Rapid magnetic resonance measurement of global cerebral metabolic rate of oxygen consumption in humans during rest and hypercapnia

Abstract

The effect of hypercapnia on cerebral metabolic rate of oxygen consumption (CMRO 2 ) has been a subject of intensive investigation and debate. Most applications of hypercapnia are based on the assumption that a mild increase in partial pressure of carbon dioxide has negligible effect on cerebral metabolism. In this study, we sought to further investigate the vascular and metabolic effects of hypercapnia by simultaneously measuring global venous oxygen saturation (S v O 2 ) and total cerebral blood flow (tCBF), with a temporal resolution of 30 seconds using magnetic resonance susceptometry and phase-contrast techniques in 10 healthy awake adults. While significant increases in S v O 2 and tCBF were observed during hypercapnia (P < 0.005), no change in CMRO 2 was noted (P > 0.05). Additionally, fractional changes in tCBF and end-tidal carbon dioxide (R 2 = 0.72, P < 0.005), as well as baseline S v O 2 and tCBF (R 2 = 0.72, P < 0.005), were found to be correlated. The data also suggested a correlation between cerebral vascular reactivity (CVR) and baseline tCBF (R 2 = 0.44, P = 0.052). A CVR value of 6.1% ± 1.6%/mm Hg was determined using a linear-fit model. Additionally, an average undershoot of 6.7%±4% and 17.1%±7% was observed in S v O 2 and tCBF upon recovery from hypercapnia in six subjects.

Cerebral Oxygen Metabolism in Neonates with Congenital Heart Disease Quantified by MRI and Optics

“…Global CMRO 2 measured with both MRI and DOS/DCS showed no population-averaged change due to hypercapnia. This observation agrees with our previous experience in healthy adults 20 and with several other publications that examined cerebrovascular reactivity to hypercapnia in patients with congenital heart defects using localized measurement techniques, such as DOS and DCS. 15,24,38 In addition to generating new physiologic data, this work also achieved several technical goals.…”

“…Specifically, S v O 2 was quantified using MRI susceptometry-based oximetry and CBF via PC MRI. Details on the pulse sequence are in Jain et al 13,20 The scan parameters were as follows: voxel size Anatomic T 1 -and T 2 -weighted high-resolution MRI was performed and neonatal brain volumes were estimated from the resulting images using standard segmentation techniques to obtain CBF and CMRO 2 in conventional units of mL/minute per 100 g and mL O 2 /100 g per minute, respectively.…”

Low-frequency calcium oscillations accompany deoxyhemoglobin oscillations in rat somatosensory cortex

“…Moreover, the good correspondence between the frequencies of the oscillations in HbO 2 and HbR and those in cellular Ca 2+ provides evidence that the HbR oscillations are driven by neurovascular coupling. The minimal effects of hypercapnia on Ca 2+ i signals or on LFPs are consistent with studies showing no large changes in neuronal metabolism during hypercapnia in rodents (39) and in awake humans (40). Our results are also consistent with prior electrophysiological findings revealing a correlation between oscillations in neuronal activity as measured with LFP and resting BOLD signals (35,41), further supporting the evidence that the resting BOLD oscillations are predominantly driven by neuronal activity.…”

Alterations in Cerebral Oxygen Metabolism after Traumatic Brain Injury in Children

“…However, it is sensitive to physiological changes induced by hypercapnia and breath holding. 36,44 In addition, it is related to injury severity and outcome in patients with TBI. 26 One important limitation however is that heterogeneous distribution of metabolic abnormalities including areas of ischemic penumbra cannot be detected.…”