Effects of normobaric and hypobaric hypoxia on ventilation and arterial blood gases in ducks.

We measured ventilation (V1) and arterial blood gases in awake Pekin ducks exposed to normoxia at sea level, normobaric hypoxia achieved by lowering FIO2 at normal barometric pressure (NORMO), and hypobaric hypoxia achieved with a low pressure chamber and 21% O2 (HYPO). Average normoxic values were: V1 = 0.46 L . (kg.min)-1, PaO2 = 99.7 Torr, PaCO2 = 30.1 Torr. At PIO2 = 90 Torr, NORMO and HYPO measurements were not significantly different (P greater than 0.05). At PO2 = 46 Torr, NORMO V1 was less than HYPO V1 but blood gases were not significantly different: VI = 1.00 vs 1.45 L . (kg.min)-1; PaO2 = 31.3 vs 33.0 Torr; PaCO2 = 11.5 vs 10.6 Torr. Although both tidal volume (VT) and respiratory frequency (fR) were greater in HYPO, similar blood gases with NORMO and HYPO suggest similar parabronchial ventilation. The results suggest increased physiologic dead space, caused by reduced efficacy of aerodynamic valving, with reduced gas density in hypobaria.