The jugular venous pulse provides direct information about the pressures in the right side of the heart because the jugular system is in direct continuity with the right atrium. During diastole, when the tricuspid valve is open, the jugular veins are continuous with the right ventricle as well. If there is no stenotic lesion at the pulmonic or mitral valves, the right ventricle indirectly monitors the pressures in the left atrium and left ventricle. The most common cause of right-sided heart failure is left-sided heart failure. Examination of the neck veins also provides information about the cardiac rhythm.
--Figure 14-8 The arterial pulse.
Figure 14-7 Physiologic splitting of the second heart sound.
The understanding of the normal physiology is important in the consideration of the jugular venous pulsation. Figure 14-9 is an enlargement of the atrial and ventricular pressure curves in Figure 14-6.
The ''a'' wave of the jugular venous pulse is produced by right atrial contraction. When the ''a'' wave is timed with the electrocardiogram, it is found to occur about 90 msec after the onset of the P wave. This time delay is related to the time from electrical stimulation of the atria to atrial contraction and to the resultant wave propagated in the neck. The ' ' x'' descent is caused by atrial relaxation, which occurs just before ventricular contraction. This drop in right atrial pressure is terminated by the c'' wave. The resulting increase in right atrial pressure is caused by tricuspid valve closure secondary to right ventricular contraction. The descent of the atrioventricular valve rings, also known as the descent of the base of the heart, produces the next change in right atrial pressure, called the ' 'x prime'' descent. As the free wall of the right ventricle approaches the septum during contraction, the atrioventricular valve rings descend toward the apex as contraction progresses. This increases the size of the atrium, causing a fall in its pressure (hence the ''x prime'' descent). During ventricular systole, the right atrium begins to fill with blood returning through the venae cavae. This increase in right atrial pressure as a result of its filling produces the ascending limb of the v'' wave. At the end of ventricular systole, right ventricular pressure falls rapidly. When it falls below the right atrial pressure, the tricuspid valve opens. This drop in right atrial pressure produces the y'' descent.
Normally, only the ''a'' and ''v'' waves are visible on examination. Because the ''c'' wave is frequently not observed, the ''x'' and ''x prime'' descents are summated into a single ''x'' descent. On occasion, the later portion of the ''c'' wave may be enlarged by a carotid artery pulsation artifact.
Evaluation of the jugular venous pulse provides information about the level of venous pressure and the type of venous wave pattern. These are described later in the section The Jugular Venous Pulse.
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