Respiratory inhibition induced by transient hypertension during sleep in unrestrained cats

The effects of transient blood pressure elevation, induced by intravenous injection of phenylephrine, were studied in drug-free, unrestrained cats during sleep and waking. Transient hypertension evoked an increase in respiratory cycle duration (Ttot), an effect which was most prominent during quiet sleep. Transient hypertension evoked no overall change in inspiratory duration (Tdi) during any sleep-waking state, although reduction of diaphragmatic EMG amplitude was observed. Thus, the ratio of diaphragmatic activity time to total respiratory cycle duration (Tdi/Ttot) was decreased following blood pressure elevation. Apneic episodes occasionally occurred, and these occurrences were more frequent during sleep states. Apneas induced during quiet sleep were often associated with transient or sustained arousal.