non-hydrostatic pulmonary edema after coronary artery...

301

Non-Hydrostatic Pulmonary Edema afterCoronary Artery Ligation in Dogs

Protective Effect of Indomethacin

J. FRANKLIN RICHESON, CRAIG PAULSHOCK, AND PAUL N. YU

With the technical assistance of C. Mark Hanna, Douglas Hollinger, and Peter Serrino

SUMMARY Pulmonary edema which develops during acute myocardial infarction is generally be-lieved to result solely from pulmonary microvascular hypertension. However, patients with myocardialinfarction and pulmonary edema occasionally are found to have normal pulmonary wedge pressure.We report data indicating that pulmonary edema develops after coronary artery ligation despite stablemicrovascular pressure. Four groups of open-chest dogs were studied: (1) nine dogs with left anteriordescending coronary artery ligation, (2) seven dogs with sham coronary ligation, (3) seven dogs ligatedafter beginning an infusion of indomethacin (5 mg/kg per hr), and (4) five dogs ligated after an infusionof the drug's vehicle was begun. Extra vascular lung water and pulmonary blood volume were measuredat hourly intervals during the 2 hours before and after coronary ligation or sham ligation. Gravimetriclung water was measured immediately thereafter. Changes of net pulmonary intravascular drivingforce (the difference of microvascular hydrostatic and oncotic pressure) after ligation or sham ligationwere small and comparable in all groups. Pulmonary blood volume did not change in any group.Pulmonary extravascular water volume remained constant in the sham group but rose significantly inthe ligated group. Gravimetric lung water also was significantly higher in the latter group. We interpretthese results to indicate that factors other than microvascular pressure can mediate the formation ofedema during acute myocardial infarction; increased pulmonary microvascular permeability may beresponsible. Indomethacin infusion blocked the formation of edema after coronary ligation, eventhough net microvascular driving force was highest in this group. Infusion of the vehicle alone did notprevent edema. The mechanism by which indomethacin exerts this protective effect is unclear butis probably a result of its inhibition of cyclo-oxygenase or cyclic nucleotide phosphodiesterase.Circ Res 50: 301-309, 1982

PULMONARY edema is commonly categorized as"cardiogenic" or "non-cardiogenic," with the impli-cation that the former type is mediated by pulmo-nary microvascular hypertension, whereas alteredendothelial permeability accounts for the develop-ment of the latter form (Robin et al., 1972; Staub,1974a, 1978). Pulmonary edema which develops inthe setting of an acute myocardial infarction (MI)is generally believed to result solely from high pul-monary microvascular pressure, since depressedmyocardial contractility, decreased left ventricularcompliance, and peripheral venoconstriction com-monly raise the pressure of the lesser circulationduring acute MI. However, radiographic and clini-cal signs of pulmonary edema during MI are notedoccasionally despite the presence of normal pul-monary wedge pressure (Nixon and Durth, 1968;Lassers et al., 1970; Kostuk et al., 1978; Timmis et

From the Cardiology Unit, Department of Medicine, University ofRochester, School of Medicine and Dentistry, Rochester, New York.

This research was supported in part by the American Heart Associa-tion, Genesee Valley Chapter, and by the National Heart Lung and BloodInstitute (Training Grant HL 07220 and New Investigator AwardHL26822).

Address for reprints: J. Franklin Richeson, M.D., Cardiology Unit,Box 679, University of Rochester Medical Center, Rochester, New York14642.

Received August 4, 1980; accepted for publication November 4, 1981.

al., 1981), and increased lung water (PEV) has beenmeasured in about 15% of patients with MI andnormal pulmonary wedge pressure (Biddle et al.,1974).

Recently, several investigators have presentedevidence that microvascular hypertension is not thesole explanation for pulmonary edema after coro-nary ligation in dogs (Gee et al., 1978; Spath andGee, 1979), cats (Massion et al., 1976, 1978), andsheep (Collins et al., 1979). These authors suggestthat post-MI puimonary edema in part results fromincreased pulmonary microvascular permeability.

The present study was undertaken to test thehypothesis that non-hydrostatic factors lead to thedevelopment of pulmonary edema after coronaryligation in dogs.

MethodsWe studied four groups of mongrel dogs weighing

21.5-36.5 kg. Nine dogs (ligated group) underwentcoronary ligation without prior drug treatment.Seven dogs (sham group) were handled identically,except that the coronary ligature was left untied. Athird group of seven dogs (indomethacin-ligatedgroup) received an intravenous infusion of indo-methacin (kindly provided by Merck, Sharp &Dohme) (5 mg/kg per hr dissolved in warm 0.1 M

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302 CIRCULATION RESEARCH VOL. 50, No. 2, FEBRUARY 1982

phosphate buffer, pH = 8.3, infused at 60-70 ml/hr)beginning 1 hour before control measurements weretaken; coronary ligation was performed 3 hoursafter drug infusion was begun. A fourth group offive dogs (vehicle-ligated) received the phosphatebuffer vehicle without indomethacin, infused atcomparable rates.

