Improvement in Myocardial Function and Coronary Blood

Flow in Ischemic Mvocarditim after Mannitol

JAMEST. WILLERSON, WM.JOHNPOWELL, JR., TIMoTHY E. GUINEY,JAMESJ. STARK, CHARLESA. SANDERS, and ALEXANDERLEAF

From the Department of Medicine (Cardiac and Renal Units), MassachusettsGeneral Hospital, and the Department of Medicine, Harvard Medical School,Boston, Massachusetts 02114

A B S T R A C T The purpose of this study was to evaluatethe effect of hyperosmolality on the performance of, andthe collateral blood flow to, ischemic myocardium. Themyocardial response to mannitol, a hyperosmolar agentwhich remains extracellular, was evaluated in anes-thetized dogs. Mannitol was infused into the aortic rootsof 31 isovolumic hearts and of 15 dogs on right heart by-pass, before and during ischemia. Myocardial ischemiawas produced by temporary ligation of either the proxi-mal or mid-left anterior descending coronary artery.

Mannitol significantly improved the depressed ventricu-lar function curves which occurred with left anterior de-scending coronary artery occlusion. Mannitol also sig-nificantly lessened the S-T segment elevation (epicardialelectrocardiogram) occurring during myocardial ischemiain the isovolumic hearts and this reduction was associ-ated with significant increases in total coronary bloodflow (P < 0.005) and with increased collateral coronaryblood flow to the ischemia area (P < 0.005).

Thus, increases in serum osmolality produced by man-nitol result in the following beneficial changes duringmyocardial ischemia: (a) improved myocardial func-tion, (b) reduced S-T segment elevation, (c) increasedtotal coronary blood flow, and (d) increased collateralcoronary blood flow.

INTRODUCTIONIt has been demonstrated that myocardial ischemia isaccompanied by a reduction of organ perfusion whencontinuity of blood flow is restored (1). Similar findingshave been noted in the brain (2) and the kidney (3).

This work has previously been presented in part at theAmerican Heart Meetings in Anaheim, California, Novem-ber 1971.

Received for publication 29 November 1971 and in revisedform 23 March 1972.

Furthermore, in these latter two organs, hyperosmolaragents which remain largely extracellular, through re-duction of ischemic cell swelling, have been demonstratedto improve the reflow of blood after arterial occlusion(4, 5). In the kidney the resulting improvement in cir-culation has recently been noted to be associated withimproved renal function (5). Because of the possibilitythat hyperosmolar agents might protect and improve thefunction of myocardium exposed to hypoxia, studies wereunidertaken to evaluate the influence of these agents onthe performance of the ische.mic left ventricle and, inparticular, on collataral blood flow to ischemic myo-cardium.

The purpose of this communication is to present dataevaluating the hemodynamic effect of hypertonic man-nitol on the function of ischemic myocardium, on totalcoronary and collateral coronary blood flow, and on thedegree of S-T segment elevation noted in the epicardialelectrocardiogram which has been shown to be a reliableindicator of myocardial injury during ischemia (6).

METHODS

Adult mongrel dogs of either sex weighing between 25 and35 kg were anesthetized with intravenous chloralose (60mg/kg) and urethan (600 mg/kg). The preparations usedin this study included the right heart bypass and the iso-volumic left ventricle. The sinus node was crushed andheart rate kept constant in both preparations by atrial pacingutilizing a Grass stimulator (Grass Instrument Co., Quincy,Mass.) (model SD-5).

Preparations. In the right heart bypass experiments, anendotracheal tube was inserted and ventilation provided by aHarvard respirator (Harvard Apparatus Co., Millis, Mass. )with 95% 02 and 5% C02. The chest was opened through amedian sternotomy and after the intravenous administrationof heparin 3 mg/kg, the superior and inferior vena cavaewere cannulated and the azygous vein divided. The cavalreturn was directed to a reservoir, through a bubble oxy-genator and heat exchanger (370 40.50C), and then re-turned through a variable speed calibrated roller pump to

