Nocturnal hemodynamic patterns in dogs

Several species which have a single daily wake-sleep cycle show a progressive fall in cardiac output and rise in total peripheral resistance during sleep, a cardiovascular response which may reflect a progressive decrease in plasma volume. The present study showed that no such progressive overnight changes in cardiac output or total peripheral resistance occur in the dog, a carnivore which tends to be awake and to drink intermittently during the night. Progressive overnight bradycardia (-12.7±3.1%) and compensatory increase in stroke volume (14.8±6.0%) were observed in this species, however. These findings are consistent with the view that differences between primates and carnivores in overnight hemodynamic function are related to species differences in sleep and ingestive behavior.