Measured Pressure Waveforms Research Articles

Photonic sensing of arterial distension.

Most cardiovascular diseases, such as arteriosclerosis and hypertension, are directly linked to pathological changes in hemodynamics, i.e. the complex coupling of blood pressure, blood flow and arterial distension. To improve the current understanding of cardiovascular diseases and pave the way for novel cardiovascular diagnostics, innovative tools are required that measure pressure, flow, and distension waveforms with yet unattained spatiotemporal resolution. In this context, miniaturized implantable solutions for continuously measuring these parameters over the long-term are of particular interest. We present here an implantable photonic sensor system capable of sensing arterial wall movements of a few hundred microns in vivo with sub-micron resolution, a precision in the micrometer range and a temporal resolution of 10 kHz. The photonic measurement principle is based on transmission photoplethysmography with stretchable optoelectronic sensors applied directly to large systemic arteries. The presented photonic sensor system expands the toolbox of cardiovascular measurement techniques and makes these key vital parameters continuously accessible over the long-term. In the near term, this new approach offers a tool for clinical research, and as a perspective, a continuous long-term monitoring system that enables novel diagnostic methods in arteriosclerosis and hypertension research that follow the trend in quantifying cardiovascular diseases by measuring arterial stiffness and more generally analyzing pulse contours.

In silico coronary wave intensity analysis: application of an integrated one-dimensional and poromechanical model of cardiac perfusion.

Coronary wave intensity analysis (cWIA) is a diagnostic technique based on invasive measurement of coronary pressure and velocity waveforms. The theory of WIA allows the forward- and backward-propagating coronary waves to be separated and attributed to their origin and timing, thus serving as a sensitive and specific cardiac functional indicator. In recent years, an increasing number of clinical studies have begun to establish associations between changes in specific waves and various diseases of myocardium and perfusion. These studies are, however, currently confined to a trial-and-error approach and are subject to technological limitations which may confound accurate interpretations. In this work, we have developed a biophysically based cardiac perfusion model which incorporates full ventricular–aortic–coronary coupling. This was achieved by integrating our previous work on one-dimensional modelling of vascular flow and poroelastic perfusion within an active myocardial mechanics framework. Extensive parameterisation was performed, yielding a close agreement with physiological levels of global coronary and myocardial function as well as experimentally observed cumulative wave intensity magnitudes. Results indicate a strong dependence of the backward suction wave on QRS duration and vascular resistance, the forward pushing wave on the rate of myocyte tension development, and the late forward pushing wave on the aortic valve dynamics. These findings are not only consistent with experimental observations, but offer a greater specificity to the wave-originating mechanisms, thus demonstrating the value of the integrated model as a tool for clinical investigation.

Importance of re-calibration time on pulse contour analysis agreement with thermodilution measurements of cardiac output: a retrospective analysis of intensive care unit patients.

We assessed the effect of re-calibration time on cardiac output estimation and trending performance in a retrospective analysis of an intensive care unit patient population using error grid analyses. Paired thermodilution and arterial blood pressure waveform measurements (N=2141) from 222 patient records were extracted from the Multiparameter Intelligent Monitoring in Intensive Care II database. Pulse contour analysis was performed by implementing a previously reported algorithm at calibration times of 1, 2, 8 and 24h. Cardiac output estimation agreement was assessed using Bland-Altman and error grid analyses. Trending was assessed by concordance and a 4-Quadrant error grid analysis. Error between pulse contour and thermodilution increased with longer calibration times. Limits of agreement were -1.85 to 1.66 L/min for 1h maximum calibration time compared to -2.70 to 2.41L/min for 24h. Error grid analysis resulted in 74.2% of points bounded by 20% error limits of thermodilution measurements for 1h calibration time compared to 65% for 24h. 4-Quadrant error grid analysis showed <75% of changes in pulse contour estimates to be within ±80% of the change in the thermodilution measurement at any calibration time. Shorter calibration times improved the agreement of cardiac output pulse contour estimates with thermodilution. Use of minimally invasive pulse contour methods in intensive care monitoring could benefit from prospective studies evaluating calibration protocols. The applied pulse contour analysis method and thermodilution showed poor agreement to monitor changes in cardiac output.

