Effects of acoustic stimulation on cardiovascular regulation during sleep

The interaction of wake-sleep states and acoustic stimulation on cardiovascular regulation was studied on rats implanted with electroencephalogram and electromyogram electrodes and an arterial catheter. Mild acoustic stimuli (1000 Hz, 90 dB, 50-ms beeps) were administered during Wakefulness (W), non-rapid eye movement (NREM) sleep and REM sleep and the changes induced in heart period (HP, ms) and mean arterial pressure (MAP, mmHg) were analyzed. Two 30-s sequences of beat-to-beat HP and MAP values were considered before (I) and after (II) acoustic stimulation, respectively. By the effect of stimulation, state-dependent stimulus-locked HP and MAP oscillations were observed, HP oscillations being grossly parallel to the MAP ones but delayed with respect to MAP in the ascending part only; HP and MAP spontaneous fluctuations (HP and MAP variability) increased in NREM and REM sleep (but not in W); HP vs MAP correlation coefficient increased in an algebraic sense. These results show that 1) acoustic stimulation primarily affects the peripheral resistance, and secondarily, through the baroreceptor reflex, HP, thereby increasing the impact of peripheral versus centrally driven autonomic influences on the heart; 2) in NREM sleep, heart excitability is higher than requested by the baroreflex function; 3) cardiac variability is increased by acoustic stimulation during sleep (but not in W); this, in addition to the effects of point 2, may favor cardiac arrhythmias in NREM sleep. Thus, mild acoustic stimuli not perturbing cardiovascular regulation during W may create a specific risk factor during sleep in pathophysiologic conditions.