Abstract
Observations on 27 patients with chronic airways obstruction, 5 other patients and 6 healthy subjects indicate that forced inspiratory tests are of limited value. The one-second forced inspiratory volume (FIV 1 ) was found to be dependent on the vital capacity (VC). Consequently the ratio of the one-second forced expiratory to forced inspiratory volumes (FEV 1 /FIV 1 ) correlated with FEV 1 as a percentage of VC ( r =0·93). The dependence of FIV 1 on VC was found to reside mainly in the inspiratory capacity (IC). The maximal inspiratory flow rate (MIFR) correlated with FIV 1 ( r = 0·87). Forced inspiratory measurements are unlikely to provide information on ventilatory function additional to that given by VC, except in cases of inspiratory obstruction due to a lesion of a main airway. It is possible that a bronchodilator response in forced inspiratory tests may be due to a dynamic improvement in airflow or an increase in ‘static’ volume (VC or IC), or both.
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