Prediction of pressure distribution between the vocal folds using Bernoulli’s equation

Determining the mechanisms of self-sustained oscillation of the vocal folds requires characterization of intraglottal aerodynamics. Since most of the intraglottal aerodynamics forces cannot be measured experimentally, most of the current understanding of vocal fold vibration mechanism is derived from analytical and computational models. Several of such studies have used the Bernoulli’s equation in order to calculate the pressure distribution between the vibrating folds. In the current study, intraglottal pressure measurements are taken in a hemilarynx model and are compared with pressure values that are computed form the Bernoulli’s equation. The hemilarynx model was made by removing one fold and having the remaining fold vibrating against a metal plate. The plate was equipped with two pressure ports located near the superior and inferior aspects of the fold. The results show that pressure calculated using Bernoulli’s equation matched well with the measured pressure waveform during the glottal opening phase and dissociated during the closing phase.

Study of detonation initiation in kerosene–oxidizer mixtures in short tubes

The paper describes experimental studies of detonation initiation in a kerosene–oxidizer mixture in a short test tube. The aim of the study is to determine the minimum diameter of the tube and the minimum level of energy that enables direct initiation of the detonation. Knowledge about these values will inform the design of a jet engine combustion chamber in which thermal energy will be generated by a rotating detonation process. The test tube and the oxidizer inside the tube were heated using specially designed heaters installed outside of the tube. The heated oxidizer provided thermal conditions similar to the conditions for a compressor with small to medium static pressure. The study was conducted for four different tube diameters and for various energies of initiation. As a result, measurements of pressure waveforms were obtained for various cases of fuel injection, which were then compared against the results of the shock wave generated by the initiator. This study provides a value for the energy (the pressure of the mixture in the initiator), which provided direct initiation of detonation for a kerosene–oxidizer mixture. Different tube diameters led to the initiation of detonation for various oxygen–nitrogen compositions as an oxidizer.

Patient-specific coronary stenoses can be modeled using a combination of OCT and flow velocities to accurately predict hyperemic pressure gradients.

Computational fluid dynamics (CFD) is increasingly being developed for the diagnostics of arterial diseases. Imaging methods such as computed tomography (CT) and angiography are commonly used. However, these have limited spatial resolution and are subject to movement artifact. This study developed a new approach to generate CFD models by combining high-fidelity, patient-specific coronary anatomy models derived from optical coherence tomography (OCT) imaging with patient-specific pressure and velocity phasic data. Additionally, we used a new technique which does not require the catheter to be used to determine the centerline of the vessel. The CFD data were then compared with invasively measured pressure and velocity. Angiography imaging data of 21 vessels collected from 19 patients were fused with OCT visualizations of the same vessels using an algorithm that produces reconstructions inheriting the in-plane (10 μm) and longitudinal (0.2 mm) resolution of OCT. Proximal pressure and distal velocity waveforms ensemble averaged from invasively measured data were used as inlet and outlet boundary conditions, respectively, in CFD simulations. The resulting distal pressure waveform was compared against the measured waveform to test the model. The results followed the shape of the measured waveforms closely (cross-correlation coefficient = 0.898 ± 0.005, ), indicating realistic modeling of flow resistance, the mean of differences between measured and simulated results was -3. 5 mmHg, standard deviation of differences (SDD) = 8.2 mmHg over the cycle and -9.8 mmHg, SDD = 16.4 mmHg at peak flow. Models incorporating phasic velocity in patient-specific models of coronary anatomy derived from high-resolution OCT images show a good correlation with the measured pressure waveforms in all cases, indicating that the model results may be an accurate representation of the measured flow conditions.

Validation of Peripheral Pulse Wave Analysis Technique to Detect Aortic Valve State in Continuous-Flow LVADs1

Validation of Peripheral Pulse Wave Analysis Technique to Detect Aortic Valve State in Continuous-Flow LVADs1

Impact of rigid sphere scattering on measurement of acoustic shocks

Multi-microphone arrays embedded in a rigid spherical housing have been used to estimate field quantities such as vector intensity. However, the measured pressure waveforms are modified by the scattering of the incident pressure wave on the sphere. The frequency response function and the corresponding impulse response function for microphones in a sphere can be created using Mie scattering theory. This permits analysis of the scattering effect on pressure measurements for shock-containing broadband waveforms, such as those produced by solid rocket motors. The abrupt pressure rises associated with shocks are seen to be either overestimated or underestimated depending on the angle of the measuring microphone. These shocks are the most affected portion of the waveform due to their high frequency content. In addition, deconvolution of measured rocket signals using the predicted impulse responses of the microphones in the array provides an apparently consistent estimate of the free-field signal at the probe center.

