When the liquid flow increases, the luminal caliber's stretching amplitude decreases, leading to a higher hydraulic pressure according to Poiseuille's law. In this study, investigators measured the caliber change of the popliteal vein under a rated pressure gradient and evaluated the relationship between popliteal vein compliance and venous clinical severity score (VCSS).

Inclusion Criteria:

• C1 to C6 disease using the CEAP (clinical, etiologic, anatomic, pathophysiologic) classification.

Exclusion Criteria:

• acute or chronic thrombosis of deep veins, previously received intravenous surgery or injection sclerotherapy, ankle brachial index<0.90, and concomitant cardiovascular, pulmonary, renal, or metabolic diseases.

Patients were prospectively enrolled in Guangdong Second Provincial General Hospital from May 2023 to October 2023. All participants gave their voluntary consent.