Blood Pressure Fall During Sleep

The study was designed to investigate the possible role of endogenous opioids in the fall in blood pressure (BP) seen during initial sleep. Seven normal men, ages 20-30 years, were studied for three consecutive nights. Each night, electroencephalogram, chin electromyogram, electrooculogram, heart rate (all continuously), and blood pressure (every 15 minutes) were recorded. Night 1 was used for orientation. On nights 2 and 3, subjects received, in randomized order, an infusion of naloxone 0.2 mg/kg over 1 minute or volume-matched saline. Blood pressure data from the first 4 hours of non-rapid eye movement sleep were combined. On the placebo night, systolic BP fell from 114.6 ± 6 mm Hg to 103.7 ± 8 mm Hg (± SD) (p < 0.05, Wilcoxon rank-sum test). On the naloxone night, systolic BP did not change. Neither diastolic BP nor heart rate were influenced by naloxone. These data suggest that endogenous opioids could be involved in the fall in systolic BP seen during initial sleep.