Lung volume and lung capacity By DR AGBARAOLORUNPO
Lung volume and lung capacity By DR AGBARAOLORUNPO F. M Department of Physiology College of Medicine University of Lagos
• Respiratory rate in adult is 12 times/minute • movement of 6 litre of air in and out of the lungs in a minute • minute ventilation or pulmonary ventilation=Tidal volume X RR • Alveolar ventilation=tidal volume-dead space X RR • (500 -150 X 12=4200 ml/min) • Movement of 500 ml of air in and out of the lung per breath(Tidal Volume, VT)
• Spirometer-for measuring volume of air exchanged during breathing and rate of ventilation • The record is called spirogram/spirometry • Inspiration is recorded as upward deflection , while expiration is recorded as downward deflection
• Spirometry measuring of breath) is the most common of the pulmonary function tests (PFTs). • It measures volume and/or speed (flow) of air inhaled and exhaled in the lung. • to diagnose asthma, pulmonary fibrosis, cystic fibrosis, and COPD.
Procedure • Generally, the patient is asked to take quiet breathing, followed by deepest breath they can, and then exhale into the sensor as hard as possible, for at least 6 seconds. • During the test, soft nose clips may be used to prevent air escaping through the nose. Filter mouthpieces may be used to prevent the spread of microorganisms
LUNG VOLUME 1. TIDAL VOLUME: The volume of air entering or leaving the lungs during normal quiet breathing=500 ml 2. Inspiratory reserve volume: Extra volume of air that can be maximally inspired above tidal volume(3 L) 3. Expiratory Reserve Volume: Extra Volume of air that can be maximally expired above tidal volume(1 L) 4. Residual Volume: volume of air in the lung after maximal expiration/exhalation(1200 ml)
LUNG CAPACITY 1. Inspiratory Capacity: IC=IRV+TV 2. Vital Capacity: Maximum volume of air that can be moved out during a single breathe following a maximal inspiration: The subject first inspires maximally, then expires maximally (VC=IRV+TV+ ERV). Use to ascertain the functional capacity of the lungs. average=4500 ml. it represent the maximum volume change possible within the lungs. 1. Functional Residual Capacity: Volume of air in the lungs at the end of a normal passive expiration (FRC=ERV+RV), 2200 ml. 2. Total lung capacity(TLC): The maximum volume of air that the lungs can hold(TLC=VC+RV)=average value=5700 ml
IRV 3. 3 1. 9 TV 0. 5** ERV 1. 0* 0. 7 RV 1. 2* 1. 1 TOTAL LUNG CAPACITY 6. 0** 4. 2** Respiratoy minute volume (6 L/min) Alveolar ventilation (rest): 4. 2 L/min**
Forced vital capacity (FVC) • Forced vital capacity (FVC) is the volume of air that can forcibly be blown out after full inspiration, • FVC is the most basic maneuver in spirometry tests. Forced expiratory volume in 1 second (FEV 1) • FEV 1 is the volume of air that can forcibly be blown out in one second, after full inspiration. • Average values for FEV 1 in healthy people depend mainly on sex and age, • Values between 80% and 120% of the average value are considered normal. • Predicted normal values for FEV 1 depend on age, sex, height, mass and ethnicity
• FEV 1/FVC ratio (FEV 1%) • FEV 1/FVC (FEV 1%) is the ratio of FEV 1 to FVC. In healthy adults this should be approximately 70– 85% (declining with age). • In obstructive diseases (asthma, COPD, chronic bronchitis, emphysema) FEV 1 is diminished because of increased airway resistance to expiratory flow;
Force expiratory volume in one second(FEV 1): Volume of air that can be expelled from lungs in 1 second with maximal effort following a maximal inhalation. FEV 1 is about 80% of the air that can be forcefully expired from maximally inflated lungs within 1 second(80% of VC forcefully expires in one second ) FEV 1 can be greatly reduced in asthma and emphysema
• Spirometry can be used to diagnosed both obstructive and restrictive lung disease Obstructive disease • Patient experiences difficulty emptying lungs than filling them • FRC and RV are elevated as a result of the additional air trapped in the lungs following expiration • FEV 1 reduced, due to the reduction in air flow rate by the airway obstruction
• FEV 1/FVC ratio is reduced below 80%
Spirogram in restrictive lung diseases • Lungs are less compliant in restrictive lung diseases ( expand less) • TLC, IC and FVC are reduced • FEV 1/VC ratio(the percentage of the VC that can be exhaled within 1 second is the normal 80%) is normal or higher because air can flow freely in the airway. • RV is normal in restrictive lung diseases
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