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RESPIRATORY PHYSIOLOGY

Mechanics of Rcspiration: Forces during Quict Breathin

pressure isubatmospheric; determined from esophageal pressurei

A. Al rcsl

1. Respiratory muscles are at rest Recoil of lung and chcst wali are equal l»ul opposite

3.    Pressure along trachcohroiu hial iree i*, atmosphcric

4.    There is no airflow

rElaslic recoil of chust wali (pleural pressure minus pressure at surface of chest) recoil of luny (alveolar pressure minus pleural pressure)

pressure (atmospheric)

Pleural pressure tincreasingly subatmuspheric)

B. During inspiration

Inspiratory muscles contract and chest expands; ahreolar pressure becomes subalmosphenc with respect to pressure at airway opening. Air flows into lungs

C. During expiration

Inspiratory musdeS relax; recoil of lung t.ausos akeolar pressure to exceed pressure at airway opening. Air llows out of lung

Pleural pressure (subalmospheric)

Alveolar pressure (greater than atmospłierir l

recoil of lung (increased)

Figurę 5.7 Forces during Quiet Breathing_

The mechanics ot ventilation involve the dynamie interaction of the lungs, chest wali, and dia|)hragm. The interplay of these structures and the resulting changes in pleural and alveolar pressures are depic ted at rest and during inspiration and CKpiration.