Journal of Applied Physiology, Vol 55, Issue 1 183-190, Copyright © 1983 by American Physiological Society
Active and passive respiratory mechanics and control of breathing in kittens
W. A. Zin, D. Marlot, M. Bonora, N. M. Siafakas, H. Gautier and J. Milic-Emili
In five spontaneously breathing kittens (12-13 days old), anesthetized with
pentobarbital sodium, we measured the passive and active elastances and
resistances of the respiratory system and the decay of inspiratory muscle
pressure (PmusI) during expiration. When normalized for body weight (BW),
passive resistance (Rrs . BW) was smaller in kittens than in adult cats,
whereas passive elastance (Ers . BW) did not differ significantly. As a
result, passive time constant (tau rs = Rrs/Ers) was shorter in kittens
(mean +/- SE: 0.073 +/- 0.011 s) than in cats (0.121 +/- 0.008 s). This,
associated with a faster decay in PmusI in kittens, results in 2-3 times
higher flows per kilogram body weight during spontaneous tidal expirations
in kittens than in cats. As in the adult cats, the average values of active
elastance and resistance were higher than the passive, the average
percentage increase amounting to 59 and 49%, respectively. The greater
active impedance reflects force-length and force-velocity properties of
inspiratory muscles. Its price is higher work of breathing; its advantage
is greater intrinsic load compensation.
