Doppler echocardiographic measurement of cardiac output using the mitral orifice method

Quantitative Doppler-Echocardiographic Determination of Regurgitant Volume in Patients with Aortic Insufficiency

Background:

The severity of aortic regurgitation (AR) can be determined by invasive or echocardiographic methods. We systematically compared quantitative invasive and echocardiographic data with semiquantitative invasive grades in a prospective series of patients.

Methods:

Using Doppler-echocardiography we determined the cardiac output over the aortic, pulmonary and mitral valve in 27 patients (20 with, 7 without AR). Aortic regurgitant volume was calculated as the difference between the cardiac output over aortic and pulmonary valve/ mitral valve. During angiography the severity of AR was assessed semiquantitatively by aortography and the regurgitant volume was calculated invasively as the difference between the left- and right ventricular cardiac output.

Results:

The echocardiographically and invasively determined regurgitant blood volume correlated closely (R≈0.8). The regurgitant volume increased with higher angiographic grade but there was significant overlap between adjoining qualitative grades.

Conclusion:

In patients with AR, quantitative echocardiographic and angiographic measurements of the regurgitant volume correlate closely.

Measurement of Volumetric Flow by Real-time 3-Dimensional Doppler Echocardiography in Children

BACKGROUND

We sought to assess the accuracy and reproducibility of an automated real-time (RT) 3-dimensional (3D) Doppler echocardiography (RT3DDE) technique for measuring volumetric flow (VF) in children.

METHODS

A total of 19 healthy children (age = 11.5 +/- 3.5 years) were studied to measure VF through mitral valve (MV), aortic valve (AV), pulmonary valve (PV), and tricuspid valve (TV) by RT3DDE. RT 3D echocardiography was also performed to measure left ventricular (LV) end-systolic volume, LV end-diastolic volume, and stroke volume (stroke volume = LV end-diastolic volume--LV end-systolic volume), which served as a reference standard for comparison with VF by RT3DDE.

RESULTS

Compared with stroke volume by RT 3D echocardiography, the correlation with VF was excellent for MV (r = 0.91), good for AV (r = 0.89) and PV (r = 0.89), but poor for TV (r = 0.20) by RT3DDE. There were good agreements for AV (bias = 0.9 +/- 5.0 mL), PV (bias = -0.4 +/- 5.7 mL), and MV (bias = 4.1 +/- 4.7 mL), and marked underestimation for TV (bias = -24.4 +/- 14.6 mL).

CONCLUSIONS

Our data demonstrated that VF measurement by RT3DDE is feasible and reasonably accurate for MV, AV, and PV but problematic for TV.

A real-time 3-dimensional digital Doppler method for measurement of flow rate and volume through mitral valve in children: A validation study compared with magnetic resonance imaging

We developed and assessed a real-time 3-dimensional (3D) digital Doppler method for measurement of flow volumes through the mitral valve in children. A total of 13 children (aged 10.46 +/- 2.5 years; 8 boys/5 girls) were enrolled. An ultrasound system (Sonos 7500, Philips, Andover, Mass) was used to acquire raw 3D velocity data for flow measurement based on Gaussian control surface theorem [flow (mL/s) = mean velocity x flow area]. Stroke volume (SV) measured by real-time 3D digital Doppler with the control surface at the mitral valve annulus or orifice was compared with the SV by phase velocity cine magnetic resonance imaging (MRI) at the ascending aorta and by left ventricular volumetric MRI measurement. The best correlation and agreement were seen at the mitral valve orifice by real-time 3D digital Doppler compared with SV by phase velocity cine MRI at the ascending aorta (r = 0.92, mean difference = -5.2 +/- 12.0 mL) and SV by left ventricular volumetric MRI measurement (r = 0.94, mean difference = -0.2 +/- 10.3 mL).

Results of the oxygen Fick method in a closed blood circulation model including "total arteriovenous diffusive shunt of oxygen"

It is considered that arteriovenous diffusive shunts of oxygen may cause inaccuracy of the oxygen Fick method as[Formula: see text] where[Formula: see text] is the pulmonary oxygen uptake,[Formula: see text] is the cardiac output, and CaO(2) and CvO(2) are the arterial and venous oxygen contents, respectively.A simple circulation model, including the whole circulation with nine well-mixed compartments (C1, ... C9), is constructed: the[Formula: see text] is assigned as constant as 6000 ml min(-1); the blood portions of 60 ml move at an interval of 600 ms. C1 and C2 compartments, each having 60 ml volume, represent the blood of pulmonary microcirculation, C3 represents the arterial blood with a volume of 1500 ml, C4, ..., C8, each also having a volume of 60 ml, represent the blood of peripheral microcirculation, whereas C9 represents the venous blood with a volume of 3000 ml. The pulmonary oxygen uptake[Formula: see text], related to C1 and C2, the oxygen release[Formula: see text], related to C4,...,C8, as well as a "total arteriovenous diffusive shunt of oxygen"[Formula: see text], from the arterial blood (C3) to the venous blood (C9), are calculated simultaneously. The alveolar gas has a constant oxygen partial pressure, and the pulmonary diffusion capacity is also constant; similar to modeling the pulmonry, oxygen diffusion, constant partial oxygen pressures for all peripheral tissues as well as constant diffusion capacities for all peripheral oxygen diffusion are also assigned. The diffusion capacities for the[Formula: see text] (between C3 and C9) are arbitrarily assigned.The Fick method gives incorrect results depending on the total arteriovenous diffusive shunt of oxygen[Formula: see text]. But the mechanism determining the magnitude of[Formula: see text] remains unclear.

