Comparative Assessment of Right Ventricular Performancefrom the Pressure-Volume Relationship in Double-Muscled

and Conventional Calves

Helene Amory, Kathleen McEntee, Annick S. Linden, Daniel J.M. Desmecht, Jean-Marie L. Beduin, Vincent D'Orio,and Pierre M. Lekeux

ABSTRACT

Forty-one and 55 records ofright-sided and systemic arterialpressures, cardiac output, and end-diastolic and end-systolic right ven-tricular volumes were collectedfrom a group of 6 conventional and6 double-muscled calves, respec-tively. In each group, the meanright ventricular pressure-volumeloop was constructed.

Global cardiac performance wassignificantly lower in the double-muscled than in the conventionalcalves. The right ventricular end-diastolic and end-systolic volumes,as well as the diastolic portion ofthe mean pressure-volume loop,were similar in the 2 groups. Thoseresults suggest that the reducedcardiac performance of double-muscled calves is not due to a low-ered ventricular preload and thatdiastolic properties of their myocar-dium are similar to those of conven-tional calves. When expressed on abody weight basis, however, theright ventricular end-diastolic andend-systolic volumes were lower inthe double-muscled than in conven-tional calves. When expressed as afunction of probable metabolicdemand, therefore, the volumetriccapacity of the cardiac pumpappears to be reduced in double-muscled calves. The significantlylower right ventricular ejectionfraction, maximal rate of ventricu-lar pressure rise and right ventricu-lar peak-systolic pressure to end-systolic volume ratio measured indouble-muscled as compared withconventional calves suggest that

reduced myocardial contractilitymay also be partly responsible forthe significantly lower stroke indexof the former calves. The cardiacpump of double-muscled cattle thusseems to be less effective than thatof conventional cattle because ofreduced volumetric capacity andlowered strength of contraction.

RESUME

Chez 6 veaux conventionnels et6 veaux hypermuscles, la pressionarterielle systemique, les pressionsde la petite circulation, le debit car-diaque et le volume ventriculairedroit en fin de diastole et en fin desystole ont ete mesures a 41 et55 reprises, respectivement. Laboucle de fonction ventriculairedroite moyenne a ete construitepour chaque groupe.La performance cardiaque glo-

bale etait significativement plusfaible chez les veaux hypermusclesque chez les veaux conventionnels.Les volumes du ventricule droit enfin de systole et en fin de diastole,exprimes en valeur absolue, ainsique la portion diastolique de laboucle de fonction ventriculairedroite moyenne etaient similairesdans les 2 groupes de veaux. Cesresultats suggerent que la perfor-mance cardiaque reduite des veauxhypermuscles n'est pas attribuablea une reduction de la prechargeventriculaire et que les proprietesdiastoliques de leur myocarde sontcomparables 'a celles des veaux con-ventionnels. D'autre part, lorsqueles volumes ventriculaires en fin de

systole et en fin de diastole etaientindexes en fonction du poids cor-porel, ceux-ci etaient significative-ment plus faibles chez les veauxhypermuscles. D'es lors, lorsque lacapacite volumetrique du ventriculeest exprimee en fonction de lademande metabolique, celle-ciapparalt reduite chez les veauxhypermuscles. La fraction d'ejec-tion du ventricule droit, la valeurmaximale de la de'rive'e premiere dela pression ventriculaire droite enfonction du temps ainsi que le rap-port entre le pic de pression et levolume en fin de systole dans le ven-tricule droit etaient significative-ment plus faibles chez les veauxhypermuscles, ce qui suggierequ'une reduction de la contractilitemyocardique pourrait aussi etrepartiellement responsable de lareduction du volume d'ejectionsystolique chez ces animaux.En conclusion, la pompe cardia-

que des bovins hypermuscles sem-ble moins performante que chez lesbovins conventionnels en raisond'une reduction de sa capacitevolumetrique et de sa force decontraction.

INTRODUCTION

Aerobic metabolic capacity is lowerin double-muscled cattle than in ani-mals with conventional conformation(1,2). This might partly explain thehigher morbidity and mortality ratesin double-muscled than in conven-tional cattle (3). Several steps in theoxygen-transport pathway may beresponsible for this lower oxidative

Laboratory for Functional Investigation, Department of Physiology (Amory, Linden, Desmecht, Lekeux), Department of Small Animal Medicine(McEntee) and Department of Genetics (Beduin), Faculty of Veterinary Medicine and Department of Intensive Care Medicine and Hemoliege, Facultyof Medicine (D'Orio), University of Liege, Belgium.Supported in part by I.R.S.I.A. (Belgium), Grant no 12252/5475 A.H. Amory is a research assistant supported by a contract with the F.N.R.S.(Belgium).Submitted January 01, 1994.

