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Pulmonary blood volume and its significance in pulmonary hemodynamics immediately after mitral commissurotomy
Pulmonary blood volume and its significance in pulmonary hemodynamics immediately after mitral commissurotomy Immediately after mitral commissurotomy, we measured pulmonary blood volume by dye-dilution method and investigated the relationships between pulmonary blood volume and other hemodynamic parameters. Pulmonary blood volume correlated directly to pulmonary mean transit time, cardiac index, stroke volume index, and mean left atrial pressure. Pulmonary blood volume increased with mean pulmonary arterial pressures up to 35 mm. Hg but decreased with elevation above this level. The same patterns were observed in the correlations between pulmonary blood volume and both pulmonary distending pressure and pulmonary vascular resistance. These observations suggest that the changes of the pulmonary vessels begin with the elevation of mean pulmonary arterial pressure above 35 mm. Hg, pulmonary distending pressure above 25 mm. Hg or pulmonary vascular resistance above 5 units. Therefore, it is desirable to maintain mean pulmonary arterial pressure below 35 mm. Hg in patients immediately after mitral commissurotomy.
Tohru Sakamoto, M.D., and Takashi Yamada, M.D., Tokyo, Japan
A n the postoperative management of patients with heart disease, the major cardiopulmonary complications that are of clinical importance include low cardiac output syndrome, respiratory failure, and pulmonary hypertension. These problems occur more frequently in patients with mitral stenosis, a condition which is often associated with pulmonary hypertension and myocardial dysfunction even before operation. Pulmonary hemodynamics are determined by three factors, namely, flow, pressure and volume, the changes of which are interrelated. Of these three factors which affect pulmonary circulation, the measurement of pulmonary blood volume can be used as an aid to estimate the condition of the pulmonary vascular bed. The purposes of this report are to investigate the correlations between the pulmonary blood volume and
From the Division of Cardiovascular Surgery, First Department of Surgery, School of Medicine, Tokyo Medical and Dental University, Tokyo, Japan. Received for publication July 19, 1976. Accepted for publication Sept. 24, 1976. Address for reprints: Tohru Sakamoto, M.D., First Department of Surgery, School of Medicine, Tokyo Medical and Dental University, No. 1-5-45, Yushima, Bunkyo-Ku, Tokyo, Japan.
578
the other hemodynamic parameters and to evaluate the significance of the measurement of pulmonary blood volume in the postoperative monitoring of patients having cardiac surgery. Materials and method Ten patients with mitral stenosis, ranging in age from 26 to 52 years, were studied immediately after mitral commissurotomy. All had been taking a maintenance dose of digitalis glycosides prior to surgery. Nine patients were treated by closed mitral commissurotomy and the other patient by open mitral commissurotomy for restenosis of the valve. At operation, 19 gauge polyethylene catheters (30 cm. in length) were placed in the trunk of the pulmonary artery and the left atrium for the measurement of pressure and the injection of indocyanine green in order to investigate the postoperative hemodynamics. Indicator-dilution curves were recorded from the peripheral artery after rapidly sequential injections of indocyanine green (5 mg.) into the trunk of the pulmonary artery and the left atrium. The cardiac output and the mean transit time were calculated from these curves by means of the Lilienfield-Kovach1 formula. The pulmonary blood volume was calculated as follows: PBV = CI x (MTTpa-sa - MTTla-sa)
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Pulmonary blood volume
Number 4 April, 1977
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Fig. 1. Relationship between pulmonary blood volume and pulmonary mean transit time (MTTpa-la). A significant direct correlation is seen between these two parameters. Pulmonary blood volume changes inversely with the velocity of pulmonary blood flow. where PBV = pulmonary blood volume (milliliters per square meter), CI = mean cardiac index (milliliters per second per square meter) derived from the average of both curves, MTTpa-sa = mean transit time (seconds) from the trunk of the pulmonary artery to a systemic peripheral artery, and MTTla-sa = mean transit time (seconds) from the left atrium to a systemic peripheral artery. The pulmonary mean transit time (MTTpa-la), pulmonary distending pressure (PDP) and pulmonary vascular resistance (PVR) were calculated as follows: MTTpa-la (sec.) = MTTpa-sa - MTTla-sa PDP (mm. Hg) = (MPAP + MLAP)/2 PVR (unit) = (MPAP - MLAP)/CO where MPAP = mean pulmonary arterial pressure (millimeters of mercury) obtained by electronic integration, MLAP = mean left atrial pressure (millimeters of mercury) obtained by electronic integration, and CO = cardiac output (liters per minute). These measurements were made 0, 1,3, 6, 15, 18, 22, 24, and 27 hours after the operation. All patients were breathing spontaneously at the time of the study.
