Central Waveform Research Articles

Cardiac function at term in human pregnancy

ObjectivesWe have previously demonstrated deterioration in cardiac function at term in human pregnancy. To explore further, we investigated central arterial hemodynamics and association with maternal weight during gestation. Study designPrimiparous women (n=32) were recruited in a tertiary referral obstetric hospital and a longitudinal cohort study with analyses at median 16 and 37weeks gestation undertaken. Subgroups of normal body mass index, <25kg/m2, and overweight, ⩾25kg/m2, at 16weeks were created. Main outcome measuresWe performed 2D speckle tracking echocardiography strain analysis and tonometric measures of central arterial pressures, waveforms and pulse wave velocity. ResultsA reduction in cardiac strain (2P=0.002) from 16 to 37weeks gestation was associated with increased systemic vascular resistance (2P=0.008), reduced arterial compliance (2P=0.004) and increased central arterial pressures (2P<0.001) and augmentation index (2P=0.001). ConclusionsBy 37weeks, compared with values in earlier pregnancy, overweight women had higher systemic vascular resistance (2P<0.05). Additionally, their central diastolic pressure was higher (2P<0.05) and their ventricular strain was lower (2P<0.05) than in normal weight pregnant women. An increase in systemic vascular resistance and central arterial pressures by term may contribute to the observed deterioration in cardiac function. This appears more prominent in overweight women.

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.

Gender-Specific Association of the Plasminogen Activator Inhibitor-1 4G/5G Polymorphism With Central Arterial Blood Pressure

The functional plasminogen activator inhibitor-1 (PAI-1) 4G/5G polymorphism has previously been associated with hypertension. In recent years, central blood pressure, rather than brachial has been argued a better measure of cardiovascular damage and clinical outcome. The aim of this study was to investigate the possible influence of the 4G/5G polymorphism on central arterial blood pressure in a cohort of elderly individuals. We studied 410 individuals, 216 men and 194 women, aged 70-88. Central pressures and pulse waveforms were calculated from the radial artery pressure waveform by the use of the SphygmoCor system and a generalized transfer function. Brachial pressure was recorded using oscillometric technique (Dinamap, Critikon, Tampa, FL). PAI-1 antigen was determined in plasma. The results showed that central pressures were higher in women carrying the PAI-1 4G/4G genotype compared to female carriers of the 5G/5G genotype, (P = 0.025, P = 0.002, and P = 0.002 for central systolic-, diastolic-, and mean arterial pressure, respectively). The association remained after adjustment for potentially confounding factors related to hypertension. No association of the PAI-1 genotype with blood pressure was found in men. Multiple regression analysis revealed an association between PAI-1 genotype and plasma PAI-1 levels (P = 0.048). Our findings show a gender-specific association of the PAI-1 4G/5G polymorphism with central arterial blood pressure. The genotype effect was independent of other risk factors related to hypertension, suggesting that impaired fibrinolytic potential may play an important role in the development of central hypertension in women.

Blood pressure regulation during the aging process: the end of the ‘hypertension era’?

The elderly blood pressure paradigm reflects all of the demographic, technological and therapeutic changes over the past 20-30 years that make it now possible to propose a more integrative approach of 'hypertension'. The aim of the present review was to address what does measured blood pressure really mean and what are its determinants during the aging process. We show that standard blood pressure measurements are not adequate or even misleading for the evaluation of cardiovascular risk especially in the elderly patients and that there is a necessity of a transition to a new approach in determining the arterial risk. Direct arterial measurements including analysis of central and peripheral arterial waveforms and assessment of pulse wave velocity can be reliable and easily performed measurements as an alternative to blood pressure-Korotkoff approach. For these measurements, there are currently sufficient clinical data showing their association with cardiovascular risk. There is also the emergence of reference values and beneficial elements of regression by treatment. This new approach as well as recent knowledge on vascular hemodynamics and biology, represent the swan song for the hypertension concept as defined by blood pressure values.

