Radial Pressure Waveform Research Articles

Validation Of A Novel Wristband Micromanometer Used For Applanation Tonometry

PURPOSE: To validate the clinical use of a newly designed wristband micromanometer. Augmentation Index (AIx), AIx normalized at 75bpm ([email protected]), and round trip travel time of the reflective waveform (Dtp) were compared to measurements produced using the traditional pencil-type micromanometer (Millar Instruments, Houston, Texas). METHODS: Resting pulse wave analysis was measured non-invasively in triplicate using radial artery applanation tonometry in 32 apparently healthy subjects (males n = 21; females n = 11). Each subject was randomized to testing first with either the novel wristband micromanometer or pencil-type micromanometer. AIx, [email protected], and Dtp were calculated from aortic pressure waveforms which were synthesized using a generalized transfer function from high fidelity radial pressure waveforms calibrated from standard brachial artery sphygmomanometry. Paired t-tests and Wilcoxon's signed rank test, for non-normally distributed variables, was performed between means and coefficients of variation; at a = 0.05. Bland-Altman analyses were performed to test for agreement between micromanometers.Table 1: Means, Coefficients of Variations, and Standard Deviations for all Variables MeasuredRESULTS: The Bland-Altman analyses show full agreement between micromanometers. The observed minor but statistically significant differences, for only 5 variables, in coefficients of variation and means will have no impact in a clinical or research interpretation model. CONCLUSIONS: Our results show that the novel wristband micromanometer is highly correlated with the traditionally accepted pencil-type micromanometer used to determine AIx, [email protected], and Dtp in males and females. These data suggest that the wristband micromanometer is a valid and reliable alternative to the pencil type micromanometer.

The Acute Effects Of Smokeless Tobacco On Central Hemodynamics

It has been shown that one time use of smokeless tobacco (ST) in habitual and recreational users increases heart rate, peripheral blood pressures, and circulating plasma levels of epinephrine. These changes suggest there may also be alteration in central hemodynamics and cardiovascular workload. PURPOSE: This study sought to examine the acute effect of a single bout of ST on central hemodynamics. METHODS: Eight apparently healthy male subjects (age = 31.5 ± 6.4 yrs), who were recreational and/or habitual ST users were given a 2.5-gram oral dose of ST after baseline measurements were recorded. ST was held in the lower lip for 30 min while measurements were taken at 10 min intervals. After removal of the ST, measurements continued at 10 min intervals for an additional 30 min. All measurements were obtained in triplicate, non-invasively using radial artery applanation tonometry. Aortic pressure waveforms were synthesized using a generalized transfer function from high fidelity radial pressure waveforms calibrated from standard brachial artery sphygmomanometry. RESULTS:TABLECONCLUSIONS: One time use of ST results in a transient significant increase in central pressures, HR, [email protected], and WLVE. Travel time of reflected pressure waves is significantly decreased following ST administration which contributes to elevated central pressures and is reflected by the significant elevations in augmentation index, ESP, and WLVE. The changes in central hemodynamics associated with one time ST use in recreational and habitual users appears to contribute to an increase in cardiac stress.

Does Wave Reflection Dominate Age-Related Change in Aortic Blood Pressure Across the Human Life Span?

Aortic systolic and pulse pressure rise with age because of aortic stiffening. Two factors are responsible: a larger incident wave because of increased aortic characteristic impedance and premature return of wave reflection from peripheral sites. This study aimed to determine the relative contribution of each factor before and after age 60 years. Aortic pressure waveforms were generated for 3682 healthy subjects using a generalized transfer function applied to radial pressure waveforms recorded by applanation tonometry. Linear regression and product of coefficient mediation analysis were performed in the cross-sectional cohort to determine the yearly contribution of the incident and reflected waves (waves measured as first systolic peak and augmented pressure, respectively) to aortic systolic and pulse pressure elevation with age. This was done separately for subjects <or=60 and >60 years of age, with both sexes initially pooled and subsequently separated. Analyses were repeated with correction for height, weight, heart rate, and mean arterial pressure. Before age 60 years, the reflected wave was a greater (P<0.05) contributor to age-related aortic systolic and pulse pressure elevations, with no significant contribution of the incident wave in this age group in sex-pooled analysis. After age 60 years, both incident and reflected waves were significant (P<0.05) and comparable contributors (P difference >0.05) to age-related aortic systolic and pulse pressure elevations. This general pattern was observed in both sexes and persisted after correction for confounders. Wave reflection is important across the life span, whereas aortic characteristic impedance contributes significantly only beyond age 60 years.

