Determining the shape of the turns-amplitude cloud during anal sphincter quantitative EMG.

We aimed to compare our normative data for quantitative interference pattern (IP) analysis of the anal sphincter to previously published data. In 28 nulliparous women, we performed IP analysis during quantitative concentric needle electromyography (QEMG) of the anal sphincter. At each sampling site, a 500-ms epoch was analyzed. The data were log transformed. Linear regression lines (with 95% confidence intervals) were calculated from the log transformed variables "turns-second" and "amplitude-turn." These confidence intervals were then transformed back into the original parameters to yield scatterplots with confidence curves. The mean turns-second were 203 (SD 174). The mean amplitude (mcv)-turn was 266 (SD 87). The regression coefficients for the log-transformed variables are constant = 1.5, slope = 0.3, and resultant cloud of raw data has a convex upper boundary. These appear slightly different than previously published reports, potentially influencing the determination of normal and abnormal studies.