Ferromagnetism and MR imaging: safety of carotid vascular clamps

Metallic extracranial carotid vascular clamps of the Selverstone, Crutchfield, Poppen-Blaylock, Salibi, Kindt, and tantalum varieties have been placed for treatment of large, giant, or inoperable intracranial aneurysms. To ascertain what adverse effect, if any, MR imaging would have on these clamps, magnetic deflection at 1.5 T was measured for various carotid clamps. Marked magnetic deflection (and torque) was displayed by stainless steel Poppen-Blaylock clamps. Relatively mild magnetic deflection was displayed by the stainless steel Selverstone, Salibi, Crutchfield, and Kindt clamps. Three patients with previously placed carotid clamps (two Selverstone, one Salibi) and one patient with a nonferromagnetic tantalum carotid clip had cranial or cervical MR studies at field strengths ranging from 0.35 to 0.60 T. No patient experienced any discomfort or neurologic sequelae as a result of MR imaging. Although the ferromagnetic clamps created severe "black-hole" artifacts and image distortion within the cervical and facial regions, no significant image degradation was apparent during spin-echo imaging of the brain. The tantalum clip created a far smaller MR artifact than did ferromagnetic clamps and allowed effective spin-echo and gradient-echo imaging in the cervical region. Our findings indicate that most patients with carotid vascular clamps (and nonferromagnetic clips) can probably be imaged safely with MR.     

Salt and Mesophase Formation in Aqueous Suspensions of Lauric Acid

The solubility and solution behavior of lauric acid (LA) and its 1:1 acid soap (potassium hydrogen dilaurate) were investigated at 32°C over a pH range of 2.5–8.5 and at varying KC1 concentrations to examine the self-association of this long-chain carboxylic acid under these conditions. LA's solubility in water exhibited the classical pH dependence of a monocarboxylic acid with no evidence of self-association. In 0.1 M KC1 between pH 6.3 and pH 7.3, filtered samples were turbid, suggesting the presence of high molecular weight aggregates (mesophase), which could be removed by ultrafiltration. The apparent LA solubility vs pH profile in ultrafiltered samples was consistent with a solid phase consisting of either the free acid (pH < 6.5) or potassium hydrogen dilaurate (pH > 6.5), again with no evidence of self-association to form low molecular weight species (dimers, etc.). Quasi-elastic light scattering (QLS) studies and mannitol trapping experiments indicated that vesicles were present in samples containing mesophase. The mesophase composition was characterized and a mass-action law for mesophase formation was developed to describe the apparent LA solubility versus pH in the mesophase region in terms of three parameters. The index of cooperativity, , indicated that the mesophase consists of approximately 25 molecules of LA with an acid:anion ratio, , of 1.7. The standard free energy of mesophase formation per mole of monomer was determined to be –6.3 kcal/mol. The aggregate size determined thermodynamically is several orders of magnitude less than that of the mesophase particle size determined by QLS measurements, suggesting that the LA monomer concentration in equilibrium with mesophase may be governed by a small unit domain of the vesicle. These observations may have a bearing on the thermodynamics of self-assembly of lipid bilayer membranes.     

Planning for hospital ethics committees: Meeting the needs of the professional staff

Hospital ethics committees (HECs) have historically been instituted top-down, often ignoring the needs of the professionals and patients who might use their services. Seventy-four physicians and 123 nurses participated in a hospital-wide needs assessment designed to [1] identify their perceptions of the functions of the HEC, [2] determine which services and educational programs were most desired, and [3] explore which forums were most preferred for discussion of ethical problems. Results indicated that utilization of the HEC focused around five areas of concern: withdrawing/withholding treatment, rationing and control of health care, children's rights, role of the patient and family in decisionmaking, and disagreements about treatment. Physicians and nurses differed widely in their attitudes. Perceptions about the appropriate functions of the HEC strongly influenced decisions regarding which HEC services to use. Needs assessment can play an important role in developing HEC goals and designing programs that meet the needs of professionals.     

