Central Aortic Blood Pressure Waveform Research Articles

A study on transfer function to estimate the central aortic blood pressure waveform

Noninvasive measurement of the central aortic blood pressure has become an important technique that has generated a lot of interest around the medicine industry because it can estimate the central aortic blood pressure waveform without inserting a pressure-sensing catheter into the ascending aorta. The accuracy of noninvasive estimation of aortic hemodynamics and cardiac contractility is still debatable in noninvasive measurement of the central aortic blood methods. The objective of this project is to investigate the transfer functions available for converting radial blood pressure waveforms to central aortic blood pressure waveforms. In this project, three different transfer functions will be investigated which are The Generalized Transfer Function, N-Point Moving Average and Adaptive Transfer Function in order to recommend the effective method in terms of accuracy. The study methodology will be conducted through the software MATLAB R2021b. The investigation of these three methods will be conducted with data collected from virtual subjects from the HaeMod database. The Generalized transfer function, N-Point Moving Average and Adaptive Transfer Function will be coded, evaluated, and analyzed as part of the methodology. The determination of the most effective method among the three transfer functions will be attributed according to output comparison of Systolic peak differences, the RMSE and the MAPE between the estimated central aortic blood pressure and the measured central aortic blood pressure.

A novel electrical impedance function to estimate central aortic blood pressure waveforms

Background and objectiveCentral aortic blood pressure waveforms convey imperative information about cardiovascular risk, but these measurements are obtained invasively. The study aims to develop an electrical impedance function (EIF) to estimate the central (aortic) blood pressure waveform from the radial blood pressure waveform without the need of invasive procedures. MethodsThis paper shows a method of using the four-element Windkessel model to derive an EIF using circuit analysis to estimate the central aortic blood pressure. The four elements were identified from radial waveforms by using the Nelder-Mead simplex algorithm and then used to construct the EIF to obtain the aortic pressure waveform, given the radial waveform. ResultsWaveforms generated by EIF gave the lowest values for Root Mean Square Error (RMSE) (5.69) and Mean Average Percentage Error (MAPE) (0.0402) compared to the generalized transfer function (GTF) and N-point moving average (NPMA), and the lowest MAPE and a comparable RMSE when compared to the Adaptive Transfer Function (ATF). Moreover, EIF has a significantly lower computing time (0.008 ms) when compared with GTF, NPMA and ATF. ConclusionsThe proposed function had comparable or better performance to existing methods when tested on both simulated and actual patient data, and was able to give a better signal shape retention at the dicrotic notch (99.94 % correlation), which is a crucial feature for cardiovascular disease detection. SignificanceOverall the EIF performance validates its use in estimating central aortic pressure waveforms, making it potentially viable for better embedded systems for non-invasive central blood pressure monitoring due to its low computation time and high accuracy.

Mechanisms behind altered pulsatile intracranial pressure in idiopathic normal pressure hydrocephalus: role of vascular pulsatility and systemic hemodynamic variables

BackgroundThe dementia subtype idiopathic normal pressure hydrocephalus (iNPH) has unknown etiology, but one characteristic is elevated intracranial pressure (ICP) wave amplitudes in those individuals who respond with clinical improvement following cerebrospinal fluid (CSF) diversion. To explore the mechanisms behind altered ICP wave amplitudes, we correlated central aortic blood pressure (BP) and ICP waveform amplitudes (intracranial aortic amplitude correlation) and examined how this correlation relates to ICP wave amplitude levels and systemic hemodynamic parameters.MethodsThe study included 29 patients with probable iNPH who underwent continuous multi-hour measurement of ICP, radial artery BP, and systemic hemodynamic parameters. The radial artery BP waveforms were used to estimate central aortic BP waveforms, and the intracranial aortic amplitude correlation was determined over consecutive 4-min periods.ResultsThe average intracranial aortic amplitude correlation was 0.28 ± 0.16 at the group level. In the majority of iNPH patients, the intracranial aortic amplitude correlation was low, while in about 1/5 patients, the correlation was rather high (average Pearson correlation coefficient > 0.4). The degree of correlation was hardly influenced by systemic hemodynamic parameters.ConclusionsIn about 1/5 iNPH patients of this study, the intracranial aortic amplitude correlation (IAACAORTIC) was rather high (average Pearson correlation coefficient > 0.4), suggesting that cerebrovascular factors to some extent may affect the ICP wave amplitudes in a subset of patients. However, in 14/19 (74%) iNPH patients with elevated ICP wave amplitudes, the intracranial aortic amplitude correlation was low, indicating that the ICP pulse amplitude in most iNPH patients is independent of central vascular excitation, ergo it is modulated by local cerebrospinal physiology. In support of this assumption, the intracranial aortic amplitude correlation was not related to most systemic hemodynamic variables. An exception was found for a subgroup of the patients with high systemic vascular resistance, where there was a correlation.

