Respiration II PT2

Air Flow

• Air flow (F) is equal to the change in pressure (∆P) divided by resistance (R)
• ∆P represents the difference in pressure between atmosphere and alveoli; increased ∆P leads to increased air flow
• R represents resistance of airways; increased R leads to decreased air flow
• ∆P is altered by inspiratory and expiratory muscle contraction
  • Quiet inspiration involves the diaphragm and intercostal muscles
  • Quiet expiration happens passively due to the lung elasticity
  • Forced inspiration uses scalenes & sternocleidomastoid neck muscles; this increases ∆P and air flow
  • Forced expiration uses abdominal wall muscles (obliques); this increases ∆P and airflow
• Resistance to flow is altered by the diameter of conducting zone airways
• The autonomic nervous system largely regulates this resistance
  • Sympathetic innervation causes bronchiole dilation, decreasing resistance and increasing airflow
  • Parasympathetic innervation causes bronchiole constriction, increasing resistance and decreasing airflow
• Mucus buildup, tumors and allergic reactions can also influence resistance, increasing it and decreasing airflow
• Lung compliance (C₁) is the ability of the lungs to stretch and expand. It is calculated as the change in volume divided by the change in pressure
• Higher lung compliance results in easier lung expansion at any given pressure
• Scarring/fibrosis impairs lung compliance

Spirometer

• Lung volumes can be assessed using a spirometer

Lung Volumes and Capacities

• Tidal Volume (TV): 500 ml in both adult males and females, is the amount of air inhaled/exhaled with each breath under resting conditions
• Inspiratory Reserve Volume (IRV): 3100 ml in males and 1900 ml in females, is the amount of air that can be forcefully inhaled after a normal tidal volume inspiration
• Expiratory Reserve Volume (ERV): 1200 ml in males and 700 ml in females, is the amount of air that can be forcefully exhaled after a normal tidal volume expiration
• Residual Volume (RV): 1200 ml in males and 1100 ml in females, is the amount of air remaining in the lungs after a forced expiration
• Total Lung Capacity (TLC): 6000 ml in males and 4200 ml in females, is the maximum amount of air contained in the lungs after a maximum inspiratory effort; TLC = TV + IRV + ERV + RV
• Vital Capacity (VC): 4800 ml in males and 3100 ml in females, is the maximum amount of air that can be expired after a maximum inspiratory effort: VC = TV + IRV + ERV
• Inspiratory Capacity (IC): 3600 ml in males and 2400 ml in females, is the maximum amount of air that can be inspired after a normal tidal volume expiration: IC = TV + IRV
• Functional Residual Capacity (FRC): 2400 ml in males and 1800 ml in females, is the volume of air remaining in the lungs after a normal tidal volume expiration: FRC = ERV + RV
• Males typically have greater lung volumes than females

Dead Space

• Dead space is the volume of air that doesn't contribute to gas exchange
• Anatomical dead space is air in the conducting zones
• Alveolar dead space is air in the respiratory zone not contributing to gas exchange
• Total dead space is the sum of anatomical and alveolar dead space