Hi LM - Going back to the basics, if one understands how the erection
process work and the principles involved, then one can go forward from
there.

How much blood pressure is required for an erection? Never seen numbers.
I assume the blood pressure in the penis is no higher than the blood
pressure any other place in the body at the same time the erection is
occurring. It's simple hydraulics. It would seem to me that he pump
(heart) only produces so much pressure which is all that's available to
every organ in the body. Every extremity must share the same blood
supply. I think the penis is a strange animal because it uses the same
blood pressure to become pressurized unlike any other body part.
Interesting.

Yes, it is all about simple hydraulics. The penis gets hard for the same
reason you can use one hand to lift your car with a hydraulic jack. The
laws of hydraulics are the reason. When you operate the handle on the
jack, you're actually forcing a small piston to pump fluid through a
small opening into the area below a much larger piston. The difference
between the surface area of the small piston and the large one
multiplies, or amplifies, the force you apply to the pump handle. Say,
for ease of explanation, the surface area of the small pump's piston is
1 sq. inch, and the surface area of the large one, which actually lifts
the car, is 10 sq. inches. (In reality the difference between the two is
many times greater) If you push down on the pump handle hard enough to
create a pressure of 50 pounds/sq inch in the small pump (meaning you
exert 50 pounds of pressure on the small piston with its surface area of
1 sq inch) then that same 50psi is exerted upwards on the large piston
which is actually lifting the car. It has a 10 sq inch surface area, so
the 50psi exerts an upward force of 10 x 50 or 500 pounds.

Here's how this analogy applies to your penis.

The penis is a unique organ among all those in your body. It has two
chambers, called the corpus cavernosa, which are a lot like sponges, and
through which most of the blood coming into your penis flows. These two
chambers are surrounded by muscles which are normally contracted,
keeping most of the blood squeezed out of the spongy tissues. Picture,
if you will, a sponge compressed inside a pipe. Fluid can be forced
through it and will come out the other end, but the sponge can't expand
due to the pipe surrounding it.

Now picture that the pipe is double-walled, and that all the fluid going
through the sponge and out the far end of the pipe is directed to a
rubber tube returning between the inner and outer walls of the pipe.

Now here's where the hydraulics comes in. Compared to the diameter of
your blood vessels, the diameter of the penis is huge, with a surface
area of quite a few square inches. When you start to become aroused ,
the muscles surrounding the spongy corpus relax, much like removing the
inner pipe in our analogy. The blood continues to pour in and the spongy
tissue begins to expand. In reality your penis is a multilayered organ,
much like the double-walled pipe analogy. The corpus cavernosa (the
sponge) is surrounded by muscles,(the inner pipe) which are in turn
surrounded by a relatively inelastic layer of tissue (the outer pipe).
The blood enters from deep arteries into the spongy tissue, runs pretty
much the length of your penis, and returns to the body through veins
(the rubber tube) located between the muscles surrounding the corpus and
the inelastic outer layer. When the muscles (called smooth muscles)
relax and the corpus begins to expand the veins returning the blood are
squeezed between the smooth muscles and the inelastic outer layer,
shutting the veins off.

Using the laws of hydraulics, a relatively small amount of arterial
pressure is amplified by the large surface area of the penis resulting
in a diamond cutter erection assuming everything is working right.
Blood's coming in at full arterial pressure. It can't get out since the
return veins are squeezed shut.

After relaxing completely initially to allow a full erection, the smooth
muscle goes into moderate contraction as sexual excitement continues.
Normally this has no effect, since the high hydraulic pressure overcomes
this contraction and keeps the return veins shut down. If the veins are
for some reason only marginally shut off, though, this small contraction
can be enough to open up the exit flow resulting in premature loss of
the erection.
To shut down the erection after ejaculation or cessation of stimulation,
the smooth muscles begin to contract more forcefully, relieving pressure
on and opening up the return veins, which reduces the interior pressure
allowing the smooth muscles to contract more, which opens up the return
veins more, etc. until your penis is again flaccid.

Venous leakage takes place when the return veins are not squeezed shut
as they should be, either because of insufficient blood flow into the
penis, the smooth muscles don't relax sufficiently, or (and here I'm a
little fuzzy) the veins aren't flexible enough to squeeze shut
completely. You can lose a previously good erection if the smooth
muscles begin to contract forcefully prematurely due to tension or worry
,like when her parents came home unexpectedly when you were making out
on the couch as a teenager, or when worry about keeping it up creates
the same kind of tension. If the smooth muscles hardly relax at all, or
the veins are incapable of being squeezed shut you'll either never get
an erection at all or you'll get a poor one. This smooth muscle
relaxation gets more iffy as we get older, which is why erections get
more chancy with advanced age.

The injections and the Muse suppository act directly on the smooth
muscle, causing it to relax. Thus you get an erection whether it's
warranted by sexual excitement or not.

Viagra, on the other hand, inhibits some of the action of the chemical
in the body responsible for causing the smooth muscle to contract,
allowing the erection to proceed more normally.

Restriction bands (cock rings) simulate the natural squeezing shut of
the return veins but don't cause smooth muscle relaxation (which is why
they work best if you can get an initial erection and later lose it
through leakage).

The pump bypasses the whole erection
biological process by creating a vacuum around the penis causing the
pressure differential to overcome the contracted smooth muscles and fill
the penis with blood. After the penis is full of blood, a restriction
band traps the blood in the penis and keeps it from returning to the
body.

Now to return to the blood pressure question ........

Due to the hydraulic action of small arteries feeding the relatively
large penile surface area, I doubt a change in blood pressure has a lot
to do with the erection process. High blood pressure through exertion or
speeding up the heartbeat artificially might or might not cause a
marginally quicker erection, but the firmness difference wouldn't be
significant.

High blood pressure without either exertion or artificially stimulating
the heart to beat faster is usually the result of poor circulation,
however, and a lack of sufficient blood supply could certainly cause an
erection problem, especially if you also have venous leakage.

Low pressure, on the other hand, could be caused either by wide open
arteries or a poorly working pump (heart). If the former, the erection
should be enhanced and happen quicker. If the latter, who knows. We're
getting a little esoteric here.
Anyway, that's my take on the whole erection process (the mechanical
part, at least).

You didn't say but if your doctor didn't want to give you hormone shots,
he probably checked and found your T levels within the range of normal.

All of this situation can weigh heavy on the mind and that is the
biggest sexual organ of all.   Mental stresses - depression, performance
anxiety, just to name a few can put a wrench in the whole works of a
good working system.

Again, I hope this helps,

~ curtis

knowledge is power - growing old is mandatory - growing wise is optional    
"Many more men die with prostate cancer than of it. Growing old is
invariably fatal. Prostate cancer is only sometimes so."
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