Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Regional cerebral blood flow (RCBF) was studied during low frequency (15/s) and high frequency (50/s) electrical stimulation of the locus coeruleus (LC) in the alpha-chloralose-anesthetized cat using the freely diffusible tracer [14C]iodoantipyrine and regional brain dissection. The responses were determined in animals spinalized at the C1/C2 level to eliminate systemic effects of pontine stimulation such as alterations in blood pressure and heart rate. The spinalization, itself, did not alter resting RCBF or reactivity to hypercapnia. Low frequency stimulation reduced regional cerebral blood flow in the cortex, basal ganglia and white matter of the corpus callosum. The reductions in RCBF were maximal (35%) in the occipital cortex whereas no changes were seen in the colliculi. No changes were seen in any brain areas with high frequency stimulation. The relevance of this brainstem effect on cerebral blood flow to pathological states such as stroke and migraine is discussed.
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PMID:Low frequency stimulation of the locus coeruleus reduces regional cerebral blood flow in the spinalized cat. 291 15

Thromboembolic brain ischemia was produced in dogs using an autologous blood clot model. The effect of postembolic treatment with flunarizine and streptokinase on hemispheric cerebral metabolic rate for oxygen (CMRO2), oxygen extraction ratio (OER), and cerebral blood flow (CBF) was studied by positron emission tomography (oxygen-15 technique) 24 hours after the insult. We studied five groups of experimental dogs and compared them with a control group of nonembolized dogs. Group I received no treatment, Group II was treated locally with 500,000 IU streptokinase starting 30 minutes after the insult, Group III received streptokinase locally 30 minutes after the insult and 0.1 mg/kg i.v. flunarizine immediately after the insult and 2 hours later, Group IV received flunarizine as Group III, and Group V was orally pretreated with 0.5 mg/kg/day flunarizine during 2 weeks preceding embolization. Compared with the contralateral hemisphere, in the embolized hemisphere a significant reduction of CMRO2 (-25% to -40%) and CBF in normocapnia (-35%) and hypercapnia (-50%) was observed in Groups I, II, and V. In Groups III and IV, CMRO2, OER, and CBF of the embolized hemisphere were within the normal range during normocapnia and hypercapnia; the extent of the ischemic lesions was markedly less than in the other groups of experimental dogs. We conclude that flunarizine treatment after experimental thromboembolic stroke had a favorable influence on brain tissue. Chronic preventive flunarizine treatment failed to have a beneficial effect.
Stroke 1989 Mar
PMID:Streptokinase treatment versus calcium overload blockade in experimental thromboembolic stroke. 292 75

The influence of blood gases on alpha 1- and alpha 2-adrenoceptor-mediated pressor responses was studied in the pithed rat by varying the inspired gas mixture or the ventilation stroke volume. Acidosis favoured the peak responses to the alpha 2-adrenoceptor agonist, xylazine, while alkalosis favoured the peak responses to the alpha 1-adrenoceptor agonist, phenylephrine. A combination of hypoxia and hypercapnia greatly depressed the alpha 1 response to phenylephrine whereas the alpha 2 response to xylazine remained relatively unaffected. When Pao2 was varied in either acidotic or alkalotic conditions the response to the phenylephrine increased as Pao2 increased. To prevent hypoxia in air ventilated rats, large stroke volumes were required. This caused alkalosis and hence decreased responsiveness to xylazine. Consequently, air ventilated pithed rats gave poorer responses to xylazine than did those ventilated on 100% O2. The results show that alpha 1- and alpha 2-adrenoceptor-mediated pressor responses can be differentially affected by blood gases. The relative contribution of alpha 1- and alpha 2-adrenoceptors to vascular tone may be either under- or over-estimated depending on the arterial blood gases.
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PMID:The influence of blood gases on alpha 1- and alpha 2- adrenoceptor-mediated pressor responses in the pithed rat. 299 76

Cerebral blood flow (CBF) and the response to hypercapnia (cerebral reactivity) have been measured in 41 patients with unilateral or bilateral internal carotid artery occlusion in an attempt to identify those with limited collateral reserve. Normocapnic CBF was within normal limits in the majority of subjects. The response to hypercapnia varied from normal to absent, with impaired reactivity becoming increasingly likely when more than one artery was diseased. In 19 patients with unilateral carotid occlusion, hemisphere reactivity was well preserved in the majority, but was significantly lower on the side of the occlusion (mean 2.9%/mm Hg) compared to the normal side (mean 3.4%/mm Hg). Reactivity on the side of the occlusion was further reduced in 15 patients with occlusion and contralateral internal carotid artery stenosis (mean 1.7%/mm Hg) and was even lower in seven patients with bilateral occlusion (mean 1.1%/mm Hg). There was no difference in reactivity between asymptomatic hemispheres in the 41 patients (mean 2.7%/mm Hg) and hemispheres in which a previous stroke had occurred (mean 2.8%/mm Hg). In contrast the response in hemispheres subject to continuing transient ischaemic attacks was significantly impaired (mean 1.6%/mm Hg), suggesting that the cerebral symptoms in some of these patients may have had a haemodynamic origin more often than suspected from the clinical history.
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PMID:Reactivity of the cerebral circulation in patients with carotid occlusion. 309 71

