State-related incidence of spontaneous breathing during high frequency ventilation.

Previous reports indicate that apnea is induced by high frequency ventilation (HFV) in anesthetized animals. We have studied conscious dogs ventilated with HFV during sleep and wakefulness to determine if this apnea is state related. Eucapnic apnea or very low breathing frequencies were observed during quiet wakefulness, quiet sleep and tonic REM sleep. However, spontaneous breathing at nearly normal rates was invariably seen during phasic REM sleep. We conclude that HFV as administered induces apnea or near apnea in conscious animals and that the inhibitory pathways causing this apnea are probably disabled during phasic REM sleep.