Control charts demonstrated limited utility for the monitoring of lung function in asthma

Statistical process control charts have been advocated for use in monitoring of lung function in asthma. We aimed to evaluate their application in asthma using existing data from a randomized trial.

Patients on optimal inhaled corticosteroid/bronchodilator therapy (n=81) were randomized to continue the same or change to corticosteroid alone. Baseline statistical control was assessed from 20 days of electronically recorded lung function (peak expiratory flow [PEF], forced expiratory volume in one second [FEV(1)]). The ability to detect lung function changes was assessed during 10 days after randomization.

PEF measurements were in statistical control during baseline for only 59-79% of patients for different combinations of five control chart rules (e.g., Rule 1: >3 standard deviations outside mean and 95% expected to be in control), with similar proportions for FEV(1). After randomization, among those previously in statistical control, Rule 1 signaled lower FEV(1) for 35% of patients randomized to treatment change compared with 6% continuing baseline treatment (P=0.004). Control charts performed poorly for PEF, signaling a decrease for 8% of patients randomized to treatment change compared with 11% continuing treatment (P=0.7). A paradoxical increase was signaled for many patients continuing treatment.

Control charts may not be suitable for use in many patients with asthma.