title: Mechanical impedances of lungs and chest wall in the cat.
abstract: In nine anesthetized and paralyzed cats, the mechanical impedances of the total respiratory system (Zrs) and the lungs (ZL) were measured with small-volume pseudorandom forced oscillations between 0.2 and 20 Hz. ZL was measured after thoracotomy, and chest wall impedance (Zw) was calculated as Zw = Zrs-ZL. All impedances were determined by using input airflow [input impedance (Zi)] and output flow measured with a body box [transfer impedance (Zt)]. The differences between Zi and Zt were small for Zrs and negligible for ZL. At 0.2 Hz, the real and imaginary parts of ZL amounted to 33 +/- 4 and 35 +/- 3% (SD), respectively, of Zrs. Up to 8 Hz, all impedances were consistent with a model containing a frequency-independent resistance and inertance and a constant-phase tissue part (G-jH)/omega alpha, where G and H are coefficients for damping and elastance, respectively, omega is angular frequency, and alpha determines the frequency dependence of the real and imaginary parts. G/H was higher for Zw than for ZL (0.29 +/- 0.05 vs. 0.22 +/- 0.04, P less than 0.01). In four cats, the amplitude dependence of impedances was studied: between oscillation volumes of 0.8 and 3 ml, GL, HL, Gw, and Hw decreased on average by 3, 9, 26, and 29%, respectively, whereas the change in G/H was small for both ZL (7%) and Zw (-4%). The values of H were two to three times higher than the quasistatic elastances estimated with greater volume changes (greater than 20 ml).
authors.affiliation: Kalmár Laboratory, József Attila University, Szeged, Hungary.
authors.forename: Z
authors.initials: Z
authors.lastname: Hantos
authors.forename: A
authors.initials: A
authors.lastname: Adamicza
authors.forename: E
authors.initials: E
authors.lastname: Govaerts
authors.forename: B
authors.initials: B
authors.lastname: Daróczy
mesh_terms: D000403:Airway Resistance / Q000502:physiology; D000818:Animals; D002307:Cardiography, Impedance; D002415:Cats; D005260:Female; D008168:Lung / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D015656:Respiratory Mechanics / Q000502:physiology; D013909:Thorax / Q000502:physiology*