Spontaneous low frequency oscillations of cerebral hemodynamics and metabolism in human adults

We investigated slow spontaneous oscillations in cerebral oxygenation in th e human adult's visual cortex. The rationale was (1) to demonstrate their d etectability by near infrared spectroscopy (NIRS); (2) to analyze the spect ral power of as well as the phase relationship between the different MRS pa rameters (oxygenated and deoxygenated hemoglobin and cytochrome-oxidase; ox y-Hb/deoxy-Hb/Cyt-ox). Also (3) influences of functional stimulation and hy percapnia on power and phase shifts were investigated. The results show tha t-in line with the literature-low frequency oscillations (LFO) centred arou nd 0.1 s(-1) and even slower oscillations at; about 0.04 s(-1) (very low fr equency, VLFO) can be distinguished. Their respective power differs between oxy-Hb, deoxy-Hb, and Cyt ox. Either frequency (LFO and VLFO) is altered i n magnitude by functional stimulation of the cortical area examined. Also w e find a change of the phase shift between the vascular parameters (oxy-Hb, tot-Hb) and the metabolic parameter (Cyt-ox) evoked by the stimulation. It is shown that hypercapnia attenuates the LFO in oxy-Hb and deoxy-Hb. Concl usions: (1) spontaneous vascular and metabolic LFO and VLFO calm be reprodu cibly detected by MRS in the human adult. (2) Their spectral characteristic s and their response to hypercapnia are in line with those described in exp osed cortex (for review see (Hudetz ef al., 1998)) and correspond to findin gs with transcranial doppler sonography (TCD) (Diehl ct al., 1995) and fMRI (Biswal et al., 1997). (3) The magnitude of and phase relation between MRS -parameters at the LFO may allow for a local noninvasive assessment of auto regulatory mechanisms in the adult brain. (C) 2000 Academic Press.