Sexual arousal
Sexual arousal in women is characterized by vasocongestion of the genital tissues, including internal and external areas (e.g., vaginal walls, clitoris, and labia). There are a variety of methods used to assess genital sexual arousal in women. Vaginal photoplethysmography (VPG) can measure changes in vaginal blood volume or phasic changes in vasocongestion associated with each heartbeat. Clitoral photoplethysmography functions in a similar way to VPG, but measures changes in clitoral blood volume, rather than vaginal vasocongestion. Thermography provides a direct measure of genital sexual arousal by measuring changes in temperature associated with increased blood flow to the external genital tissues. Similarly, labial thermistor clips measure changes in temperature associated with genital engorgement; this method directly measures changes in temperature of the labia. More recently, laser doppler imaging (LDI) has been used as a direct measure of genital sexual arousal in women. LDI functions by measuring superficial changes in blood flow in the vulvar tissues.