Noninvasive measurement of cardiac output using two-dimensional Doppler echocardiography and analysis of sources of error

The purpose of this study was (1) to analyze the factors responsible for errors in the two-dimensional Doppler echographic measurements of cardiac output (C.O.) and (2) to establish a noninvasive method for measuring C.O. The subjects were 50 cardiac patients who had neither aortic valve disease nor intracardiac shunts. The C.O. was calculated using the following formula: C.O. (l/min) = mean flow velocity (cm/sec) x pi(aortic ring diameter/2)2 (cm2) x 60/10(3) Left ventricular ejection flow velocity was recorded in the center of the aortic ring from the apical approach. Mean velocity was calculated by integration of instantaneous mean velocity in the ejection phase divided by the cardiac cycle length, and was corrected by the Doppler incident angle. The inner diameter of the aortic ring was measured in the parasternal long-axis view at the time of the maximum ejection flow velocity. The following results were obtained: 1. Sources of error in the measurement of cardiac output. 1) Accuracy of instantaneous mean velocity calculating circuit: This calculating circuit was accurate in model experiments using pulsatile flow. 2) Effect of high-pass filter: In model circuits, application of high-pass filter overestimated flow velocity. The higher the cut-off frequency of the high-pass filter, the larger the overestimation. This was probably due to the parabolic flow velocity profile in the circuit. 3) Flow velocity profile in the aortic ring: The flow velocity profile seemed to be flat in the aortic ring except near the anterior aortic wall. Therefore, the effect of the high-pass filter was considered to be negligible in case of clinical application. 4) The effects of shift and size of sample volume: The location of sample volume relative to the aortic valve ring shifted about 7 mm during systole. However, the shift and size of sample volume seemed to have little effect on the measured C.O., because the flow velocity profile was nearly flat in the aortic ring. 5) Ultrasound beam incident angle: From a practical viewpoint, it was necessary to set an incident angle of less than 50 degrees for minimizing the error. We were able to set the angle within 50 degrees in all but one of patients. 6) Diameter of the aortic ring: Two-dimensional echographic measurement of the aortic ring diameter was not so accurate; it seemed to become a major source of error in the calculation of C.O.(ABSTRACT TRUNCATED AT 400 WORDS)     

Noninvasive measurement of cardiac output by pulsed Doppler echocardiography. Correlation with thermodilution

Cardiac output was measured simultaneously by pulsed Doppler echocardiography and thermodilution in 22 patients, 18 of whom also underwent atrial pacing at different rates to give a total of 42 different measurements. The aortic diameter was measured firstly at the aortic ring at the level of insertion of the aortic cusps and then at the point of maximum separation of the valve cups in the left parasternal long-axis view. The aortic velocities were recorded in the apical 5-chamber view immediately below the level of the aortic valve. The correlations obtained at the aortic ring (R1) and at the point of maximum separation of the valve cusps (R2) were 0.77 (y = 0.67x + 1.17: standard error = 0.81 l/m) and 0.64 (y = 0.56x + 0.87; standard error = 1.01 l/mn) respectively. The correlations were much better when 7 technically unsatisfactory measurements were excluded (R2 = 0.76: y = 0.59x + 0.74: standard error = 0.79 l/mn) (R1 = 0.87: y = 0.72x + 1.04: standard error = 0.65 l/mn). THe correlations of stroke volume measured at aortic ring level also improved from r = 0.82 (y = 0.75x + 7.29: standard error = 8.9 ml) to r = 0.89 (y = 0.78x + 7.38: standard error = 7.3 ml). The measurement of cardiac output by pulsed Doppler echocardiography in the aortic root seems to be reliable. The correlations of the values of stroke volume and cardiac output with the thermodilution method are good, allowing detection of beat-to-beat variations of cardiac output, in suitable patients in the hands of experienced operators.     

