Chronotropic Action

CHRONOTROPIC ACTION, the change in heart rate under the influence of nervous, humoral, and physical effects on the automaticity of the leading part of the heart. In recent years, the term X. d. has also been used to denote effects on the frequency of automatic contractions of the intestine and other hollow organs. In humans and vertebrate animals, positive X. d. on the heart is exerted by accelerator nerves, calcium ions, adrenaline, sympathetic substance, sympathins, and sympathicomimetic poisons, as well as by increased intracardiac and coronary pressure and increased temperature. Negative X. d. is exerted by vagus nerves (especially the right one, since it innervates the sinus node, resp. the AV node of Wenckebach), potassium ions, acetylcholine, vagus substance, vagomimetic poisons, decreased intracardiac and coronary pressure, and decreased temperature. The X. d. of temperature obeys the van't Hoff-Arrhenius law within certain limits. Under prolonged action of the listed agents, X. d. weakens or disappears completely: under certain conditions they produce an inverted X. d. (e.g., upon sudden increase in temperature, there is not acceleration but slowing of the heart rate). Inverted X. d. also results from the action of the same or different agent on a heart previously treated with an agent acting in the opposite direction (e.g., warming a heart perfused with Ringer's solution with excess potassium may produce not acceleration but slowing). All the listed agents possess not only X. d., but also dromo-, iso-, and batmotropic action (see), and therefore the isolation of X. d. is of a conditional character. To obtain a more or less pure chronotropic effects, the agent is applied directly to the leading part (Filter-Blatt method of V. Kisch, thermody). But even under these conditions, X. d. is accompanied by changes in the other properties of the heart, since a change in rhythm, disturbing the established tempo of cyclic processes in the cardiac muscle and in the conducting system, simultaneously changes the amplitude of contractions, excitability, and tone of the cardiac muscle; for this reason, for example, isolated positive X. d. entails negative inotropic and positive tonotropic action, and at very significant increases in rhythm it leads to conduction block. A peculiar form of X. d. is the change in heart rate caused experimentally by rhythmic changes in the environment (e.g., rhythmic faradic stimulation of the vagus nerves or rhythmic increase in intracardiac pressure); under such influence, the heart may assimilate the imposed rhythm.

^A- Zubkov. CHRONOPHOTOGRAPHY, by the definition accepted at the present time, is a series of successive momentary photographs of a moving object taken at short intervals on the same non-displacing photosensitive surface. The same term X. is also used to denote the method of obtaining such photographs. X. is historically the first method of photoregistration of movements. As early as the 1860s, E. Muybridge in the USA produced the first (silhouette) photographs of a galloping horse, which are a prototype of X. Gradually improving his technique and using new inventions in the field of general photography, Muybridge in 1885 prepared and published many brilliant chronophotographic series of photographs of human and horse movements. A similar technique was independently developed in Germany by Anschütz. X. found its greatest development in the 1880s–1890s in the hands of the French scientist E.-J. Marey, who studied the movements of both humans and numerous animal species by this method. Marey photographed walking, running, jumping (see figure), the movements of horses and birds, and photographed fish in specially constructed pools. Marey's assistant L. Bull reached extraordinary perfection in chronophotographic photography of insect flight and, during the World War, bullet flight. In the 1890s, the Leipzig scientists W. Braune and O. Fischer began to photograph not the movements of the whole human body but the movements of long and thin Geissler tubes attached to the body segments. Since these narrow tubes did not obscure each other in successive phases of the photograph, unlike the bulky parts of the body in the previous chronophotographic technique, it became possible to take photographs at a higher frequency, many times per second. The method of Braune and Fischer served as the initial impetus for the development of modern cyclography. After the invention of cinematography in the 1890s, X. as such lost its significance and continued to be used only in rare cases, not for research but for demonstration purposes, due to the great clarity of chronophotographic photographs (e.g., Fremont's work on blacksmiths, 1920s). The frequencies of early X., measured by the number of photographs per second, were usually low, of the order of 5–15 photographs per second. Braune and Fischer worked with a frequency of 26 photographs per second. At the present time, normal cinematography is carried out at frequencies of 16–24 per second, and accelerated (rapid) up to 160–240 per second. The highest frequencies achieved by cinematography to our time are 1,200–1,500 per second (Zeiss). Modern X. reaches much higher frequencies; for example, Bull achieved a frequency of 15,000 photographs per second; according to not entirely reliable information, in Japan it was possible to reach a frequency of 60,000 photographs per second. These ultra-high frequencies no longer have application in physiology and medicine and are used only in ballistic research (study of the flight of bullets and shells).