ventricular to isometric and isotonic exercise1 ... · isotonic exercise, at one-minute intervals...

British Heart Jtournal, 1979, 42, 521-527

Ventricular response to isometric and isotonic exercise1Echocardiographic assessment

WALTER J. PAULSEN, DEREK R. BOUGHNER, ARTHUR FRIESEN,AND JOAN A. PERSAUD

From the Cardiac Investigation Unit, Department of Medicine, University Hospital, and the Departmentof Biophysics, University of Western Ontario, London, Ontario, Canada

SUMMARY The effects of supine isometric handgrip and graded isotonic bicycle ergometer exercise on

left ventricular performance were studied echocardiographically in 20 normal subjects, aged 18 to 36.Measurements of the left ventricular minor axis diameter were taken from recordings performed at rest,during each form of exercise, and during recovery. At the completion of isometric exercise, the pressure-rate product increased significantly. There was no significant change in percentage offractional shorten-ing (%AD), while there was a small but significant fall in peak velocity ofcircumferentiral fibre shortening(peak Vcf).

Isotonic exercise resulted in a significant increase in %AD and peak Vcf. The pressure-rate productalso increased and showed a positive correlation with peak Vcf.

Isotonic exercise produced a much greater stimulus to left ventricular contractility than isometricexercise and may be a useful means of detecting latent left ventricular dysfunction echocardiographically.

The echocardiogram can provide a useful assess-ment of left ventricular performance in patientswith disease processes that affect the ventricle ina uniform fashion. This technique measures strokevolume, ejection fraction (Pombo et al., 1971;Fortuin et al., 1972), percentage of fractionalshortening (McDonald et al., 1972; Stack et al.,1976), mean velocity of circumferential fibreshortening (Paraskos et al., 1971; Cooper et al.,1972; Fortuin et al., 1972), and peak velocity ofcircumferential fibre shortening (Paraskos et al.,1971; Gibson and Brown, 1973; Quinones et al.,1975; Boughner et al., 1976). These measurementsreadily detect severe left ventricular dysfunction butmild dysfunction may produce few measurablechanges at rest. We undertook this study to deter-mine the potential value of incorporating exerciseas a part of the echocardiographic evaluation. Twoforms of exercise stress testing lend themselves toechocardiographic assessment: (a) supine isometrichandgrip exercise (Stefadourous et al., 1974a) and(b) supine isotonic bicycle ergometer exercise(Stein et al., 1978).

'Supported by a grant from the Ontario Heart Foundation,Drs Boughner and Paulsen are Ontario Heart FoundationResearch Fellows.

Received for publication 12 March 1979

Subjects and method

The study population consisted of 20 healthyvolunteers (age 18 to 36; eight women, 12 men).All were considered to be normal on the basis ofhistory, physical examination, and 12 lead electro-cardiogram. None of the subjects was taking anymedications.

ECHOCARDIOGRAPHYThe echocardiograms were obtained using aUnirad, Series C echocardiograph unit equippedwith a Honeywell 1858 strip chart recorder.Patients were studied in the slight left lateralposition with the transducer positioned in thefourth or fifth left intercostal space. The leftventricular minor axis diameter was recorded bydirecting the ultrasound beam just inferior to themitral valve and recordings were made at a paperspeed of 100 mm/s. Care was taken to avoid altera-tions in transducer position during the study, thusavoiding spurious changes of left ventriculardimensions. Subjects were also instructed to avoidperforming the Valsalva manoeuvre and werecarefully observed for this.

ISOMETRIC EXERCISE PROCEDUREIsometric handgrip exercise was performed using

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Walter J. Paulsen, Derek R. Boughner, Arthur Friesen, and Joan A. Persaud

a Stoelting dynamometer. Brachial blood pressurewas measured using a Cardy-8 sphygmomanometer.

