considerations in Placement of Right Internal Jugular Cannulas

This case report describes a patient who had paroxysmal ventricular bigeminy of an unrecognized etiology. After 24 hours of observation, it was noted that the patient’s head position correlated with the bigeminy. A single-lumen infusion catheter, which had been placed through an internal jugular cannula, was transduced and demonstrated a ventricular pressure waveform. This catheter was removed and the ectopy resolved. The factors associated with this arrhythmia are discussed.

Three-Dimensional Coupled Fluid-Structure Simulation of Pericardial Bioprosthetic Aortic Valve Function

A computational, three-dimensional coupled fluid-structure dynamics model was developed for a generic pericardial aortic valve in a rigid aortic root graft with physiologic sinuses. Valve geometry was based on that of the natural valve. Blood flow was modeled as pulsatile, laminar, Newtonian, incompressible flow. The structural model accounted for material and geometric nonlinearities and also simulated leaflet coaptation. A body fitted grid was used to subdivide the flow domain into computational finite volume cells. Shell finite elements were used to discretize the leaflet volume. A finite volume computational fluid dynamics code and finite element structure dynamics code were used to solve the flow and structure equations, respectively. The fluid flow and structural equations were coupled using an implicit "influence coefficient" technique. Physiologic ventricular and aortic pressure waveforms were prescribed as the flow boundary conditions. The aortic flow field, valve structural configuration, and leaflet stresses were computed at 2 msec intervals. Model predictions on aortic flow and transient variation in valve orifice area were in close agreement with corresponding experimental in vitro data. These findings suggest that the computer model has potential for being a powerful design tool for bioprosthetic aortic valves.

Effects of sevoflurane, isoflurane, enflurane, and halothane on left ventricular diastolic performance in dogs

The effects of volatile anesthetics on active (ventricular relaxation) and passive (chamber stiffness) indices of diastolic function and on left ventricular filling rates in dogs were studied to determine how these agents affect left ventricular diastolic performance. Thirty-five mongrel dogs were randomly assigned to receive sevoflurane, isoflurane, enflurane, or halothane. Left ventricular pressure waveforms, phonocardiograms, and echocardiograms were recorded after administering the anesthetics at concentrations of 0% (control), 1%, 2%, and 3%. Ventricular relaxation was defined as the time constant of the decline in left ventricular pressure. Chamber stiffness was derived from the ventricular pressure-volume relationship during passive filling. Rapid filling rate, slow filling rate, and atrial filling rate were obtained from echocardiograms and phonocardiograms. No change in the time constant or in chamber stiffness was observed at any concentration of sevoflurane or isoflurane. However, the highest studied concentration of enflurane and halothane produced a significant increase in the time constant and in chamber stiffness. Rapid filling rate as well as atrial filling rate decreased significantly with the volatile anesthetics, especially with enflurane and halothane. Sevoflurane and isoflurane did not alter ventricular relaxation or chamber stiffness, but did affect diastolic function as manifested by their alteration of filling rates. In contrast, enflurane and halothane each prolonged ventricular relaxation and increased chamber stiffness. With the administration of the volatile anesthetics, the rapid filling rate decreased with the deterioration of diastolic function; in addition, atrial filling rates decreased and did not compensate for the reduction in early ventricular filling.

Assessment of ventricular relaxation in the developing chick embryo using a monoexponential model.

In this study, the ventricular pressure decline during isovolumic relaxation in early diastole was modeled by regressing pressure and pressure change vs. time to a monoexponential formula: P(t) = P infinity+P0e-t/tau, where P(t) is ventricular pressure at time t, P infinity is the pressure in the fully relaxed ventricle, P0 is the pressure at the end of ventricular ejection, and tau is the ventricular relaxation rate constant. Analysis was performed on 330 ventricular pressure waveforms from 22 chick embryos, stages 17, 23, and 26, during baseline and following cardiac cycle length perturbation. Three computational models were evaluated. Based on analysis of the confidence intervals of estimates of P infinity and analysis of residuals, a least-squares nonlinear regression of pressure vs. time, which allowed estimates of tau and P infinity, best approximated the pressure decline. Isovolumic pressure decline in the embryonic heart is well approximated by a monoexponential model if both P infinity and tau are estimated. Negative values of P infinity during early stages of cardiac morphogenesis support the idea that diastolic suction plays a role in ventricular filling in the developing heart.

