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Effects of experimental recurrent microembolization on pulmonary function and distribution of labeled macroaggregates of sulfur
Effects of Experimental Recurrent Microembolization on Pulmonary Function and Distribution of Labeled Macroaggregates of Sulfur MICHAEL E. REIF, MD, Oklahoma City, Oklahoma DAVID G. KASTL, BS, Oklahoma City, Oklahoma JACQUELINE J. COALSON, PhD, Oklahoma City, Oklahoma LAZAR J. GREENFIELD, MD, Oklahoma City, Oklahoma
The spectrum of pulmonary embolic disease ranges from macroemboli capable of producing acute cardiorespiratory failure to microemboli more likely to produce an insidious picture of car pulmonale. Estimates of the incidence of embolic disease in surgical patients vary greatly, but in one report, pulmonary embolization was observed postoperatively in one of every seven patients, with a mortality rate of 22 per cent [I]. Survivors of pulmonary emboli usually have clearance of their pulmonary vascular bed by autogenous lysis, but remain likely candidates for recurrent embolization and the development of chronic pulmonary hypertension and car pulmonale [Z-4]. In one autopsy series of 132 cases of nonfatal emboli, 10 per cent showed right ventricular hypertrophy related to recurrent emboli of which half were in small muscular arteries or arterioles [5] . Similarly in patients who had undergone vena caval ligation, the frequency of recurrent pulmonary embolization was recently reported to be greater than 50 per cent [6]. Since this embolization usually occurs as showers of microemboli, the diagnosis often is not suspected. Most experimental studies of pulmonary embolism have dealt with the acute responses to pulmonary emboli, and there is a need for further observations of the chronic hemodynamic and ventilatory responses to pulmonary microembolization. This study was undertaken to measure the From the Department of Surgery. University of Oklahoma Medical Center. 800 NE 13th Street, Oklahoma City, Oklahoma: and the Veterans Administration Hospital, 921 NE 13th Street, Oklahoma City, Oklahoma 73104. This investigation was supported in part by US Navy Contract N00014-68-A-0946 and the Markle Foundation. Presented at the Twenty-Third Annual Meeting of the Southwestern Surgical Congress, Las Vegas, Nevada, April 19-22, 1971.
616
effects of recurrent microembolization on pulmonary function and blood flow in the dog. In addition, a correlation of pulmonary arteriovenous shunting with radioisotope distribution to the lung and liver was made to explore this simpler method of diagnosis. Materials and Methods Adult mongrel dogs screened for dirofilaria immitis and weighing from 18 to 28 kg were anesthetized with pentobarbital sodium (20 to 25 m/kg body weight), and 6ntubated with a cuffed endotracheal tube. The animals were hyperinflated periodically by positive pressure to prevent atelectasis. A cannula was inserted in the femoral artery and a number 8 NIH cardiac catheter was positioned through the femoral vein into the pulmonary artery under flouroscopy. Expired gas samples were collected in a water-sealed spirometer for a minimum of three minutes. Simultaneous determinations of arterial PO?, PC02, and pH were performed utilizing a gas analyzer (IL Model 113) calibrated with known gas mixtures. Using these data, minute ventilation (V,), tidal volume (V,), physiologic dead space (V,) , oxygen consumption, carbon dioxide production, the respiratory quotient, and alveolar-arterial oxygen tension gradient ( A-aDO,) were calculated. During the period of gas collection, cardiac output determinations were made in duplicate by the indicator dilution technic. The area under the dye curves was determined by a Gilford 104E Dye Curve Computer and was checked periodically by semi-logarithmic plotting technics. Oscillographic recordings of systemic and pulmonary arterial pressures were used to calculate total systemic and pulmonary vascular resistance (PVR). Lung scintiphotography was performed at the same time as the sequential hemodynamic and ventilatory studies. Two millicuries of technetium 99m macroaggregated sulfur colloid was injected intravenously
The
American
Journal
of
Surgery
Experimental
I
TABLE
Dog Number 1560 1563 4478 7475 7805 7811 Mean
Time Interval (days) between Last Embolization and Restudy Periods
Three to Four Weeks (days)
Seven to Eight Weeks (days)
3 3 9
10 10 11 11 31 11
a 8 9 6.7
14
Ten to Eleven Weeks (days) 7 7 36 28 32 Died 22
slowly, and scintiphotos in three views were obtained using the Nuclear Chicago Phogamma III camera. Consistent and uniform particle size (10 to 50~) was insured by microscopic examination on a hemocytometer grid. External counts of the lung and liver for one minute were obtained within fifteen minutes of injection of the isotope utilizing the Nuclear-Chicago PhoDot rectilinear scanner with scaler and a low energy collimator. Areas of greatest radioactivity over both right and left lungs were averaged and the ratio of liver to lung counts was calculated. Seven normal dogs were studied to determine control liver to lung count ratios. Twelve animals were administered microemboli in the form of polystyrene microspheres, 300 to 850p in diameter. Embolization was performed via a chronic indwelling superior vena caval catheter at one to two week intervals for eight to twelve weeks. Pre-embolization hemodynamic and ventilatory studies were performed on all dogs. Postembolization studies were performed at three to four weeks, seven to eight weeks, and ten to eleven weeks after initiation of embolization. In the first postembolic period, a period of seven days was allowed to elapse between the last embolization and restudy to avoid transient hemodynamic changes. In the second period the average interval was fourteen days and in the third, twenty-two days, (Table I.) Initial microsphere dosages of 2 to 2.5 gm were established arbitrarily on the basis of survival experience. Subsequent doses of 1 to 2 gm were administered and the average total dose by the first restudy period was 7.3 gm. At the second and third examinations the average doses were 9.0 and 10.6 gm of beads, respectively. (Table II.) Results
