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Cardiovascular Research 1998 37(1):46-57; doi:10.1016/S0008-6363(97)00215-0
© 1998 by European Society of Cardiology
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Copyright © 1998, European Society of Cardiology

Shortening versus isometric contractions in isolated human failing and non-failing left ventricular myocardium: dependency of external work and force on muscle length, heart rate and inotropic stimulation

Ch Holubarscha,*, J Lüdemanna, S Wiessnera, Th Rufa, H Schulte-Baukloha, S Schmidt-Schwedaa, B Pieskea, H Posivalb and H Justa

aUniversity of Freiburg, Internal Medicine, Dept. of Cardiology and Angiology, Hugstetter Strasse 55, Freiburg, 79106, Germany
bDept. of Cardiovascular Surgery and Heart Transplantation, 32545 Bad Oeynhausen, Germany

* Corresponding author. Tel.: +49-761-270-3618; Fax: +49-761-270-3611.

Received 28 November 1996; accepted 28 July 1997


   Abstract
Top
 Abstract
1 Introduction
 2 Methods
 3 Statistics
 4 Results
 5 Discussion
 References
 
Background: For reasons of simplicity, studies on isolated human myocardium have been conducted using exclusively isometric contractions, although positive inotropic interventions may differently influence force development, extent of shortening and myocardial work performance. We investigated human left ventricular failing and non-failing preparations comparing isometric versus isotonic, i.e., shortening contractions. Results: (1) When muscle length is increased from 90% to 100% lmax, peak developed force increases by 36% and 43% (p<0.05) in non-failing and failing human left ventricular myocardium, respectively. Maximum performed work increases similarly in non-failing but decreases in failing myocardium. It can be shown that this discrepancy is due to significantly higher resting tension and does not present an insufficient intrinsic shortening capacity in failing myocardium. (2) When stimulation rate is increased from 0.5 to 2.0 Hz, isometric force increases significantly by 59% in non-failing and decreases by 27% in failing myocardium, whereas maximum performed work increases by 98% and decreases by 46%, respectively. (3) Pharmacological positive inotropic interventions by 7.2 mM calcium (n = 9), 3x10–8 M isoproterenol (n = 7), 3x10–8 M ouabain (n = 5), and 10–5 M EMD 57033 (n = 3) equally increased force development and extent of shortening: When the fractional effect on shortening (y) was correlated to the fractional effect on force (x), the following linear regression equation was obtained: y = 0.91x+0.26 (r = 0.86; p<0.001). Conclusions: The data presented are of clinical and pharmacological importance: (1) The Frank-Starling mechanism is demonstrated to be existent in the failing human myocardium regarding both isometric force developed and maximum work performed. (2) Both force-frequency relations and – to a greater extent – work-frequency relations are reversed in failing human myocardium. (3) Independent of the pharmacological mode of action, positive inotropic compounds increase developed isometric force to the same extent as isotonic shortening and therefore potentiate maximum performed work.

KEYWORDS Frank-Starling mechanism; Force-frequency relation; Positive inotropism; Shortening contraction; Working contraction


   1 Introduction
Top
 Abstract
 1 Introduction
2 Methods
 3 Statistics
 4 Results
 5 Discussion
 References
 
Cardiac performance is known to be regulated by at least three basic mechanisms which may be fundamentally altered in heart failure: (1) The Frank-Starling mechanism indicates that force development and stroke volume increase with sarcomere length or preload increment [1–4]. Although an attenuation or even loss of the length-dependency of contractile performance has been postulated for human left ventricular myocardium [5, 6], we recently reported full preservation of this basic mechanism in end-stage heart-failure [7]. (2) Myocardial force development is heart rate dependent: Peak isometric force development increases with heart rate in normal mammalian myocardium, but decreases in end-stage failing human left ventricular myocardium [8–10]. (3) The cardiac muscle is under the control of the sympathetic nervous system, i.e., catecholamines control contractile force and thereby guarantee the coupling between cardiac performance and peripheral circulation [11]. This control system is blunted in chronic congestive heart failure due to down-regulation of the beta-adrenoceptors [12–14]and increase in Gi-proteins [15, 16].

In some of the above mentioned studies, attempts have been made to simulate physiological conditions in vitro. For example, only if the experimental conditions were made physiological with respect to temperature and stimulation rate, clear differences between failing and non-failing left ventricular myocardium became evident [8–10]. In human cardiac muscle experiments, however, the isometric contraction mode has been used exclusively for reasons of simplicity. Therefore, for the first time, we studied isotonic shortening versus isometric contractions of human cardiac muscle comparing tissues from failing and non-failing left ventricles. These studies are important, because pathophysiological and pharmacological factors, which influence the inotropic state of the myocardium, may alter developed isometric force and extent of shortening differently in a quantitative as well as qualitative fashion. Evidence for such a dissociation comes from experiments in skeletal and cardiac muscle indicating that maximum velocity of shortening and isometric tension development may be influenced in different ways [17–19]. In addition, the duration of activation is different between isometric and isotonic contractions [20], and positive inotropic compounds like catecholamines, ouabain and calcium-sensitizers are known to exert different effects on the duration of contraction and relaxation. Furthermore, many scientists use the extent of shortening in isolated myocytes to study myocardial contractility and how it is influenced by physiological, pharmacological and pathological conditions. However, it is not known how the extent of shortening relates to isometric tension development.

We therefore compared — for the first time — isometric force development with extent of shortening and maximum performed external work of human failing and non-failing left ventricular muscle preparations. To simulate physiological and pharmacological conditions, variations of contractile performance were initiated by alterations in muscle length, stimulation frequency and some pharmacological interventions.