Observer-Based Deconvolution of Deterministic Input in Coprime Multichannel Systems With Its Application to Noninvasive Central Blood Pressure Monitoring.

Estimating central aortic blood pressure (BP) is important for cardiovascular (CV) health and risk prediction purposes. CV system is a multichannel dynamical system that yields multiple BPs at various body sites in response to central aortic BP. This paper concerns the development and analysis of an observer-based approach to deconvolution of unknown input in a class of coprime multichannel systems applicable to noninvasive estimation of central aortic BP. A multichannel system yields multiple outputs in response to a common input. Hence, the relationship between any pair of two outputs constitutes a hypothetical input-output system with unknown input embedded as a state. The central idea underlying our approach is to derive the unknown input by designing an observer for the hypothetical input-output system. In this paper, we developed an unknown input observer (UIO) for input deconvolution in coprime multichannel systems. We provided a universal design algorithm as well as meaningful physical insights and inherent performance limitations associated with the algorithm. The validity and potential of our approach were illustrated using a case study of estimating central aortic BP waveform from two noninvasively acquired peripheral arterial pulse waveforms. The UIO could reduce the root-mean-squared error (RMSE) associated with the central aortic BP by up to 27.5% and 28.8% against conventional inverse filtering (IF) and peripheral arterial pulse scaling techniques.

Integrating Patient-Specific Electrocardiogram Signals and Image-Based Computational Fluid Dynamics Method to Analyze Coronary Blood Flow in Patients during Cardiac Arrhythmias

PurposeThe aim of this study was to use the computational fluid dynamics (CFD) method, patient-specific electrocardiogram (ECG) signals, and computed tomography three-dimensional image reconstruction technique to investigate the blood flow in coronary arteries during cardiac arrhythmia.MethodsTwo patients with premature ventricular contraction-type cardiac arrhythmia and one with atrial fibrillation-type cardiac arrhythmia were investigated. The inlet velocity of the coronary artery in simulation was applied with the measured velocity profile of the left ventricular outflow tract (LVOT) from the Doppler echocardiography. The measured patient central aortic blood pressure waveform was employed for the coronary artery outlet in simulation. The no-slip boundary condition was applied to the arterial wall.ResultsFor the patient with irregular cardiac rhythms (Case I), the coronary blood flow rate under the shortened and lengthened cardiac rhythms were 0.66 and 0.96 mL/s, respectively. In Case II, the maximum velocity at the LVOT under a normal heartbeat was found to be 101 cm/s, whereas the average value was 73 cm/s. In Case III, the patient was also diagnosed with a congenital stenosis problem at the myocardial bridge (MCB) at the LAD. The measured blood flow rate at the MCB of the LAD for the three heartbeats in Case III was found to be 0.68, 1.08, and 1.14 mL/s.ConclusionThe integration of patient-specific ECG signals and image-based CFD methods can clearly analyze hemodynamic information for patients during cardiac arrhythmia. The cardiac arrhythmia can reduce the blood flow in the coronary arteries.

