“…This is not surprising because hypoxia has been found not to be important in the regulation ofthe resistance and capacitance vessels of many other vascular beds (Cuthbert, 1967;Daugherty, Scott, Dabney & Haddy, 1967;Voth & Lell, 1973;Vanhoutte, 1976). Hypercapnia, on the other hand, acts locally on the nasal capacitance vessels, most probably via dilatation of the thick-walled veins and opening up of the arteriovenous anastomoses as excess carbon dioxide or a decrease in pH has been known to be vasodilatatory in many other vascular beds (Daugherty et al 1967;Vanhoutte & Clement, 1968).…”