Carotid Artery Pressure Waveforms Research Articles

Sex-specific associations of reservoir-excess pressure parameters with age and subclinical vascular remodeling.

Central artery reservoir pressure and excess pressure (XSP) are associated with cardiovascular disease (CVD) events and mortality. However, sex differences in the trajectory of central reservoir pressure and XSP with advancing age and their relations with vascular markers of subclinical CVD risk are incompletely understood. Therefore, we tested the hypothesis that central reservoir pressure and XSP would be positively associated with advancing age and vascular markers of subclinical CVD risk in men and women. Healthy adults ( n = 398; aged 18-80 years, 60% female individuals) had central (carotid) artery pressure waveforms acquired by applanation tonometry. Reservoir pressure and XSP peaks and integrals were derived retrospectively from carotid pressure waveforms using custom written software. Carotid artery intimal-medial thickness (IMT) was measured by ultrasonography, and aortic stiffness was determined from carotid-femoral pulse wave velocity (cfPWV). Reservoir pressure peak, reservoir pressure integral and XSP integral were higher with age in both men and women ( P < 0.05), whereas XSP peak was lower with age in men ( P < 0.05). In women, both reservoir pressure peak ( β = 0.231, P < 0.01) and reservoir pressure integral ( β = 0.254, P < 0.01) were associated with carotid artery IMT, and reservoir pressure peak was associated with cfPWV ( β = 0.120, P = 0.02) after adjusting for CVD risk factors. Central artery reservoir pressure and XSP were higher with advancing age in men and women, and reservoir pressure peak was associated with both carotid artery wall thickness and aortic stiffness in women but not men. Central reservoir pressure peak may provide some insight into sex differences in vascular remodeling and subclinical CVD risk with advancing age in healthy adults.

Non-Invasive Evaluation of a Carotid Arterial Pressure Waveform Using Motion-Tolerant Ultrasound Measurements During the Valsalva Maneuver.

This work details the non-invasive evaluation of a carotid arterial blood pressure (ABP) waveform during the Valsalva maneuver. Unfocused and wide acoustic beams are insonated on the carotid artery to achieve motion-tolerant measurements with a simple two-element ultrasound scanner. Arterial flow and distension waveforms are reliably estimated from spectral Doppler and M-mode ultrasound images whose qualities are consistently maintained in different phases of the maneuver despite possible displacements of the artery. A local pulse wave velocity is estimated using a flow-area method, and it is then combined with the distension waveform to produce the ABP waveform. Human subject validation on seven healthy subjects shows that the bias in pulse pressure estimates across subjects is 0.47 ± 13.1mmHg. The average root mean square deviations of the ultrasonically measured waveform across subjects is 10.1 ± 2.43mmHg, excluding the strain phase of the Valsalva maneuver, and 17.7 ± 6.30mmHg in all phases. The mean correlation coefficient between the ultrasonically measured and reference waveform is calculated to be 0.92 ± 0.04 across subjects. Detailed morphological features and their changes across different phases are observed as reported. This uninterrupted central ABP waveform monitoring under hemodynamics changes supports the idea of a novel stress test to evaluate the health and dynamics of the cardiovascular system at a spot check in clinical settings.

