Compliance: ability of lungs and thorax to expand. 11
square5 Infant Respiratory Distress Syndrome (IRDS) square5 Surfactant only produced adequately at about 35 weeks of gestation square5 Premature babies barb2right lack of surfactant barb2right high surface tension barb2right alveoli collapse barb2right breathing difficulties square4 Higher pressures/energy are required to ventilate lungs square4 Lung compliance is low 12
square5 Exchange of air between the atmosphere and alveoli square5 Two phases square4 Inspiration -gases flow into lungs square4 Expiration -gases exit lungs square5 Air moves from a region of high pressure to one of low pressure 14
square5 Atmospheric pressure ( P atm ) square4 Pressure exerted by air surrounding body square4 760 mm Hg at sea level = 1 atmosphere square5 Respiratory pressures described relative to P atm square4 Negative respiratory pressure barb2right less than P atm square4 Positive respiratory pressure barb2right greater than P atm square4 Zero respiratory pressure barb2right = P atm 15
1. If Respiratory pressure = - 4 mm Hg, means lower than atmospheric pressure by 4 mmHg, absolute pressure in that region : 760- 4 = 756 mmHg 2. Respiratory pressure = 0 mm Hg square4 Absolute pressure = ? 3. Respiratory pressure = 4 mm Hg square4 Absolute pressure = ? 16
1. Intrapulmonary Pressure, P pul 2. Intrapleural Pressure, P ip 3. Transpulmonary pressure square4 P pul – P ip 17
square5 Intrapulmonary (intra-alveolar) pressure ( P pul ) square4 Pressure in alveoli square4 Fluctuates with breathing square4 Always eventually equalizes (at the end of each breathing) with P atm 18
19 Atmospheric pressure ( P atm ) 0 mm Hg (760 mm Hg) Thoracic wall Parietal pleura Visceral pleura Pleural cavity Transpulmonary pressure 4 mm Hg (the difference between 0 mm Hg and -4 mm Hg) Intrapleural pressure ( P ip ) -4 mm Hg (756 mm Hg) Intrapulmonary pressure ( P pul ) 0 mm Hg (760 mm Hg) Diaphragm Lung 0 – 4
square5 Intrapleural pressure ( P ip ) square4 Pressure in pleural cavity square4 Fluctuates with breathing square4 Always a negative pressure (<P atm and <P pul ) square4 Fluid level must be minimal uni25AA Pumped out by lymphatics uni25AA If accumulates barb2right positive P ip pressure barb2right lung collapse 20
21 Fig: Accumulation of fluid in pleural cavity
square5 Negative P ip caused by opposing forces square4 Two inward forces promote lung collapse uni25AA Elastic recoil of lungs decreases lung size uni25AA Surface tension of alveolar fluid reduces alveolar size square4 One outward force tends to enlarge lungs uni25AA Elasticity of chest wall pulls thorax outward 22
square5 If P ip = P pul or P atm barb2right lungs collapse square5 (P pul – P ip ) = Transpulmonary pressure square4 Keeps airways (air spaces of the lungs) open square4 Greater transpulmonary pressure barb2right larger lungs 23 ip = intrapleural pul=pulmonary
square5 Atelectasis (lung collapse) due to 1.
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- Dr Lee