Forced random noise resistance determination in childhood asthma.

The forced random noise method for measuring respiratory resistance was studied in terms of reproducibility and correlation with spirometry and flow volumes in 30 older children (four to 17 years) with asthma and in 16 infants and children below three years of age. In the 30 older children, the mean value of individual coefficient of variations for three repeated measurements was 7.4 percent. Resistance parameters correlated well with spirometric parameters with all but three correlation coefficients greater than 0.7. In 20 older asthmatic patients, 180 micrograms albuterol caused a significant reduction in resistance in 11 subjects. At the same time, FEV1 increased significantly in nine subjects but showed a paradoxic decrease in five. This paradoxic response is attributed to complex reflexes caused by the maximum inspiration and forced expiration and did not occur with resistance measurements. This method requires little subject cooperation, and therefore, is well suited for infants and children.