Six animals died before restudy could be performed, usually shortly after embolization. Postmortem examinations on these dogs revealed multiple areas of gross lung hemorrhage, pulmonary edema, right ventricular dilatation, pleural effusions, and in one case anasarca. Three dogs died after re-evaluation of their hemodynamic and ventilatory functions, again usually after
Volume 122, November 1971
TABLE
II
_~.___
--
Dog Number 1560 1563 4478 7475 7805 7811 Mean
Microembolization
Total Microemboli Restudy Period
and
Pulmonary
Doses (gm) at Each
Three to Four Weeks (gm)
Seven to Eight Weeks (gm)
6 6 8 a 8 a
a a 10 10 9 9
7.3
Function
9.0
Ten to Eleven Weeks (gm) 11 11 10 12 9 Died 10.6
additional embolization, Autopsies revealed antemortem thrombus in the pulmonary arteries in two dogs (Figure 1) and extensive collateral vasculature of the lungs. Microspheres were found in the thrombi which occluded major divisions of the right and left pulmonary arteries. In one of these animals the mean pulmonary arterial pressure prior to death was 86 mm Hg and the associated extensive thrombosis appeared to be a major contributing factor. The three surviving animals subsequently underwent pneumonectomy in preparation for lung transplantation which will be reported separately. At the time of surgery markedly dilated bronchial collateral vessels were found as well as numerous vascular adhesions between parietal and visceral pleura containing some arteries measuring 2 to 3 mm in diameter. Light microscopy (Figure 2) revealed ectasia of the bronchial arteries and microsphere emboli which appear to be encapsulated in vascular-like structures outside of adjacent pulmonary and bronchial arteries. Organizing thrombus was seen adjacent to the microspheres. No areas of organized pulmonary infarction were found. In animals that died acutely after embolization, intra-alveolar and interstitial hemorrhage and peribronchial congestion were noted. Excluding the one dog that died with extensive thrombosis of several pulmonary arterial branches and pulmonary hypertension, pulmonary arterial pressure did not remain increased significantly. (Figure 3.) Cardiac output did increase significantly from .172 L/min/kg to .212 L/min/kg (p <.05) by ten to eleven weeks after initiation of embolization. (Figure 4.) Total pulmonary vascular resistance had increased 27 per cent by the first restudy period but then returned to control values. Arterial oxygen tension dropped significantly from a mean 81.2 mm Hg to 69 and 64 mm Hg (p
617
Reif et al
Figure 1. Antemortem thrombus (marker) in left lower lobar pulmonary artery of a dog that died with pulmonary hypertension. This was the only instance of persistent hypertension after microembolization and indicates that arteries larger than those obstructed by microemboli must be blocked before pulmonary hypertension develops (forma/in-fixed specimen).
Figure 2. Light microscopy of lung removed from an animal which died after repeated microembolization. Bronchus is upper left; microspheres are impacted in a small pulmonary artery, lower right. Several ectatic bronchial arteries are seen adjacent to bronchus. Increased bronchial collateral vasculature was observed in all chronic survivors of embolization (hematoxylin and eosin stain; original magnification X83).
< .Ol) by the first and second restudy periods, respectively. The Pa.Oz had returned to normal at ten to eleven weeks which was after a longer interval after the last embolization. (Figure 5.) Similarly, the A-aOs gradient increased from a mean of 25.3 mm Hg to a maximum of 49 mm Hg mean by seven to eight weeks (p < .Ol) and then returned to control levels after embolization was stopped. (Figure 6.) Ventilatory dead space increased by 55 per cent at three to four weeks and remained significantly elevated (p < .05) despite the longer interval after the last embolization.
(Figure ‘7.) Dead space to tidal volume did not increase appreciably owing to proportionate increases in both V,, and VT. Lung scintiphotograms in all animals revealed decreased uptake of isotope, decreased peripheral perfusion, and increased uptake of isotope by the liver when compared to pre-embolization control scans. In Figure 8 these findings are illustrated with scintiphotos obtained twenty-five days after the last embolization. After the observation of increased liver uptake of isotope, liver and lung counts were obtained on seven nonembolized dogs
1 I , 1 I , , , ( 0 2 4 6 0 10 12 14 TIME ( WEEK5 1
, 16
Mean pulmonary arterial Figure 3. pressures of each chronic survivor at the specified restudy periods. Pressures represent chronic responses to embolization with polystyrene beads. Persistent pulmonary hypertension prior to death developed in only one animal.
618
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i
2
:1
iE
Mean cardiac output inFigure 4. creased significantly (p < .05) by the third restudy period in chronic survivors of microembolization. With the lack of significant elevation of pulmonary arterial pressure, pulmonary vascular resistance remained normal.
Mean arterial oxygen Figure 5. tension decreased significantly by both the first and second restudy periods (p < .Ol) but returned to control values at ten to eleven weeks. Chronic hypoxia thus occurred despite normal pulmonary vascular resistance and pressure.