Cerebral CO2-reactivity was tested by transcranial Doppler sonography (Doppler CO2 test) in 232 patients. Time averaged flow velocity in the middle cerebral artery at the 40 mm Hg blood pCO2 level was taken as a reference point, and the relative increase of flow in hypercapnia of 46.5 mm Hg pCO2 was defined as "Normalized Autoregulatory Response" (NAR). A total of 82 patients with no evidence of cerebrovascular disease gave "normal" values for NAR (23.2 +/- 5.2 SD). In 150 patients with 233 stenoses and occlusions of the internal carotid artery NAR was significantly decreased in higher-grade stenoses (P = 0.01 for 80% diameter reduction, P less than 10(-6) for 90% or more). In such stenoses, patients with NAR less than 14 had suffered more frequently (P less than 0.01) from ipsilateral transient ischemic attacks and/or stroke during the previous 6 months than patients with "normal" NAR. Preoperative NAR less than 14 always improved to "normal" values following carotid surgery, while preoperative NAR greater than 19 remained unchanged (60 cases). The transcranial Doppler CO2 test is thought to be a reliable noninvasive method to detect hemodynamically critical carotid stenoses and occlusions. This may be of interest in selecting patients for superficial temporal artery-middle cerebral artery bypass and carotid surgery. For practical use 4 categories of NAR are suggested.
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PMID:Transcranial Doppler CO2 test for the detection of hemodynamically critical carotid artery stenoses and occlusions. 310 Feb 97

Circulatory changes and the degree of sympathetic block were evaluated in 15 elderly patients with high thoracic epidural anaesthesia (T1-T5). Bupivacaine 5-6 ml 0.5% was injected via an epidural catheter at the T3-level. The quality of the sympathetic block was determined with the Valsalva manoeuvre. Induced hypercapnia was used to quantify the degree of sympathetic block. Following thoracic epidural anaesthesia (TEA), cardiac output, stroke volume and arterial blood pressure decreased. During hypercapnia, heart rate and arterial blood pressure increased both before and after established TEA. Thus the block of the sympathetic innervation to the heart with a high TEA using 0.5% bupivacaine was not sufficient to prevent mobilization of circulatory reserves during sympathetic stimulation. The most likely explanation is considered to be the lack of neural block of the efferent nerves leading to the adrenal medulla and the peripheral vascular bed.
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PMID:Circulatory effects of short-term hypercapnia during high thoracic epidural anaesthesia in elderly patients. 310 68

An index of cerebral perfusion reserve (RES%), defined as the percent change of regional cerebral blood flow over baseline per mm Hg of end-tidal CO2 tension, was determined for each middle cerebral artery (MCA) territory in patients with unilateral carotid distribution transient ischemic attacks or minor cerebrovascular accidents and was compared with that of age-matched, neurologically normal volunteers. Vasodilator responses to induced hypercapnia were tested during inhalation of 5% CO2 in 95% O2 while regional cerebral blood flow was measured by fluoromethane inhalation positron emission tomography. Mean RES% for 24 normal MCA territories was 5.2 +/- 0.8%. Mean RES% for 15 patient nonischemic MCA territories was 3.8 +/- 1.3% and for 15 ischemic MCA territories was 2.8 +/- 1.9% (both p less than 0.001). Individual RES% values and symmetry ratios between ischemic and nonischemic regions were also determined and compared with angiographic data. Areas of diminished, asymmetric, or paradoxical (two patients) CO2 reactivity appear to correspond to areas of compensatory vasodilation. We found this technique to be a safe and reproducible method for defining and recording localized areas of cerebral tissue at apparent risk for hemodynamically related damage.
Stroke 1988 Jan
PMID:Cerebral perfusion reserve indexes determined by fluoromethane positron emission scanning. 312 75