Non-invasive Estimation of the Intracranial Pressure Waveform from the Central Arterial Blood Pressure Waveform in Idiopathic Normal Pressure Hydrocephalus Patients

This study explored the hypothesis that the central aortic blood pressure (BP) waveform may be used for non-invasive estimation of the intracranial pressure (ICP) waveform. Simultaneous invasive ICP and radial artery BP waveforms were measured in 29 individuals with idiopathic normal pressure hydrocephalus (iNPH). The central aortic BP waveforms were estimated from the radial artery BP waveforms using the SphygmoCor system. For each individual, a transfer function estimate between the central aortic BP and the invasive ICP waveforms was found (Intra-patient approach). Thereafter, the transfer function estimate that gave the best fit was chosen and applied to the other individuals (Inter-patient approach). To validate the results, ICP waveform parameters were calculated for the estimates and the measured golden standard. For the Intra-patient approach, the mean absolute difference in invasive versus non-invasive mean ICP wave amplitude was 1.9 ± 1.0 mmHg among the 29 individuals. Correspondingly, the Inter-patient approach resulted in a mean absolute difference of 1.6 ± 1.0 mmHg for the 29 individuals. This method gave a fairly good estimate of the wave for about a third of the individuals, but the variability is quite large. This approach is therefore not a reliable method for use in clinical patient management.

Model-Based Blind System Identification Approach to Estimation of Central Aortic Blood Pressure Waveform From Noninvasive Diametric Circulatory Signals

This paper presents a model-based blind system identification approach to estimation of central aortic blood pressure (BP) waveform from noninvasive diametric circulatory signals. First, we developed a mathematical model to reproduce the relationship between central aortic BP waveform and a class of noninvasive circulatory signals at diametric locations by combining models to represent wave propagation in the artery, arterial pressure–volume relationship, and mechanics of the measurement instrument. Second, we formulated the problem of estimating central aortic BP waveform from noninvasive diametric circulatory signals into a blind system identification problem. Third, we performed identifiability analysis to show that the mathematical model could be identified and its parameters determined up to an unknown scale. Finally, we illustrated the feasibility of the approach by applying it to estimate central aortic BP waveform from two diametric pulse volume recording (PVR) signals. Experimental results from ten human subjects showed that the proposed approach could estimate central aortic BP waveform accurately: the average root-mean-squared error (RMSE) associated with the central aortic BP waveform was 4.1 mm Hg (amounting to 4.5% of the underlying mean BP) while the average errors associated with central aortic systolic pressure (SP) and pulse pressure (PP) were 2.4 mm Hg and 2.0 mm Hg (amounting to 2.5% and 2.1% of the underlying mean BP). The proposed approach may contribute to the improved monitoring of cardiovascular (CV) health by enabling estimation of central aortic BP waveform from conveniently measurable diametric circulatory signals.

Influence of obesity in central blood pressure.

Obesity is an important risk factor for cardiovascular disease and has become a major concern in healthcare due to its high prevalence worldwide. The aim of the present study was to investigate the impact of BMI on central blood pressure (BP) and pulse wave velocity (PWV) in normotensive and hypertensive patients. Normotensive and hypertensive adult patients who attended the outpatient clinic of cardiovascular risk were included. Peripheral BP was obtained in the brachial artery by using an oscillometric device (OMRON M-6). Central aortic BP waveform was reconstructed from the radial artery pressure waveforms (SphygmoCor, AtCor Medical, Sydney, Australia) and central BP was calculated. Carotid-femoral PWV was measured by an automatic device (Complior, Artech, France). We examined a total of 351 patients [50.7% women; 77 patients normal-weight (BMI < 25 kg/m)], 274 patients overweight or obese (BMI ≥25 kg/m). Central SBP showed a positive association with male sex and mean BP, but a negative association with overweight/obesity. PWV was positively associated with age, male sex, central BP, peripheral BP and BP treatment, whereas BMI of at least 25 kg/m led to a decrease in PWV in patients with the same central SBP levels. Likewise, PWV was lower in the overweight/obese group compared to the normal-weight group at the same central SBP. Overweight and obesity tend to have lower central SBP as compared to lean patients, mainly in women. Further research is required to assess the interaction between body weight and vascular dynamics and their clinical implications.

