Studies on Digitalis. X. Effects of Ouabain on Forearm Vascular Resistance and Venous Tone in Normal Subjects and in Patients in Heart Failure *

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Abstract
The effects of ouabaln on the vascular dynamics of the forearm were studied in 12 normal subjects and in 6 patients with congestive heart failure employing a plethysmographic technique. In the normal subjects ouabain resulted in a fall in forearm blood flow and rise of forearm vascular resistance (Av. 31%) and venous tone (Av. 47%). Since these actions were not influenced by pretreatment with the adrenergic blocking agent guanethldlne, it was concluded that the drug has a direct constricting action on the vascular smooth muscle of the normal human forearm. In contrast, in the patients in heart failure, ouabaln raised forearm blood flow and lowered forearm vascular resistance (Av. 23%) and venous tone (Av. 30%). It is suggested that these effects are indirect and result from the improvement of the failure state by the drug that diminishes reflex arterlolar and venoconstrlctlon and override the direct actions of the drug.