This study demonstrates full preservation of the Frank-Starling mechanism in failing human left ventricular myocardium regarding developed force, extent of shortening and work performance. Furthermore, both inversed force-frequency and work-frequency are found in the failing human myocardium. In addition, independent of the pharmacologic type of stimulation, alterations of peak developed force parallel the extent of shortening under all conditions.


   2 Methods
Top
 Abstract
 1 Introduction
 2 Methods
3 Statistics
 4 Results
 5 Discussion
 References
 
2.1 Source and transportation of myocardial tissue
For the present study we used n = 48 preparations from human left ventricles. All human explanted hearts were received from the Cardiac Transplantation Center, Bad Oeynhausen, Germany. N = 8 preparations were taken from eight donor hearts which could not be used for transplantation for technical reasons. N = 40 preparations were available from forty explanted hearts from patients suffering from end-stage chronic heart failure due to idiopathic dilated cardiomyopathy (New York Heart Association III–IV). Patients were between 17 and 73 years old. Mean left ventricular ejection fraction was 18±6%. All patients were treated with therapeutic levels of digitalis (digoxin or digitoxin), diuretics (furosemide, xipamide, piretanide), and angiotensin-converting enzyme inhibitors (captopril, enalapril, lisinopril). One third of the patients had intravenous low dose dopamine. Immediately after explantation, papillary muscles and parts of the free left ventricular wall were dissected and submerged into Krebs-Ringer solution at room temperature. This solution contained 30 mmol/l BDM (butanedione monoxime) [9]and 10 IU/l insulin. Transportation time during which the solution was constantly bubbled with 95% O2/5% CO2 was about seven hours for all hearts.

2.2 Solutions and instruments
Solutions used in the present study contained (mmol/l): Na+ 152, K+ 3.6, Cl– 135, HCO3– 25, Mg2+ 0.6, H2PO4– 1.3, SO42– 0.6, Ca2+ 2.5, glucose 11.2, insulin 10 IU/l. This solution was constantly bubbled with a gas mixture of 5% CO2 and 95% O2, and pH was 7.4. Solutions that were used for transportation and dissection purposes additionally contained 30 mmol/L 2, 3-butanedione monoxime (BDM; Sigma) [9].

All preparations were performed in a special dissection chamber using a stereo microscope (VMT Olympus). After a slim (see Table 1) strip preparation had been cut from the papillary muscle or the free wall of the left ventricle, the one end of the preparation was attached to a force transducer and the other end to a linear motor system by means of small tweezers (Muscle Research System; Scientific Instruments, Heidelberg, Germany). The muscle preparation was then protected by a cuvette system through which temperature-controlled (37°C) solution was pumped constantly. The force transducer has a resonance frequency of 700 Hz and a sensitivity of at least 1 mg (Muscle Research System; Scientific Instruments, Heidelberg, Germany).


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  		Table 1 Muscle length, cross-sectional area, and peak developed tension in all preparations used

 
The linear motor system is feedback controlled and allows isometric and isotonic experiments: when the given threshold force is reached during an isometric contraction phase, the contraction mode is automatically switched to isotonic conditions (Fig. 1, A and B). After maximum shortening of the muscle is reached, the muscle is stretched to its original length with a choosable velocity (Fig. 1, A and B). Developed force and extent of shortening were recorded and stored on a PC-Computer using the software programme MUDAT-3 (Scientific Instruments, Heidelberg). Using the same programme, maximal external work was calculated from force and extent of shortening (Fig. 1C,Fig. 3). In addition, quick-release experiments were performed. Immediately after the onset of contraction, the muscle was allowed to contract against a pre-defined preload which was equal to the resting tension at 90% lmax (see Fig. 5).


Figure 1
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  		Fig. 1 Typical records of force development (upper panel A) and shortening (middle panel B) obtained in a left ventricular muscle preparation contracting against a variety of afterloads. When multiplying the afterload by the respective extent of shortening, the external work performed by the muscle is obtained for each contraction. Plotting the calculated work as a function of the corresponding afterload the typical bell-shaped work-load relation is obtained (lower panel C). Note that maximum work is performed at medium afterload. Muscle length 5.5 mm, experimental temperature 37°C, stimulation rate 30 per min.

 

Figure 3
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  		Fig. 3 Work-load relationship for normal non-failing myocardium (upper diagram) and end-stage failing myocardium (lower diagram) at different muscle lengths. With increasing muscle length, peak developed force and maximum performed work increase in parallel in normal myocardium (upper diagram: {circ}, 2.5 mm; bullet, 2.6 mm; {blacktriangleup}, 2.7 mm; {blacksquare}, lmax=2.8 mm). In diseased myocardium (DCM, NYHA IV), peak developed force and maximum work increase at lower muscle lengths (lower diagram: {circ}, 4.5 mm; •, 4.6 mm; {blacktriangledown}, 4.7 mm; {blacktriangleup}, 4.8 mm). Between 90% and 100% lmax, peak developed force increases but maximum perform ed work decreaes (lower diagram: {blacktriangleup}, 4.8 mm; {blacksquare}, 5.1 mm; {diamondsuit}, lmax=5.3 mm). Conditions: 37°C experimental temperature, stimulation rate 30 per min.

 

Figure 5
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  		Fig. 5 Length-tension diagram obtained in a failing left ventricular muscle preparation (37°C, stimulation rate 30 per min). Compared to previous experiments, the preload was released during the period of shortening to a level measured at 90% lmax (dashed line). This experiment allows the muscle a greater shortening extent as compared to constant control preload at lmax. Representative experiment out of five.

