Wave Intensity Analysis: Sex-Specific Differences in Hemodynamic and Ventilatory Responses to Graded Exercise-Echocardiographic Measurements.

BACKGROUND: The differences in hemodynamic and ventilatory responses to graded exercise between men and women have not been well documented. Using wave intensity (WI) analysis, which is useful for analyzing ventriculo-arterial interaction, we aimed to elucidate the sex-specific differences. METHODS: We enrolled 48 healthy subjects (24 men and 24 women, age 21.3 ± 1.6 and 20.5 ± 0.9 years, n.s. [not significant]). Using ultrasonic diagnostic equipment, we measured WI, arterial stiffness parameter (ß), force-frequency relation (FFR) and other hemodynamic parameters in the carotid artery before and during graded bicycle exercise. We also analyzed expired gas volume (VE) during the exercise. The workload was increased stepwise by 20 W at 1-min intervals up to respiratory compensation (RC) point through the anaerobic threshold (AT). WI is defined as WI = (dP/dt) (dU/dt), where P is blood pressure, U is velocity, and t is time. The peak value of WI (W1) increases with left ventricular (LV) peak dP/dt, in other words, an index of cardiac contractility. The FFR was obtained as the linear regression line of W1 on heart rate. ß is defined as ß = ln (Ps/Pd)/[(Ds - Dd)/Dd], where D is the arterial diameter, and suffixes s and d indicate systolic and diastolic, respectively. RESULTS: There was no difference in the body mass index between men and women. Carbon dioxide outputs (VCO2) did not differ at rest, but those at AT and RC were greater in men. Oxygen consumptions (VO2) in men and women at rest did not differ, but those in men at AT and RC were greater. Workloads per body weight in men and women did not differ at AT, but they were greater in men at RC. Systolic pressures at rest, AT and RC were greater in men than women. Heart rates in men and women did not differ at any stage of the graded exercise. W1 did not differ at rest and AT, but it was greater in men than women at RC. The slope of the FFR during the period from rest to AT did not differ between men and women. However, the slope of the FFR during the period from AT to RC was greater in men. CONCLUSIONS: The reached values of workload/weight at RC, VCO2 at AT and RC, VO2 at AT and RC, W1 at RC, and the slope of the FFR during the period from AT to RC were greater in men than women.

Simulation of the aortic valve deformation by considering blood flow reflection.

We have tried to simulate the aortic valve deformation by considering the reflection of blood flow. The aortic valve opens and closes according to blood flow caused by pressure difference between the heart and the aorta. The aortic valve is elastic body while blood is fluid so that two different types of methods are usually used for the simulation; however, it is difficult to calculate collision detection and force between two different types of models. Then, in this paper, both materials are modeled with particles so that collision detection and force between two different types of models can be easily calculated. In addition, by considering the reflection of blood flow at the end of blood vessel, we have succeeded to simulate the deformation of the aortic valve and found that blood flows differently depending on the length of the aortic valve.

Intermittent, moderate-intensity aerobic exercise for only eight weeks reduces arterial stiffness: evaluation by measurement of stiffness parameter and pressure-strain elastic modulus by use of ultrasonic echo tracking.

BACKGROUND AND PURPOSE: Aerobic exercise has been reported to be associated with reduced arterial stiffness. However, the intensity, duration, and frequency of aerobic exercise required to improve arterial stiffness have not been established. In addition, most reports base their conclusions on changes in pulse wave velocity, which is an indirect index of arterial stiffness. We studied the effects of short-term, intermittent, moderate-intensity exercise training on arterial stiffness based on measurements of the stiffness parameter (ß) and pressure-strain elastic modulus (E p), which are direct indices of regional arterial stiffness. METHODS: A total of 25 young healthy volunteers (18 men) were recruited. By use of ultrasonic diagnostic equipment we measured ß and E p of the carotid artery before and after 8 weeks of exercise training. RESULTS: After exercise training, systolic pressure (P s), diastolic pressure (P d), pulse pressure, systolic arterial diameter (D s), and diastolic arterial diameter (D d) did not change significantly. However, the pulsatile change in diameter ((D s - D d)/D d) increased significantly, and ß and E p decreased significantly. CONCLUSIONS: For healthy young subjects, ß and E p were reduced by intermittent, moderate-intensity exercise training for only 8 weeks.