Anesthesia was induced by intravenous thiamylalsodium (20 mg/kg) and maintained by fluothaneinhalation (1.5-2.5% in oxygen) through an endotra-cheal tube. A tidal volume of 10-15 ml/kg wasdelivered 10-12 times/min. The expiratory line wasplaced under 3-5 cm H2O. After catheters were inplace, arterial PCO2 ranged from 30 to 40 mm Hg,and arterial Po2 ranged from 425 to 580 mm Hg.The heart was exposed through a thoracotomy inthe left fourth interspace, and 8F polyethylene cath-eters with end and side holes and pretreated with2% TDMAC-heparin (Polysciences, Inc.) were in-serted into the main pulmonary artery and leftatrium. Another cathether (12F) was advanced tothe abdominal aorta via the femoral artery. In 12animals (five ligated, seven sham) right ventricularend-diastolic pressure was monitored through a 5FSwan-Ganz catheter. Lead II of the electrocardi-ogram, left atrial mean, pulmonary arterial, andsystemic arterial pressures were monitored contin-uously (using Statham P23AA pressure transducersand Clevite Brush Mark 260 recorder). Pulmonarymicrovascular pressure (Pmv) was calculated accord-ing to the equation of Gabel and Drake (1978):

Pmv = LA + 0.5 (PA - LA), (1)

where LA and PA are end-expiratory left atrial andpulmonary arterial mean pressures, respectively.After catheters were in place, atelectatic areas ofthe cardiac lobe of the left lung were re-expanded,and an hour was allowed for equilibration beforethe study was begun.

The following were measured four times (referredto as periods I-IV) in each animal: hematocrit, totalplasma protein, cardiac output (CO), pulmonaryintravascular blood volume (PBV), and pulmonaryextravascular water volume or lung water (PEV).Two sets of measurements were taken 1 hour apartprior to the ligation or sham ligation of the coronaryartery (periods I and II). These values were aver-aged and served as control measurements. A thirdset (III) was taken 45-75 minutes after coronaryligation (or sham ligation), and a fourth set (IV)was taken 1 hour thereafter. The timing of the thirdand fourth sets of measurements varied somewhat,as several dogs had ventricular irritability at theplanned time of study. No measurements weretaken within 15 minutes of these rhythm disturb-ances. Blood loss resulting from the surgery orsampling was restored by arterial infusion of autol-ogous blood harvested 1 or 2 days before the exper-iment. Catheters were flushed with heparin-con-taining saline, but no animal received more than1000 units of heparin during the study.

After the final set of measurements was taken,the sternum was split and a filtered 4% solution ofthioflavin S (1 m/kg) was infused through the leftatrial catheter. The pulmonary hila were encircledwith umbilical tape and simultaneously ligated atend-inspiration. The lungs were excised and placedin a weighed pan. An equal weight of distilled waterwas added, and the lungs were homogenized in aWaring Blendor. Specific gravities and hemoglobincontents (cyanmethemoglobin method) of the ho-mogenate supernatant and mixed venous blood wasdetermined. The lung homogenate and blood weredried to constant weight, and the extravascularwater was determined using the equations of Pearceet al. (1965). The heart was removed, sliced trans-versely, and photographed under ultraviolet lightto outline the non-perfused zones as previouslydescribed (Richeson et al., 1978).

Coronary Artery LigationThe left anterior descending coronary artery was

dissected free immediately distal to the first diago-nal branch, and a 2-0 silk ligature was passed behindit, care being exercised to exclude the accompanyingvein(s). In the ligated, indomethacin-ligated, andvehicle-ligated groups, the suture was tied securely;in the sham group it was merely passed behind thevessel. The presence of ischemia was documentedby the occurrence of cyanosis and hypokinesis ofthe involved ventricular wall, by recording S-Tsegment elevation on the epicardial electrogram(using a mobile wick electrode), and by inspectingthe photographs of postmortem slices showingzones of non-perfusion, unstained by thioflavin S.

Cardiac OutputCardiac output was determined by injecting in-

docyanine green dye into the pulmonary artery,sampling dye density of aortic blood with a Gilforddensitometer and amplifier (model 103IR) and aHewlett-Packard 7100B strip chart recorder. Thecardiac output was computed as an inverse functionof the mean height and duration of the planime-tered primary curve. Duplicate injections were per-formed within minutes of each other and differedby an average of 4.5%.

