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Reflex contraction of pelvic floor muscles during cough cannot be measured with vaginal pressure devices

Letter to the editor concerning: Madill SJ, McLean L: Intravaginal pressure generated during voluntary pelvic floor muscle contractions and during coughing: The effect of age and continence status. Neurourol Urodyn 2010; 29:437–442. Dear Editor in Chief Professor Chris Chapple, The above-mentioned article by Madill and McLean about measurement of intra-vaginal pressure to assess pelvic floor muscle maximal voluntary contraction (MVC) and response to coughing underscores some important points that need to be noted. It has been argued that intra-vaginal pressure measurements are complex and there is the possibility that variations in intra-abdominal pressure and co-contractions of the outer pelvic muscles such as hip adductor, external rotators, gluteals, and abdominal muscles can influence the measurements. Indeed increases in intra-abdominal pressures caused by coughing and Valsalva invariably modulate intravaginal pressure and can confound the accuracy of measurements of PFM contraction and strength. Interpretation of vaginal pressure measurements during attempts of MVCmust therefore be used with vigilance, and we caution that vaginal pressure measurements is only valid if confirmed with there is a simultaneous observation of inward movement of the perineum or measurement device. If the perineum or probe is moving inwards, there it is unlikely that there is significant increase in intra-abdominal pressure and a correct contraction with squeeze and inward/forward lift is accomplished. Clearly, substantial time and training is needed to teach the patients not to co-contract other muscles such as abdominals, adductor, and gluteal muscles that can influences intravaginal pressure as well . Examination of Madill and McLean paper highlights the importance of imparting awareness to the subjects during evaluation, and suggests caution needs to be exercised in interpreting the results on MVC, endurance, and rise time during contraction. In considering the results of this paper we urge vigilance in their interpretation as there is major concern relating to additional confounding factors introduced in the measurement of PFM reflex response to coughing. Measurement of abdominal pressures, particularly in cases of co-contractions, can vary depending on sensor location and its configuration and are unlikely to uniquely reflect the PFM response. These factors need to be explicitly monitored in any protocol. It should be stressed that pressure as a measurement tool constitutes the summation of signals originating from cocontractions or feed-forward contractions. Indeed the reflex alone is too slow for this purpose and it happens before or at least at the same time rendering it difficult to distinguish possible co-contractions from the PFM during coughing and the increases in intra-vaginal pressure due to increases in intra-abdominal pressure caused by the cough itself . Clearly the measurement of the response of PFM to changes in intraabdominal pressure and during physical activity is emerging as an important area for future research requiring the design of smart abdominal pressure sensors and the quantification of imaging from dynamic MRI and ultra-sonographic scanning.