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Mechanics I—Static Lung Mechanics

3 Pages

Course Code
BIOL 1840U
Peter Cheung

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Mechanics I—Static Lung Mechanics I. Properties of Elastic Structures a. Terms i. Static Mechanics—relationship between pressure & volume in lung ii. Dynamic Mechanics—relationship between pressure & flow in lung b. Elastic Structures i. Volume is proportional to pressure ii. Transmural pressure—difference in pressure across the wall of the lung = internal surface pressure – external surface pressure = distending P 1. ↑ V => ↑ Tm 2. P Tm= Pin – Pout iii. Elastic Recoil Pressure—the equal & opposite tendency of a structure which resists the transmural pressure iv. Transmural Pressure-Volume Curve—graphs relationship between volume (y) & transmural pressure (x) 1. compliance—slope of P-V curve; compliance = ΔV/ΔP a. high compliance = easily distensible b. low compliance = stiff / non-distensible 2. elastance—opposite of compliance; elastance = ΔP/ΔV v. Terms 1. unstressed volume = Vo = volume when P Tm= 0 2. Limiting Volume = Elastic limit = max volume; ↑ P ≠ ↑ Volume 3. Elastic instability—when elastic structure either ruptures or collapses at high/ low PTms vi. Soap Bubble—has constant tension in its wall => P falls as Volume ↑ Tm II. Calculating P Tm in Respiratory System a. P ALV= alveolar pressure b. P =PLulmonary pressure c. P =Ltranspulmonary pressure = P ALV - PL d. P =BSody surface pressure (can be considered 0 b/c us. = atmospheric P) e. P CW = pressure of chest wall = PPL P BS f. P =RSressure of respiratory system = P ALV- PBS III. Pressure-Volume Curve of Lung a. Compliance of normal lung = 200 ml/ cm H2O i. => need 2.5 cm H2O of pleural pressure to overcome elastic recoil of lungs during tidal volume breath ii. => need 30 cm H2O of P toPLchieve TLC (further increases => rupture) b. Normal Values i. Unstressed lung volume ~= residual volume ii. Unstressed chest wall volume ~= 2/3 TLC (large) iii. At low volumes, chest wall => stiff b/c diaphragm reaches elastic limit * negative pleural pressure => relaxed chest wall gets smaller * mm. activation => negative pl. pressure => thorax enlarges iv. At high volumes, lung becomes stiff b/c elastic recoil increases c. Pressure-Volume curve of Lung 1 i. PTmV Curve of respiratory system is Σ PTM-V for chest wall & lung ii. Can add chest wall & lung compliances as if they’re in parallel 1 = 1 + 1 = Total _Compliance iii. C C C RS L CW iv. At FRC, P CW = Pmouth P BS IV. Determinants of Lung Volumes
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