Lung volume and capacities

1. LUNG VOLUME AND CAPACITIES

2. 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

3. Lung Volumes Four types Tidal volume Inspiratory reserve volume Expiratory persevere volume Residual volume

4. Tidal volume Normal volume of air inspired or expired during quiet breathing TV = 500 ml

5. Inspiratory reserve volume Extra volume of air inhaled after tidal volume by max inspiratory effort 3000ml in adult male (or) 3300 / 1900 = M/F

6. Expiratory Reserve Volume 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

7. Residual Volume Volume of the air left out in lungs after forceful expiration or complete expiration 1200/1100 = M/F

8. Lung capacities These are combinations of two or more lung volumes Inspiratory capacity Expiratory capacity Functional residual capacity Vital capacity Total lung capacity

9. Inspiratory capacity Max volume of air that can be inspired after normal tidal expiration IC = TV+IRV = 500 +3000 = 3500 ml

10. Expiratory Capacity Max volume of air that can be expired after normal tidal inspiration EC=TV+ERV (500+1100=1600ml)

11. Functional Residual Capacity Volume of air remaining in lungs after normal tidal expiration FRC= ERV + RV ( 1100 + 1200 = 2300ml)

12. Significance of FRC 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

13. Factors affecting FRC Old age Obstructive and restrictive lung diseases

14. Vital Capacity M ax Amount of air expelled after deepest possible inspiration VC = TV+IRV+ERV 500+3000+1100= 4600ml

15. Significance To asses strength of respiratory muscles Factors affecting VC Age Sex Strength of respiratory muscles Gravity Pregnancy Ascites Pulmonary diseases

16. Total Lung Capacity Volume of air present in lung after max inspiration TLC = VC + RV ( 4600+1200 = 5800ml )

17. Dynamic lung volumes 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

18. 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 %

19. Importance Low in obstructive lung diseases Normal or high in restrictive lung diseases

20. FEF 25-75% It’s the mean expiratory flow rate during the middle 50% of FVC Normal is 300L/min in 0.5 sec

21. Minute ventilation Aka pulmonary ventilation Volume of air inspired or expired per minute RMV = TV * RR ( 500* 12 = 6000 ml) 6 – 7.5 L/min

22. Maximum Breathing Capacity 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. Breathing Reserve Or Pulmonary Reserve 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. Dyspnoeic Index Normal DI is 60 – 90% Average of 75% Importance is dyspnoeia results when DI becomes less than 60%

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