Abstract
Increased temporal fluctuation of oscillatory mechanics parameters measured over 15 minutes has been suggested to be a specific feature of asthma, though this is still a controversial issue. We aimed to evaluate whether variability over time scales >1 day can reliably separate asthmatic from healthy subjects.
Within-breath respiratory resistance (Rrs) and reactance (Xrs) were measured by forced oscillations during 2min of tidal breathing at morning and evening for 6 months in 10 mild asthmatic and 10 healthy subjects. Short-term (within measurements) and long-term (2, 4, 8, 16 and 32 consecutive days) variability of Rrs and Xrs was characterized by their standard deviations (SDRrs and SDXrs).
Short-term variability of either Rrs or Xrs was not significantly different between asthmatic and healthy subjects (p>0.05). SDRrs was significantly larger in asthmatics than in healthy subjects with a time scale ≥4 days using morning (0.60 vs 0.32 cmH2O s L-1, p<0.03) and ≥16 days using evening (0.64 vs 0.42, p<0.05) data. When Rrs was partitioned into inspiratory (Rinsp) and expiratory (Rexp) components, long-term SDRinsp but not long-term SDRexp (p>0.05) was significantly larger in asthmatic than healthy subjects. SDRinsp was greater already for time scales ≥2 days in the morning (0.44 vs 0.24, p<0.02) and ≥4 days in the evening (0.49 vs 0.30, p<0.05). SDXrs was significantly larger in asthmatics from 2-day time scale (0.23 vs 0.11, p<0.01 morning; 0.19 vs 0.13, p<0.03 evening).
In conclusion, the assessment of FOT-based variability over a relatively long-term, i.e., few days, period provides an explanation for previous controversial findings and allows us to reliably distinguish asthmatics from normal subjects.
- © 2011 ERS