The Journal of Clinical Investigation Volume 51 December 1972 2989

the main pulmoniary artery. The rate of pumiiping into thepulmonary artery thereby determined cardiac input. Theuse of the bubble oxygenator allowed the option of switchingto total cardiopulmonary bypass by altering the route ofperfusion from the pulmonary artery to the left subclavianartery when it was necessary to prevent irreversible dis-tention of the left ventricle. A ligature placed around theproximal pulmonary artery helped to isolate the right heartwhich only received coronary venous drainage. The coronaryvenous blood draining into the right ventricle was led bysiphon drainage from the cannlulated right atrium anid veni-tricle to the venous reservoir. Timed volumetric collectionsprovided a quantitation of total coronary blood flow. Aorticpressure was maintained constant by the use of a verticalcylinder (designed by Dr. J. H. Mitchell). The height of thecolumn of blood could be varied by releasing a clamp fromone sidearm of the column and reapplying the clamp to an-other sidearm; systemic pressure varied directly with theheight of the column of blood. Blood was drained freelyfrom the large cylinder by gravity and returned to the bloodreservoir. Left ventricular pressures and left ventriculardiastolic pressures were measured through a short, wide-bore, Y-shaped metal cannula inserted through the apexof the left ventricle. Proximal aortic pressures were mea-sured through a short wide-bore polyethylene catheter in-serted into the aortic arch through the left carotid artery.A snare was placed around the proximal left anterior de-scending coronary artery (LAD)' adjacent to its origin topermit reversible ligation of the LAD. Function curves werethen constructed (7) in both the normal and ischemic canineleft ventricle before and after treatment with mannitol. Theventricular function curves were obtained between 2 and7-8 min after LAD occlusion. In two animilals autonomicblockade was effected by the beta-receptor blocking agentpropranolol (Inderal 0.5 mg/kg) and( by ganglioniic blockadewith mecamylamine hydrochlorade (Inversine, 10 mg/kg).Autonomic blockade was verified at the completion of theexperiment by the absence of a chronotropic or inotropic re-sponse to 5 ,g of isoproterenol injected into the pulmonaryartery and to the clamping of both common carotid arteries.

The isovolumetric preparation was utilized to measuretotal coronary blood flow, to measure collateral coronaryblood flow, and to measure S-T segment elevation withepicardial electrocardiography before and during ischemia,both with and without the infusion of hypertonic mannitol.This preparation was chosen for these studies in order tomake the above measurements in an environiment relativelyuninfluenced by exogenous factors. The heart was removedfrom a donor animal and retrograde perfusion of the aorticroot from the femoral artery of the support dog provided.To maintain constant pressure perfusion of the coronaryarteries, a Sarns roller pump (model No. 1800, Sarns, InIc.,Ann Arbor Mich.) was interposed in the coronary perfusionline to assure a constant rate of pumping from the supportdog independent of systemic blood pressure. The rollerpump was adjusted to maintain a continuous overflow of bloodfi om the top of a vertical column of tubing. The height ofthis column determined coronary perfusion pressure. Sub-traction of the overflow from the amount of blood pumpedallowed the determination of total coronary blood flow. Athin-walled distensible balloon was attached to a button onthe end of a short, wide-bore cannula connected to a pres-sure transducer and inserted into the left ventricle through

l Abbreviations utsed ih this paper: LAD, left anterior de-scending coronary artery; LVEDP, left ventricular end dia-stolic pressure.

the mitral annulus. A purse strinig suture around the mitralannulus assured that the balloon remained within the leftventricular cavity. A small sidearm of the button obviatedherniation into the left ventricular outflow tract. A drainwas placed into the left ventricular apex to allow drainageof the small amount of coronary flow returning to the leftventricle. Right ventricular and right atrial drainage, whichrepresented an approximation of total coronary flow, werereturned to the support dog which was ventilated with 95%.02 and 5% C02 by means of a Harvard respirator. As inthe right heart bypass studies, a snare was placed arounldthe LAD. For the epicardial mappinig and total coronlaryblood flow experiments the area of LAD occlusion was atthe midlevel of the ILAD. The epicardial electrocardiogramiiwas monitored before anid at 5 and 14 min after ligation ofthe LAD. Epicardial mapping was accomplished utilizing anelectrode with a smooth, rounded 2 mmtip. The tip of theelectrode was gently applied to an area of the epicardiumand the uniipolar epicardial electrocardiogram obtained. Eithera drawing or a Polaroid picture of the area of LAD occlu-sioIn and the 15 points to be mapped was made. This allowedone to repeat the epicardial mapping as often as necessaryusing virtually identical sites. For any given time intervalS-T segment elevations were summed from 15 points withinand adjacent to the territory supplied by the lIAD.

Collateral coronary blood flozc. An estimation of collateralcoronary blood flow was obtained using the krypton washouttechnique in the isolated isovolumetric preparation describedabove. A polyethylene loop was inserted into the proximalportion of the LAD, usually at a location just distal to theorigin of the first anterior interventricular branch. Occlu-sioIn of the proximal portion of this loop provided ischemiafor that portion of the left ventricle supplied by the LAD.2 min after the oniset of ischemia, 1.5 cc of 85Kr (32 mCi/cc)were injected just distal to the occlusion into the ischemicarea. This volume insured that the "'Kr was injected intothat portion of the left venitricle now deprived of its majorsource of blood supply, i.e., the LAD. The rate of 'Kr wash-out from the ischemic area of the left ventricle was then de-pendent on collateral coronary blood flow (8, 9). The 85Krwashout was assessed by withdrawing blood from the ve-nous drainage of the right ventricle through a counitinigchamber at 5 cc/miii. Counting was continued for 7 minafter the f'Kr was injected and the slope of disappearance ofthe 'Kr from within the ischemic area plotted on semi-logarithmic paper. Collateral coronary blood flow was thencalculated from the slope of the "Kr washout (8, 9) in thesame canine heart for the: (a) control period (no isclemia),(b) period after LAD occlusion, (c) period after LAD oc-clusion and pretreatment with mannitol, (d) period afterL-AD occlusioni, and (c) a finial control (no ischemia)period.