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Fig. 2. Relationship between pulmonary blood volume and cardiac index. A significant direct correlation is observed. ml/M* 600
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The Journal of Thoracic and Cardiovascular Surgery
5 8 0 Sakamoto and Yamada
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Fig. 4. Relationship between pulmonary blood volume and mean pulmonary arterial pressure (PAm). Pulmonary blood volume increases with mean pulmonary arterial pressure up to 35 mm. Hg, but then it decreases as mean pulmonary arterial pressure increases. Results Pulmonary blood volume was significantly correlated with pulmonary mean transit time (r = 0.7330, p < 0.001) (Fig. 1). There was a significant direct correlation between pulmonary blood volume and cardiac index (r = 0.6528, p < 0.001) (Fig. 2) and between pulmonary blood volume and stroke index (r = 0.6088, p < 0.001) (Fig. 3). Significance of these correlations may be debatable because pulmonary mean transit time and cardiac index enter into the calculation of pulmonary blood volume. However, since stroke index, which does not affect the calculation, varied directly with pulmonary blood volume, it is likely that these relationships are true. Pulmonary blood volume changed directly with the mean pulmonary arterial pressure up to 35 mm. Hg (r = 0.5980, p < 0.001), but then volume started decreasing as the mean pulmonary arterial pressure increased (Fig. 4). As shown in Fig. 5, although there was a wide scatter, pulmonary blood volume was correlated with the mean left atrial pressure (r = 0.2581, 0.02 < p < 0.05) (Fig. 5). Although the correlative coefficient was a low value, it was statistically significant because of many samples. The overestimation of pulmonary blood volume in some patients with a giant left atrium may be a
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Fig. 5. Relationship between pulmonary blood volume and mean left atrial pressure (LAm). Pulmonary blood volume is roughly correlated with mean left atrial pressure. main factor of this loose correlation between pulmonary blood volume and mean left atrial pressure. The similar changes which were observed in the relationship between pulmonary blood volume and mean pulmonary arterial pressure existed in the relation between pulmonary blood volume and pulmonary distending pressure and between pulmonary blood volume and pulmonary vascular resistance (Figs. 6 and 7). The pulmonary blood volume increased with the increase of pulmonary distending pressure up to 25 mm. Hg (r = 0.4715, p < 0.001), after which volume decreased. Similarly, pulmonary blood volume was correlated with pulmonary vascular resistance up to 5 units (r = 0.3606, 0.001 < p < 0.01), but then it changed inversely. Discussion Currently, dye-dilution methods are most widely used in determination of the pulmonary blood volume in man. There are three methods for measurement of the pulmonary blood volume by dye-dilution technique. 2-6 The first consists of dye injection into the main pulmonary artery and sampling of blood from the left atrium. In the second procedure, dye is injected sequentially into the pulmonary artery and the left atri-
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581
Pulmonary blood volume
Number 4 April, 1977
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Fig. 6. Relationship between pulmonary blood volume and pulmonary distending pressure (PDP). Pulmonary blood volume increases with the increase of pulmonary distending pressure up to 25 mm. Hg, and then it tends to fall.
Fig. 7. Relationship between pulmonary blood volume and pulmonary vascular resistance (PVR). Pulmonary blood volume is correlated with pulmonary vascular resistance up to 5 units, but then it tends to change inversely.
