Page:EB1911 - Volume 27.djvu/960

 occur but little regurgitation of blood into the venous cistern, but the cessation of flow into the auricle during its systole does produce a slight rise of pressure in the cistern, as is shown by tracings taken from the jugular pulse. The function of the auricles is to rapidly complete the filling of the ventricles.

The auriculo-ventricular valves are fioated up! and brought into apposition by eddies set up in the blood whic streams into the ventricles, and close without noise or jar at the moment when the intra-ventricular pressure exceeds in the least that in the auricles. The systole of the ventricles immediately following that of the auricles closes the auriculo-ventricular valves, and as the intra-ventricular pressure rises above that in the pulmonary artery and aorta respectively the semi lunar valves open and the blood is expelled these elastic vessels are in their turn expanded by the expulsive force of the heart so as to receive the bloo The papillary muscles, by contracting synchronouslylwith the muscular wall of the ventricles, pull down and flatten the dome-like diaphragm formed by the closed auriculo-ventricular valves, thus shortening the longitudinal diameter of the ventricles, while at the same time they enlarge the auricles and so help to fill these cavities. The outflow of blood from the ventricles is rapid at first. It becomes slower as the big arteries become distended and the pressure of blood rises within them, and ceases finally when the ressure becomes equal to that in the ventricles. As the outflow diminishes the Semilunar pockets arc filled by eddies of blood, and their thin edges are brought nearer and nearer, until finally they come into a position. The closure is From Further Advances in Physiology, by permission.

. 13.—Diagrammatic representation of the Cardiac Cycle and of the Carotid and Jugular Pulses in relation to standard movements. The scale of abscissae is 1 mm. to sec. S. C. = semilunar valve closure; A. O. = auriculo - ventricular valves open. The broken lines indicate those portions of the respective curves over which there is doubt or controversy.

effected) without jar or noise at the moment when the outflow ceases and the ventricles begin to expand. The heart, as a good pump should, works with the least possible jar. During the contraction of the ventricles blood has been pouring from the veins into the auricles, and directly the ventricular systole ceases the auriculo-ventricular valves open, and the blood begins to fill the expanding ventricular cavities. For a brief moment the ventricles remain dilated and at rest, then the auricles contract again, and the cycle of changes, once more, is repeated. During the first period of ventricular systole—the period of rising tension—all the valves are closed and the ventricle is getting up pressure. This period has been measured and is found to occupy ·02″–·04″. The second period) is that of systolic output, and lasts about ·2″, that is, from the moment when the semi lunar valves open to the moment when they close. The upstroke of the pulse curve taken in the aorta, or in the carotid artery in man, can be taken as marking the moment when the semilunar valves open, while the dicrotic notch on the pulse curve marks their closure. he second sound of the heart occurs immediately after their closure, and can be used to mark the time of this event on the impulse curve.

The intra-ventricular pressure curve may rise or fall during the output period according to the state of the peripheral resistance. If the carotid pulse be recorded s nchronously with the impulse curve, the time relations can be cihtermined for the human heart. The beginning of the upstroke of the impulse curve marks the beginning of systole, that of the pulse curve marks the opening of the semi lunar valves, and the dicrotic notch, which precedes the dicrotic wave, marks the closure of these valves and the end of the output. The first sound of the heart is synchronous' with the upstroke of the impulse curve. The maximal systolic ressure exerted by the he art varies with the degree of diastolic fillin and with the obstruction to outflow. The heart responds to the latter by a greater output of energy, and this it does with little loss in rapidity of action. The tota fluid pressure to which the wall of the heart is submitted rapidly increases as the radii of curvature become greater. Hence the greater ener required of a dilated heart, its tendency to hypertrophy and liability to fail. By its reserve power the heart may throw out three or even six times the volume of the normal output per minute, and may maintain its outlput when the aortic pressure is twice its normal value.

The maximal and minimal pressures have been accurately recorded in the heart by a manometer fitted with a valve arranged so that either only a rise or a fall of pressure is recorded. In the right ventricle of the dog the maximal pressures recorded equalled 35–62 mm. of mercury, in the left ventricle 114–135 mm., in the auricles 2–20 mm. (Michael Jäger, 1795–1838). A negative pressure, of considerable amount but of very fleeting duration, sometimes occurs in the ventricles at the beginning of diastole. This is produced by the elastic rebound of the fleshy columns of the inner wall of the heart, which become pressed together as the blood is wrung out of the ventricular cavities. The entry of the first few drops of blood from the auricles 'abolishes this negative pressure, and it has no important influence on the filling of the heart.