Enhanced diastolic reflections on arterial pressure pulse during exercise recovery

During recovery from a maximal or submaximal aerobic exercise, augmentation of central (aortic) systolic pressure by reflected pressure waves is blunted in healthy humans. However, the extent to which reflected pressure waves modify the central pulse in diastole in these conditions remains unknown. We evaluated systolic and diastolic central reflected waves in 11 endurance-trained athletes on recovery from a maximal running test on a treadmill (treadmill-max) and a 4000 m run in field conditions. On both occasions in each subject, the radial pulse was recorded with applanation tonometry in the resting preexercise state and then 5, 15, 25, 35, and 45 min after exercise termination. From the central waveform, as reconstructed by application of a generalized transfer function, we computed a systolic (AIx) and a diastolic index (AId) of pressure augmentation by reflections. At 5 min, both indices were below preexercise. At further time-points, AIx remained low, while AId progressively increased, to overshoot above preexercise at 45 min. The same behavior was observed with both exercise types. Beyond the first few minutes of recovery following either maximal or submaximal aerobic exercise, reflected waves selectively augment the central pressure pulse in diastole, at least in endurance-trained athletes.

Arterial wave reflection and subclinical left ventricular systolic dysfunction

Increased arterial wave reflection is a predictor of cardiovascular events and has been hypothesized to be a cofactor in the pathophysiology of heart failure. Whether increased wave reflection is inversely associated with left-ventricular (LV) systolic function in individuals without heart failure is not clear. Arterial wave reflection and LV systolic function were assessed in 301 participants from the Cardiovascular Abnormalities and Brain Lesions (CABL) study using two-dimensional echocardiography and applanation tonometry of the radial artery to derive central arterial waveform by a validated transfer function. Aortic augmentation index (AIx) and wasted energy index (WEi) were used as indices of wave reflection. LV systolic function was measured by LV ejection fraction (LVEF) and tissue Doppler imaging (TDI). Mitral annulus peak systolic velocity (Sm), peak longitudinal strain and strain rate were measured. Participants with history of coronary artery disease, atrial fibrillation, LVEF less than 50% or wall motion abnormalities were excluded. Mean age of the study population was 68.3 ± 10.2 years (64.1% women, 65% hypertensive). LV systolic function by TDI was lower with increasing wave reflection, whereas LVEF was not. In multivariate analysis, TDI parameters of LV longitudinal systolic function were significantly and inversely correlated to AIx and WEi (P values from 0.05 to 0.002). In a community cohort without heart failure and with normal LVEF, an increased arterial wave reflection was associated with subclinical reduction in LV systolic function assessed by novel TDI techniques. Further studies are needed to investigate the prognostic implications of this relationship.

Renal Dysfunction Does Not Affect the Peripheral-to-Central Arterial Pressure Transfer Function

Arterial generalized transfer functions (GTFs) are increasingly used to estimate central pressure from peripheral measurements. Analysis of derived central waveforms may be valuable in the assessment of patients with chronic kidney disease. The aim of this study was to assess whether the GTF is affected by renal disease. Ninety-four subjects with varying degrees of renal function (Kidney Disease Outcomes Quality Initiative stages 1 to 5; 14 controls) had simultaneous measurements of carotid and radial waveforms made by applanation tonometry. GTFs were calculated by Fourier analysis for each subject group. Derived carotid waveforms were obtained by applying an independently generated GTF to the radial waveform. Glomerular filtration rate inversely correlated with central systolic (R = -0.42; P < 0.001), mean (R = -0.34; P < 0.01) and diastolic (R = --0.27, P < 0.01) blood pressures, as well as central augmentation index (R = -0.30; P< 0.01) and carotid-femoral pulse wave velocity (R = -0.33; P < 0.001). Derived waveforms were not significantly different from measured waveforms in terms of systolic blood pressure, augmentation index, maximum slope, or the delay between the incident and reflected waves, although the derived waveforms slightly underestimated the systolic ejection period (-4.4 ± 0.9 ms; P < 0.001). Overall root-mean-square error was 2.4 ± 0.1 mm Hg. No significant relationship existed between the degree of bias of any derived waveform measure and glomerular filtration rate or chronic kidney disease stage (P > 0.16). No significant differences between chronic kidney disease stages were observed in transfer function gain or phase (P > 0.05). We conclude that the peripheral-to-central GTF is not affected by degree of renal dysfunction and can be used with equivalence in patients with varying degrees of chronic kidney disease.