Mannitol adniinistration. Mlannitol (12.5 g/50 cc) wasinfused at 3.82 cc/min with a Harvard infusion pump (model600-000) for periods varying from 13-60 min into the aorticroots of the dogs before the onset of myocardial ischemia.In every experiment, the infusion was continued during theperiod of ischemia. Coronary venous and systemic arterialosmolalities were determined before, during, and after man-nitol infusions. In all dogs the osmolality determiniation wasrepeated at the end of the ischemia period, before stoppingthe mannitol infusion, and was documented to have remainedelevated. In the majority of the right heart bypass experi-ments, five separate ventricular function curves were ob-tained as demonstrated in Fig. 1. The first and last ones(marked 1 and 5 in Fig. 1) were without LAD occlusion to

2990 Willerson, Powell, Guiney, Stark, Sanders, and Leaf

25

-I..

20

15

10

5

0I0 20 30

L VEOP (cm H,0O)

FIGURE 1 Ventricular function curves. The results from a

representative right heart bypass experiment showing theeffect of ischemia and the effect of mannitol and ischemiaon ventricular function. The first and fifth curves were ob-tained without myocardial ischemia. The second and fourthones were obtained during myocardial ischemia. The thirdfunction curve was also obtained during myocardial ischemiabut after pretreatment with hyperosmotic mannitol. LVEDP:left ventricular end diastolic pressure.

be certain that the preparation had neither spontaneouslydeteriorated nor improved during the course of the experi-ments. The second and fourth function curves were ob-tained after LAD occlusion. The third function curve wasobtained after LAD occlusion in a heart pretreated withmannitol. 30-45 min of rest on total cardiac bypass precededeach of the ventricular function curve runs.

In the isovolumetric studies, five separate measurementswere also made of S-T segment elevation and total coronaryblood flow or collateral coronary blood flow. The first andfifth were without LAD occlusion and served as controls.The second and fourth were with LAD occlusion and thethird with LAD occlusion immediately after treatment withhyperosmolar mannitol. A recovery period of 30-45 min fol-lowed each of the initial four isovolumetric studies. Usuallythe 3045 min of recovery was sufficient for the serum os-molality to return substantially toward control levels betweenthe third and fourth runs, but on occasion it was still mod-erately elevated at the onset of the fourth run.

In the majority of the above experiments pre- and post-intervention control data were obtained in the same prepara-

tion. In the event that either spontaneous deterioration orimprovement was found that experiment was not included inthe data subsequently analyzed. For the above reasons fourright heart bypass experiments, four isovolumetric studies,and two 'Kr washout experiments could not be used in thestatistical analyses.

Pressure recordings. Pressures were measured with Sta-tham P23db pressure transducers (Statham Instruments,Inc., Oxnard, Calif.); the frequency response of the pres-

sure measurement system was linear up to 30 cps. The rateof rise of left ventricular pressure LV dP/dt was obtainedutilizing an RC electronic differentiation of the full leftventricular pressure. Calibration of the LV dP/dt differenti-ator was accomplished by supplying a wave form of knownslope to the differentiating circuit which had a time con-tant of 0.0001 sec and a cut off at 160 cps.

All measured pressures were recorded on a multichannelSanborn direct writing oscillograph (Hewlett-Packard Co.,Waltham, Mass.).

Statistics. The data obtained in these studies were ana-lyzed utilizing Student's t test and mean values, standarderrors, and standard deviations were obtained.

RESULTS

Ventricular function. Mannitol was infused into theaortic root of 15 dogs on right heart bypass. This ele-vated the mean serum osmolality in the coronary circu-lation 17 (±3 SEM) mOsmabove the control level dur-ing the mannitol infusion at the time of onset of theischemia. Fig. 2 demonstrates that mannitol failed to im-prove the ventricular function curve in the normotensiveanimals without myocardial ischemia (four animals witha mean A stroke work of 0.0, 0.3, and 0.2 g-m at leftventricular end diastolic pressures (LVEDP) of 4, 6, 8,and 10 cm H20, respectively, NS). While the ventricularfunction curves were not changed in the normotensiveanimals without myocardial ischemia by the infusion ofmannitol, left ventricular dP/dt at an LVEDP-of 10 cm

H20 was slightly increased (+ 413±114 mmHg/sec,P < 0.05) in four hearts in which this measurementwas made.

