Lung function and bronchial challenges in infants: repeatability of histamine and comparison with methacholine challenges

Limited information exists regarding the repeatability of lung function and bronchial challenge tests using the rapid thoracic compression technique (RTC) in infants.

To determine the repeatability of lung function and histamine challenge test results using the RTC technique and to compare the results obtained for bronchial challenges using histamine (H) and methacholine (M).

Twelve infants [7 healthy, 5 with cystic fibrosis (CF) had pairs of H challenges 1 week apart. Eleven infants (7 healthy, 4 CF) had one H and one M challenge a week apart. The provocative concentration of H or M to cause a 40% fall in maximum flow at functional residual capacity (PC40) was determined using the RTC technique. Twenty-three comparisons were possible between maximal expiratory flow at functional residual capacity (VmaxFRC) measurements made 1 week apart.

The mean difference between pairs of VmaxFRC measurements was 6.4% of baseline, and the coefficient of repeatability was 31.1% of baseline. The mean difference between PC40(H) measurements was 0.163 doubling concentrations, with a coefficient of repeatability of 1.66 doubling concentrations. The mean difference between PC40(H) and PC40(M) was 0.75 doubling concentrations, with 95% of PC40(H) between -0.18 to 1.69 doubling concentrations of the PC40(M).

Although the repeatability of VmaxFRC using the RTC technique is less than for voluntary forced expiratory flow parameters in older children, similar results were obtained for infants as observed in older subjects for repeatability of H challenges and agreement between measures of bronchial responsiveness using H or M.