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Blood flow measurements in human coarctation
Journal of 2 6
Thoracic and Cardiovascular Surgery
Blood flow measurements in human coarctation Studies on descending aorta and left subclavian and intercostal arteries before and after excision with repair Worthington G. Schenk, Jr., M.D., Khlar E. McDonald, M.D., and Murray N. Andersen, M.D., Buffalo, N.Y.
At has been shown that large flows can continue through marked experimental stenoses1 and through areas of artificial coarctation.2 Actual blood flow measure ments through human aortic coarctation have not been previously reported and form the substance of this report, together with concomitant flow studies on regional col lateral channels. Materials and methods Five young adults (15 to 23 years of age) with typical thoracic aortic coarctation, just distal to the subclavian artery, were studied. Following dissection of the aorta and left subclavian artery with division of a patent ductus arteriosus if present, flow measurements were performed using the square-wave electromagnetic flowmeter.*
From the Department of Surgery, State University of New York at Buffalo and the Edward J. Meyer Memorial Hospital, Buffalo, N. Y. Supported in part by a Grant-in-aid from the National Heart Institute (HE-03181) of the U. S. Public Health Service. Received for publication Jan. 21, 1965. •Carolina Medical Electronics, Winston-Salem, N. C.
Following excision of the stenotic segment with end-to-end anastomosis, the flow mea surements were repeated. In 2 cases it was possible to make recordings from the high est left intercostal artery. Results No complications resulted from the study procedures. However, in two instances it was believed that flow probe placement would create some hazard to the suture line, hence no aortic flow measurements were made following excision and repair. Aortic flow. Descending aorta flow values are shown in Table I. Aortic diameter at the site of constriction varied from 3 to 4 mm. as measured by a pathologist, on the re sected specimen. This indicated a 75 to 79 per cent reduction in aortic diameter but a 94 to 95 per cent reduction in aortic crosssectional area. In spite of this striking re duction in cross-sectional area, several liters per minute flowed through the constriction in 3 of the 4 patients. This represented 45 to 52 per cent of the estimated cardiac output for these 3 patients. Patient No. 1 who had only 0.78 L. per minute aortic
Volume 50
Blood flow measurements in coarctation
Number 1
27
July, 1965
the values obtained from measurements in the left subclavian artery before and after excision and repair. This vessel was mark edly enlarged in each case, ranging from 67 to 100 per cent of aortic diameter, and carried large pre-repair flow. Following ex cision and repair, flow values decreased in every case. A pulsatile left subclavian flow tracing, prior to repair, is shown in Fig. 1. A small reverse flow phase is present. Following re pair, as seen in Fig. 3, a much more striking reverse flow pattern is seen. Intercostal flow. Due to the fragility of the vessel, it was only possible to make flow measurements on the highest left intercostal artery in 2 patients and in 1 of these the vessel had to be sacrificed to enable repair. These results are shown in Table III. The large size of these vessels is well known (3.5 and 7.0 mm. diameter in these cases).
flow had markedly low subclavian flow at the same time and was thought to be in an unstable condition clinically. Following excision and repair, aortic flow decreased slightly in the 2 patients thought to be in good clinical condition before the repair, whereas the low flow value roughly doubled in the patient whose condition was believed to be unstable prior to repair. The instantaneous flow wave form re corded from the descending aorta is shown in Fig. 1. From the zero reference shown, which was obtained by momentary aortic occlusion, it can be seen that marked for ward flow through the coarctation continues throughout diastole. A similar sort of pattern is seen in Fig. 2. Following excision and re pair it can be seen that diastole is repre sented by a nearly flat interval which is near zero flow. Left subclavian artery flow. Table II lists
Table I. Descending aorta studies before and after resection of coarctation Aortic
Case no.
Age
Flow prior to repair
diameter
L./min.
% of est.% cardiac output
94 94
0.78 3.90
12 52
78
95
-
2.25 None measurable
45
79
95
2.80
49
Wgt. (lbs.)
Prox. to coarct. (mm.)
At stenosis (mm.*) 4.0 3.5
75 76
1 2
16 19
143 164
16.0 14.5
3 4
15 23
110 115
14.3
-
3.0 3.0t
5
23
127
19.1
4.0
% re duction % re in di duction ameter in area
-
Flow after repair 1.55 Could not be safely obtained 1.80 Could not be safely obtained 2.48
♦Measurement made by pathologist on resected specimen. tNo thrill palpable at operation; felt to be "functionally" totally occluded. ÎEstimated at 100 c.c. per kilogram of body weight per minute.
