Maximum lengthening velocity during isotonic relaxation at preload in canine papillary muscle

Tamiya, Kouichi; Sugawara, M.; Sakurai, Yasuhisa

doi:10.1152/ajpheart.1979.237.1.h83

Cited by 20 publications

(11 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…3,6,7 Previous studies of isolated cardiac muscle preparations 8,9 and of in situ dog hearts 10 have shown that myocardial lengthening rate is determined by end-systolic length and loading conditions. Furthermore, the relationship between load and myocardial lengthening rate was dependent on both the timing and the magnitude of the applied load; ie, elevation of peak systolic load reduced LV lengthening rate, whereas load applied during myocardial relaxation (late load) increased lengthening rate.…”

Section: Clinical Perspective On P 2586mentioning

confidence: 99%

Determinants of Left Ventricular Early-Diastolic Lengthening Velocity

et al. 2009

View full text Add to dashboard Cite

show abstract

Section: Clinical Perspective On P 2586mentioning

confidence: 99%

Determinants of Left Ventricular Early-Diastolic Lengthening Velocity

et al. 2009

View full text Add to dashboard Cite

show abstract

“…When the extent of shortening is altered without changing the minimum length (by changing preload only), there is no change in the rate of isotonic lengthening. Thus, these data suggest that the inverse relation between the extent of shortening and maximum isotonic lengthening rate observed by Tamiya et al 24 and Cailett et al 23 is in fact a result of the inverse relation between total load (or minimum length) and maximum isotonic lengthening rate. We conclude that total load and/or minimum length is a primary determinant of maximum isotonic relaxation rate.…”

mentioning

confidence: 55%

“…Cailett et al 23 in intact dogs and Tamiya et al 24 in isolated blood-perfused canine papillary muscles observed a similar inverse relationship between the extent of shortening and maximum isotonic relaxation rate; they postulated that the extent of shortening is a primary determinant of isotonic lengthening rate. Our data and those of Strobeck et al 19 demonstrate that when preload is held constant, an increase in total load produces a decrease in the extent of shortening that is proportional to the increase in minimum length; this results in a slowed maximum isotonic lengthening rate.…”

mentioning

confidence: 82%

Mechanical determinants of maximum isotonic lengthening rate in rat left ventricular myocardium.

Zile¹,

Gaasch²,

Wiegner³

et al. 1987

Circulation Research

View full text Add to dashboard Cite

The effects of changing loading conditions and inotropic state on maximum isotonic lengthening rate ( +dL/dt, muscle lengths/sec) were examined in isolated rat myocardium. Physiologically sequenced contractions were studied in 18 left ventricular papillary muscle preparations (stimulation rate, 12/min). To study the effects of changing loading conditions, only one loading variable (preload, total load, or late load) was changed during each contraction, while the others were held constant. To study the effects of isoproterenol (10~6 M) and temperature (28 vs. 33° C) on maximum isotonic lengthening rate, preload and late load were held constant and +dL/dt was examined at a common total load. When preload was increased from 0. ), +dL/dt rose from 1.6 ± 0.1 muscle lengths/sec at 28° C to 2.4 ± 0.2 muscle lengths/sec at 33° C and 2.05 ±0.1 muscle lengths/sec with isoproterenol. Thus, the load against which the muscle shortens (and/or the length to which it shortens), the magnitude of the late load, and the time at which the late load is applied are independent determinants of maximum isotonic lengthening rate. Under any constant set of loading conditions, both isoproterenol and increased temperature increase the maximum isotonic lengthening rate. A bnormalities of left ventricular (LV) early dia-/ \ stolic chamber filling appear to be sensitive X \ -indicators of myocardial disease 1 " 7 ; chamber filling rate has also been found to be useful in following the natural history and the response to therapy of pathological processes.8 " 14 To understand the effects of disease or pharmacologic therapy on chamber filling rate, it is important to define the specific mechanical and hemodynamic factors that influence the speed of relaxation and filling in the normal heart. Once the mechanical determinants of ventricular filling rate are defined, the effects of the disease process or the effects of pharmacologic treatment on filling rate can be interpreted within the context of changes in these mechanical determinants. In the intact heart, it is difficult to create isolated changes in mechanical variables such as loading conditions. This is true because most interventions cause concomitant changes in LV volume, LV pressure, left atrial pressure, and heart rate, each of which may have an effect on filling rate. Using the isolated muscle preparation, where muscle length and load can be independently and precisely controlled, the effects of isolated changes in loading conditions on isotonic lengthening rate can be studied. In addition, data obtained using this method are not affected by neurohumoral and other factors that might influence relaxation in the intact heart. Accordingly, the purpose of the current study is to define the independent determinants of maximum isotonic lengthening rate using physiologically sequenced isolated papillary muscle preparations. We hypothesize that loading conditions, specifically preload, total load, and late load, are primary mechanical determinants of the maximum isotonic lengthening rate. Ther...

