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Respiratory System Part 3

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Simon Fraser University
Biomedical Physio & Kines
BPK 306
Mike Walsh

Respiratory Section 3 III. LUNG COMPLIANCE AND STABILITY 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 7 month of gestation. Prior birth results in respiratory distress syndrome in premature babies. D. Alveolar Stability
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