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Lung volume and capacities

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Lung volume and capacities

  1. 1.  Lung volumes and lung capacities refer to the volume of air associated with different phases of the respiratory cycle.  Lung volumes are directly measured; Lung capacities are inferred from lung volumes  Instrument is spirometry
  2. 2.  Four types 1. Tidal volume 2. Inspiratory reserve volume 3. Expiratory persevere volume 4. Residual volume
  3. 3.  Normal volume of air inspired or expired during quiet breathing  TV = 500 ml
  4. 4.  Extra volume of air inhaled after tidal volume by max inspiratory effort  3000ml in adult male (or)  3300 / 1900 = M/F
  5. 5.  Extra volume of air that can be exhaled after tidal volume by max expiratory efforts  1100 in a normal adult male (or)  1200/700 = M/F
  6. 6.  Volume of the air left out in lungs after forceful expiration or complete expiration  1200/1100 = M/F
  7. 7.  These are combinations of two or more lung volumes 1. Inspiratory capacity 2. Expiratory capacity 3. Functional residual capacity 4. Vital capacity 5. Total lung capacity
  8. 8.  Max volume of air that can be inspired after normal tidal expiration  IC = TV+IRV = 500 +3000 = 3500 ml
  9. 9.  Max volume of air that can be expired after normal tidal inspiration  EC=TV+ERV (500+1100=1600ml)
  10. 10.  Volume of air remaining in lungs after normal tidal expiration  FRC= ERV + RV ( 1100 + 1200 = 2300ml)
  11. 11.  Significance ? › Continues exchange of gases › So that conc of O2 and CO2 is maintained › Breath holding is made possible › Dilution of toxic inhaled gases › Prevents colapse of lungs › reduces workload of respiratory muscles and rt ventrcle
  12. 12.  Old age  Obstructive and restrictive lung diseases
  13. 13.  Max Amount of air expelled after deepest possible inspiration  VC = TV+IRV+ERV  500+3000+1100= 4600ml
  14. 14.  To asses strength of respiratory muscles  Factors affecting VC › Age › Sex › Strength of respiratory muscles › Gravity › Pregnancy › Ascites › Pulmonary diseases
  15. 15.  Volume of air present in lung after max inspiration  TLC = VC + RV ( 4600+1200 = 5800ml )
  16. 16.  Timed vital capacity or FVC  FVC is volume of the air that can be expired rapidly with max force following a max inspiration , and its timed by a spirograph
  17. 17.  FEV1 – volume of air expired in the first second of FVC  Fev1 is flow rate  Fev1 is expressed in percentage  Fev1 = 80%  Fev2 = 90 %  Fev3 = 98-100 % 
  18. 18. 0 1 2 3 5000 4000 3000 2000 1000 0 Time (sec) Volume(ml) FEV1 = (5000 ml -1000 ml) / 5000ml = 4000 ml / 5000 ml = 80%
  19. 19.  Low in obstructive lung diseases  Normal or high in restrictive lung diseases
  20. 20.  It’s the mean expiratory flow rate during the middle 50% of FVC  Normal is 300L/min in 0.5 sec
  21. 21.  Aka pulmonary ventilation  Volume of air inspired or expired per minute  RMV = TV * RR ( 500* 12 = 6000 ml)  6 – 7.5 L/min
  22. 22.  Aka MVV  Max volume of air that can be ventilated voluntarily for given interval of time  Subject asked to breath rapidly and deeply , for 15 seconds  Recorded by a spirometer or Douglas bag  Normal is 80- 170 L/min  Reduced in pt with emphysema and respiratory muscle weakness
  23. 23.  Maximum amount of air above the PV that can be inspired or expired in one min  PR = MVV – PV  Pulmonary reserve is expressed as % of MVV and is known as dyspnoeic index
  24. 24.  Normal DI is 60 – 90%  Average of 75%  Importance is dyspnoeia results when DI becomes less than 60%

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