Quantification of Wave Reflection Using Peripheral Blood Pressure Waveforms

This paper presents a novel minimally invasive method for quantifying blood pressure (BP) wave reflection in the arterial tree. In this method, two peripheral BP waveforms are analyzed to obtain an estimate of central aortic BP waveform, which is used together with a peripheral BP waveform to compute forward and backward pressure waves. These forward and backward waves are then used to quantify the strength of wave reflection in the arterial tree. Two unique strengths of the proposed method are that 1) it replaces highly invasive central aortic BP and flow waveforms required in many existing methods by less invasive peripheral BP waveforms, and 2) it does not require estimation of characteristic impedance. The feasibility of the proposed method was examined in an experimental swine subject under a wide range of physiologic states and in 13 cardiac surgery patients. In the swine subject, the method was comparable to the reference method based on central aortic BP and flow. In cardiac surgery patients, the method was able to estimate forward and backward pressure waves in the absence of any central aortic waveforms: on the average, the root-mean-squared error between actual versus computed forward and backward pressure waves was less than 5 mmHg, and the error between actual versus computed reflection index was less than 0.03.

Subject-specific estimation of central aortic blood pressure via system identification: preliminary in-human experimental study.

This paper demonstrates preliminary in-human validity of a novel subject-specific approach to estimation of central aortic blood pressure (CABP) from peripheral circulatory waveforms. In this "Individualized Transfer Function" (ITF) approach, CABP is estimated in two steps. First, the circulatory dynamics of the cardiovascular system are determined via model-based system identification, in which an arterial tree model is characterized based on the circulatory waveform signals measured at the body's extremity locations. Second, CABP waveform is estimated by de-convolving peripheral circulatory waveforms from the arterial tree model. The validity of the ITF approach was demonstrated using experimental data collected from 13 cardiac surgery patients. Compared with the invasive peripheral blood pressure (BP) measurements, the ITF approach yielded significant reduction in errors associated with the estimation of CABP, including 1.9-2.6 mmHg (34-42 %) reduction in BP waveform errors (p < 0.05) as well as 5.8-9.1 mmHg (67-76 %) and 6.0-9.7 mmHg (78-85 %) reductions in systolic and pulse pressure (SP and PP) errors (p < 0.05). It also showed modest but significant improvement over the generalized transfer function approach, including 0.1 mmHg (2.6 %) reduction in BP waveform errors as well as 0.7 (20 %) and 5.0 mmHg (75 %) reductions in SP and PP errors (p < 0.05).

Individualized Estimation of the Central Aortic Blood Pressure Waveform: A Comparative Study

This paper presents a comparative study on the relative performance of alternative strategies for estimating an individualized central aortic blood pressure (BP) waveform. Based on the transmission line representation of the central aortic-radial arterial line, a fully individualized (ITF 1), two partially individualized (ITF 2 and ITF 3 ), and a fully nonindividualized (NITF) transfer functions (i.e., frequency-dependent central aortic-radial BP relationships) were constructed using experimental data collected from nine swine subjects. The central aortic BP waveforms estimated by these transfer functions were compared against their measured gold standards, with the root-mean-squared waveform error and the absolute errors associated with systolic and pulse pressures as performance measures. Overall, the advantage of the individualized over the nonindividualized approach was modest but significant. The superiority of the individualized approach to its nonindividualized counterpart was increasingly pronounced under nonnominal or extreme physiologic conditions, as the subject's pulse transit time deviated from the averaged nominal value. The results suggest that the use of a fully individualized transfer function (ITF 1) is strongly recommended for nonnominal physiologic conditions, whereas a partially (ITF 2 and ITF 3) or even fully nonindividualized transfer function (NITF) may also yield acceptable performance under nominal physiologic conditions.