Increased Augmentation Index of the Radial Pressure Waveform in Patients with Paroxysmal Atrial Fibrillation

Objective: The augmentation index, a marker of wave reflection, has been reported to reflect vascular properties and to determine left ventricular (LV) characteristics. We investigated the relationship between the augmentation index and paroxysmal atrial fibrillation (AF). Methods: A total of 244 outpatients (122 patients with paroxysmal AF and 122 age-, and gender-matched controls without paroxysmal AF) were examined during sinus rhythm. The augmentation index was calculated from the radial arterial waveform using applanation tonometry methods. Results: After adjusting for age, gender, heart rate, and medications, the augmentation index was significantly higher in patients with paroxysmal AF than in subjects without paroxysmal AF (means ± SE: 88.9 ± 1.0 and 81.8 ± 1.0%, respectively; p < 0.001). In all subjects, an increase in the augmentation index was significantly correlated with LV hypertrophy and left atrial enlargement. Multiple logistic analysis revealed that an increase in the augmentation index was significantly related with paroxysmal AF, and the adjusted odds ratio of paroxysmal AF was approximately 1.8 for each 10% augmentation index increase (p < 0.01). Conclusion: An increase in the augmentation index was independently associated with paroxysmal AF. This result suggests that enhanced wave reflection may be related to the development of AF.

Abstract 2994: Gender-Related Differences in the Central Arterial Pressure Waveform Begin in Childhood and are Independent of Height

Introduction Women develop age-related LV hypertrophy and symptomatic heart failure to a greater extent than men. Contributing to this may be a higher pulsatile afterload in women, with a higher central arterial systolic augmentation pressure (AP, peak pressure minus pressure at systolic shoulder) and augmentation index (AIx, ratio of AP to pulse pressure). It is unclear if these differences are due to gender per se or shorter female stature. We studied 8-year old children to determine if gender-related differences in carotid pressure augmentation are present in early life and if so, whether they are independent of height (Ht). Methods 406 children (age 8.0 ± 0.1, 49% girls) had anthropometry, brachial systolic and diastolic BP (SBP, DBP), heart rate (HR) and carotid and radial pressure waveforms (by applanation tonometry, calibrated to mean BP and DBP) assessed. Carotid ultrasound evaluated arterial elasticity [Carotid Artery Compliance (CAC), Stiffness Index (SI) and Young’s Elastic Modulus (YEM)]. Results Boys and girls had a similar Ht (129 ± 6 v 128 ± 6 cm), BMI (17.6 ± 3.1 v 17.5 ± 3.0), SBP (100 ± 7 v 101 ± 5 mmHg), DBP (59 ± 6 v 60 ± 5 mmHg) and HR (80 ± 10 v 82 ± 10 bpm). The carotid AP and AIx were significantly higher in girls (−4 ± 3 v −6 ± 4 mmHg and −12 ± 8 v −16 ± 9 respectively, p &lt; 0.001), indicating greater systolic pressure augmentation. Time to onset of the reflected wave ( Tr ) and time to peak of the reflected wave were shorter in girls (154 ± 19 v 163 ± 18 msec, p &lt; 0.001 and 206 ± 23 v 212 ± 22 msec, p = 0.03 respectively), indicating earlier wave reflection. Girls had a higher velocity index (Vr) estimated from Ht ( Vr = Ht /Tr , 8.4 ± 1.0 v 8.0 ± 0.9 m/sec, p = 0.001). Ejection duration, maximum rate of pressure rise and time to systolic peak (indicating effect of ventricular ejection on the carotid waveform) were not significantly different between genders. Boys, however, had stiffer carotid arteries than girls [lower CAC (5.8 ± 1.5 v 6.2 ± 1.8 %/10 mmHg, p = 0.016), higher SI (2.7 ± 0.7 v 2.5 ± 0.7, p = 0.012) and YEM (735 ± 217 v 681 ± 237, p = 0.021)]. Conclusion Even in the first decade of life, girls demonstrate greater central arterial pressure augmentation than boys, with earlier wave reflection. This is independent of height and may contribute to cardiovascular morbidity in females, later in life.

