Decline in peripheral chemoreceptor excitatory stimulation during acute hypoxia in the lamb.
Chemoreceptor function was studied in eight 2- to 3-day-old unanesthetized lambs to sequentially assess hypoxic chemoreflex strength during an 18-min exposure to hypoxia [inspired O2 fraction (FIO2) = 0.08]. The immediate ventilatory (VE) drop in response to five breaths of pure O2 was measured at 3, 7, and 15 min during hypoxia. Each lamb was studied again at 10-11 days of age. At 2-3 days of age VE increased, with the onset of hypoxia, from 658 +/- 133 (SD) ml.min-1 X kg-1 to a peak of 1,124 +/- 177 ml.min-1 X kg-1. A dampening of the VE response then occurred, with a mean decline in VE of 319 ml.min-1 X kg-1 over the 18-min hypoxia period. Each pure O2 test (Dejours test) resulted in an abrupt fall in VE (delta VEDejours). This VE drop was 937 +/- 163, 868 +/- 244, and 707 +/- 120 ml.min-1 X kg-1 at 3, 7, and 15 min of hypoxia, respectively. Comparing the three O2 tests, delta VEDejours was significantly decreased by 15 min, indicating a loss of about one-fourth of the O2 chemoreflex drive during hypoxia. Testing at 10-11 days of age revealed a smaller VE decline during hypoxia. O2 tests at the beginning and end of the hypoxic period were not significantly different, indicating a smaller loss of hypoxic chemoreflex drive in the more mature animals.(ABSTRACT TRUNCATED AT 250 WORDS)
D000208:Acute Disease; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001049:Apnea / Q000139:chemically induced; D002245:Carbon Dioxide; D002628:Chemoreceptor Cells / Q000502:physiology*; D000860:Hypoxia / Q000503:physiopathology*; D010100:Oxygen; D010313:Partial Pressure; D012119:Respiration; D012129:Respiratory Function Tests; D012756:Sheep; D013990:Tidal Volume; D013997:Time Factors
D002245:Carbon Dioxide; D010100:Oxygen