Flow dependence of specific airway resistance and diagnostic of asthma in children.

Panting majors turbulent flow and contribution of larger airways to the measurement of specific airway resistance (sRaw). The hypothesis was tested that the difference between asthmatic and healthy children is enhanced by narrowing the flow interval to compute sRaw. sRaw was measured during panting in 40 asthmatic and 25 healthy children and computed using all data points (full scale flow) and limited to the flow intervals ± 1L/sec and ± 0.5 L/sec. sRaw was not different between asthmatics (0.87 ± 0.20 kPa.s) and controls (0.80 ± 0.25 kPa.s) when computed full scale, while it was significantly larger in asthmatics than controls within ± 1L/sec (0.77 ± 0.16 kPa.s vs 0.65 ± 0.15 kPa.s, P < 0.004) or ± 0.5 L/sec (0.77 ± 0.21 kPa.s vs 0.61 ± 0.17 kPa.s, P < 0.002). On the other hand, the within subject coefficient of variation was significantly larger when sRaw was computed within ± 1L/sec (13.7 ± 7.2%) or ± 0.5 L/sec (28.3 ± 18.1%) than full scale (11.0 ± 6.7%), respectively P < 0.002 and P < 0.0001. It is concluded that narrowing the flow interval to compute sRaw is associated with better discrimination between asthma and health in children, although the short term variability of sRaw is increased.