Central Pressure Waveform Research Articles

Non-invasive Estimation of Cerebrospinal Fluid Pressure Waveforms by Means of Retinal Venous Pulsatility and Central Aortic Blood Pressure

Current techniques used for cerebrospinal fluid pressure (CSFp) measurements are invasive. They require a surgical procedure for placement of a pressure catheter in the brain ventricles or in the brain tissue. The human eye provides direct visualisation of its physiological structures and due to its anatomical connection with CSF via the retrolaminar optic nerve it may provide accessible information about CSFp. A total of 25 subjects were included in this study. 15 subjects were used to characterise the relationship between intraocular pressure (IOP), spontaneous retinal venous pulsatility (SRVP), and CSFp. IOP was manipulated and SRVP amplitudes recorded dynamically using the dynamic vessel analyzer (DVA). The relationship between IOP and SRVP amplitude was established to estimate CSFp. Additionally Doppler blood flow velocity of the middle cerebral artery and arterial blood pressure (ABP) were acquired for all subjects. This was to compare and validate our findings with an alternative approach (ICM+) which uses these values to estimate CSFp. A CSFp waveform was extracted from central blood pressure (CBP) waveform by removing its cardiac component frequency. Furthermore to calibrate the CSFp to CBP waveform ratio, invasive CSFp, and ABP was measured from 10 subjects with brain tumours who had a range of normal to elevated CSFp (i.e., 0-30 mmHg). Results show good agreement between the two methods (correlation r (2) = 0.55) Mean estimated CSFp for the two techniques did not show any significant difference (p > 0.05). A significant correlation between CBP pulse (CBPp) and invasive CSFp pulse (CSFpp) was observed (i.e., CSFpp = 0.0654CBBp + 3.91, p < 0.01). Estimated CSFpp was calibrated to CBPp according to this relation. In conclusion, the study demonstrated a good correlation between two different methods of estimating CSFp non-invasively and may provide a novel method to estimate CSF waveforms non-invasively.

Pulse pressure amplification in relation to body fatness

Aortic-brachial pulse pressure amplification (PPA) is a measure of arterial elasticity and it is also an independent cardiovascular risk factor. The PPA is mainly determined by age, height, central and peripheral pressure waveforms characteristics, including measures of arterial stiffness and wave reflection. In this study, however, we demonstrate that PPA is also significantly associated with indirect indices of body fatness. As the body fatness is treatable, our findings might be used as a reference for future studies on the effects of body fat reduction on PPA and the PPA-related cardiovascular risk. AIMS Arterial pressure transfer to the periphery is accompanied by pulse pressure amplification (PPA). Pulse pressure is influence by body fat. The purpose of the present study was to evaluate any possible inter-relation between body fatness and PPA in healthy subjects. Haemodynamic and wave reflection indices were estimated by pulse wave analysis. Body fat was measured by bio-impedance. A total of 367 healthy volunteers (136 men and 231 women) was studied. Pulse pressure amplification correlated significantly with percentage of body fat (r=-0.53, P < 0.0001), age (r=-0.62, P < 0.0001), height (r= 0.43, P < 0.0001), heart rate (r= 0.28, P < 0.0001) and mean blood pressure (r=-0.29, P < 0.0001). The association of PPA with body fat was also significant in a multiple linear regression model. Age was an independent predictor of PPA and analysis of study subjects subdivided into two groups, those <50 years and those >50 years showed that body fatness correlated inversely and significantly with PPA in individuals both younger and older than 50 years (r=-0.44, P < 0.0001, r=-0.37, P < 0.0001 respectively). Augmentation pressure was also associated significantly with percentage of body fat in both subgroups (r= 0.48, P < 0.0001 and r= 0.49, P < 0.0001 respectively). This study performed on healthy subjects showed that pulse pressure amplification is related to body fatness over a wide age range. Percentage body fat is significantly associated with augmentation pressure, a component of central pulse pressure.

