Regulation of pulmonary blood flow

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Regulation of pulmonary blood flow


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Regulation of pulmonary blood flow

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A 5-year-old boy is brought to the emergency room after accidentally ingesting a small plastic bead. Chest radiography reveals a radiopaque object in the right lower lobe. The bead is suspected to be causing near complete occlusion of one of the right lower lobe bronchioles. Which of the following physiological changes will most likely take place in the affected portions of the lung?  


Okay - so pulmonary circulation starts with the right ventricle.

From there - blood is pumped into the large pulmonary trunk, which splits to form the two pulmonary arteries – one for each lung.

The pulmonary arteries divide into smaller arteries known as pulmonary arterioles and then eventually into pulmonary capillaries which surround the alveoli - which are the millions of tiny air sacs where gas exchange happens.

At that point, oxygen enters the blood and carbon dioxide enters the alveoli.

The pulmonary capillaries drain into small veins that join to form the two pulmonary veins exiting each lung, and these pulmonary veins complete the circuit by delivering oxygen-rich blood into the left atrium.

Pulmonary blood flow (Q) is the volume of blood usually in milliliters, that’s being pumped out of the right ventricle over time, usually in 1 minute.

Said differently, pulmonary blood flow is the cardiac output of the right ventricle.

And cardiac output is the stroke volume, the volume of blood pumped per beat from the right ventricle of heart, expressed as mL per heartbeat; multiplied by the heart rate in beats per minute.


Pulmonary blood flow refers to the flow of blood through the lungs, and reflects the cardiac output of the right ventricle. Pulmonary blood flow (Q) is directly proportional to the difference in pressure between the pulmonary artery and the left atrium (the delta P); and inversely proportional to the resistance of the pulmonary vasculature (R). Q=ΔP/R


  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Pulmonary pericytes regulate lung morphogenesis" Nature Communications (2018)
  6. "Regulation of the pulmonary circulation" Heart (1971)

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