Resistive-load detection in healthy school-aged children.
The ability to detect changes in respiratory resistance, which may be important in acute and chronic adaptations to airways obstruction, has not been measured previously in children. Two methods were used to measure the resistive-load detection thresholds (the added resistance that produced a "just noticeable difference" in perception) in a group of 38 healthy children and adolescents aged 7-16 years. Total respiratory system resistance (Rrs), as measured by forced oscillation, was used as an index of each child's intrinsic baseline (pre-test) resistance. To determine thresholds a computer program added various percentages of baseline resistance according to response (first method) and then in random order (second method). Thresholds by at least one of the two methods were detectable in 32 of the children (84%), and failure to detect a threshold was less common in older than in young children. Thresholds obtained by each method were significantly related to one another (r = 0.54, P < 0.05). Baseline resistance accounted for a marginally significant proportion of the variation in thresholds as assessed by the tracking method (R2 = 0.12, P < 0.10) and a large proportion of the variation in thresholds as assessed by the random method (R2 = 0.66, P < 0.0001). Thresholds expressed in terms of percent of baseline resistance were found to have mean values of 100.4-105.0%, regardless of gender or age. Results from a comparison group of adults (n = 10) indicated lower threshold by both procedures (mean values, 71.90-76.50%). We conclude that perceptual thresholds for added resistive loads are determined, in part, by growth-related changes in intrinsic resistance.