urn, and blood is sampled from a systemic artery. In the third method, dye is injected into the upper part of the inferior vena cava or the right atrium with simultaneous sampling from the pulmonary artery and the left atrium. Samet and co-workers6 evaluated these three dye-dilution methods and preferred the second method. They considered absence of a ventricular mixing chamber between injection and sampling sites as the most important source of error. The use of dye-dilution methods to estimate the pulmonary blood volume has various sources of error: (1) uneven distribution of the pulmonary blood flow and unequal dispersion of the indicator in both lungs; (2) shunts from the pulmonary circulation to the bronchial vessels; (3) inadequate and incomplete mixing of the dye injected into the left atrium; and (4) distortion of the dyedilution curves owing to recirculation. In the report by Dock and co-workers,7 an over-all error of 20 to 30 per cent in the calculation of pulmonary blood volume was estimated. In our study, a direct correlation was observed between pulmonary blood volume and pulmonary mean transit time, as has been previously reported.5' 7 Since pulmonary blood volume correlates directly with cardiac output and stroke volume, it is thought that pul-
monary blood volume acts as a blood reservoir of the left ventricle and helps to regulate cardiac output. Pulmonary blood volume changed directly with mean pulmonary arterial pressure up to 35 mm. Hg, but then it started decreasing as the mean pulmonary arterial pressure increased. Dock and co-workers7 studied the pulmonary blood volume in two groups which were subdivided by pulmonary vascular resistance at 500 dynes-sec.-cm.-5. In patients with low resistance, there was a direct correlation between these two parameters. However, patients with elevated resistance tended to have lower pulmonary blood volume than might have been expected from the pressure-volume relationship in the low resistance group. In this high resistance group, the mean pulmonary arterial pressure was elevated above 40 mm. Hg. Roy and co-workers8 reported that pulmonary blood volume increased with mean pulmonary arterial pressure up to 30 mm. Hg, remained unchanged despite an increase in the pressure from 30 to 40 mm. Hg, and decreased with its elevation above 40 mm. Hg. It is assumed from these observations that vasoconstriction or mechanical obstruction of the pulmonary vessels may take place at a mean pulmonary arterial pressure above 35 mm. Hg. In patients with heart disease who postoperatively have normal mean
582
Sakamoto and Yamada
left atrial pressure, high mean pulmonary arterial pressure above 35 mm. Hg, and normal or decreased pulmonary blood volume, the pulmonary vessels have irreversible changes even before operation. These include hypertrophy of the media, intimal proliferation, fibrosis of interstitial tissue, and pulmonary fhromboembolism. 9 , 10 Pulmonary blood volume correlated directly with mean left atrial pressure in this study, but out results were insufficient to estimate this relationship in the diseased state, since the highest mean left atrial pressure obtained was below 18 mm. Hg. Our observations support those of Roy and co-workers 8 that pulmonary blood volume correlates with mean left atrial pressure up to 27 mm. Hg but then changes inversely. The relation between pulmonary blood volume and pulmonary distending pressure showed the same pattern which was observed between pulmonary blood volume and mean pulmonary arterial pressure. However, this relationship also remains inconclusive, since mean pulmonary arterial pressure has greater influence in calculation of pulmonary distending pressure only because mean left atrial pressure was below 18 mm. Hg. In the pathogenesis of postoperative pulmonary insufficiency, elevation of pulmonary vascular pressure plays a dominant role, whereas changes in pulmonary blood volume are of secondary importance. Therefore, in the care of patients who have had heart surgery, it is reasonable to maintain mean pulmonary arterial pressure below 35 mm. Hg in order to avoid postoperative pulmonary insufficiency or pulmonary edema. This study suggests that measurement of pulmonary blood volume simultaneously with other parameters is a useful means of investigating pulmonary hemodynamics in patients after heart surgery. Summary Immediately after mitral commissurotomy, we measured pulmonary blood volume by the dye-dilution method and investigated the relationships between pulmonary blood volume and other hemodynamic parameters. Pulmonary blood volume correlated directly with pulmonary mean transit time, cardiac output, stroke volume index, and mean left atrial pressure. Pulmonary blood volume increased with mean pulmonary arterial pressures up to 35 mm. Hg but decreased with elevation of pressure above this level. The same patterns were observed in the correlations between pulmonary
