🌬️

Overview of Respiratory System Mechanics

Mar 2, 2025

Lecture Notes: Respiratory System and Breathing Mechanics

Major Muscles Involved in Breathing

  • Inhalation:
    • Diaphragm
    • External intercostal muscles
  • Exhalation (Forced):
    • Internal intercostal muscles
    • Abdominal muscles (rectus abdominis, obliques)

Breathing Mechanics

  • Quiet Breathing:
    • Inhalation: Diaphragm and external intercostals contract → thoracic cavity volume increases → lung volume increases → pressure drops to 758 mmHg → air rushes in.
    • Exhalation: Diaphragm and external intercostals relax → elastic recoil occurs → alveolar pressure increases to 762 mmHg → air moves out.

Surfactant

  • Produced by type 2 alveolar cells.
  • Reduces surface tension in alveoli, preventing collapse during exhalation.
  • Importance in Premature Babies: Lack of surfactant leads to respiratory distress syndrome due to alveoli collapse.

Lung Compliance and Diseases

  • Compliance: Ease of lung expansion, major driving force of exhalation.
  • Reduced Compliance:
    • Scar tissue
    • Paralysis
    • Edema (dilutes surfactant, increases surface tension, alveoli collapse)
    • Pneumonia: Fluid build-up dilutes surfactant, making breathing difficult.

Airway Resistance

  • Related to airway diameter.
  • Decreased diameter (e.g., asthma, anaphylaxis) increases resistance and makes breathing difficult.

Breathing Patterns

  • Eupnea: Normal breathing
  • Apnea: Breath holding, common in sleep apnea.
    • Sleep apnea: Tissue collapse blocks airway, causing frequent waking, requires treatment like CPAP.
  • Dyspnea: Difficult or painful breathing
  • Tachypnea: Rapid breathing
  • Costal Breathing: Uses intercostal muscles, common during exercise.
  • Diaphragmatic Breathing: Typical breathing pattern.
  • Modified Respiratory Movements: For actions like coughing, hiccuping.

Lung Volumes and Capacities

  • Tidal Volume (TV): Normal breathing, ~0.5 L at rest.
  • Inspiratory Reserve Volume (IRV): Maximum inhale above tidal volume.
  • Expiratory Reserve Volume (ERV): Maximum exhale below tidal volume.
  • Vital Capacity (VC): Maximal inhale + maximal exhale; measure of lung function.
    • Highest in early 20s, decreases with age, lung conditions, smoking.
  • Residual Volume (RV): Air remaining in lungs after exhale, essential for keeping airways open.
  • Total Lung Capacity (TLC): VC + RV.

Gas Exchange and Pressures

  • Atmospheric Pressure:
    • Oxygen: 159 mmHg
    • CO2: 0.3 mmHg
  • Alveolar Pressure:
    • Oxygen: 105 mmHg
    • CO2: 40 mmHg
  • Capillary Pressure:
    • Oxygen: 40 mmHg (going to tissues), 45 mmHg (coming from tissues)
    • CO2: 45 mmHg

Hyperbaric Oxygenation

  • Used for treatment of heart disorders, CO poisoning, cerebral edema, bone infections, gas embolism, crush injuries.

Additional Notes

  • Spirometry: Measures lung volumes and capacities, useful for assessing lung function.
  • Portable Spirometer: Commonly used post-surgery to ensure proper breathing ability.

This summary highlights the main concepts discussed in this lecture, focusing on the mechanics of breathing, the function of surfactant, lung compliance, and various breathing patterns and lung capacities.

Full transcript