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.

Effects of hyperoxia on aortic waveforms in normotensive subjects

Central aortic pressure and its parameters measured by pulse wave analysis are useful non-invasive methods in determining the left ventricle load. The aim of this study was to evaluate whether hyperoxia influences cardiac load assessed by parameters of central aortic pressure recorded with radial artery applanation tonometry. We analysed pulse wave in 10 young, healthy subjects (5 male and 5 female) before and after 15 min 100% oxygen breathing. Radial pressure waveforms, by use of a generalized transfer, were transformed to aortic waveforms and parameters of central pressure were calculated.

Association of augmentation index of radial pressure wave form with diurnal variation pattern of blood pressure in untreated patients with essential hypertension

The augmentation index of the radial pulse wave has been reported to be a sensitive aortic stiffness marker in relatively young but not in older individuals. We studied the relationship between augmentation index and the diurnal blood pressure profiles. Twenty-four-hour ambulatory blood pressure monitoring was performed in 90 untreated patients with uncomplicated essential hypertension. The patients were classified into four groups: dippers, extreme dippers, nondippers, and risers. Augmentation index was calculated as the percentage of the second systolic peak relative to the first systolic peak. No significant differences in the averaged whole 24-h systolic or diastolic blood pressure were observed in the whole set of patients or in subgroup patients with age 60 years or under. In the whole set of patients (58.7 +/- 12.9 years), there were significant differences in augmentation index between patients with abnormal (other than dippers) and normal diurnal blood pressure profiles (dippers). In subgroup patients with age 60 years or below (49.1 +/- 9.1 years, n = 48), the abnormal diurnal blood pressure profile group showed significantly higher augmentation index (89.6 +/- 10.3%) than dippers (80.5 +/- 11.8%). The area under the curve in the receiver operating characteristics curve for distinguishing between dippers than other dippers was 0.73 (P < 0.01). Multivariate analysis demonstrated that abnormal diurnal blood pressure profile was independently associated with increase in augmentation index. In contrast, these relationships were not significant in the over 60 years subgroup patients (69.8 +/- 5.6 years old, n = 42). The present study revealed that augmentation index was associated with dipping blood pressure patterns in untreated hypertensive patients aged 60 years or younger. Augmentation index determination would be useful for initial assessment in connection with possible abnormal diurnal blood pressure variability in patients with age 60 years or younger.

Noninvasively assessed pulsatility of ascending aortic pressure waveform is associated with the presence of coronary artery narrowing

Several hemodynamic indices, measured invasively in the ascending aorta during routine angiography, are related to the presence and severity of coronary atherosclerosis. Radial artery tonometry, when combined with a validated transfer function, offers the possibility of noninvasive assessment of central arterial pressure. We aim to evaluate the association between noninvasive indices of aortic or radial pressure waveforms and the presence of a significant coronary stenosis. Patients who underwent elective coronary angiography were studied (110 men, 91 women, mean age 53 +/- 0.9 years). Noninvasive measurement of their central hemodynamics was performed by analysis of the aortic pressure waveform derived from the radial artery. An increase in aortic fractional pulse pressure was associated with coronary artery narrowing or previous myocardial infarction. After multivariate adjustment, the odds ratio and confidence intervals (CI) of having a significant coronary aortic stenosis was 1.72 (95% CI, 1.1-2.7) and of previous myocardial infarction 1.6 (95% CI, 1.1-2.2). An increase in noninvasively assessed aortic fractional pulse pressure, but not of the peripheral index is significantly associated with the presence of coronary artery disease.

Infusion of Reconstituted HDL leads to Acute Changes in Human Atherosclerotic Plaque In Vivo

