02 Pulmonary Physiology

Lung Volumes

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• TLC: average person, 6 L total

• RV: 1 L residual volume

• TV: quiet breathing, 2.5 - 3L

• Inspiratory Reserve Volume: volume inhaled after inspiration TV

• ERV: same with expiration TV

• FRC: functional residual capacity, volume left after TV expiration

• VC: everything but residual volume

• IRV

• TV

• ERV

• RV

• bottom 2: FRC

• top 2: IC

• top 3: VC

• all 4: TLC

Ventilation

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Dead Space

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• not all alveoli exchange gas

• apex largest contributor to dead space

• ratio of physiologic (not anatomic) deadspace to TV

Lung and Chest Wall

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• lung like a balloon

• no pressure: no volume

• maximum point: no increase in volume with pressure increase

• no pressure: still has a volume

• positive pressure increase volume

• negative pressure withdraw volume

• at 0: no air movement

• at FRC: tendency for lungs to collapse balanced by tendency of chest wall to expand, no pressure on air molecules inside alveoli

Pressure

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• by convention, 0 mmHg, no difference between alveoli and atmospheric

• at end of expiration/inspiration, no movement of air, pressure equal

• exhale: pressure inside becomes positive, drive air out

• inhale: pressure inside becomes negative, drive air in

Pleural Space

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• for pressure in alveoli to be 0 (no airflow), pressure in pleural space must be negative

• positive pressure of lung to collapse balanced by negative pressure of pleural space

• intrapleural space: always negative during normal breathing

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• net sum of pressure differences acting on pleural tissue

• pressure +5 pushing in and +5 inside pushing out = 0

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• pressure surrounding alveoli become equal to pressure in alveoli

• resistance flow slowly drops pressure inside alveoli

• beyond equal pressure point: airway collapse prevented by cartilage

• bronchitis: +60 closer to alveoli

• emphysema: instead of +90, +70 in alveoli

Lung Compliance

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• stiffness of lung

• compliant: easy to stretch or move air

• infiltrate in lung: stiff (water, fibrosis)

• Aging: lung compliance increases (loss of elasticity). Chest wall compliance decreases (rib calcification, stiffening). RV increases (air trapping, like emphysema). FVC decreases (air trapping from increased RV). TLC stays same (decreased chest wall compliance balances lung compliance).

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• very slow laminar flow good for O2 transmission