Lung volume and capacity

physio

1. Lung volumes and capacities Dr. Punyalaxmi Manandhar

2. Determination of lung volumes is used to -assess the efficiency of the respiratory system -diagnose respiratory diseases Most of these volumes can be measured using a simple spirometer Static and dynamic lung volume and capacities

3. THE SPIROMETER – spirometer bell – kymograph pen

4. Tidal volume It is the volume of air inspired or expired each breath during normal quiet breathing. It is about 500 ml

5. Inspiratory reserve volume (IRV) It is maximal volume of air which can be inspired after a normal inspiration. It is about 3000 ml

6. Expiratory reserve volume (ERV) It is the maximal volume of air which can be expired after a normal expiration. It is about 1100 ml

7. Residual volume (RV) It is the volume of air remaining in the lungs after maximal expiration It is about 1200ml

8. A lung capacity is two volumes or more added together: Inspiratory capacity (IC) It is the maximal volume of air that can be inspired from the resting expiratory volume

9. Functional residual capacity (FRC) It is the volume of air which remains in the lung at the resting expiratory level (after normal expiration) FRC = RV + ERV 1100 + 1200 = 2300 ml

10. Vital capacity (VC) It is the maximum volume of air that can be expelled from lung by a maximal expiration after a maximal inspiration VC = IRV + TV + ERV 4600= 1100+ 500+ 3000 It is a good index for pulmonary efficiency

11. Total lung capacity (TLC) It the volume of air contained in the lung at the end of maximal inspiration TLC = IRV + TV + ERV + RV 5800ml = 1200 + 1100+ 500 + 3000 ml

12. Lung volumes and capacities are Decreased in The recumbent position than in standing Women than in men by about 20-25% Small persons and Old age Increased in Larger and athletic persons

13. All lung volume and capacities are measured directly by spirometer except Functional Residual capacity FRC Total lung capacity TLC Residual volume RV Because the air in the residual volume of the lung cannot be expired into the spirometer and this volume constitutes part of FRC, TLC

14. Determination of RV and FRC They are measured indirectly using helium dilution method Its low solubility in respiratory membrane so it does not diffuse into the pulmonary capillary blood It is an inert gas not utilized by the tissues The total amount of helium does not change during the test

15. Determination of RV and FRC Helium dilution Spirometer of known volume (Vs)and He Conc.(C1) connected to the patient. At end of normal expiration. -Closed circuit - After several minutes of breathing. C1XV1=C2X( Vs+VL ) C2= final He conc,VL =FRC. [He] initial · Vs = [He] final · (Vs + VL) Unknown lung volume can be calculated At beginning After several minutes

16. Clinical significance of FRC FRC maintains gas exchange with blood in between breaths The large volume of FRC prevents marked rise in alveolar pressure of oxygen during inspiration and its drop during expiration i.e. it provides stability of oxygen pressure in the alveolar air and arterial blood Normally the residual volume should be less than 30% of the total lung capacity. It exceeds that level in some pathological conditions e.g. Bronchial asthma (RV/TLC>30%)

17. Minute Respiratory Volume It is the total amount of air that moves into the respiratory passages each minute inspired or expired (total ventilation) it equals = Tidal volume X Respiratory Rate 12 breath / minute X 500ml =6000ml/min

18. Minute Respiratory Volume Minute Ventilation= TVX breathing frequency 500ml/minX12= 6000 ( 6L/min)

19. Maximal Voluntary Ventilation(MVV) It is the maximal volume of air that can be breathed per minute using the fastest rate and the deepest respiratory effort possible The subject breathes as fast and as deep as possible for 15 seconds only To avoid fatigue of the respiratory muscles- To avoid wash out of CO2 - Normal MVV = 80-160 L/min for male L /min for females 60-120 = average 100 L/minute It is a better index for respiratory efficiency and physical fitness- 2

20. Breathing reserve (BR It is the difference between MVV and minute Respiratory volume BR = MVV – MRV 94L/min = 100 – 6 It is a good test for the functional reserve of the respiratory system and the higher is the BR, the better the state of physical fitness

21. Dyspneic index It is the ratio between BR and MVV and it is usually about 90%. If it is decreased below 60% dyspnea (difficulty in breathing) occurs on slightest effect and the person is considered physically unfit

22. Factors affecting the vital capacity Posture Movement of diaphragm Strength of Respiratory Muscles Thoracic wall expansibility Resistance to air flow Lung elasticity Restrictive lung disease

23. Vital Capacity Based on Age & Gender MALE FEMALE Age (Years)

24. Timed vital capacity It is the volume of expired air at the end of the first, second or third second, when measuring vital capacity also called forced expiratory volume (FEV) The timed vital capacity is a useful test to differentiate between obstructive lung diseases COPD as emphysema and chronic bronchitis and restrictive lung diseases as interstitial lung fibrosis.

25. How to measure FVC The patient is asked to inspire as deep as possible and expires as deep and as rapid as he can into the spirometer that measures not only the volume expired but also the time taken in expiration. Normally the FVC takes place in 4 seconds

26. Normally FEV1 (which is the fraction of the forced vital capacity which can be expired by the end of the first second using the maximal expiratory effort)is about 80-83% of FVC. FEV 2 about 90-93% of FVC, andFEV3 equals 97% of FVC

27. Timed vital capacity

28. FEV1 & FVC Forced expiratory volume in 1 second (FEV1) in young trained athletes: 4 L •FVC in young trained athletes: 5 L • FEV1/FVC %= 80%-83% obstructive lung disease- the air way resistance is greatly increased, the vital capacity is reduced and FEV1 is markedly reduced FEV1/FVC is less than 80%. restrictive lung disease- FEV1/FVC is normal or even increased 90% due to proportionate decrease in both FEV1 and FVC

29. In obstructive lung diseases, the air way resistance is greatly increased, the vital capacity is reduced and FEV1 is markedly reduced FEV1/FVC is less than 80%. While in restrictive lung disease FEV1/FVC is normal or even increased 90% due to proportionate decrease in both FEV1 and FVC

30. Restrictive lung diseases

31. Lung Capacity and Disease