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Nongeometric Doppler stroke volume determination
Nongeometric David H. Spodick,
Doppler
Stroke
MD, DSc, and Hitoshi
Volume
Determination
Koito, MD
ccurate noninvasive measurement of cardiac output ity at the aortic valve orifice, the regression equation is a long-sought goal with obvious advantages. Nu- yielded the left ventricular ejection rate.5 merous methods have yielded varying success. Recent Sixteen patients in sinus rhythm and without left Doppler echocardiographic studies have produced prom- ventricular outflow obstryction who required Swanising results.132These studies depend on geometric mea- Ganz cathetersfor a variety of indications were investisurements, that is, the cross-sectional flow area of a valve gated usingpulsed Doppler measurementfor ejectional or vessel. Stroke volume is then calculated as the product flow velocity from the apical 4- or 2-chamber acoustic of the mean blood velocity by Doppler (flow velocity windows. The Doppler sample volume cursor was integral or “stroke distance”) and orifice area. Although aligned parallel and in the center of the left ventricular correlations with hemodynamically measured stroke vol- outflow for optimal recording in the aortic anulus and to ume and cardiac output have been satisfactory, many obviate angular correction. Five cycles were averaged to limitations are inherent in the requirement for accurate calculate mean velocity from the Doppler flow envelope cross-sectional flow area, including (1) changes in the integral using the Sony Medical Cardiologic Analysis flow area itself with changing cardiac output; (2) inaccu- System. This amount wasdivided by ejection time deterrate true orifice measurement because of inaccurate edge minedfrom the same doppler trace measured at basedetection by M-mode or 2-dimensional echocardiograline, leading edgeto trailing edge.4A Swan-Ganz cathephy due to poor resolution, assumption of a circular cross- ter and thermodilution computer (Edwards Lab 9520section or because the functional area may be less than A) were used to obtain 3 output values. Stroke volume the measured area (seen as a halo around a color flow jet was determinedfrom the mean of triplicate determinain cross-section); and (3) nonlaminar flow without a flat tions of minute output divided by heart rate. Simultaflow profile at the site of measurement. neous cardiac output determinations were made by A method to eliminate the need for geometric mea- Doppler, with all measurementsdone blindly and all surements when measuring blood velocity at a point calculations independently. where flow is laminar and velocity profile flat would be The results are listed in Table I. The average f advantageous. We developed a method with these char- standard deviation stroke volume by thermodilution was acteristics and preliminary results are encouraging. We 58 f 23 ml. The averagepredicted stroke volume by the report the initial investigation of this approach. The basis nongeometricmethod was 57 f 22 ml (difference = 1.4 of the nongeometric method is the relation: stroke volume f 5.8 ml). Figure 1 shows the regressionrelations be= ejection time X ejection rate (SV = ET X ER). Thus, if the ejection time and ejection rate are known, stroke ml volume can be calculated. I20 The left ventricular ejection time can be measured t with precision from Doppler flow traces4 The ejection rate can be determined indirectly-we recently demonstrated the close relation between mean velocity calculated from the Doppler spectral envelope as blood is ejected and the volume ejection rate determined by thermodilution.5 The latter was calculated from the relation: ejection rate = stroke volume/ejection time (LVER = SV/LVET). Of note, in the validation investigations the ejection time was determined using both the carotid pulse and the Doppler tracing independently.5 To ensure laminar flow with a flat velocity profile, the Doppler sample volume was placed in the center of the aortic valve orifice.6 The relation between Doppler-derived mean ejection flow velocity and thermodilution-derived volume ejection rate yielded the following regression equation5: y = 494x - 66 ml/s, where y is mean left ventricular 1 Y/’ ’ t volume ejection rate in ml/s and x is Doppler mean flow 20 40 60 60 100 m/ 120 velocity in m/s. Thus, by measuring mean Doppler velocsv Doppler A
From the Cardiology Division, Saint Vincent Hospital, and the Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01604. Manuscript received November 15, 1988; revised manuscript received December 20, 1988, and accepted December 21.
FIGURE 1. Stroke volume (SV) by Doppler versus stroke volume by thermodilutioo. The correlation is excellent (r = 0.97). The standard error of the estimate (5.4 ml) and 95% confidence interval (95% Cl) are indicated.