The American
Journal
of SurEery
Experimental
and compared with similar counts in six embolized dogs. The liver to lung mean ratio in nonembolized dogs was .023 I+ ,013, whereas the mean ratio in the embolized animals was .108 + .061. This difference is statistically significant (p < .Ol). (Table III.) Comparison of the liver to lung ratios with the A-aD0, showed a high degree of correlation (R = .91, p < .005). (Figure 9.) In five animals embolization was continued after the third restudy period. Three of these dogs survived for further evaluation after having received an additional 4 to 6 gm of beads. Pulmonary arterial pressure decreased by an average of 29 per cent and total pulmonary vascular resistance decreased an average of 30 per cent while the cardiac output was unchanged. Arterial POZ decreased by 22 per cent and the A-aD0, increased 66 per cent. VD and V,,/V, also increased by an average of 210 per cent and 65 per cent, respectively. With this small group, these changes cannot be evaluated statistically, but they do indicate lack of progressive pulmonary hypertension or increased PVR associated with increased hypoxia. (Table IV.)
TABLE III
Microembolization
and
Function
Lung and Liver One Minute Counts after Intravenous Injection of 2 mc Technetium 99m Macroaggregates
-
Pulmonary
Dog Number -._ Control Animals 7634 7636 7564 3364 3121 1997 Mean Standard deviation
of Sulfur
Mean LungCount
LiverCount
Liver to Lung Ratio
66,700 72,950
2,200 1,850
0.033 0.025
900 2,800 800 500 ...
0.008 0.042 0.013 0.010 .023
111,500 67,000 60,600 49,350 ... ...
Embolized Dogs 1563 1560 7475 4478 7637 7805 Mean Standard deviation Significance
Colloid
72,650 46,430 89,800 58,050 65,600 65,000 *..
... 1,940 3,040 15,000 10,900 6,000 7,050 ...
... ...
... ...
rt.013 0.027 0.065 0.170 0.188 0.092 0.108 .108 1tz.061 p <.Ol
Comments Although the acute response to experimental pulmonary microembolization is pulmonary hypertension [7,8], persistently elevated pulmonary arterial pressure generally is not seen [9]. However, Saleh and Hardy [IO] demonstrated elevated right ventricular pressures in dogs embolized daily with barium sulfate suspension over a period of five to six weeks. In this study, pulmonary arterial pressure and vascular resistance in six dogs followed eight to twenty-two weeks after
initiation of embolization did not change significantly from pre-embolization levels with one exception. The clinical experience that continued embolization produces pulmonary hypertension in man [Z-G] suggests that the observations in this study represent either a stage prior to the onset of irreversible pulmonary hypertension and car pulmonale or a different anatomic distribution of the emboli precluding the formation of pulmonary hypertension This latter explanation seems more
CONTROL
1)
I,# POST
tONllOL
3-4 WEEKS
7-8 WEEKS
IO-11 WEEK5
Figure 6. Mean alveolar-arterial oxygen tension gradient increased significantly (p < .Ol) by the second restudy period before returning to the control level. In view of normal pulmonary arterial pressures and PVR, arteriovenous shunting must be a major contributing factor to the increased gradient.
Volume 122, November 1971
EMBOLl
Figure 7. Mean ventijatory dead space was persistently increased in all restudy periods (p < .05). The &/VT ratio did not increase since a proportionate increase in VT occurred. Elevated dead space ventilation is further evidence that an imbalance in the ventilation-perfusion relationship exists.
Figure 8. Control scintiphoto and scintiphoto obtained twenty-five days after the last embolizatron. Posteroanterior, left oblique, and right oblique views are from left to right. Decreased peripheral perfusion and increased liver uptake of isotope were observed in all survivers of embolization.
619
Reif et al
did not reveal evidence of early liver uptake of isotope, indicating that the macroaggregates are stable during the time required for lung scintiphotography and liver counting. Thus, this early appearance of isotope in the liver (within fifteen minutes after injection) cannot be attributed to breakdown of the macroaggregates with passage on through the pulmonary capillary bed. Arteriovenous shunting has been observed in acute microembolization [S] with glass beads less than 420 p in diameter. These shunts appear to open with either elevated pulmonary arterial pressure alone or hypoxia which produces pulmonary arteriolar vasoconstriction. The lung scintigram changes with microembolization are similar to those described in dogs embolized with glass microspheres [I21 and in man [13]. Peripheral perfusion is diminished and interlobar fissures often are accentuated. Ventilatory dead space increased soon after microembolization and remained elevated. This has been described previously as a useful diagnostic aid [2,14]. Light microscopic and gross specimen examinations demonstrated increased collateral circulation. The lack of pulmonary arteriolar muscular hypertrophy indicates that the vascular bed has been protected from the development of increased resistance to flow despite the fact that the emboli are nonresolving. The visualization of emboli in vascular-like structures adjacent to pulmonary and bronchial arteries may be evidence that the beads plugged some arteriovenous shunts. The fact that thrombi were observed grossly in two dogs and microscopically in others indicates that polystyrene beads are thrombogenic and clearance of thrombi by autolysis is a possible mechanism by which arterial oxygen tensions and A-aDO improved. Since the beads are distributed d.istal to arteriovenous shunts, the lack of pulmonary hypertension is not surprising. The recurrent emboli seen clinically are more likely to occlude pulmonary blood flow in larger arterial branches
l CONTROLS 0 EMBOLIZED 60’
R = .91 p c .005
2
4
6
8
LIVER TO LUNG
IO COUNT
12
14
16
RATIOS
x
18
20
lo_2
Figure 9. Relationship of A-aDO to liver to lung ratios in control and embolized animals. The statistically significant correlation is evidence that arteriovenous shunting of the macroaggregated sulfur colloid as manifested by increased liver uptake of the isotope is also responsible for the elevated A-aDO? in microembolized animals.