Pulmonary Blood VolumePulmonary blood volume was calculated as the

product of cardiac output and the mean transit timedifference between pulmonary arterial and leftatrial injections of indocyanine green dye, bothbeing sampled at the aorta (Yu, 1969).

Pulmonary Extravascular Water VolumePEV was determined by injecting a mixture of

131I-albumin (5-9 /xCi) and 3H0H (40-80 /xCi) intothe pulmonary artery and sampling the free-flowingstream from the femoral artery into a rack of hep-arinized centrifuge tubes. The exact timing of injec-tion and of sampling was ascertained by slowly



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NON-HYDROSTATIC PULMONARY EDEMA/Richeson et al. 303

replaying a videotape of the procedure on a split-screen monitor, one camera having been focused onthe sample rack and the second on a digital timeraccurate to 0.1 second. This system allowed suffi-cient blood flow to sample every 0.7-1.1 secondswithout hemolysis. Plasma aliquots (0.3 ml) wereadded to 10 ml of Beckman scintillation solution,and the activities of 3H and I31I were determined ina Beckman LS-250 liquid scintillation counter hav-ing automatic quench compensation. PEV was cal-culated using the equation:

PEV = CO [fp (1 - Hct)(MTTw - MTTalb)+ frbc Hct (MTTw - MTTrbc)], (2)

where fp and frbc are the fractional water contentsof plasma (0.94) and red cells (0.70), respectively(Chinard, 1975; Goresky et al., 1975). MTTW,MTTaib, and MTTrbc represent the mean transittimes of water, albumin, and red blood cells, respec-tively. The mean transit times of water and albuminwere calculated with a hand-held calculator (TexasInstruments 59), programmed to extrapolate theexponential portion of the downslope and to correctfor variation in the individual sampling intervals byweighting each sample activity appropriately. Therelationhip between MTTaib and MTTrbc was deter-mined in a separate group of dogs into which mix-tures of 51Cr-labeled red cells and 125I-albumin hadbeen injected into the pulmonary artery and sam-pled at the aorta. The mean transit times werecalculated as described above. Thirty-six such mea-surements were performed in 10 animals. The equa-tion of the regression line (r = 0.997):

MTTa l b = 1.048 MTTrbc + 0.089 (3)

was applied to the numerical solution of Equation2. Coronary ligation was performed on many ofthese animals and did not alter the relationship.Although the separation of plasma and red celltransit times is sensitive to changes of cardiac out-put:

CO (ml/kg per min) =

-87.8 (MTTaib - MTTrbc)+ 139 (r = -0.69), (4)

accounting for such changes has little impact uponcalculation of PEV. In the group with the greatestfluctuation of cardiac output, adjusting the separa-tion of plasma and red cell transit times for changesin cardiac output changed the calculated PEV byonly 2.2 ± 0.4%.

ProteinTotal plasma protein was measured using the

biuret reaction (Abbott Dichromatic Analyzer).Paired samples had a precision of ±0.25% (SE).Oncotic pressure was calculated using the equationof Navar and Navar (1977).

Statistical AnalysisBecause of the multiple measurements on each

animal, a repeated measures model (Winer, 1971)was used to investigate the stability of the responsevariables over the four time periods. This modeluses each dog as its own control. The responses aremeasured as deviations from the average responsefor all time periods so that the average differencesamong the animals are eliminated from the experi-mental error. Statistical comparisons were madebetween the average of the control measurements(periods I and II) and the post-ligation (or post-sham ligation) measurements (periods III and IV).The comparisons were made for each group ofanimals. Relationships among the groups of animalswere investigated by using a multivariate analysisof covariance model [SAS, 1979 (Cary, North Car-olina)]. The response variable was the average ofthe measurements at periods III and IV. The aver-age of the control measurements was the covariate.Pairwise comparisons were made among the fourgroups. Gravimetric extravascular lung wateramong the four groups was compared using theunpaired t-test. P values <0.05 were consideredsignificant.

