根据皮肤组织解剖结构特性建立了六层层状模型, 并给出了皮肤组织各层的特性参数; 考虑了氧合血红蛋白和还原血红蛋白的吸收特性, 依据皮肤组织各层的水、 血、 脂肪、 血氧饱和度含量以及血管大小给出了皮肤组织各层的光谱吸收系数; 对不同波长散射系数做了适当简化, 给出了皮肤组织各层的光谱散射系数。 利用蒙特卡罗方法仿真血管组织在收缩与舒张两种状态下, 400～1 000 nm波长光在皮肤组织多层模型中的传输过程, 并通过统计大量光子的分布特性, 获得了皮肤组织光谱反射系数, 并利用模拟所得的两种状态下的反射系数计算得到了光谱容积脉搏波幅度。 仿真结果表明, 当入射光强一定时, 绿光的容积脉搏波幅度优于红光和蓝光。 通过计算不同波长光沿皮肤组织深度方向光能流率衰减为1/e时对应的皮肤组织深度, 获得了皮肤组织光谱穿透深度。 结果显示, 血管舒张状态下蓝光和绿光的穿透深度较小, 蓝光大部分只能达到表皮层, 绿光能到达微循环层, 红光可直达真皮层。 考虑到光在皮肤组织中传播包含了一个从收缩到舒张的动态过程, 基于此, 根据穿透深度定义了脉搏波信号产生深度, 利用血管舒张与收缩两种不同状态下的穿透深度计算得到了光谱产生深度。 结果表明, 不同波长光产生深度大于其穿透深度, 蓝光产生深度较浅, 且其受到的血液吸收调制较小, 因而其获得的脉搏信号易受噪声干扰; 红光的容积脉搏波产生深度较大, 但是相比于绿光其受血液吸收调制较小, 且绿光产生深度足够达到真皮血管层, 因而红光容积脉搏波的幅度小于绿光。 上述仿真结果明确了皮肤组织部分光谱特性, 为皮肤组织多光谱容积脉搏波的精确获取及其他相关研究提供了一定的理论基础。

According to the anatomical structure of the skin tissue, we established a six-layer model, and the characteristic parameters of each layer of skin tissue were given. We considered the absorption characteristics of oxidized hemoglobin and reduced hemoglobin, and gave the spectral absorption coefficients of each layer of skin tissue according to the contents of water, blood, fat and oxygen saturation in each layer of skin tissue, as well as the size of blood vessels. The scattering coefficients at different wavelengths were simplified properly, and then the scattering coefficient spectra of each layer of skin tissue were obtained. In this paper, we used Monte Carlo method to simulate the transmission process of 400～1 000 nm wavelength light in the multi-layer model of skin tissue under the conditions of contraction and relaxation. The spectral reflectance of the skin tissue was obtained by counting the distribution characteristics of a large number of photons. The amplitude spectrum of volume pulse wave was obtained by calculating the reflection coefficient of the two states obtained from the simulation. The simulation results showed that the volume pulse wave amplitude of green light is better than that of red light and blue light when the incident light intensity is constant. The penetration depth spectrum of skin tissue was obtained by calculating the corresponding skin tissue depth when the light flux of different wavelengths decreased to 1/e along the direction of skin tissue depth. The results showed that the penetration depth of blue light and green light is small, the blue light can only reach the surface layer, the green light can reach the micro-circulation layer, and the penetration depth of red light is the largest, which can reach the dermis directly. Considering when the light travels through the skin, it involves a dynamic process from contraction to relaxation, so we define the depth of pulse signal generation based on penetration depth, and the spectral generation depth is calculated by using the penetration depth of vasodilation and contraction in two different states. The results showed that the depth of light generation at different wavelengths is greater than the penetration depth, the depth of blue light is shallowand the blood absorption modulation is small, so the pulse signal obtained is more easily interfered by noise. The volume pulse wave of red light is deeper than that of green light, but compared with green light, its absorption and modulation by blood is smaller, and the depth of green light generation is enough to reach the dermis vascular layer, so the amplitude of red light volume pulse wave is smaller than that of green light. Our simulation results confirm some spectral characteristics of skin tissue, which provides a theoretical basis for the accurate acquisition of multispectral volume pulse waves and other related studies.