Direct quantification of transmitral flow volume with dynamic 3-dimensional digital color Doppler: a validation study in an animal model

Accurately quantifying transmitral flow volume is clinically important not only as a measure of cardiac output, but also as a value from which to subtract aortic flow, for determining the severity of mitral regurgitation. However, controversy exists over the accuracy of pulsed Doppler for mitral flow quantification because of the complexity of mitral flow geometry and dynamic changes in flow profile and flow area. To explore the feasibility of directly quantifying transmitral flow volume with a newly developed dynamic 3-dimensional digital color Doppler technique, this in vivo experimental study was conducted to validate the method. Eight open chest sheep were imaged with a multiplane transesophageal (TEE) probe placed on the heart for digital 3-dimensional gated acquisition of mitral inflow over a 180-degree acquisition. The digital velocity data were contour detected for flow area after computing the velocity vectors and flow profile perpendicular to a spherical 3-dimensional surface across the mitral annulus. Flow areas and actual velocities were then integrated in time and space and the resulting flow volumes were compared with those obtained by a reference electromagnetic flowmeter on the aorta for 26 steady hemodynamic states. The flow volumes correlated closely to the electromagnetic references (y = 0.87x + 2.49, r = 0.92, SEE = 1.9 Ml per beat). Our study shows that transmitral flow volume can be accurately determined in vivo by this dynamic 3-dimensional digital color Doppler flow quantification method.

Assessment of ventricular filling volumes with an automated color Doppler method: validation in a pulsatile flow model

OBJECTIVE

Determination of ventricular filling volumes with the use of Doppler echocardiographic measurements critically depends on the presence of a circular-shaped flow area and a flat velocity profile across it because evaluation of flow volume is usually based on echocardiographic measurements of its diameter and pulsed Doppler recordings within the center of this area. The approach may be limited at the mitral and tricuspid ring levels as a result of their noncircular shape and because nonflat velocity profiles are present. The purpose of this study was to examine in a pulsatile flow model simulating ventricular inflow conditions the accuracy of an automated method based on the analysis of color Doppler flow velocities for evaluation of flow volumes.

MATERIALS AND METHODS

A recently-developed automated Doppler method that takes into account the velocity distribution across a region of interest was examined in a pulsatile flow model by using flows with waveforms characteristic for ventricular inflow through tubes with elliptically-shaped cross-sectional areas. Color Doppler imaging was performed against flow direction along the major and minor axes of the tubes with major diameters ranging between 3 and 5 cm and major-to-minor diameter ratios of 1.5 and 2.0.

RESULTS

A close correlation was found between flow volumes measured by the Doppler technique for registrations along the minor or major axis of the ellipses and actual values (r = 0.99, standard error of the estimate = 0.44 to 1.98 mL), with a systematic underestimation or overestimation, respectively, depending on the diameter ratio. Averaging of the data derived from 2 orthogonal measurements by using the geometric mean value yielded an excellent agreement between Doppler data and actual flow volumes.

CONCLUSION

This automated color Doppler method enables reliable determination of flow volumes in a pulsatile flow model simulating ventricular inflow conditions with the use of 2 orthogonal imaging views. The data indicate that the method may improve the noninvasive evaluation of ventricular filling volumes.

Comparative overview of cardiac output measurement methods: has impedance cardiography come of age?

Cardiac output, usually expressed as liters of blood ejected by the left ventricle per minute, is a fundamental measure of the adequacy of myocardial function to meet the perfusion needs of tissue at any time. Decreases in cardiac output over time (when cardiac output is measured under similar conditions) may signal myocardial functional deterioration and the onset or progression of heart failure. Conversely, improvements in cardiac output may indicate a positive response to medical therapy. However, most methods for evaluating cardiac output are technically demanding, require specialized training and specialized environments for measurement, and are costly. Therefore, most measurement techniques are impractical for routine evaluation of disease progression and/or response to treatment in the prevention and/or management of heart failure. This paper provides a comparative overview of commonly employed cardiac output measurement strategies with emphasis on developments in impedance cardiography which suggest that impedance cardiography has the potential to make routine assessment and trending of cardiac output a viable alternative to assist in the management of both chronically and acutely ill patients, including those with heart failure. (c)2000 by CHF, Inc.

An enhanced method for measuring cardiac output using Doppler color flow echocardiography

An enhanced method for determining cardiac output using Doppler color flow imaging techniques to measure mitral orifice diameter was developed and validated in an experimental model and in clinical patients. In an in vitro circuit model, color jet width correlated well with actual orifice dimension from 12 to 24 mm (r = 0.99). In the clinical application, mitral valve area was calculated as a X b X pi/4 where a and b represent the width of the color flow stream in the mitral orifice just distal to the annulus in apical long-axis (short-diameter) and 4-chamber (90 degrees rotated, long-diameter) views, respectively. Cardiac output was then computed as the product of mitral valve area and time-velocity integral of transmitral flow from the same site. Cardiac output was also measured by thermodilution and conventional echocardiographic methods using diameters and time-velocity integrals from the left ventricular outflow tract. In 30 patients with nonvalvular heart disease, cardiac output measured by thermodilution ranged from 3.40 to 8.40 L/min. Cardiac output was determined in 28 of 30 patients (93%) by the Doppler color flow imaging technique; it ranged from 3.00 to 8.36 L/min and correlated well with thermodilution: y = 0.90x + 0.63, r = 0.91. Cardiac output was determined in 24 of 30 patients by the conventional left ventricular outflow method (80%). The cardiac output measured by the conventional method correlated less closely with thermodilution (r = 0.84), although there was no statistical difference in correlation coefficiencies between the 2 methods. These results indicate that the Doppler color flow imaging technique can be used to enhance the determination of cardiac output by echocardiography, particularly when the conventional method has resulted in technically inadequate recordings.

Transgastric, pulsed Doppler echocardiographic determination of cardiac output

OBJECTIVE

The aim of this study was to evaluate the accuracy of cardiac output measurement with transesophageal echocardiography (TEE) using a transgastric, pulsed Doppler method in acutely ill patients.

DESIGN

Cardiac output was simultaneously measured by thermodilution (TD) and a transgastric, pulsed Doppler method.

