Evaluation of two techniques for measurement of respiratory resistance by forced oscillation. A study in young subjects with obstructive lung disease.

The measurement of respiratory resistance by forced oscillation requires minimal patient co-operation and should be a useful test in children. Sixty-eight children and adolescents with obstructive lung disease were studied using two different techniques. In patients with severe obstructive lung disease, unexpectedly low values for respiratory resistance were found when the measurement was made at points of peak flow (write-out method). Measurements made at simulated resonant frequency (subtraction method) in these patients were more in keeping with other tests of respiratory function; however, they probably did not reflect true respiratory resistance. The subtraction method of measuring respiratory resistance would seem to be of value in separating the normal from the abnormal, but the absolute values in obstructed subjects are difficult to interpret.