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

A polystyrene-covered platinum electrode (100-150 mum diameter) has been used to measure cortical tissue oxygen tension in baboon brains. The method of preparation, calibration, and the importance of small residual current (less than 40 nA) as an attribute of a reliable electrode, are described. With electrodes of this size, there was a large (16 +/- 12nA/torr) and linear current output with pO2 changes. The effect of avrious gases in addition to oxygen is described; halothane inhalation increases the apparent pO2 and hydrogen, used for blood flow estimations, reduces the recorded pO2. In 48 separate electrode placements in 13 baboons, the mean cortical qo2 was 23.8 +/- 12 mm Hg, with a range from 1-79 mm Hg; following occlusion of one middle cerebral artery, 37 electrodes recorded a pO2 of less then 5 mm Hg pO2 Oscillations were invariably noted in control conditions, independent of blood pressure; these waves disappeared during MCA occlusion and appeared to be augmented following release of the clip. Blood pressure "spikes" produce immediate and synchronous changes in all electrodes entirely different from the spontaneous waves. Such blood pressure changes may mask the true effect of hypercapnia on tissue pO2 and, if ignored, may lead to erroneous assumptions regarding local neural control of the circulation, the increased pO2 secondary to hypertension being regarded as evidence of regional vasodilation. A SUdden change in inspired pO2-the "air test"-was performed in control conditions and following the ischaemic insult, and the rate of change of cortical pO2 compared. The gradient was significantly greater (P less than 0.05) following ischaemia, suggesting a changed ratio in the tissue's flow to oxygen requirements and/or a persisting vasodilatation.
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PMID:Measurements of oxygen tension in the cerebral cortex of baboons. 124 79

Cortical tissue oxygen measured by a platinum cathode, and cerebral blood flow recorded by a hydrogen clearance technique, were measured in 13 baboons before, during and after temporary occlusion of the middle cerebral artery. Mean control pO2 was 23.8 +/- 14 mm Hg and mean flow 51.3 +/- 12 ml/100g/min. During the occlusion, there was a gradation in pO2 from values in the opercular area of 3.6 +/- 5.9 mm Hg, to values in the high parietal area of 11.9 +/- 11.7, these being statistically different (P less than 0.05) from each other. The corresponding flow values were 5.5 +/- 7.5 (opercular) and 22.3 +/- 21.7 ml/100 g/min parietal (P less than 0.01). Following removal of the MCA clip, between 20% and 30% of the electrodes registered an early hyperoxia and hyperaemia, which lasted up to 5 min. A late and prolonged hyperoxia, with less evidence of hyperaemia, was also noted in about 20%. The mean tissue pO2, however, at 5-min intervals up to 40 min following the removal of the clip only reached 60-80% of control values in the most ischaemic areas. Only the parietal region showed a mean pO2 above control levels. The mean flow data were uniformly reduced in all regions to about 80% of control values. During and after a second occlusion in 6 animals, similar changes were noted but with even fewer instances of hyperoxia. The mean oxygen and flow results were lower than with the first occlusion, but the reduction was not significant. There was no overall effect of hypercapnia on cortical tissue pO2 during the control period, but there was a significant (P less than 0.05) reduction during the same procedure after the period of ischaemia. An increase in pO2 during hypercapnia could be observed if there were arousal responses of blood pressure "spikes".
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PMID:Changes in regional cortical tissue oxygen tension and cerebral blood flow during temporary middle cerebral artery occlusion in baboons. 124 80

Anesthetic management during 85 STA-MCA anastomoses with or without encephalo-myosynangiosis for 64 patients with Moyamoya disease was evaluated retrospectively. Anesthetic agents included nitrous oxide-NLA (GONLA), nitrous oxide-halothane (GOF), nitrous oxide-enflurane (GOE), and their combinations. Slight hypercarbia (40 mmHg less than PaCO2 less than 50 mmHg) was essential to avoid cerebral ischemia. Several procedures to control heart rate by beta blockade or to control hypertension by nitroglycerin were required, because tachycardia and hypertension interfered with fine surgical procedure. During microsurgery HR of GONLA anesthetized patients was significantly lower. Postoperatively the patients anesthetized by GOE showed significantly lower PaCO2 compared with the GONLA anesthetized patients. So we recommend GONLA for anastomosis in patients with Moyamoya disease.
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PMID:[Anesthetic management of revascularization for moyamoya disease]. 192 Jul 89