Supine resting measurements of blood pressureand heart rate were obtained and the resting leftventricular echocardiogram was recorded. Eachsubject was then asked to perform three minutesof supine isometric exercise at 30 per cent of theindividual's predetermined peak grip strength.Simultaneous recordings of the left ventriculardimensions (approximately 10 seconds in duration),blood pressure, and heart rate were made at one-minute intervals during exercise. After handgripexercise, similar recordings were made at one-minute intervals for two minutes during which timefull recovery occurred.

ISOTONIC EXERCISE PROCEDUREAfter an additional five minutes of rest, a further setof resting recordings were made. Isotonic exercisewas then performpd using a Siemens-Elema bicycleergometer system mounted vertically at the foot ofthe bed. Each subject was asked to perform sixminutes of supine bicycle ergometer exercise atloads of 25, 50, 75, 100, 125, and 150 watts, theload being increased at one-minute intervals.Recordings of the left ventricular dimensions,blood pressure, and heart rate were made at one-minute intervals during exercise and at two, four,and eight minutes after exercise, during which timecomplete recovery occurred.Although total cardiocirculatory adaptation to

any magnitude of exertion does not occur for twoto three minutes (Astrand and Rodahl, 1977), it wastechnically difficult to obtain adequate quality leftventricular echocardiograms throughout a gradedexercise procedure using three-minute stages. Sincethe cardiovascular adjustments to a submaximalworkload reach a nearly steady state within thefirst minute of isotonic exercise (Donald et al.,1955; Jones and Reeves, 1968; Van Citters andFranklin, 1969; Xenakis et al., 1975), we electedto increase the workload at one-minute intervalsduring the bicycle exercise.

MEASUREMENTS AND CALCULATIONSAnalysis of the instantaneous left ventricular dimen-sion and calculation of its peak rate of change wasperformed using a Hewlett-Packard Model 1838desk top computer, a model 986A digitiser, andx-y plotter combination by a method modified fromthat of Gibson and Brown (1973). The recordingsof the left ventricular echograms were placed on adigitising table and the endocardial echoes of theseptum and posterior wall were digitised beginningat the onset of the R wave and ending with the Twave. The computer noted the position of these

two echoes and automatically derived the instan-taneous left ventricular diameter. It normalisedthis diameter measurement by dividing by theinitial diameter, and this ratio was then displayedby the x-y plotter as a 'displacement ratio' versustime (Fig. 1). Peak Vcf was obtained manually bycalculating the slope of the tangent to the midportion of this curve, thus providing the normalisedpeak Vcf in circumferences per second. We decidedto calculate peak Vcf in this fashion rather thanhaving the computer calculate the instantaneousfirst derivative of the left ventricular diametercurve as described by other investigators (Gibsonand Brown, 1973; Decoodt et al., 1976) because wefound that the normalised instantaneous diametercurve or 'displacement ratio' contained sufficientnoise (produced by 'hand-shake' when tracing theecho) to make such a computer estimate of peakVcf poorly reproducible. Such irregularities couldbe easily compensated for by the manual methodresulting in a high degree of reproducibility for thepeak Vcf estimate. The computer also calculatedautomatically the percentage of fractional shorten-ing:

EDD - ESD x 100 (McDonald et al., 1972).EDD

The pressure-rate product was obtained by multi-plying the systolic blood pressure (mmHg) by theheart rate (beats/min).

0.Z

SC

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500Time (ims)

Fig. 1 Computer plot of the displacement ratio versustime curves corresponding to the ventricular echogramsof a normal subject (see Fig. 2) at rest, during threeminutes of isometric exercise, and during six minutes ofisotonic exercise. The slope of the mid portion of eachcurve provided the respective normalised peak Vcf incirc/s (displacement ratio = instantaneous left ventriculardiameter divided by end-diastolic diameter).

