Tom F. Lue, MD

Research Interests

Mechanism of Penile Erection

Lue and associates performed extensive studies of arterial and venous flow, blood gas levels, and radiologic imaging to clarify the erectile process. They found that: 1) erection is a neurovascular and neuromuscular event; 2) erection results from sinusoidal relaxation, arterial dilation, and venous compression; 3) erection has two phases - the vascular phase, which involves excitation of the autonomic nervous system with a rise in intracavernous pressure to around 90 mm Hg, and the muscular phase, which involves excitation of the somatic nervous system, resulting in contraction of the ishiocavernosus muscle, a rise in intracavernous pressure to well above the systolic blood pressure, and penile rigidity. The group also clarified the functional anatomy with scanning electron microscopic studies and found that in the flaccid state, the sinusoids are contracted, the arterioles are constricted, and the venules open freely to extrapenile veins; during erection the arterioles dilate several fold, the sinusoids expand and trap the incoming blood, and the subtunical venular plexuses are compressed between the expanding sinusoidal wall and the tunica albuginea.

Duplex Ultrasound of the Penis

Using high-resolution ultrasonography and pulsed Doppler analysis, Lue and associates formulated a technique for examining the functional status of the cavernous and dorsal arteries. When this test is performed before and after intracavernous injection of papaverine or prostaglandin E1, the degree of arterial dilation, the velocity of blood flow, the thickness of the wall, and the pulsation of the vessels can be assessed. Not only can this technique accurately evaluate the functional status of the penile arteries, but it can also detect the general health of the systemic arterial tree. Lue also simplified the functional test of the penile veins. When cavernosometry and cavernosography are performed after intracavernous injection of vasoactive agents to activate the venooclusion mechanism, the number and location of venous leaks can be depicted. These two tests have gradually become the standard test for vasculogenic impotence.

Peyronie's Disease

In impotent patients, the concentration of elastic fibers was lower than in potent patients (p = 0.0365). A significant decrease was also found in patients with Peyronie's disease. Furthermore, the concentration of elastic fibers decreased with age. Electron and light microscopy revealed the presence of distinct alterations in the tunica albuginea in impotent patients and patients with Peyronie's disease that might interfere with function.

Study of the Effect of Radiation on Penile Erectile Tissue in a Rat Model

Many patients experience impotence after radiation therapy to the prostate. In this study we found that radiation causes the following changes in the penile tissue: 1. decreased penile smooth muscle and the number of nitric oxide synthase-containing nerves; and 2. significantly less penile erection after neurostimulation. We therefore recommend shielding of the penis when giving radiation to patients with prostate cancer.

The Effect of Aging on Penile Erection, Penile Tissue, Nitric Oxide Synthase-Containing Nerves and Various Growth Factors in the Rats

The erectile mechanism appears to remain intact as rats age, but the response to central and peripheral stimulation decreases. The reduction in nitric oxide synthase (+) nerve fibers - perhaps the most important neurologic factor of age-related changes - might account for these observations. There is also a significant decrease in nitric oxide synthase-containing neurons in the pelvic ganglia and the penis. This finding may explain the higher incidence of impotence after radical prostatectomy in older patients. There is also an increase in transforming growth factor beta-1 in old penile tissue which may be the cause of increased collagen fibers seen in old rats and older men.

Regeneration of Cavernous Nerves after Neurostomy

As growth hormone has been reported to improve nerve regeneration, we studied the effect of rat growth hormone (GH) on the regeneration of nitric oxide synthase (NOS)-containing penile nerves and the neurons in the pelvic ganglia after unilateral cavernous nerve neurotomy in rats. The results show that GH injection significantly enhances the regeneration of NOS-containing fibers in the dorsal and intracavernosal nerves after unilateral cavernous nerve injury. Electrostimulation in the GH-treated group revealed a greater maximal intracavernosal pressure and a shorter latency period. We believe that GH administration may present a new and more physiologic approach to the treatment of erectile dysfunction after radical pelvic surgery.

Surgical Innovations

Lue has also developed several new operations for the correction of Peyronie's disease and vasculogenic impotence. He developed a technique of plicating the tunica albuginea after intracavernous injection of papaverine to simplify and improve the result. He also developed a technique of placing relaxation incisions on the plaque and repairing the defects with venous grafts. For venous surgery, he pioneered the technique of hilar exploration and crural dissection. Recently, Lue has designed a technique for determining which procedure should be performed during penile revascularization surgery.

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