Sarcomere length control in striated muscle

Abstract

A system that makes control of muscle length (ML), sarcomere length (SL), and force (F) possible in striated muscle preparations is described. SL was measured by light diffraction techniques and two diffractometers. Control was performed by influencing ML with a penmotor system with a frequency response of 190 Hz. SL or F could be controlled by interrupting the internal position (i.e., ML) feedback of the motor and by closing the respective loop. Velocity feedback of the motor through an internal velocity coil was maintained in all cases for optimal damping. Steady-state error of the system was minimized by an integrating loop filter. The feedback path was selected by means of potentiometers or analog switches. Electronic stops in the circuit protected the muscle against excessive stretch and load. A microprocessor-based average-response computer could be used for feedforward control to eliminate noise or to analyze longitudinal uniformity of the muscle. Responses of rat cardiac trabeculae during SL and F control are shown. Transient behavior of SL and F during control and measures to eliminate the transients are discussed.

Dynamics of viscoelastic properties of rat cardiac sarcomeres during the diastolic interval: involvement of Ca2+

“…Linear regression through the values of the maximal F variations (dF) and the corresponding length variations (dL) followed dF = adL with a = 114 mN ìm¢ (r = 0·99); the resolution of the force transducer was limited by noise (0-2 kHz) with a peak-to-peak value of 0·63 ìN. SL was measured by laser diffraction techniques as previously described (ter Keurs et al 1980;van Heuningen, Rijnsburger & ter Keurs, 1982;Daniels et al 1984). Briefly, the trabeculae diffract the incident light of a laser beam into a zero-order band and multiple symmetrical diffraction band pairs.…”

“…Its frequency response was 23 kHz (Daniels et al 1984). The first-order signal was corrected for the zero-order intensity contribution in both diffractometers as described earlier (see van Heuningen et al 1982). The detectors were calibrated (1 V ìm¢) using optical gratings before each experiment.…”

The constitutive behaviour of passive heart muscle tissue: A quasi-linear viscoelastic formulation

“…Full quantification of a three-dimensional constitutive relation can only be done on the basis of triaxial test data. At present, direct measurements from excised tissue specimens have been limited to uniaxial tests conducted on papillary muscles or strips of trabeculae (Sonnenblick, 1964;Pinto and Fung, 1973;Loeffler and Sagawa, 1975;Mirsky and Pasipoularides, 1980;Van Heuningen et al, 1982), and biaxial tests on strips of the left ventricular wall (Demer and Yin, 1983;Yin et al, 1987). Demer and Yin (1983) characterize the myocardial tissue as a highly non-linear viscoelastic material ( Fig.…”

“…In some uniaxial tests (e.g. Van Heuningen et al, 1982), however, the state of deformation of the specimen is specified by a measured sarcomere length. Thus, to characterize the constitutive behaviour, we use the uniaxial data of Van Heuningen et al (1982) in addition to the relaxation data of Pinto and Fung (1973) and the biaxial data of Demer and Yin (1983).…”

“…Van Heuningen et al, 1982), however, the state of deformation of the specimen is specified by a measured sarcomere length. Thus, to characterize the constitutive behaviour, we use the uniaxial data of Van Heuningen et al (1982) in addition to the relaxation data of Pinto and Fung (1973) and the biaxial data of Demer and Yin (1983). The aim of this paper is to formulate a constitutive law of heart muscle tissue which (1) approximates the known viscoelastic and anisotropic properties of the tissue as well as possible and (2) can easily be implemented into a biphasic finite element code of the myocardial wall.…”