Pressure-volume curves in live, intact dogs

The effect of changes in blood volume on mean circulatory pressure was studied in 10 dogs. Mean circulatory pressure increased linearly as the blood volume was expanded and decreased linearly as blood volume was lowered below the normovolemic level. For example, the mean circulatory pressure fell from a normal of 7 mm Hg down to 0 mm Hg when the animals were rapidly hemorrhaged 14.7% of their normal blood volume; when the blood volumes were expanded to 50% above normal, the mean circulatory pressure rose from the control value of 7 mm Hg up to 30 mm Hg. It is concluded that one of the major factors determining the mean circulatory pressure is blood volume.