Kiyomi Niki

A new noninvasive measurement system for wave intensity : evaluation of carotid arterial wave intensity and reproducibility

Abstract. Wave intensity (WI) is a new hemodynamic index that provides information about the dynamic behavior of the heart and the vascular system and their interaction. Carotid arterial wave intensity in normal subjects has two positive peaks. The first peak, W1, occurs during early systole, the magnitude of which increases with increases in cardiac contractility. The second peak, W2, which occurs towards the end of ejection, is related to the ability of the left ventricle to actively stop aortic blood flow. Between the two positive peaks, a negative area, NA, is often observed, which signifies reflections from the cerebral circulation. The time interval between the R-wave of ECG and the first peak (R − W1) corresponds to the pre-ejection period, and that between the first and second peaks (W1 − W2) corresponds to ejection time. We developed a new ultrasonic on-line system for obtaining WI and arterial stiffness (β). The purpose of this study was (1) to report normal values of various indices derived from WI and β measured with this system, and (2) to evaluate the intraobserver and interobserver reproducibility of the measurements. The measurement system is composed of a computer, a WI unit, and an ultrasonic machine. The WI unit gives the instantaneous change in diameter of the artery and the instantaneous mean blood velocity through the sampling gate. Using these parameters and blood pressure measured with a cuff-type manometer, the computer gives WI and β. We applied this method to the carotid artery in 135 normal subjects. The mean values of W1, W2, NA, R − W1, and W1 − W2 were 8 940 ± 3 790 mmHg m/s3, 1 840 ± 880 mmHg m/s3, 27 ± 13 mmHg m/s2, 104 ± 14 ms, and 270 ± 19 ms, respectively. These values did not show a significant correlation with age. The mean value of β was 10.4 ± 4.8 and the values significantly correlated with age (men: r = 0.66, P < 0.0001; women: r = 0.81, P < 0.0001). The reproducibility was evaluated by intraobserver intrasession (IA), intraobserver intersession (IE), and interobserver intrasession variability (IO). The reproducibility of R − W1 and W1 − W2 was high: the mean coefficient of variation (mCV) of IA was less than 3%; 95% confidence limits from the mean values (CL) were less than 8% for IE and less than 4% for IO. The reproducibility of W1 and β was good: mCV for IA was less than 10%; CL for IE and IO were less than 17%. W2 and NA showed a higher variability than other indices: mCV for IA was less than 13%, and CL for IE and IO were less than 36%. However, two sessions by the same observer and two sessions by different observers were not biased. Wave intensity measurements with this system are clinically acceptable.

Relationship between the pressure and diameter of the carotid artery in humans.

Abstract The purpose of this study was to examine the assumption of similarity between pressure and diameter-change waveforms in humans. We measured carotid arterial pressure and diameter change, simultaneously, in six patients with heart disease. In all patients, the carotid arterial pressure–diameter relationship could, in practice, be regarded as being linear.

On-line noninvasive one-point measurements of pulse wave velocity.

Abstract Pulse wave velocity (PWV) is a basic parameter in the dynamics of pressure and flow waves traveling in arteries. Conventional on-line methods of measuring PWV have mainly been based on “two-point” measurements, i.e., measurements of the time of travel of the wave over a known distance. This paper describes two methods by which on-line “one-point” measurements can be made, and compares the results obtained by the two methods. The principle of one method is to measure blood pressure and velocity at a point, and use the water-hammer equation for forward traveling waves. The principle of the other method is to derive PWV from the stiffness parameter of the artery. Both methods were realized by using an ultrasonic system which we specially developed for noninvasive measurements of wave intensity. We applied the methods to the common carotid artery in 13 normal humans. The regression line of the PWV (m/s) obtained by the former method on the PWV (m/s) obtained by the latter method was y = 1.03x − 0.899 (R2 = 0.83). Although regional PWV in the human carotid artery has not been reported so far, the correlation between the PWVs obtained by the present two methods was so high that we are convinced of the validity of these methods.

Clinical usefulness of carotid arterial wave intensity in assessing left ventricular systolic and early diastolic performance

Wave intensity (WI) is a novel hemodynamic index, which is defined as (dP/dt)·(dU/dt) at any site of the circulation, where dP/dt and dU/dt are the derivatives of blood pressure and velocity with respect to time, respectively. However, the pathophysiological meanings of this index have not been fully elucidated in the clinical setting. Accordingly, we investigated this issue in 64 patients who underwent invasive evaluation of left ventricular (LV) function. WI was obtained at the right carotid artery using a color Doppler system for blood velocity measurement combined with an echo-tracking method for detecting vessel diameter changes. The vessel diameter changes were automatically converted to pressure waveforms by calibrating its peak and minimum values by systolic and diastolic brachial blood pressures. The WI of the patients showed two sharp positive peaks. The first peak was found at the very early phase of LV ejection, while the second peak was observed near end-ejection. The magnitude of the first peak of WI significantly correlated with the maximum rate of LV pressure rise (LV max. dP/dt) (r = 0.74, P ≪ 0.001). The amplitude of the second peak of WI significantly correlated with the time constant of LV relaxation (r = −0.77, P ≪ 0.001). The amplitude of the second peak was significantly greater in patients with the inertia force of late systolic aortic flow than in those without the inertia force (3 080 ± 1 741 vs 1 890 ± 1 291 mmHg m s−3, P ≪ 0.01). These findings demonstrate that the magnitude of the first peak of WI reflects LV contractile performance, and the amplitude of the second peak of WI is determined by LV behavior during the period from late systole to isovolumic relaxation. WI is a noninvasively obtained, clinically useful parameter for the evaluation of LV systolic and early diastolic performance at the same time.

