- Email: [email protected]
Comparison of pulmonary wedge and left atrial pressure in man
Comparison of pulmonary wedge left atrial pressure in man
and
Abe Walston, II, M.D. M. Eugene Kendall, M.D. Durham, N. C.
A
s early as 1906, it was observed that pressure changes in the left atrium and pulmonary venous system could be transmitted retrograde to the end arteries of the lungs. Pulmonary wedge pressures were first described by Hellems and associates’ in 1948. The development of left heart catheterization allowed direct measurement of left atria1 pressure and provided a means for direct correlation of pulmonary wedge and left atria1 pressures. On the basis of these studies, pulmonary wedge pressures have been used as synonymous with the left atria1 pressure in the calculation of mitral valve areas and other hemodynamic indexes. The hemodynamic evaluation of patients with acute myocardial infarction has led to the use of pulmonary wedge pressure as an index of left ventricular filling pressure.2*3 This recent use of pulmonary wedge pressure has placed new emphasis on defining the precise correlation of mean pulmonary wedge and mean left atria1 pressure. Our review of the literature fails to reveal a comparison of pulmonary wedge and left atria1 pressures in a large number of patients. This study was designed to compare retrospectively mean pulmonary wedge and From
mean left atria1 pressure in a large number of patients with and without heart disease. Methods The records of 700 patients obtained at cardiac catheterization were analyzed. These hemodynamic data were obtained as part of the diagnostic cardiac catheterization at Duke University Medical Center and Durham Veterans Administration Hospital between 1959 and 1972. The patient groups included normals (23)) coronary artery disease (54), mitral stenosis (159)) mitral insufficiency (SO), aortic stenosis (65), aortic insufficiency (39), and patients with more than one valvular lesion (310). Each patient underwent right and left heart catheterization with left atria1 pressure measured directly by a transseptal left atria1 puncture. Pulmonary wedge pressure was repeated multiple times to insure that correct values were obtained. Withdrawal of 95 per cent saturated hemoglobin and “snapping” of the catheter tip on withdrawal of the wedged catheter was used as evidence of a correct wedge position. Whenever possible pulmonary wedge pressures and left atria1 pressures were recorded simultaneously on equally cali-
the Department of Medicine (Division of Cardiology). ministration Hospital, Durham. N. C. 27705. This work wa8 supported in part by United States Public and Lung Institute. Received for publication Sept. 18, 1972. Reprint requests to: Dr. Abe Walston, II, Room C-8002,
vol. 86, No. 2, pp. 159-164
August, 1973
Duke Health
Veterans
University Service
Medical Grant
Administration
Center.
HL-05736
Hospital,
and the Veterans
from
the National
Durham.
AdHeart
N. C. 27703.
American Heart Journal
159
160
Am. Heart J. Aagtcst, 1973
Walston and Kendall
Table I. Comparison of mean values, ranges, and standard deviations (mm. Hg) for mean pulmonary wedge and mean left atria1 pressures for each of the seven patient groups and for all cases
Range (mm. f-k)
Standard deviation (mm. Hg)
Correlation
7.0 6.4
2-15 2-12
*0.6 hO.4
0.92
9.6 9.1
3-31 3-25
AO.5 =+=0.5
0.91
20.4 19.2
7-43 6-48
ho.6 *0.5
0.90
13.7 12.8
4-37 3-38
*0.9 *1.0
0.93
11.0 10.8
4-41 2-42
=+=O.S *0.9
0.91
13.5 12.9
4-36 3-28
‘1.1 Al.0
0.90
16.0 15.9
3-43 2-42
AO.4 hO.4
0.93
15.4 15.0
2-43 2-48
hO.3 *0.3
0.93
Group
1. Normals pwt LA
23
2. Coronary disease PW LA 3. Mitral stenosis PW LA 4. Mitral insufficiency PW LA 5. Aortic stenosis PW LA 6. Aortic insufficiency PW LA 7. Mixed valvular disease PW L.4 8. All cases PW LA
54
*Correlation tAbbreviations:
co@cient*
159 50 6.5 39 310 700
coefficients are shcwn for the comparison of mean pulmonary wedge PW = pulmonary wedge; LA = left atrial; N = number of patients.
