The normal right atrium functions as a capacitance chamber. The mean RA pressure is often quite low, often less than 5 mmHg. When assessed externally in relationship to the sternal angle with the patient's head placed at 45° upward tilt from the horizontal, the top of the moving jugular column does not exceed 4-5 cm in vertical height above the sternal angle. The recognition of the descents and their contour will make assessment of the jugular venous pressure quite easy. The top of the pulsations in the jugulars as transmitted to the skin overlying the sternomastoid muscle must be noted. Since the jugular and superior vena cava are in direct continuity with the right atrium, the estimation of the jugular venous pressure helps in the assessment of the central filling pressure in the right heart. The latter reflects the adequacy of the volume status of the patient as well as the right heart function. One must, however, always remember that the systemic venous or sympathetic tone influences the jugular column in addition to the right atrial pressure. For any given volume status or filling pressure in the right atrium, the level to which the jugular column will rise will depend on the degree of the venous tone as well.
The derivation of the right atrial mean pressure from the jugular venous pressure usually takes into account the approximate location of the mid right atrium from the sternal angle. The sternal angle is a surface anatomical mark. The right atrium can be at a variable distance from this external reference point, depending on the position of the patient. In the usual 45° upward tilt from the horizontal in which the patient is assessed, this distance in vertical height from the surface sternal angle can vary between 8 and 10 cm. The higher the tilt, the higher is this distance. When assessed at 90° tilt, the distance is almost 12 cm (54) (Fig. 27). This distance in cm is added to the level ofjugular column in vertical height above the sternal angle in cm to derive the right atrial pressure in cmH2O. The total can then be divided by 1.36 to get mmHg of pressure.
The jugular contour, unless associated with very high venous pressure, will not be visible if the patient is tilted too much upward from the horizontal. In fact, in many normal individuals the jugular descents will be observed only when they are almost lying flat. In some ofthe normals, the top ofthe jugular column may only be visible with patient lying flat or only slightly tilted, if at all. While estimation of the right atrial pressure from the jugular venous pressure by adjusting for the vertical height of the right atrium from the sternal angle may be of interest, it is not absolutely necessary. One can simply have a normal range ofjugular venous pressure in vertical height in cm from the usual external reference point of the sternal angle. Based on this normal range one can decide whether in a given patient the jugular venous pressure is normal, low, or high. A simple figure for the normal range is 4-5 cm above the sternal angle at 45° of upward tilt. In fact, this level is usually obtained only in younger subjects. In the elderly, this level is generally even lower.
Was this article helpful?
Do You Suffer From High Blood Pressure? Do You Feel Like This Silent Killer Might Be Stalking You? Have you been diagnosed or pre-hypertension and hypertension? Then JOIN THE CROWD Nearly 1 in 3 adults in the United States suffer from High Blood Pressure and only 1 in 3 adults are actually aware that they have it.