Natural Frequency, Damping Factor and Inertance of the Chest-Lung System in Cats

¹ From the Department of Physiology and Pharmacology, Graduate School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania

A study of the local surface velocity of the chest and abdomen as a function of the frequency of sinusoidal pressure waves introduced into the airways via the trachea, was made in 15 cats. The study confirmed and extended the observations DuBois, Brody, Lewis and Burgess had previously made in human beings and demonstrated that the effects seen were not produced by any part of the airway above the trachea. Comparison is made of this data with the averaged data obtained by using a plethysmograph to integrate the surface responses of the cat. The natural frequency (9.6, S.E. = 0.6 cps), damping factor (2.0, S.E. = 0.25), resistance (k₁ = 13.5, S.E. = 2.3 cm H₂O/(l/sec.); k₂ = 76, S.E. = 21 cm H₂O/(l/sec.)², and elastance (230, S.E. = 26 cm H₂O/l.) were measured and the inertance (.09, S.E. = .008 cm H₂O/(l/sec.²)) was calculated. The implications of these concepts and measurements for respiratory mechanics and ballistocardiography are discussed.