The heart is a muscular organ with its own rhythm regulation system. It is represented by pacemaker cells that regulate the activity of the heart muscle. It is influenced by medicinal substances and mediators produced by the adrenal glands. This action is described as a positive or negative inotropic, chronotropic, dromotropic or bathmotropic effect.
Bathmotropy and chronotropy of the heart
Bathmotropy is the influence of a certain factor on cardiac activity in such a way that the excitability of pacemaker cells changes as a result. The term "excitability" refers to the ability to generate an action potential. Depression of excitability is an increase in the threshold, after which an action potential is formed. Stimulation of the excitability of the heart is a decrease in the threshold value of the membrane potential, above which rapid depolarization occurs. This process is called the appearance of an action potential. ATIn general, the term "batmotropic effect" means a change in myocardial excitability.
Chronotropic effect in myocardial electrophysiology is the frequency with which the heart rhythm is formed. A positive chronotropic effect mediates an increase in the frequency of impulse generation, that is, the action potential. Negative chronotropy - a decrease in the frequency of the rhythm. Impulse generation is the process of generating an action potential, which forms an “order” to contract. This means that the frequency of the rhythm on a he althy heart means the same as the frequency of contractions.
Differences between concepts
The terms "chronotropic" and "batmotropic effect" at first seem almost identical. But there is a fundamental difference between them, which should be explained by two theses. The essence of the first is that an increase in the frequency of heart contractions can be achieved without a decrease in the excitability threshold of the pacemaker. In the same way, slowing down the contraction does not mean at all that for this it is necessary to increase the excitability threshold, that is, to provide a negative batmotropic effect.
The second thesis boils down to the fact that a decrease in the excitability of the heart always means a decrease in the rhythm. An increase in the excitability of the heart also means that the frequency of the rhythm will increase significantly. Excitability (batmotropia) is only the ability to generate an action potential. And the frequency, that is, the chronotropy of the heart, is a measure of the quantitativedefinitions in rhythm generation. In cardiac physiology, frequency follows excitability. The higher the excitability of the myocardium, the higher the frequency of the rhythm.
Inotropia and dromotropia of the heart
In myocardial physiology there are such concepts as inotropic and dromotropic effects. Inotropy is the force of muscle cell contraction, and dromotropy is conductivity, that is, the speed of impulse propagation along the conducting system or along nexus contacts between myocardial cells. The physiology of the heart is such that the higher the force of contraction of the heart, the greater the volume of blood ejected from the left ventricle. The higher the frequency of full contractions, the more often the body receives portions of oxygenated blood.
Physiology of cardiac activity
Conditions for stimulation of cardiac activity are created due to the presence of batmotropic and dromotropic effects. That is, with an increase in myocardial excitability and with acceleration of conduction, an increase in the frequency of heart contractions and their strength can be achieved. In a situation where the body needs to quickly mobilize its functionality, for example, before physical activity and during it, the physiological processes of regulation of cardiac activity are enhanced. It all starts with a positive dromotropic and bathmotropic effect, immediately after which the chronotropic effect of mediators is enhanced. The inotropic mechanism is connected last. The fading of the effects after the cessation of stimulation with catecholamines occurs in the reverse order.
Positive bathmotropy
Positive bathmotropia is such an effect on the cells of the heart, in which their excitability increases. That is, the threshold for generating an action potential is reduced. In other words, a positive bathmotropic effect is a decrease in the value of the membrane potential necessary for the rapid depolarization of the cardiomyocyte plasmolemma. Sympathetic mediators of the nervous system (adrenaline, norepinephrine), as well as xenobiotics (cocaine and amphetamine) are distinguished by this action.
Atropine, epinephrine, norepinephrine, dopamine are used as medicinal substances, which are used to achieve positive bathmotropy, inotropy, chronotropy and dromotropy. This is necessary when resuscitating patients with cardiac arrest. Dopamine and atropine can also be used to stimulate the cardiovascular system in an intensive care setting to maintain an acceptable blood supply.
Negative bathmotropy
In the human body, normally, the negative bathmotropic effect is exerted by the parasympathetic nervous system through the activation of the vagus nerve. Its influence increases the excitability threshold of pacemakers and contractile myocardium, thereby reducing the likelihood of generating an action potential at a time when it is not required to meet the functional needs of the body.
Negative bathmotropy is characteristic of poisonous FOS, and beta-blockers, some antiarrhythmics. In a narrow sense, the negative bathmotropic effect should be considered as a processan increase in the threshold value of the membrane potential, at which fast sodium channels open. This interpretation is appropriate when analyzing the molecular mechanisms of rhythm generation.
