SLEEP INFLUENCES THE CARDIOVASCULAR RESPONSE TO HEMORRHAGE IN LAMBS

Abstract

Newborns spend a large portion of their time asleep. During the first postnatal month lambs spend about 45% of their time in quiet sleep (QS) and about 10% of their time in active sleep (AS). The extent to which sleep affects the cardiovascular response to perturbation in young lambs is unknown. We, therefore, investigated the effect of sleep on the cardiovascular response to an acute venous hemorrhage in 7 lambs aged 13 to 19 days. Each lamb was anesthetized and instrumented for measurements of electrocorticogram, electro-oculogram, nuchal and diaphragm electromyograms, pulmonary blood flow, aortic and right atrial blood pressures. The lambs were not studied before the third postoperative day. Measurements were made during a 1-min control period and during a 1-min experimental period that followed a 10 ml/kg hemorrhage during quiet wakefulness (QW), QS and AS. Hemorrhage produced similar decreases in right atrial pressure and pulmonary blood flow during the three behavioral states. However, mean aortic pressure decreased more (p<0.05 by 1-way ANOV) following hemorrhage during AS (75.5±13.9 to 65.7±11.5) than during QS (72.5±11.3 to 70.8±10.4) or QW (76.3±14.9 to 72.6±12.0). Calculated systemic vascular resistance increased more (p<0.05) during QW and QS than during AS. These results provide evidence that reflex control of the peripheral circulation is altered during AS compared to QS and QW in lambs.