A bloodstream simulation based on particle method.

Many surgical simulators use mesh method to deform CG models such as organs and blood vessels because the method can easily calculate the deformation of models; however, it has to split and reconstruct the mesh of the models when the model is broken such as bleeding. On the other hand, particle methods consider a continuous body such as solid and liquid as a set of particles and do not have to construct the mesh. Therefore, in this paper, we describe how to simulate bloodstream by using MPS (Moving Particle Semi-implicit) method that is one of particle ones. In the simulation, we use the aorta model as the blood vessel model, and the model is constructed with particles. As the result of the simulation, it took 20 ms to deform the blood vessel and to simulate bleeding with the model that is constructed with 15,880 particles for the blood vessel and 6,688 particles for the blood.

Wave intensity, an index of ventriculo-arterial interaction, increases in hypertensive subjects but decreases in normotensive subjects during the cold pressor test.

PURPOSE: Cardiovascular reactivity to the cold pressor test (CPT) is considered to be a marker for apparent and potential hypertension. We aimed to elucidate the association between the changes in wave intensity (WI) during CPT and hypertension. METHODS: We recruited 85 volunteers, 33 of whom were hypertensive and 52 normotensive. Using ultrasonic equipment during CPT, we measured carotid arterial WI, which is defined in terms of blood pressure and velocity in the carotid artery. RESULTS: The peak WI (W1) increased during CPT in 70.6% of hypertensive individuals, but decreased in 72.6% of normotensive individuals. The chi-square (χ2) test showed that the association between the direction of change in W1 (increase or decrease) and the blood pressure (hypertensive or normotensive) was very strong (P < 0.0001). CONCLUSION: Direction of change in W1 during CPT is a clear marker to discriminate cardiovascular reactivity that does not vary depending on each investigator's subjective point of view.

Changes in cardiac contractility during graded exercise are greater in subjects with smaller body mass index, and greater in men than women: analyses using wave intensity and force-frequency relations.

INTRODUCTION AND PURPOSE: Estimation of the contractility of the left ventricle during exercise is an important part of the rehabilitation protocol. It is known that cardiac contractility increases with an increase in heart rate. This phenomenon is called the force-frequency relation (FFR). Using wave intensity, we aimed to evaluate FFR noninvasively during graded exercise. METHODS: We enrolled 83 healthy subjects. Using ultrasonic diagnostic equipment, we measured wave intensity (WD), which was defined in terms of blood velocity and arterial diameter, in the carotid artery and heart rate (HR) before and during bicycle ergometer exercise. FFRs were constructed by plotting the maximum value of WD (WD1) against HR. We analyzed the variation among FFR responses of individual subjects. RESULTS: WD1 increased linearly with an increase in HR during exercise. The average slope of the FFR was 1.0 ± 0.5 m/s3 bpm. The slope of FFR decreased with an increase in body mass index (BMI). The slopes of FFRs were steeper in men than women, although there were no differences in BMI between men and women. CONCLUSIONS: The FFR was obtained noninvasively by carotid arterial wave intensity (WD1) and graded exercise. The slope of the FFR decreased with an increase in BMI, and was steeper in men than women.

Associations of increased arterial stiffness with left ventricular ejection performance and right ventricular systolic pressure in mitral regurgitation before and after surgery: Wave intensity analysis.

