Time domains of the hypoxic ventilatory response in awake ducks: episodic and continuous hypoxia.
Time-dependent ventilatory responses to episodic and continuous isocapnic hypoxia were measured in unidirectionally ventilated, awake ducks. Three protocols 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 hypoxia. Ventilation (V(I)) increased immediately within a hypoxic episode (acute response), followed by a further slow rise in V(I) (short-term potentiation). The peak V(T) response increased from the first to second moderate hypoxic episode (progressive augmentation), but was unchanged thereafter. During normoxic intervals, V(I) increased progressively (56% following the tenth episode; long term facilitation). Time-dependent changes were not observed during or following 30-min of continuous hypoxia. Although several time-dependent ventilatory responses to episodic hypoxia are observed in awake ducks, they are relatively small and biased towards facilitation versus inhibitory mechanisms.
Mitchell
G S
GS
Department of Comparative Biosciences, University of Wisconsin, 2015 Linden Drive West, Madison, WI 53706, USA. mitchell@svm.vetmed.wisc.edu
Powell
F L
FL
Hopkins
S R
SR
Milsom
W K
WK
D000818:Animals; D001784:Blood Gas Analysis; D003243:Consciousness / Q000502:physiology; D004372:Ducks / Q000502:physiology*; D006339:Heart Rate; D000860:Hypoxia / Q000145:classification / Q000503:physiopathology*; D017774:Long-Term Potentiation / Q000502:physiology; D008297:Male; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012123:Pulmonary Ventilation / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology; D013997:Time Factors