likely in view of the data obtained from determination of the alveolar-arterial oxygen tension gradient. The linear relationship between A-aDO and liver uptake of isotope confirms this technic and suggests the possibility of clinical application of this test as a simpler alternative to the A-aDO test which has been utilized to evaluate patients with both acute and chronic microembolization [2,6,11]. The A-aOz gradient is determined by the ventilation-perfusion relationship, the rate of diffusion across the alveolar-capillary membrane, and by pulmonary arteriovenous shunting. In this study the increased rate of passage of isotope through the pulmonary circulation during scintiphotography is evidence for arteriovenous shunting. The increased A-aDO observed simultaneously with the rapid isotope appearance in the liver suggests that the gradient is for the most part influenced by arteriovenous shunting since neither abnormal ventilation-perfusion ratio or decreased diffusion rate would alter the transit time of isotope through the pulmonary vascular bed. Control liver counts in nonembolized dogs
Hemodynamic and Ventilatory Data on Three Long-Term Survivors of Microemboliration (Postemboli pata Obtained Sixteen Days after the Last Embolization)
TABLE IV
Pulmonary Cog Number 1560 1563 7475 Mean changes
620
Arterial
Mean
(mm t-k)
Pulmonary Vascular Resistance
PaOz
A-aOz Gradient
(mm Rg)
(mm RR)
VDCC
VD/VT
Control
Postembolic
Control
Postembolic
Control
Postembolic
Control
Postemboltc
Control
Postembolic
Control
22.4 20.8 12.9
17.2 a.4 13.5
4.9 3.6 4.6
3.9 1.9 3.6
92 88 76
61 78 61
15 27 18
32 29 32
50 61 48
258 118 106
.38 .20 .32
-29%
-30%
-22%
+66%
.74 .37 .37 +65%
+210%
The American
Postembolic
Journal
of Surgery
Experimental
proximal to arteriovenous shunts, resulting more pulmonary hypertension than shunting.
in
Microembolization
and
Vernon Ficken, and Earle Berrell able technical assistance.
Pulmonary
Function
for their invalu-
Summary
The effects of repeated microembolization using polystyrene beads were studied in twelve dogs. Hemodynamic changes included transient pulmonary hypertension with return to control values associated with increased cardiac output. In five long-term survivors the lack of development of persistent pulmonary hypertension correlated with evidence of increased arteriovenous shunting. Measurements of alveolar-arterial oxygen gradient showed an increase of 94 per cent mean at seven to eight weeks after initiation of embolization. Increased uptake of radioisotope by the liver was observed when lung scintiphotography was performed with technetium 99m macroaggregates of sulfur colloid. Passage of these 10 to 50 p particles into the systemic circulation provided further evidence of increased pulmonary arteriovenous shunting and correlated quantitatively with changes in the A-aO_ gradient. These changes were not observed in seven control dogs. Lung scintiphotography also showed decreased peripheral perfusion and focal perfusion defects. The most pronounced ventilatory change was an increase in ventilatory dead space of 55 per cent at the three to four week restudy period and VD subsequently remained significantly elevated. VT increased proportionately with the increase in V, so that the V,,/Vfr ratio did not change. These radioisotope studies combined with determinations of A-a02 gradient and ventilatory dead space are important diagnostic tools in documenting and quantitating recurrent or chronic pulmonary microembolization. Acknowledgm~ent: Ronald Lee, Hubert
Volume 122, November 1971
We wish to thank Jennings, David
Messrs. Gordon,
References
1. Allgood RJ, Cook JH, Weedn RJ, Speed HK, Whitcomb WH, Greenfield LJ: Prospective analysis of pulmonary embolism in the postoperative patient. Surgery 68: 116, 1970. 2. Wilhelmsen L, Selander S, Soderholm B, Paulin S, Varnauskas E, Werko L: Recurrent pulmonary embolism. Medicine 42: 335, 1963. 3. Owen WR, Thomas WA, Castleman B, Bland EF: Unrecognized emboli to the lungs with subsequent co,r pulmonale. New Eng J Med 249: 919, 1953. 4. Phear D: Pulmonary embolism: a study of late prognosis. Lancet 2: 832, 1960. 5. Orell SR: The fate and late effects of non-fatal pulmonary emboli. Acta Med Stand 172: 473, 1962. 6. Piccone VA Jr, Vidal E, Yarnoz M, Glass P, LeVeen HH: The late results of caval ligation. Surgery 68: 980, 1970. 7. Daily PO, Lancaster JR, Moulder PV: The mechanism of pul’monary hypertension following miliary pulmonary embolism. Surg Gynec Obstet 120: 1009, 1965. 8. Niden AH, Aviado DM: Effects of pulmonary embolism on the pulmonary circulation with special reference to arteriovenous shunts in the lung. Circ Res 4: 67, 1956. 9. Hume M, Sevitt S, Thomas DP: Venous Thrombosis and Pulmonary Embolism, chapt 13, p 252. Cambridge, Harvard University Press, 1970. 10. Saleh SS, Hardy JD: Lung transplantation for treatment of pulmonary hypertension in dogs. Arch Surg 96: 340, 1968. 11. Nostyn EM, Luft CU: Alveolar-arterial gradients for oxygen and carbon dioxide in pulmonary embolization. Proceedings of the Tenth Aspen Emphysema Conference, 1967, p 135. 12. James AE, Eaton SB, Page DL, Potsaid MS, Fleischner FG: An experimental model to study pulmonary microembolism. Radiology 92: 924, 1969. 13. Eaton SB, James AE, Green’e RE, Lyons JH, Potsaid MS, Fleischner FG: New patterns of abnormal pulmonary perfusion associated with pulmonary emboli. I. Scintigraphic manifestations. J Nucl Med 10: 571, 1969. 14. Goodwin JF: The clinical diagnosis of pulmonary embolism. Pulmona’ry Embolic Disease (Sasahara AA, Stein M, ed). New York, Grune and Stratton, 1965.