Cerebral haemodynamic physiology during steep Trendelenburg position and CO2 pneumoperitoneum

The steep (40°) Trendelenburg position optimizes surgical exposure during robotic prostatectomy. The goal of the current study was to elucidate the influence of this patient positioning on cerebral blood flow and zero flow pressure (ZFP), and to assess the validity of different methods of evaluating ZFP. In 21 consecutive patients who underwent robotic endoscopic radical prostatectomy under general anaesthesia, transcranial Doppler flow velocity waveforms and invasive arterial and central venous pressure (CVP) waveforms suitable for analysis were recorded throughout the whole operative procedure in 14. The ZFP was determined by regression analysis of the pressure-flow plot and by different simplified formulas. The effective cerebral perfusion pressure (eCPP), pulsatility index (PI), and resistance index (RI) were determined. While patients were in the Trendelenburg position, the ZFP increased in parallel with the CVP. The PI, RI, gradient between the ZFP and CVP, and the gradient between the CPP and the eCPP did not increase significantly (P<0.05) after 3 h of the steep Trendelenburg position. Using the formula described by Czosnyka and colleagues, the ZFP correlated closely with that calculated by linear regression throughout the course of the operation. Prolonged steep Trendelenburg positioning and CO(2) pneumoperitoneum does not compromise cerebral perfusion. ZFP and eCPP are reliable variables for assessing brain perfusion during prolonged steep Trendelenburg positioning.

Central venous pressure waveform interference

Central venous pressure waveform interference

Abstract 8395: Central Pressure Profiles as Predictors of Incident Cardiovascular Events and Heart Failure: The Multiethnic Study of Atherosclerosis

Background: Experimental and physiologic data mechanistically implicate wave reflections in the pathogenesis of left ventricular failure and cardiovascular disease, but their association with these outcomes in the general population is unclear. Methods: Aortic pressure waveforms were derived from a generalized transfer function applied to the radial pressure waveforms recorded non-invasively at baseline from 5,958 participants in the Multi-Ethnic Study of Atherosclerosis. The central pressure waveform was separated into forward and reflected waves using a physiologic flow waveform. Reflection magnitude (RM=[reflected/forward wave amplitude]x100), augmentation index ([second/first systolic peak]x100) and pulse pressure amplification ([radial/aortic pulse pressure]x100) were assessed as predictors of cardiovascular events (CVE) and congestive heart failure (CHF). Results: During median 6.46 years of follow-up, aortic augmentation index and pulse pressure amplification did not independently predict CVE. After adjustment for established risk factors, RM was independently predictive of CVE (hazard ratio [HR] per 10%-increase=1.39; 95%CI=1.10-1.75; P=0.006) and strongly predictive of CHF (HR per 10%-increase=2.81; 95%CI=1.83-4.33; P&lt;0.0001). RM was a stronger predictor of CHF risk than hypertension (HTN) and other established modifiable risk factors, judging by various measures of model performance and population-attributable risk. In fully adjusted models, compared to non-hypertensive subjects with low RM, the HR for hypertensive subjects with low RM, non-hypertensive subjects with high RM and hypertensive subjects with high RM were 1.82 (95%CI=0.85-3.86), 2.31 (95%CI=1.07-5.01) and 4.55 (95%CI=2.28-10.0), respectively (Figure). Conclusions: Arterial wave reflections represent an important novel modifiable risk factor for CHF in the general population and a potential therapeutic target for primary CHF prevention.

Closer to Noninvasive Out-of-Office Aortic Blood Pressure Assessment

See related article, pp 825–832 The noninvasive assessment of central (aortic or carotid) blood pressure (BP) is a challenge to the clinical investigation of arterial hypertension. The importance of central BP was recognized decades ago on the basis of invasive hemodynamic studies1 but has become widely acknowledged during the last 15 years.2 This is largely attributed to the work of highly respected pioneers, like Michael O'Rourke's team, who created the first commercial device (SphygmoCor, AtCor, Sydney, Australia), enabling the wide application of the noninvasive assessment of aortic BP.3 In this issue of Hypertension , Weber et al4 present the validation of a novel BP recording device that noninvasively assesses aortic BP based on the brachial cuff oscillometric method and the application of mathematical transformation. The present invasive and noninvasive validation is of importance because it is a straightforward demonstration of the strengths and disadvantages of a new generation of BP devices that opens the way to out-of-office aortic BP self-assessment. After briefly reviewing the reasons for estimating central BP, we discuss the novelty of this device, the findings, and limitations of this study.4 and some of the major issues that should arise in future clinical research and practice. ### Why Assess Central Pressure? The reasons have been extensively addressed in recent expert opinions and reviews1,5 and are only summarized here. Normally, central systolic BP (SBP) and pulse pressure (PP) are lower than peripheral SBP and PP (from 1 to 30 mm Hg). This PP disparity, defined as PP amplification,1 is an undisputable physiological phenomenon and depends on the individual's hemodynamic and pathophysiological characteristics.1,6 Notably, PP amplification exhibits substantial within-subject time variability (eg, from 5 to 20 mm Hg; Figure) that is mainly attributed to variations in heart rate, pressure wave reflections, and arterial …