 
2.3 Alterations of muscle length and stimulation rate
After the muscle had been mounted between the linear motor and the force-transducer, it was prestretched by a preload of about 2.5 mN. Thereafter, BDM was washed out and stimulation started. After steady state conditions had occurred, the muscle preparation was carefully stretched using steps of 0.05 and 0.1 mm five to 10 minutes after each stretch, peak developed force was measured. lmax was defined as the muscle length at which no further increase or even a small decrease of peak developed force was observed.

In order to study muscle length-dependency of developed force and extent of shortening, the muscles were stretched to lmax as described above and allowed to contract isometrically and isotonically against a variety of different afterloads at each muscle length, respectively (Fig. 1Fig. 2).


Figure 2
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  		Fig. 2 Typical length-tension diagrams of human left ventricular muscle preparation obtained from a normal non-failing left ventricle (donor heart, upper diagram) and of an end-stage failing left ventricle (NYHA IV, lower diagram). Shortening contractions were allowed at 90% and 100% lmax. The working capacity at a given preload is given by the triangle representing peak isometric force on the one hand and extent of shortening against preload on the other. Note that peak developed force increases in failing and non-failing myocardium when the muscles are stretched from 90% to 100% lmax. In contrast, extent of shortening increases in non-failing myocardium but decreases in failing myocardium. Please note also the steep resting length-tension relationship in failing as compared to non-failing myocardium.

 
For pooling of the data and statistical purposes, developed isometric tension, extent of shortening and maximum external work were analyzed at muscle lengths 90% and 100% lmax (Fig. 3Fig. 4). Maximum external work was also normalized to 100% measured at muscle length of 90% lmax.


Figure 4
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  		Fig. 4 Changes in peak developed force, extent of shortening and maximum performed work as a function of muscle length. Left diagram: Non-failing left ventricular human myocardium. Right diagram: Failing left ventricular human myocardium. Peak developed force, extent of shortening and maximum performed work have been normalized to control contractions at low muscle length. Whereas peak developed force, extent of shortening and maximum performed work all increase with increasing muscle length in non-failing myocardium (left diagram), extent of shortening and maximum performed work decrease in failing myocardium before the muscle length lmax is reached (right diagram). Conditions: 37°C experimental temperature, stimulation rate 30 per min.

 
In the other type of experiments, heart rate was varied: 0.5, 1.0, 1.5, 2.0 and 2.5 Hz (Fig. 6).


Figure 6
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  		Fig. 6 Changes of peak developed force, extent of shortening, and external work as a function of stimulation rate in non-failing (left diagram) and failing ventricular human myocardium (right diagram). Experimental temperature is 37°C. Changes of force, extent of shortening, and work are expressed as per cent of baseline data, i.e., control contractions at 0.5 Hz stimulation rate. Peak developed force, extent of shortening, and performed work all increase in non-failing, but decrease in failing myocardium up to a stimulation rate of 2.0 Hz. *p<0.05.

 
2.4 Pharmacologic experiments
Cardiac muscle preparations were stimulated by four different interventions: (1) In n = 9 preparations, the extracellular calcium concentration was increased from 2.5 to 7.2 mmol/l. (2) In n = 5 preparations, ouabain (Serva, Heidelberg, Germany) was applied in a concentration of 3x10–8 mol/l. (3) In n = 7 preparations, isoproterenol (Serva, Heidelberg, Germany) was given at 3x10–7 mol/l. (4) In n = 3 preparations, we applied EMD 57033, a new calcium-sensitizer, which was kindly provided by Merck (Darmstadt, Germany).

Muscle dimensions and peak developed force as measured at optimum length lmax are given in Table 1.

2.5 Definition of fractional effect on shortening and force
In order to compare the differential effects of a pharmacological intervention on developed force and on extent of shortening, fractional effect was defined as follows: Fractional effect on force is the quotient of peak developed force after pharmacological intervention divided by peak developed force before pharmacological intervention (control). Fractional effect on shortening is the quotient of the extent of shortening after pharmacological intervention divided by the extent of shortening before pharmacological intervention (control). Fractional effect on shortening can then be plotted as a function of fractional effect on force (Fig. 8).


Figure 8
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  		Fig. 8 Fractional effect on shortening versus fractional effect on force induced by four different inotropic interventions: Calcium 7.2 mM/l (n = 9), isoproterenol 10–8 M/l (n = 7), ouabain 3x10–8 M/l (n = 5), EMD 57033 10–5 M/l (n = 3). The fractional effect on shortening is the quotient of the extent of shortening with compound divided by the extent of shortening without compound. The fractional effect on force is the quotient of force development with compound divided by the force developed without compound. A significant (p<0.001) linear regression correlation was found with a slope of 0.91 and an intercept of 0.26.

 
2.6 Measurements of central segment shortening
Because crush trauma at both ends of the preparations might influence the measurements in terms of central segment shortening by overstretching the weaker damaged end regions [21, 22], five additional experiments were performed: In these experiments, a central segment was marked by means of a waterproof color pencil, and these markers were followed during isometric contractions with the microscope. Amount of central segment shortening was evaluated by means of a micrometer scale within the ocular of the microscope (VMT Olympus). Central segment shortening was measured to be 0.025±0.003 mm in isometric contractions, which is about 0.5% of the muscle length and less than 5% of maximal shortening in isotonic contractions. In contrast, in isotonic contractions with maximal shortening, i.e., when the muscle was allowed to contract against its preload, per cent of shortening of the segment length was not significantly different from the percentage of muscle shortening.


