Environmentally Stable, Low Dielectric Polymers from Soluble Intermediates

We have investigated new polymers of poly(phenylene vinylene), PPV and poly(phenylene), PP. Like polyimides, these polymers can be spin-coated from soluble intermediates and converted to their thermally stable forms by elimination of small groups during a heating cycle. As such, these polymers are insulating. Both poly(phenylene vinylene) and poly(phenylene) also have the potential for metallic conductivity when properly doped. During curing, the complete removal of the leaving groups is important in determining the final behavior of the aromatized polymer film. Elimination of the leaving groups was followed by means of Rutherford Backscattering (RBS) and Forward Recoil Spectrometry (FRES) analysis for various curing conditions and environments. We will describe the curing and film-forming properties of these polymers, and discuss both their dielectric characteristics and thermal stability as a function of the curing conditions.

Continuous selective intraarterial infusion of nimodipine for therapy of refractory cerebral vasospasm

BACKGROUND

For endovascular treatment of vasospasm after aneurysmal subarachnoid hemorrhage (aSAH), an intraarterial treatment course with the calcium channel antagonist nimodipine infused for 30 min is proposed. As some patients still show ongoing vasospasm thereafter, we report on our experience with an extended time period of selective intraarterial nimodipine administration.

METHODS

In nine patients with aSAH and refractory cerebral vasospasm, we left the catheter in place within the internal carotid artery after angiography. On the neurosurgical ICU, a continuous infusion of intraarterial nimodipine was commenced, combined with intraarterial heparin anticoagulation. Therapy was controlled with extended neuromonitoring techniques.

RESULTS

Three patients died from refractory vasospasm and a fourth suffered lethal sepsis. Three patients survived in a good clinical condition, two of them without apparent neurologic deficit. The efficacy of intraarterial nimodipine was best verified with regional CBF monitoring. TCD failed to detect vasospasm in two patients and missed improvement in four. Brain tissue oxygenation increased in all patients, but was not indicative of vasospasm in one. CT perfusion reflected the treatment course adequately in the qualitative scans.

CONCLUSION

Selective continuous intraarterial nimodipine treatment for refractory cerebral vasospasm after aSAH seems feasible and may add to the endovascular therapeutic options. Appropriate monitoring technology is essential for further investigation of this novel technique.

Rapid phase-shifting fiber interferometer with optical stylus

Optical fiber interferometry holds many advantages for the online measurement of high-precision surfaces. Here, a fiber interferometer with a wavelength-scanning probe is reported. Such an interferometer requires active stabilization against the effects of temperature drift and vibration. A method of multiplexing dual wavelengths into the same fiber, combined with rapid phase shifting and real-time phase calculation, is investigated. Experimental data show the successful stabilization of the interferometer regardless of environmental perturbation.

Regulation of CYP4A expression by bezafibrate in primary culture of rat and human hepatocytes: interspecies difference and influence of N-acetylcysteine

The effects of fibrates on cytochrome P450 4A (CYP4A) expression have not been clearly evaluated in human hepatocytes, human being reported as a non-responsive species. We have evaluated the effects of clofibrate, bezafibrate (BEZA), WY-14643, nafenopin and ciprofibrate at the concentration of 250 microM on CYP4A expression in primary cultures of rat and human hepatocytes. BEZA greatly induced mRNA expression in both species. Eight out of 10 human cultures responded to BEZA 250 microM. CYP4A-dependent activity was increased in rat, but not in human hepatocytes. The antioxidant N-acetylcysteine (Nac) enhanced the inducing effect of BEZA on mRNA expression, this potentialization being higher in human compared to rat hepatocytes. By contrast, Nac decreased the inducing effect of BEZA on CYP4A-dependent activity in rat and had either no effect or decreased the activity in BEZA-treated human hepatocytes. In conclusion, the cellular environment appears as an important parameter to take into account when studying CYP4A induction and could partly explain interspecies differences in the complex regulation of CYP4A expression.