Basics of respiration


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Basics of respiration

  1. 1. Dr.Sivaramakrishnan
  2. 2.  Respiration includes two parts  External respiration  Internal respiration
  3. 3. External Respiration  The movement of gases into & out of body  Gas transfer from lungs to tissues of body  Maintain body & cellular homeostasis Internal Respiration  Intracellular oxygen metabolism  Cellular transformation  ATP generation  O2 utilization
  4. 4. Primary Goals OfThe Respiration System  Distribute air & blood flow for gas exchange  Provide oxygen to cells in body tissues  Remove carbon dioxide from body  Maintain constant homeostasis for metabolic needs
  5. 5. Respiration divided into four functional events: 1.Mechanics of pulmonary ventilation 2.Diffusion of O2 & CO2 between alveoli and blood 3.Transport of O2 & CO2 to and from tissues 4.Regulation of ventilation & respiration
  6. 6.  Lung weighs 1.5% of body weight  Alveolar tissue is 60% of lung weight  Alveoli have very large surface area  70 m2 internal surface area  Short diffusion pathway for gases  Permits rapid & efficient gas exchange into blood  1.5 µm between air & alveolar capillary RBC  Blood volume in lung (10% of total blood volume)
  7. 7.  After passing through the nasal passages and pharynx, where it is warmed and takes up water vapor, the inspired air passes down the trachea and through the bronchioles, respiratory bronchioles, and alveolar ducts to the alveoli
  8. 8.  The alveoli are surrounded by pulmonary capillaries.  In most areas, air and blood are separated only by the alveolar epithelium and the capillary endothelium, so they are about 0.5 mcm apart  300 million alveoli in humans, and the total area of the alveolar walls in contact with capillaries in both lungs is about 70 m2.
  9. 9.  Type I cells are flat cells with large cytoplasmic extensions and are the primary lining cells.  Type II cells (granular pneumocytes) are thicker and contain numerous lamellar inclusion bodies.These cells secrete surfactant  Also helps in alveolar repair
  10. 10.  Dead Space = ventilated but not perfused  The portion of tidal volume fresh air which does not go directly to the terminal respiratory units (30%)  The conducting airways do not participate in O2 & CO2 exchange  Dead space roughly 2 ml/kg ideal body weight or weight in pounds  Anatomical differs from physiological dead space also described as wasted ventilation
  11. 11.  The concept of physiologic dead space (VPD) describes a deviation from ideal ventilation relative to blood flow  Wasted ventilation includes anatomical dead space plus any portion of alveolar ventilation that does not exchange O2 or CO2 with pulmonary blood flow (alveolar dead space)  Ventilation/blood flow (V/Q) mismatch where blood flow blocked ( clot or emboli)  Wasted ventilation =VPD =VD +VAD
  12. 12.  The trachea and bronchi have cartilage in their walls.  Lined by a ciliated epithelium that contains mucous and serous glands.  Cilia are present as far as the respiratory bronchioles, but glands are absent from the epithelium of the bronchioles and terminal bronchioles  Bronchioles and term bronchioles do not have but contain more smooth muscle
  13. 13.  Abundant muscarinic receptors, and cholinergic discharge causes bronchoconstriction.  There are β2-adrenergic receptors in the bronchial epithelium and smooth muscle.  The β2 receptors mediate bronchodilation.They increase bronchial secretion while α1 adrenergic receptors inhibit secretion  Noncholinergic, non-adrenergic innervation of the bronchioles that produces bronchodilation, and there is evidence thatVIP is the mediator responsible for the dilation.
  14. 14.  Almost all the blood in the body passes via the pulmonary artery to the pulmonary capillary bed, where it is oxygenated and returned to the left atrium via the pulmonary vein  The separate and much smaller bronchial arteries come from systemic arteries.They form capillaries, which drain into bronchial veins or anastomose with pulmonary capillaries or veins  The bronchial veins drain into the azygos vein.The bronchial circulation nourishes the bronchi and pleura. Lymphatic channels are more abundant in the lungs than in any other organ
  15. 15. Tidal volume is the amount of air that moves into the lungs with each inspiration and expiration Inspiratory reserve volume is the air inspired with a maximal inspiratory effort in excess of the tidal volume The volume expelled by an active expiratory effort after tidal expiration is the expiratory reserve volume The air left in the lungs after a maximal expiratory effort is the residual volume Vital capacity is defined as the amount of air moved in out of the lungs with max inspiration and expiration Total lung capacity is the volume of gas occupying the lungs after maximum inhalation Functional residual capacity is the amount of air left in the lungs after tidal expiration • Remember: A capacity is always a sum of certain lung volumes • TLC = IRV +TV + ERV + RV • VC = IRV+TV + ERV • FRC = ERV + RV • IC =TV + IRV
  16. 16.  REMEMBER: Spirometry cannot measure Residual Volume (RV) thus Functional Residual Capacity (FRC) andTotal Lung Capacity (TLC) cannot be determined using spirometry alone.