brated gauges. Pressures were measured with Statham P23Db strain gauges and recorded on an Electronics for lledicine DR8 recorder. Mean pressures were obtained by electronic integration of the phasic pressures. Pressures used in this study were measured when the heart rate was below 100 beats per minute. No additional studies were carried out to determine the possible effect of heart rate on the relation between wedge and left atria1 pressure. Standard linear regression techniques were used for evaluation of the data.4 Results
Table I shows the mean, range, standard deviation, and correlation coefficient for the mean pulmonary wedge and mean left atria1 pressure for each of the patient groups. Despite a wide variation in the
and
mean
left
atria1
pressures.
range of wedge and left atria1 pressures, the correlation coefficients for each of the patient groups were found to be nearly identical. Fig. 1 shows a plot of mean pulmonary wedge versus mean left atria1 pressure for all patients. Linear regression analysis reveals a correlation coefficient of r = 0.93 with a standard error of k3.0 mm. Hg. Note that the degree of scatter increases as the wedge and left atria1 pressures rise. Table II and Fig. 2 reveal a comparison of mean pulmonary wedge and mean left atria1 pressure for all of the patients. For this comparison the data were grouped according to a 5 mm. Hg increment in mean wedge pressure. The mean difference for each of these groups was computed as the difference between mean left atria1 pressure and mean pulmonary wedge pressure. At wedge pressures below 25 mm. Hg, there
Volume Number
86 2
Pulmonary
wedge and left atria1 pressure
in man
161
454035B
45 Mean Pulmonary
Wedge
Pressure
(mm Hg)
Fig. 1. Plot of mean left atria1 pressure versus mean pulmonary wedge pressure (mm. Hg) for all patients. The regression line was y = 0.93x + 0.57 and the correlation coefficient was r = 0.93. were no significant differences between mean wedge and mean left atria1 pressure. In wedge pressure groups 26 to 30,3 1 to 35, and >35 mm. Hg, mean left atria1 pressure was significantly different from mean wedge pressure (P < 0.05). The 9.5 per cent confidence limits of the prediction of mean left atria1 pressure from mean wedge pressure for each of these groups are shown in Fig. 2. Note that with a mean wedge pressure of 10 mm. Hg or less, the error in predicting left atria1 pressure is only %2 mm. Hg. However, the error increases considerably when the mean wedge pressure is higher. Discussion
Hellems and colleagues’s5reported experimental evidence that the pressure recorded by a catheter wedged in an end pulmonary artery closely approximated pulmonary capillary pressure. Werko and associates,6 Connolly and co-workers,‘s8 Epps and colleagues,g and otllers10-12found good correlation between the level of pulmonary wedge and left atria1 pressure. Other investigators*3-16 in human and animal stud-
ies, found poor correlation between wedge and left atria1 pressure. However, these early comparisons were performed with left atria1 pressures measured in a variety of ways, including measurement by way of atria1 septal defect, 5*17by left atria1 puncture during open heart surgery,* measurement by transbronchial approach,g and measurement by transthoracic approach.6JzJ4 Werko and co-workers** demonstrated that balloon occlusion of the pulmonary artery proximal to the wedged catheter does not alter the pressure recorded at the tip of the catheter, demonstrating the left-sided origin of the pulmonary wedge pressure. Ankenneylg showed that phasic variations of left atria1 pressure waves were transmitted retrograde to the wedged catheter but only mean left atria1 pressure was accurately reflected in the wedge pressure tracings. Hemodynamic studies on patients with acute myocardial infarction have directed new emphasis on the ability of pulmonary wedge pressure to predict left atria1 pressure, which is used as an index of left ventricular filling pressure.233Pulmonary wedge pressures (using
162
Am. Heart J. Augast, 1973
Walston and Kendall
0
I
T I
m m Hg -IO-
o-5
6-10 Meon
II-15 Pulmonary
16-20 Wedge
21-25 Pressure
26-x) (mmHg)
31-35
>35
Fig. 2. Plot of mean difference in mm. Hg of left atria1 pressure from mean wedge pressure (mm. Hg) in groups of 5 mm. Hg of mean wedge pressure. Points above and below the zero line signify mean left atria1 pressure greater and less than, respectively, mean pulmonary wedge pressure. Brackets surrounding these mean points signify the 95 per cent confidence limits. (The 95 per cent confidence limits of the data were determined by multiplying the standard error of the mean by the appropriate T value).’
