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Biomedical subjects

W Rautenberg

Publications and source records attributed to W Rautenberg.

At least 37 records · Page 2Linked to original sources
PubMed1990

Compensatory mechanisms in patients with asymptomatic carotid artery occlusion.

Twelve patients with asymptomatic occlusion of one (n = 8) or both (n = 4) internal carotid arteries were examined by positron emission tomography (PET) and transcranial Doppler ultrasound. PET measurements included the determination of the regional cerebral blood flow (rCBF), oxygen extraction ratio (rOER), cerebral metabolic rate of oxygen (rCMRO2), and cerebral metabolic rate of glucose consumption (rCMRGlc). Transcranial Doppler ultrasound (TCD) was used to determine the pathways and efficacy of collateralization via the circle of Willis and included spectrum analysis of flow velocities within the middle and anterior cerebral arteries as well as vasoreactivity tests. In correspondence with ultrasound evidence of a haemodynamically effective intracranial collateral circulation no significant differences between patients and controls were observed for rOER, rCMRO2 and rCMRGlc, but rCBF was globally reduced. Furthermore, in all patients with unilateral carotid occlusion PET excluded side asymmetries of any parameter studied. In contrast, flow velocity parameters measured by TCD were significantly reduced ipsilateral and significantly increased contralateral to the carotid obstruction. Vasodilative capacities, however, remained preserved even in the territory of the occluded carotid system. These data indicate that patients with asymptomatic carotid occlusion compensate by haemodynamic and not by metabolic mechanisms in contrast to symptomatic patients.

Aged↗
PubMed1990

Shivering and cardiorespiratory responses during normocapnic hypoxia in the pigeon.

To study the inhibitory effect of hypoxia on the cold defense mechanism, pigeons were exposed at low ambient temperature (5 degrees C) to various inhaled gas mixtures: normoxia [0.21 fractional concentration of O2 (FIO2)], hypoxia (0.07 FIO2), and normocapnic hypoxia (0.07 FIO2 + 0.045 FICO2). Electromyographic (EMG) activity indicative of shivering thermogenesis was inhibited during hypoxia, and body temperature (Tre) fell by 0.09 degrees C/min. Respiratory frequency (f) and minute ventilation (VE) increased by 143 and 135%, respectively, compared with normoxia, but tidal volume (VT) was not changed. PO2, PCO2, and O2 contents in the arterial and mixed venous blood were decreased and pH was enhanced. During normocapnic hypoxia, shivering EMG was present at approximately 50% of the normoxic intensity; Tre fell by only 0.04 degrees C/min. Arterial and mixed venous PCO2 and pH were the same as during normoxia, but VE increased by 430% because of twofold increases in both f and VT. During normocapnic hypoxia, arterial PO2 and O2 content were higher than during hypoxia alone. We conclude that the persistence of shivering during normocapnic hypoxia is due to maintenance of critical levels of arterial PO2 and O2 content.

Animals↗
PubMed1989

High-resistance Doppler flow pattern in extracranial carotid dissection.

Internal carotid artery dissection is an increasingly recognized cause of cerebrovascular events. The diagnosis is conventionally established on the basis of characteristic clinical symptoms and arteriographic findings. However, the presence of characteristic hemodynamic features detected by ultrasound may already suggest the diagnosis, even in atypical cases. This is demonstrated in 16 (76%) of 22 patients with internal carotid artery dissection. An intense systolic low-frequency Doppler signal of alternating flow direction accessible in the neck, either along the extent of a luminal tapering stenosis or proximal to a severe obstruction at the skullbase, indicated this diagnosis. Resolution or decreasing stenosis may similarly be diagnosed noninvasively, as shown by results from subsequent arteriograms in 14 patients (64%). This occurred suddenly during sequential follow-up between 2 days and 30 weeks (mean, 6 weeks) after the diagnosis was made.

Adolescent↗
PubMed1989

Long-term follow-up of carotid disease: clinical and ultrasound aspects.

Various non-invasive techniques were used to study clinical and ultrasound aspects of extracranial arterial disease. cw Doppler was used prospectively to study the natural history of asymptomatic extracranial arterial disease (greater than 50% carotid stenosis, subclavian steal phenomena) in 401 patients. Whereas the cumulative death rate was high (44%) at 8 years, the stroke rate was low (6%). Progression of the vascular processes during follow-up correlated with later cerebrovascular events. Transcranial PW Doppler was used to study the intracranial collaterlisation in 151 asymptomatic patients with significant extracranial lesions. The majority of patients showed excellent collateralisation. The natural history of non-stenotic plaques (less than 30% carotid stenosis) was studied by means of high-resolution (10 MHz) duplex system analysis. Whilst most plaques remained constant during the subsequent follow-up period progression was seen in 24% and regression in 10%.