The Journal of Thoracic and Cardiovascular Surgery
blood volume and both pulmonary distending pressure and pulmonary vascular resistance. These observations suggest that the changes of pulmonary vessels begin with the elevation of mean pulmonary arterial pressure above 35 mm. Hg, pulmonary distending pressure above 25 mm. Hg, or pulmonary vascular resistance above 5 units. Therefore, it is desirable to maintain mean pulmonary arterial pressure below 35 mm. Hg in patients immediately after mitral commissurotomy. Moreover, the measurement of pulmonary blood volume is a useful but merely additional parameter in estimation of the condition of the pulmonary vascular bed. We are grateful to Dr. Y. Imai, The Heart Institute of Japan, Tokyo, Japan, for preparing the manuscript. REFERENCES 1 Lilienfield, L. S., and Kovach, R. D.: Simplified Method for Calculating Flow, Mean Circulation Time and Down Slope From Indicator-Dilution Curves, Proc. Soc. Exp. Biol. Med. 91: 595, 1956. 2 Yu, P. N.: Pulmonary Blood Volume in Health and Disease, Philadelphia, 1969, Lea & Febiger, Publishers. 3 Nakhjavan, F. K., Maranhao, V., Son, R. and Goldberg, H.: Determination of Pulmonary Blood Volume by Injection Into Pulmonary Artery and Sampling in Left Atrium, Br. Heart J. 29: 602, 1967. 4 Levinson, G. E., Frank, M. J., and Hellems, H. K.: The Pulmonary Vascular Volume in Man: Measurement From Atrial Dilution Curves, Am. Heart J. 67: 734, 1964. 5 Freitas, F. M., Faraco, E. Z., Nedel, N., Azevedo, D. F., and Zaduchliver, J.: Determination of Pulmonary Blood Volume by Single Intravenous Injection of One Indicator in Patients With Normal and High Pulmonary Vascular Pressure, Circulation 30: 370, 1964. 6 Samet, P., Bernstein, W. H., Lopez, A., and Levine, S.: Methodology of True Pulmonary Blood Volume Determination, Circulation 33: 847, 1966. 7 Dock, D. S., Kraus, W. L., McGuri, L. B., Hyland, J. W., Haynes, F. W., and Dexter, L.: The Pulmonary Blood Volume in Man, J. Clin. Invest. 40: 317, 1961. 8 Roy, S. B., Bhardwaj, P., and Bhaia, M. L.: Pulmonary Blood Volume in Mitral Stenosis, Br. Med. J. 18: 1466, 1965. 9 Schreiner, B. F., Murphy, G. W., and Yu, P. N.: Pulmonary Blood Volume in Congestive Heart Failure, Circulation 34: 249, 1966. 10 Walston, A., Peter, R. H., Morris, J. J., Kong, Y., and Behar, V. S.: Clinical Implications of Pulmonary Hypertension in Mitral Stenosis, Am. J. Cardiol. 32: 650* 1973.
Tohru Sakamoto, M.D., and Takashi Yamada, M.D., Tokyo, Japan
A n the postoperative management of patients with heart disease, the major cardiopulmonary complications that are of clinical importance include low cardiac output syndrome, respiratory failure, and pulmonary hypertension. These problems occur more frequently in patients with mitral stenosis, a condition which is often associated with pulmonary hypertension and myocardial dysfunction even before operation. Pulmonary hemodynamics are determined by three factors, namely, flow, pressure and volume, the changes of which are interrelated. Of these three factors which affect pulmonary circulation, the measurement of pulmonary blood volume can be used as an aid to estimate the condition of the pulmonary vascular bed. The purposes of this report are to investigate the correlations between the pulmonary blood volume and
From the Division of Cardiovascular Surgery, First Department of Surgery, School of Medicine, Tokyo Medical and Dental University, Tokyo, Japan. Received for publication July 19, 1976. Accepted for publication Sept. 24, 1976. Address for reprints: Tohru Sakamoto, M.D., First Department of Surgery, School of Medicine, Tokyo Medical and Dental University, No. 1-5-45, Yushima, Bunkyo-Ku, Tokyo, Japan.
