From Big Medical Encyclopedia

INTRACARDIAC PRESSURE — pressure in cardial cavities arising in the course of its rhythmic activity. The size of EL is various for each camera of heart and changes at the different moments of a cardial cycle. It depends on degree of a krovenapolneniye of cameras, sokratitelny function of a myocardium and size of resistance of outflow tracts of blood, and also some other cardial and noncardiac factors — the radius of curvature of cameras of heart, tightness of a connective tissue basis of heart, intrathoracic pressure.

Registration of changes of EL in time in the form of pressure curves in cardial cavities allows to characterize a condition of an endocardiac hemodynamics and blood circulation in general and to obtain necessary information on degree and the nature of disturbances of pumping function of heart at various morbid conditions (see. Blood circulation ).

Change of pressure in an aorta, a left ventricle and the left auricle in the course of a cardial cycle: 1 — the phase of filling caused by an auricular systole; 2 — a phase of asynchronous reduction; 3 — a postsphygmic period; 4 — a sphygmic interval; 5 — the protodiastolic period; 6 — a postsphygmic interval; 7 — a phase of bystry filling; 8 — a phase of slow filling; and, with, x, v and at — waves of intracardiac pressure: and — develops in time of an auricular systole; with — arises at the time of closing of atrioventricular valves; x \it is connected with relaxation of a myocardium of auricles; v \it is caused by inflow of blood from pulmonary and venas cava; at — develops at the beginning of diastolic filling of ventricles. On ordinate axis — the size of pressure. Below — an otmetchik of time.

Most of authors on the pressure curve in an auricle distinguishes three positive waves — and, with and v and two negative waves (collapse) — x and at (fig.). The beginning of a wave and on time matches the middle or the last third of a tooth of P on an ECG. At disturbances of systolic activity of auricles that takes place, e.g., at patients with a ciliary arrhythmia, the wave and on the pressure curve is absent. The wave with arises at the time of closing of atrioventricular valves, i.e. at the beginning of a systole of a ventricle. An origin of a wave with — tolchkoobrazny protrusion of the mitral valve in an auricle at the beginning of isometric contraction of a ventricle. The wave x is connected with pressure decline and on time corresponds to the period of relaxation of a myocardium of an auricle. The main reason for emergence of a wave x increase in volume of auricles owing to relaxation of muscle fibers is considered. During a wave x pressure in an auricle reaches atmospheric or decreases by several millimeters of mercury. Further the wave x is replaced by a wave of v, edges is caused by increase in inflow of blood to auricles from pulmonary and venas cava. The wave at follows after peak of a wave of v and its beginning synchronizes the moment of opening of atrioventricular valves and the beginning of diastolic filling of ventricles. During this period intra atrial pressure decreases in parallel with pressure decrease in a left ventricle to end diastolic pressure (end diastolic pressure — pressure in cavities of ventricles just before closing of atrioventricular valves). The wave at is followed hollow by the increasing part of a curve intra atrial pressure. For filling with blood of the left auricle, resilient-elastic properties to-rogo are higher, than the right auricle, more high pressure is necessary. It agrees to the data which are available in literature obtained at cardiac catheterization of healthy people in the left auricle the average size of a wave and makes 10 — 11 mm of mercury., waves of v — 12 — 14 mm of mercury. Average pressure in the left auricle, equal to the integral size of all fluctuations, is in range of 8 — 9 mm of mercury., in the right auricle — makes 3 mm of mercury.

In experiments it is established that the graph of intra atrial pressure from the volume of filling of auricles keeps linear character to 9 — 11 mm of mercury. At further increase in volume the gain of intra atrial pressure occurs in much bigger degree.

For the analysis of a cardial cycle generally investigate duration of its separate phases and determine the average and maximum speed of change of pressure in cavities of ventricles during the periods of isometric tension and a relaxation. The ventricular systole begins a phase of asynchronous reduction, during a cut there is a consecutive involvement of certain sites of a myocardium of the left and right ventricles in sokratitelny process. In this phase there is a change of a configuration of a cavity of ventricles at insignificant increase in chamber pressure. The postsphygmic period begins with the moment of closing of atrioventricular valves. Raising of a curve of chamber pressure in this phase the most abrupt is also interrupted by a small bend or a jag which reflect opening of the corresponding semi-lunar valves and synchronize the beginning of the period of exile of blood in an aorta or a pulmonary artery. The next period — the period of exile, is subdivided into phases of the maximum and reduced exile. In a phase of the maximum exile, edge normal begins with the moment of opening of the corresponding semi-lunar valves on duration there correspond 1/3 entire periods of exile, 2/3 stroke outputs of blood are thrown out.

