A 16-week, double-blind, placebo controlled, dose titration study was done on 100 normotensive patients age 45 years or older to determine the efficacy and safety of doxazosin, a selective alpha 1-adrenoceptor antagonist, in the treatment of benign prostatic hyperplasia (BPH). Of the 41 efficacy evaluable patients 88% underwent dose titration to a maximum of 8 mg. doxazosin once daily. Maximum and average urinary flow rates increased significantly above baseline with doxazosin (2.9 ml. per second and 1.4 ml. per second, respectively) compared with placebo (0.7 ml. per second and 0.3 ml. per second, respectively). A significant effect on maximum flow rate was noted as early as week 2 of double-blind treatment at the initial efficacy evaluation. Doxazosin was superior to placebo in patient and investigator assessments of total, obstructive and irritative BPH symptoms. The onset of efficacy for total patient-assessed symptoms was significant for doxazosin compared to placebo 4 weeks after the start of the treatment regimen. Statistically significant decreases in mean blood pressure of 4 to 6 mm. Hg were noted with doxazosin compared with placebo. Adverse events, primarily mild to moderate in severity, were reported in 44% of patients given doxazosin and 30% of those given placebo. Our results strongly demonstrate that doxazosin is significantly superior to placebo in the treatment of BPH in normotensive patients, with the patient experiencing significant relief early after initiation of therapy.

Magnetic resonance elastography (MRE) is a recently devel-Dynamic MR elastography utilizes the fact that the shear wave propagation in biological tissue is related to material stiffness (1-3). Stiffness parameters such as the shear modulus may serve to distinguish between healthy and pathologic tissues (3-5). In dynamic MRE, mechanical excitation of tissue is synchronized with phase-sensitive acquisition techniques (6). The recorded wave images show solely signal components related to tissue oscillations. In vivo, shear waves are applied by an oscillating transducer fixed to the surface of the body. The frequency range varies between 50 and 500 Hz. Electromagnetic actuators (1)(2)(3)7,8) and piezoelectric devices (9,10) have been employed as mechanical excitation units. Although the latter can be positioned in arbitrary orientations with respect to B 0 , the construction is quite elaborate and time-consuming. Electromagnetic actuators are easier to construct, cost less, and can be customized easily to account for special in vivo applications such as muscle, breast, or brain MRE (11,12). Applying alternating currents to an annular coil generates motion. A maximal torque acts on the coil if the normal vector of its plane is perpendicular to B 0 . The resultant periodic tilt is transformed for mechanical actuation using a pivoted rod. In this commonly used design, the orientation of the actuator coil restricts the directions available for mechanical excitation. For isotropic tissue, the direction of shear wave displacement has no influence on the determination of the shear modulus. However, in anisotropic tissue such as skeletal muscles (7,8) or pathologic tissue (3), the propagation speed of the shear waves should be determined in different spatial directions. In these cases, actuators with a variable direction of excitation are required to gain full information about tissue characteristics.In this study, an electromagnetic actuator is introduced that allows harmonic excitations with directions between 0°and 90°to the B 0 field to be generated. To demonstrate the feasibility of the new actuator, experiments on agarose phantoms are presented and compared with the performance of a conventional electromagnetic actuator. Displacement components parallel and orthogonal to the B 0 field are compared for the conventional and the new actuator. The redirection of the initial motion is determined by the angle between the connecting point of the tube [7], the pivot point [8], and the inserting point of the excitation plate [9]. An angle of 90° (Fig. 1b) results in a shear wave excitation perpendicular to B 0 . Other angles can be chosen by varying the position of the excitation plate in the different inserting points. Figure 1c shows a cross section of the actuator and details of the connection between tube [2] and redirection plate [6]. A ball-shaped head made of brass was securely fitted into the plate. The head of the ball [11] was pressed into a Teflon cylinder [10] fixed with a bushing [12] to the tube to form a gimbal ...

with a mercury manometer. Pulse rates were obtained from electrocardiograms taken simultaneously with the other measurements.Cardiac output was calculated from the oxygen consumption and the arteriovenous oxygen difference according to Fick's formula (2). Two radio-opaque cardiac catheters were introduced through the external jugular veins and, with the aid of fluoroscopy, the distal ends were placed in the right auricle and in the pulmonary artery, respectively. The proximal ends of the catheters were connected with saline manometers for the recording of mean pressures. The location of the catheters and their zero pressures were verified at post-mortem examination. To ensure maximal mixing of the blood returning to the heart, samples of venous blood were taken from the pulmonary artery. Arterial blood was obtained from the cannulated femoral artery. In the course of each experiment, 100 to 150 cc. of blood were withdrawn and replaced with isotonic saline solution. The Van Slyke-Neill technic (3) was used in the analysis of blood Qa and CO2. Hematocrits were determined by the Wintrobe method (4), arterial blood being employed.Control measurements were made when the blood pressure and respiration of the animal became stabilized. The animals were then covered with chipped-ice packs. Body temperatures were recorded from thermometers placed deeply in the rectosigmoid area and protected from the ice packs. The mean cooling period was about two hours during which the body temperatures fell to 290 C. The animal was then dried, covered with thin sheets, and exposed to radiant heat. However, the body temperatures continued to fall to 270 C, before beginning to rise.The mean rewarming period lasted five to six hours, at the end of which body temperatures usually had returned to 37°C. Ten or 11 determinations were obtained in each experiment, measurements being taken after each 2 degree change of body temperature. Evaluation of the methodMeasurements of right auricular and pulmonary arterial pressures represent only the approximate mean values. The changes in pressure were considered to be of greater significance. During periods of extreme bradypnea resulting from severe respiratory center depression, great variations in concentration of blood gases occur during each respiratory cycle, and this produces errors in the direct Fick method. This inaccuracy is further increased by the fact that the usual means of collecting blood samples makes it impossible to obtain exactly 293