Dynamic Carotid Pressure‐Area Relation across the Adult Lifespan

Carotid arterial stiffness is an established risk factor for cerebrovascular disease; however, its structural property in response to pressure pulsatility remains unclear. Therefore, we investigated the dynamic association between carotid artery pressure (CAP) and area (CAA) in healthy individuals across the adult lifespan.Methods108 participants (age range=19–85 years, 43% women) were tested. The CAA and CAP waveform were measured simultaneously from the bilateral common carotid arteries using applanation tonometry and ultrasonography respectively. To account for individual vessel size differences, CAA was normalized to the mean value and expressed in percentage. The CAP and CAA waveform were fast Fourier transformed to calculate power spectral densities (PSD), then transfer function analysis was used to estimate CAP‐CAA gain and coherence function.ResultsOlder adults showed higher systolic and pulse pressure than younger adults. Systemic arterial stiffness, as assessed by brachial‐ankle pulse wave velocity, was also elevated in older adults. Spectral analysis revealed that PSD of CAP increases whereas that of CAD decreases with advancing age, and most of the age‐related differences are observed below ~4 Hz (Figure A). Furthermore, transfer function analysis exhibited the progressive reductions of CAP‐CAD gain in middle‐aged (0.264±0.087%/mmHg) and older adults (0.232±0.092%/mmHg) when compared with younger adults (0.414±0.166%/mmHg), while its coherence function remained at similar levels (Figure B).ConclusionsThe dynamic CAP‐CAA gain is significantly reduced in middle‐aged and older adults compared to young adults. These findings suggest that the structural property of the carotid artery is altered during middle age which may increase the risk of cerebrovascular disease incidence.Support or Funding InformationThis work was supported by JSPS KAKENHI 16KK0011 and 17H02186.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Natural Resonance Frequency of the Brain Depends on Only Intracranial Pressure: Clinical Research

The need to understand and control intracranial pressure (ICP) is required for treatments in various clinical situations. The ICP value can only be measured by direct intracranial catheter or sensor placement, and a non-invasive ICP prediction method has not yet been established. We focused on the natural resonance frequency (NRF) of the brain to predict the ICP value. The ICP value, pulse waveform of intracranial pressure (PWICP) and cervical carotid pressure waveform (CCPW) were simultaneously collected from patients who had undergone ventricular drainage or ICP sensor placement for medical treatment in our institute. A total of 43 data were obtained from 27 patients, age ranged 14-48 (mean: 54) years, body height 137-187 (mean 163) cm and body weight 32-103 (mean 61) kg. The total measured time was 29,653 seconds and the measured mean ICP value in each data ranged from 3.82 to 69.39 (mean 25.9) hPa. Consecutive data was cut into 10.24 seconds, which was called a column. To decrease respiratory modulation, the largest positive peak of cardiac pulsation of CCPW was picked up in each column, as well as one ICP pulse waveform. The picked-up CCPW and PWICP were averaged by the weighted average method. The transfer characteristics from CCPW to PWICP were calculated by the transfer function method. The first initial negative peak of transfer characteristics was judged as the NRF of the brain. The relationship between the ICP value and the NRF of the brain was presented on the quadratic functions graph (ICP = 0.0329(NRF)2 + 0.0842NRF). These parameters were strongly correlated to each other (R2= 0.9952 coefficient of determination). The individual NRF, which was calculated by the transfer function method, only depends on the measured ICP value and their relationship can be presented in the simple quadratic functions. Funding: This research was funded by Japan Science and Technology Agency (JST) A-STEP feasibility study in 2012, and by Japan's New Energy and Industrial Technology Development Organization (NEDO) in 2013, and by Grants-in-Aid for scientific research in Ministry of Education, Culture, Sports, Science and Technology-Japan from 2015 to 2017 and 2018 to 2020. Receiver: Kenji Furihata. Declaration of Interest: Although the authors (T.G., K.F. and K.H.) have some patents of non-invasive intracranial pressure monitoring apparatus, the claim of the patents belong to affiliated university not to individuals. All of authors had already opened their COI disclosure in Japanese Neurosurgical Society. The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described. Our proposing theory is a quite new concept. We strongly believe that there is nothing to competing interest declaration. Ethical Approval: The simultaneous measurement of intracranial pressure and cervical carotid artery pressure waveform was approved by Ethical Committee of Shinshu University School of Medicine. “Development of non-invasive intracranial pressure monitoring” approved number 2343.