082 Non-invasive measurements of intracranial pressure: Can Coherent averaging show a tilt-dependent change in the measured Spontaneous Tympanic Membrane Displacement (STMD) signal in healthy volunteers?

IntroductionSpontaneous Tympanic Membrane Displacement can be measured quasi-continuously and shows a cardiovascular waveform (STMDVA). It is probable that this waveform is generated by intracranial pressure being transmitted to the ossicular...

Acupuncture Effects on the Pulse Spectrum of Radial Pressure Pulse in Dyspepsia

This study is to investigate the influences of acupuncture for dyspepsia on the Radial Pressure Pulse (RPP) between the Chun, Guan and Chy positions of the right/left wrist. Two series of experiments were designed; for the first series, 30 patients with dyspepsia (Group P) and 30 normal subjects (Group N) were seated to undergo the measurements of pulse pressure waveforms from radial artery by sphygmograph. The parameters of RPP included the spectral energy of 0-10 Hz (SE(0-10 Hz)), 10-50 Hz (SE(10-50 Hz)) and 13-50 Hz (SE(13-50 Hz)). For the second series, acupuncture was administered at the right and left Tsu San Li (St-36) points for the same 30 dyspepsia patients, and then their pulse pressure waveforms were re-examined. The results showed that the SE(0-10 Hz) at Right Guan (RB) (p < 0.05), the SE(10-50 Hz) at RB (p < 0.01), and the SE(13-50 Hz) at RB (p < 0.01) and Left Guan (LB) (p < 0.05) of Group P were significantly greater than that of Group N. After the acupuncture, there were significant decreases in the SE(0-10 Hz) only at RB (p < 0.01), in the SE(10-50 Hz) at RB (p < 0.01), Right Chy (RC) (p < 0.05) and LB (p < 0.05), and in the SE(13-50 Hz) RB (p < 0.01), RC (p < 0.05) and LB (p < 0.01). We concluded that the pulse-frequency spectrum at RB was a more effective characteristic for dyspepsia patients, and the acupuncture had an effect on SE(10-50 Hz) and SE(13-50 Hz) more obviously than that on SE(0-10 Hz).

Spontaneous fluctuations in the peripheral photoplethysmographic waveform: roles of arterial pressure and muscle sympathetic nerve activity

Assessment of spontaneous slow waves in the peripheral blood volume using the photoplethysmogram (PPG) has shown potential clinical value, but the physiological correlates of these fluctuations have not been fully elucidated. This study addressed the contribution of arterial pressure and muscle sympathetic nerve activity (MSNA) in beat-to-beat PPG variability in resting humans under spontaneous breathing conditions. Peripheral PPG waveforms were measured from the fingertip, earlobe, and toe in young and healthy individuals (n = 13), together with the arterial pressure waveform, electrocardiogram, respiration, and direct measurement of MSNA by microneurography. Cross-spectral coherence analysis revealed that among the PPG waveforms, low-frequency fluctuations (0.04-0.15 Hz) in the ear PPG had the highest coherence with arterial pressure (0.71 ± 0.15) and MSNA (0.44 ± 0.18, with a peak of 0.71 ± 0.16 at 0.10 ± 0.03 Hz). The normalized midfrequency powers (0.08-0.15 Hz), with an emphasis on the 0.1-Hz region, were positively correlated between MSNA and the ear PPG (r = 0.77, P = 0.002). Finger and toe PPGs had lower coherence with arterial pressure (0.35 ± 0.10 and 0.30 ± 0.11, respectively) and MSNA (0.33 ± 0.10 and 0.26 ± 0.10, respectively) in the LF band but displayed higher coherence between themselves (0.54 ± 0.09) compared with the ear (P < 0.001), which may suggest the dominance of regional vasomotor activities and a common sympathetic influence in the glabrous skin. These findings highlight the differential mechanisms governing PPG waveform fluctuations across different body sites. Spontaneous PPG variability in the ear includes a major contribution from arterial pressure and MSNA, which may provide a rationale for its clinical utility.

