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Query: UMLS:C0038454 (stroke)
 147,016 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We conducted regional cortical blood flow studies using the xenon-133 clearance technique on 12 volunteers during the administration of 25% and 50% N2O and during baseline conditions (breathing room air or 100% O2). Global cortical blood flow was very highly significantly increased above baseline measures in all subjects by 50% N2O (mean increase 37% above 100% O2 condition). A smaller but still significant increase was observed with 25% N2O. Analysis of regional cortical blood flow revealed heterogeneity in the pattern of changes; that is, the baseline pattern was altered by the inhalation of N2O, most often resulting in an accentuation of relative frontal blood flow. The anterior-posterior gradient in N2O-induced blood flow changes differs from that observed with simple vasodilatory agents, such as CO2, with which the increase is purely systemic and the baseline pattern is preserved. This indicates that N2O has differential effects on cerebral metabolism that may well reflect the typical alterations in experiential state reported by subjects.
Stroke 1990 Sep
PMID:Effects of nitrous oxide on global and regional cortical blood flow. 239 66

The purpose of the study was to compare the blood lactate accumulation and other metabolic responses by trained swimmers with varying degrees of controlled frequency breathing (CFB). Fourteen (eight males, six females) trained collegiate swimmers performed peak and submaximal tethered swim tests during which breathing was restricted to one breath every two (BR2), four (BR4), six (BR6) (N = 13), and eight (BR8) (N = 9) strokes. All submaximal swim tests were of 4-min duration, with tethered swim resistance at a constant 80% of peak resistance. Measures included oxygen uptake (VO2), carbon dioxide production (VCO2), tidal volume (TV), ventilation (VE), estimated alveolar partial pressure of O2 (PAO2) and CO2 (PACO2), respiratory exchange ratio (RER), stroke rate (SR), heart rate (HR), and change in blood lactates (delta LA). Significant differences were associated with increases in CFB for all variables except HR and delta LA. Although CFB was associated with reduced VE, compensatory adaptations resulted in increases in TV, PACO2, and SR and decreases in PAO2 and RER. VCO2 was greater for BR2 than all others, and VO2 for BR2 was greater than BR8. The results indicate that CFB does not affect blood lactate accumulation but does enhance oxygen extraction. CFB may impede proper stroke mechanics.
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PMID:Metabolic responses to controlled frequency breathing in competitive swimmers. 240 39

The effects of plasma-volume (PV) expansion on stroke volume (SV) (CO2 rebreathing) during submaximal exercise were determined. Intravenous infusion of 403 +/- 21 ml of a 6% dextran solution before exercise in the upright position increased SV 11% (i.e., 130 +/- 6 to 144 +/- 5 ml; P less than 0.05) in untrained males (n = 7). Further PV expansion (i.e., 706 +/- 43 ml) did not result in a further increase in SV (i.e., 145 +/- 4 ml). SV was somewhat higher during supine compared with upright exercise when blood volume (BV) was normal (i.e., 138 +/- 8 vs. 130 +/- 6 ml; P = 0.08). PV expansion also increased SV during exercise in the supine position (i.e., 138 +/- 8 to 150 +/- 8 ml; P less than 0.05). In contrast to these observations in untrained men, PV expansion of endurance-trained men (n = 10), who were naturally PV expanded, did not increase SV during exercise in the upright or supine positions. When BV in the untrained men was increased to match that of the endurance-trained subjects, SV was observed to be 15% higher (165 +/- 7 vs. 144 +/- 5 ml; P less than 0.05), whereas mean blood pressure and total peripheral resistance were significantly lower (P less than 0.05) in the trained compared with untrained subjects during upright exercise at a similar heart rate. The present findings indicate that exercise SV in untrained men is preload dependent and that increases in exercise SV occur in response to the first 400 ml of PV expansion. It appears that approximately one-half of the difference in SV normally observed between untrained and highly endurance-trained men during upright exercise is due to a suboptimal BV in the untrained men.
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PMID:Exercise stroke volume relative to plasma-volume expansion. 245 58