621
The spectrum of pulmonary embolic disease ranges from macroemboli capable of producing acute cardiorespiratory failure to microemboli more likely to produce an insidious picture of car pulmonale. Estimates of the incidence of embolic disease in surgical patients vary greatly, but in one report, pulmonary embolization was observed postoperatively in one of every seven patients, with a mortality rate of 22 per cent [I]. Survivors of pulmonary emboli usually have clearance of their pulmonary vascular bed by autogenous lysis, but remain likely candidates for recurrent embolization and the development of chronic pulmonary hypertension and car pulmonale [Z-4]. In one autopsy series of 132 cases of nonfatal emboli, 10 per cent showed right ventricular hypertrophy related to recurrent emboli of which half were in small muscular arteries or arterioles [5] . Similarly in patients who had undergone vena caval ligation, the frequency of recurrent pulmonary embolization was recently reported to be greater than 50 per cent [6]. Since this embolization usually occurs as showers of microemboli, the diagnosis often is not suspected. Most experimental studies of pulmonary embolism have dealt with the acute responses to pulmonary emboli, and there is a need for further observations of the chronic hemodynamic and ventilatory responses to pulmonary microembolization. This study was undertaken to measure the From the Department of Surgery. University of Oklahoma Medical Center. 800 NE 13th Street, Oklahoma City, Oklahoma: and the Veterans Administration Hospital, 921 NE 13th Street, Oklahoma City, Oklahoma 73104. This investigation was supported in part by US Navy Contract N00014-68-A-0946 and the Markle Foundation. Presented at the Twenty-Third Annual Meeting of the Southwestern Surgical Congress, Las Vegas, Nevada, April 19-22, 1971.
616
effects of recurrent microembolization on pulmonary function and blood flow in the dog. In addition, a correlation of pulmonary arteriovenous shunting with radioisotope distribution to the lung and liver was made to explore this simpler method of diagnosis. Materials and Methods Adult mongrel dogs screened for dirofilaria immitis and weighing from 18 to 28 kg were anesthetized with pentobarbital sodium (20 to 25 m/kg body weight), and 6ntubated with a cuffed endotracheal tube. The animals were hyperinflated periodically by positive pressure to prevent atelectasis. A cannula was inserted in the femoral artery and a number 8 NIH cardiac catheter was positioned through the femoral vein into the pulmonary artery under flouroscopy. Expired gas samples were collected in a water-sealed spirometer for a minimum of three minutes. Simultaneous determinations of arterial PO?, PC02, and pH were performed utilizing a gas analyzer (IL Model 113) calibrated with known gas mixtures. Using these data, minute ventilation (V,), tidal volume (V,), physiologic dead space (V,) , oxygen consumption, carbon dioxide production, the respiratory quotient, and alveolar-arterial oxygen tension gradient ( A-aDO,) were calculated. During the period of gas collection, cardiac output determinations were made in duplicate by the indicator dilution technic. The area under the dye curves was determined by a Gilford 104E Dye Curve Computer and was checked periodically by semi-logarithmic plotting technics. Oscillographic recordings of systemic and pulmonary arterial pressures were used to calculate total systemic and pulmonary vascular resistance (PVR). Lung scintiphotography was performed at the same time as the sequential hemodynamic and ventilatory studies. Two millicuries of technetium 99m macroaggregated sulfur colloid was injected intravenously
The
American
Journal
of
Surgery
Experimental
I
TABLE
Dog Number 1560 1563 4478 7475 7805 7811 Mean
Time Interval (days) between Last Embolization and Restudy Periods
Three to Four Weeks (days)
Seven to Eight Weeks (days)
3 3 9
10 10 11 11 31 11
a 8 9 6.7
14
Ten to Eleven Weeks (days) 7 7 36 28 32 Died 22
slowly, and scintiphotos in three views were obtained using the Nuclear Chicago Phogamma III camera. Consistent and uniform particle size (10 to 50~) was insured by microscopic examination on a hemocytometer grid. External counts of the lung and liver for one minute were obtained within fifteen minutes of injection of the isotope utilizing the Nuclear-Chicago PhoDot rectilinear scanner with scaler and a low energy collimator. Areas of greatest radioactivity over both right and left lungs were averaged and the ratio of liver to lung counts was calculated. Seven normal dogs were studied to determine control liver to lung count ratios. Twelve animals were administered microemboli in the form of polystyrene microspheres, 300 to 850p in diameter. Embolization was performed via a chronic indwelling superior vena caval catheter at one to two week intervals for eight to twelve weeks. Pre-embolization hemodynamic and ventilatory studies were performed on all dogs. Postembolization studies were performed at three to four weeks, seven to eight weeks, and ten to eleven weeks after initiation of embolization. In the first postembolic period, a period of seven days was allowed to elapse between the last embolization and restudy to avoid transient hemodynamic changes. In the second period the average interval was fourteen days and in the third, twenty-two days, (Table I.) Initial microsphere dosages of 2 to 2.5 gm were established arbitrarily on the basis of survival experience. Subsequent doses of 1 to 2 gm were administered and the average total dose by the first restudy period was 7.3 gm. At the second and third examinations the average doses were 9.0 and 10.6 gm of beads, respectively. (Table II.) Results
Six animals died before restudy could be performed, usually shortly after embolization. Postmortem examinations on these dogs revealed multiple areas of gross lung hemorrhage, pulmonary edema, right ventricular dilatation, pleural effusions, and in one case anasarca. Three dogs died after re-evaluation of their hemodynamic and ventilatory functions, again usually after
