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A W Wiegner

Publications and source records attributed to A W Wiegner.

35 records · Page 2Linked to original sources
PubMed1987

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

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 degrees 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 0.7 +/- 0.1 to 1.4 +/- 0.1 g/mm2, muscle length increased from 0.98 +/- 0.003 to 1.01 +/- 0.002 muscle lengths, the extent of shortening increased from 0.05 +/- 0.003 to 0.08 +/- 0.003 muscle lengths, but minimum length (0.93 +/- 0.01 muscle lengths) and +dL/dt (1.1 +/- 0.1 muscle lengths/sec) were unchanged. When total load was increased from 1.5 to 4.5 g/mm2, minimum length increased from 0.91 +/- 0.05 to 0.97 +/- 0.05 muscle lengths and +dL/dt fell from 1.4 +/- 0.1 to 0.5 +/- 0.1 muscle lengths/sec. Late load (the load borne by or applied to the muscle during isotonic lengthening) was altered by changing its magnitude (g/mm2) or time (milliseconds after stimulation) of application. As late load was increased from 1.4 +/- 0.02 to 2.1 +/- 0.3 g/mm2, +dL/dt increased from 1.3 +/- 0.2 to 2.1 +/- 0.3 muscle lengths/sec.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Spasticity.

Spasticity has been defined as velocity-dependent hyperactivity of stretch reflexes; it is therefore only one aspect of the complex syndrome produced by a lesion of the upper motoneuron. Although spasticity may be partially responsible for joint contractures, it does not produce most of the functional disability experienced by patients with upper motoneuron lesions. Paresis, fatigability, lack of dexterity, etc., account for most of these patients' complaints. The pathophysiology of spasticity is poorly understood but appears to be related to an increased excitatory state at the segmental spinal level; there is no evidence for increased sensitivity of muscle spindles in spastic patients. Several mechanisms for this increased excitability within the spinal cord have been proposed. There are different types as well as degrees of spasticity. Clinical neurophysiologic recordings of reflex activity in patients with spasticity provide the means to differentiate among the various types of spasticity, to select the therapy most likely to be effective in a particular patient, and to see the results of its employment objectively. The latter will prove whether a specific therapy is useful or not. Ablative treatment at the level of the peripheral nerve or dorsal root may be useful, particularly when spasticity is severe. Drugs such as baclofen or diazepam relieve flexor spasms but are not particularly effective against spasticity itself. Dantrolene acts to weaken muscles, but that is not often helpful. Rarely do any of these therapies increase function; there are no effective cures for paresis or related negative manifestations of chronic spasticity.

Combined Modality Therapy↗
PubMed1986

Role of agonist and antagonist muscles in fast arm movements in man.

Fast goal-directed voluntary movements of the human upper extremity are known to be associated with three distinct bursts of EMG activity in antagonistic muscles. The role of each burst (AG1, ANT, AG2) in controlling motion is not fully understood, largely because overall limb response is a complex function of the entire sequence of bursts recorded during experimental trials. In order to investigate the role of each burst of muscle activity in controlling motion, we studied fast voluntary arm movements and also developed two simulation techniques, one employing a mathematical model of the limb and the other using electrical stimulation of human arm muscles. These techniques show that two important movement parameters (peak displacement, time to reach peak displacement) are non-linear functions of the magnitude of the antagonist input (torque and stimulation voltage, respectively, in our two simulations). In the fastest movements, the agonist muscle is primarily responsible for the distance moved, while the antagonist muscle provides an effective means of reducing movement time. The third component of the triphasic pattern moderates the antagonist braking forces and redirects the movement back to the target.

Arm↗
PubMed1986

Measurement of relaxation in isolated rat ventricular myocardium during hypoxia and reoxygenation.

The effects of hypoxia and subsequent reoxygenation were examined in isolated left ventricular papillary muscles from the rat at 28 degrees C and 33 degrees C. Studies of relaxation were carried out in isometric and physiologically sequenced contractions. In studies of isometric contractions, the following variables were determined: active tension (AT), maximum rate of tension increase (+dT/dt), time to peak tension (TPT), time for tension to fall from peak to 50% of peak tension (RT1/2), maximum rate of tension decline (-dT/dt), isometric peak (-dT/dt/T), and isometric maximum (-dT/dt per T). Variables measured in physiologically sequenced contractions were the slopes of the relation between -dT/dtmax and end systolic length (SIM) and maximum rate of isotonic muscle lengthening (+dL/dtmax) and end systolic length (SIT). Tau, the exponential time constant for isometric relaxation, was also examined. Pronounced changes in active tension and +dT/dt were seen during hypoxia at both temperatures, whereas changes in measured relaxation variables were less prominent and inconsistent. At neither 28 degrees C nor 33 degrees C did TPT or RT1/2 indicate impaired relaxation during hypoxia. Isometric peak -dT/dt declined with hypoxia at both temperatures but the normalised indices, isometric peak -dT/dt/T, peak (-dT/dt per T), and tau showed consistent impairment of relaxation only at 33 degrees C. In physiologically sequenced contractions, SIM suggested impaired relaxation during hypoxia at 28 degrees C but not at 33 degrees C. SIT showed impaired relaxation at both 28 degrees C and 33 degrees C. These findings are consistent with data suggesting impairment of the cardiac relaxing system during hypoxia. Nevertheless, relaxation appears less affected than contraction, and impairment is best seen late in the cardiac cycle.