   3 Statistics
Top
 Abstract
 1 Introduction
 2 Methods
 3 Statistics
4 Results
 5 Discussion
 References
 
In the present study, paired and unpaired t-test were used. In addition, linear regression analysis (Fig. 8) was applied [23]. A p-value of <0.05 was used to indicate statistical significance.


   4 Results
Top
 Abstract
 1 Introduction
 2 Methods
 3 Statistics
 4 Results
5 Discussion
 References
 
4.1 Length-dependency of force development, extent of shortening, and external work performance in non-failing and failing human myocardium
Typical examples of length-tension relationships for non-failing and failing myocardium are shown in Fig. 2: Isometric peak developed force gradually increases in both preparations when the muscles are stretched from 90% to 100% lmax. This observation is consistent with a preserved Frank-Starling mechanism which we have described recently [7].

The purpose of the present study was to analyse in which way the extent of shortening and myocardial work is altered with increasing muscle length in non-failing and failing preparations. In the two representative experiments demonstrated in Fig. 2, the extent of muscle shortening is increased in normal non-failing myocardium but reduced in failing myocardium when muscle length is increased from 90% to 100% lmax. As a result, maximum myocardial work increases with muscle length in non-failing myocardium in parallel with the increase in isometric force development (Figs. 3 and 4Go and Table 2); in contrast, maximum myocardial work increases in parallel with increases in peak developed force only at a shorter muscle lengths, but decreases with increases in peak developed force at muscle lengths closer to lmax (Figs. 3 and 4Go and Table 2) in failing myocardium.


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  		Table 2 Peak developed force, resting force, and maximum work performed at muscle length lmax and 90% lmax in nonfailing and failing left ventricular myocardium

 
On the average, maximum myocardial work significantly (p<0.05) increased from 100% at 90% lmax to 136±11% at lmax in non-failing myocardium, but decreased from 100% at 90% lmax to 74±7% at lmax in failing myocardium (Table 2).

It is also important to note that resting tension at 100% lmax is significantly (p<0.05) higher than in non-failing human myocardium (Table 2).

Because several mechanisms may be responsible for the observed differential effect of the muscle length on developed force versus extent of shortening observed in the failing human myocardium (see discussion), five additional experiments were performed. In these experiments, instead of keeping the load of the muscle equal to the preload, the load was reduced to a pre-defined preload which was equal to the resting tension at 90% lmax (Fig. 5). From these experiments in failing myocardium, it is evident that active shortening is greater at 100% lmax than at 90% lmax when correction for high resting tension is allowed.

4.2 Rate-dependence of force development, extent of shortening, and external work performance in non-failing and failing human myocardium
Stimulation rate was altered between 30 and 150 per min using steps of 30 beats/min. In Fig. 6, changes in peak developed force, extent of shortening, and maximum performed external work are plotted as a function of stimulation rate for n = 4 preparations from donor hearts and n = 6 preparations from explanted hearts with dilated cardiomyopathy. For pooling the data and statistical purposes, peak developed force, extent of shortening, and maximum performed work are normalized to control contractions obtained at 30 beats per min. This plot not only allows a direct comparison between failing and non-failing myocardium, but also a comparison between the relative changes of external work, shortening, and force. From Fig. 6 it is evident that first work-frequency relations are positive in non-failing and negative in failing human left ventricular preparations, and second the relative effects of frequency-modulation on maximum work are considerably — by almost a factor of two — greater than those on isometric peak developed force.

4.3 Influences of different positive inotropic interventions on isometric peak developed force and extent of shortening
In this set of experiments, a variety of positive inotropic compounds was used to increase the contractile state of cardiac muscle (Fig. 7). In these experiments, isometric contractions were compared to shortening contractions in which the afterload was kept equal to the preload at optimum length lmax. For each experiment in which a specific intervention was applied, the fractional effect on the extent of shortening was plotted as a function of the fractional effect on peak isometric force. Using this analysis for all experiments and different interventions studied, a linear regression equation was found with a slope of 0.91 and an intercept of 0.26 with a correlation coefficient of r = 0.86 (p<0.001).This slope is not significantly different from unity (Fig. 8). For each specific pharmacological intervention mean data of peak developed force, extent of shortening and maximum performed external work are given in Table 3.


Figure 7
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  		Fig. 7 Representative isometric mechanograms as influenced by four different inotropic interventions in representative examples of muscle preparations obtained from failing human ventricles. Experimental temperature is 37°C and stimulation rate is 30 per min. Peak developed force was increased by high calcium (7.2 mM/l), ouabain (3x10–8 M/l), isoproterenol (3x10–7 M/l), and the calcium-sensitizer EMD 57033 (10–5 M/l). Please note that calcium and ouabain have no or little influence on contraction- and relaxation-time parameters (upper diagrams), whereas isoproterenol (left lower diagram) significantly shortens and EMD 57033 (right lower diagram) significantly prolongs contraction and relaxation times.