Determination of cardiac output by transcutaneous continuous-wave ultrasonic Doppler computer

To evaluate the accuracy of a new, portable, continuous-wave Doppler computer (Ultracom) in measuring cardiac output (CO), simultaneous thermodilution CO and Doppler CO were measured in triplicate in 39 selected patients. Technically adequate Doppler CO studies were obtained in 36 patients. Aortic root diameter was measured by echocardiography and the cross-sectional area was calculated. A continuous-wave Doppler transducer was placed in the suprasternal notch, directed toward the ascending aorta and angled until the maximal velocity signal was achieved. The systolic velocity integral was computed using fast Fourier transform technique. The Doppler CO was computed from the equation: CO = aortic cross-sectional area X systolic velocity integral X heart rate. Interobserver and intraobserver variability studies were also performed. CO measured by thermodilution ranged from 1.86 to 10.1 liters/min (mean 5.26 +/- 1.91 [+/- standard deviation]) and CO by the Doppler method ranged from 1.63 to 10.9 liters/min (mean 5.32 +/- 1.83). The correlation coefficient was 0.97 (p less than 0.001) and standard error of the estimate was 0.42. The regression equation showed that Doppler CO = 0.408 + 0.93 X thermodilution CO. The correlation in 29 volunteers for interobserver variability was 0.98 (p less than 0.001) and in 18 volunteers for intraobserver variability was 0.97 (p less than 0.001). Thus, CO can be determined accurately in many patients using this Doppler technique by trained and experienced persons; intra- and interobserver variability is small.     

Doppler echocardiographic measurement of cardiac output using the mitral orifice method

Cardiac output was determined in 20 patients with various cardiac conditions by measuring the cross sectional area of the mitral orifice by echocardiography and the transmitral flow by the Doppler technique. Cardiac output was calculated by multiplying the corrected mitral orifice area by the maximum diastolic velocity integral recorded by the pulsed mode. The results were compared with that obtained by the Fick method. The correlation for cardiac output by the two techniques was high in the whole group, particularly in patients without mitral regurgitation. There was also a good correlation for stroke volume determined by the two methods. Cardiac output was significantly overestimated by the continuous mode and in patients with mitral regurgitation. These results show that the mitral orifice method provides a new and reliable approach to the non-invasive measurement of cardiac output.     

Transesophageal Doppler echocardiographic measurement of cardiac output using mitral anulus method

The method of measuring cardiac output with transesophageal pulsed Doppler two-dimensional echocardiography was developed and validated by comparison with the thermodilution technique in 65 adult patients. With the use of transesophageal four-chamber view, the Doppler sample volume was placed in the center of the mitral ring and the mitral flow velocity-time integral was obtained through planimetric measurements of the mitral flow velocity curve. The diameter of the mitral valve anulus was measured at the time of peak rapid filling flow velocity, and the cross-sectional area of the mitral valve anulus was calculated, assuming a circular shape. Doppler-determined cardiac output was calculated by using the following formula: Cardiac output [1.min-1] = pi (D [cm] /2)2.MFVI [cm].heart rate [bpm].10(-3), where MFVI is mitral flow velocity-time integral, and D is the diameter of the mitral valve anulus. There was a weak correlation between thermodilution and Doppler measurements of cardiac output (r = 0.64, p less than 0.01), while a good correlation was observed between percent changes in thermodilution-derived cardiac output and those in Doppler-determined cardiac output (r = 0.92, p less than 0.01) during different loading conditions. It has been suggested that this method may be useful for assessing relative changes in cardiac output during short time periods.     

Changes in cardiac output determined by continuous-wave Doppler echocardiography during propafenone or mexiletine drug testing

Antiarrhythmic drugs may induce congestive heart failure in patients with malignant ventricular arrhythmias and depressed left ventricular (LV) function. Whether Doppler echocardiography can detect drug-induced depression in LV function was assessed. Continuous-wave Doppler measurements of ascending aortic blood flow velocity were obtained in 16 patients while not receiving antiarrhythmic drugs on 2 consecutive days to assess day-to-day variability, as well as while receiving maximally tolerated oral doses of mexiletine (11 patients) and propafenone (9 patients). While receiving propafenone, a drug with moderate negative inotropic activity, peak flow velocity declined by 9 +/- 8% (p less than 0.05), the flow velocity integral (termed stroke distance, representing stroke volume) declined by 8 +/- 11% (p less than 0.10), the rate-corrected stroke distance declined by 9 +/- 8% (p less than 0.02) and the minute distance, representing cardiac output, declined by 10 +/- 12% (p less than 0.05). In contrast, while receiving mexiletine, a drug with minimal negative inotropic activity, none of these parameters changed significantly. Five of 9 patients (56%) treated with propafenone showed a decline in rate-corrected stroke distance exceeding the 95% confidence limit of day-to-day variability, which was +/- 13 percent. Two of these 5 patients developed clinical signs of congestive heart failure. Continuous-wave Doppler echocardiography can detect antiarrhythmic drug-induced LV dysfunction and may be used to anticipate the development of significant clinically overt congestive heart failure.     