Regional in vivo transit time measurements of aortic pulse wave velocity in mice with high-field CMR at 17.6 Tesla.

BackgroundTransgenic mouse models are increasingly used to study the pathophysiology of human cardiovascular diseases. The aortic pulse wave velocity (PWV) is an indirect measure for vascular stiffness and a marker for cardiovascular risk.ResultsThis study presents a cardiovascular magnetic resonance (CMR) transit time (TT) method that allows the determination of the PWV in the descending murine aorta by analyzing blood flow waveforms. Systolic flow pulses were recorded with a temporal resolution of 1 ms applying phase velocity encoding. In a first step, the CMR method was validated by pressure waveform measurements on a pulsatile elastic vessel phantom. In a second step, the CMR method was applied to measure PWVs in a group of five eight-month-old apolipoprotein E deficient (ApoE(-/-)) mice and an age matched group of four C57Bl/6J mice. The ApoE(-/-) group had a higher mean PWV (PWV = 3.0 ± 0.6 m/s) than the C57Bl/6J group (PWV = 2.4 ± 0.4 m/s). The difference was statistically significant (p = 0.014).ConclusionsThe findings of this study demonstrate that high field CMR is applicable to non-invasively determine and distinguish PWVs in the arterial system of healthy and diseased groups of mice.

Calculation of Forward and Backward Arterial Waves by Analysis of Two Pressure Waveforms

We developed a technique to calculate forward and backward arterial waves from proximal and distal pressure waveforms. First, the relationship between the waveforms is represented with an arterial tube model. Then, the model parameters are estimated via least-squares fitting. Finally, the forward and backward waves are calculated using the parameter estimates. Thus, unlike most techniques, the arterial waves are determined without a more difficult flow measurement or an experimental perturbation. We applied the technique to central aortic and femoral artery pressure waveforms from anesthetized dogs during drug infusions, volume changes, and cardiac pacing. The calculated waves predicted an abdominal aortic pressure waveform measurement more accurately (2.4 mmHg error) than the analyzed waveforms (5.3mmHg average error); reliably predicted relative changes in a femoral artery flow measurement (14.7% error); and changed as expected with selective vasoactive drugs. The ratio of the backward- to forward-wave magnitudes was 0.37 ± 0.05 during baseline. This index increased by ∼50% with phenylephrine and norepinephrine, decreased by ∼60% with dobutamine and nitroglycerin, and changed little otherwise. The time delay between the waves in the central aorta was 175 ± 14 ms during baseline. This delay varied by ±∼25% and was inversely related to mean pressure.

A simulation environment for validating ultrasonic blood flow and vessel wall imaging based on fluid‐structure interaction simulations: Ultrasonic assessment of arterial distension and wall shear rate

Ultrasound (US) is a commonly used vascular imaging tool when screening for patients at high cardiovascular risk. However, current blood flow and vessel wall imaging methods are hampered by several limitations. When optimizing and developing new ultrasound modalities, proper validation is required before clinical implementation. Therefore, the authors present a simulation environment integrating ultrasound and fluid-structure interaction (FSI) simulations, allowing construction of synthetic ultrasound images based on physiologically realistic behavior of an artery. To demonstrate the potential of the model for vascular ultrasound research, the authors studied clinically relevant imaging modalities of arterial function related to both vessel wall deformation and arterial hemodynamics: Arterial distension (related to arterial stiffness) and wall shear rate (related to the development of atherosclerosis) imaging. An in-house code ("TANGO") was developed to strongly couple the flow solver FLUENT and structural solver ABAQUS using an interface quasi-Newton technique. FIELD II was used to model realistic transducer and scan settings. The input to the FSI-US model is a scatterer phantom on which the US waves reflect, with the scatterer displacement derived from the FSI flow and displacement fields. The authors applied the simulation tool to a 3D straight tube, representative of the common carotid artery (length: 5 cm; and inner and outer radius: 3 and 4 mm). A mass flow inlet boundary condition, based on flow measured in a healthy subject, was applied. A downstream pressure condition, based on a noninvasively measured pressure waveform, was chosen and scaled to simulate three different degrees of arterial distension (1%, 4%, and 9%). The RF data from the FSI-US coupling were further processed for arterial wall and flow imaging. Using an available wall tracking algorithm, arterial distensibility was assessed. Using an autocorrelation estimator, blood velocity and shear rate were obtained along a scanline. The authors obtained a very good agreement between the flow and the distension as obtained from the FSI-US model and the reference FSI values. The wall application showed a high sensitivity of distension measurements to the measurement location, previously reported based on in vivo data. Interestingly, the model indicated that strong reflections between tissue transitions can potentially cloud a correct measurement. The flow imaging application demonstrated that maximum shear rate was underestimated for a relevant simulation setup. Moreover, given the difficulty of measuring near-wall velocities with ultrasound, maximal shear rate was obtained at a distance from the wall [0.812 mm for the anterior and 0.689 mm for the posterior side (9% distension case)]. However, ultrasound shear rates correlated well with the FSI ground truth for all distension degrees, suggesting that correction of the severe underestimation by ultrasound might be feasible in certain flow conditions. The authors demonstrated a simulation environment to validate and develop ultrasonic vascular imaging. An elaborate technique to integrate FSI and FIELD II ultrasound simulations was presented. This multiphysics simulation tool was applied to two imaging applications where distensible ultrasound phantoms are indispensable: Wall distension and shear rate measurement. Results showed that the method to couple fluid-structure interaction and ultrasound simulations provides realistic RF signals from the tissue and the blood pool.