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Isometric and isotonic exercise

All measurements were taken from recordingstaken at rest (Fig. 2a), at one-minute intervalsduring isometric exercise (Fig. 2b), and during atwo-minute recovery period. They were also madefrom recordings taken just before the initiation ofisotonic exercise, at one-minute intervals duringisotonic exercise (Fig. 2c), and at two, four, andeight minutes after exercise.Measurements of four beats at each of these time

intervals were carried out to establish the degreeof beat-to-beat and interobserver variation in theventricular function indices. These were performedfor 48 sets of beats in four randomly selectedpatients. We found the coefficients of variation forpercentage of fractional shortening to be 8 per centand for peak Vcf to be 3 per cent. This indicatedgood reproducibility since the coefficient of varia-tion was well below the 12 per cent level (England,1975). It was not possible to obtain and measurethis ideal number of cardiac cycles from the eightto 10 second long tracings at each time interval inall 20 subjects. Therefore we selected a singlecardiac cycle at each time interval in which theendocardial surfaces of the septum and the posteriorleft ventricular wall just inferior to the valve wereclearly seen as continuous echoes throughoutsystole and diastole. In order to avoid the smallchanges of left ventricular dimensions with res-piration during isotonic exercise, measurements

were made only during expiration when the endo-cardial surfaces were clearly seen. During inspira-tion, those endocardial surfaces were often in-distinct.

Statistical analysis was carried out using paireddata comparison and Student's t test. Regressionanalysis was carried out by two variable analyses.

Results

RESTINGNo significant difference was shown between restingleft ventricular function indices before and afterexercise. These are listed in Tables 1 and 2 and allvalues were within normal published ranges(Paraskos et al., 1971; McDonald et al., 1972;Quinones et al., 1975; Boughner et al., 1976).

ISOMETRIC EXERCISEThree minutes of isometric handgrip exerciseresulted in a significant (P < 0 001) increase inblood pressure, heart rate, and the pressure-rateproduct. The systolic blood pressure rose 32(± 15) mmHg (mean + 1 SD) and heart rate 23(±14) beats/min (mean ± 1 SD). No significantchange in percentage of fractional shorteningoccurred. However, the peak Vcf showed a smallbut significant decrease from 1 80 ±0-27 (mean± 1 SD) circumferences/s to 1*61 ±0-22 (mean

a b

Ivs

LVPW-e-

RestHeart rate :59/minBlood pressure 1-Q-mmHg65Vcf ::1-44 c'irc/s

IsometricHecrt rate 75/ minBlood pressure 150 mmHg90

Vc.f = 1-24 circ/s

IsotonicHeart rate: 115/ minBlood pressure L7-0 mmHgVcf = 2 68 circ/s

Fig. 2 Left ventricular echogram of a normal subject, paper speed 100 mm/s (a) at rest, (b) during three minutesof isometric handgrip exercise, and (c) during six minutes of supine bicycle ergometer exercise. Note the minor fallin peak Vcf with isometric exercise and the distinct increase with isotonic exercise. IVS, interventricular septum;LVPW, left ventricular posterior wall; ECG, electrocardiogram; Vcf, peak velocity of circumferential fibreshortening.

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Walter J. Paulsen, Derek R. Boughner, Arthur Friesen, and Joan A. Persaud

Table 1 Echocardiographic variables during isometric exercise (mean ± SD)

Isomeric exercise RecoveryRest 1 mn 2mnt 3 min 4 min 5mtn

p Vcf (circ/s) 180 1-78 1-56 1-61* 1-63 1-81+ 027 ±033 +0-21 ±0-22 ±019 0-35

Percentage of fraction shortening 37 36 34 35 36 38+ 4 ± 6 + 5 + 6 ± 4 ± 6

End-diastolic diameter (mm) 50 50 51 51 51 51± 5 55 :t 5 55 + 5 + 5

Heart rate (beat/min) 58 68 78 79** 57 59+ 8 + 15 +15 +15 ± 9 ± 9

Systolic blood pressure (mmHg) 122 137 148 154** 124 122: 13 ± 16 ± 19 ± 15 + 14 + 12

BP x HR (x 103) 7 0 10-5 12-1 12-4** 7-1 7-1+ 1-1 + 2-5 +30 30 + 13 + 1-4

Note: Significant differences from resting values at completion of exercise are indicated by *P < 0 01 and **P < 0 001.Vcf, velocity of circumferential fibre shortening; HR x BP, systolic pressure-rate product.

