Diffuse reflectance spectroscopy: Systemic and microvascular oxygen saturation is linearly correlated and hypoxia leads to increased spatial heterogeneity of microvascular saturation.

The microvascular oxygen saturation (SmvO(2)) in the skin and tongue (sublingual mucosa) in pigs (n=6) was characterised using diffuse reflectance spectroscopy (DRS). The correlation between arterial oxygen saturation (SaO(2)) and SmvO(2) as well as the spatial heterogeneity of SmvO(2) was examined during hypoxia. DRS uses shallow-penetrating visible light to assess microvascular oxygen saturation (SmvO(2)) in superficial tissue. Hypoxia was induced by gradual reduction in ventilation or reduction of the inspiratory oxygen fraction. The spatial heterogeneity of SmvO(2) was expressed as the coefficient of variation (CV) of repeated SmvO(2) measurements. Baseline SmvO(2) before interventions was 20.2% (10.3%-38.1%, median with range) in groin skin, 32.9% (13.0%-49.3%) in the ear and 42.2% (32.1%-51.5%) in the tongue. SmvO(2) in the groin was significantly lower than venous oxygen saturation (SvO(2)) (p<0.05) and SmvO(2) in the tongue (p=0.03). There was a significant linear correlation between SaO(2) and SmvO(2) in all measuring sites for both interventions (p<0.05). Similarly there was a significant correlation between CV of repeated SmvO(2) measurements and SmvO(2) in all measuring sites for both interventions (p<0.01). The results from baseline measurements indicate a surprisingly high oxygen extraction in the measurement volume of DRS, especially in the groin skin. A reduction of SmvO(2) with decreasing SaO(2) was found and additionally the results suggest that spatial heterogeneity of microvascular oxygen saturation increases during hypoxia. Microvascular disturbances have been demonstrated in both local vascular diseases and systemic conditions such as shock and sepsis, an assessment of microvascular oxygen saturation using DRS may be useful in the monitoring of the microcirculation in such patients. This study is a part of an ongoing characterization of the DRS technique.

Assessments of skin and tongue microcirculation reveals major changes in porcine sepsis.

AIM: To examine the relation between central hemodynamics, clinical severity and microvascular findings in tongue and skin during sepsis. MATERIALS AND METHODS: Skin and tongue microcirculation was examined using laser Doppler and video microscopy techniques before and 200 min after inducing sepsis in pigs (n=6) by inactivated Neisseria meningitides and in two control animals. RESULTS: All infected pigs developed clinical signs of sepsis. Pericapillary bleedings developed in the tongue in the two pigs with the most severe disease. Capillary density increased in the groin skin in infected pigs after 200 min as compared to baseline (P<0·02). In the same period, mean capillary flow velocity was reduced in groin skin and tongue in septic pigs (P<0·02). At 200 min a fraction of capillaries had developed 'no flow' or 'brisk flow', patterns hardly seen at baseline. Laser Doppler perfusion was reduced in ear and tongue after 200 min (P<0·02 for both). The described pathology was more pronounced in the pigs with the most severe sepsis. CONCLUSION: Capillary bleedings may be used as an early indication of severe sepsis. Examination of skin and tongue microcirculations may be used to characterize severity of sepsis and possibly to assess effect of treatment.

Reflection spectroscopy of analgesized skin.

Analgesized skin, when subjected to heat stimuli, responds by increasing skin perfusion. This response does not originate from increased perfusion in superficial capillaries, but rather in the deeper lying vessels. The aim of this study was to assess changes in blood chromophore content, measured by reflection spectroscopy, in relation to the perfusion increase, especially regarding the chromophores oxyhemoglobin and deoxyhemoglobin. Eleven normal subjects were treated with analgesic cream (EMLA) and placebo for 20, 40, 60, 120, and 180 min. Individual reactions to local heating were classified as responses if the change in reflection data or the change in perfusion, as measured by laser Doppler blood flowmetry, exceeded 2 standard deviations of normal variation. The increase in blood perfusion or in blood content gave rise to an increased absorption, interpreted as an increase due mainly to the chromophore oxyhemoglobin. The number of responses increased with increased treatment time for EMLA-treated areas. In general, there was a good agreement between both methods; 44 of 55 classifications coincided for the two methods used. In conclusion, analgesized forearm skin, which had been exposed to local heating, responded with an elevated perfusion consisting of oxygenated blood. This strengthens the hypothesis that the flow increase occurs through dilatation of larger deeper lying skin vessels and not in the capillaries.