Table II. Studies of the left subclavian artery before and after resection of coarctation Left subclavian Vessel Case no.
mm.
1 2 3 4 5
16.0 11.1 11.1 14.3 12.7
artery
diameter %of aortic diameter
% of desc. aorta flow
100 77 78
40 25 29
— 67
130
Flow prior to repair (c.c./min.)
Flow after repair (c.c./min.)
310 986 640 735 3,700
125 563 448 512 1,730
Journal or
28
Schenk, McDonald,
Andersen
Thoracic and Cardiovascular Surgery
" COARCTATION OF THE"AORTA - P B K » T O «XOStON AND REPAIR | 1 sec, I
^'.J"
Descending Aorta Flow
Left Subclavian Artery Blow
„
M
,
Fig. 1. Case 3. Instantaneous blood flow recordings from descending aorta and left subclavian artery in patient with coarctation.
PRIOR TO REPAIR
I 1 sec
i
Deec. Aorta Flow
AFTER EXCISION AND REPAIR
Desc. Aorta Flow-
Fig. 2. Case 1. Flow tracings from descending aorta made before and after excision of aortic coarctation.
PRIOR TO REPAIR
, Left Subclavian Artery Flow
AFTER EXCISION AND REPAIR
Left Subclavian Artery Flow
Fig. 3. Case 4. Left subclavian artery flow tracings made before and after excision of aortic coarctation.
Volume 50 Number 1 July, 1965
Blood flow measurements in coarctation
Table III. Highest left intercostal artery flow before and after resection of coarctation
Case no. A
5
Vessel diameter (mm.) 7.0 3.5
Flow prior to repair (c.c./min.) 735* 58*
Flow
after repair (c.c./min.) 0 Vessel di vided be fore repair
*Flow toward aorta.
Direction of blood flow can be accurately determined with the electromagnetic flowmeter and in both instances the flow was reversed, that is, flow in the intercostal arteries was toward the aorta in the inter costal arteries. Following repair, in patient No. 4, excellent pulsations continued in the intercostal artery but no mean flow was detectable. Discussion The present evidence obtained from mea surements on human coarctation of the aorta confirms experimental studies indicating that high levels of blood flow may continue through an area of marked arterial constric tion (up to 95 per cent reduction in crosssectional area); the elevation of pressure proximal to the coarctation no doubt con tributes substantial aid to this rather high level of flow since it is known that a pres sure gradient exists across coarctation. If one considers the combined total of flow through the area of coarctation plus the high level of flow through the markedly enlarged subclavian artery and intercostal arteries, support is gained for the clinical evidence of flow which is relatively normal in amount to that portion of the body distal to the coarc tation. However, it is obvious that the flow pulse characteristic in the patient with co arctation of the aorta is markedly abnormal. The relatively narrow flow pulse with the continued high level of forward flow through the coarctation during diastole is in marked contrast to that which occurs normally.
29
These data support the concept of the proximal vascular bed as a large elastic reservoir capable of generating continued forward propulsion of blood during the cardiac diastolic phase. The variation from normal is illustrated in a striking way by the change in flow characteristics after repair in which tracings revert to those considered to be normal on the basis of previous experi mental and clinical work. If one considers the flow pulse character istic at the level of the lower thoracic aorta, which may represent that being provided to the abdominal viscera, it is evident that mea surements of flow pulse made at the level of coarctation are not representative of the characteristics at a lower level. This dis crepancy would result from the substantial portion of descending aortic flow provided by the intercostal arteries as documented here. To what extent the pulse characteristic at lower levels would vary from those mea sured at the level of the coarctation can be only speculative; however, it can reasonably be assumed that the flow pulse characteristic, as measured after repair, is representative of that being delivered to the viscera, since this limited evidence suggests that little flow continues through the intercostal arteries after the coarctation has been removed. It has been widely held that the renal factor is critical in the development of hy pertension proximal to coarctation of the aorta. Although previous data have indicated that blood flow through the kidneys is rel atively normal in amount in patients with coarctation, as measured by conventional methods, it is evident that such flow reaches the kidneys with an abnormally small pres sure pulse and flow pulse. The significance of this cannot readily be determined, but it seems the most striking difference which can be clearly demonstrated between the state of blood flow to the kidney before and after the repair of coarctation. Direct record ing of renal artery instantaneous flow would be of great interest but, as yet, the oppor tunity for making such a study has not pre sented itself.