Racial differences in relation between carotid and radial augmentation index

Background Augmented central artery wave reflection is a cardiovascular disease risk factor. Augmentation index (AI) obtained from peripheral artery waveforms provides qualitatively similar information to AI from central artery waveforms. Little information is available, however, regarding the influence of racial difference in association between central and peripheral AI. Methods We studied 47 White adults (45 ± 17 yr, 20 women) and 94 age-matched Asian adults (45 ± 14 yr, 42 women). Results The White group was significantly taller than the Asian group, whereas there were no significant group differences in blood pressure and heart rate. Carotid and radial AI tended to be lower in White compared with Asian adults ( P < 0.10 for both). Such tendency disappeared when the difference in height was taken into account using ANCOVA ( P = 0.84 and P = 0.77, respectively). Radial AI was strongly and positively correlated with carotid AI in White adults ( r = 0.75, P < 0.0001) as well as in Asian adults ( r = 0.82, P < 0.0001). The slope and intercept of linear regression line between radial and carotid AI of White adults were highly comparable with those of Asian adults. Conclusion AI in the conveniently located peripheral vasculature may provide a surrogate measure of central AI irrespective of difference in race (e.g., Asian vs. White populations).

Non-invasive model-based estimation of aortic pulse pressure using suprasystolic brachial pressure waveforms

Elevated central arterial (aortic) blood pressure is related to increased risk of cardiovascular disease. Methods of non-invasively estimating this pressure would therefore be helpful in clinical practice. To achieve this goal, a physics-based model is derived to correlate the arterial pressure under a suprasystolic upper-arm cuff to the aortic pressure. The model assumptions are particularly applicable to the measurement method and result in a time–domain relation with two parameters, namely, the wave propagation transit time and the reflection coefficient at the cuff. Central pressures estimated by the model were derived from completely automatic, non-invasive measurement of brachial blood pressure and suprasystolic waveform and were compared to simultaneous invasive catheter measurements in 16 subjects. Systolic blood pressure agreement, mean (standard deviation) of difference was −1 (7) mm Hg. Diastolic blood pressure agreement was 4 (4) mm Hg. Correlation between estimated and actual central waveforms was greater than 90%. Individualization of model parameters did not significantly improve systolic and diastolic pressure agreement, but increased waveform correlation. Further research is necessary to confirm that more accurate brachial pressure measurement improves central pressure estimation.

New insights into cardiovascular risk from the exercise central waveform

Numerous studies in healthy individuals with normal office blood pressure (BP) have shown that a hypertensive response to exercise predicts the future onset of hypertension, as well as cardiovascular morbidity and mortality, independent of office BP. The mechanisms underlying the predictive value of exercise BP are incompletely understood. However, it has been proposed that the additional cardiovascular stress imposed by exercise may unmask the presence of concealed hypertension. A new non-invasive method of exercise arterial pressure waveform analysis (and central BP estimation) may provide additional clinical information, as well as insight into mechanisms, beyond the BP obtained by traditional upper arm cuff methods.

New insights into cardiovascular risk from the exercise central waveform

New insights into cardiovascular risk from the exercise central waveform

One clinic measure of light exercise central blood pressure is a stronger correlate of left ventricular mass than 24 hour ambulatory blood pressure monitoring

Background Twenty four hour ambulatory blood pressure (24ABPM) is the gold standard for assessing blood pressure (BP) control. However, central BP during daily activity may be a stronger determinant of cardiovascular risk. This study aimed to compare 24ABPM with light exercise central BP (mimicking daily activity) for predicting left ventricular (LV) mass. Methods Study population comprised 54 patients (aged 58±7 years; 20 men) including those with treated hypertension (n=16), untreated masked hypertension (n=23) and normotensive controls (n=15). Subjects underwent 2D echocardiography for determination of LV mass (indexed; g/m2.7), resting brachial BP, 24ABPM and estimated central BP by radial tonometry during graded cycle ergometry. Central systolic BP (SBP) was estimated from the radial second systolic peak (P2) as well as the derived central waveform. Results The range of LV mass index and 24ABPM SBP were 17.8-55.1 g/m2.7 and 107-153 mmHg respectively. As expected, 24ABPM SBP was significantly associated with LV mass index (r=0.30, p=0.02), but not with clinic resting brachial (r=0.21; p=0.14) or central SBP (r=0.20; p=0.14). However, the strongest correlates of LV mass index were light exercise (50% heart rate reserve) radial P2 (r=0.54, p<0.001) and central SBP (r=0.47; p<0.001). On multiple regression analysis, radial P2, but not 24ABPM SBP, was independently associated (β=0.45; p<0.01) with LV mass index after accounting for other confounding variables. Conclusion A one-off clinic estimate of light activity central SBP outweighs 24ABPM for predicting LV mass. This rapid, noninvasive technique may provide a superior measure of BP control compared with the current gold standard.