Myocardial ischemia produced by reversible ligation ofthe LAD markedly depressed the ventricular functioncurves in nine dogs. Mannitol pretreatment significantlyimproved these depressed ischemic ventricular functioncurves. Fig. 1 illustrates the data from one animal andTables I A-I D summarize the data from nine animals.Stroke work was significantly increased at three levels of

35

30

25p0t

I:Kh

20

15F

1O

5

/-° Control-* * Mannitol

c.- - - Postcontrol

I

10 20 30

L VEDP (cm H20)

FIGURE 2 Nonischemic ventricular function curves. The lackof effect of mannitol on the ventricular function curve of theanimal without myocardial ischemia is demonstrated.

Beneficial Effect of Mannitol on Ischemic Myocardium

i Pre control

/,o 5 Postcontrol

3 Mannitol + lschemia*/f 21schemia

I X 41schemio

l-

0 /

2991

TABLE I AEffect of Mannitol on Myocardial Stroke lWTork during

Myocardial Ischemia

No. of Mean Aexps. LVEDP A Stroke wor-k Stroke work

can H2) g-m %control

8 10 +3.141* (P < 0.025) +37±7*%9 13 +3.941 (P < 0.01) +4648%8 15 +4.141.2 (P < 0.025) +47±9%

* Standard error of the mean.

LVEDP in the mannitol pretreated dogs (Table I A andFig. 3). Similarly, left ventricular end diastolic pressureswere lower during ischemia in the mannitol-treatedanimals at seven comparable levels of stroke work (Ta-ble I B). Table I C and I D present the absolute datain each animal in the sequence in which the study wascarried out. Directionally similar results were noted inthe two animals with autonomic blockade. In these twoanimals, increments in stroke work of the ischemic leftventricle produced by mannitol were + 3.5 and + 1.0

i +70

%t +60

+50

+40-

+30 ::.

+20

+ 0 r~

010 13 15

L VEDP (cm H,O/

FIGURE 3 Summary of the ischemia ventricular functioncurve data. The mean change in left ventricular stroke workis along the vertical axis, expressed as the per cent of con-trol. The three levels of left ventricular stroke work at whichthese data were obtained are along the horizontal axis. Notethe per cent increase in stroke work at three levels of enddiastolic pressure achieved by elevation of the serum os-molality during ischemia. The vertical bars represent thestandard errors of the mean.

g-m at an LVEDP of 15 cm H20, + 1.5 and + 3.0 g-mat 20 cm H20 and + 2.0 and + 5.5 g-m at 25 cm H20.Decreases in LVEDP at a stroke work of 7, 9, and I1g-m were -2 and -2 cm H20, -2 and -7 cm H20aind - 4 and - 11 cm H20, respectively. In the rightheart bypass preparation LV dP/dt measurements in fivedogs made at a comparable LVEDPwere also increased(luring myocardial ischemiiia after the administration ofmannitol. The AdP/dt at an LVEDPof 13 cm H20 Wa1S+ 280±122 mmHg/sec (P < 0.05).

In 11 animals elevation of the serumi osniolality by18±2 mOsmfrom a pre-control level of 334±+5 mOsmfailed to change significantly (+ 0.2 ±0.5%) the he-matocrit from the control level of 36±1%. During thepost-control coronary ligation experiments in these ani-mals the osmolality fell significantly (P = 0.01) but re-mained 12±4 mOsmabove the precontrol level (P =0.01). This intermediate osmolality corresponded to alevel of ventricular function which was intermediate be-tween the pre-control ischemic and the mannitol-ischemiavalues in a substantial number of experiments (TablesI C and I D).

S-T segment elevation. Mannitol infusions into theaortic roots of the isovolumetric left ventricles elevatedmean serum osmolality 47±5 (SEM) mOsmin the coro-nary circulation. Preliminary experiments demonstratedthat the administration of mannitol had no demonstrableeffect on S-T segments in the nonischemic canine heart.In three animals, the reproducibility of S-T segxmentelevation during repeated 12-min periods of ischemia wasdocumented. Fig. 4 depicts a representative experiment.The maximum S-T segment elevation during repeatedischemia was 43.5, 43, and 42 mmin the second dog and31 and 33 mmin the third dog.

Myocardial ischemia produced marked elevation ofthe S-T segments in the six hearts evaluated. Fig. 5 de-picts two representative examples. Pretreatment withmannitol markedly reduced the S-T segment elevationthat occurred after 5 and 14 min of ischemia (Table II).