 

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  		Table 3 Effects of inotropic interventions on isometric peak developed force (PDF), extent of shortening ({Delta}l), and maximal external work (Wmax)

 

   5 Discussion
Top
 Abstract
 1 Introduction
 2 Methods
 3 Statistics
 4 Results
 5 Discussion
References
 
5.1 Background and purpose of the study
Since orthotopic heart transplantation has become a routine surgical procedure in the United States of America and Europe, human cardiac muscle tissues are available in many laboratories and have been used to study functional, cellular and molecular alterations of myocardium in human heart failure. Many important observations have been made regarding beta-adrenoceptor function [12–16]and excitation-contraction coupling [8–10], although most of the experiments were conducted under non-physiological experimental conditions. For example, the use of low stimulation rates had failed to detect some important features of the failing human myocardium. Serious functional alterations of the human myocardium become only evident, when the whole physiological range of heart rate is investigated [8–10]. For reasons of simplicity, however, in almost all available studies on isolated human myocardium the contraction mode was isometric instead of allowing the muscle to shorten against a variety of different alterloads and to perform external work. Because physiological and pharmacological mechanisms may differently influence isometric force development and isotonic shortening, it was the first purpose of the present study to investigate cardiac muscle of failing and non-failing human left ventricles simulating physiological conditions regarding temperature, heart rate and mode of contraction. In addition to pharmacological interventions, the three important mechanisms known to regulate the contractile state of the myocardium were tested: Muscle length, heart rate, and catecholamines.

5.2 Non-uniformity of muscle preparations
In all types of muscle preparations, stronger myocardium of the central regions may overstretch weaker parts of the muscle due to crush trauma at both ends of a preparation [21, 22]. In order to quantify central segment shortening, markers were placed on the muscle and followed by microscope in special experiments. Central shortening of the isometric muscle was 0.025±0.003 mm in five preparations, which was 0.5% of whole muscle length. Although this internal shortening was quite small, it might partially explain why peak developed force in this study was small compared to animal studies in which sarcomere length was controlled [21, 22]. However, other factors like experimental temperature and species-dependency of force development have to be considered in addition.

Interestingly, during isotonic contraction in which the afterload was set to be equal to preload, the relative shortening of the central segment was equal to whole muscle shortening. Therefore, isometric peak developed force of muscle may have been somewhat underestimated compared to isometric sarcomeric force development, whereas extent of muscle shortening reliably reflects sarcomere shortening.

5.3 Length-dependency of force and external work
We have previously reported that length-dependency of peak developed force is maintained in failing human myocardium in ICM and DCM [7]. Again, in the present study, peak developed isometric force is increased by 43%, when failing muscle preparations are stretched from 90% to 100% lmax. This value is close to 36% obtained in normal myocardium of the present study, and only somewhat lower than we reported in our previous work (50–70%). In contrast, maximum performed work increased between 90% and 100% lmax only in non-failing myocardium, but decreased in failing myocardium (Figs. 2–4GoGo). The findings indicate that the relative location of optimum length for peak developed force coincides with that for maximal work only in non-failing human left ventricular myocardium. In contrast, in endstage failing human left ventricular myocardium, the relative location of optimum length for maximal work is around 90% of the optimum length for isometric peak force development.

Two different hypotheses may explain the dissociation between the relative locations of the optimal muscle lengths for peak developed force and maximal external work: (1) Reduced extent of shortening at optimum length lmax in human failing myocardium may indicate intrinsic failure of the muscle to shorten. (2) At optimum length lmax, there is relevant diastolic tension present in all different types of preparations. This diastolic tension comes into play during the shortening period thereby gradually increasing the load which has to be carried by the sarcomeres.

The following arguments make the first hypothesis unlikely and favour the second one: In additional experiments, quick releases were carried out at optimum length lmax immediately after the onset of contraction. In these experiments the load was clamped to a value which was equivalent to the preload at 90% lmax allowing the muscle to shorten from optimal length lmax but with an internal load identical to a contraction starting at 90% lmax (Fig. 5). Under these conditions, the extent of shortening was always considerably greater than in isotonic control contractions at optimum length lmax. These experiments exclude the possibility that there may be an intrinsic deficit of shortening in failing preparations at greater muscle lengths.

In addition, in the present study we found resting tension to be significantly higher in failing than in non-failing myocardium (Fig. 2 and Table 2). This observation is in good agreement with our previous work [7]and animal studies [24, 25]. At low frequencies, this increased resting tension is shown to be due to an increased collagen content [24–28]. Only at higher stimulation rates, diastolic activation of contractile proteins may come into play because of insufficient calcium pumping capability in failing human myocardium [29, 30]. Therefore, if resting tension is higher in the human failing myocardium at optimum length, the internal load which has to be carried by the sarcomeres is relatively larger and thereby reduces the amount of shortening. A reduced extent of shortening of the failing human myocardium as compared to the non-failing myocardium has already been described by Vahl et al. [31]. However, these authors did not discuss the possibility of an interaction between resting forces and systolic performance.

5.4 Force-frequency and work-frequency relations
Previously, we and others have shown that the relation between isometric force and stimulation rate is reversed in failing human myocardium [8–10, 29, 30, 32–34]. Again, this reversed force-frequency relationship is found in human left ventricular failing myocardium (Fig. 6). However, in the present study, we focused on the question whether alterations in frequency may differently influence the extent of shortening and work performance as compared to isometric force development: Because relative changes in the extent of shortening parallel the relative changes in isometric peak force development (Fig. 6), the relative changes in maximum work performance are potentiated resulting in substantial positive work-frequency relations in non-failing and pronounced negative work-frequency relations in end-stage failing human myocardium (Fig. 6).

As we have shown recently, the inverse force-frequency relationship in failing myocardium is due to a decrease in calcium transients with increasing stimulation rate [34]. This decrease in activation may not only be brought about by a decrease in the sarcoplasmatic reticulum calcium ATPase [30]but also by an upregulation of the sodium-calcium exchanger [35]. Nevertheless, it is evident that such a decrease in activation is responsible for both the reduction in force development and the decrease in shortening when stimulation rates are increased in failing human myocardium.

