Lung function responses to controlled inhaled cotton dust were evaluated in a group of 58 healthy subjects by spirometry (MEFV curves) and forced random noise impedance parameters. A random pressure was introduced into a subject's mouth by a loudspeaker in an enclosure. Thevenin resistance (the real part of impedance) from the forced random noise method is a reliable indicator of cotton-induced bronchoconstriction, but is not so accurate as spirometry.
