Spirometry partitions the air held and moved by the lungs into four mutually exclusive primary volumes — tidal volume (air exchanged during quiet breathing), inspiratory reserve volume (air inhalable beyond a tidal inspiration), expiratory reserve volume (air exhalable beyond a tidal expiration), and residual volume (air that necessarily remains after maximal expiration to keep the alveoli patent and prevent alveolar collapse) — plotted as lung volume against time. Because the primary volumes are non-overlapping, pulmonary capacities are defined additively as sums of two or more volumes: inspiratory capacity (TV + IRV), expiratory capacity (TV + ERV), functional residual capacity (ERV + RV), vital capacity (IRV + TV + ERV), and total lung capacity (IRV + TV + ERV + RV). This belongs to respiratory physiology within human anatomy and physiology, where static lung volumes and capacities provide the baseline description of pulmonary mechanics that dynamic tests of pulmonary function — such as forced spirometry, used to discriminate obstructive from restrictive disorders — subsequently build upon.
Spirometry partitions the air held and moved by the lungs into four mutually exclusive primary volumes — tidal volume (air exchanged during quiet breathing), inspiratory reserve volume (air inhalable…