The inspiratory flow-volume curve: the neglected child of pulmonary diagnostics.

The physiology underlying inspiratory flow has been the subject of study for a long time. In the late 1950s, Hyatt et al did seminal investigations of the pressure, flow, and volume characteristics of the lung.1 In those early days the primary interest in flow-volume curves centered on expiratory flow, what controlled it, and how it was limited in various obstructive lung diseases.2 Even in the oldest reports, inspiratory flow (including maximum inspiratory flow) was included (see Figs. 9 and 12 in Hyatt and Fry’s 1960 report).2 However, inspiratory flow and the pathophysiology of reduced inspiratory flow have generally been given short shrift. In a 1973 review of flow-volume curves,3 Hyatt and Black allocated just 2 short sentences to the usefulness of the flow-volume loop in the diagnosis of large airway lesions.