Attenuation of diet-induced atherosclerosis in rabbits with a highly selective 15-lipoxygenase inhibitor lacking significant antioxidant properties

1. 15-Lipoxygenase (15-LO) has been implicated in the pathogenesis of atherosclerosis because of its localization in lesions and the many biological activities exhibited by its products. To provide further evidence for a role of 15-LO, the effects of PD 146176 on the development of atherosclerosis in cholesterol-fed rabbits were assessed. This novel drug is a specific inhibitor of the enzyme in vitro and lacks significant non specific antioxidant properties.
2. PD 146176 inhibited rabbit reticulocyte 15-LO through a mixed noncompetitive mode with a K_i of 197 nM. The drug had minimal effects on either copper or 2,2′-azobis(2-amidinopropane)hydrochloride (ABAP) induced oxidation of LDL except at concentrations 2 orders higher than the K_i.
3. Control New Zealand rabbits were fed a high-fat diet containing 0.25% wt./wt. cholesterol; treated animals received inhibitor in this diet (175 mg kg⁻¹, b.i.d.). Plasma concentrations of inhibitor were similar to the estimated K_i (197 nM). During the 12 week study, there were no significant differences in weight gain, haematocrit, plasma total cholesterol concentrations, or distribution of lipoprotein cholesterol.
4. The drug plasma concentrations achieved in vivo did not inhibit low-density lipoprotein (LDL) oxidation in vitro. Furthermore, LDL isolated from PD 146176-treated animals was as susceptible as that from controls to oxidation ex vivo by either copper or ABAP.
5. PD 146176 was very effective in suppressing atherogenesis, especially in the aortic arch where lesion coverage diminished from 15±4 to 0% (P<0.02); esterified cholesterol content was reduced from 2.1±0.7 to 0 μg mg⁻¹ (P<0.02) in this region. Immunostainable lipid-laden macrophages present in aortic intima of control animals were totally absent in the drug-treated group.
6. Results of these studies are consistent with a role for 15-LO in atherogenesis.

     

The feasibility of a sensitive low-dose method for the in vivo evaluation of Fe in skin using K-shell x-ray fluorescence (XRF)

An x-ray fluorescence (XRF) system designed for monitoring of skin Fe concentrations has been performance tested for use on patients treated for beta-thalassaemia. The essentials of the system are: a collimated x-ray tube operated at 20 kV and 20 mA; energy selection of the x-ray beam by means of a Cu K-edge filter; use of skin phantoms containing concentrations of Fe in the range 10 to 100 parts per million (ppm); and a high-purity germanium detector placed at 90 degrees to the incident beam. For a Cu K-edge filter of 0.15 mm thickness a quasi-monoenergetic beam of approximately 8.4 keV is obtained which is close to the absorption edge of Fe (7.11 keV). For a real-time counting period of 400s the systemis capable of detecting Fe concentrations of 15+/-2 ppm at a skin dose of the order of 5 mSv. This level of Fe is at the higher end of the normal range found in the skin. In using the same system and operating parameters, measurements on a sample of ferritin obtained from a rat's liver yield an Fe concentration of 36+/-3 ppm for a measurement time of 500 s; this can be compared with suppliers' data indicating an Fe level of 36 ppm.     

Hyperalgesia caused by nerve transection: long-lasting block prevents early hyperalgesia in the receptive field of the surviving nerve

The aim of our study was to test the hypothesis that a long-lasting N-butyl tetracaine nerve block (>2 wk) would be much more effective in the prevention of hyperalgesia caused by nerve transection than the short-lasting lidocaine block. The study was performed with the use of the saphenous nerve section model in rats. The saphenous nerve was exposed and injected with saline, lidocaine (37 mM), or N-butyl tetracaine (37 mM). Ten minutes later, the nerve was transected in some of the rats. The development of mechanical hyperalgesia (pressure threshold) of the hindpaw was assessed during a 5-wk period. In rats with saphenous nerve transection without nerve block (saline injection), 3 h after the transection, the pressure threshold decreased by approximately 30% (from 175+/-11 g to 122+/-23 g, P < 0.0001); the threshold increased somewhat the next day, then it remained stable for 2 wk, with a slow process of recovery afterward. N-butyl tetracaine block without nerve transection caused a slow-developing decrease in the pressure threshold with the first statistically significant change at the sixth day. The comparison of the preventive effects of lidocaine and N-butyl tetracaine blocks on early hyperalgesia caused by nerve transection demonstrated that both lidocaine and N-butyl tetracaine prevented hyperalgesia 3 h after the transection. However, the protective effect of lidocaine disappeared the next day. In contrast, N-butyl tetracaine prevented early hyperalgesia for almost a week. The slow-developing late hyperalgesia caused by long-lasting nerve block makes it impossible to study the protective effect of such a block on late hyperalgesia caused by axotomy. As far as early hyperalgesia is concerned, the preventive effect of the N-butyl tetracaine was much longer than that of lidocaine and continued for approximately 1 wk. IMPLICATIONS: A long-lasting nerve block can prevent early hyperalgesia caused by nerve transection.