Respiratory mechanics in 1-day old chicken hatchlings and effects of prenatal hypoxia

This study examined the static and dynamic properties of the respiratory system in avian hatchlings, and the effects of incubation in hypoxia (15% O2) on these variables. In 1-day old chicken (Gallus gallus) hatchlings killed by an anesthetic overdose the static compliance of the respiratory system (Crs) was measured from the pressure-volume curve, constructed by step changes in lung volume. The dynamic compliance, Crs(dyn), resistance, Rrs, and time constant, τrs, were measured during mechanical ventilation at rates up to 90 cpm. The results indicated that (1) static Crs in hatchlings is several folds higher than in neonatal mammals of similar size, (2) during mechanical ventilation the respiratory system becomes hyperinflated and much stiffer; at 65 cpm (which is the respiratory frequency of hatchlings spontaneously breathing at rest) Crs(dyn) was about one tenth of the static value, (3) after prenatal hypoxia static Crs, Crs(dyn), Rrs and τrs were similar to controls; only the magnitude of the hyperinflation was slightly decreased. It is concluded that in avian hatchlings (a) despite the large respiratory volume of the air sacs, expiration can occur passively because the hyperinflation greatly decreases Crs(dyn) and shortens τrs, and (b) prenatal hypoxia of the level tested has no major effects on the mechanical properties of the respiratory system.