Respiratory Mechanics

Respiratory Mechanics

1. Pulmonary Ventilation

   • Inspiration & Expiration
   • Volume change of thoracic cavity and lungs
     • Boyle's Law P~1/V

2. Quiet Breathing

   • Diaphragm: Increase thoracic volume
   • External Intercostal: raise ribs and increase thoracic volume
   • Expiration: passive recoil (elastin)

3. Deep Breathing

   • Inhalation
   • Scalene, Sternocleidomastoid
     • Raise ribs and increase thoracic volume
   • Expiration
     • Internal intercostal & abdominals

4. What controls breathing factors

   • Medulla Respiration Centers
     • Brainstem
     • Starts at the Medulla Oblongata (NTS)
     • Basic breathing rhythm
     • if medulla destroyed you will have trouble breathing
   • Pons Respiratory Centers
     • Influence breathing rhythm
     • Two respiratory centers
       • Apneustic Center
         • Stimulates inspiratory neurons of the medulla
         • Makes breathing increases
       • Pneumotaxic Center
         • Antagonizes apneustic center
           • Reduction of Breathing
   • Peripheral and Central Chemoreceptors
     • Influenced breathing rhythm (rate and depth)
     • Sensitive to blood CO2, O2 and pH
     • Location
       • Medulla Oblongata CENTRAL
       • Aortic and carotid bodies (PERIPHERAL)

5. Phrenic nerve innervates the diaphragm

6. Intercostal nerves innervates the intercostal muscles

7. Chemoreceptors Mechanism

   • Central Chemoreceptors
     • Greatest effect on Ventilation
     • BBB impermeable to H+ bond enters CSF (lowest pH)
     • Formation of H2CO3 by carbonic anhydrase
     • H+ activates central chemoreceptors
   • Peripheral Chemoreceptors
     • Respond to blood pH levels
   • Most sensitive to PCO2 & pH
     • PCO2 influence blood pH
   • Hyperventilation
     • Low CO2 (HYPOCAPNIA)
   • Hypoventilation
     • Low CO2 (HYPERCAPNIA)
   • Adjusted to maintaIn 40mmHg PCO2

8. Effects of blood PO2 on Ventilation

   • low blood PO2 (Hypoxamia) has little affect on ventilation
     • Blood PO2 ust decrease from 100 mmHg to 50 mmHg to influence ventilation

9. Cerebral Cortex

   • Voluntary override
     • Breath hold
       • Panting
         • Sighing
           • Emotions

10. Other Ventilation Regulatory Mechanisms

    • Proprioreceptors
      • Temperature and pain receptors
        • Irritant receptors
          • Rapidly adapting respond to smoke smog and particulates
            • Causes cough sneezing bronchoconstriction
    • Hering-Stretch receptors activated during inspiration
      • Located in smooth muscle of airways
        • Inhibits respiratory centers to prevent overinflation of lungs

11. Assessing Pulmonary function

    • Spirometry
      • Tidal volume amount of air expired/breath
      • Tidal capacity: amount of air forcefully exhaled after a maximum inhalation
        • TV+IRV+ERV
          • Tv=tidal volume
            • Volume of gas inspired or expired in a unforced respiratory cycle
          • IRV=Inspiration Reserve Volume
            • Maximum volume of gas that can be inspired during forced breathing in addition
          • ERV= Expiration reserve volume
            • Maximum volume of gas that can be expired during forced breathing in addition

12. Terms

    • ANATOMICAL DEAD SPACE
      • air in conducting Zone
    • FORCED EXPIRATORY VOLUME )FEV1)
      • Air exhaled in forced breath in 1 second
    • FORCED VITAL CAPACITY
      • Total amount of air exhaled in FEV test