TABLE I BEffect of Mannitol on L VEDPduring Myocardial Ischemia

No. of Stroke Mean Aexps. work A LVEDP LVEDP

g-m cm H2O %control

9 4 -2.340.5* (P < 0.005) -32±9*%9 6 -3.3±0.7 (P < 0.025) -28±6%6 8 -3.2 ±0.8 (P < 0.05) -29±N4%5 10 - 5.9± 1.7 (P < 0.025) -37±5%4 12 -3.440.1 (P < 0.05) -29±9%3 14 -4.7 -38%2 16 -7.5 -45%

* Standard error of the mean.

2992 Willerson, Powell, Guiney, Stark, Sanders, and Leaf

The range of the reduction in ischemic S-T segmentsafter mannitol was 0.5 mmto -30 mm(mean -8.2 mm)after 14 min of ischemia.

TABLE I CEffect of Mannitol on Myocardial Stroke Work (g-m) during

Myocardial Ischemia at Three Levels of L VEDP

TABLE I DEffect of Mannitol on L VEDP (cm H20) during Myocardial

Ischemia at Seven Levels of Stroke Work

Stroke work levelsDogNo. 4 6 8 10 12 14 16

DogNo. 10

1 C*

II+M

IC

2 CI

I+MIC

3 CI

I+MIC

4 CI

I+MIC

5 C

I

I+MIC

6 C

I+M

C7 C

II+M

C8 C

II+M

C9 C

II +M

I

15.25.8

10.57.3

29.513.22112.3

14.89.8

16.513.5

10.46.37.58.6

11.012.2

4.04.8

11.86.95.26.84.36.0

23.55.96.36.3

12.011.24.06.55.9

10.5

LVEDPlevels

13

cm H2O

208.0

13.39.3

14.22312.9

19.61422.518.6

10.24.27.238.6

13.07.9

11.011.013.5

5.76.2

15.18.05.08.05.07.0

25.57.57.51

1314.3

5.28.07.2

15.5

15

9.014.4

9.7

1524.713

2316.825.522

12.84.88.85.4

10.4

67.0

17.58.85.98.65.68.8

26.588t

13.815.7

6.38.87.7

18.7

I C*I

I+MIC

2 CI

I+MIC

3 CI

I +MIC

4 C

I

I+MIC

5 CI

I+MIC

6 CI

I+MIC

7 CI

I+MIC

8 CI

I +M

C

9 CI

I+MIC

58.55.67.0

4.07.04.05.04.0

10.0131014837.56.555.52

109

3.35.57.56.597.516.55.55.52.53.7

10563

6.810.5

6.58.8

0.252

5.17.75.16.04.5

11.015.51215.510.3

5.39.58.57.573.2

1612.5

58.5

169.2

16.510.5

1.510.5

9.519.545.5

14.59

105.3

7.013

11

0.862.86.2

6.29.06.17.05.5

12.018141812.5

7.513.810.51085

19

6.813

13

15.51.7

19191

67.3

13.316

7.5

g-m7.5

179.5

17

1.57.347.6

7.310.2

7.08.06.5

13.020.516.3

>2214.5

9.512.511.5129.56.5

8>22

11.5>30

2.58.55.39

8.311.58.09.07.2

14.32319.5

16.512

9.5>22

13.5>30

3.312.3

6.5

9.513.09.0

10.1

15.8

18.5

10.5

18

4.218

7.6

10.814.5

9.810.7

17

20.5

10.5

8.5

2.2

7.89

3

10

9.5

* Abbreviations as in Table I C.1 The arterial osmolality only increased S mOsm/liter.

Directionally similar results were noted in three ad-ditional hearts into which control isotonic saline infu-sions at 3.82 cc/min were administered during the- pre-and post-control ischemic periods, thereby indicating thata lowering of the temperature of ischemic myocardiumby the infusion of a room temperature solution couldnot account for the changes noted in each of these threehearts. In each of the three hearts the sum of S-T seg-ment elevation after 15 min of precontrol ischemia,ischemia with mannitol and post-control ischemia was52 mm, 39 mm, and 47 mm; 23 xnm, 15 mm, and 20 mm;

Beneficial Effect of Mannitol on Ischemic Myocardium

* C, Control; I, Ischemia: I+ M, Ischemia and mannitol.t The arterial osmolality only increased 5 mOsm/liter.

2993

E50 / l Control

Ill After 30 min

.4O

30-

k 20

101

4 8 12 16 20

MINUTES

FIGURE 4 Reproducibility of S-T segment changes obtainedwith epicardial mapping by the technique des-ribed in theMethods section. Note that 14 hr after epi-ardial S-T seg-ment mapping with the first reversible ligation of the LAD,the degree of S-T segment elevation associated with a sub-sequent ligation of the LAD is similar.

and 32 mm, 25 mm, and 32.5 mm. In each of these ex-perimental runs measurement of the temperature witha Fisher Scientific Thermometer (Fisher Scientific Co.,Pittsburg, Pa.) (- 10° + 260°C with 10 calibrations)placed in the LV cavity between the balloon and the endo-cardium and with another similar thermometer heldagainst the center of the epicardial ischemic region failedto reveal a discernible change in temperature. The epi-cardial temperature in each of the three animals was 28,25, and 27°C. The endocardial temperature in each ofthe three animals was 30, 27, and 30°C.