Volume 122, November 1971
TABLE
II
_~.___
--
Dog Number 1560 1563 4478 7475 7805 7811 Mean
Microembolization
Total Microemboli Restudy Period
and
Pulmonary
Doses (gm) at Each
Three to Four Weeks (gm)
Seven to Eight Weeks (gm)
6 6 8 a 8 a
a a 10 10 9 9
7.3
Function
9.0
Ten to Eleven Weeks (gm) 11 11 10 12 9 Died 10.6
additional embolization, Autopsies revealed antemortem thrombus in the pulmonary arteries in two dogs (Figure 1) and extensive collateral vasculature of the lungs. Microspheres were found in the thrombi which occluded major divisions of the right and left pulmonary arteries. In one of these animals the mean pulmonary arterial pressure prior to death was 86 mm Hg and the associated extensive thrombosis appeared to be a major contributing factor. The three surviving animals subsequently underwent pneumonectomy in preparation for lung transplantation which will be reported separately. At the time of surgery markedly dilated bronchial collateral vessels were found as well as numerous vascular adhesions between parietal and visceral pleura containing some arteries measuring 2 to 3 mm in diameter. Light microscopy (Figure 2) revealed ectasia of the bronchial arteries and microsphere emboli which appear to be encapsulated in vascular-like structures outside of adjacent pulmonary and bronchial arteries. Organizing thrombus was seen adjacent to the microspheres. No areas of organized pulmonary infarction were found. In animals that died acutely after embolization, intra-alveolar and interstitial hemorrhage and peribronchial congestion were noted. Excluding the one dog that died with extensive thrombosis of several pulmonary arterial branches and pulmonary hypertension, pulmonary arterial pressure did not remain increased significantly. (Figure 3.) Cardiac output did increase significantly from .172 L/min/kg to .212 L/min/kg (p <.05) by ten to eleven weeks after initiation of embolization. (Figure 4.) Total pulmonary vascular resistance had increased 27 per cent by the first restudy period but then returned to control values. Arterial oxygen tension dropped significantly from a mean 81.2 mm Hg to 69 and 64 mm Hg (p
617
Reif et al
Figure 1. Antemortem thrombus (marker) in left lower lobar pulmonary artery of a dog that died with pulmonary hypertension. This was the only instance of persistent hypertension after microembolization and indicates that arteries larger than those obstructed by microemboli must be blocked before pulmonary hypertension develops (forma/in-fixed specimen).
Figure 2. Light microscopy of lung removed from an animal which died after repeated microembolization. Bronchus is upper left; microspheres are impacted in a small pulmonary artery, lower right. Several ectatic bronchial arteries are seen adjacent to bronchus. Increased bronchial collateral vasculature was observed in all chronic survivors of embolization (hematoxylin and eosin stain; original magnification X83).
< .Ol) by the first and second restudy periods, respectively. The Pa.Oz had returned to normal at ten to eleven weeks which was after a longer interval after the last embolization. (Figure 5.) Similarly, the A-aOs gradient increased from a mean of 25.3 mm Hg to a maximum of 49 mm Hg mean by seven to eight weeks (p < .Ol) and then returned to control levels after embolization was stopped. (Figure 6.) Ventilatory dead space increased by 55 per cent at three to four weeks and remained significantly elevated (p < .05) despite the longer interval after the last embolization.
(Figure ‘7.) Dead space to tidal volume did not increase appreciably owing to proportionate increases in both V,, and VT. Lung scintiphotograms in all animals revealed decreased uptake of isotope, decreased peripheral perfusion, and increased uptake of isotope by the liver when compared to pre-embolization control scans. In Figure 8 these findings are illustrated with scintiphotos obtained twenty-five days after the last embolization. After the observation of increased liver uptake of isotope, liver and lung counts were obtained on seven nonembolized dogs
1 I , 1 I , , , ( 0 2 4 6 0 10 12 14 TIME ( WEEK5 1
, 16
Mean pulmonary arterial Figure 3. pressures of each chronic survivor at the specified restudy periods. Pressures represent chronic responses to embolization with polystyrene beads. Persistent pulmonary hypertension prior to death developed in only one animal.
618
1
WELKP
i
2
:1
iE
Mean cardiac output inFigure 4. creased significantly (p < .05) by the third restudy period in chronic survivors of microembolization. With the lack of significant elevation of pulmonary arterial pressure, pulmonary vascular resistance remained normal.
Mean arterial oxygen Figure 5. tension decreased significantly by both the first and second restudy periods (p < .Ol) but returned to control values at ten to eleven weeks. Chronic hypoxia thus occurred despite normal pulmonary vascular resistance and pressure.
The American
Journal
of SurEery
Experimental
and compared with similar counts in six embolized dogs. The liver to lung mean ratio in nonembolized dogs was .023 I+ ,013, whereas the mean ratio in the embolized animals was .108 + .061. This difference is statistically significant (p < .Ol). (Table III.) Comparison of the liver to lung ratios with the A-aD0, showed a high degree of correlation (R = .91, p < .005). (Figure 9.) In five animals embolization was continued after the third restudy period. Three of these dogs survived for further evaluation after having received an additional 4 to 6 gm of beads. Pulmonary arterial pressure decreased by an average of 29 per cent and total pulmonary vascular resistance decreased an average of 30 per cent while the cardiac output was unchanged. Arterial POZ decreased by 22 per cent and the A-aD0, increased 66 per cent. VD and V,,/V, also increased by an average of 210 per cent and 65 per cent, respectively. With this small group, these changes cannot be evaluated statistically, but they do indicate lack of progressive pulmonary hypertension or increased PVR associated with increased hypoxia. (Table IV.)
