CORONARY AND TOTAL PERIPHERAL RESISTANCE CHANGES DURING SLEEP IN A PORCINE MODEL

Changes in autonomic tone in the vasculature during sleep may have imp ortant 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 ar e assessed. Catheters were chronically implanted in the aorta to measu re mean arterial pressure (MAP), and flow probes were placed on the as cending aorta and the circumflex coronary artery of 18 pigs. Electrode s determined sleep stage as either non-rapid eye movement (NREM) or ra pid eye movement (REM) sleep. The MAP was 73 +/- 3 mmHg in the quiet a wake 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 aw ake state values of 136 +/- 8 beats/min but increased by 5 beats/min i n REM sleep (P < 0.05). Coronary vascular resistance decreased from aw ake state values of 2.7 +/- 0.2 to 2.2 +/- 0.2 mmHg . ml(-1). min in R EM (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 r eduction 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.