Vaginal photoplethysmography (VPG, VPP) is a technique using light to measure the amount of blood in the walls of the

vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...

. The device that is used is called a vaginal

photometer A photometer is an instrument that measures the strength of electromagnetic radiation in the range from ultraviolet to infrared and including the visible spectrum. Most photometers convert light into an electric current using a photoresistor, ...

Use

The device is used to try to obtain an objective measure of a woman's

sexual arousal Sexual arousal (also known as sexual excitement) describes the physiological and psychological responses in preparation for sexual intercourse or when exposed to sexual stimuli. A number of physiological responses occur in the body and mind a ...

. There is an overall poor correlation (r = 0.26) between women's self-reported levels of desire and their VPG readings.

Instrument

The instrument used in the procedure is called vaginal

. The device has a clear shell, inside of which is a light source and a

photocell Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There is a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or b ...

, which senses reflected light. The use of the device is done with the assumption that the more light that is scattered back, and that the photocell senses, the more blood is in the walls of the vagina. The output of the VPG can be filtered into two types of signals, which have different properties. The

direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or ev ...

signal is a measure of vaginal blood volume (VBV) and reflects the total blood volume in the vaginal tissues.Hatch, J. P. ��Vaginal photoplethysmography: Methodological considerations””Archives of Sexual Behavior, 8, 357–374”, 1979 The

alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...

signal is a measure of vaginal pulse amplitude (VPA) and reflects the pressure change within the

blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide awa ...

s of the vaginal wall associated with each heartbeat. While changes in VBV occur in response to sexual and anxiety-inducing stimuli, changes in VPA only occur in response to sexual stimuli. VPA is defined as the peak-to-trough amplitude of the vaginal pulse wave. It is calculated by subtracting the means of all troughs from the means of all peaks experienced during stimulus presentation. VPA lacks an absolute scale of measurement; each unit of change (mV) does not correspond directly with a physiological change. Since VPA does not have a standard unit of measurement, it is difficult for researchers to make between-participant comparisons.

History

VPG was first introduced in the 1960s by Palti and Bercovici, who affixed a light source and photosensitive cell onto a gynecological speculum and recorded vaginal pulse waves. Sintchak and Geer improved on the device in the 1970s by using a vaginal probe which became the common instrument to measure vaginal blood flow.

References

{{DEFAULTSORT:Vaginal Photoplethysmograph Female genital procedures Medical testing equipment Sexology

Use

Instrument

History

See also

References