Carotid Artery Diseases↗
PubMed1988

Pulsed Doppler assessment of innominate artery obstructive diseases.

In 14 patients with severe stenosis or occlusion of the innominate artery a new high-energy, low-frequency (2 MHz) pulsed Doppler ultrasound method was used to investigate blood flow velocity patterns of both intrathoracic and intracranial cerebral arteries. Direct acquisition and evaluation of the innominate artery at its origin near the aortic arch enabled separation of it from adjacent arteries and reliable differentiation of stenosis from occlusion. Transcranial recordings from the basal cerebral arteries showed abnormal Doppler signals in 12 patients (86%). Among these abnormalities, observation of a latent steal phenomenon was closely related to the prevalence of cerebrovascular events. This latent steal phenomenon was characterized by a transient reduction of orthograde blood flow in the ipsilateral anterior, middle, and posterior cerebral arteries or in the basilar artery during postischemic hyperemia of the upper extremities. The predictive value of the latent steal phenomenon for the management and follow-up of asymptomatic patients with severe innominate artery obstructions is discussed.

Adult↗
PubMed1988

The subclavian steal phenomenon: a common vascular disorder with rare neurologic deficits.

Three hundred twenty-four patients with reversed vertebral artery blood flow were reviewed for cerebrovascular events. Neither the presence nor the type of vertebral artery steal (permanent, n = 204; intermediate, n = 120) determined neurologic symptoms, which rather were related to coincidental carotid obstructions or abnormal flow velocity patterns in the basilar artery. Most patients (n = 209; 64%) had no neurologic symptoms. Hemispheric events (n = 99; 31%) occurred most frequently in patients with additional carotid lesions and nonhemispheric events in a few patients (n = 16; 5%) often with bilateral vertebral steal. Intracranial Doppler studies from the vertebral and basilar arteries excluded spontaneous retrograde basilar artery perfusion in any of a subgroup of 50 patients examined in addition. Thus, blood flow reversal in extracranial arteries is a marker for atherosclerotic vascular disease in general, rather than an indicator of a patient's risk to develop cerebrovascular events from hemodynamic insufficiency in the territory affected. Surgical treatment is discouraged for most patients with this benign flow abnormality.

Aged↗
PubMed1987

Transcranial Doppler ultrasound for the assessment of intracranial arterial flow velocity--Part 2. Evaluation of intracranial arterial disease.

Transcranial (TC) pulsed Doppler ultrasound was used to evaluate flow velocity within the intracranial basal cerebral arteries in 71 patients with cerebrovascular disease as revealed by arteriography. Abnormalities of the fast-Fourier transformed (FFT) Doppler spectra were used to detect and classify obstructive lesions as well as dilative arteriopathy of the carotid siphon, the middle, anterior, and posterior cerebral arteries, and the basilar artery. Functional stenosis due to large shunting volumes in patients with arteriovenous malformations and in the presence of significant collateralization of extracranial obstructive lesions were similarly diagnosed.

Blood Flow Velocity↗
PubMed1987

Transcranial Doppler ultrasound for the assessment of intracranial arterial flow velocity--Part 1. Examination technique and normal values.

We present the examination technique and normal values of flow velocity from intracranial basal cerebral arteries for a recently developed pulsed Doppler system operating at 2 MHz emitting frequency. Peak systolic, peak diastolic, and mean flow velocity values are analyzed from fast-Fourier transformed (FFT) Doppler spectra at selected depths for 50 presumed normal subjects ranging in age from 22 to 79 years. Interindividual variation is high for peak flow but moderate for mean flow velocity values, which hence are more likely to discriminate normal from abnormal. Flow velocity values within the posterior cerebral artery (PCA) and the basilar artery (BA) are significantly lower than in the anterior cerebral artery (ACA) and the middle cerebral artery (MCA), which is also unique in showing significantly decreasing values with increasing age: calculated mean flow velocities are 47.3 +/- 13.6 and 45.3 +/- 13.5 cm/sec in the ACA, and 58.4 +/- 8.4 and 44.7 +/- 11.1 cm/sec in the MCA in patients less than 40 years and greater than 60 years, respectively, but 34.2 +/- 7.8 and 29.9 +/- 9.3 (PCA) (patients less than 40 years and patients greater than 60 years), and 34.9 +/- 7.8 and 30.5 +/- 12.4 (BA) (patients less than 40 years and patients greater than 60 years). A new scanning system is introduced, which we suggest will reduce interindividual variations and improve the accurate separation of nearby vessels, which are major causes for the comparatively large standard deviations at present.

