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BPK 306 Lecture Notes - Pulmonary Vein, Pulmonary Artery, Alveolar Pressure

Biomedical Physio & Kines
Course Code
BPK 306
Mike Walsh

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Respiratory System #5
A. Pulmonary Vasculature Compared With Systemic Vasculature
a. Pulmonary arteries and arterioles much thinner and larger diameter than in
systemic counterparts
b. Pulmonary arterial tree very compliant = 7 mL/mm Hg.
c. Pulmonary veins very similar to systemic veins
B. Pulmonary Blood Pressure
a. Often, systemic system is called “high pressure system”; pulmonary
system called “low pressure system”
b. Pulmonary arterial blood pressure = 25/8 mm Hg
c. Mean pulmonary arterial pressure is 15 mm Hg
d. Mean pulmonary capillary pressure is 7-10 mm Hg
e. Lower pressure b/c don’t have to transport blood great distances, and it
avoids pulmonary edema via Starling’s forces
C. Pressure Around Pulmonary Blood Vessels
a. Pulmonary caps virtually surrounded by alveoli too, so pressure
surrounding caps is almost all alveolar pressure
b. Pressure around pulmonary arteries and veins influenced by surrounding
lung parenchyma. Thus, when lungs expand (inspiration), pulmonary
arteries/veins are pulled open by surrounding tissue
c. Due to diff betw pulmonary caps, and pulmonary art/veins, caps are called
alveolar vessels, and arts/veins are extra-alveolar vessels
d. Resistance to blood flow in pulmonary caps much greather than in
systemic caps. B/c of alveolar compression of pulmonary caps
e. Overall, pulmonary circulation resistance much lower than systemic
system b/c most of resistance comes from Extra-alveolar vessels??
D. Pulmonary Blood Volume
a. About 10% (450 mL) of total blood volume.
i. This volume can decrease 50% or increase 2x under certain
(mostly abnormal conditions)
ii. At rest, cap blood volume is about 75 mL; incr during exercise to
max capacity of 200mL
E. Pulmonary Blood Flow
1. Local Effects:
a. Blood flow through lungs essentially equal to cardiac output, so
same factors affecting blood flow for both
b. Goal of pulmonary system blood flow is opposite of systemic system
c. SM of pulmonary arteries and arterioles is bathed in alveolar gas
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