Strategies for improving intraindividual reproducibility in laser Doppler flowmetry measurements

Abstract

Abstract Purpose: Scattering of blood flow data as assessed with laser Doppler flowmetry (LDF) in humans is a problem in many studies using this technique. We set out to reduce variability in LDF data by partializing out the effect of the total returning light level (DC) on LDF parameters in the choroid. Methods: In 20 healthy subjects choroidal blood flow was measured at different DC values using a portable confocal LDF device. To reduce scattering of data partializing out the effect of yield, defined as DC/gain, firstly a previously described method based on a third order polynomia fit using all obtained data was applied. Secondly a new method based on a linear fit obtained for each subject individually was used.In addition, these correction procedures were applied retrospectively to the data of a recent study investigating the effect of a nitric oxide (NO) synthase inhibitor on choroidal and optic nerve head blood flow parameters. Results: Both methods were successful in reducing scattering of LDF parameters in the choroid with varying baseline DC values. In addition, both methods minimized scattering of the effect of the NO synthase inhibitor on ocular blood flow parameters as analyzed retrospectively. Whereas, however, the previous approach altered the magnitude of the mean change induced by the NO synthase inhibitor to higher values, the new method preserved the originally reported effect. Conclusions: When systematic changes in DC occur after an intervention one needs to be careful in interpreting the obtained data. The approach presented here may represent an effective, easily applicable and valid way to reduce scattering of data from using LDF to assess blood flow in the posterior pole of the human eye.