578
the other hemodynamic parameters and to evaluate the significance of the measurement of pulmonary blood volume in the postoperative monitoring of patients having cardiac surgery. Materials and method Ten patients with mitral stenosis, ranging in age from 26 to 52 years, were studied immediately after mitral commissurotomy. All had been taking a maintenance dose of digitalis glycosides prior to surgery. Nine patients were treated by closed mitral commissurotomy and the other patient by open mitral commissurotomy for restenosis of the valve. At operation, 19 gauge polyethylene catheters (30 cm. in length) were placed in the trunk of the pulmonary artery and the left atrium for the measurement of pressure and the injection of indocyanine green in order to investigate the postoperative hemodynamics. Indicator-dilution curves were recorded from the peripheral artery after rapidly sequential injections of indocyanine green (5 mg.) into the trunk of the pulmonary artery and the left atrium. The cardiac output and the mean transit time were calculated from these curves by means of the Lilienfield-Kovach1 formula. The pulmonary blood volume was calculated as follows: PBV = CI x (MTTpa-sa - MTTla-sa)
Volume 73
ml/M1 600
ml/M1 600
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579
Pulmonary blood volume
Number 4 April, 1977
3
a. 100 ■
1
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6
7
8
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10 11 seconds
PA-LA
Fig. 1. Relationship between pulmonary blood volume and pulmonary mean transit time (MTTpa-la). A significant direct correlation is seen between these two parameters. Pulmonary blood volume changes inversely with the velocity of pulmonary blood flow. where PBV = pulmonary blood volume (milliliters per square meter), CI = mean cardiac index (milliliters per second per square meter) derived from the average of both curves, MTTpa-sa = mean transit time (seconds) from the trunk of the pulmonary artery to a systemic peripheral artery, and MTTla-sa = mean transit time (seconds) from the left atrium to a systemic peripheral artery. The pulmonary mean transit time (MTTpa-la), pulmonary distending pressure (PDP) and pulmonary vascular resistance (PVR) were calculated as follows: MTTpa-la (sec.) = MTTpa-sa - MTTla-sa PDP (mm. Hg) = (MPAP + MLAP)/2 PVR (unit) = (MPAP - MLAP)/CO where MPAP = mean pulmonary arterial pressure (millimeters of mercury) obtained by electronic integration, MLAP = mean left atrial pressure (millimeters of mercury) obtained by electronic integration, and CO = cardiac output (liters per minute). These measurements were made 0, 1,3, 6, 15, 18, 22, 24, and 27 hours after the operation. All patients were breathing spontaneously at the time of the study.
4 5 L/min/M2
Cardiac Index
Fig. 2. Relationship between pulmonary blood volume and cardiac index. A significant direct correlation is observed. ml/M* 600
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Fig. 3. Relationship between pulmonary blood volume and stroke volume index. A significant direct correlation is observed.
The Journal of Thoracic and Cardiovascular Surgery
5 8 0 Sakamoto and Yamada
ml/M 1 600
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Fig. 4. Relationship between pulmonary blood volume and mean pulmonary arterial pressure (PAm). Pulmonary blood volume increases with mean pulmonary arterial pressure up to 35 mm. Hg, but then it decreases as mean pulmonary arterial pressure increases. Results Pulmonary blood volume was significantly correlated with pulmonary mean transit time (r = 0.7330, p < 0.001) (Fig. 1). There was a significant direct correlation between pulmonary blood volume and cardiac index (r = 0.6528, p < 0.001) (Fig. 2) and between pulmonary blood volume and stroke index (r = 0.6088, p < 0.001) (Fig. 3). Significance of these correlations may be debatable because pulmonary mean transit time and cardiac index enter into the calculation of pulmonary blood volume. However, since stroke index, which does not affect the calculation, varied directly with pulmonary blood volume, it is likely that these relationships are true. Pulmonary blood volume changed directly with the mean pulmonary arterial pressure up to 35 mm. Hg (r = 0.5980, p < 0.001), but then volume started decreasing as the mean pulmonary arterial pressure increased (Fig. 4). As shown in Fig. 5, although there was a wide scatter, pulmonary blood volume was correlated with the mean left atrial pressure (r = 0.2581, 0.02 < p < 0.05) (Fig. 5). Although the correlative coefficient was a low value, it was statistically significant because of many samples. The overestimation of pulmonary blood volume in some patients with a giant left atrium may be a
■
1
10 •
LAm
1
15
'
20 mmHg
Fig. 5. Relationship between pulmonary blood volume and mean left atrial pressure (LAm). Pulmonary blood volume is roughly correlated with mean left atrial pressure. main factor of this loose correlation between pulmonary blood volume and mean left atrial pressure. The similar changes which were observed in the relationship between pulmonary blood volume and mean pulmonary arterial pressure existed in the relation between pulmonary blood volume and pulmonary distending pressure and between pulmonary blood volume and pulmonary vascular resistance (Figs. 6 and 7). The pulmonary blood volume increased with the increase of pulmonary distending pressure up to 25 mm. Hg (r = 0.4715, p < 0.001), after which volume decreased. Similarly, pulmonary blood volume was correlated with pulmonary vascular resistance up to 5 units (r = 0.3606, 0.001 < p < 0.01), but then it changed inversely. Discussion Currently, dye-dilution methods are most widely used in determination of the pulmonary blood volume in man. There are three methods for measurement of the pulmonary blood volume by dye-dilution technique. 2-6 The first consists of dye injection into the main pulmonary artery and sampling of blood from the left atrium. In the second procedure, dye is injected sequentially into the pulmonary artery and the left atri-
ml/tf
600 • PVRS5 y=38.59x*150.36 r=0.36 06 0.001
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581
Pulmonary blood volume
Number 4 April, 1977
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Fig. 6. Relationship between pulmonary blood volume and pulmonary distending pressure (PDP). Pulmonary blood volume increases with the increase of pulmonary distending pressure up to 25 mm. Hg, and then it tends to fall.