Continuous monitoring of cardiac output in neonates using an intra-aortic Doppler probe.

Continuous monitoring of cardiac output in neonates would be of considerable benefit but, as yet, there is no practical method to achieve this aim. We have now evaluated the feasibility of using an intra-aortic Doppler probe. We introduced a pulsed Doppler probe of 0.46 mm diameter via the umbilical artery in two term and four preterm neonates. Indications in all patients for umbilical arterial catheter is always an unstable cardiopulmonary state. Body weights were between 770 and 3340 g. Velocities of blood flow in the thoracic aorta were continuously recorded to estimate cardiac output on-line for 12 h. No complications were encountered. It proved possible to derive high-quality Doppler curves. The received Doppler signal was stable but it proved sensitive to pathophysiologic changes in flow. Mean velocity of flow in the descending aorta was 16.4 cm/s (range 13.3-19.0 cm/s). We quantified flow by multiplying the mean velocity of the flow by the cross-sectional area of the descending aorta. Calculated mean flow was 135 ml/kg/min (range 111-179 ml/kg/min). These values are consistent with those measured by transcutaneous Doppler, and it should not be raised by left-to-right ductal shunts. This pilot study proved the feasibility of continuous monitoring of cardiac output. The technique should prove of great value in those infants with unstable circulatory conditions, and can be used even in infants with extremely low birth weights.     

Noninvasive evaluation of left ventricular function using new systolic time intervals obtained from continuous-wave Doppler echocardiography

Left ventricular function was evaluated using parameters derived from the flow velocity waveforms at the ascending aorta as obtained at the suprasternal notch by continuous-wave Doppler echocardiography in 39 patients; 12 with chest pain but without coronary stenosis, eight with angina pectoris; and 19 with myocardial infarction. Peak flow velocity and the time interval from the beginning of the Q wave of lead II of the ECG to peak flow velocity (Q-V peak) correlated with specific invasive hemodynamic parameters, such as max dp/dt and (max dp/dt)/IP (IP: total left ventricular pressure at the same instant) during isometric contraction of the left ventricle measured with a catheter tip manometer, and left ventricular ejection fraction (LVEF) obtained by bi-plane cineangiography (using the area-length method). There was no correlation between the peak flow velocity and the invasive hemodynamic parameters. However, significant negative correlations were observed between the Q-V peak time and max dp/dt, with r = 0.40 (p less than 0.05), and between the Q-V peak time and (max dp/dt)/IP with r = -0.61 (p less than 0.01). A negative correlation was obtained between the Q-V peak time and LVEF (r = -0.75, p less than 0.01). The regression equation was LVEF = -0.67 x (Q-V peak) + 176. To compare the effectiveness for predicting LVEF between the Q-V peak and the established systolic time intervals as PEP and PEP/ET, these time intervals were measured from flow velocity waveforms invasively obtained with a catheter-type electromagnetic flowmeter inserted into the ascending aorta in 14 patients selected from the original subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Doppler echocardiographic measurement of cardiac output using the mitral orifice method.

Cardiac output was determined in 20 patients with various cardiac conditions by measuring the cross sectional area of the mitral orifice by echocardiography and the transmitral flow by the Doppler technique. Cardiac output was calculated by multiplying the corrected mitral orifice area by the maximum diastolic velocity integral recorded by the pulsed mode. The results were compared with that obtained by the Fick method. The correlation for cardiac output by the two techniques was high in the whole group, particularly in patients without mitral regurgitation. There was also a good correlation for stroke volume determined by the two methods. Cardiac output was significantly overestimated by the continuous mode and in patients with mitral regurgitation. These results show that the mitral orifice method provides a new and reliable approach to the non-invasive measurement of cardiac output.     

