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Background
Hemodynamic measurements are essential for diagnosis and guiding treatment for portal hypertension and pulmonary hypertension. A pressure gradient of 6 mmHg or more between the portal and hepatic veins (or inferior vena cava) suggests the presence of portal hypertension in most cases. When the pressure gradient is greater than 12 mmHg, portal hypertension becomes clinically significant. As the right atrium connects the outflow of the liver to the inflow of the lungs and pressure gradients have similar effects on these organs and similar rules can be applied to PA catheter measurements. It is important to measure the systemic gradients in the affected organ system prior to and following intervention to know if the intervention was effective, or if further intervention is needed.

Educational Goals / Teaching Points
Familiarize radiologists with hemodynamic measuring in interventional radiology. Review the anatomy, physiology, and key imaging findings of portal hypertension and pulmonary hypertension. Describe stepwise approach in the optimization and interpretation of intraprocedural hemodynamic measurements and how these guide treatments. Describe and briefly review the anatomy and role of imaging paramount to appropriate pressure measurements.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Review of relevant vascular anatomy (SCV, right atrium, IVC, hepatic veins, portal veins, pulmonary artery, pulmonary vein) and intervening capillary pathways. Physiology and hemodynamics of cirrhosis and pulmonary hypertension including (liver - review of the subsets of portal hypertension, specifically which subsets create gradients and why, and how these differences guide intervention, prehepatic, portal vein thrombosis, portal veins stenosis, congenital abnormalities; presinusoidal - hepatoportal sclerosis, granulomatous disease; sinusoidal - cirrhosis, steatohepatitis, amyloidosis; post sinusoidal - veno-occlusive disease; post hepatic - Budd-Chiari, cardiac failure; and lung - review of the pulmonary hypertensive physiology in acute, subacute and chronic pulmonary embolism). Review of pulmonary angiography and hepatic venography, pressure gradients, and waveforms, and how these guide intervention (thrombectomy, thrombolysis, Inari Flowtriever, TIPS, medical management). Pitfalls in equipment set up that can affect gradient measurements.

Conclusion
An accurate understanding of the pathophysiology of portal hypertension and pulmonary hypertension is essential for the diagnosis and guiding intervention to reduce the gradient causing the underlying disease. Understanding the normal waveforms is essential for troubleshooting equipment malfunction and ensuring accurate pressure measurements to guide intervention.