Impulse generator

Cardiac arrhythmias or dysrhythmias are disturbances of the normal regular rhythm which may be caused by an abnormality in the site of impulse generation, its rate or regularity, or its propagation or conduction (1,2). The more commonly encountered cardiac arrhythmias are... 

Fig. 4.1 Hypothetical model of pathogenesis of pain in DSP. (1) Injury of peripheral nerve fibers due to multifocal inflammation and secreted macrophage activation products results in abnormal spontaneous activity of neighboring uninjured nociceptive fibers ( peripheral sensitization ). (2) Furthermore, the aberrant inflammatory response in DRG leads to alterations in neuronal sodium and calcium channel expression and ectopic impulse generation. (3) This results in central remodeling within the dorsal horn due to A-fiber sprouting and synaptic formation with pain fibers in lamina 11, and maintenance of neuropathic pain ( central sensitization ). Reproduced with permission from (Keswani et al. 2002)...

Second-degree AV nodal blockade may cause bradycardia, as not all impulses generated by the SA node are conducted through the AV node to the ventricles. 

O Atrial fibrillation may be caused by both abnormal impulse formation and abnormal impulse conduction. Traditionally, AF was believed to be initiated by premature impulses initiated in the atria. However, it is now understood that in many patients AF is triggered by electrical impulses generated within the pulmonary veins.20 These impulses initiate the process of reentry within the atria, and AF is believed to be sustained by multiple reentrant wavelets operating simultaneously within the atria.21 Some believe that, at least in some patients, the increased automaticity in the pulmonary veins may be the sole mechanism of AF and that the multiple reentrant wavelet hypothesis may be incorrect.21 However, the concept of multiple simultaneous reentrant wavelets remains the predominant hypothesis regarding the mechanism of AF. 

Because the chemical signals (semiochemicals) are normally produced in minute amounts and diluted in the environment with a complex mixture of chemical compounds derived from a myriad of sources, the olfactory system in insects evolved as a remarkably selective and sensitive system, which approaches the theoretical limit for a detector. For example, it has been estimated that the male silkworm moth is able to distinguish within 1 s 170 nerve impulses generated by the female silkworm moth s sex pheromone from 1700 spontaneous nervous impulses [ 1 ], thus, operating on a remarkably low S/N ratio ... 

Sinus bradycardia. An abnormally low sinoatrial impulse rate (<60/min) can be raised by parasympatholytics. The quaternary ipratropium is preferable to atropine, because it lacks CNS penetrability (p. 107). Sympathomimet-ics also exert a positive chronotropic action they have the disadvantage of increasing myocardial excitability (and automaticity) and, thus, promoting ectopic impulse generation (tendency to extrasystolic beats). In cardiac arrest epinephrine can be used to reinitiate heart beat... 

II. Nonspecific drug actions on impulse generation and propagation. 

Effects of antiarrhythmics. Antiarrhythmics of the Na -channel blocking type reduce the probability that Na+ channeb will open upon membrane depolarization ( membrane stabilization ). The potential consequences are (A, bottom) 1) a reduction in the velocity of depolarization and a decrease in the speed of impulse propagation aberrant impulse propagation is impeded. 2) Depolarization is entirely absent pathological impulse generation, e.g., in the marginal zone of an infarction, is suppressed. 3) The time required until a new depolarization can be elicited, i.e., the refractory period, is increased prolongation of the AP (see below) contributes to the increase in refractory period. Consequently, premature excitation with risk of fibrillation is prevented. 

Local anesthetics reversibly inhibit impulse generation and propagation in nerves. In sensory nerves, such an effect is desired when painful procedures must be performed, e.g surgical or dental operations. 

The molecular mass of the combustion products in the ramburner is increased by the formation of the oxidized metal particles. However, the temperature in the ramburner is also increased by the oxidation. The results of thermochemical calculations indicate that the specific impulse generated by the combustion in the ramburner is more dependent on the average combustion temperature than the average molecular mass of the products when metal particles are added. Table 15.4 shows the heats of combustion and the major oxidized products of the soHd particles used in ducted rockets. 

The rhythm of heart contractions depends on many parameters condition of pacemaker cells and the conduction system, myocardial blood flow, and other factors consequently, arrhythmia can originate for different reasons that are caused by disruptions in electrical impulse generation or conduction. They can be caused by heart disease, myocardial ischemia, electrolytic and acid-base changes, heart innervation problems, intoxication of the organism, and so on. 