Background:High-density lipoprotein (HDL) is an inverse predictor of cardiovascular events. Recent studies have showna reduction inplaque volumeand change inplaque ultrasound characteristics after four infusions of reconstitutedHDL.Whether rHDL infusion leads to acute changes in plaque composition in humans is not known. Methods and results:Patientswith symptom limiting claudication planned for percutaneous superficial femoral artery (sfa) revascularisation were randomised to either placebo or IV r HDL infusion (80mg/kg given over 4 h). 5–7 days following the infusion patients returned and revascularisation was performed including atherectomy (Foxhollow CA) to excise plaque from the sfa. 18 patients (15 male) average age 69± 10 years (mean±S.D.) were recruited. 10 had a history of documented coronary artery disease and all patients were on aspirin and 16 on statins. 9 of the patients received r HDL and 9 placebo. In the SFA plaque there was significantly less Vascular Cell Adhesion Molecule staining (23± 9 vs. 41.8± 3, p< 0.05) evidence of eral arterial tonometry (RH-PAT) measures digital pulse volume changes during reactive hyperaemia and is an alternative assessment of endothelial function. Central pulse wave velocity (PWV) is considered the best estimate of aortic stiffness. Method: Pressure waveforms were acquired in 20 healthy males (24± 5 years) from the carotid and femoral artery and PWV calculated as the quotient of foot-to-foot pressure wave delay and distance. Salbutamol (an endothelial dependant agent) was given 25min after GTN (an endothelial independent agent) was administered. Salbutamol:GTN index is the ratio of change in augmentation index (AIx)with salbutamol relative to thatwithGTN.Peak RH-PAT ratio is the ratio of the peak digital pulse volume during reactive hyperemia divided by that at baseline. Results: Peak RH-PAT ratio was inversely associated with systolic, diastolic and mean blood pressures (all p< 0.05, r2 = 0.25, r2 = 0.26, r2 = 0.23, respectively). Radial salbutamol:GTN indexwas related to peakRH-PAT ratio (p< 0.05, r2 = 0.245) and PWV (p< 0.001, r2 = 0.52). Carotid salbutamol:GTN index was not associated with the peak RH-PAT ratio or with PWV. Conclusion: In contrast to the radial pressure waveform, changes in carotid AIx do not reflect indices of endothelial function. Thismaybe explainedby the influence of arterial stiffness during pressure propagation.

Noninvasive Pulse Waveform Analysis in Clinical Trials: Similarity of Two Methods for Calculating Aortic Systolic Pressure

Concerns persist about the validity of generalized transfer function-derived, aortic blood-pressure measurements during the administration of vasoactive agents in clinical trials. Hence, we compared this transfer-function method with another, which estimates aortic systolic pressure directly from the late systolic shoulder of the radial pressure wave, after administration of placebo, ramipril, or atenolol. We recorded radial pressure pulse waveforms, using a commercially available system, in 30 subjects with >or=1 coronary risk factor in an acute study of ramipril at 10 mg and atenolol at 100 mg. Directly recorded radial and derived aortic pressure pulse waveforms were examined individually and were ensemble-averaged, and the difference between radial and aortic pressure responses was examined. The late systolic shoulder response from radial waveforms was reduced by 15.8 mm Hg (SD, 12.2 mm Hg) more with ramipril than with atenolol. This was similar to a difference of 14.6 mm Hg (SD, 11.2 mm Hg) calculated for the aortic systolic pressure response using the transfer-function technique. Ramipril caused a greater reduction in the aortic systolic pressure response (22.2 mm Hg), whereas with atenolol, there was a modest decrease (7.6 mm Hg). The mean difference between aortic systolic pressures measured from direct radial waveforms and from derived aortic pressure between 3 and 5 h after dosing under all circumstances was 1.6 mm Hg (SD, 8.9 mm Hg). Central pressure derived from radial pressure waveforms using a generalized transfer function gave similar results for central pressure measured directly from radial waveforms. The hemodynamic benefits of angiotensin-converting enzyme inhibitor, angiotensin receptor blocker, and calcium channel blocker over beta-blocker antihypertensive therapy in recent trials were confirmed by this study.

