Frequency-resolved measurements of hemodynamic oscillations and quantitative analysis with a novel hemodynamic model

We present frequency-resolved measurements of the amplitude and phase of cerebral hemodynamic oscillations associated with paced breathing and measured with near-infrared spectroscopy on the forehead of a human subject. We have performed measurements at eleven paced breathing frequencies in the range 0.07-0.25 Hz. The resulting frequency spectra of the amplitude and phase of the hemodynamic oscillations were fit with a recently developed hemodynamic model, 1 that was able to reproduce the measured spectra and to determine a number of associated physiological parameters. The parameters measured include the blood transit times in the capillary (0.87 s) and venous (1.0 s) compartments, and the high-pass cutoff frequency of cerebral autoregulation (0.087 Hz). We also illustrate the implications of the new hemodynamic model on the basis of a phasor representation of physiological and hemodynamic oscillations. The combination of frequency-resolved measurements of cerebral hemodynamics and the phasor-based, frequency-domain solution of the new hemodynamic model provides a novel tool for cerebral hemodynamic studies with a potential for assessing a variety of physiological, functional, and pathological conditions.