Results

Sham GroupThe purpose of studying this group was to assess

the stability and reproducibility of the various mea-

TABLE 1 Hemodynamic and Pulmonary Volume Values for the Sham-Ligated Group of Dogs (n = 7, except asnoted)

Response variable Periods l-II Period III Period IV P value

Heart rate (beats/min)Cardiac output (ml/kg per min)Systemic artery mean pressure (mm Hg)Pulmonary artery mean pressure (mm Hg)Left atrial mean pressure (mm Hg)Pulmonary microvascular pressure (mm Hg)Pulmonary microvascular (P — 77) (mm Hg)Right ventricular end-diastolic pressure (mm Hg)Pulmonary blood volume (ml/kg)Pulmonary extravascular water volume (ml/kg)PEV/PBVGravimetric extravascular water volume (ml/kg) (n : 5)

104.687.192.19.23.66.4

-7.21.07.943.050.39

105.680.183.9

8.63.76.1

-6.11.07.483.050.41

103.377.187.18.83.66.2

-5 .31.48.193.090.383.72

3.852.622.300.40.40.40.60.20.210.120.020.14

0.910.050.070.480.970.840.090.250.090.960.52

Periods I and II were prior to sham ligation, whereas periods III and IV were at 1 and 2 hours after sham ligation, respectively. P values less than 0.05(') indicate that the three mean values are statistically different. The standard error of the mean (SEM) was obtained from the repeated measures model.



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surements over an extended period of anesthesia inthe open-chest dog. Dissection of the coronary ar-tery and placement of the loose suture led to nodiscernible color or wall motion change of the leftventricle and no epicardial S-T displacement. Noperfusion defects were detected in the thioflavin S-stained slices.

Table 1 presents the hemodynamic and pulmo-nary volume data collected prior to sham ligation(average of periods I and II), and 1 and 2 hoursafterward (periods III and IV). Mean systemic ar-terial pressure and cardiac output tended to fallfrom control levels, although only the change incardiac output 2 hours after sham ligation wassignificant. Calculated Pmv was constant, althoughthe net intravascular outward driving force (thedifference between intravascular hydrostatic andoncotic force, P — 77) rose slightly, owing to a slightbut progressive fall of plasma protein. Heart rate,right ventricular end-diastolic pressure, mean pul-monary artery and left atrial pressures, PBV, andPEV remained constant (see Fig. 1).

Ligated Group

Within several minutes of coronary ligation, epi-cardial S-T segment elevation was demonstrableover a variable portion of the anterior wall of theleft ventricle: usually this region was noted to becyanotic and hypokinetic. A zone of thioflavin Snon-perfusion was observed in heart slices of allanimals in this group. The extent of the perfusionabnormality was quite variable but always involvedthe anterior free wall of the left ventricle and an-terior portion of the left ventricular apex. The ex-tent of subendocardial involvement was alwayswider than that of the subepicardial region, and thelatter often showed islands and peninsulas of tissue

4.0

PEV.ml-kg-1

3.0

l-l IV

TIME PERIOD

FIGURE 1 Pulmonary extravascular water volume(PEV) is plotted against time in the four groups of dogs.The sham group is represented by open circles (O), theligated group by closed circles (9), the indomethacin-ligated group by triangles (A), and the vehicle-ligatedgroup by squares (M). Asterisks indicate that the valueis significantly different from control values.

with normal or nearly normal fluorescence. Theinterventricular septum was spared, except in threedogs in which perfusion defects were seen in theanterior and left side of the septum. A small portionof the anterior free wall of the right ventricle wasinvolved in one dog; however, right ventricular end-diastolic pressure remained constant in this dog.

Ventricular arrhythmias developed in about one-half of the ischemic animals, usually appearing25-30 minutes after ligation. Arrhythmias were nottreated, and all abated spontaneously 15-45 min-utes after their appearance. Although the severityand duration of arrhythmia were not quantified,there was no obvious relationship noted betweentheir occurrence and subsequent hemodynamic orpulmonary vascular and extravascular volumechanges.

Hemodynamic and pulmonary volume values forthe ligated group are presented in Table 2. Theligated dogs were comparable to sham-ligated dogsin all respects at the outset. Cardiac output fellsignificantly after coronary ligation. Mean systemicartery pressure was variable after coronary ligationbut fell significantly in the group of dogs. Left atrialmean pressure rose minimally but consistently. Pmvdid not change significantly throughout the experi-mental period. The greatest change in left atrialmean pressure at the study times was a rise of 3.5mm Hg. During episodes of ventricular arrhythmia,prominent "v" waves were occasionally present inthe left atrial pressure tracing and the left atrialmean pressure was slightly higher than that re-corded in Table, but even at these times the meanpressure was usually only 1-2 mm Hg higher thanthe recorded pressures. The greatest rise of leftatrial mean pressure during arrhythmia was 4 mmHg. Pulmonary artery mean pressure was un-changed after ligation. Oncotic pressure fell pro-gressively in the ligated group; hence the net out-ward intravascular driving force (P — ir)mv rosesignificantly (i.e., the difference between Pmv and77mv diminished). However, the degree of change,was small (1.9 mm Hg) and was nearly identical tothat of the sham group. Right ventricular end-dia-stolic pressure (measured in five dogs) did notchange after ligation, and was similar to that of thesham group.