TABLE III
Microembolization
and
Function
Lung and Liver One Minute Counts after Intravenous Injection of 2 mc Technetium 99m Macroaggregates
-
Pulmonary
Dog Number -._ Control Animals 7634 7636 7564 3364 3121 1997 Mean Standard deviation
of Sulfur
Mean LungCount
LiverCount
Liver to Lung Ratio
66,700 72,950
2,200 1,850
0.033 0.025
900 2,800 800 500 ...
0.008 0.042 0.013 0.010 .023
111,500 67,000 60,600 49,350 ... ...
Embolized Dogs 1563 1560 7475 4478 7637 7805 Mean Standard deviation Significance
Colloid
72,650 46,430 89,800 58,050 65,600 65,000 *..
... 1,940 3,040 15,000 10,900 6,000 7,050 ...
... ...
... ...
rt.013 0.027 0.065 0.170 0.188 0.092 0.108 .108 1tz.061 p <.Ol
Comments Although the acute response to experimental pulmonary microembolization is pulmonary hypertension [7,8], persistently elevated pulmonary arterial pressure generally is not seen [9]. However, Saleh and Hardy [IO] demonstrated elevated right ventricular pressures in dogs embolized daily with barium sulfate suspension over a period of five to six weeks. In this study, pulmonary arterial pressure and vascular resistance in six dogs followed eight to twenty-two weeks after
initiation of embolization did not change significantly from pre-embolization levels with one exception. The clinical experience that continued embolization produces pulmonary hypertension in man [Z-G] suggests that the observations in this study represent either a stage prior to the onset of irreversible pulmonary hypertension and car pulmonale or a different anatomic distribution of the emboli precluding the formation of pulmonary hypertension This latter explanation seems more
CONTROL
1)
I,# POST
tONllOL
3-4 WEEKS
7-8 WEEKS
IO-11 WEEK5
Figure 6. Mean alveolar-arterial oxygen tension gradient increased significantly (p < .Ol) by the second restudy period before returning to the control level. In view of normal pulmonary arterial pressures and PVR, arteriovenous shunting must be a major contributing factor to the increased gradient.
Volume 122, November 1971
EMBOLl
Figure 7. Mean ventijatory dead space was persistently increased in all restudy periods (p < .05). The &/VT ratio did not increase since a proportionate increase in VT occurred. Elevated dead space ventilation is further evidence that an imbalance in the ventilation-perfusion relationship exists.
Figure 8. Control scintiphoto and scintiphoto obtained twenty-five days after the last embolizatron. Posteroanterior, left oblique, and right oblique views are from left to right. Decreased peripheral perfusion and increased liver uptake of isotope were observed in all survivers of embolization.
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Reif et al
did not reveal evidence of early liver uptake of isotope, indicating that the macroaggregates are stable during the time required for lung scintiphotography and liver counting. Thus, this early appearance of isotope in the liver (within fifteen minutes after injection) cannot be attributed to breakdown of the macroaggregates with passage on through the pulmonary capillary bed. Arteriovenous shunting has been observed in acute microembolization [S] with glass beads less than 420 p in diameter. These shunts appear to open with either elevated pulmonary arterial pressure alone or hypoxia which produces pulmonary arteriolar vasoconstriction. The lung scintigram changes with microembolization are similar to those described in dogs embolized with glass microspheres [I21 and in man [13]. Peripheral perfusion is diminished and interlobar fissures often are accentuated. Ventilatory dead space increased soon after microembolization and remained elevated. This has been described previously as a useful diagnostic aid [2,14]. Light microscopic and gross specimen examinations demonstrated increased collateral circulation. The lack of pulmonary arteriolar muscular hypertrophy indicates that the vascular bed has been protected from the development of increased resistance to flow despite the fact that the emboli are nonresolving. The visualization of emboli in vascular-like structures adjacent to pulmonary and bronchial arteries may be evidence that the beads plugged some arteriovenous shunts. The fact that thrombi were observed grossly in two dogs and microscopically in others indicates that polystyrene beads are thrombogenic and clearance of thrombi by autolysis is a possible mechanism by which arterial oxygen tensions and A-aDO improved. Since the beads are distributed d.istal to arteriovenous shunts, the lack of pulmonary hypertension is not surprising. The recurrent emboli seen clinically are more likely to occlude pulmonary blood flow in larger arterial branches
l CONTROLS 0 EMBOLIZED 60’
R = .91 p c .005
2
4
6
8
LIVER TO LUNG
IO COUNT
12
14
16
RATIOS
x
18
20
lo_2
Figure 9. Relationship of A-aDO to liver to lung ratios in control and embolized animals. The statistically significant correlation is evidence that arteriovenous shunting of the macroaggregated sulfur colloid as manifested by increased liver uptake of the isotope is also responsible for the elevated A-aDO? in microembolized animals.
