The physiological basis and clinical significance of lung volume measurements

Abstract

From a physiological standpoint, the lung volumes are either dynamic or static. Both subclasses are measured at different degrees of inspiration or expiration; however, dynamic lung volumes are characteristically dependent on the rate of air flow. The static lung volumes/capacities are further subdivided into four standard volumes (tidal, inspiratory reserve, expiratory reserve, and residual volumes) and four standard capacities (inspiratory, functional residual, vital and total lung capacities). The dynamic lung volumes are mostly derived from vital capacity. While dynamic lung volumes are essential for diagnosis and follow up of obstructive lung diseases, static lung volumes are equally important for evaluation of obstructive as well as restrictive ventilatory defects. This review intends to update the reader with the physiological basis, clinical significance and interpretative approaches of the standard static lung volumes and capacities.

Keywords: Lung capacities; Lung volumes; Obstructive; Restrictive; Spirometry.

Figures

Fig. 1

Standard lung volumes and capacities from a spirometer trace. The solid black and gray arrows indicate lung volumes and capacities respectively

Fig. 2

Intrapleural and alveolar pressures towards the end of inspiration (a), expiration (b), and forceful expiration (c). The dotted line indicates the change in thoracic dimensions during a, b and c compared with the previous phase of the respiratory cycle

Fig. 3

Static PVC of the lungs and chest wall. The lung and chest wall curve was plotted by the addition of the individual lung and chest wall curves

Fig. 4

a Dynamic PVC of the lungs. b Work of breathing

Fig. 5

Work of breathing in  normal subjects (a) and patients with RLD (b) and OLD (c)

Fig. 6

Changes in static lung volume and capacities with age

Fig. 7

Typical changes in the static lung volumes and capacities in RLD and OLD