Abstract
In piglets we tested the applicability of digital video microscopy and diffuse reflectance spectroscopy for non-invasive assessments of limbal and bulbar conjunctival microcirculation. A priori we postulated that the metabolic rate is higher in limbal as compared to bulbar conjunctiva, and that this difference is reflected in microvascular structure or function between the two locations. Two study sites, Oslo University Hospital (OUH), Norway and Cleveland Clinic (CC), USA, used the same video microscopy and spectroscopy techniques to record limbal and bulbar microcirculation in sleeping piglets. Recordings were analyzed with custom-made software to quantify functional capillary density, capillary flow velocity and microvascular oxygen saturation in measuring volumes of approximately 0.1 mm3. The functional capillary density was higher in limbus than in bulbar conjunctiva at both study sites (OUH: 18.1 ± 2.9 versus 12.2 ± 2.9 crossings per mm line, p < 0.01; CC: 11.3 ± 3.0 versus 7.1 ± 2.8 crossings per mm line, p < 0.01). Median categorial capillary blood flow velocity was higher in bulbar as compared with limbal recordings (CC: 3 (1–3) versus 1 (0–3), p < 0.01). Conjunctival microvascular oxygen saturation was 88 ± 5.9% in OUH versus 94 ± 7.5% in CC piglets.Non-invasive digital video microscopy and diffuse reflectance spectroscopy can be used to obtain data from conjunctival microcirculation in piglets. Limbal conjunctival microcirculation has a larger capacity for oxygen delivery as compared with bulbar conjunctiva.
Highlights
August Krogh, the Nobel prize laureate in Physiology or Medicine in 1920, postulated that metabolically active cells must be located within a given distance of a perfused capillary to get suf ficient oxygen supply (Krogh, 1919)
As cell division and the metabolic rate and oxygen demand can be postulated to be higher at the limbus as compared to the bulbar conjunctiva, we aimed to examine and validate sensitivity of the Oxygen Delivery INdex (ODIN) concept by comparing microvascular physiology in limbal and bulbar conjunctiva
The Functional capillary density (FCD) was higher at limbus as compared with the bulbar conjunctiva (OUH: 18.1 ± 2.9 versus 12.2 ± 2.9 c/mm, p < 0.01, CC: 11.3 ± 3.0 versus 7.1 ± 2.8 c/mm, p < 0.01) (Fig. 3)
Summary
August Krogh, the Nobel prize laureate in Physiology or Medicine in 1920, postulated that metabolically active cells must be located within a given distance of a perfused capillary (the Krogh diameter) to get suf ficient oxygen supply (Krogh, 1919). He stated that within the tissue cylinder served by one capillary, the oxygen availability decreases exponentially at increasing distances from the center of the vessel. Cleveland Clinic capillary flow velocity functional capillary density Oxygen delivery index Oslo University Hospital microvascular oxygen saturation to be lower than the limbal region as the main function is to sustain an intact translucent epithelial surface and supply nutrition to the under lying sclera. As cell division and the metabolic rate and oxygen demand can be postulated to be higher at the limbus as compared to the bulbar conjunctiva, we aimed to examine and validate sensitivity of the ODIN concept by comparing microvascular physiology in limbal and bulbar conjunctiva
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