THE AMERICAN
JOURNAL
OF CARDIOLOGY
APRIL 1, 1989
883
TABLE
I Thermodilution
Versus
Doppler
Stroke
Volume
Ejection Time
Doppler Mean Flow Velocity
Predicted Stroke Volume
Pt
Age (w-h Sex
Thermodilution Stroke Volume (ml)
(9
(ml/s)
(ml)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
67, 58, 66, 70, 68, 69, 51, 77. 64, 74. 88, 67, 72, 22,
16 79 69 35 56 48 65 46 63 19 91 79 41 61
0.199 0.273 0.225 0.205 0.241 0.200 0.235 0.310 0.255 0.194 0.312 0.282 0.262 0.220
0.29 068 0 73 0 50 0.60 058 061 0.41 0.58 0.38 0.75 0.77 0.50 0.69
15 74 66 37 56 44 55 42 56 24 95 89 47 61
F M M M F M M M F F F M M M
tween nongeometric Doppler and thermodilution
stroke
volume. The regression equation (y) equals 0.993x + 1.79 ml, the correlation is 0.97, the standard error of the estimate is 5.4 ml (p X0.01) with 95% confiaence limits.
The nongeometric stroke volume calculated from Doppler flow and our ejection rate equation performed well, as indicated by the close correlation (r = 0.97). In this relatively small group of patients, unselected except for the study criteria, the stroke volumes were estimated over a large range (15 to 95 ml) with reasonable precision, with absolute stroke volume differences between the methods ranging from 0 to 10 ml (Table I). Certain limitations are obvious. Investigation of larger patient groups may increase or reduce the very high correlation coefficient. The 95% confidence intervals are rather more realistic than the r value and it is hoped that a larger series will further reduce them. We omitted patients with left ventricular outflow obstruction, although in aortic stenosis sample volumes placed just proximal to the aortic orifice record laminar flo~.~ A potential limitation is precise placement of the sample volume. However, in 2 patients who required 30” angular deviations, the mean flow velocity was divided by the cosine of 30” (cos 0). The predicted stroke volume in 1 patient did not differ from thermodilution stroke volume and in the other the volume differed by only 2 ml.
884
THE AMERICAN
JOURNAL
OF CARDIOLOGY
VOLUME
63
Stroke Volume Difference -1 -5 -3 2 0 -4 -10 -4 -7 5 4 10 6 0
This preliminary investigation indicates the feasibility and reasonable accuracy of our nongeometric determination of stroke volume by Doppler echocardiography. We recognize the need for further testing, including further refinement of the ejection rate equation and determination of changes within the same subject, although experience with the latter indicates that Doppler methods are appropriate to track relative changes even without calculating volumes and cardiac output.8 This nongeometric method should permit easy determination of these values. 1. Alkayam U, Gardin JM, Berkley R, Hughes CA, Henry WL. The use of Doppler flow velocity measurements to assess hemodynamic response to vascdilatom Circulation 1983;67:377-383. 2. Goldberg SJ, Sahn DJ, Allen HD, Valdes-Cruz LM, Hoeneke H, Calahan Y. Evaluation of pulmonary and systemic blood flow by dimensional Doppler echocardiography using fast Fourier transforms. Am J Cardiol 1982;50:1394-1400. 3. Spodick DH, Quarry-Lance V. Noninvasive stress testing. Circulation 1976;53:673-676. 4. Koito H, Spodick DH. Optimal Doppler measurement of left ventricular ejection time. Am J Cardml 2989,63:257-259. 5. Koito H, Spodick DR. Relation of left ventricular ejectional flow velocity to volume ejection rate. Am J Cardiol 1989;63:256-257. 6. Dittmann H, Voelker W, Karsh K-R, Seipel L. Influence of sampling site and flow area on cardiac output measurements by Doppler echocardiography. JACC 1987;10:818-823. 7. Otto CM, Pearlman AS, Gardner CL, Enomoto DM, Togo T, Tsuboi T, Ivey TD. Experimental validation of Doppler echocardiographic measurements of volume flow through the stenotic aortic valve. Circulation 1988;78:435-444. 8. Gibson GD. Stroke distance-an improved measure of cardiac function. Br Heart J 1985:53:121-122.
