What are pulmonary hypertension and pulmonary arterial hypertension

Pulmonary hypertension and pulmonary arterial hypertension are actually the same thing and are medical terms. Pulmonary hypertension mainly refers to the phenomenon of isolated increase in pulmonary artery blood pressure while pulmonary venous pressure is normal. However, pulmonary hypertension is different from what we usually call high blood pressure.

1. Currently, there are three main special terms in medical terminology: pulmonary hypertension, pulmonary arterial hypertension and idiopathic pulmonary arterial hypertension. Pulmonary hypertension refers to hypertension in the pulmonary circulatory system, including pulmonary arterial hypertension, pulmonary venous hypertension and mixed pulmonary hypertension. The increase in pulmonary circulation blood pressure caused by any systemic or local lesions in the entire pulmonary circulation can be called pulmonary hypertension (abbreviated as PH). Currently, pulmonary hypertension can be divided into five major categories.

2. Pulmonary hypertension refers to an isolated increase in pulmonary artery blood pressure while pulmonary venous pressure is normal. The main reason is that primary lesions of small pulmonary arteries or other related diseases lead to increased pulmonary artery resistance, which is manifested as increased pulmonary artery pressure and normal pulmonary venous pressure. The transpulmonary pressure (transpulmonary pressure = pulmonary artery pressure - pulmonary capillary wedge pressure) needs to be normal. The transpulmonary pressure requires the pulmonary capillary wedge pressure (PCWP) to calculate. The pulmonary capillary wedge pressure is equal to the pressure in the pulmonary veins. If the pulmonary artery pressure is high but the transpulmonary pressure is not high, it usually refers to pulmonary venous hypertension, which is mainly caused by left heart disease.

3. Pulmonary hypertension is a medical term that refers to a group of complex diseases in which pressure in the lungs' blood vessels is increased. It may be caused by vascular lesions of the pulmonary circulation itself or by other diseases. The disease is often caused by a lack of substances that dilate blood vessels and an increase in substances that constrict blood vessels, causing the pulmonary blood vessels to be in a state of contraction, or by changes in the pulmonary vascular structure and the formation of blood clots (called "thrombosis") in the pulmonary blood vessels, which increases the pressure in the pulmonary blood vessels, reduces the blood flow pumped by the right heart to the lungs, and finally causes right heart failure.

4. Pulmonary arterial hypertension and what we commonly call "hypertension" are two completely different diseases. What we often call "hypertension" refers to the increase in blood pressure in the systemic arteries, which can be measured by a cuff on the upper limbs and is relatively easy to measure and diagnose. Pulmonary hypertension refers to increased blood pressure in the pulmonary artery. The pulmonary artery is located in the middle of the lung lobe and is difficult to measure using non-invasive methods such as a cuff sphygmomanometer. Therefore, its diagnosis is relatively difficult (usually ultrasound estimation or direct measurement by intubation into the pulmonary artery is required). In the later stages of pulmonary hypertension, due to the stenosis and occlusion of the pulmonary blood vessels, right heart failure occurs, the blood flowing from the pulmonary circulation to the heart decreases, and the systemic blood pressure also decreases, becoming "hypotension."

5. The current diagnostic criteria for pulmonary hypertension are: at sea level and at rest, the mean pulmonary artery pressure on right cardiac catheter examination is ≥25 mm Hg (1 mm Hg=0.133 kPa). In addition, according to the different classifications of pulmonary hypertension, it is necessary to measure the pulmonary capillary wedge pressure (such as ≤15 mm Hg, which usually excludes the cause of increased pulmonary venous pressure). The data from our routine screening color ultrasound Doppler estimates can only be used as a reference, and right heart catheterization is the gold standard for diagnosing pulmonary hypertension.