PBV in the ligated group did not change signifi-cantly. However, PEV rose significantly, being 20%and 27% higher than control at periods III and IV,respectively. The ratio of PEV/PBV also rose sig-nificantly after ligation. The change of PEV in thisgroup was not highly correlated with changes insystemic artery pressure (r = 0.05), cardiac output(r = 0.14), Pmv (r = 0.29), oncotic pressure (r =0.41), or (P - 7r)mv (r = 0.31).

Indomethacin-Ligated GroupIndomethacin infusion brought about prompt he-

modynamic changes which were sustained through-out the experiment: mean systemic artery pressure



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TABLE 2 Hemodynamic and Pulmonary Volume Values for the Ligated Group of Dogs (n = 9, except as noted)Response variable Periods I—II Period III Period IV P value

Heart rate (beats/min)Cardiac output (ml/kg per min)Systemic artery mean pressure (mm Hg)Pulmonary artery mean pressure (mm Hg)Left atrial mean pressure (mm Hg)Pulmonary microvascular pressure (mm Hg)Pulmonary microvascular (P — w) (mm Hg)Right ventricular end-diastolic pressure (mm Hg) (n = 5)Pulmonary blood volume (ml/kg)Pulmonary extravascular water volume (ml/kg)PEV/PBVGravimetric extravascular water volume (ml/kg) (n = 5)

109.294.590.110.33.66.9

-6.11.67.253.050.43

110.774.180.710.04.67.3

-4.50.96.703.650.56

105.071.982.2

9.94.37.1

-4.21.17.153.870.555.04

2.574.272.480.40.30.30.30.50.230.120.020.38

0.300.003'0.04*0.750.080.740.002*0.180.230.001*0.001*

See footnote, Table 1, for definition of symbols.

rose 9.6 ± 6.2 mm Hg, pulmonary artery meanpressure rose 1.8 ± 0.4 mm Hg, left atrial meanpressure rose 1.3 ± 0.3 mm Hg, and cardiac outputfell 8.2 ± 7.4 ml/kg per min. Consequently, at thetime periods before coronary ligation, the indo-methacin-ligated group differed from the othergroups in that mean systemic arterial, left atrial andpulmonary arterial pressures, and Pmv were signifi-cantly higher and (P — 77)mv was significantly lessnegative. Cardiac output was lower in the indo-methacin-ligated group, although the difference wasnot not statistically significant.

Hemodynamic and pulmonary volume data forthis group are summarized in Table 3. Mean sys-temic artery pressure and cardiac output fell sig-nificantly after coronary ligation. Pulmonary arteryand left atrial mean pressure, and Pmv rose mini-mally, and the net outward driving force, (P - ir)mv,became slightly less negative. Despite the fact thatnet driving force was highest in this group, PEV,PBV, and PEV/PBV remained unchanged through-out the experiment.

Fluorescence photographs of the postmortemheart slices showed substantial zones of thioflavinS hypoperfusion, similar in distribution to those ofthe ligated group. Although no quantitative evalu-ation was performed to assess what fraction of thezone at risk was made ischemic, there was no no-ticeable difference between the extent of ischemiain this group and that of the ligated group.

Vehicle-Ligated GroupDuring the pre-ligation periods, the vehicle-li-

gated group of dogs was similar to the sham andligated groups, except that mean systemic arterypressure was significantly lower in this group. Withcontinued infusion of the alkaline vehicle, systemicpressure rose slightly and was comparable to thatof the sham and ligated groups.

As in the other groups, cardiac output fell sig-nificantly after coronary ligation, left atrial meanpressure and Pmv rose marginally, and net outwarddriving force became slightly less negative. PEVand PEV/PBV rose significantly after ligation (seeTable 4). The degree of change of PEV and of PEV/PBV was similar to that of the ligated group.

Postmortem slices showed ischemic zones similarin extent and distribution to those of the ligatedand indomethacin-ligated groups.

Gravimetric AnalysisGravimetric lung water was measured in all but

four ligated and two sham dogs. Group values arelisted in Tables 1-4. Pulmonary extravascular vol-umes of the sham and indomethacin-ligated groupswere similar. In both the ligated and vehicle-ligatedgroups, gravimetric extravascular water was signifi-cantly higher (P < 0.025) than in the other twogroups. The fraction of gravimetric lung water mea-sured by the indicator-dilution technique (at period

TABLE 3 Hemodynamic and Pulmonary Volume Values for the Indomethacin-Ligated Group of Dogs (n = 7)