Tuble II. Mean pukzonury wedgepressure vs. meun left atria2 pressure Pulmonary wedge pressure (mm.
group 3)
o-5 6-10 11-15 16-20 21-25 26-30 31-35 >35 *N = number tSignifies that
of patients the mean
Mean difference (mm. Hd
N*
39 207 163 111
0 0 0 0 0 -1t -3t -3
i; 28 16
Standard error of the mean (mm. Hd
*0 =J=O *0 +0 *O +1 *l *l
in each 5 mm. Hg incremental group. difference was statistically significant (P < 0.05).
the Swan-Ganz catheter) can be monitored at the bedside and, if valid, can provide vital data on left ventricular filling pressure.20,21Since left ventricular filling pressure is frequently elevated in acute myocardial infarction, correlation of pulmonary wedge with left atria1 pressure must be done over a wide range of pressures. The plot of mean wedge versus mean left atria1 pressure (Fig. 1) demonstrates little scatter around the regression line until the pressures exceed 10 mm. Hg. The near identity of the mean differences and the small standard errors between wedge and left atria1 pressure suggest that mean pulmonary wedge pressure is a moderately accurate predictor of mean left atria1 pressure at these low normal wedge pressures. The predictive ability of mean wedge pressure
(described by the 95 per cent confidence limits illustrated in Fig. 2) is directly related to the level of mean wedge pressure. When the wedge pressure is greater than 10 mm. Hg, the prediction of left atria1 pressure can be shown to contain considerable error. Ventricular filling pressure and other assessments of myocardial performance and valve areas cannot validly be calculated from the wedge pressure if it exceeds 10 mm. Hg. The increasing loss of correlation between wedge and mean left atria1 pressure at higher pressures may in part be explained by the findings of Caro and associates22who demonstrated that high pressures across the pulmonary capillary bed cause a change in the ratio of pulmonary arterial and pulmonary venous compliance promoting asymmetrical trans-
Pulmonary
mission of pressure waves across the pulmonary vascular bed. The present study was done in a retrospective manner and has all the errors in measurement which are inherent in the day-to-day operation of a diagnostic cardiac catheterization laboratory. Thus, it might be argued that meticulous attention to detail in pressure recording might yield a closer correlation. However, it is with this level of expertise in pressure measurement that hemodynamic data is collected on a routine basis.
wedge and left atria1 pressure
3.
4. 5. 6.
Summary Values of mean pulmonary wedge and mean left atria1 pressure were compared in 700 patients including normals and patients with a variety of heart diseases. An over-all correlation coefficient r = 0.93 was found between mean wedge and mean left atria1 pressure and this correlation was unrelated to the etiology of the heart disease. No significant difference between the average value of wedge and left atria1 pressure was found until the wedge pressure exceeded 25 mm. Hg. In patients with mean wedge pressures of 10 mm. Hg or less, left atria1 pressure could be predicted with an accuracy of +2 mm. Hg (9.5 per cent confidence limits). However, at higher wedge pressures the prediction of mean left atria1 pressure was subject to considerable error. Thus, caution should be employed in using mean wedge pressure as an accurate index of mean left atria1 pressure unless the wedge pressure is within the low normal range. The authors gratefully acknowledge the technical assistance of Iudith C. Rembert. Ph.D. The Deoartment of Medical Illustrations of the Durham Veterans Administration Hospital also rendered valuable support in the preparation of this paper. The secretarial assistance of Mrs. Rosa B. Ethridge and Mrs. Brenda Halev is herebv acknowledged.- Statistical analysis was performed by Philip McHale, Ph.D. The authors are also grateful to Dr. Yihong Kong of the Duke Cardiovascular Laboratory for making the catherization data available. REFERENCES 1. Hellems, H. K., Haynes, F. W., Dexter, L., and Kinney, T. D.: Pulmonary capillary pressure in animals estimated by venous and arterial catheterization, Am. J. Physiol. 155:98, 1948. 2. Forrester, James S., Diamond, George,
7,
8.
9. 10.
11. 12.
13.
14. 1.5.
16.
