Abstract
Cyanosis is a pathological condition that is characterized by a bluish discoloration of the skin or mucous membranes. It may result from a number of medical conditions, including disorders of the respiratory system and central nervous system, cardiovascular diseases, peripheral vascular diseases, deep vein thrombosis, and regional ischemia. Cyanosis can also be elicited from methemoglobin. Therefore, a simple, rapid, and simultaneous monitoring of changes in oxygenated hemoglobin and deoxygenated hemoglobin is useful for protective strategies against organ ischemic injury. We previously developed a red-green-blue camera-based spectral imaging method for the measurements of melanin concentration, oxygenated hemoglobin concentration (CHbO), deoxygenated hemoglobin concentration (CHbR), total hemoglobin concentration (CHbT) and tissue oxygen saturation (StO2) in skin tissues. We leveraged this approach in this study and extended it to the simultaneous quantifications of methemoglobin concentration (CmetHb), CHbO, CHbR, and StO2. The aim of the study was to confirm the feasibility of the method to monitor CmetHb, CHbO, CHbR, CHbT, and StO2. We performed in vivo experiments using rat dorsal skin during methemoglobinemia induced by the administration of sodium nitrite (NaNO2) and changing the fraction of inspired oxygen (FiO2), including normoxia, hypoxia, and anoxia. Spectral diffuse reflectance images were estimated from an RGB image by the Wiener estimation method. Multiple regression analysis based on Monte Carlo simulations of light transport was used to estimate CHbO, CHbR, CmetHb, CHbT, and StO2. CmetHb rapidly increased with a half-maximum time of less than 30 min and reached maximal values nearly 60 min after the administration of NaNO2, whereas StO2 dramatically dropped after the administration of NaNO2, indicating the temporary production of methemoglobin and severe hypoxemia during methemoglobinemia. Time courses of CHbT and StO2, while changing the FiO2, coincided with well-known physiological responses to hyperoxia, normoxia, and hypoxia. The results indicated the potential of this method to evaluate changes in skin hemodynamics due to loss of tissue viability and vitality.
Highlights
A patient with a bluish discoloration in the skin, known as cyanosis, is alarming to a medical doctor
The present study demonstrated the usefulness of a new non-contact imaging method based on spectral reflectance images reconstructed from a single snapshot of an RGB image by Wiener estimation method (WEM) for the simultaneous measurements of the percutaneous volume concentrations of methemoglobin, oxygenated hemoglobin, deoxygenated hemoglobin, and tissue oxygen saturation
The methemoglobin concentration rapidly increased with a half-maximum time of less than 20 min, reaching a maximal value nearly 60 min after the administration of NaNO2
Summary
A patient with a bluish discoloration in the skin, known as cyanosis, is alarming to a medical doctor. The arterial blood gas analyzer only measures dissolved oxygen, and not the actual amount of oxygen bound to hemoglobin in the blood This results in a false positive diagnosis for methemoglobinemia even though the metHb concentration is high [9,31]. The WEM has been applied to the visualization of spatiotemporal changes in peripheral hemodynamics in response to physiological stimuli [56] In this approach, multiple regression analysis is performed by using the spectral image reconstructed by the WEM at wavelengths between 500 and 600 nm as a response variable and the known extinction coefficient spectra of melanin, oxygenated hemoglobin, and deoxygenated hemoglobin as predictor variables to provide multiple regression coefficients. In order to confirm the feasibility of this method to evaluate chromophore concentrations, we performed in vivo experiments using rat dorsal skin during methemoglobinemia induced by the administration of sodium nitrite (NaNO2) and changing the fraction of inspired oxygen (FiO2), including normoxia, hypoxia, and anoxia
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