Doppler
Stroke
MD, DSc, and Hitoshi
Volume
Determination
Koito, MD
ccurate noninvasive measurement of cardiac output ity at the aortic valve orifice, the regression equation is a long-sought goal with obvious advantages. Nu- yielded the left ventricular ejection rate.5 merous methods have yielded varying success. Recent Sixteen patients in sinus rhythm and without left Doppler echocardiographic studies have produced prom- ventricular outflow obstryction who required Swanising results.132These studies depend on geometric mea- Ganz cathetersfor a variety of indications were investisurements, that is, the cross-sectional flow area of a valve gated usingpulsed Doppler measurementfor ejectional or vessel. Stroke volume is then calculated as the product flow velocity from the apical 4- or 2-chamber acoustic of the mean blood velocity by Doppler (flow velocity windows. The Doppler sample volume cursor was integral or “stroke distance”) and orifice area. Although aligned parallel and in the center of the left ventricular correlations with hemodynamically measured stroke vol- outflow for optimal recording in the aortic anulus and to ume and cardiac output have been satisfactory, many obviate angular correction. Five cycles were averaged to limitations are inherent in the requirement for accurate calculate mean velocity from the Doppler flow envelope cross-sectional flow area, including (1) changes in the integral using the Sony Medical Cardiologic Analysis flow area itself with changing cardiac output; (2) inaccu- System. This amount wasdivided by ejection time deterrate true orifice measurement because of inaccurate edge minedfrom the same doppler trace measured at basedetection by M-mode or 2-dimensional echocardiograline, leading edgeto trailing edge.4A Swan-Ganz cathephy due to poor resolution, assumption of a circular cross- ter and thermodilution computer (Edwards Lab 9520section or because the functional area may be less than A) were used to obtain 3 output values. Stroke volume the measured area (seen as a halo around a color flow jet was determinedfrom the mean of triplicate determinain cross-section); and (3) nonlaminar flow without a flat tions of minute output divided by heart rate. Simultaflow profile at the site of measurement. neous cardiac output determinations were made by A method to eliminate the need for geometric mea- Doppler, with all measurementsdone blindly and all surements when measuring blood velocity at a point calculations independently. where flow is laminar and velocity profile flat would be The results are listed in Table I. The average f advantageous. We developed a method with these char- standard deviation stroke volume by thermodilution was acteristics and preliminary results are encouraging. We 58 f 23 ml. The averagepredicted stroke volume by the report the initial investigation of this approach. The basis nongeometricmethod was 57 f 22 ml (difference = 1.4 of the nongeometric method is the relation: stroke volume f 5.8 ml). Figure 1 shows the regressionrelations be= ejection time X ejection rate (SV = ET X ER). Thus, if the ejection time and ejection rate are known, stroke ml volume can be calculated. I20 The left ventricular ejection time can be measured t with precision from Doppler flow traces4 The ejection rate can be determined indirectly-we recently demonstrated the close relation between mean velocity calculated from the Doppler spectral envelope as blood is ejected and the volume ejection rate determined by thermodilution.5 The latter was calculated from the relation: ejection rate = stroke volume/ejection time (LVER = SV/LVET). Of note, in the validation investigations the ejection time was determined using both the carotid pulse and the Doppler tracing independently.5 To ensure laminar flow with a flat velocity profile, the Doppler sample volume was placed in the center of the aortic valve orifice.6 The relation between Doppler-derived mean ejection flow velocity and thermodilution-derived volume ejection rate yielded the following regression equation5: y = 494x - 66 ml/s, where y is mean left ventricular 1 Y/’ ’ t volume ejection rate in ml/s and x is Doppler mean flow 20 40 60 60 100 m/ 120 velocity in m/s. Thus, by measuring mean Doppler velocsv Doppler A
From the Cardiology Division, Saint Vincent Hospital, and the Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01604. Manuscript received November 15, 1988; revised manuscript received December 20, 1988, and accepted December 21.
FIGURE 1. Stroke volume (SV) by Doppler versus stroke volume by thermodilutioo. The correlation is excellent (r = 0.97). The standard error of the estimate (5.4 ml) and 95% confidence interval (95% Cl) are indicated.