Journal of
30
Schenk, McDonald,
Andersen
Thoracic and Cardiovascular Surgery
The demonstration that the flow pattern in intercostal areas is reversed confirms pre vious angiographie impressions. It is interest ing to note that, following repair, flow ap pears to be nearly balanced, since no flow in either direction was measured. This situation might have been* assumed to result since, after repair, the pressure head on each end of the intercostal arteries should be equal. The marked decrease in subclavian artery flow after repair supports this observation since one should expect that, after repair, flow through subclavian vessels should be largely only that required for perfusion of the body tissues normally obtained from this vessel and the relative decrease in flow should provide an index of the percentage flow provided to the lower body via the sub clavian route in the patients with coarctation. It is obvious that in instances of complete coarctation a substantially larger percentage of the lower body flow would need to be provided through this route. However, in none of the cases presently studied was a complete coarctation present.
Summary 1. Direct electromagnetic flow recordings were made from the descending aorta, left subclavian artery, and highest intercostal artery in 5 young adults before and after excision and repair of typical thoracic aortic coarctation. 2. Descending aorta flow was high (45 to 52 per cent estimated cardiac output) in spite of constrictions representing 94 to 95 per cent reduction in aortic cross-sectional area. 3. The left subclavian artery was regular ly enlarged to 67 to 100 per cent of aortic diameter and carried high blood flows. 4. Highest intercostal flow was reversed (that is, toward the aorta) prior to repair. REFERENCES 1 Cannon, J. A., Lobpreis, E. L., Herrold, G., and Frankenberg, H. L.: Experience With a New Electromagnetic Flowmeter for Use in Blood Flow Determinations in Surgery, Ann. Surg. 152: 635, 1960. 2 Schenk, W. G., Jr., Menno, A. D., and Martin, J. W.: Hemodynamics of Experimental Coarcta tion of the Aorta, Ann. Surg. 153: 163, 1961.
Thoracic and Cardiovascular Surgery
Blood flow measurements in human coarctation Studies on descending aorta and left subclavian and intercostal arteries before and after excision with repair Worthington G. Schenk, Jr., M.D., Khlar E. McDonald, M.D., and Murray N. Andersen, M.D., Buffalo, N.Y.
At has been shown that large flows can continue through marked experimental stenoses1 and through areas of artificial coarctation.2 Actual blood flow measure ments through human aortic coarctation have not been previously reported and form the substance of this report, together with concomitant flow studies on regional col lateral channels. Materials and methods Five young adults (15 to 23 years of age) with typical thoracic aortic coarctation, just distal to the subclavian artery, were studied. Following dissection of the aorta and left subclavian artery with division of a patent ductus arteriosus if present, flow measurements were performed using the square-wave electromagnetic flowmeter.*
From the Department of Surgery, State University of New York at Buffalo and the Edward J. Meyer Memorial Hospital, Buffalo, N. Y. Supported in part by a Grant-in-aid from the National Heart Institute (HE-03181) of the U. S. Public Health Service. Received for publication Jan. 21, 1965. •Carolina Medical Electronics, Winston-Salem, N. C.
Following excision of the stenotic segment with end-to-end anastomosis, the flow mea surements were repeated. In 2 cases it was possible to make recordings from the high est left intercostal artery. Results No complications resulted from the study procedures. However, in two instances it was believed that flow probe placement would create some hazard to the suture line, hence no aortic flow measurements were made following excision and repair. Aortic flow. Descending aorta flow values are shown in Table I. Aortic diameter at the site of constriction varied from 3 to 4 mm. as measured by a pathologist, on the re sected specimen. This indicated a 75 to 79 per cent reduction in aortic diameter but a 94 to 95 per cent reduction in aortic crosssectional area. In spite of this striking re duction in cross-sectional area, several liters per minute flowed through the constriction in 3 of the 4 patients. This represented 45 to 52 per cent of the estimated cardiac output for these 3 patients. Patient No. 1 who had only 0.78 L. per minute aortic
Volume 50
Blood flow measurements in coarctation
Number 1
27
July, 1965
the values obtained from measurements in the left subclavian artery before and after excision and repair. This vessel was mark edly enlarged in each case, ranging from 67 to 100 per cent of aortic diameter, and carried large pre-repair flow. Following ex cision and repair, flow values decreased in every case. A pulsatile left subclavian flow tracing, prior to repair, is shown in Fig. 1. A small reverse flow phase is present. Following re pair, as seen in Fig. 3, a much more striking reverse flow pattern is seen. Intercostal flow. Due to the fragility of the vessel, it was only possible to make flow measurements on the highest left intercostal artery in 2 patients and in 1 of these the vessel had to be sacrificed to enable repair. These results are shown in Table III. The large size of these vessels is well known (3.5 and 7.0 mm. diameter in these cases).
