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Neuromuscular Physiology
Published in Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan, Strength and Conditioning in Sports, 2023
Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan
Differentiation of smooth muscle and striated muscle can be accomplished by a variety of methods, particularly microscopic appearance. For example, smooth muscle fibers are mononucleated and their sarcomeres (the functional units of muscle) are arranged at oblique angles. Resulting from the orientation of its sarcomeres, smooth muscle appears to be relatively indistinctive (smooth), as viewed through a light microscope. Striated muscle fibers contain protein arrays (myofibrils) in parallel to each other and thus form striations (stripes). Cardiac muscle fibers can be easily identified from skeletal muscle by appearance. For example, unlike skeletal muscle fibers, cardiac muscle fibers have a distinct end. The ends are termed intercalated discs. So, one cardiac muscle fiber consists of the substance between two intercalated discs. The intercalated discs are somewhat thicker than the striations but are usually darker and distinctive. Under a light microscope, intercalated disks appear as relatively dark lines running from one side of the fiber to the other. Cardiac muscle fibers contain only one or occasionally two nuclei and there are differences in function, such as an intrinsic ability to contract. (A detailed discussion dealing with smooth and cardiac muscle is not within the scope of this book.)
A student with a ‘hangover’
Published in Tim French, Terry Wardle, The Problem-Based Learning Workbook, 2022
Hyperkalaemia may cause cardiac arrest. Hourly U&E measurements are important to guide K+ replacement. Additionally supplementary calcium (i.e. calcium gluconate 10%) may be used to protect cardiac muscle.
Diseases of the Heart
Published in Amy J. Litterini, Christopher M. Wilson, Physical Activity and Rehabilitation in Life-threatening Illness, 2021
Amy J. Litterini, Christopher M. Wilson
For individuals with confirmed evidence of significant coronary artery disease, arrhythmias, damage to the myocardium, and/or valvular disease, surgical interventions followed by cardiac rehabilitation (including lifestyle modification) are the mainstay options for management in most countries. For individuals surviving myocardial infarction(s), with or without cardiac arrest, the above interventions are key to continued survival and recovery of damaged cardiac muscle. Options for surgical interventions to address heart disease are dependent upon the structures and underlying pathology involved (see Table 8.3).9 International guidelines on cardiac rehabilitation management for individuals with heart disease demonstrate geographical similarities, but also minor discrepancies, in approaches to care.10 Consensus among most major international societies is observed in high-intensity exercise in combination with resistance training; however, variations are noted in the need for highly technical exercise testing equipment such as electrocardiograph-monitored exercise stress testing.10 Please see Chapter 3 for additional information on physical activity recommendations.
Improving mitochondrial function in preclinical models of heart failure: therapeutic targets for future clinical therapies?
Published in Expert Opinion on Therapeutic Targets, 2023
Anna Gorący, Jakub Rosik, Joanna Szostak, Bartosz Szostak, Szymon Retfiński, Filip Machaj, Andrzej Pawlik
Improper mitochondria leads to disturbances in cellular homeostasis, affecting the function of cardiomyocytes [173]. Mitochondria dysfunction is associated with an overproduction of ROS, impaired fatty acid metabolism, and, therefore, less efficient ATP production [29,60,61]. Those factors could exacerbate the impaired function of cardiac muscle by causing apoptosis or even necrosis of cardiomyocytes. The remaining cellular homeostasis is obligatory for the optimal physiological functioning of the cell [174]. Therefore, each cell has multiple controlling and metabolite removal mechanisms. Autophagy is a process responsible for removing dysfunctional organelles or accumulated proteins. Mitophagy, or the mitochondria-specific form of autophagy, is the mechanism that enables the removal of damaged mitochondria from cardiomyocytes or other cells [175]. In recent years, the role of mitophagy in various conditions has been evaluated, including heart failure and cardiovascular diseases [176]. Proper mitophagy maintains mitochondria’s physiological function in normal conditions by removing damaged organelles and providing sufficient components to produce fresh mitochondria [174]. However, any alteration in this process under stress conditions could affect the function of mitochondria, leading to development of various cardiac conditions [177].
Diagnosis and management of cardiovascular risk in rheumatoid arthritis: main challenges and research agenda
Published in Expert Review of Clinical Immunology, 2023
Fabiola Atzeni, Silvia Maiani, Marco Corda, Javier Rodríguez-Carrio
The speckle tracking echocardiography (STE) is a tool that permits the evaluation of regional myocardial deformation expressed by a dimensionless parameter, the strain (ε), defined by the Lagrangian formula as the percent change from the original dimension [55]. The displacement reflects myocardial motion and differs from deformation. Contrary to other techniques, the STE is an angle-independent approach that make possible an accurate assessment of segmental myocardial deformation by gray-scale based imaging analysis frame by frame. Furthermore, the lack of angle-dependency is of great advantage because myocardial ε could be tracked in two-dimensional echo imaging, along the direction of the wall and not along the ultrasound beam [55,56]. This suggests that myocardial strain can be analyzed along three spatial axes according to the cardiac muscle physiology. STE appears to be a reliable tool to detect early subtle cardiac involvement in different clinical settings such as RA [57,58]. Finally, impairments observed by STE can be reduced, at least in part, by effective treatment [57].
Effect of anisotropy in myocardial electrical conductivity on lesion characteristics during radiofrequency cardiac ablation: a numerical study
Published in International Journal of Hyperthermia, 2022
Kaihao Gu, Shengjie Yan, Xiaomei Wu
Cardiac muscle is composed of myocardial fibers, which dominant the contraction of the heart [7]. Fiber orientation has been reported to affect the myocardial electrical conductivity (MEC) such that the electrical current flows preferentially along the fiber direction [8], causing the electrical conductivity throughout the heart to become anisotropic. This phenomenon influences the current distribution and thus the lesion formation of RFCA. In ablation simulation, however, to simplify the model, MEC is usually assumed to be isotropic [6]. As the electrical conductivity governs the ablation result [9], appropriate fiber orientation is essential for good accuracy. The fiber orientation can be determined using an imaging system; however, this process is time-consuming and has limited robustness [10]. Application of a rule-based method (RBM) that mathematically describes the fiber orientation based on historical observations is a more acceptable alternative, as it is more feasible for computational simulation [11–13].