Animals↗
PubMed1986

Elastic properties of muscles measured at the elbow in man: I. Normal controls.

Passive elastic stiffness of muscle acting at the elbow was assessed in 19 normal subjects by measuring displacements produced by a torque motor acting at the joint. Stiffness ranged from 0.40 to 1.8 Nm/radian and was strongly correlated (r = 0.85) with upper arm volume, allowing us to define a "normal" range for stiffness when corrected for arm volume. In addition, the angle of the elbow with the arm fully relaxed and no external torque applied ("neutral" angle) was found to be 107 degrees +/- 10 degrees. Thus, we have quantified resting stiffness or "tone" in the arm and provided normal data for comparison with patients with pathophysiological conditions such as rigidity or spasticity.

Adult↗
PubMed1986

Elastic properties of muscles measured at the elbow in man: II. Patients with parkinsonian rigidity.

A method is described to measure reproducibly stiffness, and therefore "tone", at the elbow of patients with Parkinson's disease using a torque motor. In Parkinsonian versus normal patients (previously reported) it was observed that: the neutral angle in Parkinson's disease patients was significantly smaller (92 degrees +/- 15 degrees) than in normals (107 degrees +/- 10 degrees), and in Parkinson's disease patients, even with relatively mild symptoms, the upper limb was stiffer than normals in the totally relaxed state with no electromyographic activity present. Our results suggest that changes in the passive mechanical properties of the upper limb affected by Parkinsonian rigidity may have taken place, accounting for the more flexed neutral elbow angle and greater passive stiffness. Using this technique, response to antirigidity therapy and natural progression of illness can be quantitatively assessed and followed.

Aged↗
PubMed1986

Myocardial mechanics in allylamine-induced myocardial fibrosis.

To examine the effect of fibrosis on myocardial mechanics, we studied isolated left ventricular papillary muscles from 18 rats given 0.1% allylamine, an agent known to cause myocardial fibrosis, in drinking water for 4-8 wk. Six control rats were given tap water. Left ventricular hydroxyproline concentration was higher in the allylamine-treated group [3.47 +/- 2.12 vs. 2.10 +/- 0.66 (SD) micrograms/mg dry wt; P less than 0.01]. Because of variable and heterogeneous involvement of the ventricle by fibrosis, preparations from allylamine-fed rats were divided into two subgroups; data from four papillary muscles with more than 25% fibrosis by point counting (AL-B group) were compared with eight control muscles from nonallylamine-treated rats. A third subgroup of nine muscles from allylamine-treated rats but with normal left ventricular hydroxyproline concentration and fibrosis as determined by point counting served as another control group (AL-A) for the evaluation of effects of allylamine not due to fibrosis. Myocardial fiber diameters of AL-B preparations were significantly larger than other groups (controls, 12.1 +/- 1.7 microns; AL-A group, 12.7 +/- 1.7 microns; AL-B group, 18.0 +/- 1.2 microns; P less than 0.01). Passive and active stiffness constants in AL-B muscles were significantly increased compared with control and AL-A preparations (P less than 0.05). Electromechanical delay plus time to peak tension and the time for tension to fall from its peak to one-half of that value at the peak of the length-tension curve were significantly prolonged in AL-B muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Allylamine↗
PubMed1986

Effects of hypertrophy and allylamine-induced fibrosis on mechanical properties of isolated rat heart muscles with references to the pumping function of the intact heart in the same models.

