Pulmonary artery pressure refers to the average pressure in the pulmonary artery when the body is at rest. Generally, the normal average pulmonary artery pressure is less than 25mmHg. Pulmonary hypertension is considered when the pulmonary artery pressure exceeds 25mmHg. The grading is generally divided into three levels based on the data: the first level is mild pulmonary hypertension with pulmonary artery pressure between 26-35mmHg; moderate with pressure between 36-45mmHg; and severe with pressure greater than 45mmHg. If classified by the functional impact of pulmonary hypertension, grade I pulmonary hypertension is characterized by patients who are not limited in daily activities, and do not experience symptoms such as shortness of breath, difficulty breathing, or chest tightness after physical activity. Grade II pulmonary hypertension patients are limited by mild activities, do not feel discomfort at rest, but experience symptoms like difficulty breathing, fatigue, chest tightness, and chest pain during everyday activities. Grade III pulmonary hypertension patients have significantly limited activity; they feel no discomfort at rest, but experience symptoms like difficulty breathing, fatigue, and chest pain after only mild activity, less than everyday activities. Grade IV pulmonary hypertension is severe, with patients experiencing symptoms such as difficulty breathing and feeling tightness in their chest even at rest without any activity.