Inspiratory resistive load detection in children with life-threatening asthma

The detection of inspiratory resistive (R) loads was studied in nonasthmati c children (NA), asthmatic children (A), and children with a history of lif e-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 (Del taR(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 inspirato ry baseline resistance (R-aw) was measured by the interrupter method. Ten m agnitudes of R loads and no-load were presented randomly 10 times each for a single inspiration. The loads were presented in three trials. Subjects pr essed a buff on if they detected the presence of a load. The DeltaR(50) was determined from the % detection-DeltaR curve. Rb was the sum of the subjec t's R-aw and the minimal resistance of the apparatus. The DeltaR(50)/R-0 for children with life- threatening asthma was significa ntly 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 cha nge in resistance above their baseline resistance before they sense an incr eased mechanical load such as presented to them by bronchoconstriction duri ng an asthmatic attack. (C) 2001 Wiley-Liss, Inc.