A Mathematical Model of the Canine Circulation

A lumped-parameter model of the canine closed-loop circulation has been developed. The model consists of the following components: the right heart (atrium and ventricle), pulmonary circulation (pulmonary arteries, capillaries, and veins), left heart (atrium and ventricle), systemic circulation (aorta, systemic arteries, systemic veins, and the vena cavae). The passive elements, the arteries and veins, are represented by their resistive, compliant, and inertial properties.In addition to the mathematical description of the arteries and veins of both the systemic and pulmonary circulations, this model makes use of the time-varying elastance (instantaneous pressure-volume relationship) to describe the nature of the source pumps in the intact circulation. Using elastance functions adopted for both the left and right atria and ventricles, the model produces realistic left and right atrial and ventricular pressure and volume waveforms. Model parameters associated with the systemic and pulmonary circulations have been estimated so that the pressure waveforms at various points in the circulation are in agreement with data from animal experiments. The model can generate realistic pressure waveforms on a beat-to-beat basis and yields good estimates of mean blood pressures, cardiac output and ejection fraction for a normal dog. Furthermore, the model allows the description and specification of blood volume distribution within the entire closed circulation, and the changes in blood volumes can be monitored dynamically. We conclude that our model provides a useful theoretical framework for analyzing experimental studies of the circulatory system.

Interpretation of cardiac pathophysiology from pressure waveform analysis: Simultaneous left and right ventricular pressure measurements

In addition to demonstrating constrictive and restrictive cardiac physiology, simultaneous right and left ventricular pressure measurements can be helpful to identify various aspects of myocardial dysfunction. Intracardiac conduction defects will displace the right ventricular pressure under the left ventricular pressure upstroke and identify differences in the timing of ventricular contraction. Right ventricular dysfunction will also produce abnormal right ventricular pressure waveforms which may overlap left ventricular pressure and contribute to abnormalities in right atrial and ventricular pressure waveforms.

Influence of systolic pressure profile on rate of left ventricular pressure fall

We examined the influence of the systolic left ventricular pressure (LVP) waveform on the rate of isovolumetric LVP fall, as assessed by the time constant tau. Seven open-chest dogs were instrumented with a micromanometer in the left ventricle, with segment length gauges in the anterior and posterior midwall of the left ventricle, and with a balloon-tipped catheter in the proximal aorta. The intra-aortic balloon was inflated before the onset of ejection (early) or during midejection (late) to produce timed and graded increases in peak LVP of 2-20 mmHg. The rate of LVP fall slowed significantly more with late than with early increases in LVP (tau increased 1.5 +/- 0.5 vs. 0.5 +/- 0.3%/mmHg increase in peak LVP, respectively, P less than 0.001). For a similar increase in peak LVP, there was a progressively greater increase in tau when the timing of balloon inflation was progressively delayed from early to late ejection (in 10-ms increments). The differential effect of early vs. late pressure increases on tau was not related to regional differences in segment length behavior nor to an increase in regional nonuniformity between anterior and posterior sites. We conclude that under the experimental conditions of an intact, ejecting left ventricle, the systolic pressure profile is an important determinant of the rate of pressure fall. The rate of LVP fall slows in direct proportion to the magnitude of increase in systolic pressure. The sensitivity to systolic load increases progressively throughout the ejection period, so that the rate of LVP fall slows significantly more with late than with early pressure increases.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical Utility of a Position-monitoring Catheter in the Pulmonary Artery

