Alteration of phrenic high frequency oscillation by local cooling of the ventral medullary surface

Cooling of small sites on the ventral medullary surface of the cat produces a decrease in frequency of phrenic high frequency oscillation (HFO). The effect on HFO frequency of cooling near the hypoglossal rootlets, but not the effect of cooling near the inferior cerebellar artery, can be completely offset by raising arterial pCO2 to restore phrenic activity to its precooling level. Thus, structures near the ventral medullary surface are important for generation or propagation of phrenic HFO. The effect of cooling of the 'intermediate area' cannot be entirely explained as depression of putative central chemoreceptor activity.