Borchert M S, Storrie-Lombardi M C, Lambert J L
Departments of Ophthalmology and Neurology, Children's Hospital of Los Angeles, USC School of Medicine, Los Angeles, California, USA.
Diabetes Technol Ther. 1999 Summer;1(2):145-51. doi: 10.1089/152091599317350.
Glucose in the aqueous humor appears to correlate with plasma glucose in humans. It is therefore a potential substrate for noninvasive optical glucose monitoring techniques. We wished to determine the potential for using rabbit aqueous humor as a model to develop a noninvasive method of measuring glucose with Raman spectroscopy.
Aqueous humor from 32 rabbit eyes was removed immediately after sacrifice by rapid exsanguination under anesthesia. Raman spectroscopy was performed on the aqueous humor using near infrared (NIR) excitation wavelengths. The Raman spectra from 785 nm and 787.2 nm were subtracted one from the other to eliminate broadband fluorescence. The spectra were then analyzed with linear and nonlinear multivariate analysis and assessed for ability to predict actual aqueous humor glucose concentration. Nine other rabbits were anesthetized with xylazine in order to cause elevation of blood glucose by blocking release of insulin. Blood and aqueous humor glucose were measured at various times after injection of xylazine. Correlation of aqueous humor glucose with simultaneous plasma glucose was assessed.
Partial least squares analysis of raw Raman spectra of aqueous humor showed fair correlation with actual glucose concentration (r2 = 0.76). When the fluorescence spectrum was subtracted prior to linear multivariate analysis correlation was good (r2 = 0.90). When back-propagation with an artificial neural network was added to the analysis, correlation was further improved (r2 = 0.98). Aqueous humor glucose concentration exceeded blood glucose concentration at normoglycemic levels. When blood glucose rose above 200 mg/dL, aqueous humor glucose correlated linearly with plasma glucose.
Raman spectroscopy can accurately predict glucose concentration in rabbit aqueous humor in vitro. Although rabbit aqueous humor is probably not a good model of human aqueous humor glucose physiology, its reliable correlation with plasma glucose makes it a good model on which to test noninvasive optical sensing techniques.
房水中的葡萄糖似乎与人体血浆葡萄糖相关。因此，它是无创光学葡萄糖监测技术的潜在底物。我们希望确定使用兔房水作为模型来开发一种用拉曼光谱测量葡萄糖的无创方法的潜力。
在麻醉下通过快速放血处死后，立即从32只兔眼取出房水。使用近红外（NIR）激发波长对房水进行拉曼光谱分析。将785nm和787.2nm的拉曼光谱相互相减以消除宽带荧光。然后用线性和非线性多变量分析对光谱进行分析，并评估其预测实际房水葡萄糖浓度的能力。另外9只兔子用赛拉嗪麻醉，以通过阻断胰岛素释放来引起血糖升高。在注射赛拉嗪后的不同时间测量血液和房水葡萄糖。评估房水葡萄糖与同时期血浆葡萄糖的相关性。
房水原始拉曼光谱的偏最小二乘分析显示与实际葡萄糖浓度有较好的相关性（r2 = 0.76）。在进行线性多变量分析之前减去荧光光谱时，相关性良好（r2 = 0.90）。当在分析中加入人工神经网络的反向传播时，相关性进一步提高（r2 = 0.98）。在正常血糖水平下，房水葡萄糖浓度超过血糖浓度。当血糖升至200mg/dL以上时，房水葡萄糖与血浆葡萄糖呈线性相关。
拉曼光谱可以准确预测兔房水体外葡萄糖浓度。虽然兔房水可能不是人类房水葡萄糖生理学的良好模型，但其与血浆葡萄糖的可靠相关性使其成为测试无创光学传感技术的良好模型。
