Small birth weight does not compromise ventilatory chemosensitivity in the 1-day old hatchling

Sustained hypoxia is known to decrease embryonic growth and to lower the newborn's ventilatory chemosensitivity (VCS) to hypoxia and hypercapnia. What was unclear is whether or not a difference in birth weight could per se, and independently from hypoxia, have some influence on the magnitude of VCS. VCS, defined as the relative increase in ventilation-oxygen consumption ratio (V˙E/V˙O2), was studied by a modification of the barometric technique in 1-day old chicken hatchlings born at term and selected for large differences in birth weight. The small hatchlings (SM, 35.9 ± 0.7 g) had smaller V˙O2 and V˙E than the large hatchlings (LG, 47.0 ± 0.6 g), both in air and during acute exposures to hypoxia (15% or 10% O2) or hypercapnia (2% or 4% CO2). However, when normalized by the air values, the metabolic and ventilatory responses coincided. Values of V˙E/V˙O2 in air, hypoxia or hypercapnia were the same in SM and LG, and much higher than those previously measured in hatchlings with prenatal hypoxia. It is concluded that (a) birth weight per se does not affect V˙E chemosensitivity, and (b) the blunting effects of hypoxia on body growth and chemosensitivity are parallel events, and the former does not contribute to the latter.