To examine the effects of hypertrophy and fibrosis on myocardial mechanics, we studied isolated left ventricular papillary muscles from 6-month-old male SHR and allylamine-fed rats. In SHR, the peak developed tension (DT) and the maximum rate of tension development (dT/dt) were higher compared to control male Wistar-Kyoto rats (WKY). With 15 min of hypoxia, the DT and the dT/dt declined similarly in both groups and the ratios of DT and dT/dt to their prehypoxic values after 15 min of hypoxia were not different in the two groups. From allylamine-fed rats, only 4 papillary muscles had more than 25% interstitial fibrosis by point-counting (AL-B group), but 9 muscles had no fibrotic involvement and their left ventricular hydroxyproline concentration was normal (AL-A group). The myocardial diameters, the passive stiffness constant and the duration of isometric contractions at Lmax were increased in AL-B group, but the resting tension, the DT at Lmax and the force-velocity relations did not differ from controls. The mechanical properties of the AL-A group muscles were not different from controls. However, when pumping function was examined in the intact heart from the AL-A group, the LVEDP was increased and the peak cardiac output normalized by body weight was decreased. Thus, hypertrophied muscle from SHR shows hyperfunction without an increase in susceptibility to hypoxic stress. Even if fibrosis progresses, hypertrophy can compensate for the reduction in contractile component up to a certain degree.(ABSTRACT TRUNCATED AT 250 WORDS)

Allylamine↗
PubMed1985

Effects of reperfusion after coronary artery occlusion on post-infarction scar tissue.

Early reperfusion after a coronary occlusion may reduce myocardial infarct size, but late reperfusion into necrotic myocardium may alter post-infarction healing. In rabbits, we compared 1- or 3-week-old scars resulting from permanent coronary occlusion to those resulting from a 1- or 3-hour occlusion followed by reperfusion. Reperfusion at 1 hour post-occlusion did not affect scar mechanical properties assessed at 1 week post-infarction, but at 3 weeks post-infarction, these scars had a tensile strength significantly lower than those not reperfused (78 +/- 11 vs. 158 +/- 15 g/mm2, P less than 0.001). They also were composed of a mixture of fibrous tissue (58 +/- 8%) and myocytes (43 +/- 8%) with a hydroxyproline content of 23 +/- 2.5 mg/g dry weight. The nonreperfused scars had a higher proportion of fibrous tissue (73 +/- 3%) by histological evaluation and a 35% higher hydroxyproline content (31 +/- 2 mg/g dry weight, P less than 0.001) than the scars reperfused after 1 hour. In contrast, 3-week-old scars resulting from "late" reperfusion at 3 hours post-occlusion were similar to nonreperfused scars in fibrous tissue composition and hydroxyproline content. Nonetheless, the tensile strength of these scars reperfused 3 hours post-occlusion was significantly less than that of the nonreperfused scars (72 +/- 5 vs. 158 +/- 15 g/mm2, P less than 0.001). The lower tensile strength was associated with a lower collagen cross-link density in this reperfused group of scars. At physiological stress levels (approximately 3 g/mm2), all groups of reperfused and nonreperfused scars had similar mechanical properties in terms of natural strain, stiffness, creep, and stress relaxation. Thus, although the reperfused scars ruptured more easily at high stresses, when assessed at physiological stresses their mechanical properties were not significantly different from those of nonreperfused scars.

Animals↗
PubMed1984

A STOIC-based application language for muscle mechanics research.

An application language for the control and analysis of isolated cardiac muscle experiments is described. It is defined using an extensible language, STOIC (derived from FORTH), which consists of a set of basic operations called words. The basic words are readily combined to form higher level words which perform more complex operations. A suitable set of higher level words forms an application language. The resulting language takes full advantage of system hardware capabilities, is easily used by those with little programming experience, and provides flexibility in a research environment where experimental protocols frequently change.

Animals↗
PubMed1983

Systolic time intervals: assessment by isolated cardiac muscle studies.

To document the independent effects of acute changes in preload, afterload and inotropic state on the systolic time intervals, 10 isolated rat left ventricular muscle preparations were studied. Experiments were performed using physiologically sequenced contractions that simulate the loading conditions of the intact left ventricle. The preshortening period was measured from the time of the electrical stimulus to the onset of muscle shortening, and the isotonic contraction time was measured as the duration of shortening. These variables are analogous to the preejection period and the left ventricular ejection time in the intact heart. It was found that an isolated increase in preload shortened the preshortening period and prolonged the isotonic contraction time, whereas an increase in afterload prolonged the former and shortened the latter. Isoproterenol shortened both the preshortening period and the isotonic contraction time, while an increase in calcium shortened the preshortening period and lengthened the isotonic contraction time. All changes were significant (p less than 0.01) by analysis of variance. Thus, the similar dependence of preshortening period, isotonic contraction time and clinical systolic time intervals on changes in preload, afterload and inotropic state supports the derivation of systolic time intervals from fundamental principles of myocardial mechanics. These data provide an improved basis for the rational interpretation of systolic time intervals in patients with and without heart disease.

Animals↗
PubMed1982

Mechanics of myocardial relaxation: application of a model to isometric and isotonic relaxation of rat myocardium.

