Electronic device for the recording of isopressure-flow-volume (i.p.f.v.) curves

An electronic device for the automatic recording of isopressure-flow-volume (i.p.f.v.) curves was developed using a modified version of the flow interrupter technique. Following an inspiration up to total lung capacity, the subject made an expiratory effort against a closed shutter until the mouth pressure reached a given preset level between 5 and 50 cmH₂O, at which time the shutter reopened. Expiratory flow was sampled immediately after the shutter opening. When the volume reached a level, previously adjusted to correspond to one-tenth of vital capacity, the shutter closed again. The subject made a renewed effort against the closed shutter and the whole procedure was repeated from the initial condition until the expiration terminated at the residual volume. As the sampled flow and expired volume were plotted on an X-Y plotter with the aid of an electronic circuit in parallel with to the progress of the forced expiration, a flow-volume curve at an isopressure was thus described in ten steps. I.P.F.V. curves were measured in eight normal subjects and fifteen patients with various pulmonary diseases and the practical interpretation of these curves is discussed.