L3 Compliance and Work of Breathing PDF

Compliance and work of breathing Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Review questions List he functions of intrapleural pressure? Surfactant is secreted from …………….. List the functions of surfactant? Define compliance & pressure volume loo...

Compliance and work of breathing Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Review questions List he functions of intrapleural pressure? Surfactant is secreted from …………….. List the functions of surfactant? Define compliance & pressure volume loop. Define hysteresis. List conditions accompanied by increased or decreased compliance. Define airway resistance and list factors increases or decreases airway resistance. Describe the factors involved in the work of breathing Pulmonary Compliance Definition: Means the overall distensibility and expansibility of the lungs and the thorax. The compliance is the ratio between The change in the volume ∆V and the change in the distending pressure (transmural pressure) ∆P (pressure volume loop). 𝐶 = ∆V/ ∆P Hysteresis means the compliance of the lung is more during expiration than during inspiration Average lung compliance Factor affecting Pulmonary Compliance Lung Compliance Normal compliance Increased compliance: in emphysema. Decreased compliance: in pulmonary congestion, fibrosis (restrictive lung diseases) Thoracic wall Compliance Decreased compliance: in 1. Deformity of the thoracic wall. 2. Arthritis 3. Skeletal muscle diseases 4. Obesity Airway innervation The trachea and bronchi are occupied by cartilage plates and smooth muscle. The bronchioles are almost entirely smooth muscle, except for respiratory bronchiole. The smooth muscles in the walls of bronchi and bronchiole are innervated and controlled by autonomic nervous system: Sympathetic nervous system causes relaxation of the bronchial smooth muscle → bronchial dilatation Parasympathetic nervous system causes contraction of the bronchial smooth muscle → bronchial constriction and increases mucus secretion Low compliance. Airway resistance It is the resistance produced by the respiratory passages to air flow during breathing Flow= ∆P pressure/resistance R R is directly proportionate to Length. R is directly proportionate to viscosity. R is inversely proportionate to 4th power of the radius. Length and viscosity don't change, only radius of the respiratory passage changes. So, Bronchodilation → increases radius → decreases resistance → increases air flow. Bronchoconstriction → decreases radius → increases resistance → decreases air flow Bronchial asthma is treated by epinephrine injection, why ??? Bronchial asthma attack is more in the early morning, why ??? Work of breathing Under resting conditions, the respiratory muscles normally perform “work” to cause inspiration but not to cause expiration. Types: 1. Elastic work ; compliance work: that required to expand the lungs against the lung and chest elastic forces. 65% of work of breathing. 2. Tissue resistance work; that required to overcome the viscosity of the lung and chest wall structures. 7% of work of breathing. 3. Airway resistance work; that required to overcome airway resistance to movement of air into the lungs. 28% of work of breathing. Causes of the increase in the work of breathing 1. Diseases of the lung, pneumonia, pulmonary fibrosis, pulmonary edema. 2. Increased surface tension due to decreased surfactant secretion. 3. Narrowing of the air passages, bronchial asthma. Review Questions Which of the following factors decrease work of breathing? A. Lung diseases B. Chest deformity C. Intrapleural pressure D. Bronchial asthma Pulmonary compliance increases in A. Lung fibrosis B. Emphysema C. Chest deformity D. Obesity Summary Define compliance & pressure volume loop. Define hysteresis. List conditions accompanied by increased or decreased compliance. Define airway resistance and list factors increases or decreases airway resistance. Describe the factors involved in the work of breathing Pulmonary compliance increases in A. Lung fibrosis B. Emphysema C. Chest deformity D. Obesity Summary Define compliance & pressure volume loop. Define hysteresis. List conditions accompanied by increased or decreased compliance. Define airway resistance and list factors increases or decreases airway resistance. Describe the factors involved in the work of breathing