4.2. Ventilatory chemosensitivity
It is unlikely that the observed changes inV ·
O2lung in response
to hypoxia and hyperoxia are mediated by changes in
ventilation patterns. The internally pipped embryo exhibited
an increase in VT during hypoxic exposure, with an associated
insignificant increase in VE (Table 2). However, the changes in
V ·
O2lung during hypoxic exposure were in the opposite direction
of the changes in VT and VE suggesting that the internally
pipped embryos were not relying on changes in ventilation to
respond to air cell hypoxia. While a hypoxic driven chemosensitivity
does not influenceV ·
O2lung at this stage, it appears that
this chemosensitivity is maturing in the internally pipped
embryos. An increase in VE has been observed in chicken
embryos (Menna and Mortola, 2002) and Wedge-tailed
Shearwater embryos (Pettit and Whittow, 1982) as they mature
from the internally pipped stage to hatchlings. Additionally,
externally pipped embryos exhibited stronger significant
increases in VT and VE in response to hypoxia than the
internally pipped embryos in this study (Menna and Mortola,
2003). A similar developmental progression in VE has been
observed in response to temperature. Ventilation of the lungs in
internally pipped embryos is relatively temperature independent
but exhibits temperature dependence in externally pipped
embryos (Menna and Mortola, 2002).