Aortic blood momentum – the more the better for the ejecting heart in vivo?

OBJECTIVES The aim of the present study was to test two hypotheses: (1) the momentum of the blood flowing out of the left ventricle toward the aorta (inertia force) plays an important role in the initiation of decay and the maximum rate of decay (peak (-dP/dt)) of left ventricular pressure (P); (2) a normal heart itself generates the inertia force which enhances its function. METHODS The contribution of the inertia force to (-dP/dt) was theoretically given as rho c alpha, where rho is the blood density, c the pulse wave velocity, and alpha the deceleration rate of aortic blood flow. The correlations of peak (-dP/dt) with rho c alpha and with the time constant (tau) of the pressure decay during isovolumic relaxation, which was considered to represent myocardial relaxation characteristics, were compared in seven dogs. We developed a method of grading the strength of the inertia force, using the phase loop of left ventricular pressure (dP/dt vs. P relation). The method was applied to the records of 25 patients with ischemic heart disease, from which high fidelity left ventricular pressure recordings were available. RESULTS The correlation of peak (-dP/dt) with rho c alpha was much higher than with tau (0.75 vs. -0.46). 16 of the 25 patients showed evidence of the inertia force. However, other patients showed no inertia force. The strength of the inertia force showed a significant (P < 0.05) correlation with left ventricular end-diastolic pressure (r = -0.46), cardiac index (r = 0.62), stroke volume index (r = 0.69), ejection fraction (r = 0.46), and peak (-dP/dt) (r = 0.56). CONCLUSION The inertia force of late systolic aortic flow contributed to ventricular relaxation in the normal heart.

A noninvasive method of measuring wave intensity, a new hemodynamic index: application to the carotid artery in patients with mitral regurgitation before and after surgery

SummaryWave intensity (WI) is a new hemodynamic index, which is defined as (dP/dt)(dU/dt) at any site of the circulation, where dP/dt and dU/dt are the time derivatives of blood pressure and velocity, respectively. Arterial WI in normal subjects has two positive sharp peaks. The first peak occurs during early systole when a forward-traveling compression wave is generated by the left ventricle. The magnitude of this peak increases markedly with an increase in cardiac contractility. The second peak, which occurs towards the end of systole, is caused by generation of a forward-traveling expansion wave by the ability of the left ventricle to actively stop aortic blood flow. The interval between the R wave of the ECG and the first peak of WI (R-lst peak interval) and the interval between the first and second peaks (lst–2nd interval) are approximately equal to the preejection period and left ventricular ejection time, respectively. Using a combined Doppler and echotracking system, we obtained carotid arterial WI non-invasively. We examined the characteristics of WI in 11 patients with mitral regurgitation (MR) before and after surgery, and 24 normal volunteers. In the MR group before surgery, the second peak was decreased and the (lst–2nd interval)/(R-R interval) ratio was reduced, compared with the normal group (140 ± 130 vs 750 ± 290mmHgm/s3, P < 0.0083; 20.7% ± 3.4% vs 26.7% ± 2.8%, P < 0.0083). There were no significant differences in the first peak between the normal group and the MR group before and after surgery. The second peak in the MR group was increased significantly (P < 0,016 vs before surgery) to 1150 ± 830mmHgm/s3 in the early period after surgery (stage I), and to 1090 ± 580mmHgm/s3 in the late period after surgery (stage II). These values did not differ significantly from that of the normal group. At stage I, the (R-1st peak interval)/(R-R interval) ratio was increased from 13.4% ± 2.7% to 2.6% ± 5.6% (P < 0.016 vs before surgery). At stage II, this ratio decreased to 16.2% ± 2.8% (P < 0.016 vs stage I), but was still significantly higher than that before surgery. The (1st–2nd inteval)/(R-R interval) ratio increased significantly after surgery (P < 0.016 vs before surgery) to values (27.0% ± 4.5% at stage I and 28.9% ± 2.6% at stage II) which did not differ significantly from that of the normal group. The recovery of the second peak after surgery suggests that the left ventricle had recovered the ability to actively stop aortic blood flow. Wave intensity is useful for analyzing changes in the working condition of the heart.

