A LASER-DOPPLER INSTRUMENT FOR INVIVO MEASUREMENTS OF BLOOD-FLOW IN SINGLE RENAL ARTERIOLES

A laser Doppler instrument has been developed to measure the blood flo w in single vessels for the study of the dynamics of local control mec hanisms. A commercial blood perfusion monitor, designed to measure blo od perfusion in a vascular field containing many randomly oriented blo od vessels, was modified to perform measurements of blood flow in a si ngle arteriole. In vitro tests of the instrument revealed that the rel ationship between blood flow and Doppler shift was not a simple linear function. Causes of nonlinearity are revealed and proper use of the d evice avoids the problem. The device was applied to efferent arteriole s that are visible on the surface of the rat kidney. An angiotensin co nverting enzyme inhibitor and graded doses of angiotensin II were used to perturb kidney blood flow. The induced changes in whole kidney blo od flow, measured with an electromagnetic flow probe, and in single ef ferent arteriolar blood flow, measured with the new instrument, were c orrelated. An oscillation at almost-equal-to 0.035 Hz, previously desc ribed in the tubular pressure and attributed to a local feedback mecha nism acting on arteriolar resistance, was found in the arteriolar bloo d flow. The new instrument is easy to use and provides temporal resolu tion not available with more conventional methods used for flow measur ement in the microcirculation.