Estimation of pulse transit time using two diametric blood pressure waveform measurements

This paper presents a novel method to estimate the aortic-to-peripheral pulse transit time (PTT) using the blood pressure waveforms measured at two diametric peripheral locations, for instance, one on an upper extremity and the other on a lower extremity. The method is based on a computational relationship between the two peripheral blood pressures, which is derived by first relating each peripheral blood pressure to a common central aortic blood pressure. The parameters of the computational relationship for an individual subject can be identified by fitting them to two peripheral blood pressure waveform measurements, thereby characterizing the cardiovascular dynamics, from which absolute changes in the PTT between the central aorta and each peripheral measurement site can be determined. The strength of the method is that it does not require any a priori knowledge of the peripheral measurement locations nor of the physiologic condition of the cardiovascular system. Experimental results are provided from five healthy swine subjects whose actual PTT experimentally varied from 44.9 ms to 163.0 ms (76.7 ms mean ± 26.4 ms SD). Compared to the reference PTT measurement, the novel method proposed in this paper estimated PTT within 3.7 ms mean ± 4.2 ms SD after initial calibration.

Quantitative Analysis of Sensor for Pressure Waveform Measurement

BackgroundArterial pressure waveforms contain important diagnostic and physiological information since their contour depends on a healthy cardiovascular system [1]. A sensor was placed at the measured artery and some contact pressure was used to measure the pressure waveform. However, where is the location of the sensor just about enough to detect a complete pressure waveform for the diagnosis? How much contact pressure is needed over the pulse point? These two problems still remain unresolved.MethodIn this study, we propose a quantitative analysis to evaluate the pressure waveform for locating the position and applying the appropriate force between the sensor and the radial artery. The two-axis mechanism and the modified sensor have been designed to estimate the radial arterial width and detect the contact pressure. The template matching method was used to analyze the pressure waveform. In the X-axis scan, we found that the arterial diameter changed waveform (ADCW) and the pressure waveform would change from small to large and then back to small again when the sensor was moved across the radial artery. In the Z-axis scan, we also found that the ADCW and the pressure waveform would change from small to large and then back to small again when the applied contact pressure continuously increased.ResultsIn the X-axis scan, the template correlation coefficients of the left and right boundaries of the radial arterial width were 0.987 ± 0.016 and 0.978 ± 0.028, respectively. In the Z-axis scan, when the excessive contact pressure was more than 100 mm Hg, the template correlation was below 0.983. In applying force, when using the maximum amplitude as the criteria level, the lower contact pressure (r = 0.988 ± 0.004) was better than the higher contact pressure (r = 0.976 ± 0.012).ConclusionsAlthough, the optimal detective position has to be close to the middle of the radial arterial, the pressure waveform also has a good completeness with a template correlation coefficient of above 0.99 when the position was within ± 1 mm of the middle of the radial arterial range. In applying force, using the maximum amplitude as the criteria level, the lower contact pressure was better than the higher contact pressure.

