Functional Near Infrared Spectroscopy has been used to investigate changes in cerebral hemodynamics induced by hypercapnia challenges, such as carbon dioxide CO<sub>2</sub> inhalation and breath holding. The aim of this study was to investigate CO<sub>2</sub> pressure changes dependence of frequency spectrum of cerebral hemodynamic oscillations during breath holding task. Measurements of the relative changes in concentration of deoxy-hemoglobin ([Hb]) and oxyhemoglobin ([HbO<sub>2</sub>]) are performed on nine healthy subjects during three breath holdings of 30 seconds (s.) interleaved with 90 s. of normal breathing. Power spectra are computed by continuous wavelet transform and averaged for normal and hold episodes. The percent change values between hold and normal episodes are given for frequency peaks at (0.035 Hz), where a 17% higher increase was observed for PC of [Hb] on the right side compared to left side,while this value was at 64.8% for [HbO<sub>2</sub>] . Similarly, for a peak at 0.11 Hz these values were 54.5% and 9.5% for [Hb] and [HbO<sub>2</sub>] PCs, respectively. The smallest changes were observed for breathing freq. range (around 0.2 Hz) where the values are -72% and 55.8% for [Hb] and [HbO<sub>2</sub>], respectively.
Migraine is a complex chronic neurovascular disorder in which the
interictal changes in neuronal excitability and vascular
reactivity in the cerebral cortex were detected. The extent and
direction of the changes in cerebral blood flow that affect
cerebral hemodynamics during attacks, however, are still a matter
of debate. This may have been due to the logistic and technical
problems posed by the different techniques to determine cerebral
blood flow during migraine attacks and the different definitions
of patient populations. In this study, we have investigated
hypercapnia challenges by breath holding task on subjects with and
without migraine by using functional near infrared spectroscopy
(fNIRS). Measurements of the relative changes in concentration of
deoxy-hemoglobin [Hb] and oxy-hemoglobin [HbO<sub>2</sub>] are performed on four healthy subjects during three breath holdings of 30 seconds (s.) interleaved with 90 s. of normal breathing. We have observed [Hb]increase during breath holding interval in subject without migraine whereas in subject with migraine [Hb] decreases during breath holding interval. The result of our study suggest that
hypercapnia effect on cerebral hemodynamic of subject with
migraine and without migraine could be due to different vascular
reactivity to P<sub>CO2</sub> (carbon dioxide partial pressure) in arteries.
Acquiring functional near infrared spectroscopy (fNIRS) and functional magnetic resonance-imaging (fMRI) data are usually done asynchronously. In order to correlate these two different modalities’ data, measurements must be performed at the same time. In this study, we have designed a new MR compatible continuous wave intensity based fNIRS device to overcome this problem. For MR compatible fNIRS, we used two LEDs with wavelengths at 660 and 870 nm. There are four photodiodes for light detection. LEDs operated in a sequential multiplexing mode with adjustable "on" time for each LED. Emitted and diffused light was transferred to and from the tissue through 10 m long single mode plastic optical fibers (INDUSTRIAL FIBER OPTICS, INC.). By using fibers, we overcome MR compatibility problems that can be caused by semi-conductors on probe. This MR compatible fNIRS design can provide synchronous measurements with low cost.