Cardiovascular changes associated with spontaneous and evoked K-complexes

This study examines the relationship between blood pressure and spontaneous and sound-evoked K-complexes (KCs) during stage 2 NREM sleep, in 8 volunteers studied by intraarterial blood pressure (BP) monitoring and polysomnography. A robust oscillation of blood pressure with a period of 16-30 s (Mayer waves) was seen in all subjects. Spontaneous KCs predominantly occurred during a drop (downward slope) in blood pressure. Randomly administered sound stimuli were more likely to evoke a KC if the stimulus was given during a downward slope of BP. During the last 20 s prior to a sound-evoked KC, the mean drop in systolic BP was 0.3 mmHg, and evoked and spontaneous K-complexes were preceded by a mean drop in BP of 1.9 and 2.7 mmHg, respectively. Finally, K-complexes, either spontaneous or evoked, during the first 6 s, induced a rise in systolic BP. The results indicate that if the BP falls during stage 2 NREM sleep, there is a greater likelihood that an external stimulus will evoke a K-complex and that spontaneous K-complexes may occur more frequently as well. Spontaneous and evoked K-complexes may play a role in the control of BP during NREM sleep.