Hemodynamic Factors Conditioning the Hypotensive Response to Phentolamine:Limitations of the Test in the Screening of Pheochromocytoma

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Circulatory measurements have been done in 5 normal individuals, 34 patients suffering from essential hypertension, and 1 patient with pheochromocytoma before and after i. v. injection of 5mg of phentolamine. The drug induced a prompt reduction in systemic and pulmonary vascular resistance which resulted, despite an increase in heart rate and cardiac output, in a rapid reduction both in systemic and pulmonary pressure. The systemic pressure fall was quite small in the normals and of variable magnitude in the hypertensives. In 6 of the essential hypertensive patients (19 percent of the cases) it exceeded the figure of 35/25 mmHg which is considered as positive to the diagnosis of pheochromocytoma. In one of them the drug precipitated shock. In the patient with adrenal gland tumor the hypotensive response was in the range of these 6 essential hypertensive subjects.The values of systemic vascular resistance in the control state correlated quite closely with the magnitude of the hypotensive response to phentolamine. The conclusion is drawn that the higher the resistance sustaining the hypertensive state, the larger is the response to the drug, whatever the mechanism of the elevated vascular resistance.Such findings lead to question the validity of phentolamine as a reliable and safe screening test for pheochromocytoma.
International Heart Journal刊行会の論文