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Lecture-3 Dr.Zahoor Ali Shaikh 1 LUNG VOLUMES & CAPACITIES Slide 2 Lung Volumes 2 Tidal Volume [TV] It is volume of air we breathe in or breathe out during single normal breath. It is about 500ml. Inspiratory Reserve Volume [IRV] It is volume of air that can be breathed in [inspired] forcefully, over and above normal tidal volume. IRV is about 3000ml. It is done by maximal contraction of diaphragm, external inter-costal muscles and accessory muscles of inspiration. Slide 3 Lung Volumes 3 Expiratory Reserve Volume [ERV] It is maximum volume of air that can be expired forcefully after normal tidal expiration. ERV is about 1000ml. It is done by contracting the accessory expiratory muscles of expiration [abdominal and internal-intercostal muscles]. Slide 4 Lung Volumes 4 Residual Volume ( RV ) It is volume of air remaining in the lungs after maximal expiration. RV is about 1200ml. Slide 5 Lung Capacities 5 Inspiratory Capacity [IC] It is maximum volume of air that can be inspired after normal tidal expiration. It includes tidal volume and inspiratory reserve volume. (IC = IRV + TV) It is about 3500ml. Slide 6 Lung Capacities 6 Functional Residual Capacity [FRC] It is volume of air that remains in the lungs after normal tidal expiration. (FRC = ERV + RV) Average value FRC = 2200ml. Slide 7 Lung Capacities 7 Vital Capacity [VC] It is maximum volume of air that can be expired forcefully after taking maximum inspiration [during a single breath]. (VC = IRV + TV + ERV) Average value VC = 4500ml. Slide 8 Lung Capacities 8 Total Lung Capacity [TLC] It is the maximum volume of air that the lungs can hold. (TLC = TV + IRV + ERV + RV) Average volume TLC = 5700ml [5.5-6 liter]. TLC is affected by Age, Build, Height and Weight, and presence of Lung disease. Slide 9 9 Slide 10 10 Slide 11 11 Slide 12 Forced Expiratory Volume In One Second [FEV1] 12 Forced Expiratory Volume It is volume of air that can be expired forcefully during the first second of expiration [normally we expire in 3sec]. FEV1 = 80% [80% of vital capacity(VC)] FEV2 = 92% FEV3 = 99% FEV1 indicates maximal air flow rate from the lungs. FEV1 is decreased in obstructive lung disease e.g. bronchial asthma. Slide 13 Normal FEV1, FVC Curve 13 Slide 14 Respiratory Diseases 14 Obstructive Lung Disease e.g. bronchial asthma. Restrictive Lung Disease e.g. pulmonary fibrosis. Obstructive Lung Disease Patient has difficulty in expiration [due to obstruction of bronchi]. Therefore, FEV1 and FEV1% is decreased. Example: Normal VC = 5 liters, FEV1 = 4 liters. FEV1% = (FEV1/FVC) * 100 = (4/5) * 100 = 80% In Obstructive Lung Disease, VC = 4 liters, FEV1 = 2 liters FEV1% = (2/4)*100 = 50% Slide 15 Respiratory Diseases 15 Restricted Lung Disease Lungs are smaller than normal, therefore, vital capacity[VC], TLC, all are decreased as lungs can not expand. When we do respiratory function test: FEV1 is decreased, FVC is also decreased but FEV1% is normal [80% or more]. Example: Normal VC = 5 liters, FEV1 = 4 liters. FEV1% = (FEV1/FVC) * 100 = (4/5) * 100 = 80% In Restricted Lung Disease, VC = 3 liters, FEV1 = 2.7 liters FEV1% = (2.7/3)*100 = 90% Slide 16 16 Slide 17 Flow Volume Loops 17 Slide 18 Pulmonary Ventilation & Alveolar Ventilation 18 Pulmonary Ventilation or Minute Ventilation It is volume of air we breathe in and out in 1min. Pulmonary Ventilation = Tidal Volume * Respiratory rate = 500ml * 12 = 6000ml or 6 liter Normal respiratory rate is 12 -18/min. Adult young person can increase pulmonary ventilation 25- fold to 150 liters/min [to increase pulmonary ventilation one has to increase tidal volume and respiratory rate]. Slide 19 Anatomic Dead Space 19 As we breath in, all air does not go to alveoli for gas exchange but some of the air remains in trachea and bronchi [conducting zone] and does not take part in gas exchange. It is 150ml. It is called Anatomic Dead Space. As our tidal volume is 500ml, anatomic dead space is 150ml, therefore, 350ml goes to lungs for gas exchange. Slide 20 20 Slide 21 Alveolar Ventilation 21 It is volume of air reaching the alveoli/min. It is more important than pulmonary ventilation. It is alveolar air that takes part in gas exchange. Alveolar Ventilation = TV Dead Space * Respiratory Rate[RR] = (500 150) * 12 = 350 * 12 = 4200 ml/min Alveolar Ventilation is less than Pulmonary Ventilation. Slide 22 Effect of Breathing Pattern on Alveolar Ventilation 22 Rapid shallow breathing is not good, as TV is decreased and most of the air is lost in dead space and little or no air goes to alveoli. Person may get unconscious within few minutes. Slide 23 Alveolar Dead Space 23 Normally air going into the alveoli, takes part in gas exchange, therefore, there is no alveolar dead space in healthy person. In case of disease, where alveoli are abnormal e.g. pneumonia, gas exchange does not take place in affected alveoli, therefore, alveolar dead space is there. Physiological Dead Space = Anatomical Dead Space + Alveolar Dead Space Slide 24 Dead Space 24 In Health, Physiological dead space=Anatomical dead space [As all alveoli are functioning]. In Disease, Physiological dead space is more than Anatomical dead space [As many alveoli are not functioning]. Slide 25 Ventilation and Perfusion in the Lungs 25 Regional difference exist at the top and bottom [apex and base] of the lung due to gravitational effect. Standing upright Gravity effect is more on blood flow than on airflow. Effect on Ventilation/Perfusion ratio. Slide 26 Ventilation and Perfusion in the Lungs 26 Top of the lung receives relatively more air than blood, therefore, ventilation perfusion ratio is increased. Bottom of the lung receives relatively less air than blood, therefore, ventilation perfusion ratio is decreased. Slide 27 27 Slide 28 Important Points 28 During normal breathing, lungs are not totally full nor totally deflated. At the end of normal quiet expiration, the lungs contain about 2200 ml of air. Lungs can never be completely emptied therefore gas exchange can take place after forceful expiration. Slide 29 What You Should Know From This Lecture 29 Lung volumes TV, IRV, ERV, RV Lung capacities IC, FRC, VC, TLC FEV1, FEV1% and their importance in Obstructive and Restrictive Lung Disease Alveolar Ventilation & Pulmonary Ventilation Anatomic Dead Space Physiological Dead Space Ventilation Perfusion at the Apex and base of the lung Slide 30 Thank you 30