Wave reflections and global arterial compliance during normal human pregnancy

Profound changes occur in the maternal circulation during pregnancy. Routine measures of arterial function – central systolic pressure (CSP) and augmentation index (AIx) – decline during normal human pregnancy. The objectives of this study were twofold: (1) explore wave reflection indices besides CSP and AIx that are not routinely reported, if at all, during normal human pregnancy; and (2) compare wave reflection indices and global arterial compliance (gAC) obtained from carotid artery pressure waveforms (CAPW) as a surrogate for aortic pressure waveforms (AOPW) versus AOPW synthesized from radial artery pressure waveforms (RAPW) using a generalized transfer function. To our knowledge, a comparison of these two methods has not been previously evaluated in the context of pregnancy. Ten healthy women with normal singleton pregnancies were studied using applanation tonometry (SphygmoCor) at pre‐conception, and then during 10–12 and 33–35 gestational weeks. CSP and AIx declined, and gAC increased during pregnancy as previously reported. As a consequence of the rise in gAC, the return of reflected waves of lesser magnitude from peripheral reflection sites to the aorta was delayed that, in turn, reduced systolic duration of reflected waves, augmentation index, central systolic pressure, LV wasted energy due to reflected waves, and increased brachial‐central pulse pressure. For several wave reflection indices, those derived from CAPW as a surrogate for AOPW versus RAPW using a generalized transfer function registered greater gestational increases of arterial compliance. This discordance may reflect imprecision of the generalized transfer function for some waveform parameters, though potential divergence of carotid artery and aortic pressure waveforms during pregnancy cannot be excluded.

Assessing the blood pressure waveform of the carotid artery using an ultrasound image processing method.

PurposeThe aim of this study was to introduce and implement a noninvasive method to derive the carotid artery pressure waveform directly by processing diagnostic sonograms of the carotid artery.MethodsUltrasound image sequences of 20 healthy male subjects (age, 36±9 years) were recorded during three cardiac cycles. The internal diameter and blood velocity waveforms were extracted from consecutive sonograms over the cardiac cycles by using custom analysis programs written in MATLAB. Finally, the application of a mathematical equation resulted in time changes of the arterial pressure. The resulting pressures were calibrated using the mean and the diastolic pressure of the radial artery.ResultsA good correlation was found between the mean carotid blood pressure obtained from the ultrasound image processing and the mean radial blood pressure obtained using a standard digital sphygmomanometer (R=0.91). The mean absolute difference between the carotid calibrated pulse pressures and those measured clinically was -1.333±6.548 mm Hg.ConclusionThe results of this study suggest that consecutive sonograms of the carotid artery can be used for estimating a blood pressure waveform. We believe that our results promote a noninvasive technique for clinical applications that overcomes the reproducibility problems of common carotid artery tonometry with technical and anatomical causes.

Carotid Artery Applanation Tonometry Does Not Cause Significant Baroreceptor Activation.

Carotid artery applanation tonometry is widely used in estimating local carotid artery pressure waveforms and carotid-femoral pulse wave velocity. However, the substantial pressure applied locally to the carotid artery with applanation tonometry might well evoke a baroreceptor response, resulting in bradycardia and hypotension. Therefore, when carotid and femoral tonometry are performed sequentially, baroreceptor activation could lead to different hemodynamic conditions between carotid and femoral acquisitions. Combining those acquisitions into one pulse wave velocity measure would be erroneous. In this study, we assessed whether carotid applanation tonometry has an influence on heart rate and blood pressure. In 26 hypertensive subjects, heart rate and blood pressure were assessed by continuous finger pulse waveform recording during carotid as well as femoral applanation tonometry. Both carotid and femoral acquisitions were measured in alternation and in triplicate. Median averaging over the 3 carotid and femoral measurements, respectively, was used to obtain a subject's median heart rate and blood pressure during carotid as well as femoral tonometry. Difference in heart rate during carotid and femoral tonometry was -0.7±2.2 bpm. Differences in systolic, pulse, and diastolic blood pressure were -0.7±6.8, -0.1±3.8, and -0.3±3.5mm Hg, respectively. All differences were statistically nonsignificant. Confidence intervals were used to calculate the maximum absolute difference at 95% certainty, which was 1.6 bpm for heart rate and ≤3.5mm Hg for all blood pressures. We conclude that in our study, carotid artery applanation tonometry as performed by an experienced researcher did not cause clinically significant baroreceptor activation.