Unsuspected distal migration of the tip of the pulmonary artery catheter may cause life-threatening complications. We prospectively evaluated the clinical utility of the PA Watch Catheter in 25 patients after cardiac surgery by hourly measurements of pulmonary artery (distal lumen), right ventricular (middle lumen), and central venous (proximal lumen) pressures. The catheter was considered to be in the proper position when the middle lumen port, located 10 cm from the tip, transmitted a right ventricular pressure waveform. Satisfactory initial catheter placement was obtained in 24 of 25 patients. During the 28.4 +/- 1.8 h of postoperative monitoring, clinically unsuspected distal catheter migration, indicated by the presence of a pulmonary artery pressure waveform in the middle lumen port, occurred in 12 of the 25 patients (48%). In these patients, 20 episodes occurred and required catheter withdrawal distances of 1.8 +/- 0.3 cm (range 1-6 cm). The PA Watch Catheter proved to be a useful indicator of unsuspected distal catheter migration in the postoperative period. The PA Watch Catheter allows assessment of catheter tip placement in the proximal pulmonary artery and may decrease catheter-induced complications.

Alteration of the pulsatile load in the high-altitude calf model of pulmonary hypertension

We compared main pulmonary arterial elasticity and global pulmonary arterial compliance in control and high-altitude (HA) calves to determine whether 1) changes in pulmonary arterial elasticity are contributing to an increase in the oscillatory load of the right ventricle in this model of pulmonary hypertension and 2) measured changes in stiffness of the HA calves' arterial wall are the result of both an increase in pressure and an alteration of the material properties of the HA calves' arterial wall. Newborn calves were placed at 4,300 m simulated altitude for 14 days, and control calves were kept at 1,500 m. The HA calves were then reacclimatized to 1,500 m for 24 h so that baseline pressures of the two groups were similar. Open-chest main pulmonary arterial and right ventricular micromanometric pressures, ultrasonic main pulmonary arterial diameter, and green dye flow were measured under baseline conditions and then under moderate and severely hypoxic conditions to make measurements at both baseline and increased pulmonary pressures. At elevated pressures, the pressure-diameter relationship was noted to be nonlinear, and a characteristic late systolic peaking of the right ventricular pressure waveform was seen. The Peterson pressure-strain modulus, pulse wave velocity, characteristic impedance, and global compliance (3 element windkessel) were calculated. The calculated variables were all shown to be pressure dependent, and no intrinsic differences in stiffness were seen between the control and HA animals when mean pressure was taken into account. Pulmonary arterial histology demonstrated, however, a characteristic increase in wall thickness in the HA animals. Thus, in this model of pulmonary hypertension, major changes in elasticity and pulsatile load are primarily due to an increase in pulmonary pressure. The structural changes present in the HA calves' arterial wall did not separately produce any measurable changes in arterial distensibility or the oscillatory load.

Pulmonary Artery Catheters: An Update

Pulmonary artery (PA) catheters are widely used in the care of the critically ill. Numerous catheter designs are available, and the list of indications for their use is con stantly expanding. Extensive physiological data are sup plied by catheters. Right atrial, right ventricular, PA, and PA wedge pressure waveforms, as well as cardiac output and several derived parameters (e.g., systemic vascular resistance, pulmonary vascular resistance) are easily measured. Clinical application of these data may aid in diagnosis and management of acutely ill patients. Physi cians using catheters need to be aware of the numerous complications associated with their use. Scrupulous at tention to insertion and maintenance techniques will minimize the incidence of many of these complications. The undefined risk/benefit ratio of PA catheterization has caused controversy among physicians. Prospective studies to define better the risks versus benefits of PA catheters are currently being planned. Physicians using PA catheters should recognize that the catheters have no direct therapeutic benefit and that PA catheterization should neither replace bedside clinical evaluation nor delay treatment of the patient.

