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

These experiments were designed to test the hypothesis that increases in blood flow to the lower brainstem would be greater than forebrain regions during arterial hypercapnia. Total and regional cerebral blood flow (CBF) was measured via the tracer microsphere technique in seven anesthetized New Zealand white rabbits during normocapnia (arterial PCO2 congruent to 40 torr) and hypercapnia (arterial PCO2 congruent to 80 torr). During normocapnia average CBF was 0.77 ml/min/g, and regional measurements of blood flow indicated significantly greater flow to the cerebrum (0.86 ml/min/g) than either the medulla (0.52 ml/min/g) or the pons (0.49 ml/min/g). When arterial PCO2 was increased average CBF increased 113%, and a significant linear regression was calculated for arterial PCO2 vs CBF [CBF (ml/min/g) = 0.028 PCO2 (torr) - 0.502]. The distribution of blood flow within the brain was similar to normocapnia except that blood flow to the cerebellum was now greater than any other brain region (1.97 ml/min/g for the cerebellum compared to 1.66 ml/min/g for the cerebrum). Absolute increases in blood flow to the lower brainstem were equal to or less than other areas of the brain. We conclude that ponto-medullary blood flow does not increase disproportionate to other areas of the brain during hypercapnia, but some redistribution of CBF does occur in that cerebellar blood flow increased significantly more than the cerebrum, medulla, or pons.
Stroke
PMID:Regional cerebral blood flow during hypercapnia in the anesthetized rabbit. 665 68

The role of adenosine in the regional cerebral blood flow (rCBF) response to hypoxia was evaluated in young (6 month) and aged (26-28 month) F344 rats using theophylline, an adenosine antagonist. Regional CBF was measured with radioactive microspheres under control anesthetized conditions (70% N2O, 30% O2) and at two levels of hypoxia (CaO2 = 8.7-9.0 ml . 100ml-1 and 3.2-3.7 ml . 100ml-1). Without theophylline infusion, CBF increases were similar between young and aged rats during moderate hypoxia but were increased more in young during severe hypoxia. Intracerebrovascular theophylline infusion significantly attenuated the increase in CBF during both moderate and severe hypoxia and decreased the difference between young and aged rats. Theophylline infusion produced no significant effect on the increase in CBF produced by hypercapnia, indicating the specificity of the treatment for hypoxic induced CBF changes and adenosine release. Intracerebrovascular infusion of adenosine had no effect on CBF, presumably due to the presence of the blood brain barrier. The results suggest that adenosine plays a major role in CBF increases during both moderate and severe hypoxia and in the difference in response to hypoxia between young and aged rats.
Stroke
PMID:The role of adenosine in CBF increases during hypoxia in young vs aged rats. 669 16

The ultrasonic method was used in acute experiments on cats with open chest and under artificial lung ventilation to study the coronary circulation, the minute and stroke volumes of the heart during changes in gaseous medium. Hypoxic hypoxia and hypercapnia were demonstrated to induce a considerable increase in the coronary circulation in the presence of a slightly elevated minute volume of the heart. The authors assume that the induced changes in the phasic coronary circulation point to the increased resistance of the coronary vessels to mechanical compression during systoles.
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PMID:[Coronary circulation in cats exposed to different gaseous media]. 670 17

In this report, compared in retrospect is the incidence of intraoperative stroke among 152 operations performed under hypercarbic general anesthesia without carotid artery shunting, 260 operations performed under both hypercarbia and normocarbia anesthesia with selective shunting based upon internal carotid artery back pressure and 366 operations performed under normocarbia anesthesia with routine carotid artery shunting. Chi-square analysis determined that routine carotid shunting was associated with a significant reduction in the incidence of intraoperative stroke among patients with previous transient ischemic attacks. In addition, both routine shunting and selective shunting, depending upon internal carotid artery back pressure, reduced the incidence of intraoperative stroke among patients with subtotal stenosis of the contralateral internal carotid artery. Considering the safety, simplicity and wide availability of Silastic carotid artery shunts, their routine use during carotid endarterectomy appears advisable in preference to more elaborate and expensive methods of intraoperative cerebral protection.
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PMID:A retrospective comparison of the use of shunts during carotid endarterectomy. 677 Apr 77

