Variation in intravaginal pressure measurements.

The wide variation in intravaginal pressure measurements of the circumvaginal muscles (CVM) was studied in five subjects under well-controlled conditions. Previous research and clinical observations have indicated that fluctuations in the measurement of intravaginal pressure may be associated with time of day, day of testing, and existing stress factors. Subjects were assessed four times per day, on four consecutive days, for a total of 16 assessments. At each of the 16 conditions for a given subject, 10 CVM contractions lasting 12 seconds each were recorded and the variables, maximum pressure (MP10), peak maximum pressure (PMP), and abdominal pressure were analyzed. The within-subject variance was 15.5 (SD = 3.9); the between-subject variance was 132.4 (SD = 11.5). The effects of day, time, and stressor were analyzed by ANOVA specifically designed for variance estimates; no significant differences were found. The clinical observations that led to the study were not supported when systematically investigated. However, consistent data collection procedures appeared to reduce within-subject variance.