Can J Vet Res 1995; 59: 135-141 135

capacity. Among these, the cardiovas-cular system has been suspected as apotential critical step. Indeed, in cat-tle, the selection of the gene responsi-ble for the double-muscled conforma-tion is associated with a reduction inthe heart weight-to-body weight ratio(4) and lowered cardiac pumping abil-ity during exercise (2). Moreover, ithas been recently demonstrated thatglobal cardiac performance, asexpressed in terms of cardiac output(CO), stroke volume (SV), cardiac orstroke index (CI and SI, respectively),or right or left ventricular work index(RVWI and LVWI, respectively), islower in double-muscled than in con-ventional calves (5). Among the vari-ous determinants of cardiac function,a lower myocardial contractility hasbeen suspected to be partly responsi-ble for this reduced cardiac perfor-mance (5,6). However, the validity ofthis hypothesis had to be ascertainedby direct invasive measurement ofcardiac inotropism and ventricularvolumes. The purpose of the presentstudy was to apply such techniques toconstruct right ventricular pressure-volume loops, in order to further eval-uate which determinant could beresponsible for the lower cardiac per-formance measured in double-muscled calves when compared withcalves of conventional conformation.

MATERIALS AND METHODS

ANIMALS

Two groups of animals were stud-ied. The 1st group involved 6 Friesiancalves (body weight: 185-266 kg withmean ± SEM of 213.0 ± 12.9 kg; age:174-264 d with mean ± SEM of212.2 ± 14.1 d), whose conformationwas considered as conventional. Forthe second group, 6 Belgian Whiteand Blue calves (body weight:220-279 kg with mean ± SEM of238.0 ± 9.5 kg; age: 165-244 d withmean ± SEM of 221.4 ± 11.9 d) wereselected on the basis of their double-muscled conformation.

All calves were considered healthyand free of cardiac disease as deter-mined by clinical history and byabsence of abnormalities upon physi-cal examination, auscultation and elec-trocardiography. Since their first weekof life, the calves had been regularly

submitted to various experimental pro-tocols in the same room. They weretherefore fully accustomed to the envi-ronmental conditions, used to beingrestrained, and easy to handle.

MEASUREMENTS

At 1-mo old, the calves underwent asurgical procedure, performed underxylazine (Rompun, Bayer, St-Truiden,Belgium), gaiacolate (Gujatal 10%,Aesculaap, Ghent, Belgium), and thio-pental (Pentothal, Abbott, Louvain-la-Neuve, Belgium) anesthesia, in whichthe right common carotid artery wasexteriorized in the midcervical regionand maintained in a subcutaneousposition by closure of underlyingmuscles. Twenty-four hours beforethe study, I and 2 introducers (Desilet8F, Vygon, Brussels, Belgium) wereinserted percutaneously in the rightand left jugular veins, respectively,under local analgesia and using theSeldinger technique (7). The day ofthe study, an arterial catheter (LeaderCath 18G, Vygon, Brussels, Belgium)was inserted percutaneously in thetransposed right carotid artery, underlocal anesthesia and using theSeldinger technique. Before startingthe investigation, the animals wereallowed to rest for 1 h.

All calves were investigated stand-ing in a stanchion. They were notsedated or anesthetized at the time ofthe study. An electrocardiogram(ECG) was obtained (Cardiofax GEM,Nihon-Kondem, Tokyo, Japan) using abipolar base-apex lead. The systemicarterial pressure was determined usinga fluid-filled catheter and an extra-vascular transducer (Bentley Trantecmodel 800 and Heres, ACEC,Charleroi, Belgium). A balloon-tipped, triple lumen Swan-Ganz cathe-ter equipped with a rapid responsethermistor (Elecath 7F THC-08407,Colombus Instruments, Colombus,USA) was advanced, under pressuretracing monitoring (Statham P23 XL,Gould, Brussels, Belgium and Sirecust323, Siemens, Brussels, Belgium),4-5 cm downstream from the pul-monic valve, which allowed measure-ment of the pulmonary arterial pres-sure and blood temperature. Meanpulmonary and systemic arterial pres-sure (SAPM and PAPM, respectively)were electronically integrated and dis-played. A multiple port flush catheter

(High flow 7F, Cordis, Brussels,Belgium), positioned to inject thebolus of cold saline glucose solutionfor cardiac output (CO) measurements,was inserted into the right ventricleusing the same technique (StathamP23 ID, Gould, Brussels, Belgium andSirecust 302 D, Siemens, Brussels,Belgium).Cardiac output, ejection fraction

