RELATIONSHIP OF NONSPECIFIC AIRWAY HYPERRESPONSIVENESS (AHR) TO MEASURES OF PEAK EXPIRATORY FLOW (PEF) VARIABILITY

Background: The relationship between airway hyper-responsiveness (AHR) and clinical asthma remains controversial and unclear. Aims: To test the hypothesis that serial measures of variability of peak expiratory now rate (PEF) correlate with serial measures of AHR, and to determine which mathematical expression of variability provides the best correl ation. Methods: A longitudinal study over 180 days of 20 atopic, moder ately severe asthmatics was undertaken. A diary of medication use and morning and evening PEEP before and after beta agonist was kept and AH R (PD20 histamine) was measured at three-weekly intervals. Using group data (128 sets) In PD20 was correlated with various measures of PEF v ariability over 9 days. Results: [GRAPHICS] Within the group there was a weak but highly statistically significant correlation between AHR a nd 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 statistical ly significant relationship (p < 0.05) between AHR and mean morning PE F. Conclusions: These results suggest that while PEP variability may r eflect AHR for the purposes of epidemiologic studies, it is unlikely t b be useful as a simple 'non-invasive' means of assessing AHR in indiv idual patients. More complex measures of PEF variability do not have a n advantage over simpler measures such as mean morning PEF.