17.
in man
163
McHugh, Thomas J., and Swan, H. J. C.: Filling pressures in the right and left sides of the heart in acute myocardial infarction, N. Engl. J. Med. 285:190, 1971. Rackley, C. E., and Russell, R. 0.: Left ventricular function in acute myocardial infarction and its clinical significance, Circulation 45:231, 1972. Snedecor, G. W.: Statistical methods, 5th ed., Ames, 1962, Iowa State University Press. Hellems, H. K., Haynes, F. W., and Dexter, L.: Pulmonary “capillary” pressure in man, J. Appl. Physiol. 2:24, 1949. Werko, L., Varnauskas, E., Eliasch, H., Lagerlof, H., Senning, A., and Thomasson, B.: Further evidence that the pulmonary capillary venous pressure pulse in man reflects cyclic pressure changes in the left atrium, Circ. Res. 1:337, 1953. Connolly, D. C., Tompkins, R. G., Lev, R., Kirklin, J. W., and Wood, E. H.: Pulmonaryartery wedge pressures in mitral valve disease; relationship to left atria1 pressures, Mayo Clin. Proc. 28:72, 1953. Connolly, D. C., Kirklin, J. W., and Wood, E. H.: The relationship between pulmonary artery wedge pressure and left atrial pressure in man. Circ. Res. 2:434. 1954. Epps, k. G., and Adler, k. H.: Left atrial and pulmonary capillary venous pressures in mitral stenosis, Br. Heart J. 15:298, 1953. Wilson, R. H., McKenna, W. T., Johnson, F. E., Jensen, N. K., Mazzitello, W. F., and Dempsey, M. S.: The significance of the pulmonary arterial wedge pressure, J. Lab. Clin. Med. 42(3):408, 1953. Wilson, R. H., Joseph, W., and Dempsey, M.: The interrelations of the pulmonary arterial and venous pressures, Circ. Res. 3:3, 1955. Samet, P., Litwak, R. S., Bernstein, W. H., Fiere, E. M., and Silverman, L. M.: Clinical and physiologic relationships in mitral valve disease, Circulation 19:517, 1959. Haddy, F. J., Alden, J. F., Ferrin, A. L., Hannon, D. W., Adams, W. L., and Baronofsky, I. D.: An evaluation of wedge pressures in dogs under conditions of normal and elevatedpulmonary vascular pressures, Circ. Res. 1:157, 1953. Murphy, J. P.: Inaccuracy of wedge pressure as an index of pulmonary capillary pressure, Circulation 27:199, 1958. Bernstein, W. H., Fierer, E. M., Laszlo, M. H., Samet, P., and Litwak, R. S.: The interpretation of pulmonary artery wedge (pulmonary capillarv) oressures. Br. Heart 1. 22:37. 1960. Luchsinger, P.’ C., Seipp, “H. W.,’ and Patel, D. J.: Relationship of pulmonary artery-wedge pressure to left atrial pressure in man, Circ. Res. 11:315. 1962. Calazei, P., Gerard, R., Daley, R., Draper, A., Foster. I.. and Bine. R. I.: Phvsiological studies in’ congenital heart “disease XI: A comparison of the right and left auricular, capillary and pulmonary artery pressures in nine patients
164
18.
19.
20.
Walston and Kendall
with auricular septal defect, Johns Hopkins Med. J. 88:20, 1951. Werko, L., Varnauskas, E., Eliasch, H., and Thomasson, B.: The influence of the pulmonary arterial pressure on the pulmonary capillary venous pressure in man, Circ. Res. 1:340, 1953. Ankenney, J. L.: Further experimental evidence that pulmonary capillary pressures do not reflect cyclic changes in left atria1 pressure (mitral lesions and pulmonary embolism), Circ. Res. 1:58, 1953. Ganz, W. W., Forrester, J. S., Chonette, D.,
21.
22.
Donoso, R., and Swan, H. J. C.: A new flowdirected catheter technique for measurement of pulmonary artery and capillary wedge pressure without fluoroscopy, Am. J. Cardiol. 25:96, 1970. Cohn, J. N., Khatri, I. M., and Hamosh, P.: Bedside catheterization of the left ventricle, Am. J, Cardiol. 25:66, 1970. Caro, C. G., Bergel, D. H., and Seed, W. A.: Forward and backward transmission of pressure waves in the pulmonary vascular bed of the dog, Circ. Res. 20:185, 1967.
and
Abe Walston, II, M.D. M. Eugene Kendall, M.D. Durham, N. C.
