The two basic roles of the balloon are: pre-expansion of the balloon to facilitate the smooth placement of the subsequent stent and post-expansion of the balloon to ensure adequate expansion or good fitting of the stent. There are various classifications of balloons, which are classified according to the characteristics of balloon use as Over the Wire (OTAw). Rapid exchange system. The three types of balloons are Rapid exchange system (Rapid exchange system, and fixed guidewire balloon on wire, which is basically no longer used in clinical practice), and specially designed balloons such as perfusion balloons, cutting balloons, double guidewire force balloons, and drug-carrying balloons, which can be roughly divided into small balloons (2-5mm), common balloons (5 N-12mm), and large balloons according to the size of balloon diameter. 12 mm) and large balloons (≥12 mm). Small balloons are generally used for the coronary artery, the tibiofibular artery below the carotid artery and the renal and vertebral arteries with thin diameters; common balloons are generally used for the carotid artery, renal artery, iliofemoral N artery, etc., while large balloons are generally used for the infrarenal abdominal aorta, iliac artery and vena cava. Performance indicators for evaluating balloon catheters generally include balloon outer diameter, tracking, pushability, flexibility, and compliance. I. Compliance balloon and non-compliance balloon The compliance of balloon (compliance) refers to the corresponding change in balloon shape or volume for each increase in atmospheric pressure (atm) during balloon filling, and is an indicator of balloon stretch capacity. After the balloon is completely filled, the higher the balloon compliance, the more obvious the tendency of further increase in balloon volume or shape as the filling pressure continues to increase. However, for the majority of dilated balloon catheters, the length of the balloon does not change when the filling pressure is increased, and the change in volume is mainly reflected in the change in balloon diameter. Important parameters: Nominal pressure refers to the filling pressure inside the balloon required to obtain a predetermined diameter, generally between 6-8 atm. The rated burst pressure is the maximum filling pressure at which 99.9% of the balloons will not rupture when the balloons are repeatedly filled 40 times during in vitro testing. According to the balloon compliance, the balloons currently used in clinical applications are roughly divided into compliant balloons, semi-compliant balloons and non-compliant balloons. The compliance of balloons mainly depends on the material of balloon production. The early balloons were made of polyvinyl chloride (PVC) and were compliant balloons. Nowadays, semi-compliant balloons and non-compliant balloons are mainly made of polyethylene (PE), polyurethane, nylon (Nylon, DuralynTM) and polyethylene terephthalate (PET). The latter two are the main materials used in the production of semi-compliant balloons and non-compliant balloons today. After the pressure is increased to the named pressure or expanded to a predetermined diameter, the diameter and volume of the compliant balloon can be increased continuously as the filling pressure continues to increase, and when resistance is encountered in the vessel, the balloon morphology can change and expand to the place of less resistance, which can lead to two outcomes: first, the squeezing force exerted on the surrounding disease is significantly reduced; second, the excessive expansion of the shoulders at both ends of the balloon with continuously increased filling pressure can easily lead to damage to the normal vessel wall leading to entrapment. The susceptibility of dilated stenotic lesions to entrapment makes compliant balloons generally not used for angioplasty. However, the use of compliant balloons to adapt to the morphological shaping of the blood vessel still has a role to play: for example, the Mo.Ma. balloon cerebral protection device used for carotid stenting takes advantage of the shaping properties of compliant balloons, and low-pressure expansion ensures that the balloon fits the wall completely and does not damage the intima of the vessel wall to completely block internal carotid artery blood flow. Semi-compliant balloon and non-compliant balloon Semi-compliant balloon means that the balloon diameter increases by 0.25-0.75mm above the predetermined diameter while the balloon filling pressure continues to increase between the named pressure and burst pressure. The non-compliant balloon diameter remains the same after the balloon diameter is fully filled to the specified value regardless of the further increase in pressure. Both are more resistant to high pressure and have a greater ability to squeeze lesions than compliant balloons, while being less adaptable to vessel shape than compliant balloons. The excellent high pressure resistance of noncompliant balloons allows them to squeeze lesions more than non-semi-compliant balloons and facilitates dilatation of severe or fibrotic hard