flow had markedly low subclavian flow at the same time and was thought to be in an unstable condition clinically. Following excision and repair, aortic flow decreased slightly in the 2 patients thought to be in good clinical condition before the repair, whereas the low flow value roughly doubled in the patient whose condition was believed to be unstable prior to repair. The instantaneous flow wave form re corded from the descending aorta is shown in Fig. 1. From the zero reference shown, which was obtained by momentary aortic occlusion, it can be seen that marked for ward flow through the coarctation continues throughout diastole. A similar sort of pattern is seen in Fig. 2. Following excision and re pair it can be seen that diastole is repre sented by a nearly flat interval which is near zero flow. Left subclavian artery flow. Table II lists
Table I. Descending aorta studies before and after resection of coarctation Aortic
Case no.
Age
Flow prior to repair
diameter
L./min.
% of est.% cardiac output
94 94
0.78 3.90
12 52
78
95
-
2.25 None measurable
45
79
95
2.80
49
Wgt. (lbs.)
Prox. to coarct. (mm.)
At stenosis (mm.*) 4.0 3.5
75 76
1 2
16 19
143 164
16.0 14.5
3 4
15 23
110 115
14.3
-
3.0 3.0t
5
23
127
19.1
4.0
% re duction % re in di duction ameter in area
-
Flow after repair 1.55 Could not be safely obtained 1.80 Could not be safely obtained 2.48
♦Measurement made by pathologist on resected specimen. tNo thrill palpable at operation; felt to be "functionally" totally occluded. ÎEstimated at 100 c.c. per kilogram of body weight per minute.
Table II. Studies of the left subclavian artery before and after resection of coarctation Left subclavian Vessel Case no.
mm.
1 2 3 4 5
16.0 11.1 11.1 14.3 12.7
artery
diameter %of aortic diameter
% of desc. aorta flow
100 77 78
40 25 29
— 67
130
Flow prior to repair (c.c./min.)
Flow after repair (c.c./min.)
310 986 640 735 3,700
125 563 448 512 1,730
Journal or
28
Schenk, McDonald,
Andersen
Thoracic and Cardiovascular Surgery
" COARCTATION OF THE"AORTA - P B K » T O «XOStON AND REPAIR | 1 sec, I
^'.J"
Descending Aorta Flow
Left Subclavian Artery Blow
„
M
,
Fig. 1. Case 3. Instantaneous blood flow recordings from descending aorta and left subclavian artery in patient with coarctation.
PRIOR TO REPAIR
I 1 sec
i
Deec. Aorta Flow
AFTER EXCISION AND REPAIR
Desc. Aorta Flow-
Fig. 2. Case 1. Flow tracings from descending aorta made before and after excision of aortic coarctation.
PRIOR TO REPAIR
, Left Subclavian Artery Flow
AFTER EXCISION AND REPAIR
Left Subclavian Artery Flow
Fig. 3. Case 4. Left subclavian artery flow tracings made before and after excision of aortic coarctation.
Volume 50 Number 1 July, 1965
Blood flow measurements in coarctation
Table III. Highest left intercostal artery flow before and after resection of coarctation
Case no. A
5
Vessel diameter (mm.) 7.0 3.5
Flow prior to repair (c.c./min.) 735* 58*
Flow
after repair (c.c./min.) 0 Vessel di vided be fore repair
*Flow toward aorta.