The ventricular systole comes to an end with a phase of the reduced exile. During this period pressure in ventricles gradually decreases, reaching the level of pressure in an aorta and a pulmonary artery.

The diastole of ventricles begins the short protodiastolic period which corresponds to time necessary for closing of semi-lunar valves, and usually on a curve of chamber pressure is shown by a separate tooth on the descending knee. In the postsphygmic interval coming from the moment of closing of semi-lunar valves and proceeding before opening of atrioventricular valves there is a bystry decrease in chamber pressure to level atrial. At the time of equalizing of pressure in auricles and ventricles there is an opening of atrioventricular valves and the period of bystry filling of ventricles begins. From this point the form of the curve reflecting change of pressure in a ventricle significantly does not differ from a form of the curve reflecting change of pressure in an auricle. Systolic pressure is on average equal in a right ventricle to 25 mm of mercury., diastolic. — 2 mm of mercury.; in a left ventricle respectively — 120 and 4 mm of mercury.

At clinical assessment of the data obtained by means of a method of a straight line catheterizations of heart (see), increase in final diastolic pressure can serve one of signs of disturbance of a sokratitelny condition of a myocardium in a left ventricle of St. 12 mm of mercury., in right — St. 5 mm of mercury. However these data have no absolute value since the level of final diastolic pressure in ventricles depends on several factors. So, increase final diastoli-cheskogo chamber pressure can be caused by a hypertrophy of a myocardium, increase in the rigidity of its walls caused by increase in resistance of an outflow tract from a ventricle; increase of diastolic filling of ventricles at defect of valves or inborn heart diseases with shunting. Along with it there are numerous clinical observations in which it is shown that the sharp dilatation of a cavity of a ventricle which is combined with the expressed decrease in sokratitelny ability of a myocardium can proceed at normal figures of final diastolic pressure.

Follows from told that predictive value of size of final and diastolic chamber pressure is limited and can matter in combination with other hemodynamic indicators (see. Blood circulation ). The most exact information on a functional condition of the sokratitelny device of a cardiac muscle is given by indicators of speed of shortening of muscle fibers. At the same time it is established that the mechanism of an inotropiya regulating force and speed of reduction of a cardiac muscle in the certain range of change of the loadings shown to a myocardium of a ventricle can realize the influence without change of initial length of muscle fibers. Everything told above formed a basis for introduction to clinical practice of a number of the indicators allowing to estimate directly a sokratitelny condition of a myocardium by results of intra ventricular sounding (an intra systolic indicator, time of tension, etc.)

A number of the additional data allowing to establish closer dependence between the chamber pressure and a condition of a myocardium is received.

It is established that the most exact indicator (index) of sokratitelny ability of a myocardium is the relation of the maximum speed of build-up of pressure in a ventricle in a postsphygmic period to the size of chamber pressure at the time of the maximum speed of its increase. In the conditions of an izovolyumichesky condition of ventricles the speed of shortening of sokratitelny elements of muscle fibers is equal to the speed of lengthening consistently with them the connected elastic (reactive) elements. At the invariable size of the module of elasticity of reactive elements (according to most of authors it is equal to 28) by means of mathematical transformations it is possible to receive the equation of dependence of speed of reduction of myofibrils in an isometric phase of a cardial cycle on the size of chamber pressure Vse = (dp/dt)/(K*P) where Vse — the speed of reduction of myofibrils; To — empirically calculated module of elasticity equal 28; dp/dt — the instantaneous velocity of change of chamber pressure, and P — the size of chamber pressure corresponding to this speed.

Use of computers (at constant registration of size and speed of change of chamber pressure) allows to construct a curve of change of speed of shortening of sokratitelny elements of a myocardium that gives very valuable additional information on a condition of a cardiac muscle.