BACKGROUND: The effect of increased arterial stiffness on mitral regurgitation (MR) is not clear. Using wave intensity (WI) analysis, which is useful for analyzing ventriculo-arterial interaction, we aimed to elucidate associations of increased arterial stiffness with left ventricular (LV) ejection performance and right ventricular systolic pressure (RVSP) in MR. METHODS AND RESULTS: We noninvasively measured carotid arterial WI and stiffness parameter (ß) in 98 patients with non-ischemic chronic MR before and after surgery, and 98 age-and-gender matched healthy subjects by ultrasonography. WI is defined as WI = (dP/dt)(dU/dt) [P: blood pressure, U: velocity, t: time]. The peak value of WI (W1) increases with LV peak dP/dt. The temporal WI index (Q-W1)st, which is the standardized interval between the Q wave of the ECG and W1, is a surrogate for preejection period. Ejection fraction (EF), left atrial volume index (LAVI), effective regurgitant orifice area (ERO), RVSP, and other echocardiographic data were also obtained. W1 was enhanced in the MR group before surgery compared with the normal group (10.7 ± 5.7 vs 8.5 ± 3.6 × 103 mmHg m/s3, p < 0.05). However, the results of two-way ANOVA showed this enhancement of W1 was observed only in the subgroup of MR before surgery with lower arterial stiffness (ß < 13, p< 0.0001). ERO, ß and LAVI were predictor variables before surgery to determine RVSP. EF and (Q-W1)st before surgery were predictor variables for EF after surgery. CONCLUSIONS: In the MR group before surgery, increased arterial stiffness suppresses compensatory enhancement of W1, and increases RVSP. Prolonged (Q-W1)st has the potential for predicting low EF after surgery.

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

PURPOSE: The 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. METHODS: We simultaneously measured carotid arterial blood flow velocity and diameter change using a specially designed ultrasonic system, and calculated the WI and the stiffness parameter ß. 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. RESULTS: The maximum value of WI (W 1) and the mid-systolic expansion wave (X) increased (W 1 from 9.1 ± 4.3 to 12.3 ± 5.5 × 10(3) mmHg m/s(3), P < 0.001; X from 105 ± 185 to 345 ± 370 mmHg m/s(3), P < 0.05). ß increased (from 10.5 ± 3.8 to 14.1 ± 3.8, P < 0.001). The pressure contours changed considerably. CONCLUSIONS: NTG increased W 1 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.

Noninvasive evaluation of left ventricular force-frequency relationships by measuring carotid arterial wave intensity during exercise stress.

BACKGROUND AND PURPOSE: Estimation of the contractility of the left ventricle during exercise is important in drawing up a protocol of cardiac rehabilitation. It has been demonstrated that color Doppler- and echo tracking-derived carotid arterial wave intensity is a sensitive index of global left ventricular (LV) contractility. We assessed the feasibility of measuring carotid arterial wave intensity and determining force-frequency (contractility-heart rate) relations (FFRs) during exercise totally noninvasively. METHODS: We measured carotid arterial wave intensity with a combined color Doppler and echo tracking system in 25 healthy young male volunteers (age 20.8 ± 1.2 years) at rest and during exercise. FFRs were constructed by plotting the maximum value of wave intensity (WD1) against heart rate (HR). RESULTS: We first confirmed that HR increased linearly with an increase in work load in each subject (r (2) = 0.95 ± 0.04). WD1 increased linearly with an increase in HR. The goodness-of-fit of the regression line of WD1 on HR in each subject was very high (r (2) = 0.48-0.94, p < 0.0001, respectively). The slope of the WD1-HR relation ranged 0.30-2.20 [m/s(3) (beat/min)]. CONCLUSIONS: Global LV FFRs can be generated in healthy young volunteers with an entirely noninvasive combination of exercise and wave intensity. These data should show the potential usefulness of the FFR in the context of cardiac rehabilitation.

Particle Based Simulation of the Aortic Valve by Considering Heart's Pulsation.

We have performed a dynamic simulation of the aortic valve by considering heart's pulsation. In the simulation, there are two different types of materials: elastic body for the aortic wall and the aortic valve, and fluid for blood. In order to calculate the collision detection between two different types of materials, we have used a particle method. In addition, the pressure difference between the left ventricle and the aorta causes the blood flow in the inside of the aorta. Then, the pressure change is given as the parameter of the simulation by referring to the typical pattern of the heart's pulsation. Finally, we have succeeded in performing the simulation on opening and closing of the aortic valve, and have also visualized the pressure in the inside of the aorta and the stress distribution on the aortic valve.

Human abdomen recognition using camera and force sensor in medical robot system for automatic ultrasound scan.

