Microvascular function in healthy volunteers; a comparison of manually and automatically derived measurements

Abstract

Microcirculatory dysfunction plays a significant role in the pathophysiology of critical illness, including sepsis, haemorrhage and cardiogenic shock. Studies have used video microscopic measurements of the sublingual microcirculation in acute illness, but the clinical utility of these techniques are limited by the need for time-consuming analysis that precludes near-patient data interpretation. The newest video microscopes use Incident Dark Field (IDF) illumination technology (see below) with automated analysis. However the automated analysis has not been validated and there are no data on normal ranges in healthy individuals. This limits the potential application of IDF video microscopy for microcirculation research. This study aims to examine the feasibility and accuracy of measurement of sublingual microvascular function in the awake individual establish the summary statistics of different sublingual microvascular measurements and compare these measurements in three age groups; 18–34 yrs, 35–54 yrs and over 54 yrs. Additionally, this study will correlate the automatically derived measurements of microcirculatory function in comparison to the current gold-standard of manual analysis. An observational study of 150 healthy volunteers, which will include the recording of basic physiological data, medical and drug history, followed by an assessment of the sublingual microvascular bed using CytoCam incident dark field microscopy to measure total vessel density (TVD), perfused vessel density (PVD), and microvascular flow index (MFI). Analysis using current gold standard manual analysis with automated analysis using CytoCam Tool 1.7 (Braedius Medical BV) Analysis plan: (a.) Computation of summary statistics of TVD, PVD, and MFI to determine normal ranges for both manual and automated analysis methods at the population level as well as age-related subgroup level (18-34 yrs, 35-54 yrs and 55 yrs and over). (b.) Estimation of correlation between automatically and manually derived values of TVD, PVD, and MFI within each subject. (c.) Comparison of mean TVD, PVD, and MFI between the age-related subgroup (18-34yrs, 35-54 yrs and 55 yrs and over). Progress: This study has currently recruited 91 of 150 subjects. The procedure of measurement has been found to be well tolerated, with no subjects withdrawing from the study once enrolled. Further, it has been possible, following 2 days of intense work, to train a further member of the team to make reliable, high quality recordings, demonstrating the scope for training those new to the technique to use it in the clinical setting. We look forward to producing full results in the near future.