Differentiation of the functional from the structural vascular tone using new elasticity indices of the linger artery and their psychophysiological application

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A near-infrared finger photoplethysmogram adopting a wavelength of 810nm provides for the pulsatile ac component(ΔI) superimposed on the transmitted dc components in a normal (I:tissue plus blood) and an ischemic circulatory state (I_t:tissue only). Simultaneous recording of linger blood pressure provides for the distending pulse(PP) and mean blood pressure(MBP). Based on the Lambert Beer's law, indices of the arterial compliance (CI;= ΔI/I/PP) is advocated for the linger vasculature. We introduced the exponential pressure-volume model(V=a-b×exp(-nP)) and examined the effects of functional and structural variations in the vascular tone on these parameters. Experiment 1:Twelve female subjects underwent immersions of the contralateral hand in water at two different temperatures(44℃,22℃). CI calculated at 9OmmHg(CI90) of linear regression between log CI and MBP decreased significantly during 22℃ condition. Experiment 2:The functional relationship to the transmural pressure for CI was examined using linger-occlusion during mental arithmetics in sixteen females and reactive hyperemia in five. Logarithmically transformed CI was linearly associated with the transmural pressure. Changes in parameter a were most consistent among three parameters of the exponential model. Experiment 3:Age-associated differences in parameter a,b, and n were examined during resting condition between 31 young students and 9 middle aged workers. In the middle aged subjects, the model fitness deteriorated and only the parameter n was lowered compared with the young student. Parameter n was significantly correlated with brachial-ankle pulse wave velocity(baPWV) as a measure of arterial stiffness. Flow-mediated dilation(FMD) during reactive hyperemia at the wrist radial artery was recorded by oxygenated hemoglobin using near-infrared spectroscopy. Peak time of FMD was delayed in the young group as compared with the middle aged group and negatively correlated with baPWV.