The influence of behavioural state on the cardiovascular system of newborn lambs

The influence of behavioural state, as defined by clinical observation and EEG recording, on cardiac output, heart rate, stroke volume and blood pressure was investigated in eight newborn lambs during the first 2 weeks of life. Cardiac output was measured using the technique of thermodilution. Highest mean value (mean +/- SEM) of cardiac output was found in the very alert awake state in week 1, 271 +/- 16 ml/min per kg. Other values were significantly lower; quiet sleep, 173 +/- 4 ml/min per kg; rapid-eye-movement sleep, 191 +/- 7 ml/min per kg; quiet awake, 174 +/- 3 ml/min per kg; alert awake, 180 +/- 5 ml/min per kg. Similar values were found in week 2. These values of cardiac output were lower than those previously reported for newborn lambs except in the very alert awake state. Heart rate was significantly lower during sleep than in the awake states in week 1. The heart rate was found to be significantly higher in all states except the very alert awake state in week 2 compared with week 1. Stroke volume was significantly higher in rapid-eye-movement sleep, 1.08 +/- 0.06 ml/kg, and in the very alert awake state, 1.16 +/- 0.09 ml/kg, compared with the other states in week 1, but only in the very alert awake state in week 2. Blood pressure was highest in the very alert awake state in both weeks. These findings demonstrate that behavioural state has a very significant influence on the cardiovascular system during newborn life in lambs, particularly on cardiac output values, which in the very alert awake and rapid-eye-movement sleep states significantly exceed values in the other states.