Table 2 Echocardiographic variables during supine bicycle ergometer exercise and recovery

Isotonic exercise RecoveryRest 1 min 2 min 3 min 4 min 5 min 6 min 8 min 10 min 14 min

p Vcf (circ/s) 1-78 1-83 2-04 2-13 2-29 2.49 2-89** 1-96 1-73 1-870-21 + 0-27 + 030 + 0-28 + 034 + 0-32 + 0-22 0-22 + 0-28 + 035

Percentage of fraction shortening 36 38 41 43 44 44 46** 42 38 37+ 5 + 5 + 6 6 + 4 + 5 6 + 4 + 4+ 5

End-diastolic diameter (mm) 50 51 51 51 51 51 50 52 52 50+ 5 + 5 + 5 + 5 + 6 + 6 + 6 + 6 + 6 + 6

Heart rate (beats/min) 66 90 99 108 115 123 130** 78 68 69+ 13 + 12+ 11 12 + 14 + 18 + 14 +22 + 14 + 17

Systolic blood pressure (mmHg) 124 138 144 152 161 173 183** 138 121 122+ 12 + 15 + 15 + 17 + 18 + 18 + 17 +13 + 11 15

HR x BP ( x 103) 8-1 12-3 14-3 16-4 18-4 21-2 22-9** 10-5 7-6 8-2+ 1-5 +21 19 +2-4 +2-6 30 30 +39 +2-3 1-3

Note: Significant differences from resting values at completion of exercise are indicated by **P < 0 001.Vcf, velocity of circumferential fibre shortening; HR x BP, systolic pressure-rate product.

± 1 SD) circumferences/s (P <001, Table 1 andFig. 3a).

ISOTONIC EXERCISESix minutes of isotonic exercise resulted in apronounced rise in heart rate and blood pressurewith a significant (P < 0 001) increase in thepressure-rate product to a value nearly twice thatproduced by isometric exercise. The percentage offractional shortening and peak Vcf (Table 2 andFig. 3b) rose significantly (P < 0 001).

Linear regression analysis showed a positivecorrelation between the peak Vcf and the pressure-rate product during isotonic exercise (r=0 71,N=128, P <0.001) with a standard error of theestimate of ±0 34 (Fig. 4). However, no suchcorrelation was demonstrated for these variablesduring isometric exercise (r=0-14).

Discussion

The cardiovascular responses to isometric andisotonic exercise differ in several important ways.Within seconds of initiating isometric handgrip

exercise, the heart rate begins to increase(Freyschuss, 1970; Petro et al., 1970; Nutter et al.,1972) apparently resulting from the withdrawal ofvagal influences on the heart (MacDonald et al.,1966; Nutter et al., 1972). The degree of responseis not related to the bulk of muscle involved in theisometric contraction and the exact mechanism bywhich these changes occur is not fully understood(Lind et al., 1964; Nutter et al., 1972). End-diastolic volume (preload) (Grossman et al., 1973;Stefadourous et al., 1974b) and end-diastolicpressure (Kivowitz et al., 1971; Grossman et al.,1973) do not change. Stroke volume also does notchange significantly (Grossman, 1974). Cardiacoutput increases as a result of the tachycardia and,since the systemic vascular resistance remainsunchanged (Stefadourous et al., 1974b), the arterialpressure increases. An increase in myocardialcontractility has been postulated to maintain strokevolume in the presence of an unchanged preloadand increased afterload (Helfant et al., 1971;Nutter et al., 1972; Grossman et al., 1973;Stefadourous et al., 1974a).

