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RESPIRATION

This article discusses pulmonary function tests, including spirometry and measurement of lung volumes, and explains the normal values and significance of these tests. It also covers the factors affecting lung volumes and vital capacity, as well as the differences between restrictive and obstructive lung diseases.

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RESPIRATION

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  1. RESPIRATION Dr. Zainab H.H Dept. of Physiology Lec.5,6

  2. Pulmonary Function Tests • Assessed by spirometry. • Subject breathes into a closed system in which air is trapped within a bell floating in water. • The bell moves up when the subject exhales and down when the subject inhales. • As the person breathes in & out through a tube connecting the mouth to the spirometer, the bell containing air moves up & down

  3. Pulmonary Function Tests • The bell is attached by a pulley to a pen that writes on paper attached to a rotating drum • A downward pen deflection represents expiration & an upward pen deflection represents inspiration • The recording is known as spirogram

  4. Spirometer

  5. Pulmonary Function Tests • Normal range: • Male = 5.7 liters • Female = 4.2 liters • 500 ml of air are inspired and expired • At end of quiet expiration, the lungs still contain 2,200 ml of air • Gas exchange continues during expiration Maintains constant gas content

  6. Pulmonary Function Tests • The spirogram shows 4 lung volumes & 4 lung capacities • Values given are for adult males (70 kg) • Normal values of lung volume & capacities depend on: • Age • Sex • Posture • height

  7. Lung Volumes • Tidal Volume (TV): volume of air inhaled or exhaled with each breath = 0.5 L • Inspiratory Reserve Volume (IRV):maximum volume of air that can be inhaled after a normal tidal volume inhalation = 3L

  8. Lung Volumes 3. Expiratory Reserve Volume (ERV) - the maximum amount of gas that ca be expired during forced breathing in addition to tidal volume = 1.1L 4. Residual Volume (RV) - the volume of gas remaining in the lungs after a maximal expiration = 1.2L that keep the alveoli open.

  9. Lung Capacities 1. Inspiratory Capacity (IC) - the maximum amount of gas that can be inspired after a normal tidal expiration IC = TV + IRV = 3.5 L 2. Functional Residual Capacity (FRC) - the amount of gas remaining in the lungs after a normal tidal expiration. FRC = ERV + RV = 2.3L

  10. Lung Capacities 3. Vital Capacity (VC) -the maximum amount of gas that can be expired after a maximum inspiration VC = IRV + TV + ERV (= IC + ERV) 4. Total Lung Capacity (TLC) -total amount of gas in the lungs after a maximum inspiration TLC = TV + IRV + ERV + RV (= IC + FRC) or (= VC + RV) = 5.8L

  11. Note • Volumes and capacities cannot be measured directly with spirometer are: • FRC • RV • TLC • Functional residual capacity is determined by nitrogen wash-out method or helium dilution method and then residual volume and total lung capacity are calculated.

  12. Maximal Voluntary Ventilation • Also called maximal breathing Capacity • largest volume of gas that can be moved into and out of the lungs in 1 minute by voluntary effort • Equals to 125 – 170 L/min.

  13. Factors Affecting Lung Volumes and Vital Capacity • Body build or physique • Position of the body • Strength of respiratory muscles • Pulmonary compliance

  14. Restrictive and Obstructive Disorders • Restrictive pulmonary/lung diseases • Expansion of lungs restricted & compliance of lungs  i.e., • Fibrosis • Pulmonary edema • Obstructive pulmonary diseases • Airflow limitation (resistance is high), i.e., • Chronic obstructive pulmonary diseases (COPD) • Asthma

  15. Forced Expiratory Volume in 1st second (FEV1) • FEV1 (Forced expiratory volume in 1st second): Volume of forced vital capacity (FVC) exhaled in the first second of expiration • Normal ratio of FEV1/FVC ~ 0.8 or 80% • In obstructive pulmonry diseases, ratio is  70%

  16. Maximal inspiration Maximal expiration or normal

  17. Which of the following is/are decreased in both restrictive and obstructive lung diseases: • vital capacity, • FEV1, • FEV1/FVC?

  18. In obstructive airways disease. • The increase in intrapleural pressure may act to compress airways proximal to the alveoli  further obstruction with no increase in expiratory flow and air-trapping distally.

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