DYNAMIC RESPIRATORY RESPONSES TO PREOPTIC-ANTERIOR HYPOTHALAMIC WARMING IN THE SLEEPING CAT

Timing and amplitude characteristics of diaphragmatic muscle activity following bilateral local warming of the preoptic area/anterior hypoth alamic region (POAH) were studied during sleep in free-moving intact a dult cats. Warming of the POAH increased local brain temperature by 1. 4-3.7 degrees C and elicited thermal tachypnea (panting) during quiet sleep (QS). Following transition to rapid eye movement (REM) sleep, th e tachypnea, initially induced by warming during QS, diminished, but r espiratory rates remained above baseline. REM levels, and an intermitt ent pattern of faster and slower breathing rates developed. In QS, tac hypnea resulted primarily from a decline in inspiratory time (TI), whe reas in REM sleep, reduction in expiratory time (TE) was more prominen t. Although diaphragmatic electromyographic amplitude decreased by 40% during panting in QS, the much higher respiratory rates (+350%) resul ted in apparent increases in relative ventilation and inspiratory driv e. A less pronounced respiratory rate change (+46%) emerged during REM sleep, resulting in no significant changes in ventilation and inspira tory drive in response to warning in that state. The results suggest t hat descending thermal influences on respiratory patterning differ bet ween QS and REM states in both overall respiratory rate and on relativ e TI and TE, and thus do not affect inspiratory drive exclusively.