(EF) and right ventricular end-diastolic and end-systolic volumes(EDV and ESV, respectively) weremeasured by the thermodilution tech-nique as previously described (8,9).A 5 mL/100 kg body weight icedbolus of a 5% glucose solution wasinjected into the right ventricle,via the flush catheter, by means of acompressed-air-driven pump trig-gered by the R wave of the ECG. Thepulmonary arterial temperature wasmeasured by a CO computer modifiedto allow amplification of the thermis-tor output signal (Cardiomax II,Columbus Instruments, Columbus,USA). The continuous display ofblood temperature allowed the moni-toring of each thermodilution curve,which exhibited a series of successivediastolic plateaus in the washoutcurve, each plateau corresponding tosuccessive cardiac ejections. A micro-tip catheter (PPG Hellige, DragerBallings, Brussels, Belgium) wasintroduced into the right ventricleunder pressure monitoring, after zero-ing at atmospheric pressure level. Thefirst derivative of right ventricularpressure with respect to time (dP/dt)was obtained by use of a differentiatoramplifier including filtering (ModuledP/dt, Medi-Soft Limited, Brussels,Belgium). The frequency response ofthe total circuit was found to be linearup to the frequency cutoff of 100 Hz.Pressure tracings, ECG, dP/dt andblood temperature were recordedsimultaneously on a rapid writingpolygraph (ES 1000, Gould, Brussels,Belgium).

All the pressure transducers werecalibrated for 25, 50, 75 and 100 cmH20 by using a water manometer andwere tested for linearity. For theextra-vascular pressure transducers,the zero pressure was carefully stan-dardized at the level of the scapulo-humeral joint. Calibration of the rightventricular pressure differentiatingdevice was performed by means of a

136

sawtooth signal. The latter was pro-vided by an integrating channel atfixed DC input and set at automaticzeroing.

After 5 to 10 successive measure-ments of CO, the right ventricularflush catheter was moved back intothe right atrium to measure the centralvenous pressure (CVP). The balloonof the Swan-Ganz catheter was theninflated and it was advanced until acharacteristic wedge tracing (10) wasdisplayed. The pulmonary capillarywedge pressure (PW) was thenrecorded.

In each calf, the measurementswere performed 2 to 5 times at 1-hintervals throughout the same day,and the protocol was repeated the fol-lowing day. In all, 41 and 55 sets ofmeasurements were collected in theconventional and in the double-muscled groups, respectively.

In order to avoid the effects of men-tal stress, care was taken to record thedata only when heart rate was in theresting range, i.e. lower than1 10 beats/min.

CALCULATIONS

Heart rate (HR) was calculatedfrom the ECG tracings. Stroke volumewas determined from the ratio of COto HR. Cardiac and stroke indiceswere determined by dividing CO andSV, respectively, by body weight.From the right ventricular pressuretracings issued from the microtipcatheter, proto-diastolic, end-diastolicand peak systolic pressures (RVPPD,RVPED and RVPPS, respectively) were

measured from their respective trac-ings and averaged over 10 successivecardiac cycles preceeding the ther-modilution curves records. The rightventricular pressure at the onset of theejection phase was estimated from thediastolic pulmonary arterial pressure(PAPD) determined from the tracingssimultaneous to those used for ven-tricular pressures measurements.From the tracings of dP/dt, the maxi-mal and the minimal rate of right ven-tricular pressure change (dP/dtmax anddP/dtmin9 respectively) were measuredas the average of 10 successive car-diac cycles. Pulmonary and systemicvascular resistance indices (PVRI andSVRI, respectively) were expressed indynes*s*cm-5.kg-'*10-3, and calcu-lated from the mean pressure and flow

data issued from each set of measure-ment, using the standard formulas(10):

PVRI= PAPM PW x 60 X 1.332CI

SVRI SAPM -CVP X 60 X 1.332CI

Where PAPM, PW, SAPM and CVP areexpressed in mmHg and CI inmL- min-'.kg-'.Right and left ventricular work

indices were expressed in kg*min-'kg-'. 103, and also calculated from themean pressure and flow data issuedfrom each set of measurement, usingthe standard formulas (10):

RVWI = CI x PAPM X 13.6 x 10-3LVWI=CIXSAPMX 13.6X 10-3

Where PAPM and SAPM are expressedin mmHg and CI in mL* minI'-kg-'.On each thermodilution curve, the

heights of the successive plateaus inthe pulmonary artery temperaturewere measured from the baseline. Theresidual fraction (K) was calculated asthe mean ratio of these successiveheights. Ejection fraction, EDV andESV were calculated using the stan-dard formulas (11):

EDV = SV1-K

ESV = EDV-SV

SVEF = SV

EDV

The values of HR, CO, SV, EDV, ESVand EF were averaged over 5-10 suc-cessive thermodilution curves. Car-diac index, stroke index, and end-diastolic and end-systolic rightventricular volume indices (CI, SI,EDVI, and ESVI, respectively) weredetermined by dividing CO, SV, EDVand ESV, respectively, by bodyweight.From the mean values of ESV,

EDV, RVPPD' RVPED' PAPD andRVPPS obtained in each group, theright ventricular function curve, i.e.the right ventricular pressure-volumeloop, was constructed for conven-tional and double-muscled calves.

