Blood Flow in Otorhinologic Tissue after Histamine and Papaverine

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Abstract
A method has evolved that allows one to quantitatively measure nutritional blood flow in the labyrinth. Several otic symptoms (e.g., sudden hearing loss) are thought to be due to decreased labyrinthine blood flow. Our aim was to test two common vasodilators, histamine and papaverine, to determine if they were effective in increasing blood flow to otic tissue. The method employs the intracardiac injection of radioactive microspheres (15 μ in diameter). These spheres become embolized in the microcirculation and provide a measure of blood flow in ml/gm/min. Histamine or papaverine were infused intravenously for five min at several doses. Blood flow was measured before and after infusion. Both drugs cause a significant increase in blood flow to temporal bone tissue if used in the appropriate dose range, i.e., about 1 ug/kg/min for histamine and 0.5 mg/kg/min for papaverine. If the dose of either drug is increased to the point that causes a drop of more than 15 mm Hg in systemic blood pressure, there is either no increase or a drop in otic blood flow. This reversal of the drug response is felt to be due to autoregulatory mechanisms in intracranial blood vessels.