Iatrogenic vertebrobasilar insufficiency after surgery of the subclavian or brachial artery: review of three cases

OBJECTIVE AND IMPORTANCE: Vertebrobasilar insufficiency resulting from disease of the subclavian artery is well recognized. Usually, this occurs as the "subclavian steal" syndrome in the context of chronic subclavian stenosis and is consequently well tolerated because of collateralization. Acute disruption of the hemodynamics of the aortic arch vessels, however, can produce disastrous sequelae. CLINICAL PRESENTATION: We present three cases of iatrogenic vertebrobasilar insufficiency sustained as complications of surgery of the left subclavian artery or its distal continuation. The cases were chosen from a review of approximately 400 emergency neurosurgery consultations requested at the Los Angeles County Hospital between November 1995 and February 1996. INTERVENTION: The first patient underwent repair of a traumatic brachial artery occlusion and awoke postoperatively with bilateral cortical blindness, right hemiparesis, and multiple cranial nerve deficits that were most likely caused by acute subclavian steal. The second underwent removal of a subclavian embolus and developed bilateral cerebellar infarction leading to persistent coma, possibly from inadvertent embolization of the vertebral artery during surgery. The third underwent resection and bypass grafting of a subclavian aneurysm. Good backflow was reported when the vertebral artery was disarticulated from the subclavian artery, and this vessel was not reimplanted into the graft. The patient suffered massive cerebellar infarction leading rapidly to brain death. CONCLUSION: There are myriad ways in which the inherent redundancy of the vertebrobasilar system may be jeopardized, and when this protective mechanism fails, the results can be disastrous. Flow through the vertebral arteries may be compromised by thrombosis, embolization, dissection, inappropriate ligation, excessive head rotation, hypotension, vasospasm, or acute subclavian steal. These examples illustrate the importance of understanding the complex physiology of posterior fossa circulation as the basis of pre-, intra-, and postoperative management of patients undergoing surgery of the subclavian artery.     

Perfusion of ischemic myocardium during anesthesia with sevoflurane

BACKGROUND: Sevoflurane produces direct vasodilation of coronary arteries in vitro and decreases coronary vascular resistance in vivo, pharmacologic properties that may contribute to the development of "coronary steal." This investigation examined the effects of sevoflurane on the distribution of regional myocardial perfusion in chronically instrumented dogs with steal-prone coronary artery anatomy. METHODS: Dogs were chronically instrumented for measurement of aortic and left ventricular pressure, diastolic coronary blood flow velocity and subendocardial segment length. After recovery from surgery, dogs underwent repetitive, brief, left anterior descending coronary artery (LAD) occlusions via an implanted hydraulic vascular occluder to enhance collateral development. A progressive left circumflex coronary artery (LCCA) stenosis was also obtained using an ameroid constrictor. After development of LCCA stenosis, the LAD was totally occluded to produce a model of multivessel coronary artery disease. Systemic hemodynamics, regional contractile function and myocardial perfusion measured with radioactive microspheres were assessed in the conscious state and during sevoflurane anesthesia at 1.0 and 1.5 MAC with and without restoration of arterial blood pressure and heart rate to conscious levels. RESULTS: Total LAD occlusion with simultaneous LCCA stenosis increased heart rate, mean arterial pressure, left ventricular systolic and end-diastolic pressures, end-diastolic segment length, and rate-pressure product in conscious dogs. Subsequent administration of sevoflurane caused dose-related decreases in arterial pressure, left ventricular systolic pressure, double product, and peak rate of increase of left ventricular pressure at 50 mmHg. Perfusion of normal myocardium was unchanged during sevoflurane anesthesia. In contrast, sevoflurane caused dose-dependent decreases in blood flow to myocardium supplied by the stenotic LCCA, which returned to control levels after restoration of heart rate and arterial pressure. No reduction in collaterally derived blood flow to the occluded region was produced by 1.0 or 1.5 MAC sevoflurane. No redistribution of blood flow away from the occluded LAD region to normal or stenotic myocardium occurred during sevoflurane anesthesia. In fact, increases in the ratio of blood flow between occluded and normal zones or occluded and stenotic zones were observed in the subepicardium during 1.5 MAC sevoflurane with maintenance of the heart rate and arterial pressure at conscious levels. CONCLUSIONS: The results demonstrate that sevoflurane does not reduce or abnormally redistribute myocardial blood flow derived from coronary collateral vessels in a chronically instrumented canine model of multivessel coronary artery obstruction.     

Estimation of gold-labelled macromolecules attached to cell surfaces

A method for obtaining a semi-quantitative estimation of the amount of colloidal gold label attached to a cell surface is described. The X-ray emission, in a scanning electron microscope, from an even metal coating applied by diode sputter coating is used as an internal standard. The emission from the standard is used to correct for errors which would have arisen due to factors such as variable specimen surface topography. Examples of the semiquantitative estimation of 10-nm gold-labelled wheat-germ agglutinin to L929 murine fibroblast cells are given.     

The idea of constructing microwave devices for the uniform heating of sheet materials

The idea of producing a uniform temperature distribution over the thickness of sheet dielectric materials with different electrical parameters in microwave devices, constructed using a combination of a waveguide-type system and slow-wave structures, is considered. The results of measurements of the temperature distribution over the thickness of materials in traveling-wave-type microwave devices are presented. Translated from Izmeritel’naya Tekhnika, No. 3, pp. 58–59, March, 2009.     

Measurement of the temperature-field distribution in the volume of a dielectric material treated in a microwave resonator chamber

The problem of producing a uniform temperature-field distribution in the volume of a dielectric material, treated in a microwave chamber, is considered. An experimental procedure for determining the temperature distribution inside a heated object is described. Translated from Metrologiya No. 1, pp. 22–27, January, 2009.     

