Control of blood pressure during sleep in lambs

We investigated the effect of sleep on blood pressure control in seven lambs aged 10-14 days. Each lamb had previously been anesthetized and instrumented for measurements of electrocorticogram, electron-oculogram, nuchal and diaphragm electromyograms, pulmonary blood flow (electromagnetic flow transducer), and aortic and pulmonic blood pressure. The lambs were allowed to recover from surgery at least 3 days before they were studied. Measurements were made at the highest and lowest mean aortic pressure during quiet wakefulness, quiet sleep, and active sleep. The lowest values of mean aortic pressure progressively decreased as the animals went from quiet wakefulness to quiet sleep to active sleep. Mean aortic pressure was most variable during active sleep. During active sleep, transient hypertensive episodes were superimposed upon a tonic hypotensive phase. During the transient hypertensive episodes in active sleep, changes in mean aortic pressure were primarily caused by an increase in systemic vascular resistance rather than by changes in cardiac output. Heart rate was always lower during active sleep than during quiet wakefulness or quiet sleep. These results provide evidence that sleep state has a marked influence on blood pressure control in lambs.