Regulation of pulmonary blood flow

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.

Now pulmonary blood flow is directly proportional to the difference in pressure between the pulmonary artery and the left atrium, or the delta P; and inversely proportional to the resistance of the pulmonary vasculature (R).

The blood pressure and resistance in the pulmonary circulation is normally much lower than the systemic blood pressure.