Effects of arterial blood volume, pulse pressure, and mean arterial pressure on normalized pulse volume

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A near-infrared finger photoplethysmogram adopting a wavelength of 810 nm provides for the pulsatile ac component (ΔI) superimposed on the transmitted dc components in a normal (I : tissue plus blood) and an ischaemic circulatory state (I_t : tissue only). Simultaneous recording of finger 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 finger vasculature. We introduced the exponential pressure-volume model ( V=a-b^*exp(-nP)) and examined arterial blood volume, PP, and transmural pressure on the model parameters (a,b,n). Experiment 1 : Twelve female subjects underwent immersions of the contralateral hand in water at two different temperatures (44℃, 22℃). CI calculated at 90mmHg (CI90) of linear regression between logCI and MBP decreased significantly during 22℃ condition. Experiment 2 : The functional relationship to the transmural pressure for CI was examined using finger-occlusion during mental arithmetics in sixteen females and reactive hyperaemia in five. Logarithmically transformed CI was linearly associated with the transmural pressure. Three parameters (a,b,n) of the exponential P-V relationship were systematically modified by mental arithmetics and reactive hyperaemia. Experiment 3 : Age-associated differences in parameter a, b, and n were examined during resting condition between 30 young students and 12 middle aged workers. In middle aged subjects, the model fitness deteriorated and only the parameter n was lowered compared with young student.We advocated the exponential P-V model for finger vasculature and developed the new analytical method for the elastic property of finger artery. Experimental findings supported the validity and usefulness of our model. Structural vascular change due to aging and functional vasoconstriction proved to be separated by different changes in model parameters.