likely in view of the data obtained from determination of the alveolar-arterial oxygen tension gradient. The linear relationship between A-aDO and liver uptake of isotope confirms this technic and suggests the possibility of clinical application of this test as a simpler alternative to the A-aDO test which has been utilized to evaluate patients with both acute and chronic microembolization [2,6,11]. The A-aOz gradient is determined by the ventilation-perfusion relationship, the rate of diffusion across the alveolar-capillary membrane, and by pulmonary arteriovenous shunting. In this study the increased rate of passage of isotope through the pulmonary circulation during scintiphotography is evidence for arteriovenous shunting. The increased A-aDO observed simultaneously with the rapid isotope appearance in the liver suggests that the gradient is for the most part influenced by arteriovenous shunting since neither abnormal ventilation-perfusion ratio or decreased diffusion rate would alter the transit time of isotope through the pulmonary vascular bed. Control liver counts in nonembolized dogs
Hemodynamic and Ventilatory Data on Three Long-Term Survivors of Microemboliration (Postemboli pata Obtained Sixteen Days after the Last Embolization)
TABLE IV
Pulmonary Cog Number 1560 1563 7475 Mean changes
620
Arterial
Mean
(mm t-k)
Pulmonary Vascular Resistance
PaOz
A-aOz Gradient
(mm Rg)
(mm RR)
VDCC
VD/VT
Control
Postembolic
Control
Postembolic
Control
Postembolic
Control
Postemboltc
Control
Postembolic
Control
22.4 20.8 12.9
17.2 a.4 13.5
4.9 3.6 4.6
3.9 1.9 3.6
92 88 76
61 78 61
15 27 18
32 29 32
50 61 48
258 118 106
.38 .20 .32
-29%
-30%
-22%
+66%
.74 .37 .37 +65%
+210%
The American
Postembolic
Journal
of Surgery
Experimental
proximal to arteriovenous shunts, resulting more pulmonary hypertension than shunting.
in
Microembolization
and
Vernon Ficken, and Earle Berrell able technical assistance.
Pulmonary
Function
for their invalu-
Summary
The effects of repeated microembolization using polystyrene beads were studied in twelve dogs. Hemodynamic changes included transient pulmonary hypertension with return to control values associated with increased cardiac output. In five long-term survivors the lack of development of persistent pulmonary hypertension correlated with evidence of increased arteriovenous shunting. Measurements of alveolar-arterial oxygen gradient showed an increase of 94 per cent mean at seven to eight weeks after initiation of embolization. Increased uptake of radioisotope by the liver was observed when lung scintiphotography was performed with technetium 99m macroaggregates of sulfur colloid. Passage of these 10 to 50 p particles into the systemic circulation provided further evidence of increased pulmonary arteriovenous shunting and correlated quantitatively with changes in the A-aO_ gradient. These changes were not observed in seven control dogs. Lung scintiphotography also showed decreased peripheral perfusion and focal perfusion defects. The most pronounced ventilatory change was an increase in ventilatory dead space of 55 per cent at the three to four week restudy period and VD subsequently remained significantly elevated. VT increased proportionately with the increase in V, so that the V,,/Vfr ratio did not change. These radioisotope studies combined with determinations of A-a02 gradient and ventilatory dead space are important diagnostic tools in documenting and quantitating recurrent or chronic pulmonary microembolization. Acknowledgm~ent: Ronald Lee, Hubert
Volume 122, November 1971
We wish to thank Jennings, David
Messrs. Gordon,
References
1. Allgood RJ, Cook JH, Weedn RJ, Speed HK, Whitcomb WH, Greenfield LJ: Prospective analysis of pulmonary embolism in the postoperative patient. Surgery 68: 116, 1970. 2. Wilhelmsen L, Selander S, Soderholm B, Paulin S, Varnauskas E, Werko L: Recurrent pulmonary embolism. Medicine 42: 335, 1963. 3. Owen WR, Thomas WA, Castleman B, Bland EF: Unrecognized emboli to the lungs with subsequent co,r pulmonale. New Eng J Med 249: 919, 1953. 4. Phear D: Pulmonary embolism: a study of late prognosis. Lancet 2: 832, 1960. 5. Orell SR: The fate and late effects of non-fatal pulmonary emboli. Acta Med Stand 172: 473, 1962. 6. Piccone VA Jr, Vidal E, Yarnoz M, Glass P, LeVeen HH: The late results of caval ligation. Surgery 68: 980, 1970. 7. Daily PO, Lancaster JR, Moulder PV: The mechanism of pul’monary hypertension following miliary pulmonary embolism. Surg Gynec Obstet 120: 1009, 1965. 8. Niden AH, Aviado DM: Effects of pulmonary embolism on the pulmonary circulation with special reference to arteriovenous shunts in the lung. Circ Res 4: 67, 1956. 9. Hume M, Sevitt S, Thomas DP: Venous Thrombosis and Pulmonary Embolism, chapt 13, p 252. Cambridge, Harvard University Press, 1970. 10. Saleh SS, Hardy JD: Lung transplantation for treatment of pulmonary hypertension in dogs. Arch Surg 96: 340, 1968. 11. Nostyn EM, Luft CU: Alveolar-arterial gradients for oxygen and carbon dioxide in pulmonary embolization. Proceedings of the Tenth Aspen Emphysema Conference, 1967, p 135. 12. James AE, Eaton SB, Page DL, Potsaid MS, Fleischner FG: An experimental model to study pulmonary microembolism. Radiology 92: 924, 1969. 13. Eaton SB, James AE, Green’e RE, Lyons JH, Potsaid MS, Fleischner FG: New patterns of abnormal pulmonary perfusion associated with pulmonary emboli. I. Scintigraphic manifestations. J Nucl Med 10: 571, 1969. 14. Goodwin JF: The clinical diagnosis of pulmonary embolism. Pulmona’ry Embolic Disease (Sasahara AA, Stein M, ed). New York, Grune and Stratton, 1965.
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