Pulmonary artery pressure (PAP) measures the force exerted by blood within the main artery carrying blood from the right side of the heart to the lungs. Monitoring this value is part of a complete cardiovascular assessment because it relates directly to the body’s ability to perform gas exchange. Understanding the normal range helps medical professionals identify conditions that impair blood flow through the vessels in the lungs.
Anatomy and Function of the Pulmonary Artery
The pulmonary artery originates from the right ventricle of the heart and transports deoxygenated blood from the body into the lungs for oxygenation. This pathway is a low-pressure circuit, contrasting with the high-pressure systemic circulation that delivers oxygenated blood to the rest of the body.
The right ventricle pumps blood through this circuit, where resistance is naturally low due to the wide capillaries in the lungs. This lower pressure facilitates the exchange of oxygen and carbon dioxide across the alveolar membrane. If the pressure becomes too high, it can damage the lung vessels and strain the right side of the heart.
Normal Ranges and Measurement Methods
The mean pulmonary artery pressure (mPAP) is the average pressure across a single cardiac cycle and is the most precise indicator of pressure. In a healthy adult at rest, the mPAP is typically 14 millimeters of mercury (mmHg), with an expected range of 14 ± 3 mmHg. The upper limit of normal for mPAP is 20 mmHg.
Pressure readings can also be broken down into systolic and diastolic pressures, similar to systemic blood pressure. The normal pulmonary artery systolic pressure (PASP) is approximately 21 ± 4 mmHg, with an upper limit of 30 mmHg. However, mPAP is the primary value used to determine the presence of abnormally high pressure.
The initial screening tool for estimating PAP is non-invasive transthoracic echocardiography (echo). This ultrasound technique uses Doppler technology to estimate the systolic pressure by measuring blood flow velocity across the tricuspid valve. While valuable for identifying elevated pressure, echo provides only an estimate and is not definitive for diagnosis.
The gold standard for obtaining an accurate measurement is right heart catheterization (RHC). This invasive technique involves inserting a catheter into a vein, guiding it into the right side of the heart and the pulmonary artery. The catheter directly measures the pressure within the artery and heart chambers, providing the precise mPAP needed for a definitive diagnosis.
Implications of Elevated Pressure
When the mean pulmonary artery pressure consistently exceeds the normal limit, it results in pulmonary hypertension (PH). International consensus defines PH as a resting mPAP greater than 20 mmHg. This elevated pressure signifies increased resistance to blood flow within the pulmonary circulation.
Increased resistance places a greater workload on the right ventricle of the heart. To overcome the high pressure, the right ventricle must pump harder, causing its muscular walls to thicken and enlarge. This continuous strain can eventually overwhelm the muscle, leading to right-sided heart failure, where the heart cannot effectively move blood into the lungs.
Pulmonary hypertension stems from various underlying causes, categorized into five groups by the World Health Organization (WHO):
- Group 1 is Pulmonary Arterial Hypertension (PAH), involving disease in the small pulmonary arteries themselves.
- Group 2 is the most common form, resulting from left heart disease, such as heart failure, which causes pressure to back up into the lungs.
- Group 3 is linked to lung diseases and low oxygen levels, such as chronic obstructive pulmonary disease (COPD) or sleep apnea.
- Group 4 is chronic thromboembolic pulmonary hypertension (CTEPH), caused by organized blood clots that restrict blood flow.
- Group 5 encompasses cases with unclear or multifactorial origins, including certain hematologic or systemic disorders.
Common symptoms experienced by individuals with PH include increasing shortness of breath during activity, persistent fatigue, and sometimes chest pain or lightheadedness.