Respiratory Disorders

• Normal Respiratory Structures


  • Nose
  • Pharynx
  • Larynx
  • Trachea
  • Bronchi
  • Lungs - alveoli
• Purpose and General Organization

  • Oversees gas exchanges between the blood and external environment
  • Exchange of gases takes place within the lungs in the alveoli
  • Passageways to the lungs purify, warm, and humidify the incoming air
• Respiratory Tract Divisions


  • Upper Respiratory Tract
  • Lower Respiratory Tract
• Gas Exchange


  • Gas crosses the respiratory membrane by diffusion
  • Oxygen enters the blood
  • Carbon dioxide enters the alveoli
  • Macrophages add protection
  • Surfactant coats gas-exposed alveolar surfaces
• Events of Respiration


  • Pulmonary ventilation - moving air in and out of the lungs
  • External respiration - gas exchange between pulmonary blood and alveoli
  • Respiratory gas transport - transport of oxygen and carbon dioxide via the bloodstream
  • Internal respiration - gas exchange between blood and tissue cells in systemic capillaries
• Mechanics of Breathing (Pulmonary Ventilation)

  1. Inspiration - flow of air into lung

  2. Expiration - air leaving lung
• Inspiration


  • Diaphragm and intercostal muscles contract
  • The size of the thoracic cavity increases
  • External air is pulled into the lungs due to an increase in intrapulmonary volume
• Expiration


  • Passive process dependent up on natural lung elasticity
  • As muscles relax, air is pushed out of the lungs
  • Forced expiration can occur mostly by contracting internal intercostal muscles to depress the rib cage
• Respiratory Volumes and Capacities

  • Tidal volume (TV)
  • Inspiratory reserve volume (IRV)
  • Expiratory reserve volume (ERV)
  • Residual volume
  • Functional volume
• Tidal Volume


  Normal breathing moves about 500 ml of air with each breath
• Inspiratory Reserve Volume


  Amount of air that can be taken in forcibly over the tidal volume, usually between 2100 and 3200 ml
• Expiratory Reserve Volume


  Amount of air that can be forcibly exhaled, approximately 1200 ml
• Residual Volume


  Air remaining in lung after expiration, about 1200 ml
• Functional Volume


  Air that actually reaches the respiratory zone, usually about 350 ml
• Respiratory capacities are measured with a spirometer
• Neural Regulation of Respiration

  • Activity of respiratory muscles is transmitted to the brain by the phrenic and intercostal nerves
  • Neural centers that control rate & depth are located in the medulla
  • The pons appears to smooth out respiratory rate
  • Normal respiratory rate (eupnea) is 12–15 min
  • Hyperpnea is increased respiratory rate often due to extra oxygen needs
• Pulmonary Diffusion


  • Inspired air path: bronchial tree arrives at alveoli
  • Blood path: right ventricle pulmonary trunk pulmonary arteries pulmonary capillaries
  • Capillaries surround alveoli
  • Replenishes blood oxygen supply
  • Removes carbon dioxide from blood
• Pulmonary Diffusion: Blood Flow to Lungs at Rest

  • At rest, lungs receive ~4 to 6 L blood/min
  • RV cardiac output = LV cardiac output
  • Lung blood flow = systemic blood flow
  • Low pressure circulation
  • Lung MAP = 15 mmHg versus aortic MAP = 95 mmHg
  • Small pressure gradient (15 mmHg to 5 mmHg)
  • Resistance much lower due to thinner vessel walls
• Pulmonary Diffusion: Respiratory Membrane

  • Also called alveolar-capillary membrane
  • Alveolar wall
  • Capillary wall
  • Respective basement membranes
  • Surface across which gases are exchanged
  • Large surface area: 300 million alveoli
  • Very thin: 0.5 to 4 mm
  • Maximizes gas exchange
• Pulmonary Diffusion: Partial Pressures of Gases

  • Air = 79.04% N2 + 20.93% O2 + 0.03% CO2
  • Total air P: atmospheric pressure
  • Individual P: partial pressures
  • Standard atmospheric P = 760 mmHg
  • Dalton's Law: total air P = PN2 + PO2 + PCO2
  • PN2 = 760 x 79.04% = 600.7 mmHg
  • PO2 = 760 x 20.93% = 159.1 mmHg
  • PCO2 = 760 x 0.04% = 0.2 mmHg
• Pulmonary Diffusion: Partial Pressures of Gases


