Urodynamic studies have been used as a functional tool to quantitatively evaluate symptoms of lower urinary tract (LUT) dysfunction and to identify the underlying causes through the measurement of relevant physiologic parameters [1]. It is essential for describing the status of the LUT and is highly recommended in patients with neurogenic LUT dysfunction [2]. Quality control plays a key role in ensuring reliable and accurate urodynamic data. Whether in real-time or a retrospective evaluation, typical value ranges (TVRs) and typical signal patterns (TSPs) are very efficient tools for performing quality control quantitatively and qualitatively. The initial stage of urodynamic studies is crucial because TVRs for signal patterns that are perfect in terms of physiological values usually remain present throughout the investigation [3]. Evaluating the TVRs and TSPs with regard to the initial resting pressure and cough test are crucial quality control steps at the beginning of the urodynamic study. The TVRs of the initial resting pressure can be used to confirm whether the equipment has been set up properly, while the TSPs of minor dynamic changes and cough before filling can be used to check if the signal transmission is functioning properly. The TSPs of the cough signal have been identified in real-time urodynamics [4]. It has been claimed that intravesical pressure (P_ves) and abdominal pressure (P_abd) traces show the same fine structures and equivalent major changes, while detrusor pressure (P_det) does not change significantly during cough tests. Sullivan et al. [5] identified cough signal quality by comparing the measured height of the cough spikes on P_abd and P_ves tracings, stating that a good cough signal has a smaller spike that is 70%–100% the size of the larger spike. This is a somewhat arbitrary classification of the cough signal. As a tool for quality control, coughing should be quantified to the standards used by urodynamic testing centers. Hogan et al. [6] suggested that transmitted cough amplitudes should have a minimum peak height of 15 cm H₂O above the resting pressure; however, the process of implementing such a standard has not been clarified. The aim of this study was to review the consecutive urodynamic traces obtained from neurogenic bladder patients at our center in 2014 to establish the TVRs of the initial cough (cough before bladder filling) signal and to analyze the TSPs of the initial cough.

We retrospectively reviewed 539 urodynamic traces from patients (366 male patients and 173 female patients) who received treatment in our center in 2014. Their mean age was 36±17 years. All patients had a known diagnose of neurogenic bladder, due to traumatic spinal cord injury (347), myelomeningocele (55), spinal surgery (40), and other conditions (Table 1). Of these patients, 443 underwent urodynamic testing in the supine position, while 96 patients underwent testing in the sitting position. All measurements were obtained using a Triton urodynamic analyzer (LABORIE, Mississauga, ON, Canada). A double-lumen transurethral catheter (7F, Cook, Bloomington, IN, USA) was used for filling and to record P_ves. P_abd was measured with a balloon catheter (12F, Cook, Bloomington, IN, USA). The 10-mL balloon was confirmed to be air-free and filled to a maximum volume of 20% (2 mL).

Clinical urodynamic procedures were implemented according to good urodynamic practice (GUP) standards [1] as follows. The residual urine in the bladder was drained before cystometry was performed. External transducers were zeroed to the atmospheric pressure at the height of the upper edge of the symphysis pubis. Transurethral and balloon catheters were then placed in the bladder and rectum, respectively. All connection tubes were confirmed to be free of air bubbles. Before bladder filling, the patients were asked to cough one time to test the signals. Saline with contrast medium at room temperature was infused at 10–30 mL/min. During bladder filling, the signal was tested by asking the patient to cough every 1 minute. Bladder sensations (first desire, normal desire, and strong desire to void) and overactivity of the bladder during filling were noted. X-ray images of the bladder were also obtained at each of those points. Bladder filling stopped when the patient could no longer tolerate the infusion. The patients were then asked to cough to confirm that all of the signals were being transmitted well. A pressure-flow study was performed if the patient could void. The patients were asked to cough before and after voiding. The transducers, flowmeter, and infusion pump were calibrated at least once per month.

This study was designed to measure the initial cough (cough before bladder filling) values and to characterize the initial cough signal patterns in the supine and sitting positions. All tracings were manually read and checked for quality.

For each tracing, the maximum P_ves and P_abd values were recorded during the cough. As P_det exhibits biphasic changes, the maximum P_det and the minimum P_det values were recorded. These values were determined with respect to the atmosphere. In order to isolate the pressure change above the initial resting pressure during coughing, we calculated the cough amplitude in P_ves and P_abd by subtracting the initial resting pressures from the corresponding values during the cough test. The initial resting pressures in both positions were also recorded. For each data point, the mean value, standard deviation, median, 95% confidence interval, and 95% range were calculated using SPSS 17.0 (SPSS Inc., Chicago, IL, USA). We used the 95% range of the values in the population as the reference range for all parameters.

Different initial cough signal patterns were classified. In order to analyze these signal patterns, we adjusted the P_ves, P_abd, and P_det into 1 channel and amplified the signal. Different pressures can be distinguished by the color of the lines in the single-channel display. In all relevant figures, the blue line corresponds to P_ves, the red line is P_abd, and the green line indicates P_det.

The quality of all traces was checked by 2 experienced urologists in our center. The criteria for assessing an image as high-quality were set by referencing GUP [1] and a retrospective study of urodynamic traces [5]. In addition, we suggest that apart from external pressure changes, such as talking, coughing, moving or Valsalva maneuvers, the P_abd during the bladder-filling phase should remain steady. Thus, we used the following criteria for classifying a trace as high-quality:

The distribution of high-quality traces between groups was assessed using the chi-square test.