Total coronary blood flow. The administration of man-nitol significantly increased total coronary blood flow inthe isovolumic hearts studied both immediately before andduring ischemia as demonstrated in Fig. 6 and Table II.The actual increases in total coronary blood flow by man-nitol over the control ischemic flows ranged from + 30cc/min per 100 g LV to + 70 cc/min per 100 g LV (mean+ 44.0 cc) in the control period before ligation; from + 22cc/min per 100 g LV to t- 60 cc/min per 100 g LV(mean + 38.9 cc) for the 5 min ischemic period; and

from + 25 cc/xnin per 100 g LV to + 40 cc/min per100 g LV (mean + 31.6 cc) for the 14 min ischemic pe-riod. This increase in total coronary blood flow was notexplainable by changes in wall tension as reflected in leftventricular peak systolic and end diastolic pressures.There were no statistically significant differences inthese pressures in the isovolumic hearts before and aftermannitol. Similarly the changes in coronary blood flowdid not appear secondary to changes in hematocrit in-duced by the hyperosmolality. In 8 hearts elevation ofthe serum osmolality by 36±5 mOsmfrom a control of316±3 mOsmwas associated with a mean decrease inhematocrit of only 3±1% from a control level of 40±1%.In the postcontrol coronary ligation experiments the os-molality fell significantly (P = 0.01) but remained 12±3mOsmabove the pre-control level (P = 0.01). Theseintermediate osmolalities in the postcontrol ischemiaexperiments were associated with intermediate eleva-tions of S-T segments which were 8.5±4.3 ,mm below thepre-control ischemic level (P = 0.07) but were sig-nificantly higher (P < 0.05) than the mannitol-ischemialevel at 14 min of ischemia.

Figs. 5 and 6 demonstrate the reciprocal relationshipbetween changes in coronary blood flow and changes inS-T segments in these experiments. The S-T segmentdata depicted in the left panel of Fig. 5 are from thesame experiment as the coronary blood flow data in thecenter panel of Fig. 6. Similarly, the S-T segment dataon the right of Fig. 5 correspond to those in the rightpanel of Fig. 6. For a given experiment the greatestS-T segment elevation was associated with the lowesttotal coronary blood flow and vice versa.

Collateral coronary blood flow. Collateral coronaryblood flow as estimated by the 'Kr injections into theischemic region of the left ventricle was significantly in-creased relative to control ischemic runs in each of sevenisovolumic hearts studied after pretreatment with man-nitol (Table III and Fig. 7). The range of increase incollateral coronary blood flow during ischemia aftermannitol as compared to ischemia alone was + 1.9 to+ 16.4 cc/min per 100 g LV (mean + 9.5 cc). Postcon-trol ischemic and subsequent postcontrol nonischemiccollateral coronary blood flow determinations showed areturn toward but not to the precontrol levels in all ofthe animals in which these determinations were per-formed (Table III). For these experiments the elevationof the serum osmolality of + 64±7 mOsm, from a con-trol level of 327±9 mOsmduring the mannitol-ischemiaexperiments fell significantly (P = 0.001) in the post-control coronary ligation experiments to + 17±4 mOsmabove the precontrol levels (P < 0.05). These intermedi-ate osmolalities in the postcontrol runs corresponded tocollateral blood flow determinations which were inter-mediate between the precontrol ischemic and the ischemia

2994 Willerson, Powell, Guiney, Stark, Sanders, and Leaf

1J

t4J

'4J

;t

4 8 12 16 20

MIN1UTES8 12 16 20

MINUTES

FIGURE 5 S-T segment changes. Two examples of the changes in S-T segments during myo-cardial ischemia with and without pretreatment with mannitol. Note in both experiments thedecrease in S-T segment elevation during ischemia associated with mannitol pretreatment. Inthe panel on the right the post-control S-T segments appear similar to those noted with pre-treatment with mannitol most likely because of persistent elevation of the serum osmolality aftermannitol. In the panel on the left the ischemic period was shorter than usual, lasting only 11 min.

and mannitol values (Table III). In an additional heartwhich did not receive mannitol 'Kr blood flow deter-minations were 72 cc/min in the precontrol period,20.4 cc/min during the first ischemic period, 20.7 cc/minduring the second ischemic period, and 73.0 cc/min dur-ing the postcontrol, nonischemic period.

In five additional hearts direct measurement of thebackflow with a graduated cylinder showed directionallysimilar results to the 'Kr data. The mean increase inbackflow during the ischemia experiments associatedwith the administration of mannitol and an elevation ofosmolality of 33+6 mOsmwas 28+3% over the back-flow during the control ischemic experiments.

