Anatomy Relevant to Pulmonary Embolism

by Adam Lawson BA, MSc and Terra Doucette Hiller BA, BSN, RN

Pulmonary Vasculature

If we follow the circulation of blood as it leaves the right ventricle:

Blood enters the pulmonary trunk

Rotate the man incrementally and examine the branching of the pulmonary trunk into the left and right pulmonary arteries.

The pulmonary arteries travel alongside the respiratory bronchioles of the lungs.

Examine a side view of the vessels entering and leaving the lung
...and flows into capillary beds which surround the alveoli of the lungs.

Capillaries are just large enough to allow the passage of a single folded red blood cell. Carbon dioxide and oxygen molecules exchange directly to and from blood cells without getting carried off in plasma.
After gas exchange, oxygenated blood flows through pulmonary veins into the left atrium.

The pulmonary circulation is the only vascular bed which receives the entire cardiac output. Pulmonary circulation holds a blood pressure that is lower than systemic pressure due to the lack of smooth muscle in the vasculature of the pulmonary bed.

Pulmonary Embolism

A pulmonary embolism is a blockage of the pulmonary arteries. The blockage may be a blood clot or other matter (e.g., tumor, air, fat). Click here for an animation of a pulmonary embolism.

Ischemia produces necrosis of the lung regions supplied by the blocked arteries. Total diffusion capacity becomes decreased.
To compensate for the loss of gas exchange in the affected lung region, respiration rate will increase; local airway resistances will increase to help redistribute air to functional lung tissue. These compensations, however, usually have limited effect, and the patient will develop hypoxemia.

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