Penile plethysmograph Penile plethysmography (PPG) or phallometry is measurement of bloodflow to the penis, typically used as a proxy for measurement of sexual arousal. The most commonly reported methods of conducting penile plethysmography involve the measurement of the circumference of the penis with a mercury-in-rubber or electromechanical strain gauge, or the volume of the penis with an airtight cylinder and inflatable cuff at the base of the penis. Corpora cavernosa nerve penile plethysmographs measure changes in response to inter-operative electric stimulation during surgery. The volumetric procedure was invented by Kurt Freund and is considered to be particularly sensitive at low arousal levels. The easier to use circumferential measures are more widely used, however, and more common in studies using erotic film stimuli. A corresponding device in women is the vaginal photoplethysmograph. For sexual offenders it is typically used to determine the level of sexual arousal as the subject is exposed to sexually suggestive content, such as pictures, movies or audio, although some have argued that phallometry is not always appropriate for the evaluation of sexual preferences or treatment effects. A 1998 large-scale meta-analytic review of the scientific reports demonstrated that phallometric response to stimuli depicting children, though only 32% accurate, had the highest accuracy among methods of identifying which sexual offenders will go on to commit new sexual crimes. For prostatectomy nerve-sparing surgery, the surgeon applies a mild electrical stimulation near the cavernous nerves of penis to verify their locations and avoid operative trauma. Damage to these difficult-to-see nerves can cause erectile dysfunction outcomes. At the surgery's conclusion, the electrical stimulation penile plethysmograph result is a prognosis which helps to manage the erectile function outcomes earlier than the many months required for recovery. Types There are two types of penile plethysmograph: Volumetric air chamber When this is placed over the subject's penis, as tumescence increases, the air displaced is measured. Circumferential transducer This uses a mercury-in-rubber or indium/gallium-in-rubber ring or electromechanical strain gauge and is placed around the shaft of the subject's penis to measure changes in circumference. The circumferential type is more common, but the volumetric method is believed to be more accurate at low arousal levels. Significant suppliers of PPG machines include Behavioral Technology Inc. and Medical Monitoring Systems. The device is known to be used in Brazil, Britain, Canada, China, Czech Republic, Hong Kong, New Zealand, Norway, Slovak Republic, Spain, and the United States. The surgical machine is supplied as CaverMap by Blue Torch Medical Technology, Inc. A roughly equivalent procedure for women, vaginal photoplethysmography, measures blood through the walls of the vagina, which researchers claim increases during sexual arousal. History The original volumetric was developed during the 1950s by Kurt Freund in then-Czechoslovakia. Freund later wrote, "In the early fifties homosexual interaction was still an indictable offense in Czechoslovakia. I was of course opposed to this measure, but I still thought, as did my colleagues at the psychiatric university hospital in Prague where I was working, that homosexuality was an experientially acquired neurosis". He then developed phallometry to replace psychoanalytic methods of assessment because "[P]sychoanalysis had turned out to be a failure, virtually unusable as an instrument for individual diagnosis or research....When phallometry began to look promising as a test of erotic sex and age preferences, we started using it mainly as a test of pedophilia, that is determining who has an erotic preference for children over adults". In post–World War II Czechoslovakia, Freund was assigned by the communist government the task of identifying among military conscripts men who were falsely declaring themselves to be gay to avoid the draft. "Freund (1957) developed the first device,