show abstract

“…Under these "physiological" conditions, the force decreased back to the preload before the muscle lengthened back to its preloaded length. Tamiya et al (1979) and Goethals et al (1978) both have shown that the isotonic relaxation velocity depends on the extent of shortening from the peak shortening length. Thus, the afterload imposed upon the muscles was adjusted to maintain the same absolute extent of muscle shortening under experimental as under control conditions.…”

Section: Methodsmentioning

confidence: 96%

“…Third, a series of contractions was recorded during which a physiological sequence of relaxation was created to mimic closely that observed in the intact heart. Thus, the isotonicisometric sequence normally used in in vitro studies was reversed to an isometric-isotonic relaxation sequence (Tamiya et al, 1977(Tamiya et al, , 1979Wiegner and Bing, 1977;Goethals et al, 1978). This physiological relaxation sequence was achieved by unloading the muscle against a second mechanical stop at the moment of peak shortening so that muscle length was kept at the peak shortening length until force returned to the preloaded force.…”

Section: Methodsmentioning

confidence: 99%

Load-insensitive relaxation caused by hypoxia in mammalian cardiac muscle.

Chuck

Goethals²,

Parmley³

et al. 1981

Circulation Research

View full text Add to dashboard Cite

SUMMARY The relaxation of isolated cardiac muscles from mammals was recently shown to be sensitive to the loading conditions because the time course of relaxation could be changed by changing the load. This effect apparently is related to the amount and functional status of the sarcoplasmic reticulum. The purpose of this study was to determine whether hypoxia affected the load sensitivity of papillary muscles isolated from both rats and cats. We used three mechanical tests to establish the presence of load-sensitive relaxation. First, we superimposed records of isotonic contractions at increasing afterloads up to isometric contraction. From these records we measured the ratio (tRi) which was the time from the initiation of the contraction to the initial decay of force at each isotonic afterload, divided by the time it took for the force of an isometric contraction to relax to that same afterload. If the tRi was less than 1.0, then the muscle was load sensitive. Hypoxia caused the loss of load-sensitive relaxation in isotonically contracting rat papillary muscles since the tRi ratios were not significantly different from 1.0 at all afterloads. Both hypoxia and caffeine were required to make cat papillary muscles load insensitive. Second, during hypoxia, loads added in midcontraction did not induce early relaxation in rat papillary muscles, but still did so in cat muscles. Hypoxia plus caffeine eliminated this load-induced early relaxation in cat papillary muscles. Third, physiologically contracting muscles made hypoxic did not lengthen earlier in response to an additional load. This decrease of load sensitivity under hypoxic conditions could contribute to the relaxation abnormalities observed during regional wall motion studies. Circ Res 48: 797-803, 1981 REGIONAL and global abnormalities of relaxation in the myocardium critically affect the evaluation of left ventricular function in patients with heart disease. To date, however, the underlying mechanisms for these abnormalities have not been fully elucidated. Recent studies (Brutsaert et al., 1978a(Brutsaert et al., , 1978bLeCarpentier et al., 1979) on the nature of relaxation in mammalian cardiac muscle introduced the concept that relaxation depends on the load imposed on the relaxing muscle. This concept may provide a basis for analyzing relaxation abnormalities of the ventricles. Muscular relaxation occurs when the load imposed upon the muscle exceeds the load-bearing ability of that muscle. In this process, the sarcoplasmic reticulum (SR) sequesters calcium, inactivates the contractile process, and decreases the muscle's load-bearing ability. If at this point the load exceeds the load-bearing capacity of the muscle, then relaxation occurs. The recent studies on relaxation of cardiac muscles were performed on muscles with extensive and active sarcoplasmic reticular systems. In these studies, a midcontraction increase of the imposed load initiated early relaxation, perhaps because the SR sequestered enough calcium to lower the muscle's loadbearing ability, ...

show abstract

Maximum lengthening velocity during isotonic relaxation at preload in canine papillary muscle

Cited by 20 publications

References 0 publications

Determinants of Left Ventricular Early-Diastolic Lengthening Velocity

Determinants of Left Ventricular Early-Diastolic Lengthening Velocity

Mechanical determinants of maximum isotonic lengthening rate in rat left ventricular myocardium.

Load-insensitive relaxation caused by hypoxia in mammalian cardiac muscle.

Contact Info

Product

Resources

About