Heart rate parasympathetic nervous system

PAM chloride - 2-pralidoxime chloride. See oxime, parasympathetic nervous system -the part of the autonomic nervous system that decreases pupil size, heart rate, and blood pressure and increases functions, such as secretion of saliva, tears, and perspiration. 

Figure 15.5 Effects of sympathetic and parasympathetic nervous activity on mean arterial pressure. The parasympathetic nervous system innervates the heart and therefore influences heart rate and cardiac output. The sympathetic nervous system innervates the heart and veins and thus influences cardiac output. This system also innervates the arterioles and therefore influences total peripheral resistance. The resulting changes in cardiac output and total peripheral resistance regulate mean arterial pressure.

Perhaps the most prominent and well-studied class of synthetic poisons are so-called cholinesterase inhibitors. Cholinesterases are important enzymes that act on compounds involved in nerve impulse transmission - the neurotransmitters (see the later section on neurotoxicity for more details). A compound called acetylcholine is one such neurotransmitter, and its concentration at certain junctions in the nervous system, and between the nervous system and the muscles, is controlled by the enzyme acetylcholinesterase the enzyme causes its conversion, by hydrolysis, to inactive products. Any chemical that can interact with acetylcholinesterase and inhibit its enzymatic activity can cause the level of acetylcholine at these critical junctions to increase, and lead to excessive neurological stimulation at these cholinergic junctions. Typical early symptoms of cholinergic poisoning are bradycardia (slowing of heart rate), diarrhea, excessive urination, lacrimation, and salivation (all symptoms of an effect on the parasympathetic nervous system). When overstimulation occurs at the so-called neuromuscular junctions the results are tremors and, at sufficiently high doses, paralysis and death. 

Autonomic and hormonal control of cardiovascular function. Note that two feedback loops are present the autonomic nervous system loop and the hormonal loop. The sympathetic nervous system directly influences four major variables peripheral vascular resistance, heart rate, force, and venous tone. It also directly modulates renin production (not shown). The parasympathetic nervous system directly influences heart rate. In addition to its role in stimulating aldosterone secretion, angiotensin II directly increases peripheral vascular resistance and facilitates sympathetic effects (not shown). The net feedback effect of each loop is to compensate for changes in arterial blood pressure. Thus, decreased blood pressure due to blood loss would evoke increased sympathetic outflow and renin release. Conversely, elevated pressure due to the administration of a vasoconstrictor drug would cause reduced sympathetic outflow, reduced renin release, and increased parasympathetic (vagal) outflow. 

Recall that scopolamine, an ingredient in henbane, blocks muscarinic acetylcholine receptors. This blockade essentially removes the influence of the parasympathetic nervous system on the body. In the absence of this influence, the balance of forces is upset and the sympathetic nervous system gains the upper hand thus, your heart rate increases, your pupils dilate, salivation stops, your ability to urinate is impaired, and you become constipated overall, things get very uncomfortable. But none of this is directly lethal (unless the constipation makes one commit suicide). If you do die from an overdose of henbane, it is believed to result from either a complex series of events in your brain that lead to the loss of control of your diaphragm, causing death from asphyxiation, or from cardiac arrest. This is why the deadly nightshade is so deadly and how Shakespeare chose to kill King Hamlet with henbane. 

Neural components that participate in the regulation of coronary blood flow include the sympathetic nervous system, the parasympathetic nervous system, coronary reflexes, and possibly, central control of coronary blood flow. Within the sympathetic system, stimulation of the stellate ganglion elicits coronary vasodilation, which is associated with tachycardia and enhanced contractility. This indirect coronary vasodilation is secondary to increased MVO2 related to increased heart rate, contractihty, and aortic pressure and occurs following stellate stimulation. The direct effect of the sympathetic system is a 1-mediated vasoconstriction at rest and during exercise. Other receptor types, 2 and have little influence on tone, whereas /32-stimulation produces a modest vasodUatory effect. Although coronary atherosclerosis may decrease blood flow secondary to obstruction, severe coronary atherosclerosis and obstruction also may increase the sensitivity of coronary arteries to the effects of aj-stimulation and vasoconstriction. 