Cerebral blood flow (CBF) was measured in 39 men at normocapnia and after 5% CO2 inhalation using the xenon-133 technique. Twenty-three patients had unilateral carotid artery occlusion with no angiographic evidence of contralateral carotid artery stenosis or ophthalmic collateral flow. Eleven of these patients had undergone extracranial-intracranial (EC-IC) bypass surgery. Sixteen age-matched normal men underwent CBF measurements at normocapnia and hypercapnia to provide control data. Mean hemispheric CBF was not different between hemispheres ipsilateral and contralateral to the carotid artery occlusion either in the patients who had undergone bypass surgery or in those with carotid artery occlusion alone. Considering all patients with carotid artery occlusion, mean CO2 reactivity was decreased in the hemisphere ipsilateral to the occlusion as compared to the contralateral hemisphere in both groups. Based on data from normal individuals, a hemispheric difference in CO2 reactivity of more than 0.94%/mm Hg PaCO2 or a global CO2 reactivity of less than 0.66%/mm Hg PaCO2 was considered abnormal for an individual patient. Six of 23 patients with carotid artery occlusion (three with an EC-IC bypass) had global or hemispheric abnormalities in CO2 reactivity. Patients with impaired CO2 reactivity were not distinguishable from other patients by neurological examination, presence of transient ischemic attacks, or evidence of infarction on computerized tomography scanning. This test was safe and simple to perform and may be a useful means of detecting impaired cerebrovascular collateral reserve capacity. If impaired CO2 reactivity after carotid artery occlusion proves to be associated with a high risk of subsequent stroke, the test would provide a physiological basis for selecting a subgroup of patients who could be helped by cerebral revascularization.
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PMID:Cerebrovascular CO2 reactivity after carotid artery occlusion. 313 40

The reactivity of cerebral blood vessels to changes in PaCO2 in areas of the cerebral cortex with or without diaschisis was investigated in 13 patients in a subacute or chronic stage after a small capsular infarct. A focal area of hypoperfusion (area of diaschisis) was detected in the ipsilateral sensorimotor cortex in each patient. Hyperventilation caused a significant reduction of regional cerebral blood flow in the area without diaschisis and only a tendency for regional cerebral blood flow to decrease in the area with diaschisis; CO2 inhalation induced a slight increase in regional cerebral blood flow in the area without diaschisis and a significant increase in regional cerebral blood flow in the area with diaschisis. Regional cerebral blood flow reactivity to hypocapnia was significantly less in the area with diaschisis than in the area without, whereas the hypercapnic response was more marked in the area with diaschisis than in the area without. Our results suggest that in the area with diaschisis, the arterioles may be abnormally vasoconstricted at rest such that they cannot constrict further in response to hypocapnia but can dilate more during hypercapnia than in the area without diaschisis. This excessive resting vasoconstriction may result from decreased tissue elaboration of CO2 due to local decrease of metabolic function.
Stroke 1988 Jul
PMID:Vascular response to carbon dioxide in areas with and without diaschisis in patients with small, deep hemispheric infarction. 313 40

To evaluate the CO2-induced vasomotor reactivity of the cerebral vasculature, relative changes of blood flow velocity within the middle cerebral artery were measured by transcranial Doppler ultrasonography during normocapnia and various degrees of hypercapnia and hypocapnia. We studied 40 normal individuals and 40 patients with unilateral and 15 patients with bilateral internal carotid artery occlusions. When blood flow velocity changes as percent of normocapnic values were plotted against end-tidal CO2 volume percent, a biasymptotic curve (a tangent-hyperbolic function) gave the best fit of the scattergram. The distance between the upper and lower asymptotes was defined as cerebral vasomotor reactivity. In the normal individuals, mean +/- SD vasomotor reactivity was 85.63 +/- 15.96%. In patients with internal carotid artery occlusions, vasomotor reactivity was significantly lower than normal on both the occluded (mean 45.2%, median 50.4%; p less than 0.0001) and the nonoccluded (mean +/- SD 67.7 + 13.3%, p less than 0.01) sides in the unilateral group and on both sides (mean +/- SD 36.6 +/- 15.9% and 44.9 +/- 24.6%, p less than 0.0001) in the bilateral group. The difference between vasomotor reactivity for symptomatic and asymptomatic unilateral occlusions was also highly significant (mean 37.6% and 62.9%, p less than 0.006). Vasomotor reactivity was also significantly lower in patients with low-flow infarctions on computed tomography than in patients with normal scans (mean +/- SD 36.7 +/- 25% and 60.2 +/- 16.9%, p less than 0.008). A striking association of low-flow infarctions, ischemic ophthalmopathy, and hypostatic transient ischemic attacks was found with vasomotor reactivities of less than 34% or even paradoxical reactions.(ABSTRACT TRUNCATED AT 250 WORDS)
Stroke 1988 Aug
PMID:Noninvasive assessment of CO2-induced cerebral vasomotor response in normal individuals and patients with internal carotid artery occlusions. 313 41


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