Physicians use ultrasound scans to obtain real-time images of internal organs, because such scans are safe and inexpensive. However, people in remote areas face difficulties to be scanned due to aging society and physician's shortage. Hence, it is important to develop an autonomous robotic system to perform remote ultrasound scans. Previously, we developed a robotic system for automatic ultrasound scan focusing on human's liver. In order to make it a completely autonomous system, we present in this paper a way to autonomously localize the epigastric region as the starting position for the automatic ultrasound scan. An image processing algorithm marks the umbilicus and mammary papillae on a digital photograph of the patient's abdomen. Then, we made estimation for the location of the epigastric region using the distances between these landmarks. A supporting algorithm distinguishes rib position from epigastrium using the relationship between force and displacement. We implemented these algorithms with the automatic scanning system into an apparatus: a Mitsubishi Electric's MELFA RV-1 six axis manipulator. Tests on 14 healthy male subjects showed the apparatus located the epigastric region with a success rate of 94%. The results suggest that image recognition was effective in localizing a human body part.

Clinical usefulness of wave intensity analysis.

Wave intensity (WI) is a hemodynamic index, which can evaluate the working condition of the heart interacting with the arterial system. It can be defined at any site in the circulatory system and provides a great deal of information. However, we need simultaneous measurements of blood pressure and velocity to obtain wave intensity, which has limited the clinical application of wave intensity, in spite of its potential. To expand the application of wave intensity in the clinical setting, we developed a real-time non-invasive measurement system for wave intensity based on a combined color Doppler and echo-tracking system. We measured carotid arterial WI in normal subjects and patients with various cardiovascular diseases. In the coronary artery disease group, the magnitude of the first peak of carotid arterial WI (W (1)) increased with LV max. dP/dt (r = 0.74, P < 0.001), and the amplitude of the second peak (W (2)) decreased with an increase in the time constant of LV pressure decay (r = -0.77, P < 0.001). In the dilated cardiomyopathy group, the values of W (1) were much lower than those in the normal group (P < 0.0001). In the hypertrophic cardiomyopathy group, the values of W (2) were much smaller than those in the normal group (P < 0.0001). In mitral regurgitation before surgery, W (2) decreased or disappeared, but after surgery W (2) appeared clearly. In the hypertension group, the magnitude of reflection from the head was considerably greater than that in the normal group (P < 0.0001). We also evaluated hemodynamic effects of sublingual nitroglycerin in normal subjects. Nitroglycerin increased W (1) significantly (P < 0.001). WI can be obtained non-invasively using an echo-Doppler system in the clinical setting. This method will increase the clinical usefulness of wave intensity.

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.

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

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 (R(2) = 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 (d P/d t) x (d U/d t) at any site of the circulation, where d P/d t and d U/d t 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. d P/d t) (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.

Subepicardial aneurysm after anticoagulant therapy for a mural thrombus following anterior myocardial infarction.

A subepicardial aneurysm became evident in a male patient after anticoagulant therapy. On admission, it appeared to be an old anterior infarction accompanied by a mural thrombus. After warfarin administration, the thrombus disappeared and an echo-free space emerged outside the apical myocardial wall. The echo-free space communicated with the left ventricular cavity through the apical myocardial wall. Emergency surgery was undertaken and the patient survived. The aneurysm was covered with epicardium and there was an endomyocardial rupture of the muscle in the apical wall, which was the entrance of the aneurysm. This case suggests that cautious follow-up with echocardiography is necessary when anticoagulant therapy is selected for thrombi following myocardial infarction.

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

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, W(1), occurs during early systole, the magnitude of which increases with increases in cardiac contractility. The second peak, W(2), 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 - W(1)) corresponds to the pre-ejection period, and that between the first and second peaks (W(1) - W(2)) corresponds to ejection time. We developed a new ultrasonic on-line system for obtaining WI and arterial stiffness (beta). The purpose of this study was (1) to report normal values of various indices derived from WI and beta 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 beta. We applied this method to the carotid artery in 135 normal subjects. The mean values of W(1), W(2), NA, R - W(1), and W(1) - W(2) were 8 940 +/- 3 790 mmHg m/s(3), 1 840 +/- 880 mmHg m/s(3), 27 +/- 13 mmHg m/s(2), 104 +/- 14 ms, and 270 +/- 19 ms, respectively. These values did not show a significant correlation with age. The mean value of beta 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 - W(1) and W(1) - W(2) 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 W(1) and beta was good: mCV for IA was less than 10%; CL for IE and IO were less than 17%. W(2) 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.