SETTING

The study was carried out in a surgical intensive care unit as part of the management protocol of the patients.

PATIENTS

Thirty consecutive acutely ill patients with a Swan-Ganz catheter, mechanically ventilated, sedated and with a stable hemodynamic condition were included.

MEASUREMENTS

Pulsed Doppler TEE was performed using a transgastric approach in order to obtain a long axis view of the left ventricle. Cardiac output was calculated from the left ventricular outflow tract diameter, the velocity time integral of the blood flow profile and heart rate.

RESULTS

One patient was excluded because of the presence of aortic regurgitation and another, because of the impossibility of obtaining a transgastric view. Twenty-eight simultaneous measurements were performed in 28 patients. A clinically acceptable correlation and agreement were found between the two methods (Doppler cardiac output = 0.889 thermodilution cardiac output +0.74 l/min, r = 0.975, p <0.0001).

CONCLUSION

Transgastric pulsed Doppler measurement across the left ventricular outflow tract with TEE is a very feasible and clinically acceptable method for cardiac output measurement in acutely ill patients.

Multiplane transesophageal echocardiographic doppler imaging accurately determines cardiac output measurements in critically ill patients

OBJECTIVES

To compare cardiac output and stroke volume measured by multiplane transesophageal Doppler echocardiography with that measured by the thermodilution technique.

DESIGN

Prospective direct comparison of paired measurements by both techniques in each patient.

SETTING

Cardiac surgery and myocardial infarction intensive care units.

PATIENTS

Twenty-nine patients, mean age (+/- SD) 67 +/- 8 years. Nineteen had undergone open heart surgery and 10 had suffered acute myocardial infarction.

METHODS

Cardiac output and stroke volume were measured simultaneously by the thermodilution technique and multiplane transesophageal Doppler echocardiography via the transgastric view (119 +/- 8 degrees) with the sample volume positioned at the level of the left ventricular outflow tract.

RESULTS

Stroke volume and cardiac output measurements were obtained in 29 of 33 patients (88%). Mean values were 50 +/- 13 mL and 4.8 +/- 1.3 L/min by Doppler and 51 +/- 14 mL and 4.9 +/- 1.4 L/min by thermodilution (r = 0.90, r = 0.91, p < 0.001). The mean differences in values obtained with the two techniques were 1 +/- 6 mL (2 +/- 12%) and 0.1 +/- 0.7 L/min (2 +/- 12%).

CONCLUSIONS

Multiplane transesophageal echocardiography enhances the ability to estimate accurately cardiac output and stroke volume by providing new access to left ventricular outflow tract in critically ill patients.

Proximal jet size by Doppler color flow mapping predicts severity of mitral regurgitation. Clinical studies

BACKGROUND

Recent studies have shown that many instrument and physiological factors limit the ability of color Doppler total jet area within the receiving chamber to predict the severity of valvular regurgitation. In contrast, the proximal or initial dimensions of the jet as it emerges from the orifice have been shown to increase directly with orifice size and to correlate well with the severity of aortic insufficiency. Only limited data, however, are available regarding the value of proximal jet size in mitral regurgitation, and it has not been examined in short-axis or transthoracic views. The purpose of the present study, therefore, was to evaluate the relation between proximal jet size and other measures of the severity of mitral regurgitation.

METHODS AND RESULTS

In 49 patients, the anteroposterior height of the proximal jet as it emerges from the mitral valve was measured in the parasternal long-axis view; proximal jet width and area were measured in the short-axis view at the same level. Results were compared with regurgitant volume and fraction by pulsed Doppler subtraction of aortic and mitral flows in 47 patients without more than trace aortic insufficiency; with angiographic grade determined within 24 hours in 33 catheterized patients; and with angiographic regurgitant fraction in 13 patients who were in normal sinus rhythm and had no significant aortic and tricuspid insufficiency. Proximal jet height, width, and area correlated well with Doppler regurgitant volume and fraction (r = .86 to .95; SEE = 7.7 to 9.0 mL; 5.9% to 7.3%). Proximal jet size could also be used to distinguish angiographic grades of mitral regurgitation with minimal overlap (P < .0001) and correlated well with angiographic regurgitant fraction (r = .85 to .91; SEE = 4.1% to 5.1%).

CONCLUSIONS

Proximal jet size correlates well with established measures of the severity of mitral regurgitation. It is conveniently available with transthoracic clinical scanning and should be useful in the routine evaluation of patients with mitral regurgitation.

Two-dimensional mitral flow velocity profiles in pig models using epicardial Doppler echocardiography

OBJECTIVES

This study investigated the velocity distribution across the natural mitral valve.

BACKGROUND

Information about the blood velocity distribution across the mitral valve is of interest in basic fluid dynamic studies of the natural mitral valve and is needed for precise cardiac output estimates by Doppler echocardiography.

METHODS

The velocity distribution across the mitral valve was measured by epicardial Doppler echocardiography in ten 90-kg anesthetized pigs. By rotating the ultrasound transducer in 30 degrees intervals from the apical position, we constructed two-dimensional velocity profiles across the left ventricular inflow tract from diameters from each rotation arranged around a reference point. The time-averaged mitral velocity profile was calculated to estimate the error in cardiac output calculations that may occur with pulsed Doppler ultrasound when a single sample volume is used to record the mean velocity across the mitral orifice.

RESULTS

The time-averaged diastolic cross-sectional mitral velocity profiles at the level of the mitral annulus and leaflet tips were variably skewed because of the development of a large anterior vortex in the left ventricle during the deceleration of early diastolic inflow and atrial systole. The ratio of the time-velocity integral of the center sample volume to the spatially averaged time-velocity integral was 1.13 +/- 0.15 (mean +/- SD) (range 0.80 to 1.32). Using regression analysis, we found a correlation between the degree of nonuniformity of the cross-sectional velocity distribution and the peak velocity of the anterior vortex (r = 0.65, p < 0.01).

