Primary coronary vasodilation associated with pauses in heart rhythm during sleep.

We observed 162 episodes of pause in heart rhythm in chronically instrumented dogs primarily during transitions from deep slow-wave sleep to other stages of sleep. These pauses lasted 1.1-8.0 s and were followed by increases in coronary blood flow (CBF) averaging 30% and ranging up to 84%. The postpause surges in CBF do not appear to be mediated by local metabolic factors because the flow surges occurred without significant changes in the heart rate x systolic blood pressure (HRxSBP) product, a standard index of cardiac metabolic activity. Enhanced vagal tone is suggested by the background of marked respiratory sinus arrhythmia, low average heart rates, and the hallmark event, the pause in heart rhythm. In a series of experiments in alpha-chloralose-anesthetized dogs, we demonstrated that direct vagus nerve stimulation can induce both the pause in heart rhythm and the postpause increase in CBF in a pattern similar to that observed during sleep. This response was markedly attenuated after pericoronary denervation. These observations provide suggestive evidence but not definitive proof that enhanced vagal activity may be involved in the increase in CBF after spontaneous pauses in heart rhythm during sleep.