Use of pulmonary function tests in the assessment and treatment of patients with airway hyperreactivity

Simple spirometry at each office visit (and if feasible, determination of lung volume) along with regular assessment of peak flow by the patient are important determinations that facilitate assessment of the progress of the disorder, as well as the impact of therapy. When there is a trend towards falling air flow rates, determination of the arterial blood gas tensions and calculation of the P(A-a)O2 will foster early recognition of the development of increased flow resistance in the peripheral lung units, so that intervention can be instituted. In the early stages of peripheral airway obstruction, the arterial PO2 and the P(A-a)O2 are sensitive indicators of the severity of the disturbance, whereas changes in FEV1 may be minimal. If intervention is not instituted early enough, the work of breathing may increase significantly and reach a stage where hypoxemia is associated with a rising PaCO2, which is indicative of serious deterioration.