Pulmonology

• Respiratory Physiology


  The study of the physiological processes involved in respiration
• Main sections


  • Pulmonary ventilation
  • Diffusion of gases
  • Transport of gases
  • Control of respiration
• Objectives


  • Describe the anatomy of the respiratory system and its relation to function
  • Explain the structure of the chest wall and diaphragm and to relate these to respiratory mechanics
  • Describe the inspiratory and expiratory process involving the chest wall, diaphragm, pleura and lung parenchyma

  
• Ventilation


  Movement of air into and out of lungs
• External respiration


  Gas exchange between air in lungs and blood
• Transport of oxygen and carbon dioxide in the blood


  The process of transporting these gases in the blood
• Internal respiration


  Gas exchange between the blood and tissues
• Respiratory System Functions


  • Gas exchange: Oxygen enters blood and carbon dioxide leaves
  • Regulation of blood pH: Altered by changing blood carbon dioxide levels
  • Voice production: Movement of air past vocal folds makes sound and speech
  • Olfaction: Smell occurs when airborne molecules drawn into nasal cavity
  • Protection: Against microorganisms by preventing entry and removing them

  
• Respiratory System Divisions


  • Upper tract: Nose, pharynx and associated structures
  • Lower tract: Larynx, trachea, bronchi, lungs

  
• Nose


  Functions: Passageway for air, Cleans the air, Humidifies, warms air, Smell, Resonating chamber for speech
• Pharynx


  Common opening for digestive and respiratory systems, Three regions: Nasopharynx, Oropharynx, Laryngopharynx

  
• Larynx


  Functions: Maintain an open passageway for air movement, Epiglottis and vestibular folds prevent swallowed material from moving into larynx, Vocal folds are primary source of sound production
• Trachea


  Windpipe, Divides to form primary bronchi, Carina: Cough reflex
• Tracheobronchial Tree


  Conducting zone: Trachea to terminal bronchioles which is ciliated for removal of debris, Passageway for air movement, Cartilage holds tube system open and smooth muscle controls tube diameter

  Respiratory zone: Respiratory bronchioles to alveoli, Site for gas exchange
• Terminal respiratory unit (TRU)

  The functional unit of the lung, Consists of respiratory bronchioles, alveolar ducts, and alveolar sacs, Site of gas exchange with the pulmonary capillary blood

  
• Alveolus and Respiratory Membrane


  The normal adult human lung weighs about 1000g and consists of about 50% blood and 50% tissue by weight, About 10% of the total lung volume is composed of various types of conducting airways and some connective tissue, The remaining 90% is the respiratory or gas exchange portion of the lung, composed of alveoli and supporting capillaries

  
• Thoracic Walls


  Muscles of Respiration
• Mechanics of Ventilation


  Air is delivered to alveoli as a consequence of respiratory muscle contraction, Contraction of the diaphragm leads to downwards displacement of the thoracic cavity and contraction of external intercostals muscles leads to lifting of the thoracic cage leading to increase in the antero-posterior diameter, Inspiration is due to muscle contraction, Expiration is usually passive, resulting from relaxation of the inspiratory muscles and powered by elastic recoil of lung tissue, Active expiration is due to internal intercostals muscles and the abdominal recti
• Thoracic Volume


  The volume of the thoracic cavity
• Pleural fluid


  Produced by pleural membranes, acts as lubricant, helps hold parietal and visceral pleural membranes together
• Ventilation


  Movement of air into and out of lungs, air moves from area of higher pressure to area of lower pressure, pressure is inversely related to volume

  
• Air flow through bronchioles

  1. Directly proportional to pressure difference

  2. Inversely proportional to frictional resistance to flow

  
• Alveolar pressure changes


  Caused by lung recoil, elastic recoil, surface tension, pleural pressure

  
• Surfactant


  • Reduces tendency of lungs to collapse
• Pneumothorax


  Opening between pleural cavity and air causes loss of pleural pressure
• Pneumothorax causes one lung to collapse since each lung is in a separate pleural compartment
• Transpulmonary pressure


  Pressure difference between alveolar pressure and pleural pressure, measure of elastic forces leading to lung collapse

  
• Pulmonary elastance/compliance


  Lung is an elastic structure that promotes collapse, elastance opposes lung inflation, compliance is the reciprocal of elastance and measures ease of deformation/inflation

  
• Conditions that decrease compliance


  • Pulmonary fibrosis, pulmonary edema, respiratory distress syndrome
• Lung compliance


  Change in volume divided by change in pressure, 1/3 to overcome pleural pressure, 2/3 to overcome surface tension

  
• Surfactant


  Surface active agent secreted by type II alveolar cells, removed by alveolar macrophages, lowers surface tension and prevents alveolar collapse
• Fetal lung surfactant not fully functional until 7th month of gestation, related to respiratory distress syndrome
• Surfactant deficiency or inactivation can also occur in adults who breathe 100% O2 for prolonged periods or have prolonged pulmonary artery occlusion, leading to adult respiratory distress syndrome
• The first breath of life is difficult as newborn must overcome great surface tension forces to inflate partially collapsed alveoli, requiring 15-20 times the transpulmonary pressure of subsequent breaths

  
• Mechanical ventilators and exogenous surfactant can help save babies with respiratory distress syndrome by keeping them alive until their lungs mature, but exogenous surfactant does not help treat adult ARDS
• Work of breathing


  Components:

  • Compliance work: against elastic forces of lung + cage
  • Tissue resistance work: against viscosity of both lung and cage
  • Airway resistance work
• During quite breathing, 3-5% of total energy of the body are spent for respiration, while in heavy exercise, it increases up to 50 folds
• Lung volumes


  Anatomical measurements of lung gas volumes

  
• Lung capacities


  Sum of two or more basic lung volumes

  
• Pulmonary Volumes


  • Tidal volume
  • Inspiratory reserve volume
  • Expiratory reserve volume
  • Residual volume