The effects of caffeine or placebo on blood pressure, heart rate, and baroreflex activation (elicited by phenylephrine) were studied on young normotensive volunteers after a 7-day caffeine-free period. Subjects received oral doses of either 250 mg caffeine (n = 6) or placebo (n = 4), and hemodynamic changes were studied at 0, 30, 60, 120, and 180 minutes after drug administration. Thirty minutes after the caffeine dose, blood pressure had risen from 127 +/- 8/57 +/- 4 mm Hg to 136 +/- 3/68 +/- 5 mm Hg, heart rate was unchanged, and the baroreflex slope had decreased from 31 +/- 7 msec/mm Hg to 11.6 +/- 2 msec/mm Hg. Baroreflex sensitivity remained inhibited for the rest of the single-dose experimental period. In contrast, no significant changes were observed after either long-term caffeine ingestion in the same group or in the placebo group during the single- or multiple-dose study. These findings indicate that single but not multiple caffeine administration inhibits baroreflex activation in normotensive volunteers and this could contribute to the acute hemodynamic effects of caffeine.

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SYNOPSISPervaporation of water-ethanol mixtures through acrylamide-plasma graft-polysulfone (AAm-p-PSF), a PSF membrane on which AAM is grafted by plasma polymerization, was investigated in this work. The effects of plasma treatment conditions and feed compositions on the pervaporation performances were studied for the un-ionized and ionized AAm-p-PSF membranes. It was found that the separation factor of the AAm-p-PSF membrane is higher than those of the unmodified membranes. The ionized membrane possesses a separation factor of 10.4 and a permeation rate of 718.1 g/m2 h. In addition, the surface properties of the prepared membrane were characterized by ESCA, SEM, and a water contact angle meter; and the relationship between the grafting yield and the plasma pretreatment time was obtained. 0 1996 John Wiley & Sons, Inc. I N T R O D U CTlO NPervaporation is an attractive process for separation of azeotropic mixtures, heat-sensitive mixtures, close boiling point mixtures, and the removal of water from organic liquids.'-3 It is known that the pervaporation performance can be improved by elevating the hydrophilicity of membranes. Therefore, many research workers attempted to increase the membrane hydrophilicity by using grafting blending, and block copolymerization. In the authors' previous articles several methods, such as 6oCo y-ray irradiation4s5 and chemical grafting,6 were introduced to improve the membrane morphology and the pervaporation performance. In the present work, the plasma graft polymerization technique is used to modify the surface of polysulfone (PSF) membrane for improving its performance in pervaporation. The graft polymerization technique has been widely used to prepare the pervaporation membrane for separation of aqueous alcohol mixtures. Membranes grafted by acrylic acid,7 methacrylic acid,' and butylacrylateg have been studied. Acrylamide

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