Coherent Hemodynamics Spectroscopy Based on a Paced Breathing Paradigm — Revisited

A novel hemodynamic model has been recently introduced, which provides analytical relationships between the changes in cerebral blood volume (CBV), cerebral blood °ow (CBF), and cerebral metabolic rate of oxygen (CMRO2), and associated changes in the tissue concentrations of oxyand deoxy-hemoglobin ( O and D) measured with near-infrared spectroscopy (NIRS) [S. Fantini, Neuroimage 85, 202–221 (2014)]. This novel model can be applied to measurements of the amplitude and phase of induced hemodynamic oscillations as a function of the frequency of oscillation, realizing the novel technique of coherent hemodynamics spectroscopy (CHS) [S. Fantini, Neuroimage 85, 202–221 (2014); M. L. Pierro et al., Neuroimage 85, 222–233 (2014)]. In a previous work, we have demonstrated an in vivo application of CHS on human subjects during paced breathing [M. L. Pierro et al., Neuroimage 85, 222–233 (2014)]. In this work, we present a new analysis of the collected data during paced breathing based on a slightly revised formulation of the hemodynamic model and an e±cient ̄tting procedure. While we have initially treated all 12 model parameters as independent, we have found that, in this new implementation of CHS, the number of independent parameters is eight. In this article, we identify the eight independent model parameters and we show that our previous results are consistent with the new formulation, once the individual parameters of the earlier analysis are combined into the new set of independent parameters.