Effects of chronic right-to-left cardiac shunt on hypoxic sensitivity of mongrel dogs.
Resting ventilation (VI), blood gases, hypoxic sensitivity, and the ventilatory responses to intravenous sodium cyanide (NaCN, 100 micrograms/kg), doxapram (DOX, 500 micrograms/kg), and dopamine (DOPA, 20 micrograms/kg) were analyzed in four normal mongrel dogs (group I-N) and seven mongrel dogs with chronic (5-11 yr) right-to-left cardiac shunt (group II). The group I-N animals were also studied during steady-state isocapnic hypoxia (group I-H). The shunt procedure used for these studies produced a model for ventilatory studies during chronic shunt hypoxemia. The increases in VI per percent decrease in O2 saturation, which occurred during a four-breath N2 test, were 30, 43, and 13 ml X kg-1 X min-1 in groups I-N, I-H, and II, respectively. The decrease in hypoxic sensitivity of the group II animals, compared with groups I-N and I-H, occurred in the presence of an increase in PaCO2 from 21.9 to 26.0 Torr during the four-breath N2 test. A decrease in PaCO2 from 34.7 to 30.0 and from 33.6 to 30.4 Torr was observed in groups I-N and I-H. The response to DOX, a general analeptic agent, was greatest in group II and least in group I-N. However, the ventilatory responses to NaCN and DOPA were not sufficiently different among the three groups to suggest a difference in carotid body function as assessed by these drugs.
D000818:Animals; D001794:Blood Pressure; D002344:Carotid Body / Q000503:physiopathology*; D002628:Chemoreceptor Cells / Q000503:physiopathology; D004285:Dogs; D004298:Dopamine / Q000494:pharmacology; D004315:Doxapram / Q000494:pharmacology; D006330:Heart Defects, Congenital / Q000503:physiopathology*; D006339:Heart Rate; D000860:Hypoxia / Q000503:physiopathology*; D012018:Reflex / Q000502:physiology*; D012119:Respiration / Q000187:drug effects; D012966:Sodium Cyanide / Q000494:pharmacology; D014692:Ventilation-Perfusion Ratio
D004315:Doxapram; D012966:Sodium Cyanide; D004298:Dopamine