Phasic registration of venous diameter changes in-situ with the induction angiometer

The method of induction angiometry has been used for observation of active and passive venous vasomotion, without surgical exposure of the blood vessel. The diameter sensor is a resilient loop introduced into the vasculature through a fine No. 5 French (1 mm i.d.) angiographic catheter or a needle of comparable internal diameter. An extracorporeal a. c. magnet induces an electromotive force (e.m.f.) in the loop which acts as the secondary of a transformer, the electromagnet being the primary. Pulsations in the blood vessel diameter vary the loop area and with it the induced e.m.f. thus providing a linear measure of relative changes in vascular diameter. Changes in the order of 2 micra in a venous diameter of 5 mm can be resolved in-situ. Examples are given of registration of phasic venous diameter changes at the frequencies of the heart beat, respiration and Mayer waves. Pharmacological tests illustrate the ability to detect venous vasomotion in response to a dose below 0.1 microgram/kg of nitroglycerin in dogs.