A
s early as 1906, it was observed that pressure changes in the left atrium and pulmonary venous system could be transmitted retrograde to the end arteries of the lungs. Pulmonary wedge pressures were first described by Hellems and associates’ in 1948. The development of left heart catheterization allowed direct measurement of left atria1 pressure and provided a means for direct correlation of pulmonary wedge and left atria1 pressures. On the basis of these studies, pulmonary wedge pressures have been used as synonymous with the left atria1 pressure in the calculation of mitral valve areas and other hemodynamic indexes. The hemodynamic evaluation of patients with acute myocardial infarction has led to the use of pulmonary wedge pressure as an index of left ventricular filling pressure.2*3 This recent use of pulmonary wedge pressure has placed new emphasis on defining the precise correlation of mean pulmonary wedge and mean left atria1 pressure. Our review of the literature fails to reveal a comparison of pulmonary wedge and left atria1 pressures in a large number of patients. This study was designed to compare retrospectively mean pulmonary wedge and From
mean left atria1 pressure in a large number of patients with and without heart disease. Methods The records of 700 patients obtained at cardiac catheterization were analyzed. These hemodynamic data were obtained as part of the diagnostic cardiac catheterization at Duke University Medical Center and Durham Veterans Administration Hospital between 1959 and 1972. The patient groups included normals (23)) coronary artery disease (54), mitral stenosis (159)) mitral insufficiency (SO), aortic stenosis (65), aortic insufficiency (39), and patients with more than one valvular lesion (310). Each patient underwent right and left heart catheterization with left atria1 pressure measured directly by a transseptal left atria1 puncture. Pulmonary wedge pressure was repeated multiple times to insure that correct values were obtained. Withdrawal of 95 per cent saturated hemoglobin and “snapping” of the catheter tip on withdrawal of the wedged catheter was used as evidence of a correct wedge position. Whenever possible pulmonary wedge pressures and left atria1 pressures were recorded simultaneously on equally cali-
the Department of Medicine (Division of Cardiology). ministration Hospital, Durham. N. C. 27705. This work wa8 supported in part by United States Public and Lung Institute. Received for publication Sept. 18, 1972. Reprint requests to: Dr. Abe Walston, II, Room C-8002,
vol. 86, No. 2, pp. 159-164
August, 1973
Duke Health
Veterans
University Service
Medical Grant
Administration
Center.
HL-05736
Hospital,
and the Veterans
from
the National
Durham.
AdHeart
N. C. 27703.
American Heart Journal
159
160
Am. Heart J. Aagtcst, 1973
Walston and Kendall
Table I. Comparison of mean values, ranges, and standard deviations (mm. Hg) for mean pulmonary wedge and mean left atria1 pressures for each of the seven patient groups and for all cases
Range (mm. f-k)
Standard deviation (mm. Hg)
Correlation
7.0 6.4
2-15 2-12
*0.6 hO.4
0.92
9.6 9.1
3-31 3-25
AO.5 =+=0.5
0.91
20.4 19.2
7-43 6-48
ho.6 *0.5
0.90
13.7 12.8
4-37 3-38
*0.9 *1.0
0.93
11.0 10.8
4-41 2-42
=+=O.S *0.9
0.91
13.5 12.9
4-36 3-28
‘1.1 Al.0
0.90
16.0 15.9
3-43 2-42
AO.4 hO.4
0.93
15.4 15.0
2-43 2-48
hO.3 *0.3
0.93
Group
1. Normals pwt LA
23
2. Coronary disease PW LA 3. Mitral stenosis PW LA 4. Mitral insufficiency PW LA 5. Aortic stenosis PW LA 6. Aortic insufficiency PW LA 7. Mixed valvular disease PW L.4 8. All cases PW LA
54
*Correlation tAbbreviations:
co@cient*
159 50 6.5 39 310 700
coefficients are shcwn for the comparison of mean pulmonary wedge PW = pulmonary wedge; LA = left atrial; N = number of patients.