Changes of regional cerebral blood flow from rest to mental activation by a visually presented spatial reasoning test were measured during normo- and hypercapnia in 10 healthy subjects. Hypercapnia, elicited by inhalation of 6% CO2, resulted in similar flow increases in all 32 cortical regions measured. Increases of flow during testing were seen in post-central regions of the brain whether the resting level was augmented by hypercapnia or not. The results show that an elevated local functional level in the cortex causes an automatic local vasodilatory response which is totally independent of the basal level of perfusion and availability of metabolic substrates.
Stroke
PMID:Cerebral hemodynamic response to mental activation in normo- and hypercapnia. 677 50

Ventilatory and heart-rate responses to hypercapnia were evaluated by a CO2 rebreathing technique in 56 patients with acute ischemic stroke and 14 normal controls. Both ventilatory and heart-rate responses were increased in patients with hemispheral lesions, but not in patients with brainstem lesions. In patients with hemispheral infarct, there was a decrease in CO2 sensitivity 1 to 3 weeks later. Acute hemisphere lesions may result in a transient decrease of cerebral inhibition of brainstem-mediated autonomic responses to a chemical stimulus.
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PMID:Altered cerebral inhibition of respiratory and cardiac responses to hypercapnia in acute stroke. 677 48

Following 5 minutes of global ischemia, local cerebral blood flow (LCBF) was shown to have an initial reactive hyperemia that was followed, within the first hour, by persistent hypoperfusion (Part I). Intracranial pressure (ICP) was never elevated during the period of poor reperfusion. These experiments attempted to reverse the state of subnormal LCBF by inducing hypercarbia or hyocarbia or maintaining normocarbia. Although hypocarbia did increase LCBF at several electrode sites, neither the intracerebral steal syndrome nor the "squeeze" syndrome are a dominant consequence of hypercarbia in this model of global ischemia. Hypercarbia was consistently more effective in elevating LCBFs and in recovery of the electrocorticogram. It appears that, in the absence of raised ICP, hypercarbia may be preferred to normal or low PACO2,. Even though hypercarbia was superior to normocarbia or hypocarbia, hypercarbia was not a completely satisfactory regimen for reversing the state of poor reperfusion.
Stroke
PMID:Local cerebral blood flow following transient cerebral ischemia. II. Effect of arterial PCO2 on reperfusion following global ischemia. 677 97

The effects of hypercapnia on enhancement of reduced cerebral perfusion were re-evaluated in areas of ischemia produced by occlusion of the canine middle cerebral artery. Perfusion was measured by 85Kr (beta-ray) and 133Xe (gamma-ray) clearances, fluorescein angiography and diameter measurement of arteries. Between 45 and 55 mm Hg of PaCO2 rCBF measured with both isotopes increased significantly. When PaCO2 was elevated above 55 mm Hg, there was a remarkable dissociation in the rCBF measured by both isotopes. Cortical blood flow measured by 85Kr clearance decreased and, conversely, rCBF measured by 133Xe continued to increase. Arteries of less than 50 mu in diameter in areas of ischemia dilated significantly during hypercapnia. At PaCO2 above 65 mm Hg, progressive sub-pial hemorrhage and extravasation of dye were observed as side effects of hypercapnia. The use of mannitol combined with hypercapnia appeared to be harmful. A PaCO2 level between 45 and 55 mm Hg increases perfusion in areas of mildly reduced rCBF.
Stroke
PMID:Effects of hypercapnia on enhancement of decreased perfusion flow in non-infarcted brain tissues. 678 86