CONCLUSIONS

The assumption of a flat mean velocity profile across the mitral valve can introduce errors of +13 +/- 15% (mean +/- SD) in cardiac output measured with pulsed Doppler ultrasound when one is interrogating a single center sample volume.

A new integrated system for three-dimensional echocardiographic reconstruction: development and validation for ventricular volume with application in human subjects

OBJECTIVES

The purpose of this study was to improve three-dimensional echocardiographic reconstruction by developing an automated mechanism for integrating spark gap locating data with corresponding images in real time and to validate use of this mechanism for the measurement of left ventricular volume.

BACKGROUND

Initial approaches to three-dimensional echocardiographic reconstruction were often limited by inefficient reconstructive processes requiring manual coordination of two-dimensional images and corresponding spatial locating data.

METHODS

In this system, a single computer overlays the binary-encoded positional data on the two-dimensional echocardiographic image, which is then recorded on videotape. The same system allows images to be digitized, traced, analyzed and displayed in three dimensions. This system was validated by using it to reconstruct 11 ventricular phantoms (19 to 271 ml) and 11 gel-filled excised ventricles (21 to 236 ml) imaged in intersecting long- and short-axis views and by apical rotation. To measure cavity volume, a surface was generated by an algorithm that takes advantage of the full three-dimensional data set.

RESULTS

Reconstructed cavity volumes agreed well with actual values: y = 0.96x + 2.2 for the ventricular phantoms in long- and short-axis views (r = 0.99, SEE = 2.7 ml); y = 0.95x + 2.9 for the phantoms, reconstructed by apical rotation (r = 0.99, SEE = 2.7 ml); and y = 0.99x + 0.11 ml for the excised ventricles (reconstructed in long- and short-axis views; r = 0.99, SEE = 5.9 ml). The mean difference between three-dimensional and actual volumes was 3% of the mean (3.0 ml) for the phantoms and 6% (4.6 ml) for the excised ventricles. Observer variability was 2.3% for the phantoms and 5.6% for the excised ventricles. Application to 14 normal subjects demonstrated feasibility of left ventricular reconstruction, which provided values for stroke volume that agreed well with an independent Doppler measure (y = 0.97x + 0.94; r = 0.95, SEE = 3.2 ml), with an observer variability of 4.9% (2.4 ml).

CONCLUSIONS

A system has therefore been developed that automatically integrates locating and imaging data in no more time than the component two-dimensional echocardiographic scans. This system can accurately reconstruct ventricular volumes in vitro over a wide range and is feasible in vivo, thus laying the foundation for further applications. It has increased the efficiency of three-dimensional reconstruction and enhanced our ability to address clinical and research questions with this technique.

Quantitative Doppler assessment of valvular regurgitation

BACKGROUND

Quantitation of valvular regurgitation remains a challenge. The accuracy of quantitative Doppler is controversial, and its ability to measure regurgitant volume is unknown; therefore, it is not widely used.

METHODS AND RESULTS

In 120 patients (20 without regurgitation, 19 with aortic regurgitation, and 81 with mitral regurgitation), the stroke volume through the mitral annulus and left ventricular outflow tract were measured using pulsed-wave Doppler concurrently with left ventricular stroke volume calculated using left ventricular volumes measured by two-dimensional echocardiography Simpson's biapical method. Regurgitant volume and fraction were thus computed using Doppler or ventricular methods. In normal patients there were good correlations between Doppler and left ventricular measurements of stroke volume. Doppler regurgitant volume and fraction were 4.4 +/- 4.4 mL and 5.3 +/- 4.5%, respectively. In patients with aortic regurgitation, there were good correlations between Doppler and left ventricular measurements of stroke volume, regurgitant volume, and regurgitant fraction (r = 0.97, r = 0.95, and r = 0.93, respectively; p < 0.0001). In patients with mitral regurgitation, despite good correlations between Doppler and ventricular methods for stroke volume, regurgitant volume, and regurgitant fraction (r = 0.94, r = 0.93, and r = 0.94, respectively; p < 0.001), these variables were overestimated by Doppler. However, in the last 54 patients compared with the first 27, overestimation decreased significantly for regurgitant volume (5 +/- 10 mL versus 18 +/- 27 mL, p < 0.05) and regurgitant fraction (3.3 +/- 6.7% versus 6.2 +/- 6.8%, p = 0.05).

CONCLUSIONS

Quantitative Doppler can be performed in large numbers of patients in a clinical laboratory. Its potential limitation was identified as overestimation of mitral regurgitation, which is overcome with increased experience. Its achieved accuracy in mitral and aortic regurgitation allows measurement not only of regurgitant fraction but most importantly of regurgitant volume.

Cross-sectional early mitral flow-velocity profiles from color Doppler in patients with mitral valve disease

BACKGROUND

Cross-sectional flow-velocity profiles from early mitral flow in 20 patients (10 with mitral regurgitation and 10 with mitral stenosis) were constructed from the velocity data from each point in sequentially delayed two-dimensional digital Doppler ultrasound maps.

METHODS AND RESULTS

The data suggested that the early mitral flow studied in an apical four-chamber view was variably skewed in both patient groups. The maximum flow velocity overestimated the cross-sectional mean velocity at the same time by a factor of 1.12-1.86. The maximum time-velocity integral was 1.13-1.77-fold greater than the cross-sectional mean time-velocity integral. In patients with mitral regurgitation, the cross-sectional flow-velocity profile appeared to be most skewed at the level of the mitral leaflet tips. The level of the mitral annulus appeared to give the most homogenous flow-velocity distribution in both patient groups.

CONCLUSIONS

When calculations of volume flow are based on pulsed Doppler ultrasound recordings with a single sample volume, the possibility of a skewed flow-velocity profile must be taken into account.

