Autonomic nervous system cardiac effects

The hypothalamus plays a particularly important role in regulating the autonomic nervous system, which innervates cardiac muscle, smooth muscle, and glands. Many of these effects involve ascending or descending... 

Figure 15.4 Effects of the autonomic nervous system on mean arterial pressure. The baroreceptors, chemoreceptors, and low-pressure receptors provide neural input to the vasomotor center in the brainstem. The vasomotor center integrates this input and determines the degree of discharge by the sympathetic and parasympathetic nervous systems to the cardiovascular system. Cardiac output and total peripheral resistance are adjusted so as to maintain mean arterial pressure within the normal range.

Their efficacy in many illnesses is explained by the competitive binding of )3-adrenore-ceptors in the autonomic nervous system by basically any of the employed drags of the l-aryloxy-3-aminopropanol-2 class, which result in reduction of heart rate and strength of cardiac beats, slowing of atrioventricular conductivity, reduction of the level of renin in the plasma, and reduction of blood pressure. The main effects of 8-adrenoblockers are expressed at the level of the vasomotor center in the hypothalamus, which result in a slowing of the release of sympathetic, tonic impulses. Included in the main group of... 

The cardiovascular effects of local anesthetics result in part from direct effects of these drugs on the cardiac and smooth muscle membranes and from indirect effects on the autonomic nervous system. As described in Chapter 14, local anesthetics block cardiac sodium channels and thus depress abnormal cardiac pacemaker activity, excitability, and conduction. At extremely high concentrations, local anesthetics can also block calcium channels. With the notable exception of cocaine, local anesthetics also depress myocardial contractility and produce direct arteriolar dilation, leading to systemic hypotension. Cardiovascular collapse is rare, but has been reported after large doses of bupivacaine and ropivacaine have been inadvertently administered into the intravascular space. 

In addition to the modulators of the autonomic nervous system, angiotensin II was found to be effective in regulating cardiac gap junction conductance. In adult ventricular cell pairs De Mello [1992] observed a 55% reduction in gap junction conductance gj within 20 s following the administration of... 

Agelink MW, Klimke A, Cordes J, Sanner D, Kavuk I, Malessa R, Klieser E, Baumann B (2004) A functional-structural model to understand cardiac autonomic nervous system (ANS) dysregulation in affective illness and to elucidate the ANS effects of antidepres-sive treatment. Eur J Med Res 9 37-50... 

From the influence of the autonomic nervous system it follows that all sympatholytic or sympathomimetic and parasympatholytic or parasympathomimetic drugs can produce corresponding effects on cardiac performance. These possibilities are exploited therapeutically for instance, p-blockers for suppressing excessive sympathetic drive (p. 96) ipratropium for treating sinus bradycardia (p. 108). An unwanted activation of the sympathetic system can result from anxiety, pain, and other emotional stress. In these cases, the heart can be protected from harmful stimulation by psychopharmaceuticals such as benzodiazepines (diazepam and others important in myocardial infarction). 

The authors reviewed the biphasic effect of marijuana on the autonomic nervous system. At low to moderate doses it causes increased sympathetic activity, producing a tachycardia and increase in cardiac output blood pressure therefore increases. At high doses it causes increased parasympathetic activity, leading to bradycardia and hypotension. They thought that this patient most probably had adrenergic atrial flutter. 

Cardiovascular system. Both caffeine and theophylline directly stimulate the myocardium and cause increased cardiac output, tachycardia and sometimes ectopic beats and palpitations. This effect occurs almost at once after i.v. injection and lasts half an hour. Theophylline contributes usefuUy to the relief of acute left ventricular failure. There is peripheral (but not cerebral) vasodilatation due to a direct action of the drugs on the blood vessels, but stimulation of the vasomotor centre tends to counter this. Changes in the blood pressure are therefore somewhat unpredictable, but caffeine 250 mg (single dose) usually causes a transient rise of blood pressure of about 14/10 mmHg in occasional coffee drinkers (but has no additional effect in habitual drinkers) this effect can be used advantageously in patients with autonomic nervous system failure who experience postprandial hypotension (2 cups of coffee with breakfast may suffice for the day). In occasional coffee drinkers 2 cups of coffee (about 160 mg caffeine) per day raise blood pressure by 5/4 mmHg. Increased coronary artery blood flow may occur but increased cardiac work counterbalances this in angina pectoris. 

