4.4. Conclusions
The transition from CAM respiration to lung respiration
occurs over a two day period in the hatching chicken. During this
time, the embryo uses both the CAM and lungs to acquire O2,
with a gradual increase in V ·
O2lung and decrease in V · O2CAM.
Associated with this change in the relative contribution of the
lungs and CAM to V ·
O2total is a functional right-to-left shunt
through the ductus arteriosi and the interatrial foramina. In
response to mild hypoxia or hyperoxia, there is an inverse
relationship between the change inV ·
O2lung andV ·
O2CAM such that
V ·
O2total remains constant. We have found that this is mainly
achieved by altering blood flow to the lungs and CAM through
the ductus arteriosi and the interatrial foramina. Interestingly, the
changes inV ·
O2lung are not associated with changes in ventilation
patterns (Table 2). It appears that the CO2 chemosensitvity is
functional and the O2 chemosensitivity is weak and developing.