brated gauges. Pressures were measured with Statham P23Db strain gauges and recorded on an Electronics for lledicine DR8 recorder. Mean pressures were obtained by electronic integration of the phasic pressures. Pressures used in this study were measured when the heart rate was below 100 beats per minute. No additional studies were carried out to determine the possible effect of heart rate on the relation between wedge and left atria1 pressure. Standard linear regression techniques were used for evaluation of the data.4 Results
Table I shows the mean, range, standard deviation, and correlation coefficient for the mean pulmonary wedge and mean left atria1 pressure for each of the patient groups. Despite a wide variation in the
and
mean
left
atria1
pressures.
range of wedge and left atria1 pressures, the correlation coefficients for each of the patient groups were found to be nearly identical. Fig. 1 shows a plot of mean pulmonary wedge versus mean left atria1 pressure for all patients. Linear regression analysis reveals a correlation coefficient of r = 0.93 with a standard error of k3.0 mm. Hg. Note that the degree of scatter increases as the wedge and left atria1 pressures rise. Table II and Fig. 2 reveal a comparison of mean pulmonary wedge and mean left atria1 pressure for all of the patients. For this comparison the data were grouped according to a 5 mm. Hg increment in mean wedge pressure. The mean difference for each of these groups was computed as the difference between mean left atria1 pressure and mean pulmonary wedge pressure. At wedge pressures below 25 mm. Hg, there
Volume Number
86 2
Pulmonary
wedge and left atria1 pressure
in man
161
454035B
45 Mean Pulmonary
Wedge
Pressure
(mm Hg)
Fig. 1. Plot of mean left atria1 pressure versus mean pulmonary wedge pressure (mm. Hg) for all patients. The regression line was y = 0.93x + 0.57 and the correlation coefficient was r = 0.93. were no significant differences between mean wedge and mean left atria1 pressure. In wedge pressure groups 26 to 30,3 1 to 35, and >35 mm. Hg, mean left atria1 pressure was significantly different from mean wedge pressure (P < 0.05). The 9.5 per cent confidence limits of the prediction of mean left atria1 pressure from mean wedge pressure for each of these groups are shown in Fig. 2. Note that with a mean wedge pressure of 10 mm. Hg or less, the error in predicting left atria1 pressure is only %2 mm. Hg. However, the error increases considerably when the mean wedge pressure is higher. Discussion
Hellems and colleagues’s5reported experimental evidence that the pressure recorded by a catheter wedged in an end pulmonary artery closely approximated pulmonary capillary pressure. Werko and associates,6 Connolly and co-workers,‘s8 Epps and colleagues,g and otllers10-12found good correlation between the level of pulmonary wedge and left atria1 pressure. Other investigators*3-16 in human and animal stud-
ies, found poor correlation between wedge and left atria1 pressure. However, these early comparisons were performed with left atria1 pressures measured in a variety of ways, including measurement by way of atria1 septal defect, 5*17by left atria1 puncture during open heart surgery,* measurement by transbronchial approach,g and measurement by transthoracic approach.6JzJ4 Werko and co-workers** demonstrated that balloon occlusion of the pulmonary artery proximal to the wedged catheter does not alter the pressure recorded at the tip of the catheter, demonstrating the left-sided origin of the pulmonary wedge pressure. Ankenneylg showed that phasic variations of left atria1 pressure waves were transmitted retrograde to the wedged catheter but only mean left atria1 pressure was accurately reflected in the wedge pressure tracings. Hemodynamic studies on patients with acute myocardial infarction have directed new emphasis on the ability of pulmonary wedge pressure to predict left atria1 pressure, which is used as an index of left ventricular filling pressure.233Pulmonary wedge pressures (using
162
Am. Heart J. Augast, 1973
Walston and Kendall
0
I
T I
m m Hg -IO-
o-5
6-10 Meon
II-15 Pulmonary
16-20 Wedge
21-25 Pressure
26-x) (mmHg)
31-35
>35
Fig. 2. Plot of mean difference in mm. Hg of left atria1 pressure from mean wedge pressure (mm. Hg) in groups of 5 mm. Hg of mean wedge pressure. Points above and below the zero line signify mean left atria1 pressure greater and less than, respectively, mean pulmonary wedge pressure. Brackets surrounding these mean points signify the 95 per cent confidence limits. (The 95 per cent confidence limits of the data were determined by multiplying the standard error of the mean by the appropriate T value).’