Cerebral blood flow (CBF) was measured with 133xenon inhalation and single photon emission computed tomography in 33 cases of internal carotid artery occlusion, in the resting state and 25 minutes after acetazolamide (Diamox) administration. The patient population consisted of 24 males and nine females with a mean age of 57 years, who presented with transient ischemic attacks or stroke. Acetazolamide inhibits carbonic anhydrase, and CBF increases as a result of dilatation of cerebral arteries due to CO2 accumulation. The mean CBF was 46 ml/100/g/min on the affected hemisphere and 56 ml/100/g/min on the unaffected hemisphere. The mean CBF value obtained by the same method in 10 normal volunteers was 55 ml/100/g/min. Thus, in the patients, CBF decreased on the affected side. The average increase in CBF after acetazolamide administration was 9% on the affected side and 17% on the unaffected side. The average increase in 10 normal volunteers was 32%. The reduced cerebral arterial reactivity to acetazolamide administration was bilateral in the patient group, which suggests that the cerebral arteries were dilated in order to maintain normal CBF. Extra-intracranial (EC-IC) bypass surgery was performed in nine patients. Preoperatively, the mean CBF was 48 ml/100 g/min on the affected side and 57 ml/100 g/min on the unaffected side; the postoperative CBF was 48 ml/100 g/min on the affected side and 56 ml/100 g/min on the unaffected side. Thus, there was no notable change in CBF on either side after surgery.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Measurement of cerebral blood flow by single photon emission computed tomography in cases of internal carotid artery occlusion]. 247 52

The effect of the angiotensin-converting enzyme (ACE) inhibitor captopril on regional cerebral blood flow (rCBF) was studied in 12 patients within 5 days after their first acute stroke. rCBF was studied by xenon-133 inhalation and single-photon emission computed tomography (SPECT) scan before and 1 h after oral administration of 25 mg captopril. No increase in rCBF was observed in any of the 12 patients included in the study. In only one patient was there a slight redistribution of blood flow in favor of the low-flow area, but the absolute flow value did not increase. Captopril did not cause any significant change in mean hemispheric blood flow, mean arterial blood pressure (MAP), or end-expiratory CO2 fraction (FECO2). The assumption that ACE inhibition might increase cerebral blood flow in the periinfarct zone and preserve some still viable brain tissue could not be verified in the present study.
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PMID:Angiotensin-converting enzyme inhibition and regional cerebral blood flow in acute stroke. 248 Nov 86

In patients with an internal carotid artery (ICA) occlusion who suffer from ipsilateral transient ischaemic attacks or minor stroke extra/intracranial (EC/IC) bypass surgery may be useful only where there is insufficient collateral supply. The transcranial Doppler CO2 test offers a simple method of investigating the residual autoregulatory capacity which gives quantitative information about the efficiency of the collaterals. In 155 patients with 162 ICA occlusions there was a significant correlation between a markedly decreased or exhausted autoregulatory capacity and a recent ipsilateral ischaemic event (p less than 0.001). The Doppler CO2 test may enable the exclusion of patients not in need of EC/IC bypass surgery. In the reported series this affected more than 80% of all ICA occlusions.
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PMID:The Doppler CO2 test to exclude patients not in need of extracranial/intracranial bypass surgery. 249 3

Apnea is often observed during high-frequency oscillatory ventilation (HFOV). This study on anesthetized dogs varied the oscillator frequency (f) and determined the stroke volume (SV) at which apnea occurred. Relaxation functional residual capacity (FRC) and the eupneic breathing end-tidal CO2 level were held constant. Airway pressure and CO2 were measured from a side port of the tracheostomy cannula. An arterial cannula was inserted for blood gas analysis. Diaphragm electromyogram (EMG) was recorded with bipolar electrodes. Apnea was defined as the absence of phasic diaphragm EMG activity for a minimum of 60 s. During HFOV, SV was increased at each f (5-40 Hz) until apnea occurred. The apnea inducing SV decreased as f increased. SV was minimal at 25-30 Hz. Frequencies greater than 30 Hz required increased SV to produce apnea. The f-SV curve was defined as the apneic threshold. Increased FRC resulted in a downward shift (less SV at the same f) in the apneic threshold. Elevated CO2 caused an upward shift (more SV at the same f) in the apneic threshold. These results demonstrate that the apnea elicited by HFOV is dependent on the interaction of oscillator f and SV, the FRC, and CO2.
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PMID:High-frequency ventilation-induced apnea: interaction of frequency, volume, FRC, and CO2. 250 Dec 85