Piezoelectric sensor to non-invasively detect age associated changes in human carotid pulse

The arterial pressure waveform reflects the physics of blood flow in the arterial tree. There are definite changes that occur in the vasculature with age and cause changes in the shape of arterial waveforms. These changes are mainly attributed to increase in the pulse wave velocity caused by the arterial stiffness that causes the reflected wave to return early. Arterial waveforms can be used to non-invasively detect the condition of the cardiac system. There are various methods that have been used to non-invasively detect the arterial pressure waveform like the applanation tonometry, ausculcatory method, palpatory method etc. The developed work presents a simple and cost-effective method wherein carotid artery pressure waveform of subjects of different age groups is recorded using piezoelectric sensor and then analysed using MATLAB to find the systolic, diastolic and inflection points. These points are used to calculate augmentation index and find the changes that occur in the augmentation index with age.

Gaussian fitting for carotid and radial artery pressure waveforms: comparison between normal subjects and heart failure patients

It has been reported that Gaussian functions could accurately and reliably model both carotid and radial artery pressure waveforms (CAPW and RAPW). However, the physiological relevance of the characteristic features from the modeled Gaussian functions has been little investigated. This study thus aimed to determine characteristic features from the Gaussian functions and to make comparisons of them between normal subjects and heart failure patients. Fifty-six normal subjects and 51 patients with heart failure were studied with the CAPW and RAPW signals recorded simultaneously. The two signals were normalized first and then modeled by three positive Gaussian functions, with their peak amplitude, peak time, and half-width determined. Comparisons of these features were finally made between the two groups. Results indicated that the peak amplitude of the first Gaussian curve was significantly decreased in heart failure patients compared with normal subjects (P<0.001). Significantly increased peak amplitude of the second Gaussian curves (P<0.001) and significantly shortened peak times of the second and third Gaussian curves (both P<0.001) were also presented in heart failure patients. These results were true for both CAPW and RAPW signals, indicating the clinical significance of the Gaussian modeling, which should provide essential tools for further understanding the underlying physiological mechanisms of the artery pressure waveform.

Determination of ventricular isovolemic contraction solely by means of pulse contour analysis

It has been shown that the heart influences the arterial pulse contour before the aortic valve opens and aortic systole starts. In earlier work we suggested that the start of the isovolemic contraction period could be identified in the aortic and carotid arterial pressure waveform as the start of a temporary pre-systolic pressure increase (ADICS, aortic determined isovolemic contraction start), and presented the coronary retrograde flow as the most likely origin. In our current work we have shown that in 11 pigs this ADICS occurs significantly later than left ventricular systolic foot (LV systolic foot: 31.9±22.9ms, ADICS: 47.2±26.1, both relative to R-top ECG, difference inter-animal mean ± SD: 15.3 ± 6.3ms, p<0.001). Minimum pre-systolic coronary flow occurred 90.1±23.1ms after the R-top of the ECG, indicating that this flow is not the cause of the pre-systolic pressure increase, as aortic valve opening occurred shortly after this minimum flow (96.2±22.7 ms after the R-top of the ECG). Indeed, despite briefly occluding LAD, LCX and RCA coronary arteries, the pre-systolic pressure increase remained present in the aortic pressure waveform. For 8 pigs, an early peak in LV dP/dt coincided with the ADICS. Combining this observation with the LV pressure at which ADICS occurs (29.3±7.9mmHg), we propose that the abrupt closure of the mitral and tricuspid valve causes the pre-systolic aortic pressure increase.