Tuble II. Mean pukzonury wedgepressure vs. meun left atria2 pressure Pulmonary wedge pressure (mm.
group 3)
o-5 6-10 11-15 16-20 21-25 26-30 31-35 >35 *N = number tSignifies that
of patients the mean
Mean difference (mm. Hd
N*
39 207 163 111
0 0 0 0 0 -1t -3t -3
i; 28 16
Standard error of the mean (mm. Hd
*0 =J=O *0 +0 *O +1 *l *l
in each 5 mm. Hg incremental group. difference was statistically significant (P < 0.05).
the Swan-Ganz catheter) can be monitored at the bedside and, if valid, can provide vital data on left ventricular filling pressure.20,21Since left ventricular filling pressure is frequently elevated in acute myocardial infarction, correlation of pulmonary wedge with left atria1 pressure must be done over a wide range of pressures. The plot of mean wedge versus mean left atria1 pressure (Fig. 1) demonstrates little scatter around the regression line until the pressures exceed 10 mm. Hg. The near identity of the mean differences and the small standard errors between wedge and left atria1 pressure suggest that mean pulmonary wedge pressure is a moderately accurate predictor of mean left atria1 pressure at these low normal wedge pressures. The predictive ability of mean wedge pressure
(described by the 95 per cent confidence limits illustrated in Fig. 2) is directly related to the level of mean wedge pressure. When the wedge pressure is greater than 10 mm. Hg, the prediction of left atria1 pressure can be shown to contain considerable error. Ventricular filling pressure and other assessments of myocardial performance and valve areas cannot validly be calculated from the wedge pressure if it exceeds 10 mm. Hg. The increasing loss of correlation between wedge and mean left atria1 pressure at higher pressures may in part be explained by the findings of Caro and associates22who demonstrated that high pressures across the pulmonary capillary bed cause a change in the ratio of pulmonary arterial and pulmonary venous compliance promoting asymmetrical trans-
Pulmonary
mission of pressure waves across the pulmonary vascular bed. The present study was done in a retrospective manner and has all the errors in measurement which are inherent in the day-to-day operation of a diagnostic cardiac catheterization laboratory. Thus, it might be argued that meticulous attention to detail in pressure recording might yield a closer correlation. However, it is with this level of expertise in pressure measurement that hemodynamic data is collected on a routine basis.
wedge and left atria1 pressure
3.
4. 5. 6.
Summary Values of mean pulmonary wedge and mean left atria1 pressure were compared in 700 patients including normals and patients with a variety of heart diseases. An over-all correlation coefficient r = 0.93 was found between mean wedge and mean left atria1 pressure and this correlation was unrelated to the etiology of the heart disease. No significant difference between the average value of wedge and left atria1 pressure was found until the wedge pressure exceeded 25 mm. Hg. In patients with mean wedge pressures of 10 mm. Hg or less, left atria1 pressure could be predicted with an accuracy of +2 mm. Hg (9.5 per cent confidence limits). However, at higher wedge pressures the prediction of mean left atria1 pressure was subject to considerable error. Thus, caution should be employed in using mean wedge pressure as an accurate index of mean left atria1 pressure unless the wedge pressure is within the low normal range. The authors gratefully acknowledge the technical assistance of Iudith C. Rembert. Ph.D. The Deoartment of Medical Illustrations of the Durham Veterans Administration Hospital also rendered valuable support in the preparation of this paper. The secretarial assistance of Mrs. Rosa B. Ethridge and Mrs. Brenda Halev is herebv acknowledged.- Statistical analysis was performed by Philip McHale, Ph.D. The authors are also grateful to Dr. Yihong Kong of the Duke Cardiovascular Laboratory for making the catherization data available. REFERENCES 1. Hellems, H. K., Haynes, F. W., Dexter, L., and Kinney, T. D.: Pulmonary capillary pressure in animals estimated by venous and arterial catheterization, Am. J. Physiol. 155:98, 1948. 2. Forrester, James S., Diamond, George,
7,
8.
9. 10.
11. 12.
13.
14. 1.5.
16.
17.
in man
163
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