Development of a non-invasive real-time measurement system of wave intensity

Time-normalized wave intensity (WI) is a new hemodynamic index, which is defined as (dP/dt)(dU/dt) at any site of the circulation, where dP/dt and dU/dt are the time derivatives of blood pressure and velocity, respectively. WI provides information about the dynamic behavior of the heart and vascular system and their interaction. We have developed a new real-time measurement system for obtaining WI based on a conventional color Doppler system. The blood pressure waveforms were obtained non-invasively from the arterial diameter-change waveforms by an echo-tracking method. Using a 7.5 MHz linear array probe, we obtained carotid arterial WI, and analyzed the characteristics of the heart and vascular interactions. The results suggest that the system has great potential for clinical usefulness.

Relationship between blood pressure obtained from the upper arm with a cuff-type sphygmomanometer and central blood pressure measured with a catheter-tipped micromanometer

Recently, the importance of central blood pressure for cardiovascular risk stratification has been emphasized. Accordingly, the differences in peak systolic and bottom diastolic pressures between the ascending aorta and the brachial artery should be clarified. Study subjects consisted of 82 consecutive patients with suspected coronary artery disease who underwent cardiac catheterization, and in whom ascending aortic pressure waveform was obtained using a catheter-tipped micromanometer, and at the same time systolic and diastolic pressures were measured (single measurement) from the right upper arm with a cuff-type sphygmomanometer based on the oscillometric technique. No significant systematic difference (bias) was found between the peak pressure obtained in the ascending aorta and the systolic pressure from the right upper arm (133.6 ± 25.1 vs 131.8 ± 21.5 mmHg, not significant). Bland–Altman analysis showed only a small bias of +1.8 mmHg, and the limits of agreement were 25.4 mmHg and −21.8 mmHg. In contrast, the bottom pressure in the ascending aorta was significantly lower compared with the diastolic pressure from the upper arm (68.5 ± 10.7 vs 73.0 ± 12.4 mmHg, P < 0.0001). Bland–Altman analysis showed a small but significant bias of −4.5 mmHg, and the limits of agreement were 14.1 mmHg and −23.1 mmHg. The observed biases seemed to remain within practical range. However, random variation in the two measurements was rather large. This is considered to be caused by the random error in the single measurement with the cuff-type sphygmomanometer.

Effects of sublingual nitroglycerin on working conditions of the heart and arterial system: analysis using wave intensity

PurposeThe effects of nitroglycerin (NTG) on the vascular system are well known. However, the effects of NTG on the heart are still obscure, because these effects are modified by those on the vascular system, and vice versa. Therefore, to evaluate the hemodynamic effects of NTG, it is important to understand the interaction between the heart and the vascular system. Wave intensity (WI) is a new hemodynamic index that provides information about working conditions of the heart interacting with the arterial system. The purpose of this study was to evaluate the interactive effects of NTG on the cardiovascular system in normal subjects using wave intensity.MethodsWe simultaneously measured carotid arterial blood flow velocity and diameter change using a specially designed ultrasonic system, and calculated the WI and the stiffness parameter β. Measurements were made in 13 normal subjects (9 men and 4 women, aged 47 ± 10 years) in the supine position before and after sublingual NTG.ResultsThe maximum value of WI (W1) and the mid-systolic expansion wave (X) increased (W1 from 9.1 ± 4.3 to 12.3 ± 5.5 × 103 mmHg m/s3, P < 0.001; X from 105 ± 185 to 345 ± 370 mmHg m/s3, P < 0.05). β increased (from 10.5 ± 3.8 to 14.1 ± 3.8, P < 0.001). The pressure contours changed considerably.ConclusionsNTG increased W1 and the mid-systolic expansion wave, which suggests enhanced cardiac power during the initial ejection and mid-systolic unloading. These results are new findings about the effects of NTG that can be added to the widely known late systolic unloading and preload reduction. NTG also increased arterial stiffness, which reduces the Windkessel function. By using an echo-Doppler system, WI can be obtained noninvasively. WI has the clinical potential to provide quantitative and detailed information about working conditions of the heart interacting with the arterial system.

Out-of-plane visual servoing method for tracking the carotid artery with a robot-assisted ultrasound diagnostic system

Up to now, there are different kinds of robot-assisted ultrasound diagnostic systems proposed in the last decade. However, the compensation of the ultrasound probe position according to the patient movement is still one of the most important and useful functions required for those systems. For this purpose, in this research, we aim at developing an automated diagnostic system for the measurement of the wave intensity which is usually measured at the common carotid artery. In particular, in this paper, we focus on proposing a robust visual servoing method for tracking out-of-plane motion for a robot-assisted medical ultrasound diagnostic system by using a conventional 2D probe. A robotic device which manipulates the ultrasound probe firstly scans a small area around the target position and records several B-mode images at a regular interval. In order to track the out-of-plane motion, an inter-frame block matching method has been proposed and implemented on the Waseda-Tokyo Womens Medical-Aloka Blood Flow Measurement System No. 2 Refined (WTA-2R). A set of experiments was proposed to verify the effectiveness of the proposed method. From the experimental results, we could confirm its robustness while doing the task with real human tissues.