Central arterial pulse wave augmentation is greater in girls than boys, independent of height

Central arterial pulse wave augmentation, quantified by the augmentation index (AIx), is a key marker of arterial health, an important contributor to cardiac afterload and is significantly greater in older women than men. We measured carotid AIx in 8-year-old children to examine the influences of sex, height and arterial stiffness on central arterial pulse wave augmentation Four hundred and five children (age 8.0 +/- 0.1 years, 49% girls) had anthropometry, brachial systolic and diastolic blood pressure, heart rate and carotid artery pressure waveforms (by applanation tonometry), diastolic diameter and distensibility assessed. Carotid AIx was significantly higher in girls than boys (-11.7 +/- 8.1 versus -16.5 +/- 9.3%, respectively, P < 0.001). Boys and girls had similar height (129 +/- 6 versus 128 +/- 6 cm), systolic blood pressure (100 +/- 7 versus 101 +/- 7 mmHg), diastolic blood pressure (59 +/- 6 versus 60 +/- 5 mmHg) and heart rate (80 +/- 10 versus 82 +/- 10 bpm). Carotid diastolic diameter was smaller in girls than boys (0.45 +/- 0.03 versus 0.47 +/- 0.04 cm, P < 0.001). The sex difference in AIx remained significant after adjustment for height, heart rate, blood pressure, diastolic diameter and birth weight. The time to the onset of the reflected wave was shorter in girls (155 +/- 19 versus 163 +/- 18 ms, P < 0.001). Girls had greater carotid artery distensibility (6.2 +/- 1.8 versus 5.8 +/- 1.5% per 10 mmHg, P = 0.016), suggesting lower regional carotid artery stiffness. Greater pulse wave augmentation in prepubertal girls results from earlier wave reflection and is independent of height, carotid artery diameter and stiffness. When combined with age-related changes in arterial compliance, this may contribute to adverse cardiovascular outcomes in older women.

Noninvasive assessment of central and peripheral arterial pressure (waveforms): implications of calibration methods

Noninvasive estimation of central blood pressure (BP) from radial artery pressure waveforms is increasingly applied. We investigated the impact of radial artery waveform calibration on central BP assessment and calculated pressure amplification, with focus on the one-third rule used to estimate mean arterial BP (MAP). Pressure waveforms were noninvasively measured at the radial and carotid arteries in 1873 individuals (age 45.8+/-6.1 years). Radial and carotid artery waveforms were calibrated using brachial artery DBP and SBP, MAP estimated with the one-third rule and MAP estimated as brachial DBP along with 40% of brachial artery pulse pressure. Central SBP obtained via a transfer function was 123.5 +/- 15.7, 117.8 +/- 14.2 and 126.0 +/- 15.4 mmHg (mean +/- SD) following above-mentioned three calibration schemes, respectively. Using the same calibration schemes, carotid artery SBP was 131.4 +/- 15.2, 118.4 +/- 14.4 and 126.8 +/- 15.7 mmHg, respectively. Central-to-brachial amplification was 13.0 +/- 3.6 mmHg using second method as compared with 4.6 +/- 3.8 mmHg with third method. Brachial-to-radial amplification was actually negative (-6.3 +/- 4.5 mmHg) using second method, whereas 3.4 +/- 5.5 mmHg was found with third method. Both carotid artery SBP and central SBP obtained via a transfer function are highly sensitive to the calibration of the respective carotid artery and radial artery pressure waveforms. Our data suggest that the one-third rule to calculate MAP from brachial cuff BP should be avoided, especially when used to calibrate radial artery pressure waveforms for subsequent application of a pressure transfer function. Until more precise estimation methods become available, it is advisable to use 40% of brachial pulse pressure instead of 33% to assess MAP.

