Lesson 1

Lesson 1: Ventilation

  • Gas exchange (O2 & CO2) between the atmosphere and lungs.

  • Requires brain and respiratory muscle coordination.

  • Diaphragm and external intercostals contract for inspiration.

  • Exhalation is passive, driven by chest wall recoil.

Breathing Muscles

Muscles of Inspiration

  • Diaphragm, external intercostals, sternocleidomastoid, scalene muscles.

Muscles of Expiration

  • Internal intercostals, rectus abdominis, external & internal obliques, transverse abdominis.

  • Active expiration needed for increased ventilation or in lung diseases.

Capacity for Coughing

  • Vital capacity of at least 15 mL/kg is necessary for effective cough.

Airway Zones

  1. Conducting Zone:

    • No gas exchange (anatomic dead space).

    • Extends from nares/mouth to terminal bronchioles.

  2. Transitional Zone:

    • Serves as air conduit and participates in gas exchange.

  3. Respiratory Zone:

    • Gas exchange occurs; extends from respiratory bronchioles to alveolar sacs.

Transpulmonary Pressure (TPP)

  • TPP = Alveolar pressure - Intrapleural pressure.

  • Positive TPP keeps airways open, negative TPP causes collapse.

  • During tidal breathing: TPP is positive, intrapleural pressure is negative.

Summary of Pressures During Breathing

  • FRC: Airflow = None, TPP = +5.

  • During Inspiration: TPP increases, airflow in.

  • During Expiration: TPP decreases, airflow out, can become negative during forced expiration.