Respiratory Module Part I PDF

# Respiratory Module Part I ## Decreased surfactant - lung collapse (atelectasis), difficult inflation and hypoxemia. ## Respiratory distress syndrome - Long-term inhalation of 100% oxygen and pump oxygenator in cardiac surgery. - Occlusion of one branch of pulmonary artery (thrombus); alveoli that...

# Respiratory Module Part I ## Decreased surfactant - lung collapse (atelectasis), difficult inflation and hypoxemia. ## Respiratory distress syndrome - Long-term inhalation of 100% oxygen and pump oxygenator in cardiac surgery. - Occlusion of one branch of pulmonary artery (thrombus); alveoli that receive no blood supply fail to synthesise surfactant. - Cigarette smoking. - Hypothyroidism: surfactant production requires the hormone thyroxine. - Hypocorticism: as cortisol accelerates maturation of lung surfactant. - Hyperinsulinism: insulin inhibits surfactant secretion (RDS occurs more in infants born to diabetic mothers (fetal hyperinsulinism)). # Pulmonary Volumes and Capacities ## Measured using a spirometer The following are the lung volume and capacities obtained from a healthy 70 kg male sitting at rest. The volumes would be 10% smaller for a female. ## Pulmonary Volumes - **Tidal volume (TV)**: Volume of air inspired or expired in one respiratory cycle at rest = 500 ml. - **Inspiratory reserve volume (IRV):** Maximum volume of air inspired by forced inspiration after normal inspiration = 3000 ml. - **Expiratory reserve volume (ERV):** Maximum volume of air expired by forced expiration after normal expiration = 1100 ml (decrease in asthma (increased resistance of air passages) and emphysema (decreased lung elasticity)). - **Residual volume (RV):** Volume of air remaining in lungs after maximum expiration = 1200 ml. (20% of total lung capacity) It can only be expelled by opening the chest wall. ## Importance Aerates blood between breaths. ## Increased in COPD Asthma and emphysema (up to 70% of the total lung capacity). ## Measurement and calculation Cant' be measured by spirometry (measures only air moving in/out of lungs). Calculated by helium dilution method. ## N.B - Minimal air: Small volume of air remaining in lungs even after opening of chest wall and lung collapse. - Medico-legal importance: If lung floats in water it indicates that infant was born alive and has taken breath. If lung sinks in water, infant was born dead. # Pulmonary Capacities Lung capacities are sums of more than one lung volume. - **Inspiratory capacity (IC):** Maximum volume of air inspired at the end of normal expiration: IC = TV + IRV = 3500 ml. - **Vital capacity (VC):** Maximum volume of air expired following a maximum inspiration: VC = VT + IRV + ERV = 4600 ml. - **Functional residual capacity (FRC):** Volume of air remaining in lungs at end of normal expiration (between breaths; relaxed respiratory muscles): FRC = ERV + RV = 2300 ml. It can’t be measured by spirometry. - **Total lung capacity (TLC):** Volume of air in lungs at end of maximum inspiration: TLC= TV+IRV+ERV+RV= 5800ml. It can’t be measured by spirometry. ## Determination of FRC, RV, and TLC ### Helium Dilution Method The subject is connected to a spirometer filled with 10% helium (inert and insoluble gas) in air. Concentration of helium = C1 and the volume in spirometer = V1. Subject breathes helium-air mixture, and helium concentration in lungs becomes the same as in the spirometer after equilibration = C2. Unknown volume in lungs = V2 (FRC). Therefore: C1 x V1= (C2 x V1) + (C2 x V2) The image shows a diagram of healthy and collapsed alveoli in lungs. It also shows a diagram displaying the capacity of the lungs.