Cardiovascular instability during sleep and calm waking state in normal man

Stroke volume, blood pressure, heart rate and blood flow in the calf and forearm were sampled every 20 min during the night sleep in eleven normal subjects. Stroke volume was measured by an impedance method with the use of a Minnesota cardiograph, and blood flow with venous occlusion plethysmography. The electroencephalogram was monitored routinely. Large variations in all sampled cardiovascular parameters were observed in all subjects. These variations were not interrelated nor were they correlated with any sleep stages. Variability in stroke volume ranged from 23% to 174%. Variability in vascular conductance in the calf was from 26% to 898%, in the forearm it was from 12% to 805%, in systolic blood pressure from 62% to 132%, diastolic blood pressure from 50% to 141% and in heart rate from 53% to 152%. In eight subjects sampling of cardiovascular parameters was carried out during the day, in a quiet but waking state. All sampled parameters varied, although during the day variations were smaller. It was therefore concluded that in normal man the cardiovascular system is in a state of perpetual oscillation during sleep or waking state until a specific pattern of adjustment is commanded by the central neurones.