Inspiratory resistive load detection in children with life‐threatening asthma

The detection of inspiratory resistive (R) loads was studied in nonasthmatic children (NA), asthmatic children (A), and children with a history of life‐threatening asthma (LTA). It was hypothesized that the LTA children would have a reduced ability to detect added mechanical loads as measured by the Weber fraction, which assesses the resistive load detection threshold (ΔR 50 /R 0 ). Subjects were separated from the investigator, were seated in a soundproofed room, and breathed through a nonrebreathing valve with the inspiratory port connected to the loading manifold. The subject's inspiratory baseline resistance (R aw ) was measured by the interrupter method. Ten magnitudes of R loads and no‐load were presented randomly 10 times each for a single inspiration. The loads were presented in three trials. Subjects pressed a button if they detected the presence of a load. The ΔR 50 was determined from the % detection‐ΔR curve. R 0 was the sum of the subject's R aw and the minimal resistance of the apparatus. The ΔR 50 /R 0 for children with life‐ threatening asthma was significantly greater than for asthmatic and nonasthmatic children. The increased ΔR 50 /R 0 suggests that children with LTA are at risk of life‐threatening asthma attacks, in part because it requires a greater change in resistance above their baseline resistance before they sense an increased mechanical load such as presented to them by bronchoconstriction during an asthmatic attack. Pediatr Pulmonol. 2001; 32:44–48. © 2001 Wiley‐Liss, Inc.