Overview Lung Volumes Lung volumes are measured by spirometry Tidal Volume (TV) normal, quiet breathing involves inspiration and expiration of TV TV ~ 500 mL Inspiratory Reserve Volume (IRV) additional volume of gas that can be inspired above TV on maximal inspiration IRV ~ 3,000 mL Expiratory Reserve Volume (ERV) additional volume of gas that can be expired below TV on maximal expiration ERV ~ 1,200 mL Residual Volume (RV) volume of gas that remains in lungs following maximal expiration RV ~ 1,200 mL cannot be measured by spirometry Lung Capacities a lung capacity includes ≥ 2 lung volumes Inspiratory Capacity (IC) TV + IRV IC ~ 3,500 mL Functional Residual Capacity (FRC) ERV + RV volume of gas that remains in lungs following normal TV expiration equilibrium volume of lungs FRC ~ 2,400 mL Vital Capacity (VC) IC + ERV = TV + IRV + ERV volume of gas that can be expired following maximal inspiration VC ~ 4,700 mL Total Lung Capacity (TLC) VC + RV = TV + IRV + ERV + RV TLC ~ 5,900 mL Pulmonary Vascular Resistance Lowest at FRC higher at volumes greater and less than FRC Contributions from both the intraalveolar vessels (bigger influence) and extraalveolar vessels Increased by inhalation increased pressure on intra-alveolar vessels by expanding alveoli forced exhalation increased intrathoracic pressure compresses pulmonary vessels