Lung impedance in healthy humans measured by forced oscillations from 0.01 to 0.1 Hz.
Lung impedance was measured from 0.01 to 0.1 Hz in six healthy adults by superimposing small-amplitude forced oscillations on spontaneous breathing. Measurements were made with an almost constant-volume input (160-180 ml) or with an almost constant-flow input (20-30 ml.s-1). No significant difference was found between the two conditions. Lung resistance (RL) sharply decreased from 0.97 kPa.l-1.s at 0.01 Hz to 0.27 kPa.l-1.s at 0.03 Hz and then mildly to 0.23 kPa.l-1.s at 0.1 Hz. Lung effective compliance (CL) decreased slightly and regularly from 0.01 Hz (2.38 l.kPa-1) to 0.1 Hz (1.93 l.kPa-1). The data were analyzed using a linear viscoelastic model adapted from Hildebrandt (J. Appl. Physiol. 28:365-372, 1970) and complemented by a Newtonian resistance (R): RL = R + B/(9.2f); CL = 1/(A + 0.25B + B.log2 pi f), where f is the frequency and B/A is an index of lung tissue viscoelasticity. A good fit was generally obtained, with an average difference of 10% between the observed and predicted values. The ratio B/A was not affected by the breathing and was 10.6 and 13.6% in the constant-volume and constant-flow conditions, respectively, which agrees with Hildebrandt's observations in isolated cat lungs. R was systematically larger than the plethysmographic airway resistance, suggesting that lung tissue resistance might also include a Newtonian component.
Suki
B
B
Unité 14 Institut National de la Santé et de la Recherche Médicale, Physiopathologie Respiratoire, Vandoeuvre-les-Nancy, France.
Peslin
R
R
Duvivier
C
C
Farré
R
R
D000328:Adult; D000403:Airway Resistance / Q000502:physiology; D004548:Elasticity; D006801:Humans; D008168:Lung / Q000502:physiology*; D008297:Male; D008433:Mathematics; D008954:Models, Biological; D010992:Plethysmography, Impedance; D012119:Respiration / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology*; D013990:Tidal Volume; D014783:Viscosity