Measurement of Intra-individual Airway Tone Heterogeneity and its Importance in Asthma

While airways have some degree of baseline tone, the level and variability of this tone is not known. It is also unclear whether there is a difference in airway tone or in the variability of airway tone between asthmatic and healthy individuals. This study examined airway tone and intra-individual airway tone heterogeneity (variance of airway tone) in vivo in 19 individuals with asthma compared to 9 healthy adults. All participants underwent spirometry, body plethysmography and HRCT at baseline and after maximum bronchodilation with albuterol. Airway tone was defined as the percent difference in airway diameter after albuterol at total lung capacity compared to baseline. The amount of airway tone in each airway varied both within and between subjects but the difference between the two groups did not reach statistical significance (p=0.09). In contrast, the two groups differed in intra-individual airway tone heterogeneity (p=0.016). Intra-individual airway tone heterogeneity was strongly correlated with airway tone (r= 0.78, p<0.0001). Also, it was negatively correlated with the magnitude of the distension of the airways from FRC to TLC at both baseline (r= -0.49, p= 0.03) and after maximum bronchodilation (r= -0.51, p= 0.02) in the asthma, but not the healthy group. We did not find any relationship between intra-individual airway tone heterogeneity and lung function. Intra-individual airway tone heterogeneity may be an important marker of airway pathophysiology in asthma.

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