Sleep. 3(1):95-97
© 1980 Raven Press. New York
Technical Note
Quantification of Penile "Buckling" Force
Pierre M. Hahn and Ron Leder
Long Island Research Instftute and Sleep Disorders Program, Department of
Psychiatry and Behavioral Science, State University of New York at Stony Brook,
Long Island, New York
Summary: A hand-held transducer was developed for measuring penile
rigidity. This instrument gives a quantitative measure of the force at which the
penis "buckles." The transducer consists of a cantilever beam with strain
gages that is rugged, easy to calibrate, and adaptable to most graphic recorders.
Key Words: Erectile failure-Transducer-Noctumal penile tumescencePenile "buckling."
The evaluation of erec.tile failure in men will often require measures of penile
tumescence during two or more consecutive sleep-nights (Karacan and Hara,
1978). These data are obtained by measuring the sleep parameters of the electroencephalogram, electromyogram, and electro-oculogram and the changes in the
circumference of the penis both at the tip and base by me<lns of mercury strain
gages (Karacan, 1969) or by other devices for the measurement of diameter (Laws
and Bow, 1976), pulsatile blood flow (Hatch et aI., 1979), or volume changes
(Freund et al., 1965).
During the second or third night, the evaluation protocol involves awakening at
a "maximal" erection in order that both the patient and the clinician in attendance
can evaluate the quality of the erection. Photographs are used to document this
evaluation. The Houston group (Karacan et al., 1978) also measures "buckling"
pressure by means of a specially designed pressure device which is pressed
against the glans of the penis, toward the penis base. The laboratory at Stony
Brook is using a device which we have named the tonometer to measure the
"buckling" force in the same manner. As with Karacan's device, the tonometer is
pressed against the glans of the penis toward the penis base, and the resulting
force is recorded on the polygraph. A sharp drop in recorded force is noted when
the penis "buckles" (Fig. 1).
Accepted for publication July 1980.
Address correspondence and reprint requests to Mr. Hahn at Department of Psychiatry, SUNY HSC
lOT, Stony Brook, New York 11794.
95
96
P. M. HAHN AND R. LEDER
FIG. 1. Oscillogram of tonometer output used to measure buckling force. Asterisk indicates buckling
point, 330 g force.
The linear relationship between the force at the cup and the output of the bridge
allows the calibration to be accomplished with only two points. For the first point,
the tonometer is held horizontally with the cup pointing upward; this is the
"zero-force" condition. Then a weight (e.g., 200 g) is placed in the cup to obtain
the second point. An electrical analog of the calibration is available when using
Grass DC amplifiers (7Pl or 7P122) by means of the bridge calibration feature. By
comparing this signal with the one obtained with the weight, the equivalent value
of this electrical calibration is easily calculated. This feature facilitates sensitivity
adjustment to match the expected range of measurement. The bridge calibration
feature also provides quick calibration before and after the measurements are
made.
We have found the tonometer to be very useful because (1) it is rugged and
almost indestructible; (2) the measurement is made in easily quantifiable units and
requires only two calibration points; (3) there is an on-line graphic representation
of the measurement process, and this trace gives unambiguous indication of the
buckling force; (4) when the force is applied in a steady manner, the variability of
measurements between technicians or devices is minimized; and (5) it is adaptable
to most graphic recorders.
The tonometer (Fig. 2) is a hand-held beam, strain-gaged to measure the
bending due to the reactive force at the cup (which is in contact with the glans).
The beam is of rectangular cross section and is made of aluminum. The strain
gages (type EA-13-062AQ-350 option L: Micro-Measurements, P.O. Box 306,
Romulus, Michigan 48174) are cemented per the manufacturer's instructions at
approximately 120 mm from the cup's center and wired to form a full Wheatstone
bridge to measure bending. A handle made from a piece of 18 mm i.d. polyvinyl
chloride pipe is then slipped over the end of the beam to within 5 mm of the strain
gages. The width of the beam has a 1 mm taper to provide an interference fit.
Silicone rubber (RTV Sealant #108, General Electric) is used as a moisture seal
for the gages and to fill the space between the beam and the handle. A connector
(Cannon WK6-22C-A95) is installed at the open end of the handle. Resistor R5 is
used in conjunction with an amplifier which has a bridge calibration feature. A
sensitivity of about 0.25 microvolt/volt/gram can be expected with the above
design.
Sleep, Vol. 3, No. I, 1980
97
PENILE "BUCKLING" FORCE
~r--------------------200mm
I
~------------ 120mm----------~·
3a4ST~N~S
_...... '" .... '" ... p=9-------------------------.,..."..,
~--------------~I~------------~
........... -.---.- .. rY'
~~~~----;::::=~
I a 2 STRAIN GAGES
6mm
FIG. 2. Cross-sectional views of the tonometer and schematic diagram of the strain gage bridge used.
References
Freund K, Sedlacek F, and Knob K. A simple transducer for mechanical plethysmography of the male
genital. J Exp Anal Behav 8: 169-170, 1965.
Hatch JP, Heiman JR, and Hahn PM. A photo plethysmographic device for measuring changes in penile
blood volume pulse during sexual arousal in humans. (AbstL) Psychophysiology 17:287, 1980.
Karacan I. A simple and inexpensive transducer for quantitative measurements of penile erection
during sleep. Behav Res Methods lnstrum 1(7):251-252, 1969.
Karacan I and Hara R. Diagnostic advances in impotency. Encephale 4:81-92, 1978.
Karacan I, Salis PJ, and Williams RL The role of the sleep laboratory in diagnosis and treatment of
impotence: NPT and the diagnostic evaluation of impotent men. In: RL Williams and I Karacan
(Eds), Sleep Disorders: Diagnosis and Treatment, Wiley, New York, 1978, pp 365-366.
Laws DR and Bow RA. An improved mechanical strain gauge for recording penile circumference
change. Psychophysiology 13:596-599, 1976.
Sleep. Vol. 3, No.1, 1980