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BPK 306 Lecture Notes - Alveolar Cells, Pulmonary Compliance, Transpulmonary Pressure

Biomedical Physio & Kines
Course Code
BPK 306
Mike Walsh

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Respiratory Section 3
A. Compliance of the Lung
1. Degree to which lung expands/fills for change in transpulmonary
pressure (pressure betw pleural space and alveolar space)
2. Inspiration: (fig 21-15)
i. Small compliance in the beginning
ii. Increase compliance in the middle
iii. Compliance levels off at the end
3. Expiration: (fig 21-15)
i. Different V/P relation than inspiration
ii. Hysteresis
1. Mostly due to surface tension due to surface tension on
innerwall of alveoli.
2. Also, V/P relation not the same b/c energy is lost as heat
under cyclic loading and unloading of a spring. Greater
energy loss at higher tidal volumes
4. Saline
i. Fill excised lung with saline
ii. increases compliance by 3x
iii. water-water interface inside alveoli
iv. air-water interface in air-filled lung
v. Difference due to surface tension on inside of alveoli
B. Surface Tension
1. Less interaction of water with solid surface, the more water will bead up
due to surface tension
2. Water molecs have greater attraction for each other than for air
3. Soap makes better bubbles b/c it reduces water’s surface tension
4. Moisture in inside of alveolus walls generates surface tension that wants
to make alveolus collapse
C. Surfactant
1. Pattle noticed fluid from induced pulmonary edema formed stable
bubbles due to surfactant.
2. On inside of alveolar surface
3. Excreted by type II alveolar cells
4. Phospholipid protein w/ 14 hr half life
5. Secretion begins about 7th month of gestation. Prior birth results in
respiratory distress syndrome in premature babies.
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