Cerebral Blood Flow and Blood Volume in Response to O2 and Co2 Changes in Normal Humans

Fortune, John B.; Feustel, Paul; deLuna, Carlo; Graca, Linda; Hasselbarth, Julie; Kupinski, Ann Marie; Shah, Dhiraj M.

doi:10.1097/00005373-199407000-00047

Cited by 18 publications

(21 citation statements)

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“…For further evaluation of the robustness of our proposed method and to test the effect on global CBV, 10 additional subjects were studied under hypocapnia, known to significantly increase CCT and decrease CBF and CBV (Fortune et al, 1995;Reinstrup et al, 2001). The observed CCT increase of 0.26 s/mm Hg (4%/mm Hg) in our study corresponds well with the previously reported ultrasonographically derived CO 2 reactivity of 0.3 s/mm Hg (5%/mm Hg) (Schreiber et al, 2002).…”

Section: Figsupporting

confidence: 86%

“…Few data exist on CO 2 -dependent changes in global CBV in healthy human subjects. Fortune et al (1995) reported a CBV reduction of 0.2% per mm Hg using a scintigraphic method that detects 99m-Tc-labeled red blood cells, and Reinstrup et al (2001) found a significant relative CBV decrease of 0.9%/mm Hg. These findings suggest that the effective magnitude of global CBV change that can be achieved by a 10-mm Hg reduction in CO 2 reactivity is very small, at least under physiologic circumstances.…”

Section: Figmentioning

confidence: 98%

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Ultrasonographic Assessment of Global Cerebral Blood Volume in Healthy Adults

Doepp

Schreiber

Brunecker

et al. 2003

J Cereb Blood Flow Metab

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Summary:The authors describe a new ultrasonographic method for analysis of global cerebral blood volume (CBV) and its application under controlled hyperventilation. CBV was determined as the product of global cerebral blood flow volume (CBF) and global cerebral circulation time. CBF was measured by duplex sonography and calculated as the sum of flow volumes in both internal carotid arteries and vertebral arteries. Extracranial Doppler assessed cerebral circulation time by determining the time interval of echo-contrast bolus arrival between internal carotid artery and contralateral internal jugular vein. Forty-four healthy volunteers (mean age 45 ± 19 years, range 20-79 years) were studied. Mean CBV was 77 ± 13 mL.

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Section: Figsupporting

confidence: 86%

Section: Figmentioning

confidence: 98%

Ultrasonographic Assessment of Global Cerebral Blood Volume in Healthy Adults

Doepp

Schreiber

Brunecker

et al. 2003

J Cereb Blood Flow Metab

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“…The rise in Sp O 2 during mild hypercapnia is well known as the “Bohr effect” and is attributed to the reduced affinity of hemoglobin for O 2 at elevated CO 2 blood levels (i.e., a rightward shift of the oxyhemoglobin equilibrium curve), enhancing the release of O 2 into the blood. The range of variation in Pet CO 2 and Sp O 2 in our study is consistent with previous findings during carbogen breathing (9, 11, 22, 23). A quantitatively similar change of the relative BOLD‐weighted signal (however, with a negative sign) was also found during hypocapnia in hyperventilation experiments performed with a conventional SE‐EPI sequence and parameters matching those of our study (12).…”

Section: Discussionsupporting

confidence: 93%

Hypercapnia‐induced effects on image contrast based on intermolecular double‐quantum coherences

