The RA pressure (RAP) can be estimated by the size and respiratory collapsibility of the inferior vena cava. For simplicity and uniformity of reporting, specific values of RAP, rather than ranges, should be used in the determination of RVSP.

IVC diameter:

< 2.1 cm that collapses >50% with a sniff suggests normal RA pressure of 3 mm Hg (range, 0-5 mm Hg),

> 2.1 cm that collapses < 50% with a sniff suggests high RA pressure of 15 mm Hg (range, 10-20 mm Hg);

In scenarios in which IVC diameter and collapse do not fit this paradigm, an intermediate value of 8 mm Hg (range, 5-10 mm Hg).

In young athletes, IVC may be dilated in the presence of normal pressure. IVC is commonly dilated and may not collapse in patients on ventilators, so it should not be used in such cases to estimate RA pressure.