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Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This investigation determined the effects of sustained hypercapnia on cerebral blood flow (CBF; radiolabeled microspheres), cerebral metabolic rates for O2 and glucose (CMRO2 and CMRglc), and brain water content in conscious sheep instrumented with aortic, left ventricular, vena cava, and brain sagittal sinus catheters. PaCO2 was elevated from 38 +/- 3 to 53 +/- 3 (mean +/- SD) mm Hg and PaO2 from 109 +/- 7 to 131 +/- 4 mm Hg for 96 h in an environmental chamber. Hypercapnia did not alter sheep behavior, food and water intake, arterial pressures, core temperature, or brain lactate release. Total and regional CBF and CBF/CMRO2 reached peak values at 1 h and then readjusted, to stabilize at lower, but still elevated levels at 24 h and thereafter. CMRO2 and CMRglc increased at 6 h and thereafter during hypercapnia. PaCO2, CBF, CMRO2, and CMRglc remained elevated at 3 h after restoration to room air, while CBF/CMRO2 returned to the control value. Frontal and occipital lobe wet-to-dry weight ratios increased modestly but significantly after hypercapnic exposure. It is concluded that sustained hypercapnia induces stable and nonadapting increases in both CBF and brain metabolism that persist for at least 3 h after restoration to room air in association with hypoventilization and modest elevations of brain water.
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PMID:Cerebral blood flow and metabolic responses to sustained hypercapnia in awake sheep. 779 28

Cholinergic projections from the basal forebrain are capable of influencing local cortical blood flow (CoBF). The effect of age on this influence was investigated by measuring CoBF and tissue gas partial pressures (PtO2, PtCO2) by mass spectrometry in conscious young adult (2-4 months) and aged (22-28 months) Fischer 344 rats. Electrical stimulation (50 microA) of the substantia innominata (SI) increased frontal (+100.9%) and parietal (+28.4%) CoBF in young rats, but the effects were less in aged rats (frontal, +48.6%, P < 0.05; parietal, +18.9%, difference N.S.). Frontal PtO2 was increased in young but not aged rats (P < 0.01.). During standard hypercapnia, changes in CoBF, PtO2 and PtCO2 did not differ between young and aged rats. Under physostigmine infusion (0.15 mg/kg/h, i.v.), the CoBF increases to SI stimulation were approximately doubled in both cortices, in young and aged rats, and PtO2 increases were also significantly greater. However, frontal PtO2 increases were significantly smaller in aged (+7.6%) than in young (32.7%) rats, as were frontal PtCO2 reductions. We conclude: (i) the influence of the SI on frontal CoBF and PtO2 is substantially reduced with age; (ii) although physostigmine treatment potentiates this influence in both groups, the beneficial effects are relatively limited for aged rats.
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PMID:Basal forebrain control of cortical blood flow and tissue gases in conscious aged rats. 785 69

The reduction in cerebrovascular reactivity to CO(2) and/or endothelial function that occurs in the early hours after waking are potential causes for the increased risk for cardiovascular events at this time point. It is unknown whether cerebral autoregulation is reduced in the morning. We tested the hypothesis that early morning reduction in endothelium-dependent vascular reactivity would be linked to changes in cerebrovascular reactivity to CO(2) and cerebral autoregulation (CA). Overnight changes in a dynamic cerebral autoregulation index (ARI) were determined from continuous recordings of blood flow velocity in the middle cerebral artery (MCAv) and arterial blood pressure (BP) during transiently induced hypotension in 20 individuals. Frontal cortical oxygenation (near infrared spectroscopy) and cerebral haemodynamics were also monitored during hypercapnia and before and during 3 min of active standing. Brachial artery flow-mediated endothelium-dependent vasodilatation (FMD) and endothelium-independent dilatation (NFMD) were also monitored. From evening to morning, there was a significant lowering in ARI (5.3 +/- 0.5 versus 4.7 +/- 0.6 a.u.; P < 0.05), cerebrovascular reactivity to CO(2) (5.3 +/- 0.6 versus 4.6 +/- 1.1% mmHg(-1); P < 0.05) and FMD (7.6 +/- 0.9 versus 6.0 +/- 1.4%; P < 0.05). The lowered FMD was related to the decrease in cerebrovascular reactivity to CO(2) (r = 0.76; P < 0.05). Transient reductions in morning MCAv and cortical oxyhaemoglobin concentrations were observed upon resuming a supine-to-upright position (P < 0.05 versus evening). The early morning reduction in cerebral autoregulation may facilitate the onset of cerebrovascular accidents; this may be of particular relevance to at-risk groups, especially upon resuming the upright position.
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PMID:Early morning impairment in cerebral autoregulation and cerebrovascular CO2 reactivity in healthy humans: relation to endothelial function. 1738 17