Ventilation frequency ( f ) and tidal volume (VT) were measured
with a pneumotachograph connected to a Validyne pressure
transducer using methods adapted from Glass et al. (1978).
The voltage output from the pressure transducer was recorded
by a Powerlab 8SP and Chart 5.2 Data Acquisition Software
(ADInstruments). Ventilation frequency was calculated by detecting
the peak in ventilation using Chart 5 cycle measurement
calculations. Tidal volume was measured in volts providing a
relative measure of the change in an embryo's tidal volume
under different conditions similar to that of Price et al. (2007).
Minute ventilation (VE) was calculated as f ⁎VT. Lung ventilation
was measured under control conditions at the air cell
(12% O2, 5%CO2, and 83% N2) and the rest of the egg (21% O2
and 79% N2). The gas flowing into the air cell was then either
made hypoxic (5% O2 and 5% CO2) or hyperoxic (21% O2 and
5% CO2) while the rest of the egg was maintained at normoxia.
Measurements were then made after 60 min of exposure. This
was followed by decreasing the CO2 flowing to the air cell from
5% to 2.5%, while maintaining the experimental air cell hypoxia
or hyperoxia. Ventilation data is presented as the mean %
change from the previous level.