These data are in agreement with those obtained in ferret ventricular muscle [17]. However, in these animal experiments the effect of stimulation rate on isometric force was 1.5 to 2.0 times larger than on the fractional effect on shortening. In the cited study, experimental temperature was only 30°C as compared to physiological temperature (37°C) in the present study which might easily explain these quantitative differences.

5.5 Positive inotropism and extent of shortening
Beside of muscle length and stimulation frequency, positive inotropic compounds with different modes of pharmacological action may effect force development and shortening capability in different ways for the following reasons:

(1) Contraction and relaxation times are altered quite differently (see Fig. 7). Whereas beta-adrenoceptor stimulators like isoproterenol shorten both the contraction and relaxation phase, and the calcium-sensitizer EMD 57033 has pronounced opposite effects, an increase in the calcium concentration or addition of ouabain exert positive inotropism with no or very little alterations of the isometric time parameters (Fig. 7). Therefore, a longer contraction-relaxation cycle may allow the muscle to shorten to a greater extent as compared to a shorter contraction-relaxation cycle.

(2) A certain positive inotropic intervention may alter intrinsic shortening velocity allowing more or less muscle shortening extent within the same time [36, 37].

(3) With EMD 57033 cross-bridge mechanics may become altered in the sense of a longer attachment time or a greater force production per cycle [38, 39]. No studies are available investigating the question in what way this pharmacological way of positive inotropism has influence on extent of shortening and — thereby — myocardial work performance.

Expecting a broad range of differential influences of the compounds on the extent of shortening, we compared the fractional effect on force and shortening induced by high calcium, ouabain, isoproterenol, and EMD 57033. Interestingly, a highly significant linear regression equation was found when pooling all data obtained under all four different interventions (Fig. 8). As shown in Table 3, percent values for peak developed force and those of extent of shortening are not significantly different. These data indicate that — under all circumstances — the relative change in force development is closely related to the relative change in shortening independent of the pharmacologic type of myocardial stimulation.

The mechanisms of positive inotropic stimulation used in the present study are quite different. High calcium and ouabain lead to a modest increase in calcium transients as shown by aequorin light [40, 41]and heat measurements [42, 43]. Isoproterenol leads to an excessive increase in calcium transients [40, 41]and activation heat [42, 43], but at the same time desensitization of the contractile proteins [44, 45]takes place as well as faster calcium pumping [46]. In contrast, with EMD 57033 no increase in calcium transients could be found [47, 48]indicating a sensitization of the contractile proteins towards calcium. Interestingly, Hgashiyama et al. [49]have compared the effect of EMD 57033 on isovolumic contractions with its effect on ejecting beats. The effect of the compound on developed pressure was greater for ejecting than isovolumic beats. However, these authors did not analyse the effect of EMD 57033 on stroke volume by keeping the developed pressure constant.

In the light of the very different pharmacological mechanisms of the compounds, the parallelism between force increment and increase in extent of shortening is quite astonishing. There must be a fundamental coupling between activation mechanisms, the degree of calcium sensitivity and cross-bridge kinetics.

5.6 Conclusions and clinical implications
Our observations are of pharmacological and clinical relevance. The strong quantitative coupling between force development and shortening capability allows to conclude that positive inotropism observed in experimental isometric contractions implicates improved shortening and increased work performance independent of the specific pharmacological mode of action. Furthermore, the Frank-Starling mechanism is preserved in endstage failing human myocardium both in isometric and isotonic shortening contractions. Because alterations in force parallel the extent of shortening under all physiological and pharmacological conditions (length, stimulation rate, compounds), relative changes in work performance are potentiated as compared to those of isometric force development or extent of shortening.

This work was supported by the Deutsche Forschungsgemeinschaft HO-915/4-2.

Time for primary review 42 days.


   References
Top
 Abstract
 1 Introduction
 2 Methods
 3 Statistics
 4 Results
 5 Discussion
 References
 

