GLOSSARY

Exhalation (expiration) is the phase in which air leaves the lungs, achieved by decreasing thoracic volume and thereby raising alveolar pressure above atmospheric pressure.

Quiet (Passive) Exhalation

• Relaxation of the diaphragm and external intercostals.
• Elastic recoil of the lungs and chest wall.
• Alveolar pressure about +1 cm H₂O; air flows out.
• No muscular energy required.

Active (Forced) Exhalation

• Abdominal muscles: raise intra-abdominal pressure and push the diaphragm upward.
• Internal intercostals: pull the ribs down.
• Uses: exercise, coughing, sneezing, singing, playing wind instruments, and spirometry testing.

Inspiration-to-Expiration Ratio

About 1:2 at rest, meaning expiration is longer; during exercise the ratio approaches 1:1.