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

Four groups of male volunteers have been exposed in a tight climatical chamber to PICO2 of 14, 21, 28 and 32 torr; exposure periods varied from two to 30 days, between two reference periods in normal air. The results deal with the evolution of arterial blood acid-base equilibrium and that of renal response in relation to PICO2. In all exposures, the carbon dioxide alveolar overload increases by several torr during the first 24 hours on account of attenuation of the initial hyperventilation. Kinetics of the respiratory acidosis compensation differs according to hypercapnia which is moderate (PICO2 of 14 and 21 torr) or relatively severe (PICO2 of 28 and 32 torr). The decrease in arterial pH lessens as early as the 24th hour at PICO2 28 and 32 torr, and only after two days at PICO2 14 and 21 torr. The renal response is characterized by a significant increase in aciduria during the first 24 hours at PICO2 28 and 32 torr; the changes are smaller and start latter at PICO2 14 torr.
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PMID:[Kinetics of the compensation of respiratory acidosis induced by experimental chronic hypercapnia in man (author's transl)]. 1 89

It has been proposed that the responses of the cerebral circulation to hypoxia, hypercapnia and hypotension may be partially mediated by an autonomic reflex with receptors in the carotid body or sinus serving as sensors and the efferent limbs being the 7th cranial nerves. Transection of the 7th cranial nerve has been reported to impair the cerebral circulatory response to isolated chemoreceptor stimulation by hypoxia and hypercapnia. To test this hypothesis we measured cerebral blood flow (CBF) by an intra-arterial 133Xe technique in 10 baboons during periods of induced hypoxia and hypercapnia, both before and after transection of the 7th cranial nerve, We found that the responses of CBF were unaltered by either unilateral or bilateral section of the nerve. Our results showing the preservation of normal CBF responses, following transection, suggest that neurogenic control of the cerebral circulation by an autonomic reflex involving the 7th nerve is unlikely.
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PMID:Responses of the cerebral circulation to hypercapnia and hypoxia after 7th cranial nerve transection in baboons. 1 41

An isolated perfused lung (IPL) preparation was used to investigate the influence of acute environmental stress on lung substrate metabolism. The IPL apparatus consists of four perfusion flasks housed in a temperature-controlled Lucite box with a circulation fan. Lungs are ventilated by a positive pressure ventilation pump. The ventilation is arranged so that the lung can be ventilated with any desired gas composition with concomitant collection of expired gases. The perfusion medium is circulated at 10 ml/min with a peristaltic blood pump, and passes through a specially designed chamber to dampen pulmonary pressure and remove emboli. The perfusion medium presently used in our experiments consisted of washed bovine red blood cells resuspended to a 15% hematocrit with Krebs-Henseleit bicarbonate buffer containing 6% dialyzed Pentex bovine serum albumin. Circulating substrates include 6muM glucose and 0.4muM palmitate. The pH is adjusted to 7.4 with 0.8M Na carbonate. Lungs perfused for 1.5 hr with this apparatus maintain viability, show little edema, maintain blood gases, and show linear incorporation of labeled glucose into lung lipids. Perfused lungs made hypocapnic show a significant (p less than 0.05) rise in lactate and pyruvate, while perfused lungs made hypercapnia show a significant decrease in pyruvate with no change in lactate.
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PMID:Perfused lung preparation for studying altered gaseous environments. 1 88

Experiments were carried out on dogs kept in a sealed chamber. Changes in the O2 and CO2 concentrations as well as variations of physiological functions, the so-called survival curves, were studied under the conditions of terminated O2 supply and CO2 utilization. The criteria of investigation, mathematical and physiological analysis were chosen from the point of view of predicting hazardous states during failures of the environmental control system. Tolerance limits during slow and rapid changes of the environment, phases of changes of the body state and mechanisms of a combined effect of increasing hypercapnia and hypoxia were considered.
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PMID:[Patterns in the change in the body state of dogs during a breakdown of the atmosphere regeneration system in a pressurized space]. 1 77

To study the role of carbonic anhydrase in the CSF [HCO3] increase in respiratory acidosis and its effect on brain ammonia, anesthetized rats were subjected to hypercapnia (7% CO2) for 2 hours. The animals received periodic intraventricular injections of either 'mock' CSF or 'mock' CSF and acetazolamide for 45 minutes prior and during hypercapnia when: (a) plasma [HCO3-] was allowed to increase normally and (2) plasma [HCO3] increase was prevented by i.v. HC1 infusion, CSF [HCO3] increased 8.5 mM/L after 2 hours of hypercapnia (delta PCO2 40) in the rats with intraventricular 'mock' CSF injections, and only 6 mM/L in the animals with acetazolamide injections. CSF [HCO3-] increased 7 mM/L during hypercapnia and HCl infusion with intraventricular 'mock' CSF injections, but only 2 mM/L with acetazolamide injections. Changes in total brain CO2 (increase) and brain glutamic acid (decrease) in hypercapnia were not affected by intraventricular acetazolamide and i.v. HCl. The increase of brain NH4+ and glutamine in hypercapnia was reduced in these conditions. It is concluded that there are at least two sources for the CSF [HCO3-] increase in hypercapnia; one formed in the CNS and dependent on carbonic anhydrase, and the other derived from plasma [HCO3-] increase.
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PMID:The CSF HCO3 increase in hypercapnia relationshp to HCO3, glutamate, glutamine and NH3 in brain. 1 66

