Respiratory physiology DR. AMIR SAMADIAN M.D. DEPARTMENT OF PHYSIOLOGY SPRING 2020 Learning objectives Pulmonary ventilation Mechanism of breathing – breathing muscles, intrathoracic and intrapulmonary pressure. Surface tension in alveoli, surfactant. Application of the law of Laplace in lungs. Respiratory work. Pneumothorax. Transport of gases through alveolar-capillary membrane Composition of atmospheric and alveolar air. Diffusion through the alveolar-capillary membrane. Oxygen –haemoglobin dissociation curve, the Bohr effect. CO2 dissociation curve. Regulation of breathing Neuronal regulation – respiratory centre. Chemoreceptors – effect of hypoxia and hypercapnia. Mechanoreceptors in lungs – Hering–Breuer reflexes. Protective reflexes of respiratory system. Response of the ventilation to physical activity. Diagnostic and therapeutic methods in clinical practice Spirometry – flow-volume loop. Pneumotachography. Pneumography. Measurement of the death space. Measurement of residual volume of the lungs. Artificial ventilation. 1. 1. Overview of respiratory system Respiratory mechanics Forces acting on the lung 1.elasticity of lung (elastic recoil) (collapsing force) 2.Lung surface tension (collapsing force) 3.Chest wall recoil (opening force) 4.Intrapleural pressure-IPP (opening force) mage result for forces acting on the lung Lung recoil and chest wall recoil mage result for forces acting on the lung Intrapleural pressure elated image Major forces acting on the lung Important points ØIntrapleural pressure > Lung recoil à Lung Expands ØIntapleural pressure < lung recoil à lung collapse ØIntrapleural pressure = Lung recoil à lung size constant Transmural pressure elated image mage result for forces acting on the lung Respiratory compliance Compliance vs elastance elated image Lung compliance changes Surface tension Surface tension Pneumothorax Pneumothorax Total work of respiratory muscles at quiet breathing Elastic (static) work (65%) •To overcome the elastic forces of the chest and lungs Dynamic work (35%) • To overcome the resistence of air passage during the air movement - aerodynamic resistence (28%) •To overcome the friction during mutual movement of inelastic tissue – Viscous resistence (7%) Respiratory work The lung and the transport of O2 Factors affecting PACO2 Factors affecting PAO2 Solubility vs Hem affinity of Gasses Oxygen-hemoglobin sat curve Carbon dioxide transport Respiratory center Regulation of Respiration Other receptors Irritants receptors on mucose of respiratory system – quickly adaptated, Stimulus: chemical substances (histamin, serotonin, cigarette smoke). Respons: increase mucus secretion, constriction of larynx and brochus C-receptors (=J receptors)– free nerve ending of n.vagus (type C) in intersticium of bronchus and alveolus; Mechanical irritans (pulmonary hypertension, pulmonary oedema) Response: hypopnoe, bronchoconstriction, cough Stretch receptors slowly adaptation, in smooth muscle trachea and bronchus; its irritants triggered decrese activity of respiratory centre – Hering-Breuer´s reflexes. Respiratory response to high altitude Respiratory response to Exercise (FEV1/FCV < 80%) = Obstructive pattern FEV1/FVC = or > 80% (restrictive pattern) Obstructive vs restrictive diseases studies Flow-volume loop Obstructive vs restrictive lung diseases Anatomic dead space Measurement of Dead space (nitrogen wash out) -video Pneumograph Hyperventilation Definition: Both, accelerated and deep breathing ◦In humans, hyperventilation coming as combination of anxiety and pain ◦During hyperventilation is expired CO2 (hypocapnia) and the increase of pO2 (hyperoxia) à vasoconstriction of cerebral vessels ◦ ◦Symptoms: tingling in the ears, feeling light in the head, headache etc. ◦ ◦Tx : by increasing pCO2 in the body – e.g.: by breathing into and out of the bag (re-breathing) Hypoxia qHypoxia is a general name for a lack of oxygen in the body or individual tissues. qHypoxemia is lack of oxygen in arterial blood. qComplete lack of oxygen is known as anoxia. Classification of hypoxia THANK YOU Resources 1.First Aid for USMLE Step 1 2020 2.Costanzo Physiology 3.Kaplan Physiology 4.Illustrations à Drawittoknowit