The mean circulatory pressure, reproducibility of its measurements and the effect of phenylephrine with a note on the effect of pentobarbital

With 7 repeated measurements of the mean circulatory pressure (MCP) over a course of 35 minutes in one and the same dog, and also with paired measurements of MCP 10 minutes apart in 6 other dogs, the MCP was shown to be stable and reproducible in anesthetized, open-chest and vagus-intact dogs. Administered to 7 dogs with initial mean arterial blood pressure as low as 64 mmHg in dose of 20 μg/kg intravenously, phenylephrine nearly doubled the mean arterial blood pressure, total peripheral resistance and the MCP, indicating a marked vasoconstrictor effect on the resistance and capacitance blood vessels of the systemic circulation. The effect was transient and there were signs of tachyphylaxis. Influence of a cardiotoxic dose of pentobarbital on the peripheral circulation was discussed.