Pulmonary Artery

The pulmonary artery is a large artery that transports poor-oxygenated blood from the right ventricle of the heart to the lungs for oxygenation. It is a special artery because most arteries contain oxygen-rich blood, whereas the pulmonary artery consists of oxygen-poor blood.

1.0Anatomy of Pulmonary Artery

• Origin - The pulmonary artery arises from the heart's right ventricle through the pulmonary valve.
• Branching - After emerging, the pulmonary artery gives off two primary branches shortly after its origin.
• Right Pulmonary Artery: It supplies blood to the right lung.
• Left Pulmonary Artery: It perforates to the left lung.
• Branches - Later, these arteries further divide into arterioles and finally into capillaries, which encircle the air sacs(alveoli) in the lungs for gas exchange.
• Pulmonary Trunk - It's one single vessel that originates from the right ventricle and ascends to the point where it divides into the right and left pulmonary arteries.

2.0Pulmonary Circulation Overview

• The pulmonary artery is one of the core elements of pulmonary circulation, which is different from systemic circulation:
• Pulmonary circulation involves blood drawn from the right ventricle into the lungs and then oxygenated back to the heart's left atrium.
• Pulmonary veins, unlike pulmonary arteries, return oxygenated blood from the lungs to the heart.

3.0Function of Pulmonary Artery

1. Transportation of Deoxygenated Blood

• The pulmonary artery carries deoxygenated blood. It is rich in carbon dioxide but low in oxygen, and it moves from the heart to the lungs.

2. Gas Exchange

• Blood is allowed into the capillaries surrounding the lungs' alveoli, where oxygen is dissolved into the blood and carbon dioxide leaves to get into the alveoli to be expelled.

3. Pressure Regulation

• The pulmonary artery operates at a lower pressure than the systemic arteries. 
• This is because the right side of the heart is well-rested. 
• Severe health conditions arise when there is high pressure in the pulmonary artery, known as pulmonary hypertension.

4.0Histology of the Pulmonary Artery

• The pulmonary artery has three layers, just like any other artery, but it is modified in some ways:
• • Tunica Intima: The innermost layer is covered by endothelial cells, which contribute to forming a smooth surface on which blood flows.
  • Tunica Media: This middle layer contains smooth muscle cells and elastic fibres but is of thinner proportions than those in systemic arteries because the pressure in the pulmonary circulation is relatively much lower.
  • Tunica Adventitia: The outer layer consists of connective tissue that bears structural support.
  • The pulmonary artery's elastic fibers enable it to stretch and accommodate the flow pulsation from the right ventricle with every heartbeat.

5.0Associated Diseases and Disorders

1. Pulmonary Hypertension (PH)

• Definition: Increased pulmonary arterial pressure makes it very difficult for the blood to pass from the right ventricle to the lungs.
• Types: Pulmonary Arterial Hypertension (PAH): A category where the pulmonary arteries are narrowed, thickened, or obstructed. Secondary Pulmonary Hypertension is caused by other diseases, such as heart disease, lung disease, or a blood clot.
• Pathophysiology: In pulmonary hypertension, the increased resistance in the pulmonary arteries leads to right ventricular hypertrophy and, subsequently, heart failure.
• Symptoms: Shortness of breath, fatigue, chest pain, swelling.
• Diagnosis: Echocardiography and right heart catheterization are used to assess pulmonary artery pressures.
• Treatment: Medications include vasodilators, endothelin receptor antagonists, and phosphodiesterase-5 inhibitors. In severe cases, transplantation into the lungs is performed.

2. Pulmonary Embolism (PE)

• Definition: A pulmonary embolism is the presence of a blood embolus in the pulmonary artery that obstructs the flow of blood to part of the lung.
• Cause: The clot often arises from a deep vein in the legs, called deep vein thrombosis.

• Pathophysiology: As a consequence, a ventilation-perfusion mismatch results in poorly oxygenated blood in the area and over-staining of the right ventricle.
• Symptoms: Sudden onset of breathlessness, chest pain, palpitation, and coughing may contain blood.
• Diagnosis: The gold standard for diagnosis is through CT Pulmonary Angiography.
• Treatment: Treatment primarily includes anticoagulants, such as drugs like heparin and warfarin, to avoid clot formation. Large clots may be dissolved by thrombolytic therapy, or in extreme cases, surgical embolectomy may be required.

3. Pulmonary Artery Stenosis

• Definition: Pulmonary artery stenosis is when the pulmonary artery or one of its branches narrows and subsequently impedes blood flow.
• Causes: It can be congenital, but most of the time, it is caused by inflammatory diseases, infections, or post-surgery conditions.
• Symptoms: Shortness of breath, fatigue, and Cyanosis (blue skin due to insufficient oxygen).
• Diagnosis: Echocardiography and MRI angiography show the narrowing and assess it.
• Treatment: Balloon angioplasty or surgical correction can be used to enlarge the artery to re-establish blood circulation.

4. Pulmonary Artery Aneurysm

• Definition:  A pulmonary artery aneurysm is an outpouching or ballooning of the pulmonary artery wall caused by a weakened vessel.
• Causes: Often results from pulmonary hypertension, congenital heart defects, or infections.
• Symptoms: Most are asymptomatic, although large aneurysms can cause chest pain, coughing, or shortness of breath.
• Diagnosis: Observed by means of imaging techniques: CT scan or MRI.
• Treatment: Surgery might be required to correct or resect the aneurysm if it will likely rupture.

5. Pulmonary Artery Atresia

• Definition: Non formation of pulmonary artery or absence of pulmonary artery at the time of birth that causes no normal flow of blood from heart to lungs
• Other Syndromes and Condition with This Defect: It is normally presented as a combination with other heart conditions like tetralogy of Fallot.
• New-born signs/symptoms: Primarily Cyanosis, respiratory condition, failure of heart.
• Treatment: Surgical intervention and joining of the right ventricle with pulmonary artery.

6.0Diagnostic Techniques

• Echocardiography: Non-invasive imaging procedure: assessing the structure and function of the heart and pulmonary arteries. Used most often to estimate pulmonary artery pressures.
• Right Heart Catheterization: This is the invasive procedure that measures pressures directly in the right heart and pulmonary artery and is considered to be the gold standard for diagnosing pulmonary hypertension
• CT Pulmonary Angiography (CTPA): The contrast-enhanced CT scan reveals obstruction in pulmonary arteries and is commonly used for the detection of pulmonary embolism.
• MRI: It is primarily used to show more detailed images of the pulmonary arteries. This technique is very well suited for the evaluation of an aneurysm or complex defects.
• Pulmonary Function Tests: Assess lung capacity and can give some clues for pulmonary artery related disorders.