Response variable Periods I-II Period HI Period IV P value

Heart rate (beats/min)Cardiac output (ml/kg per min)Systemic artery mean pressure (mm Hg)Pulmonary artery mean pressure (mm Hg)Left atrial mean pressure (mm Hg)Pulmonary microvascular pressure (mm Hg)Pulmonary microvascular (P — IT) (mm Hg)Pulmonary blood volume (ml/kg)Pulmonary extravascular water volume (ml/kg)PEV/PBVGravimetric extravascular water volume (ml/kg)

104.381.7

108.411.66.89.2

-3.17.072.990.44

114.365.4

105.912.07.99.9

-2.27.373.120.44

109.956.998.712.27.49.8

-1.97.092.910.413.39

2.74.32.20.50.40.40.40.280.140.020.45

0.070.0050.02*0.670.290.450.130.700.550.65




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TABLE 4 Hemodynamic and Pulmonary Volume Values for the Vehicle-Ligated Group of Dogs (n = 5)

Response variable Periods I-II Period III period IV P value

Heart rateCardiac output (ml/kg per min)Systemic artery mean pressure (mm Hg)Pulmonary artery mean pressure (mm Hg)Left atrial mean pressure (mm Hg)Pulmonary microvascular pressure (mm Hg)Pulmonary microvascular (P — w) (mm Hg)Pulmonary blood volume (ml/kg)Pulmonary extravascular water volume (ml/kg)PEV/PBVGravimetric extravascular water volume (ml/kg)

104.196.278.810.54.07.2

-6.08.512.920.34

99.269.586.210.15.17.6

-4.98.503.750.44

100.672.187.211.45.78.5

-4 .38.343.620.444.84

3.34.03.50.50.40.40.70.270.100.020.20

0.580.003*0.240.220.04'0.130.310.870.001*0.02*


IV) varied considerably, but this fraction (0.81 ±0.04) was not significantly different among the fourgroups.

Comparison of Group Responses to CoronaryLigation or Sham Ligation

A multivariate analysis of covariance was per-formed to compare the responses of the four groupsof dogs; the average of the control measurements(periods I-II) was used as the covariate. The groupresponses for most variables were comparable, al-though the fall of cardiac output of the indometh-acin-ligated group was greater than that of thevehicle-ligated group (P < 0.05), and the change ofPmv in the vehicle-ligated group was greater thanthat of the ligated group (P < 0.05). The moststriking differences of group responses are thechanges of PEV and PEV/PBV. The sham andindomethacin-ligated groups demonstrated similarresponses of PEV and PEV/PBV, and the responsesof the ligated and vehicle-ligated groups also weresimilar. However, the response of PEV in the ligatedgroup differed significantly from the response of thesham group (P < 0.01) and the indomethacin-li-gated group (P < 0.01), and the PEV response ofthe vehicle-ligated group differed from the responseof the sham group (P < 0.01) and the indomethacin-ligated group (P < 0.01). The rise of PEV/PBV inthe ligated group differed from the responses of thesham group (P < 0.001) and the indomethacin-ligated group (P < 0.001), and the PEV/PBV re-sponse of the vehicle-ligated dogs differed fromthose of the sham group (P < 0.01) and indometh-acin-ligated dogs (P < 0.05).

DiscussionAccording to the Starling relationship, the rate

and direction of fluid movement (Qf) across themicrovascular endothelium is determined by theconductance of the endothelial barrier (Kf) and thedriving forces on either side of the endothelium:

Qf = Kf [ ( P m v — Ppmv) — v)] (5)pmv) — 0 ( 7 W — 77pmv

where Pmv and Ppmv denote microvascular and peri-microvascular hydrostatic pressures, respectively,

and (77mv — 77pmv) represents the oncotic gradientacross the capillary endothelium, modified by thereflection coefficient a.

The pulmonary transudation that often occursafter acute myocardial infarction is generally be-lieved to result solely from elevated pulmonarymicrovascular pressure. Although microvascularhypertension is a frequent cause of pulmonaryedema in this setting, occasionally the two do notco-exist. Discrepancies between pulmonary wedgepressure on the one hand and lung water measure-ments (Biddle et al., 1974), clinical (Nixon andDurth, 1968; Timmis et al., 1981), and radiographic(Lassers et al., 1970; Kostuk et al., 1978) evidenceof pulmonary edema on the other usually have beenattributed to a phase lag between lowering of pres-sure and water clearance from the lung. Nonhy-drostatic mediation has not generally been sus-pected.

