A view of the cardiac rhythm control: Intrinsic regulation

Abstract

by Nozdrachev, Kotel'nikov, Mazhara, Naumov. † Mechanisms regulating the heart rate (HR) continue to be the focus of various studies, which is due to the development of new noninvasive methods for assessing the state of the autonomic nervous system. One such method is spectral analysis of HR variability. It should be noted that the mechanisms responsible for oscillatory modulation of the cardiac rhythm and, consequently, for its spectrum are still obscure to a great extent. To gain a better understanding of them, it is necessary to elucidate the mechanisms controlling the HR. The HR control involves the mechanisms regulating the blood pressure, cardiac output, and total peripheral resistance. However, these issues have been considered in numerous original papers and reviews and are beyond the scope of this work.It is commonly accepted that the HR is determined by the rhythmic activity of pacemaker cells of the sinoatrial node. These cells are capable of spontaneous diastolic depolarization of the membrane potential. Comprehension of the mechanisms of diastolic depolarization is of immense importance for a better understanding of the neural and humoral regulation of the HR.Quantitative studies of ionic currents in pacemaker cells and mathematical models based on their results † Deceased. made it possible to assume the following scenario for rhythm generation [1,2].It is known that the algebraic sum of inward and outward ionic currents across the cell membrane is zero at physiological rest. This is the condition for constancy of the resting potential. Inward currents are carried mostly by sodium ions and, to a lesser extent, by calcium ions. Outward currents are due to potassium ions. A change in their balance to a prevalence of inward currents over outward currents leads to depolarization and, consequently, allows autorhythmic activity. At least two conditions are necessary for this activity to be sustained: (1) at the resting potential, the net inward current exceeds the net outward current by a value sufficient for initiating regenerative depolarization, and (2) at the action potential, the outward current increases to a level sufficient for membrane repolarization such that it abolishes the inactivation of channels carrying the inward current and inactivates channels carrying the outward current. Condition (1) can be accomplished either by primarily increasing the inward (fast or slow) current or by primarily decreasing the outward current. A combination of such changes is also possible. Pacemaker cells employ both of these mechanisms (see below).A specific feature of pacemaker cells of the sinoatrial node is a higher constant background sodium REVIEWS Abstract -Regulation of the cardiac rhythm is intricate and occurs at least at two major levels, intrinsic and extrinsic. In turn, each of these levels can be divided into several sublevels. The factors regulating the cardiac activity eventually affect the duration of spontaneous diastolic depolarization of pacemaker myocytes of the sinoatrial node and, to a ...

Spontaneous myogenic fasciculation associated with the lengthening of cardiac muscle in response to static preloading

“…Myogenic control is the intrinsic autoregulation of cardiac rhythm and is considered to be the first sublevel in the control of cardiac function 1 . Myogenic control has been demonstrated in the autoregulation of the mesenteric, skeletal muscular, cerebral, renal, and coronary circulation systems but rarely in heart muscles.…”