Akimitsu Harada

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.

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.

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.

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.

A New Method for Evaluation of Fracture Healing by Echo Tracking

Assessment of bone healing on radiographs depends on the volume and radio-opacity of callus at the healing site, but is not necessarily objective, and there are differences of judgment among observers. To overcome this disadvantage, a clinical system was developed to quantify the stiffness of healing fractures of the tibia in patients by the echo tracking (ET) method in a manner similar to a three-point bending test. The purpose of this study was to ensure that the ET system could clinically assess the progress, delay or arrest of healing. The fibular head and the lateral malleolus were supported. A 7.5-MHz ultrasound probe was placed on the proximal and distal fragments and a load of 25 N was applied. Five tracking points were set along the long axis of the ultrasound probe at intervals of 10 mm. With a multiple ET system, two probes measured the displacement of five tracking points on each of the proximal and distal fragments of the tibia, thereby detecting the bending of the two fragments generated by the load. ET angle was defined as the sum of the inclinations of the proximal and distal fragments. Eight tibial fractures in seven patients treated by a cast or internal fixation were measured over time. In patients with radiographically normal healing, the bending angle decreased exponentially over time. However, in patients with nonunion, the angle remained the same over time. It was demonstrated that the ET method could be clinically applicable to evaluate fracture healing as a versatile, quantitative and noninvasive technique.

Development of a Robotic Carotid Blood Flow Measurement System - A Compact Ultrasonic Probe Manipulator Consisting of a Parallel Mechanism

We developed a robot system for the wave intensity measurement of carotid blood flow using ultrasonic diagnostic equipment in order to reduce the inconvenience for the patient and doctor. The robot system has an ultrasonic probe manipulator consisting of a 6-DOF linear parallel link mechanism. There are two control modes for the robotic measurements: direct positioning by hand using virtual compliance control and remote control by using a 6-axis force/torque sensor. We confirmed that the probe manipulator works effectively to measure the blood flow by experiments using human subjects

2A-1 A New Method for Measuring Bone Strength using Echo-Tracking

To evaluate bone strength, it is significant to measure the degree of deformation or strain of bone under a certain load. However no method has been available to non-invasively measure bone deformation. To obtain bone mechanical properties such as elasticity, viscoelasticity and plasticity, we need to externally apply a load to a bone and to accurately measure the small displacement of a specific point on the surface of the bone. For the displacement measurements, we improved the echo-tracking (ET) system. The ET system consists of a diagnostic ultrasound system with a 7.5 MHz linear probe and a PC. PZF echo signals were sampled at 50 MHz and interpolated to eight times the sampling frequency. Then the PC calculated and displayed the small displacement. Furthermore we developed a multi-point ET system and defined ET strain: ETS = D/L, where L was the distance from the first tracking point to the last, and D was the maximum distance from the spline fitting curve of the displacement to the straight line connecting the first tracking point to the last. Then we conducted in vitro experiments using three-point bending (TPB) tests of a porcine tibia placed on a testing machine. As a reference of the bone strain, we used strain gauges attached to the surface of the bone and compared the ETS. With respect to the displacement, there was excellent linearity between the data obtained by the ET system and the linear potentiometer (r = 0.999). In the TPB tests of the porcine tibia, the strain gauge readings and the ETS also showed excellent linearity (r = 0.998 for both the proximal and the distal strain gauges). The results suggest that our method has great potential of non-invasive quantitative diagnosis for bone healing and bone strength

Development of a New Diagnostic System for Human Liver Diseases Based on Conventional Ultrasonic Diagnostic Equipment

In this paper, the authors present the experimental results of using a quantitative ultrasonic diagnosis technique for human liver diseases using the fractal dimension (FD) of the shape of the power spectra (PS) of RF signals. We have developed an experimental system based on a conventional ultrasonic diagnostic system. As a result, we show that normal livers, fatty livers and liver cirrhosis can be identified using the FD values.

A minute bone bending angle measurement method using echo-tracking for assessment of bone strength in vivo

The purpose of this study is to develop a new ultrasound diagnostic system for non-invasive and quantitative assessment of mechanical properties of the bone or bone healing. In the previous papers, we reported that we had developed a new ultrasound system to measure a minute bone deformation using a multi-point echo-tracking (ET) and that it had a great potential for non-invasive and quantitative diagnosis of bone healing. In this paper, we present a newly developed measurement system with improved accuracy for assessing deformation of intact tibia in vivo. It consists of a dedicated probe, a transmitting/receiving system and analysis software calculating a minute bending angle of the bone surface under a three-point bending (TPB) test. And, we report results of a performance evaluation of the developed system by using test measurements. Furthermore, we evaluated the reproducibility of the in vivo measurement by repeatedly measuring the bending angle of the tibias of 5 healthy volunteers every week for one month. As a result, the evaluation of the accuracy of the measured bending angle using the metallic plate for calibration showed that the standard deviation (SD) of the measurement in range of 0 to 0.1 degrees was 0.004 degrees. Then, we performed an in vivo measurement of normal tibia. The results showed that the mean bending angle of the normal adult tibias under a load of 25 N and a supporting span of the tibial length of each subject was 0.058 degrees with a SD of 0.01 degrees. In addition, SD of the data for the measurement repeatability was 0.006 degrees. We developed a bending angle measurement system for the human tibia using a TPB test and obtained an excellent accuracy of the system and also confirmed through the measurement of the tibia of human volunteers that the repeatability was sufficient to quantitatively assess bending property of the intact tibia.