The RVPPS/ESV and the (RVPED -

RVPPD/EDV - ESV) ratio were cal-culated from the respective meanpressures and volumes data issuedfrom each set of measurement.

STATISTICAL ANALYSIS

In order to examine the effect ofbreed on right ventricular functionalvariables, a random linear model wasfitted to the data (12) and analysedusing a computer program (SASSoftware, SAS Institute Inc., Cary,North Carolina, USA). The linearnested model took the general form:

Y = ,u + Bi + aii + b. (Xijk - X)+ eijkl

whereY = right ventricular functional vari-

able;= overall mean;

Bi = fixed effect of the I'h breed;a = random effect of the jth individual

of the Ith breed;b = linear regression coefficient for

each right ventricular functionalvariable on heart rate (X); and

eijkl= residual errorIn a second step, the same analysis

was made within each breed and theleast square means were calculated.

RESULTS

The global cardiac performance,whether expressed as CO, CI, SV, SI,RVWI or LVWI, was significantlylower (P < 0.001) in double-muscledthan in conventional calves (Table I).Heart rate was similar in the conven-tional and the double-muscled calves.The EDV and ESV were not signifi-cantly different between the 2 groups,but their indices (EDVI and ESVI)were significantly lower (P < 0.001and 0.05, respectively) in double-muscled than in conventional calves.Vascular pressures were similarbetween the 2 groups, except SAP andRVPPS, which were significantlyhigher (P < 0.05 and 0.001, respec-tively) in the conventional than in thedouble-muscled calves. The PVRI andSVRI were significantly higher (P <

0.001) in the double-muscled calves.The EF was significantly lower (P <

0.001) in double-muscled than in con-ventional calves.

137

LS C calves

101.2 ± 1.432.8 ± 0.4

*** 313.3 ± 4.2696.0± 14.1382.7 ± 11.8

*** 156.3 + 2.21.49 ± 0.023.30 ± 0.07

* 1.82± 0.0624.4 ± 1.015.3± 1.011.5 ± 1.0-0.9 ± 1.0

* 114.1 ± 1.34.5± 0.37.8 ± 0.3

38.6 ± 0.86.37 ± 0.5458.1 ± 1.148.7± 1.3

*** 244.0 ± 5.445.8 ± 0.7

** 0.105± 0.0040.007 ± 0.0015

DM calves

104.4± 1.328.6 ± 0.3

272.5 ± 3.2662.5 ± 10.5389.9 ± 8.8120.5 ± 1.61.15 ± 0.022.81 ± 0.051.66 ± 0.0426.2 ± 0.717.5 ± 0.811.3± 0.7- 1.3 ± 0.5110.6± 0.9

4.8 ± 0.27.8 ± 0.2

34.5 ± 0.69.08 ± 0.3875.1 ± 0.839.0 ± 0.9180.0 ± 3.741.6 ± 0.5

0.090 ± 0.0030.006 ± 0.002

R2

0.350.650).710.490.470.870.870.700.550.490.600.440.620.640.450.630.740.530.870.780.830.650.500.52

***: P < 0.001; **: P < 0.01; *: P < 0.05; R' = determination coefficient of the mathematicalmodel; HR = heart rate; CO = cardiac output; SV = stroke volume; EDV and ESV = right ventricu-lar end-diastolic and end-systolic volume, respectively; CI and SI = cardiac and stroke index,respectively; EDVI and ESVI = right ventricular end-diastolic and end-systolic index, respectively;PAP,, PAPD, PW, CVP, and SAP,N = mean and diastolic pulmonary arterial, pulmonary capillarywedge, central venous and mean systemic arterial pressure, respectively; RVPPD, RVPED and RVPps= right ventricular proto-diastolic, end-diastolic and peak-systolic pressure, respectively; PVRI andSVRI = pulmonary and systemic vascular resistance index, respectively; RVWI and LVWI = rightand left ventricular work index, respectively; EF = right ventricular ejection fraction

The dP/dtmax was significantlylower (P < 0.001) in the double-muscled group, whilst dP/dtmjn was

not significantly different in the2 groups (Fig. 1).The mean right ventricular pres-

sure-volume loops obtained in eachgroup are shown in Fig. 2. The dias-tolic part of the loops were closelysimilar between the 2 groups, as illus-trated by the similar (RVPED -

RVPPD/EDV - ESV) ratio (Table I).On the contrary, the mean loopobtained in each group showedmarked differences in systole, as

illustrated by the significantly higher(P < 0.01) RVPPS/ESV ratio of theconventional calves (Table I).