  1. Frank O. Zur Dynamik des Herzmuskels. Z Biol (1895) 32:370–447. translation from German.
  2. Chapman C.B., Wasserman E.B. Am Heart J. (1959) 58:282–317.
  3. Starling EH. Linacre lecture on the law of the heart. London: Longmans, 1918.
  4. Sarnoff S.J., Berglund E. Ventricular function. Starling's law of the heart studied by means of simultaneous right and left ventricular function curves in the dog. Circulation (1954) 9:706–718.[Web of Science][Medline]
  5. Böhm M., Beuckelmann K.D.J., Schwinger R.H.G., Erdmann E. Aktuelle pathophysiologische Aspekte der Herzinsuffizienz. Internist (1993) 34:886–901.[Web of Science][Medline]
  6. Schwinger R.H.G., Böhm M., Koch A., Schmidt U., Morano J., Eissner H.-J., Überfuhr R., Reichart B., Erdmann E. The failing human heart is unable to use the Frank-Starling mechanism. Circ Res (1994) 74:959–969.[Abstract/Free Full Text]
  7. Holubarsch Ch., Ruf Th., Goldstein D.J., Ashton R.C., Nickl W., Pieske B., Pioch K., Lüdemann J., Wiesner S., Hasenfuss G., Posival H., Just H., Burkhoff D. Existence of the Frank-Starling mechanism in the failing human heart. Investigations on the organ, tissue and sarcomere level. Circulation (1996) 94:683–689.[Abstract/Free Full Text]
  8. Feldman M.D., Gwathmey J.K., Phillips P., Schoen F., Morgan J.P. Reversal of the force-frequency relationship in working myocardium from patients with end-stage heart failure. J Appl Cardiol (1988) 3:273–283.[Web of Science]
  9. Mulieri L.A., Hasenfuss G., Ittleman F., Leavitt B., Allen P.D., Blanchard E.M., Alpert N.R. Altered myocardium force-frequency relation in human heart failure. Circulation (1992) 85:1743–1750.[Abstract/Free Full Text]
  10. Pieske B., Hasenfuss G., Holubarsch Ch., Schwinger R., Böhm M., Just H. Alterations of the force-frequency relationship in the failing human heart depend on underlying cardiac disease. Basic Res Cardiol (1992) 87(Suppl. 1):213–221.[Web of Science][Medline]
  11. Sarnoff S.J., Brockmann S.K., Gilmore J.P., Linden R.J., Mitchel J.H. Regulation of ventricular contraction. Influence of cardiac sympathetic and vagal nerve stimulation on atrial and ventricular dynamics. Circ Res (1960) 8:1108–1122.[Abstract/Free Full Text]
  12. Bristow M.R., Ginsburg K., Minobe W.A., Cubicciotti R.S., Sageman W.S., Lurie K., Billingham M.E., Harrison D.C., Stinson E.B. Decreased catecholamine sensitivity and β-adrenergic density in failing human hearts. N Engl J Med (1982) 307:205–211.[Abstract]
  13. Bristow M.R., Hersberg R.E., Port J.D., Minobe W., Rasmussen B. β1- and β2-adrenergic receptor-mediated adenylate cyclase stimulation in nonfailing and failing ventricular myocardium. Mol Pharmacol (1988) 35:295–303.[Web of Science]
  14. Brodde O.E. β1- and β2-adrenoceptors in the human heart: Properties, function and alterations in chronic heart failure. Pharmacol Rev (1991) 43:202–242.
  15. Feldmann A.M., Cates A.E., Veazey W.B., Hershberger R.E., Bristow M.R., Banghmann K.L., Baumgartner W.A., VanDop C. Increase of the 40.000-mol wt pertussis toxin substrate (G-protein) in the failing human heart. J Clin Invest (1988) 82:189–197.[Web of Science][Medline]
  16. Neumann J., Schmitz W., Scholz H., von Meyerinck L., Döring V., Kalmar P. Increase in myocardial Gi-proteins in heart failure. Lancet (1988) II:936–937.
  17. Lee A.J., Allen P.D. Comparison of the effect of inotropic interventions on isometric tension and shortening in isolated ferret ventricular muscle. Cardiovasv Res (1989) 23:748–755.[CrossRef]
  18. Cooke R., Pate E. The effect of ATP and phosphate on the contraction of muscle fibers. Biophys J (1985) 48:789–798.[Web of Science][Medline]
  19. Kentish J.L., Stienen G.J.M. Differential effects of length on maximum force production and myofibrillar ATPase activity in rat skinned cardiac muscle. J Physiol (London) (1994) 475:175–185.[Abstract/Free Full Text]
  20. Brutsaert D.L., Meulemans A.L., Sipido K.R., Sys S.U. Effects of damaging the endocardial surface on the mechanical performance of isolated cardiac muscle. Circ Res (1988) 62:358–366.[Abstract/Free Full Text]
  21. de Tombe P.P., ter Keurs H.E.D.J. Force and velocity of sarcomere shortening in trabeculae from rat heart. Effects of temperature. Circ Res (1990) 66:1239–1254.[Abstract/Free Full Text]
  22. de Tombe P.P., ter Keurs H.E.D.J. Sarcomere dynamics in cat cardiac trabeculae. Circ Res (1991) 68:588–596.[Abstract/Free Full Text]
  23. Sachs L. Statistische Methoden 2: Planung und Auswertung. New York, Heidelberg: Springer, 1990:94-101.
  24. Bing O.H.L., Matsushita S., Fanburg B.L., Levine H.J. Mechanical properties of rat cardiac muscle during experimental hypertrophy. Circ Res (1971) 28:23–245.[Abstract/Free Full Text]
  25. Thiedemann K.U., Holubarsch C.H., Medugorac J., Jacob R. Myocardial stiffness and connective tissue in pressure induced cardiac hypertrophy. A combined study of morphologic, morphometric, mechanical and biochemical parameters. Bas Res Cardiol (1983) 78:140–155.[CrossRef][Web of Science][Medline]
  26. Hess O.M., Schneider J., Koch R., Bamert C., Grimm J., Krayenbuehl H.P. Diastolic functional and myocardial structure in patients with myocardial hypertrophy. Special reference to normalized viscoelastic data. Circulation (1981) 63:360–371.[Free Full Text]
