RESPIRATORY SYSTEM (LUNG VOLUMES & CAPACITIES) بسم الله الرحمن الرحيم RESPIRATORY SYSTEM (LUNG VOLUMES & CAPACITIES) Dr. Mohammed Sharique Ahmed Quadri Assistant Prof. physiology Al maarefa college

Lung normally operate at about “half full “ 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. Important benefit of it that we get is Gas content of lungs leaving lungs remains constant Work of breathing is reduced

Spirometer

Lung Volumes Tidal Volume [TV] It is volume of air we breathe in or breathe out during single breath. Under resting condition It is about 500ml. Inspiratory Reserve Volume [IRV] It is extra volume of air that can be breathed in [inspired] forcefully, over and above normal tidal volume. IRV is about 3000ml. It is achieved by maximal contraction of diaphragm, external inter-costal muscles and accessory muscles of inspiration.

Lung Volumes 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].

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

Lung Capacities 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.

Lung Capacities 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.

Lung Capacities Vital Capacity [VC] It is maximum volume of air that can be expired after taking maximum inspiration [during a single breath]. (VC = IRV + TV + ERV) Average value VC = 4500ml.

Vital Capacity

Lung Capacities 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.

Forced Expiratory Volume In One Second [FEV1] 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.

Normal FEV1, FVC Curve

Respiratory Dysfunction 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%

Respiratory Dysfunction Restricted Lung Disease Lungs compliance is reduced , 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%

Obstructive

Flow Volume Loops

Pulmonary Ventilation & Alveolar Ventilation 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].

Anatomic Dead Space 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.

Alveolar Ventilation It is volume of air exchange between atmosphere and 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.

Effect of Breathing Pattern on Alveolar Ventilation 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.

Alveolar Dead Space 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

Dead Space 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].

Ventilation and Perfusion in the Lungs 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.

Ventilation and Perfusion in the Lungs 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.

Local control to match the ventilation & perfusion

Local control to match the ventilation & perfusion

References Human physiology by Lauralee Sherwood, seventh edition Text book physiology by Guyton &Hall,11th edition Text book of physiology by Linda .s contanzo,third edition