Uncontrolled CHF cardiogenic shock sinoatrial, AV and intraventricular disorders of impulse generation or conduction (eg, sick sinus node syndrome, AV block) in the absence of an artificial pacemaker bradycardia marked hypotension bronchospastic disorders manifest electrolyte imbalance hypersensitivity to the drug. 

Cardiac arrhythmias result from alterations in the orderly sequence of depolarization followed by repolarization in the heart. Cardiac arrhythmias may result in alterations in heart rate or rhythm and arise from alterations in impulse generation or conduction. The clinical implications of disordered cardiac activation range from asymptomatic palpitations to lethal arrhythmia. 

Contraindications Bradycardia bronchospastic disorders cardiogenic shock electrolyte imbalance sinoatrial, AV, and intraventricular impulse generation or conduction disorders, such as sick sinus syndrome or AV block, without the presence of a pacemaker uncontrolled CHF... 

Historically and romantically, the heartbeat is recognized as the quintessential hallmark of life. Normally, the heart beats at 60-100 beats per minute (bpm), with each beat yielding a ventricular contraction that ejects blood out to the body. Each heartbeat is an electrical event that originates from a collection of electrically excitable cells within the heart called the sinoatrial node (SA), anatomically located at the upper pole of the heart. The sinoatrial node is the primary pacemaker of the heart. The electrical impulse generated in the sinoatrial node spreads rapidly downward from the atria chambers of the heart and reaches the atrioventricular node (AV), a collection of electrically excitable cells that constitutes the electrical interface between the atria and ventricles of the heart. Erom the AV node, the impulse propagates throughout the ventricles via an electrical conduction system referred to as the His-Purkinje system. The electrical transmission... 

This type of detonator is designed to deliver a detonating impulse when acted upon by a heat impulse or a detonating impulse generated by a previous element. In the latter case it serves for boostering the detonating impulse. Heat impulses may result from the flash of a delay element in delay type fuzes or the flash from a primer in instantaneous type fuzes. When initiation results from the functioning of a previous detonator, the flash type detonator usually serves in the capacity of a relay where the gap over which the detonation must be transmitted is too... 

Tachyarrhythmias (sinus rate more than 100 per minute) are produced by a disturbances of impulse generation or of impulse conduction in the heart. Tachyarrhythmias due to disturbed impulse formation are associated with irregular and rhythmic discharge from ectopic pacemaker activity in areas of the heart other than the SA node. The characteristic of myocardial cells, which enables them to generate spontaneous depolarization, is called automaticity. 

Cardiac muscle is highly dependent on calcium influx for normal function. Impulse generation in the sinoatrial node and conduction in the atrioventricular node—so-called slow-response, or calcium-dependent, action potentials—may be reduced or blocked by all of the calcium channel blockers. Excitation-contraction coupling in all cardiac cells requires calcium influx, so these drugs reduce cardiac contractility in a dose-dependent fashion. In some cases, cardiac output may also decrease. This reduction in cardiac mechanical function is another mechanism by which the calcium channel blockers can reduce the oxygen requirement in patients with angina. 

Fig 9 presents static and dynamic impulses of spherical and cylindrical EO FAE s and compares them (on an equal energy basis) with Pentolite and point source detonations. Note the greatly enhanced impulses generated by cylindrical FAE s, as well as the greater impulses of FAE s vs Pentolite or point source detonation for R/Rc< 1.5... 

Some homeopathic remedies like polycrests produce a wide variety of symptoms common to many diseases. They may act through multifunctional neural networks. For this, treatment of a chronic disease with a high potency of a polycrest sometimes results in brief recapitulation of past diseases, particularly their pain components which are connected with the same multifunctional neural network. According to the neuromatrix theory pain is a multidimensional experience produced by characteristic neurosignature patterns of nerve impulses generated by a widely distributed neural network. The neuromatrix concept fits in with the holistic approach of homeopathy. 

Abnormal impulse generation. The normal automatic rhythm of the cardiac pacemaker cells has been disrupted. Injury and disease may directly render the SA and AV cells incapable of maintaining normal rhythm. Also, cells that do not normally control cardiac rhythm may begin to compete with pacemaker cells, thus creating multiple areas of automaticity. 

Simultaneous abnormalities of impulse generation and conduction. A combination of both previously listed factors may cause cardiac arrhythmias. 

---