Schäfer¹,

Zysset²,

Heinke³

et al. 2008

Magnetic Resonance in Med

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Intermolecular double-quantum coherences (iDQCs) are well known to be sensitive to magnetic-field perturbations inside tissues. However, the exact relation between iDQC contrast in magnetic resonance imaging (MRI) and the underlying physiology is less well understood. To investigate parameters that influence iDQC signal changes observed during neuronal activation, carbogen-inhalation experiments were performed to produce a pure hemodynamic response without affecting oxidative metabolism. Eight human volunteers were studied at 2.9 T using gradientrecalled echo (GRE) and spin-echo (SE) variants of a single-shot sequence selecting iDQCs. Results were compared with conventional recordings of the blood oxygen level-dependent (BOLD) effect. Maps of voxels responding to the carbogen challenge showed similar distributions for iDQC and conventional MRI after adjustment for different sensitivities. In magnetic resonance imaging (MRI) experiments sensitized to intermolecular multiple-quantum coherences (iMQCs), contrast originates in long-range dipolar couplings on a spatial scale from tens of micrometers to millimeters (1,2). Such interactions between nuclear spins in different molecules separated by the so-called "correlation distance" can be observed by suppressing the signal contributions from conventionally detected single-quantum coherences (SQCs) in the imaging sequence. Previous work has demonstrated a strong susceptibility of intermolecular double-quantum coherences (iDQCs) to local magnetic field perturbations. This suggests a potential for oxygenation studies (for example, in tumor evaluation and detection [3]), and has already been exploited for functional magnetic resonance imaging (fMRI) experiments (4 -6).Currently, the origin of activation-induced signal changes in iDQC imaging is not completely understood. While conventional fMRI employing T 2 *-weighted or T 2 -weighted sequences reflects the average strength of the internal field gradient within an imaging voxel, the iDQC signal is a function of the resonance frequency difference of the two interacting spins. It was thus speculated if previously observed differences in the activation maps recorded with iDQC-based and conventional fMRI might reflect true differences in the physiological parameters influencing the signal (4). In this case, iDQC contrast would be fundamentally different from the conventional blood oxygen level-dependent (BOLD) effect. However, differences in the activation maps may alternatively just reflect differences in the sensitivities and signal stabilities of the two techniques.The BOLD-weighted fMRI signal depends on multiple physiological parameters, including changes in the cerebral blood flow (CBF), the cerebral blood volume (CBV), and the cerebral metabolic rate of oxygen (CMRO 2 ) (7). For further investigation of parameters influencing iDQC contrast, it would be useful to manipulate such physiological parameters more selectively as achieved in simple taskactivation studies. Previously, iDQC imaging was shown to be sensitive to...

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“…Enhanced hypoxic sensitivity may contribute to the long-term facilitation of sympathoexcitation in these patients. Upright hyperventilation and hypocapnia reduces cerebral blood flow (8) and contributes to light-headedness and to cognitive impairment during daily life.…”

Section: Clinical Implications For Potsmentioning

confidence: 99%

Baroreceptor unloading in postural tachycardia syndrome augments peripheral chemoreceptor sensitivity and decreases central chemoreceptor sensitivity

Taneja¹,

Medow

Clarke³

et al. 2011

American Journal of Physiology-Heart and Circulatory Physiology

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While orthostatic tachycardia is the hallmark of postural tachycardia syndrome (POTS), orthostasis also initiates increased minute ventilation (Ve) and decreased end-tidal CO(2) in many patients. We hypothesized that chemoreflex sensitivity would be increased in patients with POTS. We therefore measured chemoreceptor sensitivity in 20 POTS (16 women and 4 men) and 14 healthy controls (10 women and 4 men), 16-35 yr old by exposing them to eucapneic hyperoxia (30% O(2)), eucapneic hypoxia (10% O(2)), and hypercapnic hyperoxia (30% O(2) + 5% CO(2)) while supine and during 70° head-upright tilt. Heart rate, mean arterial pressure, O(2) saturation, end-tidal CO(2), and Ve were measured. Peripheral chemoreflex sensitivity was calculated as the difference in Ve during hypoxia compared with room air divided by the change in O(2) saturation. Central chemoreflex sensitivity was determined by the difference in Ve during hypercapnia divided by the change in CO(2). POTS subjects had an increased peripheral chemoreflex sensitivity (in l·min(-1)·%oxygen(-1)) in response to hypoxia (0.42 ± 0.38 vs. 0.19 ± 0.17) but a decreased central chemoreflex sensitivity (l·min(-1)·Torr(-1)) CO(2) response (0.49 ± 0.38 vs. 1.04 ± 0.18) compared with controls. CO(2) sensitivity was also reduced in POTS subjects when supine. POTS patients are markedly sensitized to hypoxia when upright but desensitized to CO(2) while upright or supine. The interactions between orthostatic baroreflex unloading and altered chemoreflex sensitivities may explain the hyperventilation in POTS patients.

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Cerebral Blood Flow and Blood Volume in Response to O2 and Co2 Changes in Normal Humans

Cited by 18 publications

References 0 publications

Ultrasonographic Assessment of Global Cerebral Blood Volume in Healthy Adults

Ultrasonographic Assessment of Global Cerebral Blood Volume in Healthy Adults

Hypercapnia‐induced effects on image contrast based on intermolecular double‐quantum coherences

Baroreceptor unloading in postural tachycardia syndrome augments peripheral chemoreceptor sensitivity and decreases central chemoreceptor sensitivity

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