Introduction: In a number of tissue microcirculations, the phenomenon of vasomotion occurs where only a proportion of the total number of capillaries present are open at the same time; they normally open and close in a random or chaotic order, partly determined by the metabolic state of their surrounding cells.
Aim: A pilot to examine by photoplethysmography whether the vaginal microcirculation shows evidence of vasomotion and the effect when sexual arousal is induced.
Methods: The vaginal microcirculation in 14 healthy, premenopausal women was monitored by intravaginal infrared photoplethysmography using the vaginal pulse amplitude (VPA) as the index of blood content in the basal condition and during sexual arousal induced by video and/or clitoral stimulation.
Main outcome measure: Analysis and interpretation of vaginal photoplethysmographic traces.
Results: The basal traces in all the sexually unaroused subjects (N = 14) showed at least two populations of their VPAs: a high amplitude VPA (h-VPA) with rapid ascending phase (short duration of systolic infill) and descending phase (short duration of diastolic outflow) among which were pseudorandomly scattered, low amplitude VPAs (l-VPA) with less acute ascending and descending phases; the l-VPAs were usually half the amplitude of the h-VPAs. On sexual arousal, the l-VPAs were converted into h-VPAs so that the l-VPAs decreased and in some cases practically disappeared, and the h-VPAs usually showed an increase; with cessation of the vasodilatory stimulus (N = 6), there was a slow recovery of the l-VPAs. The induction of orgasm did not appear to facilitate their recovery. Even during a short duration of sexual arousal (1 minute), the decrease in the l-VPAs (N = 6) was a more sensitive index of the occurrence of genital arousal than relying solely on changes in the maximum amplitude of the VPA.
Conclusion: Because of vasomotion, the vaginal microcirculation can react to a vasodilatory stimulus with one of four theoretical photoplethysmographic responses, viz., Type 1 (full response), where there is a significant increase in the amplitude of the h-VPA signal and the number of l-VPAs are greatly reduced with a near corresponding increase in the h-VPAs; Type 2 (partial response), where the amplitude (and in some cases the number) of the h-VPAs increases but there is no decrease in the number of l-VPAs; Type 3 (partial response), where the amplitude of the h-VPAs changes little but the number of l-VPAs is reduced and the number of h-VPAs are correspondingly increased; and Type 4, where neither the amplitude of the h-VPAs (or their number) nor the number of the l-VPAs change significantly (a noneffective stimulus). This new analysis allows a more comprehensive and better discriminatory assessment of vaginal vasodilatation (genital arousal) and its return to the basal state in response to sexual arousal and now includes a new measure that is independent of an increase in the h-VPA maximum amplitude (Type 3 response).