1 Respiratory system L2 Faisal I. Mohammed, MD, PhD University of Jordan

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4 Airflow Air pressure differences drive airflow 3 other factors affect rate of airflow and ease of pulmonary ventilation  Surface tension of alveolar fluid Causes alveoli to assume smallest possible diameter Accounts for 2/3 of lung elastic recoil Prevents collapse of alveoli at exhalation  Lung compliance High compliance means lungs and chest wall expand easily Related to elasticity and surface tension  Airway resistance Larger diameter airway has less resistance Regulated by diameter of bronchioles & smooth muscle tone University of Jordan

Surfactant Complex mixture of phospholipids, proteins, ions Produced by type II alveolar epithelial cells It reduces surface tension forces by forming a monomolecular layer between aqueous fluid lining alveoli and air, preventing a air/water interface Function  Reduces surface tension  Prevents alveolar collapse  Increases compliance  Reduces work of breathing

6 However, the high surface tension and collapse of the alveoli is prevented by surfactant.

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Compliance Distensibility (stretchability):  Ease with which the lungs can expand. Change in lung volume per change in transpulmonary pressure. DV/DP 100 x more distensible than a balloon.  Compliance is reduced by factors that produce resistance to distension.

9 Lung volumes and capacities Minute ventilation (MV) = total volume of air inhaled and exhaled each minute Normal healthy adult averages 12 breaths per minute moving about 500 ml of air in and out of lungs (tidal volume) MV = 12 breaths/min x 500 ml/ breath = 6 liters/ min Alveolar ventilation = (tidal volume – dead space)* respiratory rate e.g Alveolar ventilation = ( )*12= 4.2 liters/min University of Jordan

10 Spirometer

Lung volumes and capacities Spirometer - measurement of lung volumes - measurement of the oxygen consumption

12 Spirogram of Lung Volumes and Capacities University of Jordan

Restrictive and Obstructive Disorders Restrictive disorder:  Vital capacity is reduced.  FVC is normal. Obstructive disorder:  Diagnosed by tests that measure the rate of expiration. VC is normal. FEV 1 is < 80%. Insert fig

14 Lung Volumes Only about 70% of tidal volume reaches respiratory zone Other 30% remains in conducting zone Anatomic (respiratory) dead space – conducting airways with air that does not undergo respiratory gas exchange Alveolar ventilation rate – volume of air per minute that actually reaches respiratory zone Inspiratory reserve volume – taking a very deep breath University of Jordan

15 Lung Volumes Expiratory reserve volume – inhale normally and exhale forcefully Residual volume – air remaining after expiratory reserve volume exhaled Vital capacity = inspiratory reserve volume + tidal volume + expiratory reserve volume Total lung capacity = vital capacity + residual volume University of Jordan

16 Thank You University of Jordan