Blood pressure waveform analysis by means of wavelet transform

The assessment of cardiovascular function by means of arterial pulse wave analysis (PWA) is well established in clinical practice. PWA is applied to study risk stratification in hypertension, with emphasis on the measurement of the augmentation index as a measure of aortic pressure wave reflections. Despite the fact that the prognostic power of PWA, in its current form, still remains to be demonstrated in the general population, there is general agreement that analysis and interpretation of the waveform might provide a deeper insight in cardiovascular pathophysiology. We propose here the use of wavelet analysis (WA) as a tool to quantify arterial pressure waveform features, with a twofold aim. First, we discuss a specific use of wavelet transform in the study of pressure waveform morphology, and its potential role in ascertaining the dynamics of temporal properties of arterial pressure waveforms. Second, we apply WA to evaluate a database of carotid artery pressure waveforms of healthy middle-aged women and men. Wavelet analysis has the potential to extract specific features (wavelet details), related to wave reflection and aortic valve closure, from a measured waveform. Analysis showed that the fifth detail, one of the waveform features extracted applying the wavelet decomposition, appeared to be the most appropriate for the analysis of carotid artery pressure waveforms. What remains to be assessed is how the information embedded in this detail can be further processed and transformed into quantitative data, and how it can be rendered useful for automated waveform classification and arterial function parameters with potential clinical applications.

Abstract 3431: Pulse Pressure Is Inversely Related to Aortic Root Diameter: Implications for the Pathogenesis of Systolic Hypertension

Background: The age-associated increase in central arterial stiffness manifests as a rise in pulse pressure, which leads to a marked increase in the prevalence of systolic hypertension among older individuals. Aortic root diameter (AoD) also increases with advancing age. According to the prevailing views, hypertension contributes to a further increase in AoD. Conversely, it has been suggested that the age-associated increase in AoD may partially compensate for the increased arterial stiffness. We tested the hypothesis that AoD is inversely associated with pulse pressure. Methods: The study population comprised 1256 individuals, aged 30 –79 years (48% women, 48% hypertensive), none of whom were on antihypertensive medications. Brachial pulse pressure (bPP) was calculated as the difference between sphygmomanometric systolic and diastolic blood pressures. Central pulse pressure (cPP) was derived from calibrated carotid artery pressure waveforms. AoD was measured by echocardiography at the level of the Sinuses of Valsalva. The relationships of AoD with bPP and cPP were evaluated with multiple regression analyses. Results: bPP was 54 ± 18 mmHg in women and 50 ± 14 mmHg in men, and AoD was 28.9 ± 3.5 mm in women and 31.9 ± 3.5 mm in men. After adjusting for age, age 2 , height, weight, and mean arterial pressure, bPP was inversely associated with AoD in both sexes. This inverse association persisted even after adjusting for aortic pulse wave velocity, carotid intima-media thickness, reflected waves, and left ventricular end-diastolic diameter and wall thickness. In the fully adjusted models predicting bPP, the regression coefficients for AoD were −0.48 in men (p = 0.0003, model R 2 =0.51) and −0.40 in women (p = 0.01, model R 2 = 0.61). Similarly, cPP was inversely associated with AoD in both men (coefficient = −0.45, p = 0.0007, model R 2 =0.50) and women (coefficient = −0.40, p = 0.01 model R 2 = 0.61). Thus, each 1 mm increase in AoD was associated with a 0.4 – 0.5 mmHg decrease in bPP and cPP in both sexes. Conclusions: Contrary to the prevailing views, AoD is independently and inversely associated with both bPP and cPP. These findings suggest that a small AoD may contribute to the pathogenesis of systolic hypertension. Longitudinal studies are needed to examine this possibility.

