Spontaneous fibrillation

Nguyen HD, Hall CK (2004) Molecular dynamics simulations of spontaneous fibril formation by random-coil peptides. Proc. Natl. Acad. Sci. USA 101 16180-16185... 

Our studies showed the optimal viscosity ratio (riLcp/ tipp) for formation of small LCP domains and their spontaneous fibrillation to range from about 0.5 to 1. At lower viscosity ratios, the fiber structure was coarser, while at viscosity ratios above unity the LCP domains tended to be spherical or cluster-like. As the temperature and shear rate dependencies of LCP and the matrix polymer may well be different, it is extremely important to know the viscosity ratio under the actual processing conditions. Its effect on spontaneous fibrillation of the LCP domains forms the basis for material selection, but the final processing conditions determine how well the LCP phases will be fibrillated and oriented in... 

Dynamics Simulations of Spontaneous Fibril Formation by Random-Coil Peptides. 

BMG of the quadriceps and biceps showed increased recruitment of abnormally small, sometimes polyphasic, motor-unit potentials. Those "BSAPs" and "BSAPPs" [1], evident during slight voluntary contraction, indicated "fractionated" motor units, which can be caused by either a myopathic or a distal-axonal-twig neuropathic disturbance (see Chapters 1 and 2). It also showed spontaneous fibrillations and positive waves at rest, indicating separation of viable muscle fibers from their motor-neuron control (on a neuropathic or myopathic basis), which would normally prevent such spontaneous activity. Nerve conductions were normal. 

These are used to prevent spontaneous fibrillation of oriented polypropylene film in processing equipment. These additives are usually natural or synthetic rubber added at concentrations up to 10%. 

Amyloid Fibrils Seeded Versus Spontaneous Fibrillation. 126... 

Abnormal initiation of electrical impulses occurs as a result of abnormal automaticity. If the automaticity of the SA node increases, this results in an increased rate of generation of impulses and a rapid heart rate (sinus tachycardia). If other cardiac fibers become abnormally automatic, such that the rate of initiation of spontaneous impulses exceeds that of the SA node, other types of tachyarrhythmias may occur. Many cardiac fibers possess the capability for automaticity, including the atrial tissue, the AV node, the Purkinje fibers, and the ventricular tissue. In addition, fibers with the capability of initiating and conducting electrical impulses are present in the pulmonary veins. Abnormal atrial automaticity may result in premature atrial contractions or may precipitate atrial tachycardia or atrial fibrillation (AF) abnormal AV nodal automaticity may result in junctional tachycardia (the AV node is also sometimes referred to as the AV junction). Abnormal automaticity in the ventricles may result in ventricular premature depolarizations (VPDs) or may precipitate ventricular tachycardia (VT) or ventricular fibrillation (VF). In addition, abnormal automaticity originating from the pulmonary veins is a precipitant of AF. 

Atrial fibrillation is classified as paroxysmal, persistent, or permanent (Fig. 6-4).23 Patients with paroxysmal AF have episodes that start suddenly and spontaneously, last minutes... 

CPR, cardiopulmonary resuscitation D5W, 5% dextrose in water PEA, pulseless electrical activity PVT, pulseless ventricular tachycardia ROSC, return of spontaneous circulation VF, ventricular fibrillation. 

Since fibril assembly can be regarded in part as a spontaneous self-assembly process, the limitation of fibril size could be ascribed to a physical equilibrium between soluble procollagen molecules and the growing insoluble fibril. Fibril-forming collagens are synthesized as precursor... 

Hove-Madsen, L., Llach, A., Bayes-Genis, A., Roura, S., Rodriguez Font, E., Aris, A., and Cinca, J. (2004). Atrial Fibrillation is Associated with Increased Spontaneous Calcium Release from the Sarcoplasmic Reticulum in Human Atrial Myocytes. Circulation 110(11) 1358-63. 

Haissaguerre M, et al. Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins. N Engl J Med 1998 339(I0) 659 666. 

Endogenous norepinephrine stimulates cardiac beta receptors. Receptor-linked cAMP-dependent protein kinases phosphorylate calcium channels to increase intracellular calcium. Elevated intracellular calcium increases conduction velocity (phase 0) and decreases the threshold potential in normal SA and AV node cells (see Figure 12.13). Beta blockers slow spontaneous conduction velocity in the SA node by approximately 10-20 percent. In addition, beta blockers can slow conduction velocity while increasing the refractory period of the AV node. These effects control the ventricular rate in atrial fibrillation or flutter and terminate paroxysmal supraventricular tachycardias. They are also safer, although somewhat less effective, than other drugs for suppression of premature ventricular complexes (PVCs). Drugs in this class approved by the FDA for treatment of various arrhythmias include propranolol, acebutolol, and esmolol. Problems with the beta blockers include drowsiness, fatigue, impotence, and depressed ventricular performance. 

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