THE AMERICAN
JOURNAL
OF CARDIOLOGY
APRIL 1, 1989
883
TABLE
I Thermodilution
Versus
Doppler
Stroke
Volume
Ejection Time
Doppler Mean Flow Velocity
Predicted Stroke Volume
Pt
Age (w-h Sex
Thermodilution Stroke Volume (ml)
(9
(ml/s)
(ml)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
67, 58, 66, 70, 68, 69, 51, 77. 64, 74. 88, 67, 72, 22,
16 79 69 35 56 48 65 46 63 19 91 79 41 61
0.199 0.273 0.225 0.205 0.241 0.200 0.235 0.310 0.255 0.194 0.312 0.282 0.262 0.220
0.29 068 0 73 0 50 0.60 058 061 0.41 0.58 0.38 0.75 0.77 0.50 0.69
15 74 66 37 56 44 55 42 56 24 95 89 47 61
F M M M F M M M F F F M M M
tween nongeometric Doppler and thermodilution
stroke
volume. The regression equation (y) equals 0.993x + 1.79 ml, the correlation is 0.97, the standard error of the estimate is 5.4 ml (p X0.01) with 95% confiaence limits.
The nongeometric stroke volume calculated from Doppler flow and our ejection rate equation performed well, as indicated by the close correlation (r = 0.97). In this relatively small group of patients, unselected except for the study criteria, the stroke volumes were estimated over a large range (15 to 95 ml) with reasonable precision, with absolute stroke volume differences between the methods ranging from 0 to 10 ml (Table I). Certain limitations are obvious. Investigation of larger patient groups may increase or reduce the very high correlation coefficient. The 95% confidence intervals are rather more realistic than the r value and it is hoped that a larger series will further reduce them. We omitted patients with left ventricular outflow obstruction, although in aortic stenosis sample volumes placed just proximal to the aortic orifice record laminar flo~.~ A potential limitation is precise placement of the sample volume. However, in 2 patients who required 30” angular deviations, the mean flow velocity was divided by the cosine of 30” (cos 0). The predicted stroke volume in 1 patient did not differ from thermodilution stroke volume and in the other the volume differed by only 2 ml.
884
THE AMERICAN
JOURNAL
OF CARDIOLOGY
VOLUME
63
Stroke Volume Difference -1 -5 -3 2 0 -4 -10 -4 -7 5 4 10 6 0
This preliminary investigation indicates the feasibility and reasonable accuracy of our nongeometric determination of stroke volume by Doppler echocardiography. We recognize the need for further testing, including further refinement of the ejection rate equation and determination of changes within the same subject, although experience with the latter indicates that Doppler methods are appropriate to track relative changes even without calculating volumes and cardiac output.8 This nongeometric method should permit easy determination of these values. 1. Alkayam U, Gardin JM, Berkley R, Hughes CA, Henry WL. The use of Doppler flow velocity measurements to assess hemodynamic response to vascdilatom Circulation 1983;67:377-383. 2. Goldberg SJ, Sahn DJ, Allen HD, Valdes-Cruz LM, Hoeneke H, Calahan Y. Evaluation of pulmonary and systemic blood flow by dimensional Doppler echocardiography using fast Fourier transforms. Am J Cardiol 1982;50:1394-1400. 3. Spodick DH, Quarry-Lance V. Noninvasive stress testing. Circulation 1976;53:673-676. 4. Koito H, Spodick DH. Optimal Doppler measurement of left ventricular ejection time. Am J Cardml 2989,63:257-259. 5. Koito H, Spodick DR. Relation of left ventricular ejectional flow velocity to volume ejection rate. Am J Cardiol 1989;63:256-257. 6. Dittmann H, Voelker W, Karsh K-R, Seipel L. Influence of sampling site and flow area on cardiac output measurements by Doppler echocardiography. JACC 1987;10:818-823. 7. Otto CM, Pearlman AS, Gardner CL, Enomoto DM, Togo T, Tsuboi T, Ivey TD. Experimental validation of Doppler echocardiographic measurements of volume flow through the stenotic aortic valve. Circulation 1988;78:435-444. 8. Gibson GD. Stroke distance-an improved measure of cardiac function. Br Heart J 1985:53:121-122.