INDICES OF VASCULAR STIFFNESS AND WAVE REFLECTION IN RELATION TO BODY MASS INDEX OR BODY FAT IN HEALTHY SUBJECTS

1. Obesity appears to influence vascular stiffness, an important cardiovascular risk factor. An accurate picture of arterial stiffness may be obtained when a combination of various techniques is used. 2. The purpose of the present study was to assess whether the body mass index (BMI) and body fat content obtained by bioimpedance were of equal value in estimating the influence of body fatness on various indices of vascular stiffness and wave reflection. 3. A total of 175 healthy subjects was studied. Anthropometric measurements and total body bio-impedance analysis were performed to assess fat mass as a proportion of total body composition. Arterial stiffness and wave reflection were assessed using digital volume pulse analysis and tonometric measurement of the wave reflection indices and central haemodynamics. 4. Significant differences in the stiffness index (SI(DVP); P < 0.0001), peripheral augmentation index (pAI(x); P < 0.0001), central augmentation index (cAI(x); P < 0.0001), peripheral pulse pressure (pPP; P = 0.026) and central pulse pressure (cPP; P < 0.0001) were found when the population examined was divided accordingly to tertile of body fat content. However, subdividing various indices of arterial stiffness according to the tertile of BMI did not reveal any significant differences between groups, except for pPP and cPP. 5. Body fat content was significantly correlated with SI(DVP), pAI(x), cAI(x), pPP and cPP. The BMI correlated weakly with SI(DVP), pPP and cPP. 6. In conclusion, the BMI is not very useful in predicting changes in arterial stiffness and wave reflection due to obesity. However, stiffness and wave reflection indices derived from digital volume pulse analysis, the characteristics of radial and aortic pressure waveforms and peripheral and aortic pulse pressure are all related to body fat content, as estimated by bioimpedance.

Radial pressure waveform dP/dt max is a poor indicator of left ventricular systolic function

The first derivative of left ventricular (LV) pressure over time (dP/dt max) is a marker of LV systolic function that can be assessed during cardiac catheterization and echocardiography. Radial artery dP/dt max has been proposed as a possible marker of LV systolic function and we sought to test this hypothesis. We compared simultaneously recorded radial dP/dt max (by high-fidelity tonometry) with LV dP/dt max (by high-fidelity catheter and echocardiography parameters analogous to LV dP/dt max). In study 1, beat-to-beat radial dP/dt max and LV dP/dt max were recorded at rest and during supine exercise in 12 males (aged 61 +/- 12 years) undergoing cardiac catheterization. In study 2, 2D-echocardiography and radial dP/dt max were recorded in 54 patients (separate to study 1; 39 men; aged 64 +/- 10 years) at baseline and peak dobutamine-induced stress. Three basal septum measures were taken as being analogous to LV dP/dt max: 1. Peak systolic strain rate; 2. Strain rate (SR-dP/dt max) during isovolumic contraction (IVCT) and; 3. Tissue velocity during IVCT. In study 1 there was a significant difference between resting LV dP/dt max (1461 +/- 383 mmHg s(-1)) and radial dP/dt max (1182 +/- 319 mmHg s(-1); P < 0.001), and a poor, but statistically significant, correlation between the variables (R(2) = 0.006; P < 0.05). Similar results were observed during exercise. In study 2 there were weak (R(2) = -0.12; P = 0.01) to non-significant associations between radial dP/dt max and all echocardiographic measures analogous to LV dP/dt max at rest or peak stress. Radial pressure waveform dP/dt max is not a reliable marker of LV systolic function.

Effects of Resistance Exercise Training on Arterial Function in Young, Healthy Men and Women

PURPOSE: There is evidence that resistance exercise (RT) can increase central arterial stiffness during high-intensity and high-volume training regimens. The purpose of this study was to determine whether RT, when performed in accordance with ACSM guidelines, has deleterious effects upon central arterial function in young, healthy men and women. METHODS: Previously untrained subjects were assigned either to a group that performed RT 3 days/week for 12 weeks (TRAIN; n=22; 19.8 ± 1.4 yrs) or to a control group that did not train (CONTR; n=12; 20.7 ± 2.9 yrs). Training consisted of 2 sets of 12 repetitions performed to volitional failure on 7 variable resistance machines. Resting aortic augmentation index normalized at 75 bpm (AIa), round trip travel time of aortic pressure waves (Dtp), and regional arterial pulse wave velocity (PWV) were measured non-invasively using applanation tonometry. Regional PWV (m/sec) between the carotid-radial (CRPWV), carotid-femoral (CFPWV), and femoral-dorsalis pedis (FDPWV) arteries were calculated by determining the delay between the appearance of the pressure waveform foot in each site with simultaneous ECG. AIa and Dtp were calculated from aortic pressure waveforms, which were synthesized using a generalized transfer function from high fidelity radial pressure waveforms calibrated from standard brachial artery sphygmomanometry in triplicate. RESULTS: AIa and Dtp were unchanged in TRAIN (from-1.6±14.1 to 1.2±10.5 %; from 157.4±28.3 to 155.5±12.8 msec) and CONTR (from-4.0±9.1 to-3.4±10.2 %; from 151.3±11.6 to 154.7±10.6 msec). CRPWV, CFPWV, and FDPWV were unchanged in TRAIN (from 8.4±1.1 to 8.0±1.0 m/s; from 6.2±0.6 to 6.3±0.8 m/s; from 9.4±1.5 to 9.6±1.4 m/s) and CONTR (from 8.2±0.7 to 8.0±0.6 m/s; from 7.0±0.7 to 6.9±0.8 m/s; from 8.3±1.1 to 8.1±1.1 m/s). TRAIN significantly (p=0.05) increased Chest Press (+37.5%) and Leg Extension (+41.9%) strength. CONTR values for Chest Press (+1.0%) and Leg Extension (+0.5%) strength did not change. CONCLUSION: RT had no adverse effects upon either amplitude and timing of aortic reflected pressure or regional arterial PWV in young, healthy men and women when training was performed consistent with ACSM guidelines.