Characterization of the Upper Limb Arterial Properties during Reactive Hyperemia

The radial artery (RA) pressure waveform is commonly used to reconstruct the central aortic pressure waveform. Because the RA pressure waveform has been used as input to this process, its features that are dependent on the local arterial properties can influence the final reconstructed aortic waveform. In this study, we determined the effects of altered upper limb pulse wave velocity (PWV) and local wave reflection parameters on RA pressure waveform augmentation (RA-AIx). Twenty healthy volunteers (10 men) between the ages of 18 and 35 years of age were recruited. Simultaneous pressure waveforms were acquired using arterial tonometers from the right carotid and the radial arteries, prior to and following tourniquet induced hyperemia. The phase velocities from the pressure wave transfer function were used to estimate the pulse wave velocity (PWV(infinity)), the local reflection coefficient (Gamma) and an estimate of the terminal impedance of the upper limbs, PWV(0+). The RA-AIx was represented as a linear, three-parameter model that included the input (the AIx of the carotid artery pressure waveform, CA-AIx), the Gamma and PWV(infinity) of the arm. Tourniquet induced hyperemia did not alter Gamma but reduced PWV(infinity), and PWV(0+) and increased RA-AIx. Multiple linear regression analysis indicated that RA-AIx was increased by high levels of CA-AIx and PWV(infinity) and decreased by elevated Gamma. The relative weighing of CA-AIx, Gamma and PWV(infinity) on RA-AIx were 3:2:1, respectively. The AIx of RA is determined to an equal extent by the input and local factors. Interpretation of the AIx of the RA and the reconstructed central aortic waveform should be made in the context of this relationship.

Relationship between augmentation index obtained from carotid and radial artery pressure waveforms

Increased aortic and carotid arterial augmentation index (AI) has been directly linked with cardiovascular disease risk, mortality and morbidity. The aim of this study was to examine whether AI obtained directly from radial artery pressure waveforms (radial AI) can provide information comparable with carotid arterial AI measurements. In a cross-sectional study of 204 apparently healthy subjects (88 men and 116 women) aged 19-76 years (51 +/- 15 years, mean +/- SD), carotid AI [(second peak carotid systolic pressure - first peak carotid systolic pressure)/carotid pulse pressure*100] and radial AI [(second peak radial systolic pressure - diastolic pressure)/(first peak radial systolic pressure - diastolic pressure)*100] were measured using applanation tonometry. Radial AI was strongly correlated with carotid AI (r = 0.86, P < 0.0001, SD of difference 10.0%), although radial AI was consistently approximately 66% higher than carotid AI. In 16 apparently healthy young adults (11 men and five women, aged 23 +/- 3 years) handgrip exercise was immediately followed by post-exercise muscle ischaemia (PEMI) to compare changes in carotid and radial AI during increased sympathetic nervous activity. PEMI caused parallel increases in carotid and radial AI (26 and 19%). Accordingly, changes in radial AI with PEMI were strongly correlated with corresponding changes in carotid AI (r = 0.86, P < 0.0001, SD of difference 7.3%). These results suggest that AI obtained directly from radial arterial pressure waveforms could provide equivalent information to carotid arterial AI, and has potential as a surrogate marker of cardiovascular disease.

Decrease in left ventricular ejection time on digital arterial waveform during simulated hypovolemia in normal humans.

Left ventricular ejection time (LVET) measured in central arteries is modified during hypovolemia. We compared modifications of the pulse wave in a central artery (carotid) and in a peripheral artery (digital) during central hypovolemia induced by lower body negative pressure (LBNP) in conscious volunteers. Hypovolemia was simulated with progressive LBNP (baseline, -10, -20, and -30 mm Hg) in nine young healthy volunteers. The carotid arterial pressure waveform was recorded using a Millar tonometric method. The digital pulse wave was measured with a volume-clamp method (Finapres) and the stroke volume with a thoracic impedance method (Biomed). Mean arterial pressure did not change during LBNP. Compared with baseline values, heart rate increased significantly at the -30 mm Hg level (68 +/- 13 beats/min vs. 59 +/- 11 beats/min), and stroke volume decreased as soon as -10 mm Hg was achieved (113 +/- 41 mL vs. 127 +/- 35 mL). Both carotid and digital LVET decreased significantly at the -10 mm Hg level (337 +/- 26 and 339 +/- 24 ms vs. 360 +/- 35 and 361 +/- 24 ms, respectively). Peripheral LVET could reflect variation of central LVET during LBNP and be a reliable noninvasive parameter for monitoring hypovolemia.

Analysis of the arterial blood pressure waveform during left ventricular nonpulsatile assistance in animal models.

