Chemoreflex drive of ventilation during exercise in ducks.

To determine if arterial chemoreceptors contribute to the ventilatory response during exercise, we measured minute ventilation (VI) in spontaneously breathing Pekin ducks (Anas platyrhynchos) during rest and running exercise when the inspired gas was switched from either 21% or 12% O2 to 100% O2 for 45 s (O2-test). In normoxia at rest (PaO2 = 99 Torr), inhaling 100% O2 reduced VI by 30%, while during resting hypoxic conditions (PaO2 = 56 Torr), 100% O2 inhalation reduced VI by 66%. During exercise, abruptly inhaling 100% O2 decreased VI by only 14% and 33% in normoxic and hypoxic conditions, respectively. Thus, only a small fraction of the ventilatory response during exercise under normoxic conditions is due to an arterial chemoreceptor input. However, during exercise in hypoxic conditions, arterial chemoreceptors provide a substantial portion of the total drive to ventilation.