Clinical use of indices determined non-invasively from the radial and carotid pressure waveforms

To evaluate the clinical use of radial and carotid artery applanation tonometry as an independent supplement to cuff sphygmomanometry. In 44 patients, radial and carotid tonometric pressure recordings were taken at short intervals apart by two persons who had prolonged experience with both. Comparisons were made between directly recorded radial and carotid waveforms and between aortic waves synthesized from both, using SphygmoCor. Focus was on waveform features: time intervals between wavefoot and incisura, denoting ejection duration, between wavefoot and first systolic peak or shoulder T1, and augmentation index - the rise in pressure from this point to systolic peak divided by pulse pressure. No patient had discomfort with radial tonometry, whereas many found carotid tonometry uncomfortable. Beat-to-beat variability was lower for the radial than carotid site. The device's operator "quality index" was achieved for 78% of radial waveforms but just 20% of carotid waveforms (P<0.05). Interobserver variability was lower for all indices derived from radial, cf. carotid, waveforms. For the two observers combined, there was no difference between aortic indices determined from carotid and radial sites except for T1 (radial-derived 117+ or -17 ms, cf. carotid-derived 103+ or -17 ms, P<0.05), but this did not influence the value of augmentation index (radial-derived 26+ or -13%, cf. carotid-derived 28+ or -14%, P=NS). The present study conforms with most published results, and indicates superiority of radial to carotid tonometry in clinical practice.

Nonlinear Dynamics of Blood Pressure Variability After Caffeine Consumption

The occurrence of continuous blood pressure (BP) fluctuations is an intrinsic feature of the cardiovascular system and is related to complex cardiovascular mechanisms and environmental stimulations or daily habits such as coffee drinking. The aim of this study was to investigate the effect of caffeine on indices expressing the complex and "chaotic" nonlinear characteristics of BP variability. Fourteen healthy subjects consumed 240 mg of caffeine or placebo according to a randomized, double-blind, crossover design. Continuous radial pressure waveforms were recorded by applanation tonometry at baseline and at 30, 60, 90 and 120 minutes after ingestion of caffeine or placebo. Approximate entropy (ApEn) was determined to assess BP irregularity. Detrended fluctuation analysis was also used to quantify the fractal correlation properties of the BP data by estimating the scaling (self-similarity) exponent alpha. Analysis of variance for repeated measurements was used to detect significant changes in the measured variables at 30, 60, 90 and 120 minutes after ingestion of caffeine or placebo. BP fluctuations demonstrated high regularity and predictability as indicated by the low values of ApEn (0.2 +/- 0.3), and they remained unchanged after caffeine ingestion. In contrast, the long-term scaling exponent alpha of the BP time series was significantly increased from 0.99 to 1.04 (p=0.01) after caffeine ingestion, while the placebo induced no significant change. Caffeine induced greater "randomness" in BP fluctuations, possibly by triggering cardiovascular mechanisms that could not be directly specified but should be investigated in future studies.

