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Reflex Venomotor Activity in Normal Persons and in Patients with Postural Hypotension

By W. W. Pryor


Reflex venomotor activity has been observed and measured in normal subjects by means of the pressures developed within isolated segments of superficial veins. Strong contractions are caused by the Valsalva maneuver, tilting, cold, exercise, and hyperventilation. After the Valsalva and after tilting there is a brief elevation of central venous pressure. Pulmonary vascular pressures are also increased after the Valsalva. This is taken to indicate a widespread venoconstriction with central shifting of blood. Persons with postural hypotension show little or no segment or central venous pressure response to these stimuli, indicating impaired reflex venomotor activity. T HE existence of reflex venomotor ac-tivity is well established, " 2,. 4 and it is evidently important in many circula-tory adjustments in health and disease. How-ever, there is little quantitative information on venomotor activity in man because it has been difficult to measure. Recently Duggan, Love, and Lyons5 have introduced the simple technic of measuring pressure changes within a superficial vein segment temporarily isolated by external pressure and have found prompt reflex responses to various stimuli. It is the purpose of this report to extend these observations to include additional stimuli of physiologic significance, and to describe the results of such measurements in persons with orthostatic hypotension. In addition measure-ments have been made of changes in the central venous pressure with such stimuli to determine to what extent the central venous pressure may reflect changes in peripheral venomotor activity. METHODS A modification of Duggan's technic was used. This consisted of isolating a superficial venous seg-ment temporarily by applying pressure at the ends of the segment. In this way the volume of the seg-ment was held constant and contraction of the vei

Year: 2016
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