  27. Brilla Ch.G., Janicki J.S., Weber K.T. Cardioreparative effects of lisinopril in rats with genetic hypertension and left ventricular hypertrophy. Circulation (1991) 83:1771–1779.[Abstract/Free Full Text]
  28. Weber K.T., Brilla Ch.G. Pathological hypertrophy and cardiac interstitium. Fibrosis and renin-angiotensin-aldosterone system. Circulation (1991) 83:1849–1865.[Abstract/Free Full Text]
  29. Gwathmey J.K., Slawsky M.T., Hajjar R.J., Briggs C.M., Morgan J.P. Role of intracellular calcium handling in force-interval relationships of human ventricular myocardium. J Clin Invest (1990) 85:1599–1613.[Web of Science][Medline]
  30. Hasenfuss G., Reinecke H., Studer R., Meyer M., Pieske B., Holtz J., Holubarsch Ch., Posival H., Just H., Drexler H. Relation between myocardial function and expression of sarcoplasmatic reticulum Ca2+-ATPase in failing and non-failing human myocardium. Circ Res (1994) 75:434–442.[Abstract/Free Full Text]
  31. Vahl C.F., Bonz A., Timel T., Hagl S. Intracellular calcium transients of working human myocardium of seven patients transplanted for congestive heart failure. Circ Res (1994) 74:952–958.[Abstract/Free Full Text]
  32. Feldman M., Alderman J.R., Aroesty J.M., Royal H.D., Fergusen J.J., Owen R.M., Grossman W., McKay R.G. Depression of systolic and diastolic reserve during atrial pacing tachycardia in patients with dilated cardiomyopathy. J Clin Invest (1988) 82:1661–1669.[Web of Science][Medline]
  33. Hasenfuss G., Holubarsch Ch., Hermann H.-P., Astheimer K., Pieske B., Just H. Influence of the force-frequency relationship on hemodynamics and left ventricular function in patients with nonfailing hearts and in patients with dilated cardiomyopathy. Eur Heart J (1994) 15:164–170.[Abstract/Free Full Text]
  34. Pieske B., Kretschmann B., Meyer M., Holubarsch Ch., Weirich J., Posival H., Minami K., Just H., Hasenfuss G. Alterations in intracellular calcium handling associated with the inverse force-frequency relation in human dilated cardiomyopathy. Circulation (1995) 92:1169–1178.[Abstract/Free Full Text]
  35. Studer R., Reinecke H., Bilger J., Eschenhagen T., Böhm M., Hasenfuss G., Just H., Holtz J., Drexler H. Gene expression of the cardiac Na+–Ca2+ exchanger in end-stage human heart muscle. Circ Res (1994) 75:443–453.[Abstract/Free Full Text]
  36. Sonnenblick E.H. Force-velocity relations in mammalian heart muscle. Am J Physiol (1962) 202:931–939.[Abstract/Free Full Text]
  37. Saeki Y., Shiozawa K., Yanagisawa K., Shibata T. Adrenaline increases the rate of cross-bridge cycling in rat cardiac muscle. J Mol Cell Cardiol (1990) 22:453–460.[CrossRef][Web of Science][Medline]
  38. Holubarsch Ch. Drug-induced modulation of cardiac economy. J Muscle Res Cell Motil (1995) 16:445.
  39. Kraft T., Lues I., Brenner B. Effects of EMD 57033 in skinned fibers of rabbit psoas muscle at different levels of calcium-activation. J Muscle Res Cell Motil (1995) 16:454.
  40. Pieske B., Kretschmann B., Burmeister C., Schlotthauer K., Meyer M., Blümke M., Kriste G., Holubarsch Ch., Hasenfuss G. Influence of isoproterenol and endothelin on intracellular Ca2+-transients and isometric force in isolated human ventricular myocardium. Circulation (1993) 88(Suppl.):3065.
  41. Allen D.G., Kurihara S. Calcium transients in mammalian ventricular muscle. Eur Heart J (1980) 1(Suppl. A):5–15.[Free Full Text]
  42. Holubarsch Ch., Hasenfuss G., Just H., Blanchard E.M., Mulieri L.A., Alpert N.R. Modulation of myothermal economy of isometric force generation by positive inotropic interventions in the guinea pig myocardium. Cardioscience (1990) 1:33–41.[Web of Science][Medline]
  43. Holubarsch Ch., Hasenfuss G., Just H., Alpert N.R. Positive inotropism and myocardial energetics: Influence of β-receptor stimulation, phosphodiesterase inhibition and ouabain. Cardiovasc Res (1994) 2:994–1002.
  44. Holroyde M.J., Howe E., Solaro S.J. Modification of calcium requirements for activation of cardiac myofibrillar ATPase by cyclic AMP dependent phosphorylation. Biochim Biophys Acta (1979) 586:63–69.
  45. Hope L., McCellande G., Winegrad S. Calcium sensitivity of the contractile system and phosphorylation of troponin in hypermeable cardiac cells. J Gen Physiol (1980) 75:271–282.[Abstract/Free Full Text]
  46. Sasaki T., Inui M., Kimura Y., Kuzuya T., Tada M. Molecular mechanism of regulation of Ca2+ pump ATPase by phospholamban in cardiac sarcoplasmic reticulum. Effects of synthetic phospholamban peptides in Ca2+ pump ATPase. J Biol Chem (1992) 267:1674–1679.[Abstract/Free Full Text]
  47. White J., Lee J.A., Shah N., Orchard C.H. Differential effects of the optical isomere of EMD 53998 on contraction and cytoplasmatic Ca2+ in isolated ferret cardiac muscle. Circ Res (1993) 73:61–70.[Abstract]
  48. Solaro J., Gambassi G., Warshaw D., Keller M.R., Spurgeon H.A., Beier N., Lakatta E.G. Stereoselective actions of thiadiazinones on canine cardiac myocytes and myofilaments. Circ Res (1993) 73:981–990.[Abstract/Free Full Text]
  49. Hgashiyama A., Watkins M.W., Chen Z., LeWinter M.M. Effects of EMD 57033 on contraction and relaxation in isolated rabbit hearts. Circulation (1995) 92:3094–3104.[Abstract/Free Full Text]

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