Awake dogs were studied before (control) and after chronic bilateral carotid denervation (denervated) at rest and running for 3 min on a treadmill at 8 km . h-1 and at various grades, in an altitude chamber operated either at 140 m or at 4000 m for 3 h. Steady-state pulmonary ventilation (Vg) and breathing pattern (VT, fR), oxygen consumption (MO2), O2 concentrations (C) and pressures (P) in the arterial (a) and mixed venous blood (v), hematocrit (Ht) and acid-base status in arterial blood, and heart frequency (fH) were measured. From these data cardiac output (Vb) and stroke volume (Vs), ventilatory and circulatory requirements (Vg/Mo2, Vb/MO2), extraction of O2 from inspired gas (EairO2) and blood (EbO2), and capacitance coefficient of blood for oxygen (beta bO2) were calculated. Ventilatory responses to transient O2-inhalation were also studied and the aortic (AP) and pulmonary (PP) blood pressures measured in resting conditions. 1. After chronic carotid denervation the hypoxic chemoreflex drive of ventilation was reduced by about half, maximal MO2 remained unaffected at 140 m, but at 4000 m decreased 50% compared to 30% in controls. 2. In all experimental conditions, Vg/MO2, PaO2 and CaO2 were less in denervated animals than in controls, and EairO2, PaCO2 and H+ ion concentration were higher. 3. At 140 m, circulatory O2 convective transport was identical in the two groups of dogs. At 4000 m, beta bO2 increased similarly in both groups, but Vb and Vb/MO2 were higher in denervated dogs than in controls, in relation with reduced CaO2-CVO2 difference which contributed to restore PVO2 towards higher values. 4. At 140 m, mean resting AP and PP were similar in both groups of dogs. At 4000 m, AP increased not significantly in controls, and decreased in denervated animals; PP increased in controls, but not in denervated dogs. It is concluded that integrity of the arterial chemoreceptor drive is essential in determining the eupneic level of ventilation and normal acid-base status of the blood in both resting and exercising dogs, at low and at high altitude, and in reducing the O2 circulatory requirement at high altitude. At 4000 m, the lack of carotid chemosensitivity is accompanied by severe hypoxemia, in association with hypercapnia and acidosis, and by increased cardiac blood flow, most presumably due to decreased peripheral resistance and increased venous return; despite these compensatory changes in circulatory O2 convective transport, denervated animals reach a maximum O2 uptake at lower work load than controls.
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PMID:Carotid chemoreceptor function in ventilatory and circulatory O2 convection of exercising dogs at low and high altitude. 678 82

1. In eighteen anaesthetized cats, action potentials in non-myelinated vagal afferent neurones were recorded in the nodose ganglion by means of extracellular micro-electrodes. 2. The pulmonary or bronchial origin of these C fibres was assessed in closed chest preparations by injecting phenyl diguanide into either the right atrium or the ascending aorta (bronchial circulation). This was confirmed in two animals by local mechanical stimulation. 3. Eighty per cent of bronchopulmonary C fibres increased their discharge frequency when the end-tidal CO2 concentration (FA,CO2) increased from 0.02 to 0.10. Most of these C endings showed a maximal response when FA,CO2 reached 0.04. For the others a further increase in discharge occurred when CO2 concentration reached 0.08-0.10. Continuous measurement of C fibre discharge frequency indicated that they detected preferentially changes in the inspired CO2 content, but adapted when a high CO2 level was maintained. Their activation by hypercapnia was followed by an increase in lung resistance. 4. Lowering the O2 content of the inspired gas had no effect on the spontaneous activity of bronchopulmonary C endings. 5. When the stroke volume of the pump was doubled, the spontaneous activity of bronchopulmonary C fibres decreased in intact chest preparations. Inflation of the lungs had the opposite effect after the chest was opened. In both cases hyperdeflation was a potent stimulus to these receptors. 6. In tracheotomized cats, the tracheal temperature was 28-29 degrees C. When normal thermal conditions were restored in the tracheal lumen (33-34 degrees C) the spontaneous discharge frequency of some bronchial C fibres was greatly increased. 7. It is concluded that the spontaneous activity of most of the bronchial or pulmonary C fibres was maximal when chemical and physical physiological conditions were restored in the lungs. It appears that changes in alveolar CO2 concentration constitute the usual stimulus for these fibres.
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PMID:Changes in activity of vagal bronchopulmonary C fibres by chemical and physical stimuli in the cat. 679 95


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