lesions. With semi-compliant balloons, the diameter of the balloon can be precisely regulated by controlling the pressure after filling beyond the named pressure. However, semi-compliant balloons are prone to dogbone at pressures above 14 atm, where the extrusion pressure on the lesion is not sufficient to dilate a hard lesion, and the protruding balloons at the ends of the lesion may damage the normal vessel wall tissue at the ends of the lesion, causing a marginal effect leading to restenosis at the ends of the stent or entrapment of the lesion. At pressures as high as 20 atm, not only may the lesion not be dilated, but also serious vessel rupture and perforation or entrapment may occur. In addition, incomplete stent expansion or apposition to the wall is often an important factor in in-stent thrombosis and distant restenosis. Therefore, in cases of severe calcification with high resistance, stents or semi-compliant balloons are usually not sufficient to fully dilate the lesion or to allow adequate stent apposition. In contrast, the ultra-high-pressure resistance of noncompliant balloons ensures that high pressure is continuously applied to the lesion and can fully dilate the lesion or allow adequate stent apposition. For such lesions, if the lesion indentation does not disappear with semi-compliant balloon dilatation pressure increasing to 16 atm or exceeding the balloon burst pressure, especially if there is significant calcification of the artery in the vessel wall on fluoroscopy, consideration should be given to switching to a noncompliant balloon, cutting the balloon, or using plaque spinning. The balloon pressure should not be increased to avoid serious complications such as vessel rupture and perforation. Non-compliant balloons are usually indicated for pre-dilatation before stenting for severe calcified Chi lesions or post-dilatation at high pressure after stenting to allow adequate expansion or complete apposition of the stent to the wall. Noncompliant balloons are also used for lesions that are not easily expandable such as bifurcation lesions, open lesions, stent overlaps and in-stent restenosis due to their high expansion power. Non-compliant long balloons used in long occlusive lesions can significantly reduce the incidence of entrapment due to endothelial injury after angioplasty. Post-expansion of self-expanding stents is also usually performed with noncompliant balloons to allow complete wall apposition. The late thrombosis of drug-eluting balloon is related to the inhibition of endothelial repair and healing process by the polymeric carrier of the stent. The use of drug-eluting balloon can prevent the occurrence of restenosis by inhibiting endothelial proliferation with anti-proliferative drugs and avoid the late thrombosis caused by the long-term retention of the metal skeleton and polymeric carrier of the drug-eluting stent in the vessel wall. The stent can also avoid late thrombosis caused by the long-term retention of the metal skeleton and polymer carriers in the vessel wall. Unlike the slow and continuous release of drug from drug-washed stents, the drug-carrying balloon (paclitaxel-eluting balloon) is filled with paclitaxel in microscopic pores on the balloon surface, which is rapidly released into the local arterial wall through contact between the balloon expansion and the lesion. The use of the collapse technique before filling the balloon prevents the drug from being washed away prematurely as the balloon moves forward in the bloodstream. Balloon expansion simultaneously allows 75% of the drug dose to penetrate into the local arterial wall, preventing intimal proliferation, while the remaining 25% of the drug dose is washed away by rapid blood flow during balloon expansion. Cryoballoon The special balloon catheter used for cryoplasty consists of the mechanical dilating force of the normal balloon for angioplasty and the rapid freezing of the vessel wall. The cryoplasty effect, by generating most of the tiny fissures in the vessel wall and lesion surface, can achieve a neater dilatation effect than the normal balloon, effectively reducing the incidence of local intimal tears or entrapment; also by changing the physical properties of collagen and elastic fibers, theoretically reducing the elastic retraction of the vessel wall and decreasing the possibility of negative vascular remodeling in the long term; in addition, it can induce apoptosis of vascular smooth muscle cells, reducing the incidence of intimal proliferation or restenosis. In addition, it can induce apoptosis of vascular smooth muscle cells and reduce the incidence of intimal proliferation or restenosis. The use of frozen balloons may theoretically reduce the incidence of immediate intraoperative entrapment, reduce the need for stents due to acute complications, alter the vascular remodeling process and induce apoptosis of vascular smooth muscle to reduce the chance of restenosis, but there is a lack of strong evidence that the long-term efficacy and endpoint event rates of frozen balloons are superior to those of conventional balloons or stents.