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Pulmonary Ventilation Dr. Walid Daoud MBBCh, MSc, MD, FCCP Director of Chest Department, Shifa Hospital, A. Professor of Chest Medicine Slide 2 Slide 3 The air passages Slide 4 Alveolo-capillary membrane. Slide 5 Types of respiration 1. External respiration: It is the exchange of oxygen and carbon dioxide between the alveoli of the lungs dioxide between the alveoli of the lungs and pulmonary blood capillaries and pulmonary blood capillaries 2. Internal respiration: It is the exchange of oxygen and carbon dioxide between the tissue blood capillaries and tissue cells. dioxide between the tissue blood capillaries and tissue cells. Slide 6 Slide 7 Process of respiration 1. Pulmonary ventilation 2. Diffusion 3. Perfusion 4. Gas transport function of the blood Slide 8 Respiratory mechanics 1. Mechanism of inspiration 2. Mechanism of expiration Slide 9 Intra-pulmonary (intra-alveolar) pressure During normal inspiration. : -1 mm Hg During normal expiration. : +1 mm Hg During forced inspiration with the glottis closed : -80 mm Hg During forced inspiration with the glottis closed : -80 mm Hg During forced expiration with the glottis closed : + 100 mm Hg Slide 10 Intrapleural (intrathoracic) pressure Causes of negative intrapleural pressure 1.The recoil tendency of the lungs 2.The expansion tendency of the chest wall Values of negative intrapleural pressure: Importance of I.P.P Slide 11 Slide 12 Compliance Compliance is the change in volume for each unit increase in transpulmonary pressure. = V = V P P 1. Lung compliance 2. Chest wall compliance 3. Compliance of the respiratory system Slide 13 Elastic forces of the lungs These forces tend to collapse the lung: 1. Elastic forces of lung tissues: Elastin and collagen Elastin and collagen 2. Elastic forces caused by surface tension of fluid lining the alveoli of fluid lining the alveoli Slide 14 Compliance When transpulmonary pressure increases 1 cm. water, the lung volume will increase 200 mL. Lung compliance = 200 mL/cm.water Compliance diagram of the lungs:. Inspiratory compliance curve. Expiratory compliance curve Slide 15 Compliance diagram of the lungs Slide 16 Surfactant and surface tension Surface water molecules in the alveoli tend to attract each other and tend to collapse the alveoli and the lung. This is called surface tension elastic force. Slide 17 Surfactant Source: secreted by type II alveolar epithelial cells Composition: a complex mixture: Phosphoplipid; dipalmitoylphosphatidylcholine, apoprotein and calcium ions Function: It prevents development of water-air interface and decreases the surface tension thus prevents alveolar collapse and preserve alveolar stability. Slide 18 Pressure in occluded alveoli caused by surface tension Pressure = 2 x Surface tension Radius of alveolus Radius of alveolus Congenital deficiency of surfactant: Respiratory distress syndrome of newborn Slide 19 Work of breathing in inspiration 1. Compliance or elastic work: Work required to expand the lungs against Work required to expand the lungs against lung and chest elastic forces. lung and chest elastic forces. 2. Tissue resistance work: Work required to overcome the viscosity of Work required to overcome the viscosity of the lung and chest wall structures. the lung and chest wall structures. 3. Airway resistance work: Work required to overcome airway resistance Work required to overcome airway resistance to movement of air into the lungs. to movement of air into the lungs. Slide 20 Energy required for respiration During quiet resting breathing, the energy needed for pulmonary ventilation is 3-5% of the total energy expended by the body. During exercise the amount of energy needed can increase 50-folds, especially if the person has any degree of increased airway resistance or decreased lung compliance. O2 cost of breathing. Slide 21 Lung volumes 1. Tidal volume 2. Inspiratory reserve volume 3. Expiratory reserve volume 4. Residual volume Slide 22 Lung capacities 1. Inspiratory capacity 2. Functional residual capacity 3. Vital capacity 4.Total lung capacity Slide 23 Slide 24 Vital capacity It is the maximal volume of air that can be expired following maximal inspiration. Significance Timed VC Slide 25 Slide 26 Measurement of Lung Function (FEV 1 ) 1 Time (sec) 2345 FEV 1 Volume Normal Subject Asthmatic (After Bronchodilator) Asthmatic (Before Bronchodilator) Note: Each FEV 1 curve represents the highest of three repeat measurements Slide 27 Measurements of Lung Function ______________________________________ FEV1 12% or 200 ml from FEV1 12% or 200 ml from prebronchodilator value denotes reversibility prebronchodilator value denotes reversibility and establish diagnosis of asthma. and establish diagnosis of asthma. FEV1/FVC% < 80% in adults and < 90% in FEV1/FVC% < 80% in adults and < 90% in children denotes airflow limitation. children denotes airflow limitation. Preoperative assessment. Preoperative assessment. Slide 28 Peak Expiratory Flow (PEF) ______________________________________ 1.To confirm the diagnosis of asthma: - 60 L/min or 20% of prebronchodilator PEF - 60 L/min or 20% of prebronchodilator PEF - Diurnal variation in PEF < 20% - Diurnal variation in PEF < 20% (with twice daily readings