DISCUSSION

In the evaluation of the factorsinfluencing cardiac performance inthe intact ventricle, contractile stateof the myocardium is the most diffi-cult and controversial, remaining an

important problem in clinical practice

and physiological investigation(13-16). There are an impressivenumber of indices for estimatingmyocardial contractility, though thevalidity of these is disputed (17,18).The indices derived from isovolumicpressure tracings are useful in detect-ing directional changes in myocardialinotropic state in response to acuteinterventions, but they are of little or

no help in assessing the absolute levelof myocardial contractility in a givensubject, because of the great overlapbetween values in normal individualsand those in subjects with obviouslyimpaired cardiac function (18).Ejection phase indices, such as EF forinstance, are of limited use in detect-ing changes in contractility, butappear to offer a preferable mode fordefining the basal level of inotropicstate ( 15,1 8,19). In fact, in the assess-

ment of myocardial contractility forthe purpose of comparing one subject(or one group of subjects) to another,the problem has always been the limi-tations imposed by dependence ofmost contractility indices on loading

conditions (19). On the contrary, theslope of the regression line connect-ing end-systolic pressure-volumecoordinates issued from multiplepressure-volume loops over a physio-logic range of loading conditions,referred to as maximum elastance ofthe ventricle (Ees) by Suga andSagawa (20,2 1), is an index which hasbeen shown to correlate well withmeasures of basal myocardial contrac-tility and to be sensitive to inotropicmodulation of the right (22-24) or left(25-30) ventricle, while being rela-tively independant of loading condi-tions and heart rate within physiologi-cal limits. Moreover, Ees has beenshown to be more sensitive than ejec-tion phase indices in detecting subtlechanges in myocardial function inpatients with cardiac diseases (27,28,31). Therefore, application of an esti-mate of this index was very appropri-ate to the present study, in order tocompare the basal myocardial con-tractile states of two groups ofanimals.However, certain limitations of the

present study need to be emphasized. Infact, we did not measure the true Ees asoriginally described, i.e. evaluating theventricular pressure-volume relation-ship at end-systole, and the slope beingconstructed from several pointsobtained under different loading condi-tions (20,21,32,33). Instead, we usedthe RVPPS/ESV ratio, which is anapproximate, but reasonable, estimateof this index (27,32,34,35). Therefore,the technique of Ees measurement wassimplified in four major ways.

First, the right ventricular peak-sys-tolic pressure was used instead ofend-systolic pressure. Such simplifi-cation is done to obviate the problemof determining the exact moment ofend-systole. Several authors demon-strated that the use of peak-systolicrather than end-systolic ventricularpressure gives equally good results inEes measurement (26-28,34-36),except if a large difference is evidentbetween the peak- and end-systolicventricular pressures, as for instancein cases of aortic regurgitation(32,37).Second, Ees was not calculated

from the slope of the regression lineconnecting end-systolic pressure-vol-ume coordinates from multiple pres-sure-volume loops over different

138

TABLE I. Least square mean, standard error and level of significance (LS) of breed effect onright ventricular functional parameters in 6 conventional (C, n = 41) and 6 double-muscled(DM, n = 55) calves

Parameters

HR (min l)CO (L minSV (mL)EDV (mL)ESV (mL)CI (mL min '-kgSI (mL.kg l)EDVI(mL.kg l)ESVI (mL kg I)PAPM, (mmHg)PAP,) (mmHg)PW (mmHg)CVP (mmHg)SAP,1 (mmHg)RVPp,) (mmHg)RVP, , (mmHg)RVPpS (mmHg)PVRI (dynes s.cm 5.kg '.10 3)SVRI (dynes.s.cm i.kgl.10)RVWI (Kgm-min kg 10')LVWI (Kgm-min '-kg 10')EF (%)RVPpS/ESV (mmHg-mL )RVPE)-RVPpI)/ESV-ESV (mmHg-mL-)

1000 measured data is therefore no longeran end-systolic ventricular elastance(37). In our study, to minimiize theerrors inherent to this technical limit.

800 richt ventricular pressures and PAPwere measured maniually fromn theaverage of the 10 car-diac cyclesdirectly preceeding the series of ther-_modilution curves records.

Finally, original works on Ees mea-surement validation have used ani-

400 -mals with surgical bilateral vagotomy(38,39) and/or pharmacological syrn-pathectomry (28.30,38,39) and cardiac

200 _ _ pacing (28) in order to avoid reflex200 -

chanies in autonomic tone. Thecalves used in the present study were

_not premedicated or paced. Therefore,0- chances in basal autonomic tone

Max dP/dt Min dP/dt mi;ht have induced variations in theComparison of the least square mean +SE values of Nlax and Mmin dP/dt in 6 conven- ventricular pressure/volume relation-( n = 41) and 6 double-muscled (*, ni = 55) calves. * = significantly different from ip However the problem of reflexobtained in C calves, P< 0.001). chances in autonomic tone has been

shown to be mostly important duringmaneuvers aimed to alter ventricularloading conditions (32), maneuvers\which were not performed in the pre-sent study. Moreover, during data col-lection in our study. maximal carewas taken in order to reduce the ani-/mals mental str-ess (39), and thusvariations in their autonoimiic tone.