Direction of blood flow can be accurately determined with the electromagnetic flowmeter and in both instances the flow was reversed, that is, flow in the intercostal arteries was toward the aorta in the inter costal arteries. Following repair, in patient No. 4, excellent pulsations continued in the intercostal artery but no mean flow was detectable. Discussion The present evidence obtained from mea surements on human coarctation of the aorta confirms experimental studies indicating that high levels of blood flow may continue through an area of marked arterial constric tion (up to 95 per cent reduction in crosssectional area); the elevation of pressure proximal to the coarctation no doubt con tributes substantial aid to this rather high level of flow since it is known that a pres sure gradient exists across coarctation. If one considers the combined total of flow through the area of coarctation plus the high level of flow through the markedly enlarged subclavian artery and intercostal arteries, support is gained for the clinical evidence of flow which is relatively normal in amount to that portion of the body distal to the coarc tation. However, it is obvious that the flow pulse characteristic in the patient with co arctation of the aorta is markedly abnormal. The relatively narrow flow pulse with the continued high level of forward flow through the coarctation during diastole is in marked contrast to that which occurs normally.
29
These data support the concept of the proximal vascular bed as a large elastic reservoir capable of generating continued forward propulsion of blood during the cardiac diastolic phase. The variation from normal is illustrated in a striking way by the change in flow characteristics after repair in which tracings revert to those considered to be normal on the basis of previous experi mental and clinical work. If one considers the flow pulse character istic at the level of the lower thoracic aorta, which may represent that being provided to the abdominal viscera, it is evident that mea surements of flow pulse made at the level of coarctation are not representative of the characteristics at a lower level. This dis crepancy would result from the substantial portion of descending aortic flow provided by the intercostal arteries as documented here. To what extent the pulse characteristic at lower levels would vary from those mea sured at the level of the coarctation can be only speculative; however, it can reasonably be assumed that the flow pulse characteristic, as measured after repair, is representative of that being delivered to the viscera, since this limited evidence suggests that little flow continues through the intercostal arteries after the coarctation has been removed. It has been widely held that the renal factor is critical in the development of hy pertension proximal to coarctation of the aorta. Although previous data have indicated that blood flow through the kidneys is rel atively normal in amount in patients with coarctation, as measured by conventional methods, it is evident that such flow reaches the kidneys with an abnormally small pres sure pulse and flow pulse. The significance of this cannot readily be determined, but it seems the most striking difference which can be clearly demonstrated between the state of blood flow to the kidney before and after the repair of coarctation. Direct record ing of renal artery instantaneous flow would be of great interest but, as yet, the oppor tunity for making such a study has not pre sented itself.
Journal of
30
Schenk, McDonald,
Andersen
Thoracic and Cardiovascular Surgery
The demonstration that the flow pattern in intercostal areas is reversed confirms pre vious angiographie impressions. It is interest ing to note that, following repair, flow ap pears to be nearly balanced, since no flow in either direction was measured. This situation might have been* assumed to result since, after repair, the pressure head on each end of the intercostal arteries should be equal. The marked decrease in subclavian artery flow after repair supports this observation since one should expect that, after repair, flow through subclavian vessels should be largely only that required for perfusion of the body tissues normally obtained from this vessel and the relative decrease in flow should provide an index of the percentage flow provided to the lower body via the sub clavian route in the patients with coarctation. It is obvious that in instances of complete coarctation a substantially larger percentage of the lower body flow would need to be provided through this route. However, in none of the cases presently studied was a complete coarctation present.
Summary 1. Direct electromagnetic flow recordings were made from the descending aorta, left subclavian artery, and highest intercostal artery in 5 young adults before and after excision and repair of typical thoracic aortic coarctation. 2. Descending aorta flow was high (45 to 52 per cent estimated cardiac output) in spite of constrictions representing 94 to 95 per cent reduction in aortic cross-sectional area. 3. The left subclavian artery was regular ly enlarged to 67 to 100 per cent of aortic diameter and carried high blood flows. 4. Highest intercostal flow was reversed (that is, toward the aorta) prior to repair. REFERENCES 1 Cannon, J. A., Lobpreis, E. L., Herrold, G., and Frankenberg, H. L.: Experience With a New Electromagnetic Flowmeter for Use in Blood Flow Determinations in Surgery, Ann. Surg. 152: 635, 1960. 2 Schenk, W. G., Jr., Menno, A. D., and Martin, J. W.: Hemodynamics of Experimental Coarcta tion of the Aorta, Ann. Surg. 153: 163, 1961.