Impact of changes in heart rate and stroke volume on the cross sectional flow velocity distribution of diastolic mitral blood flow. A study on 6 patients with pacemakers programmed at different heart rates

The effect of changes in stroke volume on the cross sectional velocity distribution in the mitral orifice during passive mitral inflow was studied in six patients with total atrioventricular block, atrial fibrillation and VVI pacemakers during periods with different heart rates. The time velocity integrals recorded both in the left ventricular outflow tract and at the mitral orifice decreased significantly as the heart rate was increased from 60 to 80 and from 80 to 100 beats per minute. Instantaneous cross sectional flow velocity profiles were constructed by time interpolation of the velocity data from each point in sequentially delayed two dimensional digital ultrasound maps. Each patient had a characteristic cross sectional flow velocity profile in the mitral orifice recorded at the level of the leaflet tips in a four chamber view. The velocity profiles varied between the patients. With increase in heart rate only minimal changes in the flow profiles from individual patients were seen. The maximum velocity through the mitral orifice overestimated the cross sectional mean velocity at the same time by a factor of 1.4-1.9. The maximum time velocity integral overestimated the cross sectional mean by a factor of 1.4-1.8. The observed cross sectional skew varied between patients but did not change significantly with increasing heart rate and decrease in stroke volume.

Comparative accuracy of Doppler echocardiographic methods for clinical stroke volume determination

Numerous Doppler echocardiographic methods to measure stroke volume have been proposed in experimental or clinical studies, but their relative accuracy in patients compared with an invasive reference standard remains uncertain. Accordingly, we compared Doppler with thermodilution stroke volume measurement in 18 hospitalized patients, 16 with an acute manifestation of coronary artery disease and two with chronic cardiomyopathies. Doppler time-velocity integrals were measured by darkest line (modal velocity) and the leading edge (maximal velocity) techniques at the aortic annular plane, the mitral orifice, and the mitral annular plane. Two-dimensional echocardiography was used to measure cross-sectional areas (M-mode-corrected at the mitral orifice). The combination of aortic annular cross-sectional area and the leading edge technique of measuring the time-velocity integral of blood flow at this site provided the most accurate measure of stroke volume (r = 0.87, p less than 0.0001, standard error of estimate = 11 cm3; mean difference from thermodilution = 2.8 ml +/- 8.9 ml, p = NS). It also resulted in the most accurate measurement of cardiac output (r = 0.88, p less than 0.0003; mean difference from thermodilution = 0.11 L/min +/- 0.69 L/min, p = NS). Other methods yielded values that correlated less closely and deviated systematically from thermodilution measurements. We therefore conclude that of the six common methods evaluated, the aortic annular leading edge method measures stroke volume with the best accuracy and is most suitable for clinical application.

Left ventricular filling at elevated diastolic pressures: relationship between transmitral Doppler flow velocities and atrial contribution

The relationship between transmitral Doppler blood flow velocities and atrial contribution to left ventricular (LV) filling was investigated in seven open-chest dogs. At LV filling pressures greater than 15 to 20 mm Hg, LV volume approaches a maximum. Thus we hypothesized that when LV pressure before the onset of atrial systole exceeds this level, the atrial contribution would decrease and the ratio between peak early (E) and atrial-induced (A) mitral velocities would increase. Atrial contribution was measured as LV diameter increase during atrial contraction expressed as a percentage of the total LV diameter change during diastole (sonomicrometry). When left ventricular end-diastolic pressure (LVEDP) was progressively increased from 10 +/- 1 (mean +/- standard deviation) to 28 +/- 3 mm Hg by intravenous saline solution, the atrial contribution decreased from 34 +/- 14% to 8 +/- 10% (p less than 0.001). Concomitantly the A velocity decreased from 39 +/- 7 to 24 +/- 8 cm.sec-1 (p less than 0.01), and the E/A ratio increased from 1.8 +/- 0.3 to 3.6 +/- 1.5 (p less than 0.001). The E/A ratio and the atrial contribution were constant until LVEDP exceeded 17 to 20 mm Hg, at which level marked changes in both parameters were noted. Thus when LV filling pressure was increased, the E/A ratio increased, indicating a filling shift towards early diastole. The reduced atrial contribution during increased preload was explained by the curvilinear shape of the LV pressure-volume curve. At markedly elevated filling pressures, near-maximum LV diameter was achieved before atrial contraction; hence the atrial contribution decreased and the E/A ratio increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-invasive determination of cardiac output by Doppler echocardiography and electrical bioimpedance

Cardiac output measured by thermodilution in 25 patients within 24 hours of acute myocardial infarction was compared with cardiac output measured by Doppler echocardiography (24 patients) and electrical bioimpedance (25 patients). The mean (range) cardiac outputs measured by Doppler (4.03 (2.2-6.0) 1/min) and electrical bioimpedance (3.79 (1.1-6.2) 1/min) were similar to the mean thermodilution value (3.95 (2.1-6.2) 1/min). Both non-invasive techniques agreed closely with thermodilution in most patients. None the less, three results with each method disagreed with thermodilution by more than 1 1/min. Both non-invasive techniques were reproducible and accurate in most patients with acute myocardial infarction. Doppler echocardiography was time consuming and technically demanding. Electrical bioimpedance was simple to use and had the additional advantage of allowing continuous monitoring of the cardiac output.

Cross sectional early mitral flow velocity profiles from colour Doppler

Instantaneous cross sectional flow velocity profiles from early mitral flow in 10 healthy men were constructed by time interpolation of the velocity data from each point in sequentially delayed two dimensional digital Doppler ultrasound maps. This interpolation allows correction of the artificially produced skewness of velocities across the flow sector caused by the time taken to scan the flow sector for velocity recording of pulsatile blood flow. These results suggested that early mitral flow studied in an apical four chamber view is variably skewed both at the leaflet tips and at the annulus. The maximum flow velocity overestimated the cross sectional mean velocity at the same time by a factor of 1.2-2.2. Also the maximum time velocity integral overestimated the cross sectional mean time velocity integral to the same extent. This cross sectional skew must be taken into account when calculation of blood flow is based on recordings with pulsed wave Doppler ultrasound from a single sample volume.