Central Pressure and Pulse Wave Amplification in the Upper Limb

To the Editor: The important review of pulse pressure (PP) amplification1 was directed at better understanding of central (ascending aortic or carotid) pressure generated from upper limb measurements of cuff arterial pressure and pressure waveforms. One important issue, not addressed by the authors, is how 2 different …

Dynamic responsiveness of the vascular bed as a regulatory mechanism in vasomotor control

The dynamics of blood supply to a vascular bed depend on lumped mechanical properties of that bed, namely the compliance (C), resistance (R), viscoelasticity (K), and inertance (L). While the study of regulatory mechanisms has so far placed the emphasis largely on R, it is not known how the remaining properties contribute collectively to the play of dynamics in vasomotor control. To examine this question and to establish some benchmark values of these properties, simultaneous measurements of pressure and flow waveforms in the vascular bed of the forearm were obtained from three groups: young healthy individuals, older hypertensives with controlled blood pressure, and older hypertensives with uncontrolled blood pressure. The values of R and C were found to vary within a wide range in each of the three groups to the extent that neither R nor C could be used independently as an indicator of health or age of the subjects tested. However, higher level dynamic properties of the bed, such as the time constants and damping index, which depend on combinations of C,K, and L, and which may reflect measures of the dynamic responsiveness or “sluggishness” of the system, were found to be maintained over a wide range of pulse pressures. These findings support a hypothesis that the pulsatile dynamics of blood supply to a vascular bed are adapted to the individual baseline values of R and C in different subjects with the effect of optimizing the level of dynamic responsiveness to changes in pressure or flow, and that this dynamic property of the vascular bed may be a protected and/or regulated property.

Improved impulse response for hydrophone measurements in therapeutic ultrasound fields.

The accurate measurement of pressure waveforms in high intensity focused ultrasound (HIFU) fields is complicated by the fact that many devices operate at output levels where shock waves can form in the focal region. In tissue ablation applications, the accurate measurement of the shock amplitude is important for predicting tissue heating since the absorption at the shock is proportional to the shock amplitude cubed. To accurately measure shocked pressure waveforms, not only must a hydrophone with a broad bandwidth (>100 MHz) be used, but the frequency response of the hydrophone must be known and used to correct the measured waveform. In this work, shocked pressure waveforms were measured using a fiber optic hydrophone and a frequency response for the hydrophone was determined by comparing measurements with numerical modeling using a KZK‐type equation. The impulse response was separately determined by comparing a measured and an idealized shock pulse generated by an electromagnetic lithotripter. The frequency responses determined by the two methods were in good agreement. Calculations of heating using measured HIFU waveforms that had been deconvolved with the determined frequency response agreed well with measurements in tissue phantom. [Work supported by NIH DK43881, NSBRI SMST01601, NIH EB007643, and RFBR.]

FLUID FLOW IN DISTENSIBLE VESSELS

1. Flow in single vascular conduits is reviewed, divided into distended and deflated vessels. 2. In distended vessels with pulsatile flow, wave propagation and reflection dominate the spatial and temporal distribution of pressure, determining the shape, size and relative timing of measured pressure waveforms, as well as the instantaneous pressure gradient everywhere. Considerable research has been devoted to accessing the information on pathological vascular malformations contained in reflected waves. Slow waves of contraction of vessel wall muscle, responsible for transport of oesophageal, ureteral and gut contents, have also been modelled. 3. The pressure gradient in a vessel drives the flow. Flow rate can be predicted both analytically and numerically, but analytical theory is limited to idealized geometry. The complex geometry of biological system conduits necessitates computation instead. Initially limited to rigid boundaries, numerical methods now include fluid-structure interaction and can simultaneously model solute transport, thus predicting accurately the environment of the mechanosensors and chemosensors at vessel surfaces. 4. Deflated vessels display all phenomena found in distended vessels, but have additional unique behaviours, especially flow rate limitation and flow-induced oscillation. Flow rate limitation is widespread in the human body and has particular diagnostic importance in respiratory investigation. Because of their liquid lining, the pulmonary airways are also characterized by important two-phase flows, where surface tension phenomena create flows and determine the patency and state of collapse of conduits. 5. Apart from the vital example of phonation, sustained self-excited oscillation is largely avoided in the human body. Where it occurs in snoring, it is implicated in the pathological condition of sleep apnoea.