Coherent hemodynamics spectroscopy in a single step

Abstract

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.

Fast blood flow monitoring in deep tissues with real-time software correlators

“…4(A)); this noise assignment, in turn, prompted the need for increased temporal averaging. Interestingly, although heartbeat oscillations are well recognized in the NIRS community [63][64][65], the DCS community has been comparatively slow to appreciate the full potential of fast blood flow measurements.…”

Optical oximetry of volume-oscillating vascular compartments: contributions from oscillatory blood flow

“…22 As shown above for the arterial saturation, if blood flow contributions are negligible, then Arg½D − Arg½O ¼ 0. However, we have previously demonstrated, [13][14][15][16]29 and we will show again here that this is not the case for brain measurements, where blood flow contributions cannot be neglected. Hence, it is not correct to use the ratio jOj∕jTj to obtain S ðvÞ from data collected during paced or normal breathing, since O ≠ O V .…”

“…We have repeatedly shown that oxy-and deoxyhemoglobin measurements on muscle tissue are in phase 14 at the respiratory frequency, indicating that blood volume changes are dominant and blood flow changes can be considered negligible. However, cerebral measurements have shown a consistent out of phase behavior between oxy-and deoxyhemoglobin, [14][15][16][17][18][19] indicating that blood flow changes are not a negligible contributor to the optical signals. The reason for this is that blood volume changes are smaller in the brain than other tissues due to the rigid enclosure of the skull, 20 damping the magnitude of vessel diameter changes.…”

“…In our previous applications of the hemodynamic model, which is an analytical model that takes into account dynamic autoregulation and the microvascular blood transit times, we have focused on low-frequency cerebral hemodynamics (of the order of 0.1 Hz or less) [13][14][15][16][17][18]29 for the assessment of blood flow, autoregulation, and blood volume in the microvasculature. In this work, we demonstrate that the pulsatile signals measured in the brain at the heart rate and at the respiration frequency can be quantitatively described by the model and that CBF changes should be taken into account to obtain reliable measurements of the oxygen saturation of hemoglobin of timevarying vascular compartments.…”

Blood-pressure-induced oscillations of deoxy- and oxyhemoglobin concentrations are in-phase in the healthy breast and out-of-phase in the healthy brain

“…The search regions for the fitting parameters are defined by ranges found in the literature. 18 The analytical expressions derived from the hemodynamic model and the simplifying assumptions relating these six hemodynamic parameters and the CHS spectra are described in detail in Kainerstorfer et al 19 In the case of breast measurements, because the phasors Dðω i Þ, Oðω i Þ, and Tðω i Þ were found to be in-phase with each other at all measured frequencies, the amplitude ratio jOðω i Þj∕jTðω i Þj provides a measure of the oxygen saturation of hemoglobin in the volume-oscillating vascular compartments, 9 which we indicate here with S V . This measure of hemoglobin saturation is a weighted average of the saturations of the volume-oscillating compartments, where each vascular compartment is weighted according to its relative contributions to the overall blood volume oscillations:…”