Age-dependency of left ventricular filling dynamics and relaxation as assessed by pulsed Doppler echocardiography

Left ventricular diastolic function was assessed from transmitral flow velocity curves as measured by Doppler echocardiography in healthy individuals aged 21-69 years, each decade comprising 12 subjects. By ageing, progressive changes in the various filling parameters were observed. When comparing the youngest and oldest age groups, the ratio between peak velocities in early and late diastole decreased from 2.0 +/- 0.3 to 1.2 +/- 0.3 (P less than 0.001). The filling fraction of first third of diastole decreased from 54 +/- 5% to 45 +/- 4% (P less than 0.001). Isovolumic relaxation time increased from 61 +/- 11 ms to 77 +/- 12 ms (P less than 0.01). Correlation coefficients of velocity ratio, filling fraction and isovolumic relaxation time vs. age were r = -0.71 (P less than 0.001), r = -0.56 (P less than 0.001) and r = 0.44 (P less than 0.001), respectively. When isovolumic relaxation time and age were used together in multivariate regression analysis, only age was an independent predictor of velocity ratio and filling fraction. Stroke volume, peak velocity in left ventricular outflow tract, heart rate and systolic blood pressure were similar in all age groups. Thus, velocity ratio and filling fraction indicated a relative filling shift towards late diastole by ageing and were more sensitive than systolic parameters in reflecting age-related changes in cardiac function. The changes could be explained neither by delayed relaxation nor by change in systolic parameters. When using Doppler echocardiography for evaluation of left ventricular filling, age-matching of reference groups is necessary.

Effects of verapamil on left ventricular relaxation and filling dynamics in coronary artery disease: a study by pulsed Doppler echocardiography

The effect of verapamil on left ventricular diastolic function in coronary artery disease was assessed by Doppler echocardiography of transmitral flow velocities in 20 patients. At baseline, isovolumic relaxation time was prolonged compared with that in 18 age-matched normal subjects (95 +/- 13 msec versus 74 +/- 12 msec, p less than 0.001), but decreased to 80 +/- 14 msec (p less than 0.001) after treatment. The ratio between early and atrial-induced transmitral velocities (E/A-ratio) at baseline was lower in patients than in normal subjects (1.1 +/- 0.2 versus 1.4 +/- 0.3, p = 0.01), as was the filling fraction of the first third of diastole (43% +/- 5% versus 50% +/- 4%, p less than 0.001). Verapamil treatment increased the E/A-ratio to 1.3 +/- 0.4 (p less than 0.001) and filling fraction to 45% +/- 4% (p = 0.055) because of increased early filling. No change in systolic performance or heart rate was observed. Thus, coronary artery disease was associated with retarded relaxation and impairment of early filling. However, verapamil treatment enhanced relaxation and induced a filling shift toward early diastole, which indicated improved diastolic performance. The changes probably reflected reduced myocardial ischemia.

Calculation of transmitral flow by Doppler echocardiography: a comparison of methods in a canine model

Although several Doppler echocardiographic methods for measuring transmitral flow have been described, the optimal method for calculation of flow remains unclear. Seven time/shape combinations were tested in an experimental preparation in which mitral flow could be precisely controlled and measured. Annular shape was considered to be either circular or elliptical, and the mitral orifice area was calculated from the anteroposterior and/or the mediolateral dimension(s) recorded at early and middiastole. In addition the orifice area was calculated from the maximal mitral leaflet area corrected for diastolic variation. Transmitral flow ranged between 0.4 and 4.6 L/min. Good correlations with measured transmitral flow (r = 0.83 to 0.92) were observed for all methods of calculating the mitral orifice area. Methods that assumed a circular geometry and used the mediolateral annular diameter overestimated flow. Conversely, flows calculated by means of the anteroposterior diameter with the assumption of a circular anulus underestimated flow. The best approximations of transmitral flow were obtained with the assumption of an elliptical configuration that used measurements made in early diastole (Y = 1.04x + 0.2) and with the Fisher method (y = 0.94x + 0.08). Thus in the canine model approximation of the mitral orifice as an ellipse provides the most accurate measurement of transmitral flow.

Noninvasive evaluation of the ratio of pulmonary to systemic flow in ventricular septal defect by means of Doppler two-dimensional echocardiography

Left ventricular inflow volume (LVIV) and outflow volume (LVOV) were determined by pulsed Doppler echocardiography, and the ratio of pulmonary to systemic flow (Qp/Qs) was estimated as a ratio of LVIV to LVOV (LVIV/LVOV). Seventy-seven patients were studied, 47 control subjects and 30 patients with ventricular septal defect (VSD). LVOV was calculated from the left ventricular ejection flow velocity and left ventricular outflow tract diameter; LVIV was calculated from the transmitral flow velocity and mitral valve motion as traced by M-mode echocardiography. Cardiac input (COin) and cardiac output (COout) were calculated as the product of LVIV or LVOV and heart rate. Cardiac output was also determined by the dye dilution method (COdye) in control subjects. A close correlation was observed between COdye and COin (y = 1.18x - 243, r = 0.85, p less than 0.005, SEE = 1026 ml/min) and COdye and COout (y = 1.16x - 323, r = 0.90, p less than 0.005, SEE = 639 ml/min). LVIV and LVOV were highly correlated in control subjects (y = 0.95x + 5.3, r = 0.94, p less than 0.005, SEE = 6.6 ml). LVIV/LVOV was 0.97 +/- 0.1 (mean +/- SD) in control subjects, whereas LVIV/LVOV (1.87 +/- 0.88) was significantly higher in patients with VSD (p less than 0.01). In patients with VSD, LVIV/LVOV correlated with Qp/Qs determined invasively (y = 0.97, SEE = 0.23, n = 16). Thus with our method LVIV and COin can be accurately determined, and we suggest that Doppler-determined LVIV/LVOV is clinically useful for evaluating the shunt flow magnitude in VSD.