Autonomic Nervous System that part of the nervous system that governs involuntary functions, such as heart rate, reflexes, and breathing. It consists of the sympathetic and parasympathetic nervous system. 

Both the sympathetic and parasympathetic nervous systems innervate oigans within the body. The sympathetic system excites the oigan while the parasympathetic system inhibits the organ. For example, the sympathetic system increases the heart rate while the parasympathetic system decreases the heart rate. 

Dmgs can affect cardiac contraction by stimulating or inhibiting the heart. Contractions are also influenced by the autonomic nervous system (ANS). The sympathetic nervous system increases heart rate and the parasympathetic nervous system decreases heart rate. (See Chapter 15.)... 

Heart rate (HR), heart rate variability and blood pressure are regulated, in part, by the sympathetic and parasympathetic nervous systems. Changes in one or more may inerease the risk of cardiovascular events (e.g. arrhythmias, myocardial infarction). Decreases in heart rate variability have been associated with cardiovaseular mortality/morbidity in older adults and those with significant heart disease. Eine particles in ambient concentrations have recently been implicated in deereases of heart rate variability (Timonen et al. 2006), increased risk of arrhythmias (Metzger et al. 2004 Lanki et al. 2006) and increased blood pressure (Timonen et al. 2006) in particular in older subject with compromised health. Additionally inhaled particles seem to enhance blood coagulation (Riickerl et al. 2007a, b). 

Baroreceptors monitor the pressure in the carotid sinuses, the aortic arch, and other large systemic arteries and increase their firing rate when the pressure increases. Their response is nonlinear and depends on whether they are exposed to mean pressure only, pulsatile pressure only, or a combination of both. Katona et al. [1967] developed a model of baroreceptor feedback that has become the basis for many CV neural control models. The output of the baroreceptor model is often passed through a low pass filter representing the CNS and then mapped back to changes in heart rate, contractility, vascular resistances, and vascular unstressed volumes through the sympathetic and parasympathetic nervous systems (Figure 10.8), for example, see Yu et al. [1990]. 

Further, heart rate does not provide diagnostic information about the soitree of mental workload. O Donnell and Eggemeier (1986) define diagnosticity as the "capability of a technique to discriminate the amount of workload imposed on different operator capacities or resources" (p. 42-3). Backs (1995) offers two reasons for heart rate s limited diagnostic utility. First, heart rate is affected by physical derrtands that may be independent of mental workload. Second, heart rate does not provide information about the separation of the sympathetic and parasympathetic nervous system activity. 

A multivariate approach of analyzing the psychophysiological measures obtained from heart period has been proposed as a method for obtaining cardiac autonomic information (Backs, 1995,1998). The multivariate approach attempts to improve the sensitivity and diagnosticity of heart rate by identifying the neurogenic activity of the sympathetic and parasympathetic nervous systems responsible for the observed heart rate in a task. Principal components analysis (PCA) was used in the present study to extract information about the sympathetic and parasympathetic nervous systems common to RSA, low-frequency HRV, residual heart period, and heart period. Details of how the components were derived are presented in the Method section. 

Cardiac autonomic (parasympathetic) nervous system function respiratory variation in heart rate (R-R interval) measured in ECG recordings (12 standard leads) in supine position during normal, deep breathing... 

Cardiac variability-vagal tone Changes in heart rate as a function of stimulation are related to changes in respiratory sinus arrhythmia that reflect changes in the parasympathetic nervous system (Posner, 2001)... 

Humans exposed to cedrol fumes showed significant decreases in heart rate, diastolic and systolic blood pressure, and respiratory rate. Tests indicted that cedrol inhalation also caused a reduction in sympathetic and an increase in parasympathetic nervous system activity, results supporting the alleged relaxant effect of cedar oU. In addition, a decrease in nonrapid eye movement sleep latency was found in humans exposed to cedar essence. ... 

---