Parkinson-like effects and acute dystonias may be seen. Central nervous system (CNS) effects include somnolence and seizure activity, as well as a lack of core temperature regulation due to hypothalamic effects. Autonomic effects include dry mouth, blurred vision, and urinary retention, coupled with cardiovascular effects such as tachycardia, cardiac arrhythmias, and hypotension. 

Carbon dioxide is a rapid, potent stimulus to ventilation. Inhalation of 10% CO can produce minute volumes of 75 L/min in normal individuals. Carbon dioxide acts at multiple sites to stimulate ventilation. Elevated Pco causes bronchodilation, whereas hypocarbia causes constriction of airway smooth muscle these responses may play a role in matching pulmonary ventilation and perfusion. Circulatory effects of CO result from the combination of direct local effects and centrally mediated effects on the autonomic nervous system. The direct effects are diminished contractility of the heart and vascular smooth muscle (vasodilation). The indirect effects result from the capacity of CO to activate the sympathetic nervous system these indirect effects generally oppose the local effects ofCO. Thus, the balance of opposing local and sympathetic effects determines the total circulatory response to CO. The net effect of CO inhalation is an increase in cardiac output, heart rate, and blood pressure. In blood vessels, however, the direct vasodilating actions of carbon dioxide appear more important, and total peripheral resistance decreases when the Pco is increased CO also is a potent coronary vasodilator. Cardiac arrhythmias associated with increased Pco are due to the release of catecholamines. 

The heart is innervated by both sympathetic and parasympathetic nerve fibers of the autonomic nervous system. Although the heart can generate its own heartbeat independently of nervous control, stress, exercise, and physical trauma make it advantageous to adjust cardiac contraction to meet the needs at the time. Thus, the cardiovascular control system (Figure 6.20.5), which is located in the brain, controls the contractility of the myocardium (the muscle of the heart), and produces both inotrophic (force of contraction) and chronotrophic (rate of contraction) effects. 

Fetotoxicity Cocaine exposure in utero may have a direct effect on autonomic nervous system regulation, cardiac control mechanisms, and cardiovascular functioning in neonates [33 ]. In 21 prenatally cocaine-exposed infants and 23 non-exposed controls, studied within 120 hours of birth, there was a positive interaction between prenatal cocaine exposure and orthostatic stress. Whereas both exposed and non-exposed infants had increased heart rates and heart rate variability, the responses of the exposed... 

The autonomic nervous system guides the electrical and mechanical functions of the heart. The heart is innervated by both the sympathehc and parasympathetic systems, which have opposite effects and are activated reciprocally. They play important roles in arrhythmia susceptibility. Sympathetic shmulation originates from the intermediolateral column of the thoracic spinal cord. Its neurotransmitter, norepinephrine, is released from neurons of postganglionic fibers of stellate ganglia and epinephrine is released from the adrenal medulla. Both of these act on cardiac p-adrenergic receptors. Sympathetic nerves are predominantly on... 

Zipes DP, Miyazaki T. The autonomic nervous system and the heart basis for understanding interaction and effects on arrhythmia development. In Zipes DP, Jalife J, eds. Cardiac Electrophysiology From Cell to Bedside. Philadelphia WB Saunders, 1990. 

E. The effect of ganglionic blockade depends upon the predominant autonomic tone exerted within various organ systems. Since the activity of the parasympathetic nervous system predominates in the eye, the effect of ganglionic blockade is mydriasis, not miosis. Similarly, stimulation of the genital tract and urinary retention would be decreased. Since sympathetic nervous system activity predominates in blood vessels and the ventricles, vasodilation and a decreased cardiac output would follow ganglionic blockade. 

In humans, a prominent effect of cocaine consists in increased vigilance and elevated mood. While cocaine itself is not used clinically, several catecholamine and serotonin reuptake blockers are used as antidepressants. Imipramine (Figure 10.13) is a classic but not so very specific in addition to inhibiting the reuptake of serotonin and of norepinephrine, it also has antihistaminic and antimuscarinic activity. This will lead to side effects in both the central nervous system and the peripheral autonomic system. A prominent one is the causation or deterioration of cardiac arrhythmias due to its antimuscarinic action. 

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