Collective polyelectrolyte diffusion as a function of counterion size and dielectric constant

We report studies of the effect of counterions on the properties of solutions of a strong polyelectrolyte for a wide range of solvent dielectric constant. For this purpose we investigated the dynamic properties of polystyrene sulfonate in N‐methylformamide whose dielectric constant changes significantly with temperature. By means of dynamic light scattering and NMR spectroscopy, polymers of different molecular weights and various counterions were investigated, including large phosphazene counterions P₁, P₂ and P₄ measured for the first time. It was found that the order of counterion binding of ionomers in the solvent changed with an increase of dielectric constant. The order for low dielectric constant (high temperature) was Na < Rb < Cs < P₁ < P₂ < P₄, whereas for a solvent with high dielectric constant no influence of counterion nature was observed. The solvation–desolvation effect together with electrostatic interactions are responsible for the observed phenomenon. © 2012 Society of Chemical Industry     

Terahertz oscillator based on nonlinear frequency conversion in a double vertical cavity

The feasibility of producing a vertical-cavity laser that operates in the far IR region and is based on the three-wave mixing due to the lattice nonlinearity of a GaAs/AlGaAs system is analyzed. It is shown that the use of a double Bragg cavity with the parameters tuned both to high-frequency oscillations (sources of nonlinear polarization) and to the difference frequency allows one to raise the intensity of the radiation in the far IR region. The power density of the radiation at a wavelength of 49.5 μm equals approximately 5 × 10^?4 μW/μm² at a drive current density of 5 kA/cm². It is suggested that a drive current should be supplied with the use of intercavity contacts, to be located in the vicinity of a node in the difference mode; then, the absorption of radiation by free charge carriers will be reduced to a minimum.     

Retinoic acid-induced type II collagen degradation does not correlate with matrix metalloproteinase activity in cartilage explant cultures

OBJECTIVE: To determine the role of matrix metalloproteinases (MMPs) in retinoic acid (RetA)-induced degradation of type II collagen in cartilage. METHODS: Bovine nasal cartilage explants were cultured with 1 microM RetA or in 3 nM interleukin-1alpha (IL-1alpha). Release of proteoglycan and type II collagen into the medium was measured by colorimetric assay and immunoassay, respectively. MMP activity in the medium was determined using a quenched fluorescent substrate assay, while specific collagenases were identified by Western immunoblotting. In some cases the effects of low molecular mass synthetic MMP inhibitors and serum on collagen degradation were studied. RESULTS: RetA promoted maximal breakdown of type II collagen after 4 or 5 weeks in culture, compared with 3 weeks in culture with IL-1alpha. In IL-1alpha-stimulated cultures, collagen degradation was coincident with a large increase in MMP activity in the culture medium, whereas in RetA-stimulated cultures, there was only a small increase. In Western immunoblots of culture media containing RetA, prointerstitial collagenase and active collagenase 3 were sometimes detected, but not in all experiments. In IL-1alpha cultures, active interstitial collagenase was always detected, and active collagenase 3 was detectable in some experiments. Neutrophil collagenase was not detected in any cultures. IL-1alpha-stimulated collagen degradation was effectively inhibited by a potent, broad-spectrum inhibitor of MMPs, whereas it was poorly inhibited by a weak MMP inhibitor. The same 2 compounds were both only weak inhibitors of RetA-induced collagen degradation. When fetal calf serum was included in cartilage cultures, MMP activity in the culture medium was reduced to low levels. This resulted in a marked inhibition of IL-1alpha-induced type II collagen degradation, whereas there was no inhibition of RetA-induced collagen degradation. CONCLUSION: Unlike IL-1alpha, RetA induces degradation of type II collagen in cartilage explants by a mechanism that is mainly independent of those MMPs that can be detected in the culture medium.     

Variable and invariable DNA repeat characters revealed by taxonprint approach are useful for molecular systematics

BACKGROUND: Normally the lateral hypothalamic area (LHA) and the ventromedial nucleus (VMN) interact to regulate food intake (FI), the product of meal number (MN) and meal size (MZ), by changes in neurotransmitters, mainly dopamine and serotonin. Change in LHA dopamine influences meal size; while in VMN, decreasing dopamine and increasing serotonin levels influence meal number. Whether this situation exists in early cancer anorexia was tested in a series of studies to examine the role of the hypothalamus in the pathogenesis of early cancer anorexia. MATERIALS AND METHODS: In experiment 1, male Fischer tumor-bearing (TB) rats and weight-matched controls had FI, MN, and MZ measured continuously via a computerized rat eater meter. At onset of anorexia, feeding patterns were measured. In experiment 2, the VMN was temporarily blocked with 0.32 microgram of colchicine in TB rats, while TB controls had an equal volume of intra-VMN saline, and changes in feeding patterns were measured. In experiment 3, changes in VMN dopamine and serotonin were measured via microdialysis at anorexia and after tumor resection. RESULTS: In experiment 1, with the onset of anorexia, food intake decreased significantly in TB rats, initially by a decrease in MN and then by a decrease in both MN and MZ. No change occurred in controls, suggesting that VMN versus LHA played a more significant role in mediation of cancer anorexia. In experiment 2, following VMN block, FI increased significantly in anorectic TB rats, achieved by an almost exclusive increase in MN with minimal change in MZ, thus supporting the role of the VMN in anorexia. In experiment 3, at the onset of anorexia, FI decreased significantly in TB rats versus controls. TB rats had a significant increase in VMN serotonin and a significant decrease in VMN dopamine. After tumor resection, food intake improved and high levels of serotonin normalized with no change in dopamine. CONCLUSION: Serotoninergic and dopaminergic systems are involved in the etiology of cancer anorexia. The changes in food intake are mediated via the VMN by a decrease in meal number.