Heart rate, stimulation

The CNS effects of CG (C) are also due to binding to Na /K -ATPases. Enhanced vagal nerve activity causes a decrease in sinoatrial beating rate and velocity of atrioventricular conduction. In patients with heart failure, improved circulation also contributes to the reduction in heart rate. Stimulation of the Lullmann, Color Atlas of Pharmacology 2000 Thieme All rights reserved. Usage subject to terms and conditions of license. 

Dreyer AC, Offermeier J. The influence of desipramine on the blood pressure elevation and heart rate stimulation of levonordefrin and felypressin alcme and in the resence of local anr aesthetics. J Dent Assoc S Afr ( 9Z6) 41,615-18. 

It has also been shown that intrathecally injected T influences body temperature regulation in dogs and that intrathecally administered T3 in rats causes greater heart rate stimulation than intravenous 13. These studies indicate that thyroid hormones can regulate certain body functions by effects exerted at specific sites within the brain in addition to direct effects on the organs themselves and that these sites can be approached through the CSF. 

M. Goldman, M.B. Dratman, F.L. Crutchfield, A.S. Jennings, J.A. Maru-niak and R. Gibbons, Intrathecal triiodothyronine administration causes greater heart rate stimulation than intravenously delivered hormone, J Clin Invest 76 1622-1625 (1985). 

Another experimental result compatible with direct effects of the hormone on nerve cell activity comes from studies showing earlier heart rate stimulating properties of intrathecally as compared with intravenously delivered T3 to hypothyroid rats (Fig. 7). Thus, though sparse, presently available functional results demonstrate that thyroid hormones play a continuing role in adult brain, which may be synaptically mediated. 

Isoproterenol. Isoproterenol hydrochloride is an nonselective P-adrenoceptor agonist that is chemically related to NE. It mimics the effects of stimulation of the sympathetic innervation to the heart which are mediated by NE. It increases heart rate by increasing automaticity of the SA and AV nodes by increasing the rate of phase 4 diastoHc depolarization. It is used in the treatment of acute heart block and supraventricular bradyarrhythmias, although use of atropine is safer for bradyarrhythmias foUowing MI (86). 

Although blood pressure control follows Ohm s law and seems to be simple, it underlies a complex circuit of interrelated systems. Hence, numerous physiologic systems that have pleiotropic effects and interact in complex fashion have been found to modulate blood pressure. Because of their number and complexity it is beyond the scope of the current account to cover all mechanisms and feedback circuits involved in blood pressure control. Rather, an overview of the clinically most relevant ones is presented. These systems include the heart, the blood vessels, the extracellular volume, the kidneys, the nervous system, a variety of humoral factors, and molecular events at the cellular level. They are intertwined to maintain adequate tissue perfusion and nutrition. Normal blood pressure control can be related to cardiac output and the total peripheral resistance. The stroke volume and the heart rate determine cardiac output. Each cycle of cardiac contraction propels a bolus of about 70 ml blood into the systemic arterial system. As one example of the interaction of these multiple systems, the stroke volume is dependent in part on intravascular volume regulated by the kidneys as well as on myocardial contractility. The latter is, in turn, a complex function involving sympathetic and parasympathetic control of heart rate intrinsic activity of the cardiac conduction system complex membrane transport and cellular events requiring influx of calcium, which lead to myocardial fibre shortening and relaxation and affects the humoral substances (e.g., catecholamines) in stimulation heart rate and myocardial fibre tension. 

Hi-receptors in the adrenal medulla stimulates the release of the two catecholamines noradrenaline and adrenaline as well as enkephalins. In the heart, histamine produces negative inotropic effects via Hr receptor stimulation, but these are normally masked by the positive effects of H2-receptor stimulation on heart rate and force of contraction. Histamine Hi-receptors are widely distributed in human brain and highest densities are found in neocortex, hippocampus, nucleus accumbens, thalamus and posterior hypothalamus where they predominantly excite neuronal activity. Histamine Hrreceptor stimulation can also activate peripheral sensory nerve endings leading to itching and a surrounding vasodilatation ( flare ) due to an axonal reflex and the consequent release of peptide neurotransmitters from collateral nerve endings. 

We examined the effects of selective activation of histamine Hj receptors on coronary hemodynamics in two groups patients with atypical chest pain and normal coronary arteries, and patients with vasospastic angina [48]. Selective Hj receptor stimulation was achieved by infusing histamine intravenously (0.5 pg/kg/min) for 5 min after pretreatment with cimetidine to antagonize the H2 receptors. Heart rate was kept constant (100 beats/min) by coronary sinus pacing. 

True. Caffeine is a mild stimulant that in moderate dosage does little harm and provides a lift . When taken in excess it can have an adverse effect on heart rate. 

Drugs related to PCP are known to alter the carotid sinus reflex. Mechanical stimulation of the carotid sinus in the neck normally results in a slowing of heart rate and a decrease in blood pressure. Carotid sinus stimulation, coupled with the effects of PCP on blood vessels, might result in a marked fall in the blood pressure that could lead, ultimately, to death. Individuals intoxicated with PCP may be at a higher risk to complications of carotid compression neck holds. Hence, additional cases would be expected to become medicolegal issues. 

Traditional CNS stimulants have the potential to increase blood pressure and heart rate when used long term. In addition, excessive CNS stimulation can cause tremors and tics and can carry over into evening hours, where initiation of normal nighttime sleep can be disrupted. Caution should be used in patients with underlying cardiovascular or cerebrovascular disease and in patients with a history of seizures because stimulants may lower the seizure threshold. 

The most common physiological effects of placebos are those that are associated with changes in subjective experience. When placebo stimulants make people feel energized and alert, for example, they also increase their blood pressure and heart rate,... 

Although placebo effects are generally referred to as nonspecific, there is also a sense in which they are very specific. The effect of the placebo is specific to the beliefs that people have about the substance they are ingesting. Placebo morphine, for example, reduces pain, whereas placebo antidepressants reduce depression. Even the side effects that people report when given a placebo tend to be the same side effects that are produced by the real drug.12 In other words, the effect of a placebo is specific to the effect that the person expects it to have. When given placebo stimulants like decaffeinated coffee (presented as regular coffee), people feel more alert, and their heart rate and... 

An example of this type of reflex is the baroreceptor reflex (see Figure 1.2). Baroreceptors located in some of the major systemic arteries are sensory receptors that monitor blood pressure. If blood pressure decreases, the number of sensory impulses sent from the baroreceptors to the cardiovascular control center in the brainstem also decreases. As a result of this change in baroreceptor stimulation and sensory input to the brainstem, ANS discharge to the heart and blood vessels is adjusted to increase heart rate and vascular resistance so that blood pressure increases to its normal value. 

---