The effect of local hypercapnic acidosis or local hypocapnic alkalosis on pial arterioles were studied in anesthetized cats equipped with a cranial window for the direct observation of the pial microcirculation of the parietal cortex. Changes in PCO2 and pH of the extracellular fluid were induced by perfusing the space under the cranial window with artificial cerebrospinal fluid equilibrated with different concentrations of CO2, while PaCO2 was maintained constant. Hypercapnic acidosis dilated and hypocapnic alkalosis constricted pial arteioles markedly. The results indicate that a basis exists for considering CO2 as a mediator for local regulation of brain blood flow. The vasodilation associated with arterial hypercapnia was abolished by a reduction in CSF PCO2 equal in magnitude to the rise in arterial blood PCO2, suggesting that the action of CO2 is entirely local.
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PMID:Local mechanism of CO2 action of cat pial arterioles. 1 34

The authors report the values of mean hemispheric blood-flow and cerebral arterial consumption they found in 34 neurosurgical comatous cases in acute state. In basal conditions, mean values of mean hemispheric bloodflow and oxygen consumption are lowered. There seems to be a relation between the values found and the comatous stage on one hand, the prognosis on the other hand. The cerebral response to hypercapnia (16 assays) allows to separate 2 groups, one with a noticeable improvement of cerebral bloodflow, the other with only a minimal response. There was no significant variation of cerebral oxygen consumption in both group. Cerebral response to CO2 seems to be clearly related to the stage of coma (low in the most severe cases) but pronostic incidence remained uncertain. A hypertensive test by means of Aramine (18 assays) allows to separate 3 groups : 1 group (8 cases) where the mean hemispheric bloodflow remained stable during hypertension as did the cerebral oxygen consumption -(autoregulation remained unchanged), 1 group (4 cases) where mean hemispheric bloodflow and cerebral oxygen consumption were lowered (excessive autoregulation), 1 group (6 cases) where mean hemispheric bloodflow increases clearly while under Aramine perfusion (loss of autoregulation). Those dynamic tests, either hypercapnic or hypertensive, allow, in comparing oxygen consumption variations with cerebral bloodflow variations, the distinction between : patients where metabolic autoregulation seems maintained (good prognosis) - (10 cases), patients where metabolic regulation is lost with either "luxury perfusion" (14 cases) - poor prognosis, or "insufficient perfusion" (10 cases). The authors are discussing the treatment concerning those last mentioned patients.
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PMID:[Value of cerebral metabolic exploration in post-traumatic coma states in the acute phase]. 1 86

In experiments with rats, subjected to single and repeated simultaneous effect of hypercapnia, hypoxia and cooling, contents of pyridine nucleotides (NAD, NADP, NAD-H2 and NADP-H2) and macroergic substances were studied and also the activity of dehydrogenases of the pentose pathway was determined in brain and myocardium. In brain NADP was not practically determined and in heart its content was increased after the first and the second treatments. Content of NADP-H2 was distinctly decreased in both tissues after the single treatment. NAD was not altered in the tissues in all the periods studied. The amount of NAD-H2 was decreased in brain after the single treatment and it was increased in myocardium after the repeated one. In the activity of dehydrogenases marked alterations were not observed. Total macroergic substances were not altered in brain after the single treatment and after the repeated one they were increased mainly due to the ATP increase. In myocardium total macroergic substances were decreased after the both treatments.
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PMID:[Pyridine nucleotide content in the brain and myocardium of rats under combined effect of hypercapnia, hypoxia and cooling]. 1 90

The effects of induced hypo- and hypercapnia upon the rate of hydroxylation of tryptophan and tyrosine in the rat brain were studied by measuring the accumulation of 5-HTP and DOPA following administration of the aromatic L-aminoacid decarboxylase inhibitor 3-hydroxybenzylhydrazine HCl (NSD 1015). The results suggest that the hydroxylation of tryptophan varies directly with the tissue Po2. On the other hand, the hydroxylation of tyrosine did not show a simple relationship to Po2 but appeared to be influenced by pH changes.
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PMID:Effect of hypercapnia and hypocapnia on tryptophan and tyrosine hydroxylation in rat brain. 1 38

CSF HCO3- increases more than plasma HCO3- in hypercapnia, and there are at least two sources for the CSF HCO3- increase--one derived from the simultaneous increase in plasma HCO3-, and the other, HCO3-formed from hydration of CO2 in the choroid plexus and glia and susceptible to inhibition by acetazolamide (J. Appl. Physiol. 38: 504-512, 1975). It was proposed that the H+ formed in the CNS in CO2 hydration is actively exchanged for plasma Na+ utilizing the Na-K ATPase pump. H+ transport from the CNS was therefore studied in four groups of dogs breathing 5% CO2 at constant VA for 4 h with repeated injections of saline, acetazolamide 5 mg/ml, ouabain 0.1 mg/ml, and acetazolamide and ouabain together into lateral cerebral ventricles. Arterial HCO3-increased 2.5 meq/l at 4 h of hypercapnia in all groups. CSF HCO3-increased 5.8 meq/l in the saline-injected animals, but it increased only about 2 meq/l and equaled plasma HCO3- rise in the other three groups. Therefore CNS HCO3- formation in hypercapnia can be blocked by inhibiting the CO2 hydration reaction with acetazolamide or by blocking H+ removal by inhibiting Na-K ATPase with ouabain. The data support the thesis of active H+ removal from the CNS in exchange for plasma Na+ in hypercapnia.
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PMID:H+ transport from CNS in hypercapnia and regulation of CSF [HCO3-]. 1 62


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