Assessment of central blood pressure waveforms—let the buyer beware: different approaches result in different results

Assessment of central blood pressure waveforms—let the buyer beware: different approaches result in different results

Central Venous Catheter-Induced Cardiac Tamponade

Editori have read with great interest the review (1)written by Pittiruti et.al. followed by their multicenter study (2) regarding the use of EKG for central venous catheter (CVC) positioning.Late cardiac tamponade is a fatal complication that might arise if the CVC tip is left within the pericardial reflection by continuously eroding the atrial wall over time (3). it is there-fore that i do not understand why the authors in their study (2) aimed to position the CVCs so low. only procedures that require free blood flow (dialysis, hemofiltration, plasmapher-esis, etc.) are indications for a very low CVC position. in the review the authors claim that the EKG assisted CVC positioning technique is superior to fluoroscopy. Since EKG will position the CVC at the cava-atrial junction it will leave its tip within the pericardial reflection. Additional positioning as well as chest x-ray (CXR) is therefore required. Since CXR is needed to preclude other pathologies (such as pneumotho-rax) the use of expensive EKG catheters did not add any safety to the patients.The recommendations by Pittiruti in his review and study will expose patients to the danger of incorrect (deep) CVC position while using unnecessary expensive equipment. it is my recommendation to use the CVC lengths cited by Kim et. al. (4)and verify the position by CXR.

Arterial functions: how to interpret the complex physiology

Arterial pressure is a cyclic phenomenon characterized by a pressure wave oscillating around the mean blood pressure, from diastolic to systolic blood pressure, defining the pulse pressure. Aortic input impedance is a measure of the opposition of the circulation to an oscillatory flow input (stroke volume generated by heart work). Aortic input impedance integrates factors opposing LV ejection, such as peripheral resistance, viscoelastic properties and dimensions of the large central arteries, and the intensity and timing of the pressure wave reflections, associated with the opposition to LV ejection influenced by inertial forces. The two most frequently used methods of arterial stiffness are measurement of PWV and central (aortic or common carotid artery) pulse wave analysis, recorded directly at the carotid artery or indirectly in the ascending aorta from radial artery pressure curve. The arterial system is heterogenous and characterized by the existence of a stiffness gradient with progressive stiffness increase (PWV) from ascending aorta and large elastic proximal arteries to the peripheral muscular conduit arteries. Analysis of aortic or carotid pressure waveform and amplitude concerns the effect of reflected waves on pressure shape and amplitude, estimated in absolute terms, augmented pressure in millimetre of mercury, or, in relative terms, 'augmentation index' (Aix in percentage of pulse pressure). Finally, if the aortic PWV has the highest predictive value for prognosis, the aortic or central artery pressure waveform should be recorded and analysed in parallel with the measure of PWV to allow a deeper analysis of arterial haemodynamics.