Pulse Wave Analysis Is a Reproducible Technique for Measuring Central Blood Pressure During Hemodynamic Perturbations Induced by Exercise

Central blood pressure (BP) and markers of wave reflection (augmentation index; AIx) measured by radial tonometry have prognostic value independent from brachial BP. The measurement of the central waveform is increasingly used during altered hemodynamics, including exercise, but reliability of the test has not been reported under changed loading conditions. This study aimed to test the technique's reproducibility during major hemodynamic perturbations induced by exercise. Radial waveforms were recorded (SphygmoCor) in 28 healthy subjects (aged 53 +/- 11 years) at rest, during submaximal exercise (cycling at 50, 60, and 70% of maximal age-predicted heart rate (HR)) and immediately after maximal treadmill exercise on two occasions separated by 9 +/- 5 days. Data were compared between testing days. Waveforms were calibrated with brachial BP measured using a mercury sphygmomanometer. Pulse pressure amplification (PPAmp) was defined as the ratio of brachial to central pulse pressure. There was very good reproducibility between visits at all exercise intensities for all waveform measures, including AIx, central pulse pressure, and PPAmp (intraclass correlations at 50% exercise were 0.93, 0.89, and 0.89, respectively; P < 0.001). The mean difference between tests at this intensity was 0 +/- 4% for AIx, 4 +/- 6 mm Hg for central pulse pressure, and -0.02 +/- 0.09 for PPAmp. There were no significant differences between visits for HR, PPAmp, or AIx at rest or with exercise (P > 0.05 for all). Radial tonometry is a reproducible technique for measurement of central waveform indices during perturbations induced by exercise. It should, therefore, be suitable for use in intervention studies in which hemodynamics are altered.

Arterial transfer functions and the reconstruction of central aortic waveforms: myths, controversies and misconceptions

Continuing reports in the literature regarding the potential of central pulse wave analysis in clinical practice and a recent consensus statement demonstrate the increasing interest in the clinical application of arterial transfer functions. A number of misconceptions, however, persist regarding their use. In spite of ongoing controversy, there are considerable published data that would permit users to assess the validity and accuracy of the technique. We provide a comprehensive review of available data, all of which appear to be clear and consistent. The technique does not permit accurate reconstruction of central waveforms from entirely non-invasively acquired data. We should move on from the misconception that what is being studied is central aortic data when transfer functions are applied non-invasively, and accept that it is radial waveform data that have been passed through a single mathematical transformation. We have a readily applicable, non-invasive and reproducible technique for acquiring radial waveform data, with or without the application of a generalized arterial transfer function. We must explore the potential of this technique in an analytical manner, and without untenable preconceptions, if we are to learn the secrets that it may yet reveal.

Arterial pulse wave velocity but not augmentation index is associated with coronary artery disease extent and severity: implications for arterial transfer function applicability

The aim of this study was to test the hypothesis that coronary artery disease extent and severity are associated with central aortic pressure waveform characteristics. Although it is thought that central aortic pressure waveform characteristics, particularly augmentation index, may influence cardiovascular disease progression and predict cardiovascular risk, little is known of the relationship between central waveform characteristics and the severity and extent of coronary artery disease. Central aortic waveforms (2F Millar pressure transducer-tipped catheters) were acquired at the time of coronary angiography for suspected native coronary artery disease in 40 patients (24 male). The severity and extent of disease were assessed independently by two observers using two previously described scoring systems (modified Gensini's stenosis and Sullivan's extent scores). Relationships between disease scores, aortic waveform characteristics, aorto-radial pulse wave velocity and subject demographic features were assessed by regression techniques. Both extent and severity scores were associated with increasing age and male sex (P < 0.001), but no other risk factors. Both scores were independently associated with aorto-radial pulse wave velocity (P < 0.001), which entered a multiple regression model prior to age and sex. This association was not dependent upon blood pressure. Neither score was associated with central aortic augmentation index, by either simple or multiple linear regression techniques including heart rate, subject demographic features and cardiovascular risk factors. Aorto-radial pulse wave velocity, but not central aortic augmentation index, is associated with both the extent and severity of coronary artery disease. This has potentially important implications for applicability of a generalized arterial transfer function.