Adult↗
PubMed1987

Natural history of asymptomatic extracranial arterial disease. Results of a long-term prospective study.

The natural history of asymptomatic extracranial arterial disease (EAD) was studied prospectively in 339 patients admitted for serial ultrasound Doppler examinations. Annual mortality was high at 7%, but stroke mortality was low at 0.6%: 82 patients (24%) died during the follow-up period, which lasted up to seven years (median: 29 months), only 10 from stroke but 41 from cardiac causes. The risk of suffering a stroke without premonitory transient ischaemic attacks (TIAs) was similarly low at 0.4%. Progression of EAD was the only predictor established to indicate the individual patient's cerebrovascular prognosis among a series of criteria tested (age, sex, degree and extent of carotid and/or vertebral disease, risk factors and indicators of atherosclerosis). Deterioration of EAD was observed in 108 (36%) of 296 patients by repeated Doppler examination, 174 (59%) remained constant and 14 (5%) showed an improvement. The observed low rate of strokes without premonitory TIAs is not in favour for early carotid endarterectomy in the majority of neurologically asymptomatic patients.

Adult↗
PubMed1986

Cardiorespiratory responses to shivering in vagotomized pigeons during normoxia and hypoxia.

We measured respiratory, cardiovascular and blood gas responses to shivering during normoxia and hypoxia in five bilaterally, cervically vagotomized pigeons and compared these data with those previously reported in pigeons with intact vagi (Gleeson et al. 1986). Such neural section in birds denervates, among other receptors, the carotid bodies and intrapulmonary chemoreceptors. Normoxic breathing frequency (fR) and ventilation (VE) were decreased after vagotomy. Intact pigeons showed increases in oxygen consumption (VO2), tidal volume (VT), fR and VE during shivering. Vagotomized pigeons showed similar though slightly smaller increases in fR, VO2 and VE during shivering, but VT did not change. Normoxic heart rate was greater after vagotomy and was increased during shivering as in intact pigeons. Mean arterial blood pressure (MBPa) and stroke volume were not affected by vagotomy or shivering. At the onset of shivering both intact and vagotomized pigeons exhibited immediate increases in ventilation and heart rate. Exposure of vagotomized pigeons to hypoxic gas (fractional inspired oxygen concentration, FIO2 = 0.12) during cooling completely abolished shivering electromyogram (EMG) activity. In contrast, shivering in intact pigeons was not completely inhibited until the FIO2 fell below 0.10. We conclude that bilateral, cervical vagotomy in the pigeon causes hypoventilation and tachycardia during normoxia, but that these denervated birds are still able to rapidly effect cardiorespiratory adjustments to shivering. It is suggested that these responses are mediated mainly via afferent feedback from the shivering muscles. Hypoxia inhibits shivering in both intact and vagotomized birds and the mechanism is probably related to the reduced O2 delivery to the central structures that integrate thermoregulatory demand and coordinate appropriate responses.

Animals↗
PubMed1986

The effects of hypoxia on the metabolic and cardiorespiratory responses to shivering produced by external and central cooling in the pigeon.

Respiratory, cardiovascular and blood gas responses of pigeons to spinal cord cooling (36 +/- 1 degrees C), to ambient cooling (Ta = 5 degrees C) and to simultaneous spinal cord and ambient cooling were measured at three different levels of fractional inspired oxygen concentration (FIO2 = 0.209, 0.10 and 0.07). Shivering and the 'extra' VO2 provoked by ambient and/or spinal cord cooling were more or less reduced during hypoxic exposure depending on the intensity of cold stress and hypoxic states. At FIO2 = 0.10 shivering was markedly reduced and sometimes inhibited, whereas at FIO2 = 0.07 any pattern of cold tremor was inhibited. The accompanying cardiorespiratory responses were similar to those of thermoneutral controls exposed to the same FIO2. The amount by which VO2 was reduced in the pigeons exposed to hypoxia during ambient and/or spinal cord cooling was correlated, at both levels of hypoxia, to the thermoregulatory VO2 (viz. the 'extra' VO2 produced by cooling) prior to exposure to the hypoxic gas. The effect of hypoxia on shivering and associated cardiorespiratory adjustments was rapid and was completely reversible on return to air. We conclude that the thermoregulatory system in pigeons is sensitive to hypoxia, as is the case for mammals. The FIO2 that begins to inhibit thermoregulatory and metabolic responses to cold is lower in birds, perhaps as a result of the better ability of the bird to increase intrapulmonary gas and blood O2 convective transports when exposed to hypoxic gas.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Effect of bilateral vagotomy on arterial acid-base stability during panting in the pigeon.