When the ear is applied over the cardiac region of the chest, or a stethoscope is employed, two sounds are heard, the first, heard most intensely over the apex, is a duller and longer sound than the second, which is shorter and sharper and is heard best over the base of the heart. The syllables lub, dupp express fairly well the characters of the two sounds, and the hem the accent is on lub when the stethoscope is over the apex, thus—lúb-dupp—lúb-dup—lúb-dupp, and on the second sound when over the base, thus—lub-dúpp—lub-dúpp—lub-dupp. The sounds of the heart have been successfully recorded by means of the microphone. Hürthle inserted the microphone in the primary circuit of an E. Du Bois-Reymond induction coil, and placed the nerve of a frog-muscle preparation in the secondary circuit. The muscle, being attached to a lever, recorded its contraction on a revolving drum at the moment when the sound of the heart reached the microphone and closed the primary circuit. A capillary electrometer can be inserted in place of the frog-muscle indicator, and the movements of the electrometer photographed on a sensitized plate moved by clockwork (Willem Einthoven). Each sound gives rise to a succession of vibrations of the mercury meniscus of the capillary electrometer. The first sound is formed of many component tones derived from the sudden tension, and consequent vibration, of the ventricular muscle, and of the auriculo-ventricular valves with their Chordae tendineae. The first sound can be resolved by a trained musical ear into two.tones, one deep and the 'other high. The deeper tone alone is heard on the contraction of the excised and bloodless heart, while the higher tone is produced by throwing the auriculo-ventricular valves into tension (John Berry Haycraft). In the cold-blooded animal, such as the turtle, the heart muscle does not become tense rapidly enough to produce a sound (Allen). This sound is not produced by fluid friction as the blood rushes through the arterial orifices, for the velocity of outflow is too small to produce in this way any noise. Nor is it produced by sudden opening of the semi lunar valves, for these open quietly and without jar at the moment when the intra-ventricular pressure rises above that in the aorta.

The second sound of the heart is produced by the tension of the semi lunar valves in the aorta and pulmonary artery at the moment when the ventricles pass into diastole. These valves close without any jar or shock so soon as the arterial pressures rise to the slightest degree above that in the ventricles. In the next moment the ventricles dilate, and the valves, no longer supported on one side, become taut. The elastic vibrations of the walls of the distended arteries probably share in the production of this sound.

When the sounds and the impulse are recorded together the record shows that the first sound begins about 0·01 sec. before the car diagram marks the beginning of systole, and for the first 0·06 sec. of its duration this sound is heard only over the apex. Over the base of the heart the first sound is heard just at the time when the semi lunar valves open and the output begins. The first sound ceases before the ventricular contraction is over, for it is the sudden tension, not the continuance of contraction, that causes it. The beginning of the second sound marks the sudden tension of the semi lunar valves which immediately follows their closure.

For practical purposes it is important to bear in mind what is happening in the heart whilst one listens to its sounds. During the first sound we have (1) contraction of the ventricles, closure of the auriculo-ventricular valves and impulse of the apex against the chest; (2) rushing of the blood into the aortic and pulmonary artery, and filling of the auricles. With the second sound we have closure Of the semi lunar valves from the elastic recoil of the aorta and pulmonary artery, relaxation of the ventricular walls, opening of the auriculo-ventricular valves so as to allow the passage of blood from auricle to ventricle, and diminished pressure of apex a ainst chest wall. With the long pause there are (1) gradual refilling of the ventricle from the auricle, and (2) contraction of the auricle so as to entirely fill the ventricle. The sound of the tricuspid valve is heard loudest at the junction of the lower right costal cartilages with the sternum, »of the mitral over the apex beat, of the aortic semi lunar valves in the direction of the aorta where it comes nearest to the surface at the second right costal cartilage, and of the valves of the pulmonary orifice over the third left costal cartilage, to the left and external to the margin of the sternum. The sounds are changed in character by valvular lesion or muscular weakness of the heart, and afford important signs to the physician. Murmurs are produced by eddies setting some part of the membranous walls or valve flaps in vibration.

If a stethoscope be placed over a large artery, a murmur will be