DISCUSSION

The data obtained fromn these studies demonstrate thathypertonic mannitol improves ventricular contractilityduring myocardial ischemia as evidenced both by a shiftto the left of the ventricular function curve and by anincrease in left ventricular dP/dt. The ability of mannitolto increase total coronary blood flow during ischemiaand, even more importantly, to increase collateral coro-nary blood flow into the ischemic region of the left ven-tricle are demonstrated. It seems likely that the increasein coronary blood flow after mannitol importantly con-tributes to the improved ventricular function that occursduring myocardial ischemia. The reduction in ischemic

TABLE I IEffect of Mannitol on S-T Segment Elevation and Total Coronary Blood Flow during Myocardial Ischemia

Time afteronset of Mean A total

No. of myocardial Mean A S-T coronaryExps. ischemia A S-T segments* segments A Total coronary blood flow blood flow

min mm %control cclmin per 100 g LV %control

6 5 -10.014.4t (P < .05) 33414t % +38.945.01 (P < .001) 147449t %4 14 -8.242.9 (P <.025) 22-7% +31.643.7 (P <.005) 2464185%

* A Sumof S-T segments from 15 points mapped epicardially.t Standard error of the mean.

Beneficial Effect of Mannitol on Ischemic Myocardium 2995

MINUErS MINUrES MINUTES

FIGURE 6 Coronary blood flow changes. The changes in total coronary blood flow during myo-cardial ischemia with and without pretreatment with mannitol are demonstrated. Note in allthree experiments the increased coronary blood flow during ischemia associated with mannitolpretreatment. The data depicted in the center panel are from the same experiment as the S-Tsegment data in the left panel of Fig. 5. Similarly, the data in the right panel correspond tothose on the right of Fig. 5.

S-T segment elevation is probably also the result of thisincrease in coronary blood flow.

This combination of beneficial factors, i.e. improvedventricular function, increased total and the fast com-poulnds of collateral coronary blood flow, and reducedS-T segment elevation is to date unique for mannitol.Agents which previously have been noted to reduce S-Tsegments depress myocardial contractility (6). Otherroutinely used inotropic agents that increase myocardialcontractility such as isoproterenol and digitalis alsofurther elevate S-T segments during ischemia (6). It islikely that these latter agents act directly on the ischemicmyocardium to increase contractility and myocardial oxy-

geni demands. This increase in metabolism in the presenceof a limited blood supply may result in further ischemiawlhich would then explain a further increase of epi-cardial S-T segment elevation.

In the present experiments, the increase in contrac-tility was not associated with further S-T segment ele-vation but was actually accompanied by a lowering of theS-T segments. This reduction of S-T segment elevationin the face of increasing contractility suggests that ex-tracellular hyperosmolality does not augment tissue in-jury in association with increasing performance of theischemic myocardium. There is, however, an increase incollateral blood flour to the ischemic area. Thus, it seems

TABLE I I ICollateral Coronary Blood Flow* as Measured by 85Kr lVashout

A Increase incollateral

No Isclemia- flow after NoExp. ischemia Isclemia mannitol mannitol Ischemia ischemia

1 34.7 9.9 23.1 +13.2 46.42 36.6 9 10.9 +1.9 9.1 20.03 41.4 18.3 34.7 +16.4 23.1 53.44 45.6 17.6 29 +11.4 24 32.65 29.5 2.6 7.6 +5.0 1 16 + 10.9 20.4 +9.5 19.77 2.2 11.4 +9.2 7.7

Meani 37.6 (42.8) 10.1 (42.4) 19.6 (43.8) +9.5 (±41.8)(P <.005)

* Expressed as cc/min per 100 g left ventricle.Not measured.

2996 Willerson, Powell, Guiney, Stark, Sanders, and Leaf

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likely that extracellular hyperosmolality improves thefunction of .ischemic myocardium by directly increasingthe blood supply to the ischemic area. This salutory ef-fect may be a property of other hyperosmolar agents aswvell.

It is probable that the reduced S-T segment elevationiaiccompanying the administration of mannitol is directlycorrelated with reduced myocardial cellular injury.Recent work by Maroko et al. (6) demonstrates a closecorrelation between the magnitude of early S-T seg-ment elevation in epicardial recordings after acute coro-nary artery occlusion and the later development of cel-lular damage as evidence by depression of myocardialcreatine phosphokinase activity. This inverse relationshipbetween S-T segment elevation and myocardial creatinephosphokinase depression has also been demonstrated tobe present during pharmacologic interventions (adminis-tration of isoproterenol and propranolol) which alterischemic S-T segment elevation (6). Other investigatorshave also emphasized the correlation between S-T seg-ment elevation and myocardial cellular injury (10, 11).