Noninvasive cardiac output monitoring during exercise before and after coronary artery bypass surgery

A computerized continuous wave Doppler instrument was used to monitor changes in cardiac output and stroke volume during supine symptom limited graded bicycle exercise in 30 subjects. Eight patients were studied before and after coronary artery bypass graft (CABG) and were found to have patent grafts (group 1). Six patients were symptomatic after CABG and had at least one graft occluded (group 2). Sixteen age matched asymptomatic subjects served as controls (group 3). In group 1 patients before CABG, the duration of exercise was 5 +/- 2 mins (mean +/- standard deviation), the double product was 162 +/- 25, the percentage change in cardiac output with exercise was 33 +/- 7 and the percentage change in stroke volume was 1 +/- 5. Following CABG in group 1 patients, the duration of exercise increased to 9 +/- 2 mins, the double product to 186 +/- 16, the percentage change in cardiac output to 74 +/- 14 and the stroke volume to 13 +/- 12% (P less than 0.05). These results were not significantly different from those obtained in the group 3 patients (controls) in whom the duration of exercise was 10 +/- 3 mins, double product 211 +/- 24, percentage change in cardiac output 95 +/- 30 and the percentage change in stroke volume was 13 +/- 5.(ABSTRACT TRUNCATED AT 250 WORDS)     

Accuracy of determination of changes in cardiac output by transcutaneous continuous-wave Doppler computer

The value of a previously validated portable, continuous-wave Doppler computer was assessed for measuring changes in cardiac output (CO). Simultaneous thermodilution and Doppler CO values were measured in triplicate in 16 patients undergoing clinical intervention with vasodilator therapy. A continuous-wave Doppler transducer was placed in the suprasternal notch and directed toward the ascending aorta and angled until the maximal velocity signal was obtained. The correlation coefficient was 0.92 (standard error of the estimate [SEE] = 0.48 liter/min) at rest; with intervention it was 0.88 (SEE = 0.52 liter/min). Our data indicate that the Doppler computer technique, when used in selected patients, is reliable in detecting changes in CO after vasodilator therapy. It may be of value in clinical situations in which hemodynamic monitoring is impractical.     

Noninvasive cardiac output monitoring during exercise stress test

A computerized continuous wave Doppler instrument was used to monitor changes in cardiac output during symptom limited supine bicycle exercise in 41 individuals. Eight (19%) had technically unsatisfactory Doppler signals. Of the remaining 33 patients, 21 had clinical and 18 had angiographic evidence of coronary artery disease (group 1) and 12 age-matched asymptomatic subjects served as controls (group 2). In eight group 1 patients, cardiac output determined simultaneously by Doppler and thermodilution technique correlated well at rest and peak exercise (Y = 1.71x + 0.69, SEE = 0.57, r = 0.86, P less than 0.001). During exercise, group 1 patients increased their cardiac output from 5.2 +/- 1 to 6.9 +/- 1.4 (mean +/- SD), group 2 subjects increased their cardiac output from 5.5 +/- 1.3 to 10.9 +/- 2. Group 1 patients, when compared to group 2 control subjects, had a lesser increase in cardiac output (34% versus 103%, P less than 0.05), a shorter duration of exercise (6.1 versus 9.7 mins, P less than 0.05) and a lower double product (172 +/- 18 versus 211 +/- 27, P less than 0.05). This new Doppler technique provides reasonably accurate estimates of cardiac output at rest and on moderate exercise in selected patients. In selected clinical situations, it may be a valuable addition to other measurements that are usually determined during exercise.     

Calculation of cardiac output using Doppler echocardiography

The authors describe the theoretical basis and general methods for calculating Cardiac Output (CO) by Doppler Echocardiography, using triangulation and planimetric methods ro obtain the Average Velocity (AV) of the flows. They point the more advisable Bidimensional Echocardiography views plans for the measurement of aortic, mitral, pulmonary and tricuspid cross sectional areas (CA) used in calculating the respective outputs (CO = CA x AV x cardiac frequency) and the rate Pulmonary Flow/Systemic Flow (PF/SF). They point out the main technological limitations, alternative methods and places for calculating CO in certain situations (Aortic stenosis, Pulmonary stenosis, etc.). They stress that these are alternative methods to the invasive techniques in the clinic Cardiac Pathologies (infants and adults), many of them treated in Intensive Care units, where the prolonged non invasive monitorization of CO is facilitated by the use of the same CA.     

