Use of magnetometers to volume-reference flow-volume curves

Chest wall diameters measured by magnetometers were used to indicate a lung volume reference for repeated interrupted partial flow-volume curves (IPFVC's) and IPFVC's, and total respiratory conductances were measured before and after bronchodilation in normals. With posture rigidly controlled, subjects matched the magnetometer display on an X-Y oscilloscope to a previously marked point on the screen. Seven subjects performed six inspiratory capacities (IC's) from the reference point, completely reposturing before each maneuver. For a mean IC of 2.25 liters the standard deviation was 5.5%. IPFVC's were performed through a valve system triggering open at 60 cmH2O and shutting after 1 liter of expiration. Ten subjects each performed five sets of IPFVC's volume-referenced by magnetometers and the pooled flow variability was 5% or 0.15 l/s. Respiratory conductances by forced oscillations and IPFVC's were measured in five normal subjects before and after inhaled isoproterenol. In each subject the flow increase was always greater than the conductance increase (about 2.5:1.0) for P less than 0.05. We conclude that magnetometers may be used in normals to volume-reference IPFVC's with excellent reproducibility.