Mesenteric Blood Flow as Influenced by Progressive Hypercapnia

Abstract

The influence of hypercapnia on mesenteric blood flow was studied in dogs subjected to progressive increments in CO₂ content of inspired air produced by rebreathing from a large spirometer. Oxygen content was maintained above 21 volumes %. Although some animals showed an initial tendency for mesenteric blood flow to decrease and arterial pressure to increase in the range 0–5 volumes % of CO₂, the usual hemodynamic change in the range 5–16 volumes % was an increase in mesenteric blood flow resulting from decrease in intestinal vascular resistance, accompanied by a decline in arterial pressure. Portal venous pressure was progressively elevated. Heart rate slowed in association with an increase in pulse pressure. The observations suggest that in higher ranges of hypercapnia, CO₂ has a direct dilating action on the mesenteric vasculature.