The RA pressure pulse is transmitted through the superior vena cava to the internal jugular vein. The internal jugular vein runs underneath the sternomastoid muscle. It extends in direction from the angle of the jaw to the hollowness between the two heads of the sternomastoid muscle attachments to the upper sternum and the medial portion of the clavicle. Often positioning the patient with a comfortable tilt of the neck with adequate light coming from the sides will make the jugular pulsations more easily visible. Sometimes having the patient lie in the left lateral decubitus position again with the head tilted somewhat also helps bring out the jugular pulsations. Directing the light source in such a way as to cause a shadow of a fixed nonmoving object to fall on the skin overlying the sternomastoid will reveal the pulsations of the jugulars underneath it since the edge of the shadow can be shown to move because of the jugular movement. The object could be the patient's chin, an observer's finger, or a pen held at a fixed point on the neck of the patient by the observer. Often if the light source is appropriate, one may be able to have the shadow ofthe laterally placed clavicular head of the sternomastoid fall on the hollow space between the two heads of that muscle.
Since normal RA pressure waves (the a and the v waves) have slow rises and are often of low amplitude, they are usually not appreciated in the jugulars. On the other hand, the descents in the RA pressure pulse are better transmitted and appreciated in the jugulars. They are generally rapid movements moving away from the eye and thus easily seen. In addition, their appreciation is made easier in that they reflect acceleration of flow velocity (40,47) The descents in the internal jugular vein reflect a fall in pressure in the right atrium during cardiac cycle. The reflected light intensity on the hollow area between the two heads ofthe sternomastoid varies when the jugular pressure rises as opposed to when the jugular pressure falls, and this is easily appreciated at the bedside as well as in video recordings of jugular pulsations. When the descents occur, there is less reflected light overlying the jugulars and the area looks darker. Slight anatomical variations from patient to patient may occur. The descents may be sometimes appreciated more anteriorly at the medial edge of the sternomastoid. Sometimes it could be somewhat lateral. In others it may be seen over a wide area in the neck.
The descents can be timed to either the radial arterial pulse or the second heart sound. The x' descent corresponds to the systolic flow. Because of transmission delay this descent falls almost on to the second heart sound, and it coincides with the radial arterial pulse. The diastolicy descent is out of phase with the arterial pulse and occurs after the second heart sound, reflecting the diastolic flow velocity (40).
In normal subjects, a single dominant descent is noted during systole (x') because of the descent of the base corresponding to the dominant systolic flow. The y descent is often not visible in the adult, although it may be noted in young subjects, pregnant women, and thyrotoxic and anemic patients. In these the y descent may become visible because of its exaggeration due to rapid circulation and increased sympathetic tone. However, in these conditions the right ventricular systolic contraction is often normal and the x' descent will still be the dominant descent.
As stated previously, the normal a and v wave rises are not seen, but their presence can be inferred by the descents that follow. During normal sinus rhythm, the wave preceding x' descent is the a wave and the one that precedes the y descent is the v wave.
Generally the external jugular vein will not always reflect the descents. This vein usually runs superficially over the mid- portion of the sternomastoid muscle. If it should exhibit the descents that could be timed to the cardiac cycle, then one could use them for assessment ofwaveform and pressure much as one would normally use the internal jugular pulsations. Jugular pulsation is easily distinguished from the arterial pulse in the neck because it moves in the opposite direction due to the usually dominant x' descent (Figs. 2 and 9) (see JVP Videofiles [1st-4th patient] in Jugular Venous Pulse, Normal on the Companion CD).
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