Chest
Volume 81, Issue 5, May 1982, Pages 586-591
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Normal Values of Total Respiratory Resistance and Reactance Determined by Forced Oscillations: Influence of Smoking

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Impedance Measurements

The technique used has been described in detail elsewhere.7 The seated subject supports his cheeks with his hands and breathes quietly via a screen pneumotachograph. A pseudorandom noise pressure signal, containing all harmonics of 2 Hz to 24 Hz (peak-to-peak amplitude smaller than 0.2 kPa) is applied at the mouth by means of a loudspeaker. Mouth pressure and flow signals, recorded by two identical differential transducers(Validyne MP 445), are fed into a Fourier analyzer. The latter performs

Results

Figure 1 shows the mean curve of respiratory resistance, Rrs, and reactance, Xrs vs frequency in the nonsmokers. Data at 2 Hz were omitted because the coherence function was generally not satisfactory at this frequency. There is almost no frequency dependence of resistance, except for a small increase of Rrs at the lower frequencies. Xrs increases with frequency and resonance occurs at about 8.5 Hz (± 1.5).

The resistance or reactance-frequency curves are significantly influenced by the values

Discussion

The number of reports of normal values for total respiratory impedance is limited. Fisher et al1 measured the resistance of the respiratory system, Rrs, at 5 to 8 Hz during spontaneous breathing in 42 healthy subjects, and found a mean value of 0.23 (SD ± 0.05) kPa.1−1.s. There was no difference between smokers and nonsmokers. The values were not correlated with VC, age, height, or body weight. The values in women were 0.04 kPa.1−1.s higher than in men. Sobol10 investigated 34 healthy smokers

Statistical Procedure

To describe accurately the course of Rrs (or Xrs) with frequency, f, a fourth-degree polynomial was fitted on the measured values in each subject i: Rrs (or Xrs)=a, f4+ b1 f3+C1 f2+di f+ei.The sample covariances of the coefficients of the polynomial regression are generally different from zero. Accordingly, these coefficients were not utilized directly for prediction equation but used to compute an average value of Rrs (and Xrs) and its first, second, third, and fourth derivatives with

Prediction Equations for the Nonsmokers

The equations express Rrs or Xrs (kPa.1−1.s) as a function of oscillatory frequency, f (between 4 and 24 Hz): Rrs (or (Xrs)= af4+ bf3+ cf2+ df + efor Rrs, a = −4.5258 × 10−5 A + 3.1825 × 10−6

  • b = 8.2068 × 10−7 W + 3.3064 × 10−6 A – 2.6789 × 10−4

  • c = −3.7684 × 10−5 W − 8.3893 × 10−5 A + 7.6011 × 10−3

  • d = 8.6633 × 10−5 H + 4.3259 × 10−4 W + 8.5705 × 10−4 A − 9.390 × 10−2

  • e = 5.2399 × 10−3 H + 7.9009 × 10−4 W − 3.2371 × 10−3 A + 1.2844

for Xrs, a = 1.1 × 10−7 H − 1.1394 × 10−7 W −

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Supported by a grant from the Commission of the European Communities.

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