Several recent clinical studies (Carlson et al.,1979; Fein et al., 1979) have attempted to differen-tiate "hydrostatic" and "permeability" pulmonaryedema by measuring the ratio of protein concentra-tion in edema fluid to that of plasma. A higher ratiowould denote abnormal protein flux and thus al-tered endothelial integrity. The authors of thesereports did not characterize the pulmonary edemafluid of myocardial infarction patients per se; how-ever, in both studies the edema fluid: plasma proteinratios from patients with acute myocardial infarc-tion were intermediate between the high ratios ofpatients with permeability edema and the low ratiosof patients with left ventricular failure withoutacute myocardial infarction. In one of these studies(Carlson et al., 1979), the number of patients withacute infarction was sufficient that their proteinratios differed significantly from those of the groupwith heart failure without myocardial infarction (P< 0.01) and from those of the group with permea-bility edema (P < 0.05). These data suggest that, inpatients with acute myocardial infarction, both mi-crovascular hypertension and altered permeabilitymay be causes of their pulmonary edema.

Massion et al. (1976, 1978) presented indirectevidence that microvascular permeability may bealtered by proteases liberated from or activated by



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the acutely ischemic myocardium, since the pro-tease-inhibitor aprotinin prevented pulmonaryedema in cats after coronary ligation. Gee andSpath (1978) measured greater protein flow throughthe right lymphatic duct in volume-loaded dogswith circumflex artery ligation than that in a shamgroup of dogs. Myocardial contribution to lymphprotein could account for these findings in part,however. Dogs after coronary ligation have highergravimetric lung water than control dogs with com-parable Pmv (Spath and Gee, 1979). Lung lymphflow and pulmonary protein clearance in anesthe-tized sheep rises shortly after coronary ligationdespite minimal change in Pmv (Collins et al., 1979).

One purpose of the present study was to testwhether pulmonary edema would develop after cor-onary ligation in the presence of normal and un-changing pulmonary microvascular pressure. Themodel employed (open-chest, anesthetized, me-chanically ventilated dog) is far from physiological;however, the stability of the lung water in the shamgroup indicates that these factors are not responsi-ble for the changes observed in other groups.

The assumptions upon which the indicator-dilu-tion technique is based, and the fact that it definesan operational, rather than an anatomic or physio-logical space, require that studies using this methodbe interpreted with these reservations in mind. Chi-nard (1975) and Staub (1974b) have reviewed thelimitations of this method. The reliance of the cur-rent study upon directional changes of sequentialmeasurements in the same animal circumventsmany of these potential objections. The principallimitation of the indicator-dilution technique is thatit measures only a fraction of the gravimetricallydetermined lung water. The higher gravimetric lungwater in the ligated and vehicle-ligated dogs arguesagainst the notion that the post-ligation rise of PE Vmerely reflects a greater measured fraction of truelung water. It was not possible, using these tech-niques, to measure the filtering surface area of thepulmonary microvascular bed, but PBV remainedstable in all groups. In those groups in which a riseof PEV was observed (ligated and vehicle-ligated),a weak correlation was present between PEV andPBV (r = 0.35, P < 0.05); however, changes of PEVand PBV were not highly correlated (r = 0.28). Thisand the minimal change of Pmv suggest that addi-tional vascular recruitment cannot account for thechange of PEV.

Our data show that shortly after coronary liga-tion in anesthetized dogs, pulmonary edema devel-ops in the face of a stable Pmv. Although the changeof outward driving force was significant only for theligated group of dogs, the degree of this change wassmall (1.9 mm Hg), and pairwise comparisons (usingmultivariate analysis of covariance) of outwarddriving force showed that the response of this var-iable was similar in all four groups of dogs.

We have assumed that pulmonary vascular re-

sistance was equally distributed proximal and distalto the microvascular bed, as found in normal dogsby Gabel and Drake (1978), and remained sothroughout the experiment. If, in fact, such werenot true, Pmv might rise, even with stable pulmonaryartery and left atrial pressures. In the extreme case,if all of the resistance were to shift to sites distal tothe filtering bed, Pmv would rise to equal meanpulmonary artery pressure (a rise of 2.8 mm Hg inthe ligated group). Such a small change would seemincapable of inducing pulmonary edema; thus redis-tribution of vascular resistance provides an unsat-isfactory explanation of our data.

The constancy of right ventricular end-diastolicpressure in the ligated group assured us that bron-chial venous and pulmonary lymphatic hyperten-sion were not responsible for the rise of PEV (Milleret al., 1978).

The pulmonary edema in the ligated and vehicle-ligated groups of dogs must have resulted from analteration of either lymphatic drainage or one ofthe unmeasured elements of the Starling relation-ship: perimicrovascular hydrostatic or oncotic pres-sure, or microvascular permeability. The stabilityof lung water in the sham group indicates the effectof anesthesia upon lung lymphatic pulsatile flow(Staub, 1974b) does not account for the changeobserved in the ligated and vehicle-ligated groups.Perimicrovascular hydrostatic and onocotic pres-sures were not measured in the current study. It ispossible that increased filtration may have resultedfrom changes of these variables, but it seems un-likely that myocardial ischemia would exert a pri-mary change upon the pulmonary interstitium.