Limitations in assessing the severity of aortic stenosis by Doppler gradients

Continuous wave Doppler echocardiography was performed before cardiac catheterisation in 69 consecutive patients with suspected aortic stenosis. Agreement between the maximum and the mean Doppler gradients and catheterisation gradients was good. Doppler echocardiography, however, systematically underestimated the maximum and mean gradients, particularly in the high range. Stepwise regression analysis of the small pressure difference between the two methods showed that it could not be explained by age, sex, stroke volume, differences in heart rate, ejection fraction, the presence of coronary artery disease, or severity of aortic regurgitation. There was a negative curvilinear correlation between the maximum and mean Doppler gradients and the aortic valve areas that were measured at catheterisation in patients with pure aortic stenosis. The degree of correlation decreased when patients with concomitant aortic regurgitation were included. The scatter of gradients above and below the correlation line was large and this was caused by low and high transvalvar flow. These results show that the usefulness of Doppler gradients for judging the severity of aortic stenosis, both in relation to immediate diagnosis and follow up, is severely limited if transvalvar flow is not taken into account.

Differing mechanisms of exercise flow augmentation at the mitral and aortic valves

To determine the mechanisms by which blood flow increases across the mitral and aortic valves during exercise, 18 normal men were studied during graded supine and upright bicycle exercise at matched workloads. Mitral valve orifice and ascending aortic blood velocities were recorded by Doppler echocardiography during steady states at each stage of exercise. Parasternal two-dimensional echocardiographic imaging of the ascending aorta adjacent to the aortic valve orifice and the mitral valve orifice at the tips of the valve leaflets was used to calculate changes in cross-sectional area during exercise. Heart rate increased from rest to exercise from 67 to 150 beats/min (124%) during supine exercise and from 72 to 147 beats/min (104%) during upright exercise. Stroke volume increased 20% during supine and 46% during upright exercise; the increase in stroke volume was statistically significant when rest and exercise were compared and when the magnitude of change was compared vs position (p less than .05). The increase in stroke volume measured at the ascending aorta was accomplished by an increase in the velocity-time integral (+15% supine and +48% upright, p less than .05), with little change in aortic cross-sectional area (5% supine and 0% upright, p = NS). By contrast, the increase in flow rate measured at the mitral valve was predominantly due to an increase in mean diastolic cross-sectional area (+29% supine and 34% upright, p less than .05); the velocity-time integral did not increase significantly (-10% supine and 4% upright; p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler echocardiographic measurement of mitral flow volume: validation of a new method in adult patients

Instantaneous intracardiac flow volumes can be calculated as the product of instantaneous flow velocity and instantaneous orifice area. This was accounted for in a new method of measuring stroke volume and cardiac output in the mitral orifice by pulsed Doppler echocardiography. This method was compared with simultaneous thermodilution in 30 adult patients in sinus rhythm without substantial atrioventricular or pulmonary valve abnormalities. The mitral orifice was assimilated to a conduit with 1) an ellipse-shaped inlet and outlet, 2) the same (and constant) long axis for the inlet and outlet ellipses (that is, the mediolateral anulus diameter measured on apical four chamber views), and 3) a varying outlet short axis (that is, the mitral anteroposterior leaflet separation derived from left parasternal M-mode recordings). This method design avoided the need for a short-axis view of the whole circumference of the mitral outlet orifice, which is difficult to obtain in many adult patients. The mitral flow velocity was recorded from the apex under two-dimensional guidance, within the mitral canal, close to the outlet section. Integration of instantaneous mitral leaflet separation multiplied by instantaneous flow velocity was performed using Simpson's rule. In addition to the proposed "instantaneous orifice area" method (method A), a "mean orifice area" method (method B) was also compared with thermodilution. In this simplified method, mitral flow was the product of mean orifice area and the diastolic mitral velocity integral, both derived from the same recordings as for method A.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of sampling site and flow area on cardiac output measurements by Doppler echocardiography

In 40 patients cardiac output was simultaneously determined by pulsed Doppler echocardiography and thermodilution (range 4.0 to 10.2 liters/min). The sample volume was located in the center of the mitral anulus, at the tips of the mitral leaflets and in the center of the aortic anulus. Circular cross-sectional areas of the mitral anulus, aortic anulus and aortic bulbus were calculated from M-mode and two-dimensional echocardiographic diameters. The varying short axis of the elliptical mitral opening area was obtained from the diastolic leaflet separation in the M-mode, and the long axis was derived from the maximal mitral orifice area or mitral anulus diameter. Cardiac output was calculated by multiplying time-velocity integrals with the different areas and heart rate. Doppler flow measurements correlated significantly with the thermodilution method (r = 0.79 to 0.93). Flow measurements at the aortic anulus were most accurate (r = 0.93, SEE = 0.589 liter/min) if the annular area was derived from the M-mode tracing. Measurement of the anulus in the apical five chamber view yielded a significant underestimation and the area of the aortic bulbus provided an overestimation of cardiac output. Left ventricular inflow was underestimated at the mitral leaflet tips and overestimated at the mitral anulus. The accuracy of pulsed Doppler cardiac output measurements strongly depends on the assumed flow area and sampling site. Both should be determined at the same level in the inflow or outflow tract of the left ventricle. Measurement of cardiac output in the center of the aortic anulus provided the highest accuracy.

