Relationship of non-specific airway hyperresponsiveness (AHR) to measures of peak expiratory flow (PEF) variability

The relationship between airway hyper-responsiveness (AHR) and clinical asthma remains controversial and unclear.

To test the hypothesis that serial measures of variability of peak expiratory flow rate (PEF) correlate with serial measures of AHR, and to determine which mathematical expression of variability provides the best correlation.

A longitudinal study over 180 days of 20 atopic, moderately severe asthmatics was undertaken. A diary of medication use and morning and evening PEFR before and after beta agonist was kept and AHR (PD20 histamine) was measured at three-weekly intervals. Using group data (128 sets) in PD20 was correlated with various measures of PEF variability over 9 days.

[Table: see text] Within the group there was a weak but highly statistically significant correlation between AHR and measures of PEF variability--the strongest correlation being with mean morning PEF. Within individual subjects, however, the correlation was not a consistent finding and only four patients had a statistically significant relationship (p < 0.05) between AHR and mean morning PEF.

These results suggest that while PEF variability may reflect AHR for the purposes of epidemiologic studies, it is unlikely to be useful as a simple 'non-invasive' means of assessing AHR in individual patients. More complex measures of PEF variability do not have an advantage over simpler measures such as mean morning PEF.