Although the above possibilities cannot be com-pletely refuted by our data, we believe that altera-tion in microvascular permeability is the most ten-able explanation for the observed rise of extravas-cular water after coronary ligation.

Although several laboratories have reported sim-ilar conclusions using different methods (Massionet al., 1976; Gee et al., 1978; Collins et al., 1979), themediator(s) of this rise in permeability has not beenidentified. Berger and co-workers (1976) haveshown that after coronary ligation in the anesthe-tized dog, there is release of prostaglandins E andF from the ischemic myocardiium. Spath and col-leagues (1980) suggest a role for prostacyclin in themediation of pulmonary edema, as their volume-expanded dogs demonstrated a rise of prostacyclinlevels in right lymphatic duct protein-rich lymphafter coronary ligation. No such rise was seen insham-ligated animals. It is possible that the pros-tacyclin was formed as a response to edema ratherthan being responsible for it. Indeed, Demling et al.(1981) have shown that prostacyclin infusion atten-uates the increased permeability of the pulmonaryvasculature during edema caused by endotoxin.Moreover, Brigham (1978) cites salicylate-inducedpulmonary edema as evidence that prostaglandins



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have a protective effect upon the pulmonary vas-cular endothelium.

Our results show that the indomethacin infusionblocks the formation of post-myocardial infarctionpulmonary edema in this model. Since infusion ofthe drug's vehicle alone at a comparable rate didnot prevent edema formation, indomethacin itselfappears to be responsible for the salutary effect.Since the fall of cardiac output in this group wasgreater than in the other groups, it is possible thata derecruitment of filtering surface area played arole in this protective effect. However, the intravas-cular net driving force was highest in the indometh-acin-ligated group, and the extent of myocardialischemia was comparable to that of other ligatedanimals. Thus it seems unlikely that the protectiveeffect was hydrostatic or due to myocardial preser-vation.

The mechanism whereby indomethacin pre-vented edema is unclear. Cyclo-oxygenase inhibi-tion is the most fully studied action of indomethacin(Flower, 1974); thus interference with prostaglan-din, prostacyclin, or thromboxane synthesis is aleading consideration. Whereas the vasomotor ef-fects of this group of agents are well-known, theability of prostaglandins to alter microvascularpermeability is not fully understood. Infusion ofarachidonate (Ogletree and Brigham, 1980), or thecyclic endoperoxide PG-H2 or its 9-methylene etheranalogue (PG-H2-A) (Bowers et al., 1979) into sheepwith lung lymph fistulas leads to enhanced flow ofprotein-poor lymph. Microvascular permeability isnot altered. Prostacyclin is capable of increasinglung lymph flow and protein clearance into thelymph without altering pulmonary artery pressure(Ogletree and Brigham, 1978); however, this is nowthought to reflect a change in filtering surface arearather than an increase in permeability (Ogletree,1981).

In the peripheral circulation, prostaglandins maypromote edema indirectly, by potentiating the al-teration of permeability caused by other phlogisticagents such as histamine (Komoriya et al., 1978) orbradykinin (Peck and Williams, 1978). The poten-tiating effect of prostaglandins upon other media-tors in the lung has not been studied.

Among the other actions of indomethacin, cyclicnucleotide phosphadiesterase inhibition could alsoexplain the salutary effect of indomethacin in thisstudy. The rise of cyclic AMP which would resultfrom phosphodiesterase inhibition might stabilizelysosomal membranes and prevent release of otherphlogistic mediators (Weiss and Hait, 1977).

In conclusion, this study has shown that extra-vascular lung water increases shortly after coronaryligation in the dog in the face of trivial changes inintravascular driving force. Of the non-hydrostaticmechanisms which could explain this, we believethat an alteration of microvascular permeability isthe most likely. The degree of pulmonary edema in

the ligated dogs was not great, probably reflectingonly interstitial accumulation. However, if alteredpermeability is the cause, the significance of thisfinding becomes progressively greater at higher mi-crovascular pressures, as is frequently the case afterhuman myocardial infarction. Pre-ligation infusionof indomethacin prevented edema in this model,although the mechanism of this protective effect isnot clear.

AcknowledgmentsWe are deeply indebted to Mr. Hubert Wood for his invalu-

able advice and assistance in performing the statistical analysisof the data.

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J F Richeson, C Paulshock and P N Yunindomethacin.

Non-hydrostatic pulmonary edema after coronary artery ligation in dogs. Protective effect of

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