Cerebrovascular CO2 reactivity was studied in 40 healthy subjects (HSs) and 40 patients suffering from cerebrovascular disorders (CVD). Transcranial Doppler (TCD) sonography was used to investigate MCA flow velocity modifications during PaCO2 changes induced by ventilatory rate modifications and closed-circuit air re-breathing. HS responses were correlated with age, whereas the roles of either multiple ischemic brain lesions or carotid occlusions were studied in the Pt group. Results were as follows: i) age did not prove to affect vasomotor response to PaCO2 variations; ii) in hypercapnia, patients with multifocal ischemic lesions showed an impaired response in both hemispheres, whereas altered vasoreactivity was unilateral in patients with carotid occlusion (and ipsilateral to the thrombosis); iii) no significant differences were found between HS and Pt responses in hypocapnia. These findings confirm previous reports obtained with the 133 Xenon technique, stressing the usefulness of cerebrovascular reactivity investigation in CVD pts for diagnostic and prognostic purposes.
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PMID:Pathophysiology of the vasomotor reactivity to hypo- and hypercapnia: role of aging and chronic cerebrovascular disorders. 251 48

It is has been demonstrated that clinical outcome following head injury is correlated with the reactivity of the cerebrovasculature to carbon dioxide changes. Since CBF measurements are difficult to perform in these patients, a new technique is proposed utilizing the ICP response to capnic stimuli. In 40 head injured patients, the responses of ICP, pressure volume index (PVI) and middle cerebral artery velocities to hypocapnia and to hypercapnia were determined. Hypocapnia reduced ICP and MCA velocity while hypercapnia was followed by ICP and MCA velocity increases. Both changes were in the same magnitude supporting the concept the global ICP response reflects vascular reactivity. The fact that the velocity response to hypocapnia in lesioned hemispheres was less compared to the ICP response indicates the loss of ability to dilate in injured vessels and is consistent with earlier findings relating reduced reactivity to poor outcome.
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PMID:Measurement of vascular reactivity in head injured patients. 790 77

Cerebrovascular carbon dioxide (CO2) reactivity is an important hemodynamic index in cerebrovascular disease. In the present study T2*-weighted magnetic resonance image (T2* WI) was evaluated as a non-invasive method to investigate changes in CO2 reactivity. Fourteen rats were subjected to permanent or, 30 and 90 min of temporary middle cerebral artery occlusion. A series of T2* WIs and diffusion-weighted magnetic resonance images (DWI) was performed hourly under normo- and hypercapnic conditions. Triphenyltetrazolium chloride (TTC) staining of brain sections was obtained at the end of experiment to evaluate ischemic damage. During ischemia, a 4-6% signal increase upon hypercapnia was observed on T2* WI in the non-ischemic hemisphere, while no such reactivity was seen in the putamen and cortex ipsilateral to the MCA occlusion. After reperfusion, CO2 reactivity recovered in the putamen and cortex in the 30 min ischemia group and in the cortex alone of the 90 min ischemia groups. The areas with irreversible CO2 reactivity dysfunction coincidentally revealed no recovery on DWI and lack of TTC staining. The results indicate that T2* WI can be used to monitor changes in CO2 reactivity after various ischemic insults that may indicate tissue viability.
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PMID:T2*-weighted magnetic resonance imaging of cerebrovascular reactivity in rat reversible focal cerebral ischemia. 902 80

In occlusive cerebrovascular disease cerebral blood flow (CBF) autoregulation can be impaired and constant CBF during fluctuations in blood pressure (BP) cannot be guaranteed. Therefore, an assessment of cerebral autoregulation should consider not only responsiveness to CO2 or Diamox. Passive tilting (PT) and Valsalva maneuver (VM) are established tests for cardiovascular autoregulatory function by provoking BP changes. To develop a comprehensive test for vasomotor reactivity with a potential increase of sensitivity and specificity, the authors combined these maneuvers. Blood pressure, corrected to represent arterial pressure at the level of the circle of Willis, middle cerebral artery Doppler frequencies (DF), heart rate (HR) and endtidal partial pressure of CO2 (PtCO2) were measured continuously and noninvasively in 81 healthy subjects (19-74 years). Passive tilt and Valsalva maneuver were performed under normocapnia (mean, 39 + 4 mmHg CO2) and under hypercapnia (mean, 51 + 5 mm Hg CO2). Resting BP, HR, and DF increased significantly under hypercapnia. Under normocapnia and hypercapnia, PT induced only minor, nonsignificant changes in mean BP at the level of the circle of Willis compared to baseline (normocapnia: + 2 + 15 mm Hg; hypercapnia: -3 +/- 13 mm Hg). This corresponded with a nonsignificant decrease of the mean of DF (normocapnia: -4 +/- 11%; hypercapnia -6 +/- 12%). Orthostasis reduced pulsatility of BP by a predominantly diastolic increase of BP without significant changes in pulsatility of DF. Valsalva maneuver, with its characteristic rapid changes of BP due to elevated intrathoracic pressure, showed no significant BP differences in changes to baseline between normocapnic and hypercapnic conditions. Under both conditions the decrease in BP in phase II was accompanied by significantly increased pulsatility index ratio (PIDF/PIBP). Valsalva maneuver and PT as established tests in autonomic control of circulation provoked not only changes in time-mean of BP but also in pulsatility of BP. The significant increase in pulsatility ratio and decrease of the DF/BP ratio during normocapnia and hypercapnia indicated preserved CBF autoregulation within a wide range of CO2 partial pressures. Hypercapnia did not significantly influence the autoregulatory indices during VM and PT. Physiologically submaximally dilated cerebral arterioles can guarantee unchanged dynamics of cerebral autoregulation. Combined BP and MCA-DF assessment under hypercapnia enables investigating the effect of rapid changes of blood pressure on CO2-induced predilated cerebral arterioles. Assuming no interference of hypercapnia-induced vasodilation, VM, with its rapid, distinct changes in BP, seems especially to be adequate provocation for CBF autoregulation. This combined vasomotor reactivity might provide a more sensitive diagnostic tool to detect impaired cerebral autoregulation very early.
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PMID:Multimodality monitoring during passive tilt and Valsalva maneuver under hypercapnia. 1020 9