Contraction and relaxation-induced oscillations of the left ventricle of the heart during the isovolumic phases

A theoretical analysis is presented for the transient dynamical response of the left ventricle of the heart during the isovolumic contraction and relaxation phases of the cardiac cycle. Small oscillations of the left ventricular cavity pressure and wall motion are excited by the initial rates of filling and emptying of the ventricle as well as the rate of change in muscle fiber activation. The analysis applies to the genesis of the first and second heart sounds. The ventricle is modeled as a finite, thick-walled incompressible cylinder having a continuum of imbedded axial and circumferential active muscle fibers, which interacts with a fixed volume of an incompressible, ideal fluid. The solution is obtained using a two-timing asymptotic expansion procedure. The theoretical calculations of left ventricular pressure waveforms compare favorably with published recorded pressure waveforms. The amplitude spectra of computed waveforms contain information concerning the active elastic modulus of the fibers, which is a measure of cardiac contractility.

Estimation of signal-to-noise ratio of a quasiperiodic cardiovascular signal using coherency and correlation techniques

Two algorithms, based on coherency and correlation functions, are proposed for estimating the signal-to-noise ratio of physiological signals including the effect of flicker noise. New sampling techniques based on converting a single continuous signal into two time series that satisfy the requirements of the algorithms are proposed. The algorithms are applied to a computer-generated signal and noise composite of known SNR, as well as to quasiperiodic left ventricular pressure (LVP) waveforms transduced from ten patients. Both coherency and correlation methods were used to estimate the known SNR of the computer-generated compsite, signal and noise to within ±5 per cent, for SNR values between 10 and 30 dB. When applied to LVP waveforms, the two methods gave SNR values which were almost identical. Flicker noise associated with the LVP waveforms was computed to be 14 dB higher than the white noise. It is concluded that flicker, or 1/f noise, which has been heretofore ignored in SNR calculations of pressure and flow signals, must now be included.

Vagal stimulation decreases rate of left ventricular relaxation.

We determined the effects of vagal stimulation on the time constant (tau) of left ventricular isovolumic pressure decay and on the maximum rates of left ventricular pressure change (dP/dt) during contraction and relaxation in anesthetized dogs. In each dog, the atria were paced at a constant rate of 150 beats/min. We recorded left ventricular pressure waveforms in the absence (control) and in the presence of vagal stimulation at frequencies of 1, 2, and 3 Hz. During the control periods and during vagal stimulation at each frequency, we determined tau, the maximal rate of contraction, and the maximal rate of relaxation from left ventricular pressure waveforms recorded at medium (100 mmHg), high (130 mmHg), and low (73 mmHg) afterloads. Vagal stimulation at a frequency of 3 Hz increased tau by 23%. This effect of vagal stimulation on tau was most pronounced at the high afterload. Vagal stimulation at 3 Hz decreased the maximal rate of relaxation by 19%, but it decreased the maximal rate of contraction by only 8%. Thus vagal stimulation significantly decreased the rate of left ventricular relaxation and had a greater depressant effect on ventricular relaxation than on contraction.

Noninvasive estimation of the left ventricular pressure waveform throughout ejection in young patients with aortic stenosis

Validation of a totally noninvasive method for estimating instantaneous left ventricular pressure and constructing a pressure waveform throughout ejection in patients with aortic stenosis is reported. In 20 patients (aged 8.75 ± 10 years) with congenital aortic stenosis (measured peak left ventricular pressure 120 to 260 mm Hg; transvalvular gradient 18 to 165 mm Hg), transaortic valve continuous wave Doppler ultrasound, indirect carotid pulse tracing, peripheral blood pressure and measured left ventricular pressure were recorded simultaneously at cardiac catheterization. Data were entered into a microcomputer using a digitizing tablet and the instantaneous Doppler gradient was calculated and added to instantaneous aortic pressure, derived from the time-corrected and calibrated carotid pulse tracing, to estimate instantaneous left ventricular pressure.Estimated left ventricular pressure waveforms reproduced measured left ventricular pressure closely. The mean error at peak left ventricular pressure was 0.2 ± 4.8 mm Hg (r = 0.98, p = 0.001). The average error throughout ejection was 0.9 ± 5.1 mm Hg. The error of estimated pressure was not related to age or the severity of aortic stenosis. The Doppler peak instantaneous gradient was observed to correlate closely (r = 0.97, p = 0.001) with peak to peak gradient.With this technique, the left ventricular pressure wave-form throughout ejection can be accurately estimated non-invasively in patients with aortic stenosis. This methodology enables determination of mean, total and instantaneous systolic left ventricular pressure.

