Lung Volumes

Lung volumes are set by the elastic properties of lung parenchyma and surrounding tissues, alveolar surface tension, power generated by respiratory muscles, lung reflexes and properties of airways. Pressure-volume relationship between lungs and chest wall defines the properties of total lung capacity (TLC), functional residual capacity (FRF) and residual volume (RV). Lung volumes are measured by gas dilution methods such as helium dilution and nitrogen washout or directly by body plethysmography. Lung volume measurement provides important information about lung hyperinflation in obstructive lung diseases. Lung volumes are reduced in restrictive diseases which may be useful in the assessment of underlying disease. This review covers the physiology of static lung volumes, definitions, methods of measurement, assessment of pulmonary hyperinflation and restrictive ventilatory defect.