Time domains of the hypoxic ventilatory response in awake ducks: episodic and continuous hypoxia

Time-dependent ventilatory responses to episodic and continuous isocapnic h ypoxia were measured in unidirectionally ventilated, awake ducks. Three pro tocols were used: (1) ten 3-min episodes of moderate hypoxia (10% O-2) with 5-min normoxic intervals; (2) three 3-min episodes of severe hypoxia (8% O -2) with 5-min normoxic intervals: and (3) 30-min of continuous moderate hy poxia. Ventilation ((V) over dot I) increased immediately within a hypoxic episode (acute response), followed by a further slow rise in (V) over dot I (short-term potentiation). The peak VT response increased from the first t o second moderate hypoxic episode (progressive augmentation), but was uncha nged thereafter. During normoxic intervals, (V) over dot I increased progre ssively (56% following the tenth episode; long term facilitation). Time-dep endent changes were not observed during or following 30-min of continuous h ypoxia. Although several time-dependent ventilatory responses to episodic h ypoxia are observed in awake ducks, they are relatively small and biased to wards facilitation versus inhibitory mechanisms. (C) 2001 Elsevier Science B.V. All rights reserved.