A laser Doppler instrument for in vivo measurements of blood flow in single renal arterioles

A laser Doppler instrument has been developed to measure the blood flow in single vessels for the study of the dynamics of local control mechanisms. A commercial blood perfusion monitor, designed to measure blood perfusion in a vascular field containing many randomly oriented blood vessels, was modified to measure blood flow in a single arteriole. In vitro tests of the instrument revealed that the relationship between blood flow and Doppler shift was not a simple linear function. Causes of nonlinearity are revealed, and it is shown that proper use of the device avoids the problem. The device was applied to efferent arterioles that are visible on the surface of the rat kidney, and changes in the kidney blood flow were induced and measured. An oscillation in the tubular pressure at 0.035 Hz, that was previously described and attributed to a local feedback mechanism, was found in the arteriolar blood flow. The instrument is easy to use and provides temporal resolution.