MECHANICS OF BREATHING

Annotations:

• Subtopic of inspiration (inhalation)

1. Ribs and sternum moved by the external intercostals muscles
2. Diaphragm contracts, flattening down toward the abdomen (move inferiorly)
3. This action expands the thoracic cage, in turn expanding the lungs.
4. The air within them has more space to fill (the pressure within the lungs decrease)
5. The pressure in the lungs is less than the pressure of the at outside the body - air rushes into the lungs to reduce the pressure difference
6. Force breathing/ inspiration: - The scalenes and sternocleidomastoid in the neck and the pectorals in the chest help raise the ribs even more than during regular breathing
7. Air flows into the lungs through the respiratory passage

1. Air flows out of the lungs from the respiratory passage
2. Diaphragm relaxes and returns to its normal upward position (move superiorly)
3. External intercostals muscles relax, the ribs and sternum lower back into their resting positions
4. The elastic nature of the lung tissue causes it to recoil to its resting size
5. This increases the pressure in the thorax - air is forced out of the lungs
6. Force breathing/ expiration: - The internal intercostals muscles pull the ribs down, assisted by the latissimus dorsi and quadratus lumborum muscles

1. Used to assess a person's respiratory status:
   1. Tidal volume (Tv) - Amount of air inhaled or exhaled with each breath under resting conditions
   2. Inspiratory reserve volume (IRV) - Amount of air that can be forcefully inhaled after a normal tidal volume inhalation
   3. Expiratory reserve volume (ERV) - Amount of air that can be forcefully exhaled after a normal tidal volume exhalation
   4. Residual volume (RV) - Amount of air remaining in the lungs after a forced exhalation

1. The respiratory capacities always consist of two or more lung volumes. Include:
   1. Inspiratory capacity (IC) - Maximum amount of air that can be inspired after a normal expiration (IC = TV + IRV)
   2. Functional residual capacity (FRC) - Volume of air remaining in the lungs after a normal tidal volume expiration (FRC = ERV + RV)
   3. Vital capacity (VC) - Maximum amount of air that can be expired after a maximum inspiratory effort (VC = TV + IRV + ERV)
   4. Total lung capacity (TLC) - Maximum amount of air contained in lungs after a maximum inspiratory effort (TLC = TV + IRV + ERV RV)

1. Some inspired air never contributes to gas exchange
2. Anatomical dead space: volume of the conducting zone conduits (~150ml)
3. Alveolar dead space: alveoli that cease to act in gas exchange due to collapse or obstruction
4. Total dead space: sum of above nonuseful volumes

1. Most of the air movements result from reflex activity, but some are produced voluntarily
   1. Air movements:
      1. - Coughing, sneezing, crying (involved emotional induced mechanism), laughing (involved emotional induced mechanism), yawning, hiccupping, snoring