Use of magnetometers to volume-reference flow-volume curves

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Abstract
Chest wall diameters measured by magnetometers were used to indicate a lung volume reference for repeated interrupted partial flow-volume curves (IPFVC), and total respiratory conductances were measured before and after bronchodilation in normal humans. 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 6 inspiratory capacities (IC) from the reference point, completely reposturing before each maneuver. For a mean IC of 2.25 l, the SD was 5.5%. IPFVC were performed through a valve system triggering open at 60 cm H2O and shutting after 1 l of expiration. Subjects [10] each performed 5 sets of IPFVC volume-referenced by magnetometers and the pooled flow variability was 5% or 0.15 l/s. Respiratory conductances by forced oscillations and IPFVC were measured in 5 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 < 0.05. Magnetometers may be used in normals to volume-reference IPFVC with excellent reproducibility.

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