Noninvasive evaluation of aortic regurgitation by continuous-wave Doppler echocardiography

Continuous-wave Doppler echocardiography was used to examine the aortic regurgitant flow velocity pattern in 32 patients with aortic regurgitation (AR) and 10 patients without AR. The aortic regurgitant flow velocity patterns, characterized by a rapid rise in flow velocity immediately after closure of the aortic valve, high peak flow velocity, and a gradual deceleration until the next aortic valve opening, were successfully obtained in 30 of the 32 patients with AR (sensitivity 94%, specificity 100%). The velocity decline was greater in patients with severe AR; thus, the slope of the velocity decline (deceleration) and the time to decline to half the peak velocity (half-time index) were measured from the flow velocity pattern. The deceleration became greater and the half-time index shortened in accordance with angiographic grading of AR (p less than .01). The deceleration and the half-time index also correlated well with the aortic regurgitant fraction (r = .79, p less than .01; r = -.89, p less than .01). Because the half-time index could be measured easily and independently of Doppler incident angle, it seemed a simple and accurate index of assessing the severity of AR. Thus continuous-wave Doppler echocardiography permitted the noninvasive evaluation of AR.     

Noninvasive measurement of the time constant of left ventricular relaxation using the continuous-wave Doppler velocity profile of mitral regurgitation.

BACKGROUND. The time constant of isovolumic relaxation (tau) is an important parameter of ventricular diastolic function, but the need for invasive measurement with high-fidelity catheters has limited its use in general clinical cardiology. The Doppler mitral regurgitant velocity spectrum can be used to estimate left ventricular (LV) pressure throughout systole and may provide a new noninvasive method for estimating tau. METHODS AND RESULTS. Mitral regurgitation was produced in nine dogs, and ventricular relaxation was adjusted pharmacologically and with hypothermia. High-fidelity ventricular pressures were recorded, and tau was calculated from these hemodynamic data (tau H) assuming a zero-pressure asymptote. Continuous-wave mitral regurgitant velocity profiles were obtained, and the ventriculo-atrial (VA) pressure gradient was calculated by the simplified Bernoulli equation; tau was calculated from the Doppler data from the time of maximal negative dP/dt until LV-LA pressure crossover. Three methods were used to correct the Doppler VA gradient to better approximate the LV pressure before calculating tau: 1) adding actual LA V wave pressure (to yield tau LA); 2) adding 10 mm Hg (tau 10); and 3) no adjustment at all (actual VA gradient used to calculate tau 0). The agreement between tau H and the three Doppler estimates of tau was assessed by linear regression and by the mean and standard deviation of the error between the measurements (delta tau). the measurements (delta tau). tau H ranged from 29 to 135 msec. Without correction for LA pressure, the Doppler estimate of tau seriously underestimated tau H: tau 0 = 0.30 tau H + 9.4, r = 0.79, delta tau = -35 +/- 18 msec. This error was almost completely eliminated by adding actual LA pressure to the VA pressure gradient: tau LA = 0.92 tau H + 7.6, r = 0.95, delta tau = 2 +/- 7 msec. Addition of a fixed LA pressure estimate of 10 mm Hg to the VA gradient yielded an estimate that was almost as good: tau 10 = 0.89 tau H + 4.9, r = 0.88, delta tau = -2 +/- 12 msec. In general, tau was overestimated when actual LA pressure was below this assumed value, and vice versa. Numerical analysis demonstrated that assuming LA pressure to be 10 mm Hg should yield estimates of tau accurate to +/- 15% between true LA pressures of 5 and 20 mm Hg. CONCLUSIONS. This study demonstrates that the Doppler mitral regurgitant velocity profile can be used to provide a direct and noninvasive measurement of tau. Because mitral regurgitation is very common in cardiac patients, this method may allow more routine assessment of tau in clinical and research settings, leading to a better understanding of the role of impaired ventricular relaxation in diastolic dysfunction and the effect of therapeutic interventions.