Fig. 7. Relationship between pulmonary blood volume and pulmonary vascular resistance (PVR). Pulmonary blood volume is correlated with pulmonary vascular resistance up to 5 units, but then it tends to change inversely.
urn, and blood is sampled from a systemic artery. In the third method, dye is injected into the upper part of the inferior vena cava or the right atrium with simultaneous sampling from the pulmonary artery and the left atrium. Samet and co-workers6 evaluated these three dye-dilution methods and preferred the second method. They considered absence of a ventricular mixing chamber between injection and sampling sites as the most important source of error. The use of dye-dilution methods to estimate the pulmonary blood volume has various sources of error: (1) uneven distribution of the pulmonary blood flow and unequal dispersion of the indicator in both lungs; (2) shunts from the pulmonary circulation to the bronchial vessels; (3) inadequate and incomplete mixing of the dye injected into the left atrium; and (4) distortion of the dyedilution curves owing to recirculation. In the report by Dock and co-workers,7 an over-all error of 20 to 30 per cent in the calculation of pulmonary blood volume was estimated. In our study, a direct correlation was observed between pulmonary blood volume and pulmonary mean transit time, as has been previously reported.5' 7 Since pulmonary blood volume correlates directly with cardiac output and stroke volume, it is thought that pul-
monary blood volume acts as a blood reservoir of the left ventricle and helps to regulate cardiac output. Pulmonary blood volume changed directly with mean pulmonary arterial pressure up to 35 mm. Hg, but then it started decreasing as the mean pulmonary arterial pressure increased. Dock and co-workers7 studied the pulmonary blood volume in two groups which were subdivided by pulmonary vascular resistance at 500 dynes-sec.-cm.-5. In patients with low resistance, there was a direct correlation between these two parameters. However, patients with elevated resistance tended to have lower pulmonary blood volume than might have been expected from the pressure-volume relationship in the low resistance group. In this high resistance group, the mean pulmonary arterial pressure was elevated above 40 mm. Hg. Roy and co-workers8 reported that pulmonary blood volume increased with mean pulmonary arterial pressure up to 30 mm. Hg, remained unchanged despite an increase in the pressure from 30 to 40 mm. Hg, and decreased with its elevation above 40 mm. Hg. It is assumed from these observations that vasoconstriction or mechanical obstruction of the pulmonary vessels may take place at a mean pulmonary arterial pressure above 35 mm. Hg. In patients with heart disease who postoperatively have normal mean
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Sakamoto and Yamada
left atrial pressure, high mean pulmonary arterial pressure above 35 mm. Hg, and normal or decreased pulmonary blood volume, the pulmonary vessels have irreversible changes even before operation. These include hypertrophy of the media, intimal proliferation, fibrosis of interstitial tissue, and pulmonary fhromboembolism. 9 , 10 Pulmonary blood volume correlated directly with mean left atrial pressure in this study, but out results were insufficient to estimate this relationship in the diseased state, since the highest mean left atrial pressure obtained was below 18 mm. Hg. Our observations support those of Roy and co-workers 8 that pulmonary blood volume correlates with mean left atrial pressure up to 27 mm. Hg but then changes inversely. The relation between pulmonary blood volume and pulmonary distending pressure showed the same pattern which was observed between pulmonary blood volume and mean pulmonary arterial