Reproducibility of cardiac stroke volume estimated by Doppler echocardiography

Doppler echocardiography was used to measure cardiac stroke volume in 10 patients with coronary artery disease who were treated with cardioactive drugs. Stroke volume estimates were determined at the aortic orifice by multiplying area by systolic velocity integral measured both from the suprasternal and the apical approach. Recordings were done independently by 2 experienced observers on the same day and repeated once after 1 to 21 days. Analysis of variance showed that no systematic differences were introduced by the 2 observers and Doppler approaches or by measuring on different days. The coefficient of variation between any pair of measurements in each patient was 9%. This variability is probably a result of the method or spontaneous fluctuations of the stroke volume and not of the varying recording conditions. The ultrasonic method detects day-to-day changes of cardiac stroke volume larger than 20% with a probability greater than 0.95.

Recommendations concerning use of echocardiography in hypertension and general population research

Use of echocardiography to quantify left ventricular structure and function requires standardization of recording conditions and techniques, accurate machine calibration, and definition of requirements for measurable images. Measurement of left ventricular muscle mass should use M-mode, two-dimensional, or three-dimensional echocardiographic methods that have been anatomically validated to maximize accuracy and comparability of results among studies. Body size and sex influence ventricular muscle mass sufficiently to be taken into account for clinical and research purposes, while age and physical activity are of less certain importance. Echocardiographic studies have clarified the prevalence of left ventricular hypertrophy in hypertensive patients and the effect of blood pressure during normal activity on left ventricular muscle mass, and they have provided data suggesting that left ventricular hypertrophy is a major cardiac risk factor in hypertensive and general populations. Further research is needed to obtain definitive results in these areas, to track the hitherto elusive transition from functionally compensated cardiac hypertrophy to congestive heart failure, and to determine the degree and selectivity of beneficial cardiac effects of antihypertensive treatment. Three-dimensional echocardiographic reconstruction and Doppler measurement of intracardiac blood flow and systemic hemodynamics are likely to extend the usefulness of echocardiography for hypertension and general population research.

Doppler determination of cardiac output in infants and children: comparison with simultaneous thermodilution

Ten children, aged six weeks to 13 years, without intracardiac shunts or lesions that could cause turbulent flow in the ascending aorta or aortic regurgitation, underwent cardiac catheterization, including cardiac output measurements by thermodilution. Simultaneously with each of six consecutive thermodilution injections, mean and maximal blood velocities in the ascending aorta were measured by pulsed Doppler echocardiography from the suprasternal notch. Aortic root and aortic orifice diameters were measured with M-mode and cross-sectional echocardiography. One patient had to be excluded from the analysis because of inadequate Doppler recordings. The best agreement with the results of the thermodilution was observed when internal systolic aortic root diameter was combined with mean velocity (r = 0.97, y = 0.90x + 0.28, SEE = 0.31 liters/min). When cardiac output was normalized for body size, there was still a good correlation between the results of these two methods.

Measurement of aortic regurgitation by Doppler echocardiography

In an attempt to develop a new approach to the non-invasive measurement of aortic regurgitation, transmitral volumetric flow (MF) and left ventricular total stroke volume (SV) were measured by Doppler and cross sectional echocardiography in 23 patients without aortic valve disease (group A) and in 26 patients with aortic regurgitation (group B). The transmitral volumetric flow was obtained by multiplying the corrected mitral orifice area by the diastolic velocity integral, and the left ventricular total stroke volume was derived by subtracting the left ventricular end systolic volume from the end diastolic volume. The aortic regurgitant fraction (RF) was calculated as: RF = 1 - MF/SV. In group A there was a close agreement between the transmitral volumetric flow and the left ventricular total stroke volume, and the difference between the two measurements did not differ significantly from zero. In group B the left ventricular total stroke volume was significantly larger than the transmitral volumetric flow, and there was good agreement between the regurgitant fractions determined by Doppler echocardiography and radionuclide ventriculography. Discrepancies between the two techniques were found in patients with combined aortic and mitral regurgitation or a low angiographic left ventricular ejection fraction (less than 35%). The effective cardiac output measured by Doppler echocardiography accorded well with that measured by the Fick method. Doppler echocardiography provides a new and promising approach to the non-invasive measurement of aortic regurgitation.

A comparison of information obtained by ultrasound examination and cardiac catheterisation in paediatric patients with congenital heart disease

Fifty-eight paediatric patients were studied by cross-sectional echocardiography and pulsed Doppler ultrasound in a blind fashion. The information obtained was compared with data collected at cardiac catheterisation. The correct anatomical diagnosis was made by ultrasound in almost all cases but in 11 patients the diagnosis was incomplete or incorrect. Flow measurements made at the tricuspid valve, the pulmonary trunk and the ascending aorta using pulsed Doppler ultrasound correlated well with Fick measurements (r greater than 0.9 at all three sites). The correlation of pressure gradients by the two methods was 0.94. Measurement of the time to peak velocity in the pulmonary trunk provided a method for the identification of patients with elevated pulmonary pressure but the relationship with measured pressures was not sufficiently strong to provide a high degree of reliability.

Measurement of mitral regurgitation by Doppler echocardiography

In an attempt to develop a new approach to the non-invasive measurement of mitral regurgitation, Doppler echocardiography and left ventriculography were performed in 20 patients without valvar heart disease (group A) and in 30 patients with pure mitral regurgitation (group B). Volumetric flows through the aortic and the mitral orifices were determined by Doppler echocardiography. Aortic flow (AF) was calculated as the product of the aortic orifice area and the systolic velocity integral. The mitral flow (MF) was calculated as the product of the corrected mitral orifice area and the diastolic velocity integral. The mitral regurgitant fraction (RF) was calculated as RF = 1 - AF/MF. In group A aortic and mitral flow were very similar and the difference between the two did not differ significantly from zero. In group B the mitral flow was significantly larger than the aortic flow. There was a good correlation (r = 0.82) between the regurgitant fraction determined by Doppler echocardiography and the regurgitant grades determined by left ventriculography. The regurgitant fraction increased significantly with each grade of severity. These results show that Doppler echocardiography can be used to give a reliable measure of both aortic and mitral flow. This technique is a new and promising approach to the non-invasive measurement of mitral regurgitation.