When the rotary blood pump is used as a left ventricular assist device (LVAD), the arterial blood pressure waveform changes with the LVAD condition. Based on evidence from an in vitro study, the change of the arterial blood pressure waveform during left ventricular assistance was evaluated using animal models. After the left pleural cavity was opened through the fifth intercostal space under general anesthesia, a rotary blood pump was implanted as an LVAD into 6 healthy calves. The direct left carotid arterial blood pressure waveform was measured and recorded by an oscilloscope. The Fast Fourier Transform technique was utilized to analyze the arterial blood pressure waveform and calculate the pulsatility index (PI) and the pulse power index (PPI). Similar to the in vitro study, the PI and PPI decreased exponentially with the increase of the LVAD assist ratio. By using this analysis methodology, a physiologically effective ventricular assistance might be achieved.

Effect of reflection of arterial pressure on carotid circulation in essential hypertension

Pressure wave reflection plays a pivotal role in the augmentation of systolic blood pressure. In the present study, the association between reflection of pressure wave and structural and functional alteration, including blood flow, in the common carotid artery was investigated in 70 hospitalized essential hypertensive patients. The reflection of pressure was estimated by the “augmentation index” of the carotid arterial pressure waveform. The carotid augmentation index was significantly related to age (r = 0.36), body height (r = −0.30), intima-media thickening (r = 0.28), number of plaques (r = 0.44), stiffness of the carotid artery (r = 0.38), diastolic carotid flow velocity (r = −0.31), and left ventricular mass index (r = 0.33). Furthermore, the reflection of arterial pressure showed a significant negative correlation with diastolic/systolic ratio of blood flow velocity in the carotid artery (r = −0.41, P = .0005). Stepwise regression analysis revealed that age and left ventricular mass index were independent determinants for the carotid augmentation index. These findings indicate that the reflection of arterial pressure is related to morphological and functional alterations of the carotid artery, including a relative reduction of diastolic blood flow.

An impedance index in normal subjects and in subarachnoid hemorrhage

The impedance of a hemodynamic system is defined as the ratio of each harmonic component of blood pressure to that of flow. Calculation of impedance curves has been extensively performed in the systemic circulation, leading to the recognition of reflected pressure and flow waves and clarifying the shape of ultrasound waveforms. Impedance in the human cerebral circulation has not been measured primarily because of the relative inaccessibility of simultaneous flow and pressure data in the human cerebral circulation. We defined an impedance index using the transcranial Doppler waveform for that of flow and a noninvasive applanation measure of the carotid artery pressure waveform. Middle cerebral artery velocities and carotid artery pressure waveforms were simultaneously recorded in 16 vessels from 10 normal volunteers, 42 vessels in 14 patients with aneurysmal subarachnoid hemorrhage, and 14 vessels in 7 subjects during conditions of hypocapnia, normocapnia and hypercapnia. Impedance was calculated by dividing the harmonic associated with pressure divided by that of flow, and averaging 10 to 20 such calculations. Relative impedance curves were calculated by dividing by the impedance at the first harmonic. Impedance was also studied in an electrical model consisting of a Windkessel element containing inductance in series with a second Windkessel to model the large vessel and vascular bed, respectively. Model parameters were taken from the literature for these calculations. For the normal subjects, the shape of the impedance index curve was similar to those found in the systemic circulation. The impedance index curves for patients in vasospasm (middle cerebral velocity greater than 180) showed a peak at the second or third harmonic, which appeared more frequently than the nonspasm group ( p < 0.01). Furthermore, the ratio of the second harmonic to the first harmonic was significantly >1.0 in the spasm group but significantly <1.0 in the normal group ( p < 0.05). Calculations from the electrical model replicated the appearance of these peaks at the second or third harmonic for vasospasm parameters. A statistically significant peak appeared at the second or third harmonic in the impedance index curves for patients in vasospasm, which was replicated quantitatively by our electrical model. Although such peaks can be explained in the systemic circulation by the presence of reflected waves, the distance to the reflection site is larger than expected for the cerebral circulation. This suggests the importance of the inertia of blood as a stenosis worsens and as the origin for the observed changes in the impedance index curves.