The penis does not obey the order of its master, who
tries to erect or shrink it at will. Instead, the penis erects freely
while its master is asleep. The penis must be said to have its own mind,
by any stretch of the imagination. – Leonardo Da Vinc
Functional Anatomy of the Penis
The
penis is composed of three cylindrical structures, the paired corpus
cavernosum and the corpus spongiosum, which houses the urethra, covered
by a loose subcutaneous layer and skin. The flaccid length of the penis
is controlled by the contractile state of the erectile smooth muscle and
varies considerably, owing to emotion and outside temperature. In one
study, the erect length of the penis measured from pubopenile junction
to the meatus was 8.8 cm flaccid, 12.4 cm stretched, and 12.9 cm erect,
with neither a man's age nor the size of the flaccid penis accurately
predicting erectile length (Wessells et al, 1996). In another study, the
author concluded that about 15% of men have a downward curve during
erection; erection angle is below horizontal in one fourth of men; and
shorter erection lengths in the range of 4.5 to 5.75 inches occur in 40%
of men (Sparling, 1997). Regarding penile morphology and erection, a
study shows that during erection, the penile buckling forces are
dependent not only on intracavernosal pressures but also on penile
geometry and erectile tissue properties. Therefore, in patients with
normal penile hemodynamics but without adequate penile rigidity, other
structural causes should also be sought (Udelson et al, 1998). The
functions of various components of the penis are listed in Table 45–1.
Discussion of Treatment Options
Informing
the patient (and partner) of the available treatment options is an
important aspect of the initial office consultation. Most patients will
request the least invasive treatment. If the first option is not
satisfactory, others will be tried until the most acceptable is found.
The treatment options currently available, their costs, and advantages
and disadvantages are listed in Table 46–6. Recommendations of the First
International Consultation on ED include modifying risk factors (both
lifestyle factors and psychological factors); providing education where
information is lacking on sexual function; changing drug dosages or
classes; hormone replacement therapy but not supplementation; specific
pharmacotherapies with adjustments for risks, costs, and invasiveness;
counseling; and surgical therapies (see Table 46–2).
In the late 1970s and early 1980s, the
penile prosthesis and psychosexual therapy were the only two effective
treatments for ED. The NPT test was used to differentiate psychogenic
from organic impotence and to direct the patient to one or the other. In
the 1980s, sophisticated neurologic and vascular tests were added to
the armamentarium to allow more accurate diagnosis. The success of
noninvasive treatments has many questioning the wisdom of the
traditional medical approach: extensive testing to make an accurate
diagnosis and following it up with a specific treatment. Although
finding and correcting the exact cause of ED seem to be the most logical
approach, the current medical-economic climate argues against it
(Shabsigh et al, 2000). We propose the goal-directed approach (Lue,
1990) or the First International Consultation Algorithm on ED (Jardin et
al, 2000) as a good way to initiate evaluation and management of
patients. The extent of the initial work-up is based on the patient's
age, general health, treatment goals, and complexity of presentation
(see Tables 46–1 and 46–3).
Vascular Evaluation
Historical and Investigational Evaluations of Penile Blood Flow
Penile Brachial Pressure Index. The
penile brachial index (PBI) represents the penile systolic blood
pressure divided by the brachial systolic blood pressure. Use of the
Doppler signal transducer to measure penile blood flow was introduced by
Abelson in 1975. He reported that normal penile systolic blood pressure
in the flaccid state was no more than 30 mm Hg below brachial systolic
pressure. This test gained some initial popularity because of its low
cost and noninvasiveness. The technique involves applying a small
pediatric blood pressure cuff to the base of the flaccid penis and
measuring the systolic blood pressure with a continuous-wave Doppler
probe. A PBI of 0.7 or less has been used to indicate arteriogenic
impotence (Metz and Bengtsson, 1981).
Despite the initial enthusiasm, this
test has many limitations. First, measurement in the flaccid state will
not reveal the full functional capacity of the cavernous arteries in the
erect state, and errors may also occur from improper fitting of the
blood pressure cuff. Second, the continuous-wave Doppler probe does not
discriminately select the arterial flow of the paired cavernous
arteries, which are the vessels primarily involved in producing
erection. In the flaccid state, the probe detects all pulsatile flow
within its path and usually detects the higher blood flow of the dorsal
penile artery, which is located superficially and supplies the glans
penis, rather than the lower flow of the cavernous arteries. This error
will sometimes lead to the finding of a normal PBI in a patient with
true arteriogenic impotence. Therefore, a normal PBI cannot be relied on
to exclude arteriogenic impotence. Indeed, attempts to correlate PBI
and other more established techniques have been disappointing. For
example, Mueller and associates (1990) found only a 39% correlation
between PBI and pudendal arteriography. In another study, Aitchison and
associates (1990) reported that up to 20% of patients deemed normal by
one observer would be deemed abnormal by a second. They conclude that
the PBI is inaccurate and poorly reproducible and suggest no
justification for its continued use.
Penile Plethysmography (Penile Pulse
Volume Recording). This test is performed by connecting a 2.5- or 3-cm
cuff to an air plethysmograph. The cuff is inflated to a pressure above
brachial systolic pressure, which is then decreased by 10-mm Hg
increments, and tracings are obtained at each level. The pressure
demonstrating the best waveform is recorded. The normal waveform is
similar to a normal arterial waveform obtained from a finger: a rapid
upstroke, a sharp peak, a lower downstroke, and, occasionally, a
dicrotic notch. In patients with vasculogenic ED, the waveform shows a
slow upstroke, a low rounded peak, slow downstroke, and no dicrotic
notch. Its height varies considerably; patients with vascular
insufficiency usually have the lowest mean height (17.3 mm) (deWolfe,
1988). The proponents of this method argue that because penile pulse
volume recording measures the contributions of all the vessels at the
root of the penis, it is more accurate than recording the pressure in an
individual artery (as in PBI). However, this study is performed in the
flaccid state and cannot distinguish whether the dorsal or the cavernous
artery is impaired.
Biochemical Study. It has been suggested
that penile hypercoagulability predisposes to penile vascular changes
and impotence. Thromboxane A2 is a potent vasoconstrictor and a stimulus
of platelet aggregation, which may contribute to hypercoagulability.
Contrarily, PGI2 has exactly the opposite effect. Because the ratio of
the prostacyclin concentration to the thromboxane A2 concentration is
constantly maintained in normal hemostatic responses, an imbalance
between the two may be a factor in initiating vascular disease and
decreasing blood flow. Kim and colleagues (1990) assessed the usefulness
of the prostacyclin–to–thromboxane A2 ratio in penile blood during
erection for the diagnosis of arteriogenic impotence. The ratio in these
patients was significantly lower than in patients with psychogenic and
venogenic impotence. Measurement of the major urinary metabolites,
11-dehydro-thromboxane B2 and 2,3-dinor-6-keto-prostaglandin F1α
(PGF1α), by radioimmunoassay can accurately reflect in vivo the
biosynthesis of thromboxane A2 and PGI2, respectively; and Lin and
coworkers (1992) have reported that the mean urinary
11-dehydro-thromboxane B2 level of patients with arteriogenic impotence
is significantly greater than that of controls but that there is no
significant difference in PGF1α levels. Kohler and colleagues (1993)
have also shown that the systemic prostacyclin–to–thromboxane A2 ratio
differs significantly between control rabbits and rabbits with
hyperlipidemia. However, they could find no significant difference
between patients suffering from organic and psychogenic ED.
