LUNG VOLUMES & CAPACITIES

Lecture-3Dr.Zahoor Ali Shaikh1LUNG VOLUMES & CAPACITIESLung Volumes2Tidal Volume [TV] It is volume of air we breathe in or breathe out during normal single 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.Lung Volumes3Expiratory 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 Volumes4Residual Volume ( RV )It is volume of air remaining in the lungs after maximal expiration. RV is about 1200ml.Lung Capacities5Inspiratory 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 Capacities6Functional 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 Capacities7Vital 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.

Lung Capacities8Total 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.

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Forced Expiratory Volume In One Second [FEV1]12Forced Expiratory VolumeIt 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 Curve13

Respiratory Diseases14Obstructive Lung Disease e.g. bronchial asthma.Restrictive Lung Disease e.g. pulmonary fibrosis.

Obstructive Lung DiseasePatient 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 litersFEV1% = (2/4)*100 = 50%Respiratory Diseases15Restricted Lung DiseaseLungs 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 litersFEV1% = (2.7/3)*100 = 90%

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Flow Volume Loops17

Pulmonary Ventilation & Alveolar Ventilation18Pulmonary Ventilation or Minute VentilationIt 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 Space19As 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. 20

Alveolar Ventilation21It 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/minAlveolar Ventilation is less than Pulmonary Ventilation.Effect of Breathing Pattern on Alveolar Ventilation22Rapid 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 Space23Normally 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 Space24In 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 25Regional difference exist at the top and bottom [apex and base] of the lung due to gravitational effect.Standing uprightGravity effect is more on blood flow than on airflow. Effect on Ventilation/Perfusion ratio.Ventilation and Perfusion in the Lungs 26Top 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.

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Important Points 28During 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. What You Should Know From This Lecture29Lung volumes TV, IRV, ERV, RVLung capacities IC, FRC, VC, TLCFEV1, FEV1% and their importance in Obstructive and Restrictive Lung DiseaseAlveolar Ventilation & Pulmonary VentilationAnatomic Dead SpacePhysiological Dead SpaceVentilation Perfusion at the Apex and base of the lung

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