Sensitive detection of the effects of reperfusion on myocardium by ultrasonic tissue characterization with integrated backscatter.

We have shown recently that tissue characterization of myocardium with ultrasound reflects changes associated with contractile function throughout the cardiac cycle. To determine whether ultrasonic tissue characterization can sensitively detect the impact of ischemic injury and reperfusion on contractile properties of the heart, we studied the time course of change of backscatter after 5, 20, and 60 min of coronary occlusion followed by reperfusion in 15 dogs. The time-averaged integrated backscatter (IB) and the amplitude and phase of cyclic variation of IB (phase relative to the left ventricular pressure waveform) were measured. A novel ultrasonic index of acute injury was identified, the phase-weighted amplitude of cyclic variation, and calculated by weighting the amplitude of cyclic variation of IB with respect to the phase. We hypothesized that backscatter variables would change dramatically after occlusion and that their restitution after reperfusion would sensitively reflect the extent and time course of reversibility of ischemic injury. After coronary occlusion, segmental wall thickening decreased from approximately 55% to 5% regardless of the duration of ischemia. Changes in backscatter associated with this decrease included an increase in time-averaged IB of approximately 5 dB, a 5 dB decrease in cyclic variation, an 80 degree phase shift, and a 7 dB decrease in phase-weighted amplitude. Wall thickening after reperfusion immediately after the 5, 20, or 60 min occlusions recovered to 45%, 27%, and 12% of baseline values, respectively. Within 3 hr it recovered to 53%, 44%, and 22%. Time-averaged IB recovered initially by 89%, 61%, and 44% (all p less than .05) and continued to recover subsequently although more slowly. Ultimate recovery was virtually complete. In contrast to the rapid recovery of time-averaged IB, phase-weighted amplitude recovered initially to only 72%, 41%, and -7% of baseline (all p less than .05) and manifested slower and incomplete recovery when ischemia had been present for 20 or 60 min. After reperfusion, the time course of both cyclic variation and phase were reflected by changes in the phase-weighted amplitude. The backscatter variables assessed appear to sensitively delineate the duration, time course of recovery, and reversibility of ischemic injury in response to reperfusion. The results suggest that early recovery of time-averaged IB corresponds in part to the restoration of tissue ultrastructural integrity.(ABSTRACT TRUNCATED AT 400 WORDS)

The use of left ventricular end-ejection pressure and peak pressure in the estimation of the end-systolic pressure-volume relationship.

The end-systolic pressure-volume relationship (ESPVR) as derived from left ventricular pressure-volume loops has gained increasing acceptance as an index of ventricular contractile function. In animal experiments the ESPVR has been defined as a line connecting the upper left corners of several differently loaded pressure-volume (P-V) loops with a slope parameter Ees and a volume axis intercept parameter Vo. In the clinical setting, several variants of the ESPVR have been determined with use of peak left ventricular pressure, end-ejection pressure, and end-ejection volume. The maximum P-V ratio has also frequently been measured. We attempted to determine which of these alternatives resulted in good approximations of the reference ESPVR in eight isolated canine ventricles that ejected into a simulated arterial impedance system with resistance, compliance, and characteristic impedance. We determined various versions of the ESPVR from the same set of beats quickly obtained with little change in inotropic background. To vary ventricular pressure wave forms, each of the arterial impedance parameters was independently controlled at 50%, 100%, and 200% of normal. Against each of the nine combinations of the impedance parameters four P-V loops were obtained under four preloads and from each of the sets of four P-V loops, the reference ESPVR, linear regression of the peak pressure on end-ejection volume (ESPVRPP-EEV), and linear regression of end-ejection pressure on end-ejection volume (ESPVREEPV) were determined. In addition, the maximum P-V ratio (MPVR) was calculated for each P-V loop.(ABSTRACT TRUNCATED AT 250 WORDS)