Respiratory

• Inspiration


  Movement of air into lungs
• Expiration


  Movement of air out of lungs
• Air always flows from high pressure to lower pressure
• Boyle's Law


  Pressure (P) and Volume (V) are inversely proportional to one another
• Intrapulmonary pressure (Ppul)


  Pressure within the alveoli

  
• Intrapleural pressure (Pip)


  Pressure within the pleural cavity
• Atmospheric pressure (Patm)


  Pressure within the atmosphere (equal to 760 mm Hg at sea level)
• Inspiration


  Lungs move down, pressure decreases
• Expiration


  Lungs move up, pressure increases

  
• Factors preventing lung collapse

  • Surfactants reduce surface tension on alveoli
  • Negative intrapleural pressure (-4 mm Hg) due to adhesive force of pleura
  • Residual lung volume - air that remains in lungs after expiration

  
• Lung compliance


  The ease with which lungs can be expanded

  
• Factors that diminish lung compliance include scar tissue/fibrosis, blockage of smaller respiratory passages, reduced bronchiole diameter, reduced surfactant production, and decreased flexibility of thoracic cage
• Respiratory volumes


  • Tidal volume (TV)
  • Inspiratory reserve volume (IRV)
  • Expiratory reserve volume (ERV)
  • Forced expiratory volume (FEV)
  • Residual volume (RV)

  
• Respiratory capacities


  • Inspiratory capacity (IC)
  • Functional residual capacity (FRC)
  • Vital capacity (VC)
  • Total lung capacity (TLC)

  
• Minute respiratory volume


  Amount of air ventilated within a minute, calculated as TV x RR
• Anatomical dead space


  Air trapped in conducting zone structures and unavailable for gas exchange (~ 150 ml)
• Alveolar ventilation rate (AVR)


  Measures the rate of ventilation within the alveoli within a minute, calculated as RR x (TV - dead space)

  
• Lung volumes


  Sum of all lung volumes (approximately 6000 ml in males)
• Respiratory Volumes and Capacities

  • Forced in
  • All the air you can hold
  • Everything the lungs can hold
  • Resting out
  • Forced out
  • No access

  
• Minute Respiratory Volume (MRV)


  Amount of air ventilated within a minute
• Calculating MRV


  1. TV x RR (# breaths/min)

  2. e.g. 500 ml/breath x 12 breaths/min = 6000 ml/min
• Normal Respiratory Rate (adult) = 12-20 breaths/min
• Alveolar Ventilation


  Measures the rate of ventilation within the alveoli within a minute
• Calculating Alveolar Ventilation Rate (AVR)

  1. RR x (TV - dead space)

  2. e.g. 12 breaths/min x (500 ml - 150 ml) = 4200 ml/min

  
• Oxygen is bound to Hemoglobin (Hb) in the lungs
• Dalton's Law


  The partial pressure of each gas in a mixture is directly proportional to its percentage in the mixture
• Partial pressure of O2 (PO2) = 160 mm Hg (assuming Patm = 760 mm Hg and O2 = ~21% of air mixture)
• O2 and CO2 always move from Higher to Lower Partial Pressure in the body
• Ventilation-Perfusion Coupling (V/P Ratio)


  • Ventilation: amount of gas reaching alveoli
  • Perfusion: blood flow reaching alveoli

  
• Ventilation and perfusion rates must be matched for optimal, efficient gas exchange
• Ventilation-Perfusion Coupling


  • PO2 controls perfusion by changing arterial diameter
  • PCO2 controls ventilation by changing bronchiolar diameter
• Lower V/P Ratio


  Reduced gas exchange (occurs in chronic bronchitis, asthma, pulmonary edema)
• Higher V/P Ratio


  Wasted gas exchange (occurs with emphysema and pulmonary embolism)
• Oxyhemoglobin (HbO2)


  Oxygen bound to hemoglobin within red blood cells
• 98.5% of oxygen is bound to hemoglobin (Hb) within red blood cells
• Up to 4 molecules of oxygen can bind to 4 heme (Fe) groups in a reversible reaction
• 1.5% of oxygen is dissolved in plasma
• Oxygen-Hemoglobin Dissociation Curve


  Describes the percentage of Hb saturation with oxygen at any PO2
• PO2 (lungs) = 100 mmHg, PO2 (tissues at rest) = 40 mmHg, PO2 (tissues during exercise) = 15 mmHg
• pH, CO2, Temperature, BPG, or exercise

  Shifts the oxygen-hemoglobin dissociation curve to the right (decreases Hb/O2 affinity, increases O2 unloading)