Relationship between bronchial responsiveness to hyperventilation with cold and methacholine in asthma

Twenty-seven subjects with asthma and normal baseline lung function were challenged with aerosols of methacholine (M) and by isocapnic hyperventilation with cold air (HV). Stimulus-effect relationships were determined for each provocational technique on separate days and were expressed as the dose required to produce a 20% fall in forced expired volume in 1 sec (FEV 1) obtained by linear interpolation from log stimulus vs. response curves (PD 20). Each stimulus was applied with a sufficient intensity to produce a 20% or greater fall in FEV 1 in each subject. The PD 20 for M correlated significantly with the PD 20 for HV (p < 0.001) when the latter was expressed in liters per minute. The correlation between cumulative M PD 20 and HV PD 20 expressed as a percent of maximal voluntary ventilation was significant but less strong. We conclude that the airway response to HV reflects nonspecific bronchial hyperresponsiveness and that the dose of HV is best determined as the absolute level of ventilation.