Impedance measurements were performed on equipment described by Landser et al. Briefly, the seated subject, wearing a noseclip, supports the cheeks with his hands and breathes quietly via a tube. A pseudorandom noise pressure signal containing all harmonics of 4 up to 52 Hz is applied at the mouth by means of a loudspeaker. Mouth pressure and flow signals are recorded by transducers with identical frequency characteristics (Validyne MP45) and analyzed by spectral analysis techniques. The relationship between pressure and flow is called impedance. Impedance is partitioned into the real part or resistance (R) and the imaginary part or reactance (X). The accuracy of the computations is evaluated at each frequency by means of a coherence function. Only the values with coherence functions exceeding or equal to 0.95 are retained; a value of 1.00 would represent complete absence of noise or alinearities. Allergies pills Click Here Three successive measurements, each lasting 8 s, were performed in each subject. Of the obtained impedance data, analyzed parameters included the following: resistance at 8 Hz (R8) and at 28 Hz (R28), the difference between R28 and R8 (frequency dependence (FD); signifying the course of the resistance vs frequency curve) the reactance at 8 Hz (X8) and the resonant frequency fo- The apparatus was calibrated daily and all subjects were measured by the same investigator.
Flow volume curves were measured using a dry “rolling seal” spirometer (Vicatest-V, Mijnhardt, Bunnik, the Netherlands), according to American Thoracic Society criteria. The spirometer was calibrated daily and all subjects were measured on the same spirometer by the same investigator. Parameters analyzed were FVC, FEVi, FEVi/FVC, peak expiratory flow (PEF), and forced expiratory flow at 25 percent and 75 percent of the expired VC (FEF25, FEF75), and maximal midexpiratory flow (MMEF).