Gandjbakhche A H, Bonner R F, Arai A E, Balaban R S
Laboratory of Integrative and Medical Biophysics, National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA.
Am J Physiol. 1999 Aug;277(2):H698-704. doi: 10.1152/ajpheart.1999.277.2.H698.
Empirical data between 510 and 590 nm of diffuse reflected light from the pig heart in vivo have shown that myoglobin and cytochrome c absorption peaks with little apparent contribution of red blood cell (RBC) Hb. Monte Carlo simulations of photon migration in tissue were performed to compare the effects of myoglobin and cytochromes with those of blood Hb on photon pathlengths and diffuse reflectance of visible wavelengths (450-600 nm) from the pig heart in vivo. Wavelength dependence of the input parameters, including the transport-corrected scattering coefficients (1.1-1.2 mm(-1)) and the absorption coefficients of blood-free solubilized heart tissue (0.43-1.47 mm(-1)), as well as the absorption coefficients of Hb, were determined by an integrating sphere method and standard spectrophotometry, respectively. The Monte Carlo simulations indicate that in the 510- to 590-nm range the mean path length within the myocardium for diffusely reflected light varies from 1.4 to 1.2 mm, whereas their mean penetration depth within the epicardium is only 330-400 micrometer for blood-free heart tissue. Analysis shows that the blood Hb absorption extrema are only observable between 510 and 590 nm when RBC concentration in tissue is >0.5%. Blood within vessels much larger than capillaries does not contribute significantly to the spectral features, because virtually all light in this spectral range is absorbed during transit through large vessels (>100 micrometer). This analysis suggests that diffuse reflected light in the 510- to 590-nm region will show spectral features uniquely associated with myoglobin and cytochrome c oxygenation states within 400 micrometer of the surface of the heart in situ as long as the capillary RBC concentration remains <0.5%.
对猪心脏活体漫反射光在510至590纳米之间的实验数据表明，肌红蛋白和细胞色素c的吸收峰明显，而红细胞（RBC）血红蛋白的贡献很小。进行了组织中光子迁移的蒙特卡罗模拟，以比较肌红蛋白和细胞色素与血液血红蛋白对猪心脏活体可见波长（450 - 600纳米）的光子路径长度和漫反射率的影响。输入参数的波长依赖性，包括经传输校正的散射系数（1.1 - 1.2毫米⁻¹）、无血可溶性心脏组织的吸收系数（0.43 - 1.47毫米⁻¹）以及血红蛋白的吸收系数，分别通过积分球法和标准分光光度法测定。蒙特卡罗模拟表明，在510至590纳米范围内，心肌内漫反射光的平均路径长度在1.4至1.2毫米之间变化，而对于无血心脏组织，其在心外膜内的平均穿透深度仅为330 - 400微米。分析表明，当组织中红细胞浓度>0.5%时，血液血红蛋白吸收极值仅在510至590纳米之间可观察到。比毛细血管大得多的血管内的血液对光谱特征的贡献不大，因为在这个光谱范围内几乎所有光在穿过大血管（>100微米）时都会被吸收。该分析表明，只要毛细血管红细胞浓度保持<0.5%，510至590纳米区域的漫反射光将显示与原位心脏表面400微米内肌红蛋白和细胞色素c氧化状态独特相关的光谱特征。
