Comparison of sublingual microcirculatory parameters measured by sidestream darkfield videomicroscopy in anesthetized pigs and adult humans

Background:This study aimed to compare sublingual microcirculatory parameters between anesthetized pigs and conscious adult humans using sidestream darkfield videomicroscopy.The overarching aim of the work was to validate the pig as an experimental model of changes in microcirculatory function following traumatic haemorrhagic shock and resuscitation.Methods:Fourteen large white pigs and 14 humans were recruited for the study.Sublingual sidestream darkfield videomicroscopy clips were captured in anesthetized pigs and conscious humans.Clips underwent manual analysis in Automated Vascular Analysis 3.2 software.The total vessel density(TVD),perfused vessel density(PVD),proportion of perfused vessels(PPVs)and microvascular flow index(MFI)were quantified.An independent samples t test was used for between species comparison of microcirculatory parameters.Results and Conclusions:Conscious humans had a significantly lower TVD,PVD and MFI than anesthetized pigs.No significant difference in PPVs was observed between the species.Perfusion of the microcirculation is a critical determinant of tissue metabolic function and viability.Whilst it may not be surprising that some inter species differences in the sublingual microcirculatory anatomy were identified between pig and human subjects,it is interesting to report the insignificant difference in PPVs.This direct microcirculatory measure represents a relative change which should hold translatable value across species.We therefore conclude the pig is a suitable model for microcirculatory research and may be a suitable species to investigate changes in microcirculatory perfusion following perturbations in cardiovascular homeostasis,for example during traumatic haemorrhagic shock and resuscitation.