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 (DeltaR(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 DeltaR(50) was determined from the % detection-DeltaR curve. R(0) was the sum of the subject's R(aw) and the minimal resistance of the apparatus. The DeltaR(50)/R(0) for children with life- threatening asthma was significantly greater than for asthmatic and nonasthmatic children. The increased DeltaR(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.