For assessment of biomechanics of heart knowledge of the nature of diastolic relaxation of a myocardium is extremely important. It agrees biophysical, change of systolic tension of myofibrils by a diastolic relaxation is provided to ideas of muscular contraction with the active, connected with energy consumption release of myofibrils from calcium ions. The maximum speed of a diastolic relaxation of ventricles can serve as an efficiency factor of functioning of the intracellular system which is carrying out binding of calcium.

For receiving rather complete idea of a condition of an endocardiac hemodynamics it is necessary to know the following indicators: the size of each wave and average pressure in auricles, the maximal systolic pressure, the minimal diastolic pressure in ventricles and final diastolic pressure in them.

In a wedge, practice measurement and registration of EL are applied most often to differential diagnosis heart diseases (see), estimates hypertensia of a small circle of blood circulation (see), identifications of early or latent stages cardiovascular insufficiency (see) various origins.

Devices for measurement of intracardiac pressure represent manometers (electromanometers) which sensitive element directly perceives changes of pressure in the explored area. For this purpose it or is reported through a catheter with the studied cavity, or directly entered into this cavity (see. Catheterization of heart ). Devices for measurement of EL belong to devices of direct measurement of blood pressure (see. Heart , tool methods of a research). The measured size usually is the instantaneous value of pressure in a certain point, or an average (an average dynamic), or the maximum and minimum values of pressure during a cardial cycle.

The optical manometer of Frank, with the help to-rogo Franck (O. of Frank) was the first device allowing to register well EL in 1906 — 1910 received the first records of pressure in cardial cavities. By means of this device of Uiggers (S. of Wiggers, 1921) wrote down EL and pressure in the main vessels that gave it the chance in details to describe structure of a cardial cycle. By means of the optical manometer developed in 1934 by W. Hamilton, A. Cournand wrote down EL at the person (A. Cournand suggested to use a catheter for measurement of EL).

From 40th years for measurement of EL electronic manometers (electromanometers) are used: capacity Lille (Lilly, 1942) and Hansen (Hansen, 1949), manometers of resistance of Lambert and Wood (E. Lambert, E. H. Wood, 1947), etc. They differ from only optical in the fact that moving to them of a sensitive element (membrane) will be transformed to electric indicators. Use of electronics allowed to receive tiny designs of manometrical converters. Vetterrer (Wetterrer, 1943), Gower and Dzhaynepp (O. of H. Gauer, Gienapp, 1950), A. G. Semenov (1956) developed the sensors entered into an organism to dia. 2 — 3 mm.

Devices for measurement of EL consist of two main components: measuring part (electromanometer) and calibration and flowing system. The first perceives, measures and will transform a signal for giving on a recorder. The second serves for filling of all of the communications containing fluid medium with normal saline solution, calibration of the electromanometer, for creation of a direct current of liquid during the periods between measurements, functioning at the same time as infusional system.

The electromanometer consists of three consistently connected links: a link of transfer of pressure — a catheter (or the needle connected to a catheter), the measuring instrument of pressure and the functional converter.

The measuring instrument of pressure will transform the signal having physical. a form of pressure, in electric, convenient for transfer on the functional converter or directly on registrar. An entrance element of the measuring instrument is the sensitive membrane answering with deformation change of pressure.

The functional converter is entered in need of high-quality transformation of a signal with the purpose to give it new information sense, napr, for differentiation or integration (determination of average dynamic pressure), finding of the maximum or minimum values. As registrar usually serves the multichannel electrocardiograph.

See also Blood pressure .

Bibliography The Volynsk Yu. D. Izmeneniya of an endocardiac hemodynamics at heart diseases, L., 1969; Zorin A. B., Kolesov E. V. and Silin V. A. Tool diagnostic methods of heart diseases and vessels, L., 1972; M e sh and l to and N of E. H. Sounding and contrast research of heart and main vessels, M., 1954; Petrosyan Yu. S. of Kateterization of heart at rheumatic defects, M., 1969; F. G. Corners, Nek l of experts Yu. F. and Gerasin V. A. Kateterization of heart and the selection angiocardiography, L., 1974, bibliogr.; Uiggers K. D. Dinamika of blood circulation, the lane with English, M., 1957; Cardiac mechanics, Physiological, clinical and mathematical considerations, ed. by S. Mirsky, a. o., N. Y., 1974; Zimmermann H. A. Intravascular catheterization, Springfield, 1966.

A. A. Abinder, S. M. Kamenker; E. K. Lukyanov (tekhn.).