  17. 17.  Chest wall compliance is a major determinant of FRC  FRC reached at a point where outward thoracic cage recoiling counterbalances inward lung recoiling  Measured FRC in infants is higher than expected  Increased chest wall compliance is a distinct disadvantage
  18. 18.  Poorly equipped to sustain large workloads  Easily fatigable thereby limiting their ability to maintain ventilation in lung disease  In poor compliance conditions, there is greater retraction of chest wall leading to more loss of FRC  Obstructive lung diseases produce greater chest recoil and reduced FRC  PEEP beneficial in these conditions
  19. 19. Multiple factors required to alter lung volumes  Respiratory muscles generate force to inflate & deflate the lungs  Tissue elastance & resistance impedes ventilation  Distribution of air movement within the lung, resistance within the airway  Overcoming surface tension within alveoli
  20. 20.  Airflow requires a pressure gradient  Air flow from higher to lower pressures  During inspiration alveolar pressure is sub- atmospheric allowing airflow into lungs  Higher pressure in alveoli during expiration than atmosphere allows airflow out of lung  Changes in alveolar pressure are generated by changes in pleural pressure
  21. 21.  Elastance  Property of a substance to oppose deformation or stretching  Calculated as change in pressure / change in volume  Elastic recoil is a property that enables it to return to its original state after it is no longer subjected to pressure
  22. 22.  Compliance  Is the reciprocal of elastance  Refers to distensibility  Resistance  Amount of pressure required to generate flow of gas across the airways  Poiseuille’s law – R = 8 Lη/Πr⁴
  23. 23.  Newborns and young infants have inherently smaller airways  Prone to marked increase in airway resistance from inflamed tissues and secretions.  In diseases in which airway resistance is increased, flow often becomes turbulent.
  24. 24.  Re =2rvd/η  Turbulance in airflow is most likely if Re number exceeds 2000  Neonates and young infants are predominantly nose breathers and, therefore, even a minimal amount of nasal obstruction is poorly tolerated.
  25. 25. Active Phase Of Breathing Cycle  Motor impulses from brainstem activate muscle contraction  Phrenic nerve (C 3,4,5) transmits motor stimulation to diaphragm  Intercostal nerves (T 1-11) send signals to the external intercostal muscles  Thoracic cavity expands to lower pressure in pleural space surrounding the lungs
  26. 26.  Pressure in alveolar ducts & alveoli decreases  Lungs expand passively as pleural pressure falls(-2.5mmHg to -6mmHg)  Fresh air flows through conducting airways into terminal air spaces until pressures are equalized  The act of inhaling is negative-pressure ventilation
  27. 27. Most Important Muscle Of Inspiration  Responsible for 75% of inspiratory effort  Thin dome-shaped muscle attached to the lower ribs, xiphoid process, lumbar vertebra  Innervated by Phrenic nerve (Cervical segments 3,4,5)
  28. 28.  During contraction of diaphragm  Abdominal contents forced downward & forward causing increase in vertical dimension of chest cavity  Rib margins are lifted & moved outward causing increase in the transverse diameter of thorax  Diaphragm moves down 1cm during normal inspiration  During forced inspiration diaphragm can move down further  Paradoxical movement of diaphragm when paralyzed  Upward movement with inspiratory drop of intrathoracic pressure  Occurs when the diaphragm muscle is denervated
  29. 29. The Passive Phase Of Breathing Cycle  Chest muscles & diaphragm relax contraction  Elastic recoil of thorax & lungs return to equilibrium  Pleural & alveolar pressures rise  Gas flows passively out of the lung  Expiration - active during hyperventilation & exercise