The effect of inhalation of 30% carbon dioxide on the peripheral circulation of the human subject.

Inhalation of 30% carbon dioxide for 1 to 2 min. caused a transient increase followed by a marked fall in blood flow through the normal forearm and calf. Since there was an associated large increase in arterial blood pressure, the fall in flow was due to intense vasoconstriction. It is likely that the vasoconstriction in the forearm occurred deep to the skin because the oxygen saturation of the superficial venous blood did not fall during the inhalation. Since there was a slight decrease in flow through the nerve-blocked forearm in spite of the increased blood pressure, it is unlikely that nervous vasoconstriction can completely account for the marked decrease in muscle flow.