Validation of a novel hemodynamic model for coherent hemodynamics spectroscopy (CHS) and functional brain studies with fNIRS and fMRI

J. Innov. Opt. Health Sci.

Pierro

et al. 2014

Self Cite

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 (CMRO 2 ), and associated changes in the tissue concentrations of oxy-and deoxy-hemoglobin (ÁO and ÁD) 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.

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confidence: 73%

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confidence: 99%

Coherent Hemodynamics Spectroscopy Based on a Paced Breathing Paradigm — Revisited

J. Innov. Opt. Health Sci.

Pierro

et al. 2014

Self Cite

“…The lower limit (0.045 Hz) was chosen to avoid slow temporal drifts in the data, which could potentially obscure this very low frequency response. The amplitude and phase of the oscillations of deoxy-and oxy-hemoglobin concentrations [respectively |D| and arg(D), |O| and arg(O)] at a given frequency were assessed by the analytic signal method, as described previously [27], resulting in time-resolved measurements of instantaneous amplitude ratios and phase differences. Averaging over the 20 s time window following cuff deflation for the step response protocol, or over the 60 s time window for each oscillatory frequency in the periodic inflation/deflation protocol yielded average amplitude ratios |D|/|O|, |O|/|T|, as well as average phase differences arg(D) -arg(O), and arg(O) -arg(T), at each frequency considered.…”

Section: Methodsmentioning

confidence: 99%

Coherent hemodynamics spectroscopy in a single step

Fantini

2014

Biomed. Opt. Express

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Coherent Hemodynamics Spectroscopy (CHS) is a technique based on inducing cerebral hemodynamic oscillations at multiple frequencies, measuring them with near-infrared spectroscopy (NIRS), and analyzing them with a hemodynamic model to obtain physiological information such as blood transit times in the microvasculature and the autoregulation cutoff frequency. We have previously demonstrated that such oscillations can be induced one frequency at a time. Here we demonstrate that CHS can be performed by a single inflation of two pneumatic thigh cuffs (duration: 2 min; pressure: 200 mmHg), whose sudden release produces a step response in systemic arterial blood pressure that lasts for ~20 s and induces cerebral hemodynamics that contain all the frequency information necessary for CHS. Following a validation study on simulated data, we performed measurements on human subjects with this new method based on a single occlusion/release of the thigh cuffs and with the previous method based on sequential sets of cyclic inflation/deflation one frequency at a time, and demonstrated that the two methods yield the same CHS spectra and the same physiological parameters (within measurement errors). The advantages of the new method presented here are that CHS spectra cover the entire bandwidth of the induced hemodynamic response, they are measured over ~20 s thus better satisfying the requirement of time invariance of physiological conditions, and they can be measured every ~2.5 min thus achieving finer temporal sampling in monitoring applications.

“…(1) and (2) for any given value of the capillary transit time , and the subscripts \mCTT" indicate the multiple capillary transit times that result in the integration of the phasors Oð; !Þ and Dð; !Þ over the entire range of transit times weighted by hð; ; Þ. For comparison with experimental data collected in CHS, we are interested in the phasor ratios [10][11][12] :…”

Section: Extended Hemodynamic Modelmentioning

confidence: 99%

“…We named this method of inducing blood volume and°ow oscillations (and therefore oxy and deoxy hemoglobin oscillations) in target organs at di®erent frequencies as coherent hemodynamics spectroscopy (CHS). The oscillations can be induced by di®erent methods such as paced breathing, 10 leg cu®s in°ations, 11 tilt bed, etc. Since the absolute value of modulus and phase of the output phasors (which are measured) are often di±cult to control, [10][11][12] in CHS we measure the spectra of phasor ratios: D(!)/O(!)…”

Section: Introductionmentioning

confidence: 99%

Study of capillary transit time distribution in coherent hemodynamics spectroscopy

J. Innov. Opt. Health Sci.

Fantini

2015

Self Cite

A recently proposed analytical hemodynamic model 1 [S. Fantini, NeuroImage 85, 202-221 (2014)] is able to predict the changes of oxy, deoxy, and total hemoglobin concentrations (model outputs) given arbitrary changes in blood°ow, blood volume, and rate of oxygen consumption (model inputs). One assumption of this model is that the capillary compartment is characterized by a single blood transit time. In this work, we have extended the original model by considering a distribution of capillary transit times and we have compared the outputs of both models (original and extended) for the case of sinusoidal input signals at di®erent frequencies, which realizes the new technique of coherent hemodynamics spectroscopy (CHS). For the calculations with the original model, we have used the mean value of the distribution of capillary transit times considered in the extended model. We have found that, for distributions of capillary transit times having mean values around 1 s and a standard deviation less than about 45% of the mean value, the original and extended models yield the same CHS spectra (i.e., model outputs versus frequency of oscillation) within typical experimental errors. For wider capillary transit time distributions, the two models yield di®erent CHS spectra. By assuming that Poiseuille's law is valid in the capillary compartment, we have related the distribution of capillary transit times to the distributions of capillary lengths and capillary speed of blood°ow to calculate the average capillary and venous saturations. We have found that, for standard deviations of the capillary transit time distribution that are less than about 80% of the mean value, the average capillary saturation is always larger than the venous saturation. By contrast, the average capillary saturation may be less than the venous saturation for wider distributions of the capillary transit times.