Despite all the simplifications here-above mentioned, the right ventricularfunction curve obtained from double-muscled calves, as compared with

l /./ ! | those obtained from conventionalcalves, appeared to indicate reducedimyocardial contractile properties in

// j ___~ the former calves. This conclusionmight be in agreement with a previousstudy which demonstrated thatechocardiographic left ventricular

0 100 200 300 400 500 600 700 indices were lower in double-muscledthan in conventional calves (6). Even

Right ventricular volume (mL) if isovolumic and ejection phaseRight ventricular mean pressure-volume loop in 6 conventional (Zs solid lines, n = 41) indices are insufficiently sensitive forlouble-muscled (U, dotted lines, n = 55) calves.

assessment of the absolute level ofmyocardial contractile state, due to

ig conditions. Only an approxi- dysfunction (26.27,31,34) and to cor- their dependence on loading condi-n of Ees was made, by using the relate satisfactorily with the true tions (16.18,19,40). the significantly,/ESV ratio; i.e. by using the simultaneously measured Ees (35). lower EF and dP/dt, ,;,\ measured inof the line extrapolated from a Third, pressure and volume mea- double-muscled calves as comparedend-systolic pressure-volume surements were not simultaneous with conventional calves was, in the

to zero. Such a ratio does not because ESV measurement by the present study. an additional indicationrepreseint Ees. However, even if thermodilution technique was depen- that myocardial basal contractilityccurate, a single-point pressur-e- dent upon indirect derivation from might be reduced in the former calves..e ratio has been found to reason- sequential thermodilution plateaus. For technical reasons, the present*pproximate Ees and to be clini- When pressure and volume data are study was performed on the rightuseful in segreglating normal measured at two instants of time, the ventricle. However, because the

Its from patients with ventricular pressure/volume ratio calculated from reduced cardiac performance found in

139

t)bx

Fig. 1.tional (values

40

w::EE

1-

._

Fig. 2.and 6 d

loadi i

in atio0RVPPpslopesinglepointtruly Xless a(

volumably a

callypatien

I

the double-muscled calves wasinduced by genetic selection, the con-tractile state of the left ventriclemight also be reduced in these calves.The findings of lower echocardio-graphic left ventricular contractilityindices in double-muscled than inconventional calves (6) further sup-port this hypothesis.On the other hand, when expressed

per kg body weight, right ventricularvolumes in the double-muscled calvesappeared to be significantly lowerthan in conventional calves. Thislower cardiac volume per kg bodyweight might partly explain thereduced CI and SI obtained in double-muscled cattle.The right ventricular pressure-vol-

ume loops obtained from conven-tional and double-muscled calvesdemonstrated that diastolic propertiesof the heart did not differ betweengroups. This was illustrated by thediastolic part of the loops, which wereclosely similar in the 2 groups, and bythe (RVPED - RVPPD/EDV - ESV)ratio, which was not statistically dif-ferent between the 2 groups. Thisfinding was further supported by thecomparable dP/dtmin values obtainedin the 2 groups; this parameter beingconsidered as an indicator of the dias-tolic relaxation properties of the myo-cardium (41). Thus, right ventricularcompliance and preload appeared tobe similar in double-muscled and con-ventional calves and did not, there-fore, seem to account for the reducedventricular performance of double-muscled cattle. This was in agreementwith a previous study based on pres-sures and flow data (5), in which itwas concluded that the reduced strokevolume in double-muscled calves wasnot due to a reduced ventricularpreload.

In conclusion, ventricular volumeper kg body weight and myocardialcontractile state appear to be lower indouble-muscled than in conventionalcattle. This may be partly responsiblefor the reduced global cardiac perfor-mance of double-muscled cattle. Thegenetic selection of the double-muscled conformation appears thus togenerate animals in which the cardiacpump exhibits a reduced volumetriccapacity and a reduced strength ofcontraction.

140

ACKNOWLEDGMENTS

The authors gratefully acknowledgethe secretarial assistance ofM. Leblond. Thanks are also due to C.Bots, D. Delhaise, J.-C. Leroy,M. Motkin and I. Sbai for their techni-cal help and to S. Nelson for theEnglish revision of the manuscript.

REFERENCES

1. HOLMES JHG, ASHMORE CR,ROBINSON DW. Effects of stress on cat-tle with hereditary muscular hypertrophy.J Anim Sci 1973; 36: 684-694.