DRUG EFFECTS ON THE MECHANICAL PROPERTIES OF LARGE ARTERIES IN HUMANS

1. Arteries become stiffer with increasing age and various disease states. A complete description of arterial mechanical properties in vivo is not possible, although a number of methods have been used. 2. Detailed discussion in the present review is limited to pulse wave velocity and estimates of central waveform morphology derived by the application of a generalized arterial transfer function. 3. Many drugs affect these parameters, either increasing or decreasing apparent stiffness. However, the extent to which changes reflect changes in blood pressure rather than more fundamental vessel wall properties remains unclear. Similarly, it is as yet unknown whether determining the need for, or assessing the effectiveness of, drug treatment by the assessment of arterial mechanical properties will offer any advantage and the usefulness of these techniques as routine clinical tools remains to be established.

Noninvasive (Input) Impedance, Pulse Wave Velocity, and Wave Reflection in Healthy Middle-Aged Men and Women

The relation between arterial function indices, such as pulse wave velocity and augmentation index with parameters derived from input impedance analysis, is still incompletely understood. Carotid pressure, central flow waveforms, and pulse wave velocity were noninvasively acquired in 2026 apparently healthy, middle-aged subjects (1052 women and 974 men) 35 to 55 years old at inclusion. Input and characteristic impedance, reflection coefficient, the ratio of backward-to-forward pressure amplitude (reflection magnitude), and augmentation index were derived. Pulse wave velocity increased by 15% (from 6.1 to 7.0 m/s) both in men and women. In qualitative terms, input impedance evolved from a pattern indicative of wave transmission and reflection to a pattern more compatible with a windkessel-like system. In women, a decrease in total arterial compliance led to an increased input impedance in the low frequency range, whereas few changes were observed in men. Characteristic impedance did not change with age in women and even decreased in men (P<0.001) and could not be identified as the primary determinant of central pulse pressure. Augmentation index increased with age, as was expected, and was systematically higher in women (P<0.001). Reflection coefficient and reflection magnitude increased with age (P<0.001) without gender differences. We conclude that, in healthy middle-aged subjects, the age-related increase in arterial stiffness (pulse wave velocity) is not fully paralleled by an increase in arterial impedance, suggesting a role for age-dependent modulation of aortic cross-sectional area. Wave reflection increases with age and is not higher in women than in men.

Letter by Dart et al Regarding Article, “Differential Impact of Blood Pressure-Lowering Drugs on Central Aortic Pressure and Clinical Outcomes: Principal Results of the Conduit Artery Function Evaluation (CAFE) Study”

To the Editor: We read with interest the recent article from the Conduit Artery Function Evaluation (CAFE) investigators1 on estimated central aortic blood pressure. The use of central arterial waveforms and estimates of central pressures in routine clinical practice would be justified if such measures materially add to the prognostic information provided by “routine” blood pressure measures, most usually obtained from brachial artery sphygmomanometry. The results from CAFE confirm our own recent findings from a substudy of The Australian National Blood Pressure Study 2 (ANBP2) 2 showing that this is not the …

Reverse Pulse Pressure Amplification: Its Role in Predicting Coronary Artery Disease and Abnormal LV Remodeling

Introduction: Normally, the arterial pressure wave reflection affects the peak systolic pressure of the peripheral but not central waveform, leading to pulse pressure (PP) amplification in the periphery. In cases of decreased aortic compliance, it is possible for the reflected wave to affect the peak systolic pressure of the central waveform more so than in the periphery and augment central aortic PP more than peripheral PP. Hypothesis: We hypothesized, that hypertensive patients who demonstrate this reverse pattern in PP amplification are at a higher risk for the presence of abnormal LV remodeling and coronary disease.

How to assess arterial compliance in humans

How to assess arterial compliance in humans