Hemodynamic Patterns during Desynchronized Sleep in Intact Cats and in Cats with Sinoaortic Deafferentation

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Abstract
In unanesthetized, unrestrained cats, placed in a sound-attenuated cage, stroke volume and cardiac output were continuously monitored by an electromagnetic flow transducer chronically implanted around the ascending aorta, arterial pressure was measured by means of a femoral catheter connected to a strain-gauge transducer, and heart rate by a cardiotachograph. Total resistance was computed by dividing arterial pressure by cardiac output. Electroencephalograms, cervical electromyogram, and ocular movements were also monitored to obtain evidence of naturally occurring sleep. In animals with intact sinoaortic reflexes the fall in arterial pressure occurring during desynchronized sleep was associated with a small decrease in cardiac output and a relatively greater reduction in total resistance. After sinoaortic deafferentation, the conspicuously exaggerated fall in arterial pressure occurring during the same type of sleep was almost entirely due to a parallel exaggeration of the reduction in total resistance; changes in cardiac output were only slightly greater than before deafferentation. Only in the few episodes of desynchronized sleep in which extreme hypotension was accompanied by signs of cerebral anoxia, did cardiac output greatly decrease; in these cases, calculated resistance was found to increase. Both small and large changes in cardiac output were independent of heart innervation.