Wave Intensity Analysis and Central Blood Pressure

In this issue of Hypertension , Manisty and colleagues1 provide, using wave intensity analysis (WIA), new insight into hemodynamic mechanisms of blood flow and energy transfer in conduit arteries which are relevant to the basic pathophysiology of cardiovascular disease. WIA provides a further computational approach to assessing central arterial function and determinants of central blood pressure (the authors provide a summary of the principles involved in WIA as an online supplement to their article). The reported results are pertinent to 3 important, obviously interrelated, but as yet very incompletely understood issues: 1. A growing, but currently unproven, perception that there may be differences between antihypertensive drug types, or even intragroup differences, in their affect on cardiovascular outcome over and above equivalent effects on clinic (brachial) blood pressure. 2. The likely but again unproven association of central blood pressure independent of peripheral (brachial) blood pressure with adverse cardiovascular outcome; 3. An improved understanding of the underlying mechanisms determining central blood pressure waveform, important in view of point 2 above and because of the popular application of techniques of pulse wave analysis (PWA). There is reasonable evidence supporting the contention that brachial, and more particularly central, blood pressure indices can usefully be considered as biomarkers of cardiovascular disease (ie, of underlying arterial dysfunction) rather than as being a primary determinant of disease in their own right. This highlights growing awareness that there is more to assessment of vascular health than measurement of brachial blood pressure and traditional clinical assessment. The notion underlies interest in local and distributed arterial mechanical properties (eg, PWV, cross-sectional distensibility) as well as in PWA. PWA commonly uses the concept of augmentation pressure (AP) expressed either absolutely or …

Arterial stiffness, hypertension, and rational use of nebivolol

Arterial stiffness plays a key role in the pathophysiology of the cardiovascular system. Some indices of arterial stiffness (pulse wave velocity, augmentation index, characteristics of central blood pressure waveform) may be presently calculated and evaluated in the clinical setting. Age and blood pressure are the two major clinical determinants of increased arterial stiffness, while molecular determinants of arterial stiffness are related to fibrotic components of the extracellular matrix, mainly elastin, collagen and fibronectin. Increased arterial stiffness has been consistently observed in conditions such as hypertension, dyslipidemia and diabetes. Arterial stiffness evaluated by means of carotid-femoral pulse wave velocity yielded prognostic significance beyond and above traditional risk factors. A more favorable effect of calcium channel blockers, diuretics and ACE inhibitors compared with beta-blockers on indices of arterial stiffness was observed in several studies. It is conceivable that newer beta-blockers with additional vasodilating properties, such as nebivolol, which has favorable effects on carbohydrate and lipid metabolism, as well as on endothelial function and on oxidative stress, may have favorable effects on arterial stiffness, compared with atenolol. In fact, in recent studies, nebivolol was demonstrated to improve artery stiffness to a greater extent than older beta-blockers. Because endothelial dysfunction and increased arterial stiffness play an important role in the early atherosclerotic processes and are associated with poor outcomes and increased mortality, independently of blood pressure, the ability of nebivolol to enhance release of endothelium-derived nitric oxide, and consequently improve endothelial function and arterial stiffness, may have significant clinical implications for the use of this agent in the treatment of hypertension and cardiovascular diseases.

Is there any Additional Prognostic Value of Central Blood Pressure Wave Forms Beyond Peripheral Blood Pressure?

For a long time the consideration of blood pressure was based exclusively on measurements of peripheral (brachial) blood pressure. However, there is now a growing interest in the investigation of central (aortic) pressure. There is increasing awareness that the central hemodynamics, reflected by central pressure wave forms and arterial stiffness, can provide new and better insight into the pathophysiology of cardiovascular disorders associated with ageing, hypertension, diabetes, as well as end-stage renal disease. Understanding the concept of arterial stiffness, elevated central blood pressure and pulse pressure has given a new view on the mechanisms of target organ damage and their prevention and treatment. Hence, the measurements of arterial stiffness and central blood pressure, and not only peripheral pressure, have been performed in a few recent interventional trials. Not surprisingly, it was found that observed disparity in cardiovascular events obtained by different antihypertensive drugs might be attributed to their diverse effect on central pressure wave forms, despite similar control of peripheral blood pressure. Putting all currently available data together it appears certainly that there is an additional prognostic value of central pressure wave forms beyond peripheral blood pressure. The aim of this article is to provide the pathophysiology and predictive role for cardiovascular events of central pressure wave forms that are beyond peripheral blood pressure. Crucially, we will review data supporting the view that improvement of central blood pressure can result in reduction of cardiovascular events. Lastly, the future perspectives in this exciting and promising field will be presented.

Predictive value of carotid augmentation index and arterial stiffness on left ventricular mass in healthy subjects

Background: Late systolic augmentation of the central pressure waveform contributes to the after load experienced by the left ventricle. The ratio of the augmented central arterial pressure to pulse pressure (augmentation index/AIx) has been proposed as a predictor of both left ventricular hypertrophy and cardiovascular risk.