Bilateral, cervical vagotomy denervates, among other receptors, the known peripheral chemoreceptors in birds. To test the importance of afferent vagal input to cardiorespiratory control during thermal panting, we measured responses to an increase in body temperature (Tb) induced by ambient heating in 6 bilaterally, cervically vagotomized pigeons. These responses were compared with those we previously reported in intact pigeons (control animals). At thermoneutral conditions, respiratory frequency (fR) was lower after vagotomy compared to controls, and PaCO2 was higher. During increases in Tb in both control and vagotomized pigeons, fR, PaO2, pHa, heart rate and oxygen consumption increased, and PaCO2 decreased. However, fR rose less, PaCO2 decreased more, and pHa increased more in the vagotomized pigeons than in controls. All three were more variable than in controls. Heart rate and blood pressure were higher than controls; blood pressure was more variable. We conclude that bilateral, cervical vagotomy compromises the ability of pigeons to maintain stable respiratory and cardiovascular responses to hyperthermia.

Acid-Base Equilibrium↗
PubMed1986

Cardiorespiratory responses to hypoxia in intact and bilaterally vagotomized pigeons.

Bilateral, cervical vagotomy in birds denervates, among other receptors, the carotid bodies. To test whether such neural section removes sensitivity to hypoxia, we measured respiratory, cardiovascular, and blood gas responses to hypoxia at 84-, 70-, and 49-Torr inspiratory O2 partial pressure (PIO2) in five pigeons with intact vagi and in five bilaterally, cervically vagotomized pigeons. Normoxic respiratory frequency (fresp) and expiratory flow rate (VE) were decreased after vagotomy. Intact pigeons showed large increases in VE in response to hypoxia, effected mostly by increases in fresp. VE also increased greatly in response to hypoxia in vagotomized pigeons, but increases were largely the result of tidal volume. O2 consumption, CO2 production, and respiratory exchange ratio increased slightly in all pigeons during hypoxia. Normoxic heart rate was greater after vagotomy; cardiac output increased in all pigeons in response to hypoxia, but stroke volume increased only in intact pigeons. During normoxia, arterial and mixed venous O2 partial pressure, O2 concentration, and pH were lower and arterial and mixed venous CO2 partial pressure was higher, after vagotomy. In all pigeons during hypoxia, arterial and mixed venous O2 and CO2 partial pressure and O2 concentration decreased and arterial and mixed venous pH increased; changes were roughly parallel in intact and vagotomized pigeons. The arteriovenous O2 concentration differences during normoxia and hypoxia were similar in all pigeons. We conclude that bilateral, cervical vagotomy in the pigeon causes hypoventilation and tachycardia during normoxia, but strong respiratory and cardiovascular responses to hypoxia are still present.

Animals↗
PubMed1986

Different complement and granulocyte activation in patients dialyzed with PMMA dialyzers.

Plasma C3a and C5a levels as well as plasma levels of granulocyte lactoferrin, granulocyte myeloperoxidase and granulocyte elastase in complex with alpha 1-proteinase inhibitor (E-alpha 1PI) were investigated in 10 patients (52.7 +/- 5.9 years) undergoing maintenance hemodialysis (39.4 +/- 12.4 months) with hollow fiber dialyzers made from polymethylmethacrylate. Plasma levels of lactoferrin increased from 166.5 +/- 28.5 to 712.5 +/- 165.9 ng/ml, myeloperoxidase from 59.0 +/- 15.3 to 210.5 +/- 33.9 ng/ml and E-alpha 1PI from 114.2 +/- 18.1 to 681.8 +/- 102.6 ng/ml during dialysis. In contrast, plasma C3a levels rose from 179.8 +/- 33.6 to maximal 276.2 +/- 45.4 ng/ml and C5a from 55.7 +/- 8.1 to maximal 101.1 +/- 14.8 ng/ml. Our data indicate that degranulation of granulocytes occurs during dialysis despite only little complement activation and mild initial granulocytopenia.

Biocompatible Materials↗