A number of questions remain to be answered regard-ing the mechanism(s) by which these beneficial changesoccur. First, it remains to be determined whether the in-crease in coronary blood flow reflects reduced myocardialatnd endothelial cellular edema with subsequent increasedpatency of myocardial capillaries. It has been demon-strated in the heart (1, 12), the brain (2), and the kid-ney (5) that during ischemia cellular edema occurs as aconsequence of impaired metabolism with the insufficientenergy available to maintain active extrusion of sodiumfro,m cells. Recently, Leaf has emphasized that the regu-lation of intracellular volume may be important inischemia and has speculated that the prevention of cellswelling during ischemia might have a beneficial effecton organ function by increasing blood flow and reducingtissue injury (13). Evidence for this has been accumu-lated in the brain (4) and the kidney (5). In these previ-ous studies, elevation of the extracellular osmolality hasbeen shown to reduce the area which is underperfusedwhen the blood supply is re-established after ischemia.Presumably, this beneficial effect of hypertonic manni-tol is the result of its remaining for the most part extra-cellularly and thus acting osmotically to reduce the intra-cellular edema that occurs during ischemia. Alternatively,the possibility exists that the increase in total coronaryand collateral coronary blood flow observed in the pres-ent experiments may occur as the result of a direct reduc-tion in coronary arteriolar resistance. Whatever themechanism, improvement of myocardial blood flow byhyperosmotic mannitol during ischemia, can alone ex-plain the improved ventricular function and reduced S-Tsegments demonstrated in this study.

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ISCHEMIA +MANNITOL

FIGURE 7 Summary of the 'Kr collateral blood flow data.This illustration shows the increase in collateral blood flowas measured by the 'Kr washout technique during ischemiawhich is associated with an elevation of the serum osmolality.

In addition to a considerationi of coronary blood flow,other questions remain to be resolved. Specifically, issome of the positive inotropic effect of mannitol onischemic myocardium independent of its influence onblood flow? Previous investigators have demonstratedthat certain hyperosmolar agents, including mannitol,increase dP/dt in the whole heart and developed tensionand its first derivative in the papillary muscle in well-oxygenated systems within a cetrain osmolality range(14-16). The present data which include the results ofexperiments done with autonomic blockade, and the re-cent study by Atkins, Wildenthal, and Horowitz (17)suggest that this increase in contractility is due to a di-rect effect on the myocardium rather than a neurohu-moral response to stimulation of a peripheral receptor(18).

From this, it would appear that mannitol has inotropicproperties independent of its effect on blood flow butwhether increases in contractility occur in a hypoxic en-vironment is as yet unknown. Similarly, it is not knownwhether mannitol is capable of improving the contrac-tility of myocardium which is depressed by interventionsother than ischemia. Also remaining to be determined iswhether this inotropic property, if it is present in hy-poxic situations, is mediated solely by maintenance ofa more favorable intracellular volume or by another as

Beneficial Effect of Mannitol on Ischemic Myocardium 2997

yet undetermined mechanismii. It is of initerest that Fer-rans, Buja, Levitsky, and Roberts have recently demon-strated the importance of increasing the osmolality intissue preservation specifically as regards the preventionof swelling of sarcoplasmic reticulum mitochondrialdamage, and interstitial edema (19).

The potential clinical application of the informationobtained from these studies is, as yet, unknown. Theexact method and circumstances involved in the ad-ministration of mannitol to patients with imyocardial is-chemia will have to be determined in the course of theclinical evaluation of the efficacy of hyperosmiiolar agentsin myocardial ischemia.

It seems clear that hyperosmniolar manniitol exerts apositive inotropic influence oni ischemic myocardiunwhile improving total coronary and the faster componentsof collateral coronary blood flow and reducing the areaof ischemic danmage. This particular combination ofbeneficial changes occurring during nmyocardial ischemiais thus far unique for mannitol and invites further in-vestigation both in experimental and clinical settings.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the expert technical as-sistance of Mr. J. L. Guerrero, Mr. Stephen M. Vecchiarelli,Mr. Michael A. Bissanti, Mr. Stuart R. Rosenthal, and Mr.Alvin G. Denenberg and the typing assistance of Miss JoanAnn Kowalczyk.

This paper was supported in part by National Institutes ofHealth U. S. Contract PHS 43-67-1443 and Grants HL-14292, HL-06664 (H.E.P.P.), and HL-5196.

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18. Lasser, R. P., M. R. Schoenfeld, D. F. Allen, and C. K.Friedberg. 1960. Reflex circulatory effects elicited byhypertonic and hypotonic solutions injected into femoraland brachial arteries of dogs. Circ. Res. 8: 913.

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2998 Willerson, Powell, Guiney, Stark, Sanders, and Leaf