The brain of neurosurgical patients are exposed to various manipulations in the ICU or during surgery. Under such conditions brain O2 balance may become negative and as a result brain vitality and function will deteriorate. In order to evaluate brain vitality in real time it is important to measure more than one parameter. The multiparametric monitoring system used in our previous study to monitor comatose patients (Mayevsky et al., Brain Res. 740: 268-274, 1996) was changed into a "simplified" tissue spectroscope for real time monitoring of brain O2 balance. Mitochondrial function was evaluated by monitoring the NADH redox state by surface fluorometry. Microcirculatory blood flow was assessed by laser Doppler flowmetry. The combined optical probe was located on the surface of the brain during various neurosurgical procedures and the responses were recorded and presented in real time to the surgeon. A total of 32 patients were monitored during various procedures. The results could be summarized as follows: 1. Hypercapnia led to 3 different types of responses. In two patients the 'stealing' like event was recorded. In the other 7 patients the responses to high CO2 was not detectable. In the last group of 6 patients a clear CBF elevation was recorded with variable response of mitochondrial NADH. 2. Our monitoring device was able to evaluate the efficacy of the STA-MCA anastomosis during aneurysm surgery. 3. A significant correlation was recorded between CBF and NADH redox state during changes in blood pressure, papaverine injection, spontaneous drop in blood supply to the brain or during releasing of high ICP levels. We conclude that in order to evaluate the metabolic state of the brain during neurosurgical procedures it is necessary to monitor both CBF and mitochondrial NADH by using the tissue spectroscope.
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PMID:The evaluation of brain CBF and mitochondrial function by a fiber optic tissue spectroscope in neurosurgical patients. 1216 49

The reactivity of cerebral arteries have been examined in three groups of patients (young, middle and adult ages). The medium meanings of the blood flow velocity (V) and the pulsativity index (Pi) were registrated in MCA and PCA under hypercapnia, hyperventilation and light stimulation. It was revealed that the reactivity of cerebral arteries in middle and especially in adult groups was decreased.
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PMID:[Decrease of reactivity of cerebral arteries at late stages of life]. 1257 94

The new two-breath CO(2) method was employed to test the hypotheses that small alterations in arterial P(CO(2)) had an impact on the magnitude and dynamic response time of the CO(2) effect on cerebrovascular resistance (CVRi) and the dynamic autoregulatory response to fluctuations in arterial pressure. During a 10-min protocol, eight subjects inspired two breaths from a bag with elevated P(CO(2)), four different times, while end-tidal P(CO(2)) was maintained at three levels: hypocapnia (LoCO(2), 8 mmHg below resting values), normocapnia, and hypercapnia (HiCO(2), 8 mmHg above resting values). Continuous measurements were made of mean blood pressure corrected to the level of the middle cerebral artery (BP(MCA)), P(CO(2)) (estimated from expired CO(2)), and mean flow velocity (MFV, of the middle cerebral artery by Doppler ultrasound), with CVRi = BP(MCA)/MFV. Data were processed by a system identification technique (autoregressive moving average analysis) with gain and dynamic response time of adaptation estimated from the theoretical step responses. Consistent with our hypotheses, the magnitude of the P(CO(2))-CVRi response was reduced from LoCO(2) to HiCO(2) [from -0.04 (SD 0.02) to -0.01 (SD 0.01) (mmHg x cm(-1) x s) x mmHg Pco(2)(-1)] and the time to reach 95% of the step plateau increased from 12.0 +/- 4.9 to 20.5 +/- 10.6 s. Dynamic autoregulation was impaired with elevated P(CO(2)), as indicated by a reduction in gain from LoCO(2) to HiCO(2) [from 0.021 +/- 0.012 to 0.007 +/- 0.004 (mmHg x cm(-1) x s) x mmHg BP(MCA)(-1)], and time to reach 95% increased from 3.7 +/- 2.8 to 20.0 +/- 9.6 s. The two-breath technique detected dependence of the cerebrovascular CO(2) response on P(CO(2)) and changes in dynamic autoregulation with only small deviations in estimated arterial P(CO(2)).
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PMID:Two-breath CO(2) test detects altered dynamic cerebrovascular autoregulation and CO(2) responsiveness with changes in arterial P(CO(2)). 1504 83


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