Using a simple model for cardiac muscle relaxation which takes into account muscle length, activation, elasticity and a rate constant for the decay of activation, we are able to use easily measured mechanical parameters to assess the state of the cardiac relaxing system. In isolated trabeculae carneae from the left ventricle of the rat, performing physiologically sequenced contractions, observations have been made (1) at varying preloads and afterloads, (2) with changes in temperature from 23 degrees to 33 degrees C, (3) with changes in bath Ca2+ concentration and (4) with the addition of isoproterenol. During isometric relaxation, the slope (SIM) of the curve relating maximum rate of decline of force (-dF/dtmax) to end-systolic muscle length is load-independent and sensitive to interventions which directly affect the cardiac relaxing system (e.g., temperature, isoproterenol); it is only slightly sensitive to bath calcium concentration. During isotonic relaxation, the maximum velocity of lengthening (+dL/dtmax) is in negative linear proportion to muscle shortening at a given preload, the slope (SIT) of the curve relating +dL/dtmax to end-systolic length is sensitive to the interventions which directly affect the cardiac relaxing system but insensitive to calcium-mediated inotropic interventions. The model provides a theoretical basis for the use of SIM and SIT as measures of the relaxation process.

Animals↗
PubMed1981

Mechanical and structural correlates of canine pericardium.

We have assessed viscoelastic properties of pericardium within the physiological range of stresses and related mechanical behavior to fiber direction as defined by scanning electron microscopy. Stiffness, stress relaxation, and creep were measured in samples taken from the anterior surface of 14 canine pericardia. Stress-strain relations generally were not exponential; stiffness at a stress of 1 g/mm2 ranged from 12.9 to 239 g/mm2 during stretch and varied both from pericardium to pericardium and with the orientation of the strip within the sample (anisotropy). The strips exhibited hysteretic behavior which was not promotional to rate of strain. Following a rapid increase in stress, creep averaged less than 1% and stress relaxation, 34% in a 30-minute test period. The orientation of the strip with the greatest stiffness was consistent from pericardium to pericardium, and correlated with a layer of collagen fibers oriented along the major axis of te strip.

Animals↗
PubMed1979

Laser scanner measurement of central segment performance in isolated cardiac muscle preparations.

A laser scanning system has been developed to facilitate the study of isolated cardiac muscle by excluding the possibly damaged tissue at the ends of the preparation. The laser scanner monitors the length of a central segment of the muscle that has been delineated by markers consisting of single loops of 8-0 silk suture. Focused laser light traverses the length of the muscle at 150 Hz. Scattered light is detected by a photodiode and the length of the central segment is calculated electronically. This system provides an accurate measure of central segment length in both resting and active muscle with no apparent damage to the preparation.

Animals↗
PubMed1978

Isometric relaxation of rat myocardium at end-systolic fiber length.

In a "physiologically sequenced" contraction (PSC), which loads the isolated muscle preparation in a manner which approximates that of the intact heart, isometric relaxation precedes isotonic relaxation and occurs at minimum ("end-systolic") length. We studied the effects of inital muscle length, load, temperature, calcium, and isoproterenol on the isometric relaxation phase of physiologically sequenced contractions to define the determinants of the rate of isometric relaxation of rat left ventricular myocardium. At the baseline temperature (28 degrees C), relaxation was found to be nonexponential, and the maximum rate of decline of force (-dF/dtmax) was used to evaluate changes in relaxation. Three factors, shortening, end-systolic length, and total load, were examined as possible mechanical determinants of -dF/dtmax. We found that -dF/dtmax is linearly related to end-systolic muscle length for lengths below 94% of Lmax; -dF/dtmax is also strongly related to total load for lightly loaded contractions, but peaks at loads of approximately 80% of peak developed force and declines thereafter. Shortening is poorly correlated with -dF/dtmax. The slope of the linear portion of the relation between -dF/dtmax and end-systolic length appears to be independent of muscle-loading conditions and sensitive to factors known to alter relaxation.

Animals↗
PubMed1977

Altered performance of rat cardiac muscle follows changes in mechanical stress during relaxation.

We compared two sets of loading conditions for their effect on the mechanical performance of isolated rat trabecular muscle: (1) loading which approximated that of the intact ventricle; (2) nonphysiological afterloaded isotonic contractions. Improved performance, manifested by increased shortening and rate of shortening at constant load, was seen when lengthening occurred at light loads, as in the intact heart. In contrast, lengthening occurring at the same load against with shortening had taken place was followed by diminished performance. Viscous elements in series with the muscle could not account for this phenomenon. The results suggest the presence of an autoregulatory response of myocardium to mechanical stress during relaxation.

Animals↗