2. GUSTIN P, DHEM AR, LOMBA F,LEKEUX P. Cardio-pulmonary functionvalues in double-muscled cattle duringmuscular exercise. Vet Res Commun 1988;12: 407-416.

3. GUSTIN P, BAKIMA M, ART T,LEKEUX P, LOMBA F, VAN DEWOESTIJNE KP. Pulmonary functionvalues and growth in Belgian White andBlue double-muscled cattle. Res Vet Sci1988; 45: 405-410.

4. ANSAY M, HANSET R. Anatomical,physiological and biochemical differencesbetween conventional and double-muscledcattle in the Belgian Blue and White breed.Livest Prod Sci 1979; 6: 5-13.

5. AMORY H, DESMECHT DJM,LINDEN AS, McENTEE K, ROLLINFA, BEDUIN JML, GENICOT BC,D'ORIO V, LEKEUX P. Comparison ofcardiac function in double-muscled calvesand in calves with conventional muscularconformation. Am J Vet Res 1994; 55:56 1-566.

6. AMORY H, KAFIDI N, LEKEUX P.Echocardiographic evaluation of cardiacmorphological and functional variables.Am J Vet Res 1992; 53: 1540-1547.

7. SELDINGER SI. Catheter replacement ofthe needle in percutaneous arteriography.Acta Radiol 1953; 39: 368-376.

8. AMORY H, LINDEN A, DESMECHTD, ROLLIN F, GENICOT B, LEKEUXP. Validation of the thermodilution tech-nique for the estimation of the cardiac out-put in the unsedated calves. J Vet MedA 1991; 38: 409-417.

9. AMORY H, McENTEE K, LINDEN A,DESMECHT D, LEKEUX P. Measure-ment of right ventricular ejection fractionand volume by the thermodilution tech-nique in the unsedated calf. Res Vet Sci1994; 56: 75-81.

10. DAROVIC GO. Hemodynamic Monitor-ing. Invasive and Noninvasive ClinicalApplication, Kay, D. (Ed.), Saunders W.B.Company, Philadelphia, 1987.

11. YANG SS, BENTIVOGLIO LG,MARANHAO V, GOLDBERG H. Car-diac chamber volume and left ventricularmass. In: From Cardiac CatheterizationData to Hemodynamic Parameters, FA.Davis Company (Ed.), Philadelphia, 1988:73-113.

12. SEARLE SR. In: Linear models. New York:Wiley and Sons, 1971.

13. MASON DT, SPANN JF Jr, ZELIS R.Quantification of the contractile state ofthe human heart. Maximal velocity of con-tractile element shortening determined byinstantaneous relation between the rate ofpressure rise and pressure in the left ventri-cle during isovolumic systole. AmJ Cardiol 1970; 26: 248-257.

14. PATTERSON RE, KENT BB, PEIRCEEC. A comparison of empiric contractileindices in intact dogs. Cardiology 1972;57: 277-294.

15. ROSS J, PETERSON KL Jr. On theassessment of cardiac inotropic state.Circulation 1973; 47: 435-438.

16. PETERSON KL, SKLOVEN D,LUDBROOK P, UTHER JB, ROSS J Jr.Comparison of isovolumic and ejectionphases indices of myocardial performancein man. Circulation 1974; 49: 1088-110 1.

17. VAN DEN BOS GC, ELZINGA G,WESTERHOF N, NOBLE MIM. Prob-lems in the use of indices of myocardialcontractility. Cardiovasc Res 1973; 7:834-848.

18. KNOWLEN GG, OLIVIER NB,KITTLESON MD. Cardiac contractility:a review. J Vet Int Med 1987; 1: 188-198.

19. BRAUNWALD E, ROSS J. Control ofcardiac performance. In: AmericanPhysiological Society (ed.) Handbook ofPhysiology, Section 2, Circulation, Vol 1.Bethesda: Williams & Wilkins, 1979:533-580.

20. SUGA H, SAGAWA K, SHOUKAS AA.Load independence of the instantaneouspressure-volume ratio of the canine leftventricle and effects of epinephrine andheart rate on the ratio. Circ Res 1973; 32:3 14-322.

21. SUGA H, SAGAWA K. Instantaneouspressure-volume relationships and theirratio in the excised supported canine leftventricle. Circ Res 1974; 35: 117-126.

22. PIENE H, SUND T. Performance of theright ventricle: a pressure plane analysis.Cardiovasc Res 1980; 14: 217-222.

23. BRENT BN, MALHER D, BERGER HJ,MATTHAY RA, PYTLIK L, ZARETBL. Augmentation of right ventricular per-formance in chronic obstructive pulmonarydisease by terbutaline: a combined radio-nuclide and hemodynamic study. AmJ Cardiol 1982; 50: 3 13-319.