  • Henry's Law: gases dissolve in liquids in proportion to partial P
  • Also depends on specific fluid medium, temperature
  • Solubility in blood constant at given temperature
  • Partial P gradient most important factor for determining gas exchange
  • Partial P gradient drives gas diffusion
  • Without gradient, gases in equilibrium, no diffusion
• Gas Exchange in Alveoli: Oxygen Exchange


  • Atmospheric PO2 = 159 mmHg
  • Alveolar PO2 = 105 mmHg
  • Pulmonary artery PO2 = 40 mmHg
  • PO2 gradient across respiratory membrane 65 mmHg (105 mmHg – 40 mmHg)
  • Results in pulmonary vein PO2 ~100 mmHg
• Gas Exchange in Alveoli: Carbon Dioxide Exchange

  • Pulmonary artery PCO2 ~46 mmHg
  • Alveolar PCO2 ~40 mmHg
  • 6 mmHg PCO2 gradient permits diffusion
  • CO2 diffusion constant 20 times greater than O2
  • Allows diffusion despite lower gradient
• Oxygen Transport in Blood

  • Can carry 20 mL O2/100 mL blood
  • ~1 L O2/5 L blood
  • More than 98% bound to hemoglobin (Hb) in red blood cells
  • O2 + Hb: oxyhemoglobin
  • Hb alone: deoxyhemoglobin
  • Less than 2% dissolved in plasma
• Transport of Oxygen in Blood: Hemoglobin Saturation

  • Depends on PO2 and affinity between O2, Hb
  • High PO2 (i.e., in lungs): Loading portion of O2-Hb dissociation curve, small change in Hb saturation per mmHg change in PO2
  • Low PO2 (i.e., in body tissues): Unloading portion of O2-Hb dissociation curve, large change in Hb saturation per mmHg change in PO2
• Factors Affecting Hemoglobin Saturation

  • Blood pH
  • Blood temperature
• Blood pH


  More acidic O2-Hb curve shifts to right, Bohr effect, more O2 unloaded at acidic exercising muscle
• Blood temperature


  Warmer O2-Hb curve shifts to right, promotes tissue O2 unloading during exercise
• Diagnostic Tests


  • Chest X-ray
  • Computerized Tomographic scan (CT scan)
  • Oximetry
  • Arterial Blood Gases
  • Overnight Oximetry
  • Sleep Study (Polysomnography)
  • Body Plethysmography (Body Box)
  • Diffusing Capacity
  • Spirometry
  • Maximal Inspiratory/Expiratory Pressure (MIPS and MEPS)
• Chest X-ray


  Helps evaluate lungs, heart and diaphragm, can show emphysema, rule out or confirm other problems like pneumonia, tuberculosis or lung cancer
• Computerized Tomographic scan (CT scan)


  Allows seeing a detailed picture of the lungs, used to better define areas not well seen on x-ray
• Oximetry


  Measures oxygen in the blood, done at rest, on exertion and during sleep to see if extra oxygen is needed
• Arterial Blood Gases


  Measures oxygen and carbon dioxide levels in blood directly from the heart and lungs, helps see how well the respiratory system is working
• Overnight Oximetry


  Measures oxygen levels during sleep to see if breathing problems affect oxygen and carbon dioxide levels
• Sleep Study (Polysomnography)


  Assesses breathing through the night, monitors heart, lungs, brain and muscle movement
• Body Plethysmography (Body Box)


  Measures how much air the lungs can hold and how much air is in the lungs when breathing, shows if lungs are large or small, stiff or floppy, or have trapped air
• Diffusing Capacity


  Measures the thickness of the membrane between the alveoli and blood vessels, shows if oxygen can pass easily into the blood
• Spirometry


  Measures the flow of air through the lungs, shows if airways are narrow making it harder to breathe
• Maximal Inspiratory/Expiratory Pressure (MIPS and MEPS)


  Measures the strength of the breathing muscles, both inspiratory and expiratory
• General Manifestations of Respiratory Disease

  • Sneezing
  • Coughing
  • Sputum
  • Breathing patterns and characteristics
  • Breath sounds
  • Dyspnea
  • Cyanosis
  • Pleural pain
  • Friction rub
  • Clubbed fingers
  • Changes in ABG (arterial blood gases)