Association of Arterial Stiffness With the Angiotensin-Converting Enzyme Gene Polymorphism in Healthy Individuals

Arterial stiffness is an important determinant of cardiovascular morbidity and mortality. The I/D polymorphism of angiotensin-converting enzyme (ACE) gene is associated with cardiovascular disease. However, the relationship between ACE polymorphism, arterial stiffness, and wave reflections in healthy, low-risk population has not been defined yet. The study included 282 apparently healthy, low-risk individuals (mean age 39.7 +/- 8.9 years, 178 males). Carotid-femoral pulse wave velocity (PWV) was measured as an index of aortic stiffness, while wave reflections were assessed by augmentation index (AIx) of the central pressure waveform. I/D polymorphism of the ACE gene was determined in all subjects for the prevalence of the DD, ID, and II genotype (39, 44, and 17%, respectively). C-reactive protein (CRP) levels were determined as a marker of chronic, subclinical inflammation. After adjustment for potential confounding factors, presence of D allele was associated with lower values of PWV compared to II genotype (P < 0.05), implying lower aortic stiffness for D allele carriers. There was no association between ACE genotype and wave reflections or peripheral and central systolic pressures. In apparently healthy individuals, D allele is associated with lower aortic stiffness, whereas there is no association of the ACE polymorphism with wave reflections. This finding provides new insights into the possible links between ACE gene, regulation of large artery stiffness, and has implications for cardiovascular risk.

Peripheral and central pressure waveform parameters are associated with normal tension and primary open-angle glaucoma

Peripheral and central pressure waveform parameters are associated with normal tension and primary open-angle glaucoma

Use of generalized transfer function-derived central blood pressure for the calculation of baroreflex gain

Peripheral blood pressure measurement underestimates pressure changes during baroreflex testing, resulting in an overestimation of baroreflex gain. This error might be reduced by measuring central blood pressure; the invasive measurement, however, may represent ethical and practical problems. The solution may be the derivation of central blood pressure from the peripheral pulse using a generalized transfer function. In the current study, we tested the agreement between catheter-measured and generalized transfer function derived central blood pressure measurements and corresponding baroreflex gains. ECG and blood pressure waveforms were monitored continuously during a phenylephrine-induced pressure rise in 22 subjects undergoing cardiac catheterization. Pressure was measured with a catheter positioned in the aorta and with applanation tonometry in the radial artery. Radial pressure waveforms were subject to a generalized transfer function built in the SphygmoCor device to derive central pressure waveforms. Radial tonometric signal was calibrated with catheter-measured (invasive) and sphygmomanometric (noninvasive) pressures. Baroreflex gains were calculated from the linear regressions between heart period and systolic pressure changes. When radial tonometric signal was calibrated invasively, there was no group difference between baroreflex gains calculated from SphygmoCor-derived and catheter-measured pressures (8.2 +/- 1.2 vs. 7.2 +/- 1.2 ms/mmHg, P = NS). When radial tonometric signal was calibrated noninvasively, however, baroreflex gains calculated from SphygmoCor-derived pressures overestimated those calculated from catheter-measured pressures. Using a generalized transfer function is an accurate method to derive central pressure changes for baroreflex gain calculation. The technique, however, requires invasive pressure measurements for calibration, leaving the problem of a fully noninvasive central pressure measurement unresolved.

Pressure Waves as a Noninvasive Tool for Artery Stiffness Estimation

In hypertension and aging, central elastic arteries become stiffer and hence the central pulse pressure is augmented due to the increase in the pulse wave velocity and the early return of reflected waves to the heart from the periphery. Valuable information on arterial properties, such as stiffness, can be obtained from both central (aortic) and peripheral (radial) pressure wave forms. A feasibility study for the noninvasive estimation of arterial stiffness using pressure waves detected by a pneumatic cuff wrapped around the upper arm is presented. The propagation and reflection of arterial pressure waves (generated by the heart) in the central elastic arteries are simulated using a simplified water hammer acoustic model. Furthermore, a lumped parameter model is used to describe the transmission of the pressure waves from the brachial artery to the cuff external wall. By combining the two models, we were able to simulate the pressure contours in the brachial artery and illustrate how these pressures transmit to the cuff’s external wall. The effects of aortic stiffness are investigated by simulating the model at different values of aortic elastic moduli and observing the pressure augmentation and the timing of feature points. This work was done as part of the development of a noninvasive diagnostic device by Pulsecor Ltd. The model results obtained in this work are in agreement with published experimental results and the device output; hence, the model can be used to develop the device’s stiffness estimation algorithm.