24. KONSTANN MA, IDOINE J, WYNNEJ, GROSSMAN W, COHN L, BECK JR,KOZLOWSKI J, HOLMAN BL. Rightventricular function in adults with pul-monary hypertension with and withoutatrial septal defect. Am J Cardiol 1983; 51:1144-1148.

25. GROSSMAN W, BRAUNWALD E,MANN T, MCLAURIN LP, GREENLH. Contractile state of the left ventriclein man as evaluated from end-systolicpressure-volume relations. Circulation1977; 56: 845-852.

26. MARSH JD, GREEN LH, WYNNE I,COHN PF, GROSSMAN W. Left ventric-ular end-systolic pressure-dimension andstress-length relation in normal human sub-jects. AmJCardiol 1979; 44: 1311-1317.

27. NIVATPUMIN T, KATZ S, SCHEUERJ. Peak left ventricular systolic pressure/end-systolic volume ratio: a sensitivedetector of left ventricular disease. AmJ Cardiol 1979; 43: 969-974.

28. MEHMEL HC, STOCKINS B,RUFFMAN K, OLSHAUSEN KV,SCHULER G, KUBLER W. The linearityof the end-systolic-pressure-volume rela-tion in man and its sensitivity for theassessment of left ventricular function.Circulation 1981; 63: 1216-1222.

29. SODUMS MT, BADKE FR, STARLINGMR, LITTLE WC, O'ROURKE RA.Evaluation of left ventricular contractileperformance utilizing end-systolic pres-sure-volume relationships in consciousdog. Circ Res 1984; 54: 731-739.

30. SPRATT JA, TYSON GS, GLOWERDD, DAVIS JW, MUHLBAIER LH,OLSEN CO, RANKIN JS. The end-systolic pressure-volume relationship inconscious dogs. Circulation 1987; 75:1295-1309.

31. CARABELLO BA, NOLAN SP,McGUIRE LB. Assessment of preopera-tive left ventricular function in patientswith mitral regurgitation: value of the end-systolic wall stress-end-systolic volumeratio. Circulation 1981; 64: 1212-1217.

32. CARABELLO BA, SPANN JF. The usesand limitations of end-systolic indexes ofleft ventricular function. Circulation 1984;69: 1058-1064.

33. SHROFF SGF, WEBER KT, JANICKIJS. End-systolic relations: their usefulnessand limitations in assessing left ventricularcontractile state. Int J Cardiol 1984;5: 253-259.

34. SLUTSKY R, KARLINER J, GERBERK, BATTLER A, FROELICHER V,GREGORATOS G, PETERSON K,ASHBURN W. Peak systolic blood pres-sure/end-systolic volume ratio: assessmentat rest and during exercise in normal sub-jects and patients with coronary heart dis-ease. Am J Cardiol 1980; 46: 813-820.

35. McKAY RG, AROESTY JM, HELLERGV, ROYAL HD, WARREN SE,GROSSMAN W. Assessment of the end-systolic pressure-volume relationship inhuman beings with the use of a time-varying elastance model. Circulation 1986;74: 97-104.

36. KONO A, MAUGHAN WL, SUNAGAWAK, HAMILTON K, SAGAWA K,WEISFELDT WL. Use of left ventricularend-ejection pressure and peak pressure inthe estimation of the end-systolic pressure-volume relationship. Circulation 1984; 70:1057-1065.

37. SAGAWA K. The end-systolic pressure-volume relation of the ventricle: definition,modifications and clinical use. Circulation1981;63: 1223-1227.

38. KAAS DA, YAMAZAKI T, BURKHOFFD, MAUGHAN WL, SAGAWA K.Determination of left ventricular end-systolic pressure-volume relationships bythe conductance (volume) catheter tech-nique. Circulation 1986; 73: 586-595.

39. AMORY H, LINDEN A, DESMECHTD, ROLLIN F, McENTEE K, LEKEUXP. Technical and methodological require-ments for reliable haemodynamic measure-ments in the unsedated calf. Vet ResCommun 1992; 16: 391-401.

39. BAAN J, VAN DER VELDE ET. Sen-sitivity of left end-systolic pressure-volume relation to type of loading inter-vention in dogs. Circ Res 1988; 62:1247-1258.

40. MAHLER F, ROSS J Jr, O'ROURKERA, COVELL JW. Effects of changes inpreload, afterload and inotropic state onejection and isovolumic phase measures ofcontractility in the conscious dog. AmJ Cardiol 1975; 35: 626-634.

41. GAASCH WH, BLAUSTEIN AS,ANDRIAS CW. Myocardial relaxation. II.Hemodynamic determinants of rate of leftventricular isovolumic pressure decline.Am J Physiol 1980; 239: HI-H6.

141