Erik Häggblad

Improved model for myocardial diffuse reflectance spectra by including mitochondrial cytochrome aa3, methemoglobin, and inhomogenously distributed RBC

The aim of this study was to compare a previously used light transport model (I) comprising the chromophores hemo- and myoglobin, fat, and water, with two extended models, where the chromophores of cytochrome aa3, methemo- and metmyoglobin are added (model II), and in addition, accounting for an inhomogenous hemoglobin distribution (model III). The models were evaluated using calibrated diffuse reflectance spectroscopy measurements on the human myocardium. Model II proved a significantly better spectral fitting, especially in the wavelength ranges corresponding to prominent absorption characteristics for the added chromophores. Model III was significantly better than model II and displayed a markedly higher tissue fraction and saturation of hemo- and myoglobin. The estimated tissue chromophore fractions, saturation and oxidation levels, were in agreement with other studies, demonstrating the potential of diffuse reflectance spectroscopy measurements for evaluating open heart surgery. However, the choice of chromophores and vessel packaging effects in the light transport model has a major effect on the results.

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.

Visible hyperspectral imaging evaluating the cutaneous response to ultraviolet radiation

In vivo diagnostics of skin diseases as well as understanding of the skin biology constitute a field demanding characterization of physiological and anatomical parameters. Biomedical optics has been successfully used, to qualitatively and quantitatively estimate the microcirculatory conditions of superficial skin. Capillaroscopy, laser Doppler techniques and spectroscopy, all elucidate different aspects of microcirculation, e.g. capillary anatomy and distribution, tissue perfusion and hemoglobin oxygenation. We demonstrate the use of a diffuse reflectance hyperspectral imaging system for spatial and temporal characterization of tissue oxygenation, important to skin viability. The system comprises: light source, liquid crystal tunable filter, camera objective, CCD camera, and the decomposition of the spectral signature into relative amounts of oxy- and deoxygenized hemoglobin as well as melanin in every pixel resulting in tissue chromophore images. To validate the system, we used a phototesting model, creating a graded inflammatory response of a known geometry, in order to evaluate the ability to register spatially resolved reflectance spectra. The obtained results demonstrate the possibility to describe the UV inflammatory response by calculating the change in tissue oxygen level, intimately connected to a tissues metabolism. Preliminary results on the estimation of melanin content are also presented.

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.

A diffuse reflectance spectroscopic study of UV-induced erythematous reaction across well-defined borders in human skin.

Introduction: The colour of tissue is often of clinical use in the diagnosis of tissue homeostasis and physiological responses to various stimuli. Determining tissue colour changes and borders, however, often poses an intricate problem and visual examination, constituting clinical praxis, does not allow them to be objectively characterized or quantified. Demands for increased inter‐ and intra‐observer reproducibility have been incentives for the introduction of objective methods and techniques for tissue colour (e.g. erythema) evaluation. The aim of the present paper was to study the border zone of a UVB‐provoked erythematous response of human skin in terms of blood volume and oxygenation measured by means of diffuse reflectance spectroscopy using a commercial probe.