Journal of Applied Physiology, Vol 59, Issue 5 1477-1486, Copyright © 1985 by American Physiological Society
Ontogeny of respiratory control and pulmonary mechanics in newborn rabbits
M. M. Grunstein and D. T. Tanaka
Maturation of the respiratory pattern and the active and passive mechanical
properties of the respiratory system were assessed in 19 tracheotomized
rabbits (postnatal age range: 1-26 days) placed in a body plethysmograph.
With maturation both minute ventilation and tidal volume significantly
increased, whereas respiratory frequency decreased. When normalized for
body weight (kg) both the passive (Rrs X kg) and active (R'rs X kg)
resistances of the respiratory system significantly increased with age,
whereas the corresponding passive (Crs X kg-1) and active (C'rs X kg-1)
compliances significantly decreased. At any given age R'rs X kg only
slightly exceeded Rrs X kg, whereas C'rs X kg-1 was significantly lower
than Crs X kg-1. Moreover, the maturational increases in Rrs X kg and R'rs
X kg exceeded the corresponding decreases in Crs X kg-1 and C'rs X kg-1,
resulting in significant age-related increases in both the passive (tau rs)
and active (tau'rs) time constants of the respiratory system. Due to the
age-related increases in tau'rs, producing a delayed volume response to any
given inspiratory driving pressure, the relative volume loss obtained at
any time during inspiration was greater in the maturing rabbit. On the
other hand, because of concomitant compensatory changes in respiratory
pattern, evidenced by increases in inspiratory duration with age, the
end-inspiratory tidal volume loss in the maturing animal was maintained
generally less than 10% at all postnatal ages. Thus maturational changes in
respiratory pattern appear coupled to changes in the active mechanical
properties of the respiratory system. The latter coupling serves to
optimize the transduction of inspiratory pressure into volume change in a
manner consistent with establishing the minimum inspiratory work of
breathing during postnatal development.
