Search results for "Contraction"
showing 10 items of 1092 documents
ACTION POTENTIAL, MEMBRANE CURRENTS AND FORCE OF CONTRACTION IN MAMMALIAN HEART MUSCLE FIBRES TREATED WITH QUINIDINE
1978
The effects of quinidine on electrical and mechanical activity were investigated in atrial and/or ventricular heart muscle preparations from guinea pigs and cats. Quinidine (1--100 micrometer) exerted negative inotropic effects in papillary muscles from guinea pigs and cats. In guinea-pig left atria, a positive inotropic effect was superimposed on the negative inotropic effect in response to quinidine. Quinidine (100 micrometer) prolonged the duration of the action potential in guinea-pig atria but shortened it in guinea-pig ventricular muscle. In cat papillary muscles, the late repolarization was markedly prolonged by quinidine, but virtually no change of the plateau phase was observed. Th…
Wirkung und Wechselwirkung von Theophyllin und Chinin auf die neuromuskuläre Übertragung und die elektromechanische Kopplung am M. gastrocnemius
1982
It has been reported that theophylline improves the effect of quinine in relieving patients from nocturnal muscle cramps. We therefore examined the actions and interactions of quinine and theophylline on mechanical and electrical properties of the rabbit’s N. ischiadicus — M. gastrocnemius nerve-muscle preperation in situ. Maximal tension, rate of rise of tension, contraction time, relaxation time and latency of single maximal twitch, evoked by electrical stimulation of N. ischiadicus were measured before and after i.p. or iv. application of therapeutic doses of quinine and theophylline given alone or in combination. In addition, changes of conduction velocities of action potentials of the …
Estimation of Personalized Minimal Purkinje Systems From Human Electro-Anatomical Maps
2021
The Purkinje system is a heart structure responsible for transmitting electrical impulses through the ventricles in a fast and coordinated way to trigger mechanical contraction. Estimating a patient-specific compatible Purkinje Network from an electro-anatomical map is a challenging task, that could help to improve models for electrophysiology simulations or provide aid in therapy planning, such as radiofrequency ablation. In this study, we present a methodology to inversely estimate a Purkinje network from a patient's electro-anatomical map. First, we carry out a simulation study to assess the accuracy of the method for different synthetic Purkinje network morphologies and myocardial junct…
C-X-C Motif Chemokine Receptor 4 Blockade Promotes Tissue Repair After Myocardial Infarction by Enhancing Regulatory T Cell Mobilization and Immune-R…
2019
Background: Acute myocardial infarction (MI) elicits an inflammatory response that drives tissue repair and adverse cardiac remodeling. Inflammatory cell trafficking after MI is controlled by C-X-C motif chemokine ligand 12 (CXCL12) and its receptor, C-X-C motif chemokine receptor 4 (CXCR4). CXCR4 antagonists mobilize inflammatory cells and promote infarct repair, but the cellular mechanisms are unclear. Methods: We investigated the therapeutic potential and mode of action of the peptidic macrocycle CXCR4 antagonist POL5551 in mice with reperfused MI. We applied cell depletion and adoptive transfer strategies using lymphocyte-deficient Rag1 knockout mice; DEREG mice, which express a diphth…
Stretch-shortening cycle: a powerful model to study normal and fatigued muscle.
2000
Stretch-shortening cycle (SSC) in human skeletal muscle gives unique possibilities to study normal and fatigued muscle function. The in vivo force measurement systems, buckle transducer technique and optic fiber technique, have revealed that, as compared to a pure concentric action, a non-fatiguing SSC exercise demonstrates considerable performance enhancement with increased force at a given shortening velocity. Characteristic to this phenomenon is very low EMG-activity in the concentric phase of the cycle, but a very pronounced contribution of the short-latency stretch-reflex component. This reflex contributes significantly to force generation during the transition (stretch-shortening) pha…
Preferential Type II Muscle Fiber Damage From Plyometric Exercise
2012
Context: Plyometric training has been successfully used in different sporting contexts. Studies that investigated the effect of plyometric training on muscle morphology are limited, and results are controversial with regard to which muscle fiber type is mainly affected. Objective: To analyze the skeletal muscle structural and ultrastructural change induced by an acute bout of plyometric exercise to determine which type of muscle fibers is predominantly damaged. Design: Descriptive laboratory study. Setting: Research laboratory. Patients or Other Participants: Eight healthy, untrained individuals (age = 22 ± 1 years, height = 179.2 ± 6.4 cm, weight = 78.9 ± 5.9 kg). Intervention(s): Partici…
Deducing the stage-discharge relationship of rectangular broad and sharp-crested contraction devices
2023
Flumes with a local contraction of the channel width are a common way for accurately measuring the flow discharge. In this paper, the outflow process of rectangular broad and sharp-crested contraction devices is modeled using the dimensional analysis and the incomplete self-similarity condition. The proposed theoretical stage-discharge relationship is tested using measurements available in the literature. The proposed power equation is characterized by a value of the exponent close to 1.5 and a coefficient depending on the contraction ratio. The proposed flow-measuring flumes are characterized by a good accuracy of the measured discharge (ranging from -2.71 to 3.28% for the broad-crested co…
Postmenopausal hormone replacement therapy modifies skeletal muscle composition and function: a study with monozygotic twin pairs
2009
We investigated whether long-term hormone replacement therapy (HRT) is associated with mobility and lower limb muscle performance and composition in postmenopausal women. Fifteen 54- to 62-yr-old monozygotic female twin pairs discordant for HRT were recruited from the Finnish Twin Cohort. Habitual (HWS) and maximal (MWS) walking speeds over 10 m, thigh muscle composition, lower body muscle power assessed as vertical jumping height, and maximal isometric hand grip and knee extension strengths were measured. Intrapair differences (IPD%) with 95% confidence intervals (CI) were calculated. The mean duration of HRT use was 6.9 ± 4.1 yr. MWS was on average 7% (0.9 to 13.1%, P = 0.019) and muscle…
The effects of metoclopramide on acetylcholine release and on smooth muscle response in the isolated guinea-pig ileum
1982
The effects of metoclopramide on smooth muscle contraction and on release of acetylcholine were studied in the guinea-pig myenteric plexus longitudinal muscle preparation. Acetylcholine was determined either as endogenous acetylcholine, or as labelled transmitter from strips preloaded with 3H-choline. Metoclopramide caused an increase in resting tension of longitudinal muscle as well as an increase in resting output of either endogenous or labelled acetylcholine. Tetrodotoxin abolished the metoclopramide-evoked increase in transmitter release. The increase in smooth muscle tension was clearly related to the increase in resting output. The effects of metoclopramide on both longitudinal muscl…
Lactate level and handgrip test in migraine and fibromyalgia after self-myofascial release treatment
2019
The Aim of the study was to determine the effect of self-myofascial release (SMFR) treatment on handgrip test score in patients with fibromyalgia and migraine, investigating also if the lactate levels influenced the result. Twenty-five subjects affected by migraine (age 49.7±12.5; height 164.9±6.62 cm; weight 68.6±16.9 kg) and ten subjects affected by fibromyalgia (age 43.7±21.2; height 158±5.65 cm; weight 70±28.9 kg) were enrolled in the study. The assessments included a handgrip test, in order to evaluate isometric strength of both hands and forearm muscles and the lactate levels evaluation. The treatment was performed in the three most painful trigger points indicated from subjects as to…