[A comparative study of the depressive effects of halothane and isoflurane on medullary respiratory neurons in cats].
The depressive effects of halothane (H) and isoflurane (I) on the same respiratory neuron were studied in cats. Using a tungsten microelectrode, activities of medullary inspiratory neurons were recorded around nucleus ambiguus. The number of spikes (Spike) of each respiratory cycle and inter-spike interval (ISI) were measured. At 1 MAC, in 9 units out of 11, Spike was significantly fewer with I than with H. In 2 units out of 11, Spike was not significantly different between H and I. These results indicate that each respiratory neuron shows different sensitivity to H and I at 1MAC concentration. With increasing depth of anesthesia, Spike showed a concentration-related depression. During the course of respiratory depression, the spikes were 75.9 (1MAC), 63.3 (1.5MAC), 48.0 (2MAC), 24.2 (2.5MAC), 5.0 (3MAC) with H, and 77.4 (0.5MAC), 51.9 (1MAC), 23.5 (1.5MAC) with I. These spikes were completely depressed at 3.5MAC in H and 2MAC in I. Both H and I increased ISI with increasing depth of anesthesia. The effects of H and I on the phrenic nerve discharges closely resembled their effects on the respiratory neurons. We conclude that the respiratory depression produced by I exceeds that produced by equal MAC of H.
Doi
K
K
Kasaba
T
T
Kosaka
Y
Y
D000818:Animals; D002415:Cats; D003864:Depression, Chemical; D006221:Halothane / Q000494:pharmacology*; D007530:Isoflurane / Q000494:pharmacology*; D008526:Medulla Oblongata / Q000187:drug effects* / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology
D007530:Isoflurane; D006221:Halothane