We studied the hemodynamic effects of acute alterations in PaCO2 in ten ventilator-dependent children after open heart surgery. Despite end-tidal CO2 monitoring, five children inadvertently developed PaCO2 greater than 50 torr during the study. Increasing and decreasing PaCO2 in these children resulted in significant parallel changes in cardiac index (CI), oxygen delivery, physiologic shunt, mean pulmonary pressure, and right ventricular stroke work index, and inverse changes in systemic vascular resistance index (p less than .01). No significant hemodynamic changes were observed with alterations in PaCO2 in children whose PaCO2 remained less than 50 torr. These findings are partly related to significantly larger reductions in PaCO2 which occurred in the hypercarbic children compared to the others (25 vs. 12 torr; p less than .001). Heart rate, mean arterial BP, and venous filling pressures did not change significantly in either group. We conclude that mean alterations in PaCO2 less than or equal to 12 torr (range 28 to 50) have no significant effect on CI in children after open heart surgery. However, moderate hypercarbia and its correction to a mean PaCO2 of 30 torr are associated with significant effects on central hemodynamics. Moreover, no significant changes in the commonly monitored physiologic variables were observed despite large variations in PaCO2.
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PMID:Hemodynamic responses to PaCO2 in children after open heart surgery. 250 38

The cardiovascular effects of exogenously administered histamine were investigated in conscious newborn piglets aged 10-11 days during normoxia (21% (v/v) O2) and during isocapneic alveolar hypoxia (10% O2, 3% CO2, 87% N2) to determine its influence on preexisting vascular tone. In the first set of experiments (n = 6), four histamine doses (1,10,50,100 micrograms/kg) were tested in sequence during normoxia. Histamine was injected intravenously and cardiovascular variables were recorded. Heart rate increased at all doses studied. Pulmonary and systemic arterial pressures, cardiac output and stroke volume were unchanged at the low histamine doses (1 and 10 micrograms), but all decreased at the high doses (50 and 100 micrograms). Pulmonary and systemic vascular resistances were unchanged at each dose. In the second set of experiments (n = 7), two histamine doses (1 and 5 micrograms/kg) were administered during alveolar hypoxia. Hypoxia caused increases in heart rate and pulmonary arterial pressure and resistance. After injection of each dose of histamine, pulmonary pressure and resistance decreased but remained higher than baseline. No other measured cardiovascular variables were altered. Thus, during normoxia histamine did not alter vascular tone, but high doses did adversely affect myocardial function. During alveolar hypoxia histamine caused weak pulmonary vasodilation at doses that did not alter systemic vascular tone. Histamine is not a potent modifier of the circulation in the newborn piglet during conditions of normoxaemia or hypoxaemia.
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PMID:Cardiovascular response to histamine during normoxaemia and hypoxaemia in piglets. 250 66

We evaluated the topographic distributions of regional cerebral blood flow in 51 normal subjects (mean age 41 years) by the xenon-133 inhalation technique. Forty-five of these subjects were divided by age into young normals less than 30 years old (mean age 24 years), middle-aged normals 30-50 years old (mean age 40 years), and elderly normals greater than 50 years old (mean age 62 years); there were 15 subjects in each group. The distributions of vascular CO2 reactivity to hypocapnia were also evaluated in 20 of the normal subjects (mean age 34 years), including 11 younger normals less than 30 years old (mean age 24 years) and nine older (middle-aged or elderly) normals greater than or equal to 30 years old (mean age 45 years). The hyperfrontal distribution of regional cerebral blood flow observed in the young and middle-aged normals was not observed in the elderly normals. The hyperfrontal distribution of vascular CO2 reactivity observed in the younger normals was absent in the older normals. In addition, the correlation between regional cerebral blood flow and vascular CO2 reactivity observed in the younger normals was disturbed in the older normals. The data show a hyperfrontal distribution of regional cerebral blood flow in normal subjects that diminishes during the fifth and sixth decades, along with a distribution of vascular CO2 reactivity in younger normal subjects that is not homogeneous throughout the frontoparietal regions.(ABSTRACT TRUNCATED AT 250 WORDS)
Stroke 1989 Dec
PMID:Changes in hyperfrontality of cerebral blood flow and carbon dioxide reactivity with age. 251 91


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