pressure. However, this relationship also remains inconclusive, since mean pulmonary arterial pressure has greater influence in calculation of pulmonary distending pressure only because mean left atrial pressure was below 18 mm. Hg. In the pathogenesis of postoperative pulmonary insufficiency, elevation of pulmonary vascular pressure plays a dominant role, whereas changes in pulmonary blood volume are of secondary importance. Therefore, in the care of patients who have had heart surgery, it is reasonable to maintain mean pulmonary arterial pressure below 35 mm. Hg in order to avoid postoperative pulmonary insufficiency or pulmonary edema. This study suggests that measurement of pulmonary blood volume simultaneously with other parameters is a useful means of investigating pulmonary hemodynamics in patients after heart surgery. Summary Immediately after mitral commissurotomy, we measured pulmonary blood volume by the dye-dilution method and investigated the relationships between pulmonary blood volume and other hemodynamic parameters. Pulmonary blood volume correlated directly with pulmonary mean transit time, cardiac output, stroke volume index, and mean left atrial pressure. Pulmonary blood volume increased with mean pulmonary arterial pressures up to 35 mm. Hg but decreased with elevation of pressure above this level. The same patterns were observed in the correlations between pulmonary
The Journal of Thoracic and Cardiovascular Surgery
blood volume and both pulmonary distending pressure and pulmonary vascular resistance. These observations suggest that the changes of pulmonary vessels begin with the elevation of mean pulmonary arterial pressure above 35 mm. Hg, pulmonary distending pressure above 25 mm. Hg, or pulmonary vascular resistance above 5 units. Therefore, it is desirable to maintain mean pulmonary arterial pressure below 35 mm. Hg in patients immediately after mitral commissurotomy. Moreover, the measurement of pulmonary blood volume is a useful but merely additional parameter in estimation of the condition of the pulmonary vascular bed. We are grateful to Dr. Y. Imai, The Heart Institute of Japan, Tokyo, Japan, for preparing the manuscript. REFERENCES 1 Lilienfield, L. S., and Kovach, R. D.: Simplified Method for Calculating Flow, Mean Circulation Time and Down Slope From Indicator-Dilution Curves, Proc. Soc. Exp. Biol. Med. 91: 595, 1956. 2 Yu, P. N.: Pulmonary Blood Volume in Health and Disease, Philadelphia, 1969, Lea & Febiger, Publishers. 3 Nakhjavan, F. K., Maranhao, V., Son, R. and Goldberg, H.: Determination of Pulmonary Blood Volume by Injection Into Pulmonary Artery and Sampling in Left Atrium, Br. Heart J. 29: 602, 1967. 4 Levinson, G. E., Frank, M. J., and Hellems, H. K.: The Pulmonary Vascular Volume in Man: Measurement From Atrial Dilution Curves, Am. Heart J. 67: 734, 1964. 5 Freitas, F. M., Faraco, E. Z., Nedel, N., Azevedo, D. F., and Zaduchliver, J.: Determination of Pulmonary Blood Volume by Single Intravenous Injection of One Indicator in Patients With Normal and High Pulmonary Vascular Pressure, Circulation 30: 370, 1964. 6 Samet, P., Bernstein, W. H., Lopez, A., and Levine, S.: Methodology of True Pulmonary Blood Volume Determination, Circulation 33: 847, 1966. 7 Dock, D. S., Kraus, W. L., McGuri, L. B., Hyland, J. W., Haynes, F. W., and Dexter, L.: The Pulmonary Blood Volume in Man, J. Clin. Invest. 40: 317, 1961. 8 Roy, S. B., Bhardwaj, P., and Bhaia, M. L.: Pulmonary Blood Volume in Mitral Stenosis, Br. Med. J. 18: 1466, 1965. 9 Schreiner, B. F., Murphy, G. W., and Yu, P. N.: Pulmonary Blood Volume in Congestive Heart Failure, Circulation 34: 249, 1966. 10 Walston, A., Peter, R. H., Morris, J. J., Kong, Y., and Behar, V. S.: Clinical Implications of Pulmonary Hypertension in Mitral Stenosis, Am. J. Cardiol. 32: 650* 1973.