Impact of Aging on Central Pressure Wave Reflection During Exercise

PURPOSE: Age is associated with increases in arterial stiffness and pulse wave velocity, which cause profound changes in arterial pressure waves, including increases in augmented pressure (AG), augmentation index (AIx) and wasted left ventricular energy. We examined the impact of aging on the central blood pressure (BP) waveform and wave reflection responses during light and moderate upright bicycle exercise. METHODS: Sixteen older (48 ± 2 yr) and 14 younger (24 ± 1 yr) men were recruited for this study. Central blood pressure and wave reflection characteristics were measured non-invasively using applanation tonometry at rest and during cycling exercise (45-65% of age predicted maximal heart rate). RESULTS: Older men had increased central pressures and AIx (26 ± 2 vs. 12 ± 2 %) and lower pulse pressure amplification (PPA; 1.29 ± 0.03 vs. 1.50 ± 0.04) than their younger counterparts at rest (P < 0.05). Central pressures and AIx (10 ± 3 vs. −8 ± 3 %) continued to be greater, while PPA (1.61 ± 0.04 vs. 1.85 ± 0.03) was lower in the older group compared to the younger group during moderate intensity exercise (P < 0.05). However, the relative changes from baseline for central pressures, AIx (−15 ± 2 vs. −19 ± 3), and PPA (0.32 ± 0.03 vs. 0.35 ± 0.04) were similar for both groups (P > 0.05). CONCLUSIONS: The findings of the present study suggest that older men have a greater central BP and AIx and lower PPA during light and moderate levels of exercise. However, the magnitude of the central hemodynamic responses (i.e. change from baseline) during exercise do not differ between older and younger men.

Contribution of abnormal arterial function to cardiac syndrome X: a study of pressure waveform analysis and exercise haemodynamics

Increased central systolic loading may contribute to ischaemic symptoms in cardiac syndrome X (CSX). Resting and exercise-induced central pressure waveforms were recorded in 20 CSX patients and 20 controls. Patients with CSX had significantly higher wave reflection and reduced pulse pressure amplification, which may help to explain symptoms in CSX.

‘Generalizability’ of a radial-aortic transfer function for the derivation of central aortic waveform parameters

Arterial transfer functions (TFs) describe the relationship between the pressure waveform at different arterial sites. Generalized TFs are used to reconstruct central aortic waveforms from non-invasively obtained peripheral waveforms and have been promoted as potentially clinically useful. A limitation is the paucity of information on their 'generalizability' with no information existing on the number of subjects required to construct a satisfactory TF, nor is adequate prospective validation available. We therefore investigated the uniformity of radial-aortic TFs and prospectively estimated the capacity of a generalized TF to reconstruct individual central blood pressure parameters. Ninety-three subjects (64 male) were studied by simultaneous radial applanation and high-fidelity (Millar Mikro-tip catheter) direct measurement of central aortic BP during elective coronary procedures. Subjects were prospectively randomized to either a derivation or validation group. Increasing numbers of individual TFs from the derivation group were averaged to form a generalized TF. There was minimal change with greater than 20 TFs averaged. In the validation group, the error in most reconstructed parameters related to the absolute value of the directly measured parameter [systolic blood pressure (SBP) and pulse pressure, P<0.05; systolic pressure-time interval, subendocardial viability index, augmentation index, and times to the inflection point, peak and end systole, all P<0.01]. Aorto-radial delay was related to error in reconstructed central aortic SBP and pulse pressure (negatively) and time to peak systole (positively) (all P<0.001). Reconstruction of augmentation index was poor. Inclusion of more than 20 individual TFs in the construction of a generalized TF does not improve 'generalizability'. There appear to be systematic errors in derived central pressure waveforms and derived aortic augmentation index is inaccurate compared to the directly measured value.