Comparative Study on Tube-Load Modeling of Arterial Hemodynamics in Humans

In this paper, we assess the validity of two alternative tube-load models for describing the relationship between central aortic and peripheral arterial blood pressure (BP) waveforms in humans. In particular, a single-tube (1-TL) model and a serially connected two-tube (2-TL) model, both terminated with a Windkessel load, are considered as candidate representations of central aortic-peripheral arterial path. Using the central aortic, radial and femoral BP waveform data collected from eight human subjects undergoing coronary artery bypass graft with cardiopulmonary bypass procedure, the fidelity of the tube-load models was quantified and compared with each other. Both models could fit the central aortic-radial and central aortic-femoral BP waveform pairs effectively. Specifically, the models could estimate pulse travel time (PTT) accurately, and the model-derived frequency response was also close to the empirical transfer function estimate obtained directly from the central aortic and peripheral BP waveform data. However, 2-TL model was consistently superior to 1-TL model with statistical significance as far as the accuracy of the central aortic BP waveform was concerned. Indeed, the average waveform RMSE was 2.52 mmHg versus 3.24 mmHg for 2-TL and 1-TL models, respectively (p < 0.05); the r² value between measured and estimated central aortic BP waveforms was 0.96 and 0.93 for 2-TL and 1-TL models, respectively (p < 0.05). We concluded that the tube-load models considered in this paper are valid representations that can accurately reproduce central aortic-radial/femoral BP waveform relationships in humans, although the 2-TL model is preferred if an accurate central aortic BP waveform is highly desired.

Subject-Specific Estimation of Central Aortic Blood Pressure Using an Individualized Transfer Function: A Preliminary Feasibility Study

This paper presents a new approach to the estimation of unknown central aortic blood pressure waveform from a directly measured peripheral blood pressure waveform, in which a physics-based model is employed to solve for a subject- and state-specific individualized transfer function (ITF). The ITF provides the means to estimate the unknown central aortic blood pressure from the peripheral blood pressure. Initial proof-of-principle for the ITF is demonstrated experimentally through an in vivo protocol. In swine subjects taken through wide range of physiologic conditions, the ITF was on average able to provide central aortic blood pressure waveforms more accurately than a nonindividualized transfer function. Its usefulness was most evident when the subject's pulse transit time deviated from normative values. In these circumstances, the ITF yielded statistically significant reductions over a nonindividualized transfer function in the following three parameters: 1) 30% reduction in the root-mean-squared error between estimated versus actual central aortic blood pressure waveform (p < 10 (-4)), 2) >50% reduction in the error between estimated versus actual systolic and pulse pressures ( p < 10 (-4)), and 3) a reduction in the overall breakdown rate (i.e., the frequency of estimation errors >3 mmHg, p < 10 (-4)). In conclusion, the ITF may offer an attractive alternative to existing methods that estimates the central aortic blood pressure waveform, and may be particularly useful in nonnormative physiologic conditions.

Caution Using Brachial Systolic Pressure to Calibrate Radial Tonometric Pressure Waveforms: Lessons From Invasive Study

To the Editor: We were very interested to read the recent article by Segers et al1 that prompted the correspondence from O’Rourke and Takazawa,2 who were concerned about the reliability of brachial artery tonometry and the lack of relevant invasive data, as well as the subsequent response from Segers et al.3 We have recently conducted an invasive study that may help resolve …

Association between systemic arterial stiffness and age-related macular degeneration

A number of epidemiological studies suggest that age-related macular degeneration (AMD) and cardiovascular disease share the same risk factors. Systemic arterial stiffness is a clear indicator of cardiovascular disease. We investigated whether there is an association between directly measured systemic arterial stiffness and the presence of AMD. We used a SphygmoCor 2000 system to noninvasively measure two indicators of the systemic arterial stiffness, the arterial pulse wave velocity (PWV) and the central aortic blood pressure waveform, from which the augmentation pressure is determined. We studied 50 patients with AMD (12 men, 38 women, aged 60 to 91 years, mean 77 years) and 11 age-matched control subjects (3 men, 8 women, aged 66 to 92 years, mean 75 years). All study subjects received a complete ophthalmic examination including digital fundus photography. All of the patients with AMD were classified as stage 3 or worse in at least one eye according to the AREDS system. Pulse wave velocity was significantly higher in the patients with AMD (8.2+/-1.1 m/s, mean +/- SD) compared with controls (7.1+/-0.8 m/s, p=0.0025), indicating increased arterial stiffness. There was no significant difference in PWV in AMD patients with and without choroidal neovascularization. There was no association between PWV and the presence of hypertension in either the patients or the controls. The central aortic augmentation pressure was significantly higher in the AMD patients than in the controls (p=0.040), also indicating increased arterial stiffness. Patients with AMD have increased systemic arterial stiffness compared with age-matched controls. Treatments aimed at preventing or reversing systemic arterial stiffness may also be effective in preventing the onset or slowing the progression of AMD.