Coronary and total peripheral resistance changes during sleep in a porcine model

Changes in autonomic tone in the vasculature during sleep may have important implications for silent ischemia and sudden cardiac death. Few models exist in which both cardiac output and coronary blood flow are continuously measured during natural sleep and autonomic mechanisms are assessed. Catheters were chronically implanted in the aorta to measure mean arterial pressure (MAP), and flow probes were placed on the ascending aorta and the circumflex coronary artery of 18 pigs. Electrodes determined sleep stage as either non-rapid eye movement (NREM) or rapid eye movement (REM) sleep. The MAP was 73 +/- 3 mmHg in the quiet awake state, did not change in NREM, and decreased to 64 +/- 2 mmHg in REM sleep (P < 0.05). In NREM sleep, heart rate did not change from awake state values of 136 +/- 8 beats/min but increased by 5 beats/min in REM sleep (P < 0.05). Coronary vascular resistance decreased from awake state values of 2.7 +/- 0.2 to 2.2 +/- 0.2 mmHg.ml-1.min in REM (P < 0.05); total peripheral resistance decreased from awake values of 0.061 +/- 0.004 mmHg.ml-1.min to 0.050 +/- 0.003 in REM sleep (P < 0.05). Those changes appear to have been mediated primarily by reduction of alpha-adrenergic activity. Spectral analysis of heart rate suggests that power in the high-frequency range (a presumed indicator of parasympathetic tone) was lower in REM sleep than NREM sleep.