Effect of Acute Cold Pressor Test on Amplitude and Timing of Central Pressure Wave Reflection in Young Healthy Adults

Physiological states of chronic elevated sympathetic nervous system (SNS) activity (e.g., aging, heart failure) are associated with increased central artery stiffness. However, the role of acute SNS activation on central arterial pressure wave reflection properties and arterial stiffness are unknown. PURPOSE: To investigate the effects of acute SNS activation on aortic pressure wave reflection properties and arterial stiffness in young, healthy adults. METHODS: Ten subjects (age 25.0±3.3 yrs; 7M/3F) performed a cold pressor test (CPT) via hand immersion in ice water (4°C) for 3 min. Aortic pressure waveforms were synthesized using a generalized transfer function from non-invasive radial pressure waveforms (calibrated from brachial sphygmomonometry) obtained via applanation tonometry on the contralateral arm before (PRE), immediate-post (IP), 90 sec-post, and 180 sec-post CPT. Aortic augmentation index (AIa), a measure of amplitude and timing of arterial wave reflection, and AT, the roundtrip travel time of the reflected wave to and from the periphery, were used as indices of arterial stiffness. One-way ANOVA w/repeated measures and pairwise comparisons w/Bonferonni correction were used for analysis. RESULTS: Blood pressure (BP) and hemodynamic variables (mean±SD) are displayed n the table below (*p<0.0167 vs. PRE):TableThe IP change in mean BP was significantly correlated to IP change in AIa (r=0.80, p=0.01), but not to the IP change in AT (r=−0.41, p=0.26). Furthermore, the magnitude of increase in systolic BP (28.0±15.4% vs. 20.4±13.4%, p=0.016) and pulse BP (25.7±26.5% vs. 11.4±17.2%, p=0.02) was greater in the aorta than in the brachial artery, respectively. CONCLUSIONS: Acute elevation in SNS activity via CPT results in a significant increase in AI due in part to increased mean arterial BP. However, the larger increase in systolic and pulse BP in the aorta than in the brachial artery suggests an increased amplitude and/or early return of the central arterial reflected wave from the periphery also contributes to increased arterial stiffness during acute SNS activation.

Alterations of calf venous and arterial compliance following acclimation to heat administered at a fixed daily time in humans

We investigated the effects of heat acclimation on venous and arterial compliance in humans. Four male and four female volunteers were exposed to an ambient temperature of 40 degrees C and relative humidity of 40% for 4 h (1330-1730 hours) per day for 9-10 consecutive days. The calf venous compliance (CV) was estimated using venous occlusion plethysmography with a mercury-in-silastic strain gauge placed around the right calf at its maximum girth. The compliance of the small (CSA) and large (CLA) arteries were assessed by reflective and capacitance compliance by analyzing the radial artery blood pressure waveforms, basing on the use of a modified Windkessel model. The calf CV, CSA, CLA, systolic and diastolic blood pressures, heart rate and core temperature were determined twice a day, 0930-1100 hours (AM test) and 1500-1630 hours (PM test), in both heat-acclimated and non-heat-acclimated (control) conditions. Heat acclimation appeared to decrease blood pressures, heart rate and significantly lowered core temperature only in the PM test. In the control condition, the calf CV was not affected by the time of day and the CSA was significantly depressed in the PM test. After acclimation to heat, the calf CV significantly increased and the CSA did not decrease in the PM test. The results presented suggest that repeated heat exposure in humans, for 4 h at a fixed time daily, increases the calf CV and the CSA particularly during the period when the subjects were previously exposed to heat.

Pulse‐wave morphology and pulse‐wave velocity in healthy human volunteers: Examination conditions

Objective. Applanation tonometry for pulse‐wave analysis (PWA) and determination of pulse‐wave velocity (PWV) is a non‐invasive method for assessment of the central aortic pressure waveform and indices of arterial stiffness. The objective of this study was to examine the influence of eating and smoking on PWA and PWV measurements in order to establish standard examination conditions. Furthermore, intra‐ and interobserver reproducibility and the effects of varying the site of measurements were observed. Material and methods. Duplicate measurements of the radial pressure waveform and of the brachial and aortic PWV on the right and left side of the body were recorded in 23 healthy subjects by two trained observers. Measurements were performed in the fasting state and 3 h after a high‐calorie meal, and before and 1 h after smoking a cigarette. Results. Intake of a high‐calorie meal as well as smoking caused significant changes in both PWA and PWV parameters and an inter‐arm difference was observed. Intra‐ and interobserver reproducibility was good. Conclusions. Pulse‐wave measurements by applanation tonometry should be undertaken in the same arm during fasting and smoking abstinence.