Pressures in Interventional Radiology

Absolute Pressures

• Normal right atrial pressure: 2-6 mm Hg
• Normal right ventricular pressure: 15-25 mm Hg (systolic)/0-8 mm Hg (Diastolic)
• Normal main pulmonary artery pressure: 22/8 mm Hg, with a mean of 13 mm Hg.
  • Pulmonary arterial hypertension: > 30 mm Hg systolic, or
  • Mean pulmonary artery pressure > 25 mm Hg at rest, or
  • Mean pulmonary artery pressure > 30 mm Hg with exercise.
• Normal left atrial pressure: Estimated by pulmonary capillary wedge pressure. Between 6-12 mm Hg.
  • Cephalization: 12-18 mm Hg.
  • Interstitial edema: 15-25 mm Hg.
  • Alveolar edema: > 25 mm Hg.
• Portal hypertension: Absolute portal venous pressure > 10 mm Hg.

Pressure Gradients

• A pressure gradient > 2mm Hg between the inferior vena cava and the renal vein is suggestive of renal venous hypertension due to outflow obstruction.
• A pressure gradient > 2mm Hg across the hepatic vein or inferior vena cava webs in patients with Budd-Chiari syndrome suggests that intervention may be beneficial.
• May-Thurner syndrome can be divided into three venographic stages. The first stage is asymptomatic compression of the left common iliac vein with no collaterals and a pressure gradient < 2 mmHg. Stage 2 is the presence of intraluminal webs or spurs, and stage 3 is thrombosis.
• Pressure gradient > 3 mm Hg across a lesion in the inferior vena cava is considered significant.
• The normal hepatic vein pressure gradient (also known as corrected sinusoidal pressure) is < 5 mm Hg. Portal hypertension is hepatic vein pressure gradient (see below)> 5 mm Hg. Hepatic vein pressure gradient > 12 is associated with variceal hemorrhage. Hepatic vein pressure gradient is measured as follows: Pressure in a hepatic vein is measured using an uninflated occlusion balloon catheter giving us the free hepatic venous pressure. The occlusion balloon is then inflated and the wedged hepatic venous pressure is measured. The free pressure is subtracted from the wedged pressure to give the gradient.
• Pressure gradient > 20 mm Hg between the aorta and a point distal to a renal artery narrowing suggests the diagnosis of renal artery stenosis. However, this has no physiologic foundation and has not been validated clinically. 10-15 is considered borderline under this scheme.
• Pressure gradient < 20 mm Hg across an area of apparent aortic narrowing suggests pseudocoarctation.

Augmented pressure gradients can be obtained in arteries by injecting a vasodilator (200-300 mcg of nitroglycerin, or 15-25 mg tolazoline) distal to the lesion. This will induce hyperemia and may unmask a gradient.

References

• Interventional Radiology: The Requisites.
• Drieghe B, Madaric J, Sarno G, Manoharan G, Bartunek J, Heyndrickx GR, Pijls NH, De Bruyne B. Assessment of renal artery stenosis: side-by-side comparison of angiography and duplex ultrasound with pressure gradient measurements. Eur Heart J. 2008 Feb;29(4):517-24.
• Gluecker T, Capasso P, Schnyder P, Gudinchet F, Schaller MD, Revelly JP, Chiolero R, Vock P, Wicky S. Clinical and radiologic features of pulmonary edema. Radiographics. 1999 Nov-Dec;19(6):1507-31;