Isotonic exercise also results in an immediate

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Fig. 3 (a) Percentage change in peak Vcf duringisometric exercise and recovery. Note the minor fall inpeak Vcf with exercise (vertical bars denote mean± 1standard deviation). (b) Percentage change in peak Vcfduring isotonic exercise and recovery. Note the distinctincrease in peak Vcf with exercise (vertical bars denotemean± 1 standard deviation).

increase in heart rate (Donald et al., 1955; Xenakiset al., 1975). In the supine position, preload doesnot change (Rushmer, 1959), myocardial contrac-tility increases, and cardiac output rises (Marshalland Shepherd, 1968). Stroke volume in the restingsupine position seems to be at or near the maximallevel reached during heavy work, and exercise inthis position produces little or no increase in strokevolume (Rushmer, 1959). This differs from theerect posture in which the end-diastolic volumeand stroke volume are lower at rest (Rushmer,1976). These lower values are restored to approxi-mately those of the recumbent position with even

the mildest exercise and heavy exertion producesonly modest additional increases (Rushmer, 1976).Our results show the distinct differences between

the cardiac response to isometric and isotonicexercise and illustrate the ease with which theymay be detected echocardiographically. With iso-

4 8 12Pressure -rote

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Fig. 4 The linear correlation between peak Vcf andpressure-rate product during isotonic exercise. Theregression line for the 20 subjects is indicated by thesolid line while the dotted lines indicate one standarderror of the estimate.

metric exercise, we observed no alteration in end-diastolic diameter on the echocardiogram, a findingthat is consistent with previous reports(Stefadourous et al., 1974a). In contrast to thosereports, we recorded a slight fall in the percentagefractional shortening and a small statisticallysignificant fall in the velocity of circumferentialfibre shortening. This would be consistent withprevious observations where Vcf was found to beinversely related to ventricular afterload (Quinoneset al., 1975). However, the failure of peak Vcf tofall much during isometric exercise suggests thatmyocardial contractility increased sufficiently toalmost maintain the resting contraction velocities.

In contrast, supine isotonic exercise produced apronounced increase in the velocity of circumferen-tial fibre shortening, indicating a major augmenta-tion in myocardial contractility. We observed nochange in the end-diastolic diameter, implying thatan alteration in preload did not play a significantpart in this increased contraction velocity (Rushmer,1959; Stein et al., 1978). Percentage fractionalshortening rose significantly as would be expected.

It has been suggested that isometric exercise at25 to 50 per cent of maximum voluntary contractionwhen performed during cardiac catheterisationcan be useful in detecting latent left ventriculardysfunction (Helfant et al., 1971; Kivowitz et al.,

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1971; Grossman et al., 1973; Grossman, 1974). Anabnormal end-diastolic pressure may be producedduring such exercise or, in patients in whom theventricular end-diastolic pressure is already raised,a further increase may be produced. However, our

results indicate that isometric exercise at 30 percent of maximum voluntary contraction is unlikelyto produce a sufficiently dramatic change incontractility to be a useful part of the echocardio-graphic assessment of left ventricular function.Though a severely diseased ventricle might beexpected to show a definite fall in myocardialcontraction velocity under these circumstances, a

ventricle with borderline dysfunction might not.In contrast, isotonic exercise produces a dramatic

stimulus to myocardial contractility and would bea more suitable provocative test for uncoveringlatent left ventricular dysfunction as determinedby echocardiography.

Although we were able to obtain satisfactoryrecordings during isotonic exercise in all of therelatively young individuals studied, it may not bepossible to achieve the same degree of success inolder patients or in those with some degree ofemphysema.

CLINICAL IMPLICATIONSThis study has shown that echocardiographicassessment of left ventricular function in normalsubjects during both supine isometric and isotonicexercise is practical. Whereas isometric exercisehas little measurable effect on left ventricularperformance, isotonic exercise produces a dramaticand easily measurable stimulus to myocardialcontractility and may be a useful means of detectingleft ventricular dysfunction in disease processesthat affect the left ventricle in a uniform fashion.

The authors wish to thank Dr. Brian Findlay forwriting the computer programmes and Dr. WilliamKostuk for his continued interest and assistance.The ultrasound equipment was provided by a grantfrom the Ivey Foundation.

References

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Requests for reprints to Dr Derek R. Boughner,Cardiac Investigation Unit, University Hospital,PO Box 5339, Terminal A, London, Ontario,Canada N6A 5A5.

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