Comparison of measurements obtained with microtip and external water pressure transducers

The aim of this study was to compare pressure readings obtained with catheter-mounted microtip and external water pressure transducers using a mechanical model for vesical pressure during Valsalva straining and coughing. The two catheter-mounted pressure transducers were simultaneously placed in a vinyl IV bag designed to mimic the parameters of the human bladder to allow comparison of simultaneous readings from both transducers. Simulated cough and Valsalva maneuvers of various strengths at different volumes (100 ml, 200 ml, 300 ml) were performed and the pressure readings generated by the two systems compared. The Pearson correlation coefficient between the systems was 0.998 for coughs and 0.998 for Valsalva efforts. Data were also analyzed by volume and strength of simulated cough and Valsalva effort, and correlations were found to be high (0.940) for all subgroup analyses. Mean absolute differences between events recorded by the two systems were small, as indicated by the y-intercept of 3.76 cmH₂O pressure. Neither transducer recorded consistently higher pressures than the other. We concluded that there is a high correlation between pressure measurements obtained from microtip and external water pressure transducers during simulated cough and Valsalva efforts in this model. As similar correlation should exist in vivo, urodynamic data generated by the two transducer types should be comparable.Abbreviations ISD Intrinsic sphincter deficiency - LPP Leak-point pressureEditorial Comment: There are many technical variations in urodynamic testing, including the type of catheter used. These authors found that results obtained with perfusion and microtip catheters were highly correlated. As would be expected, they were able to demonstrate a time lag in the pressure recordings from perfusion catheters. As a result of this lag the amplitude of a cough leak point might be underestimated by a perfusion catheter. However, their results suggest that the magnitude of this underestimation would not be clinically relevant. In summary, this paper suggests that the pressures measured by microtip catheters and perfusion catheters are similar. It remains to be seen whether these results can be replicated in vivo.     

A Comparison of Urethral Profilometry using Microtip and Fiberoptic Catheters

This paper compares urethral profilometry measurements using two different types of catheter: the Millar microtip transducer and the FST fiberoptic catheter. Outcome variables were functional urethral length (FUL), maximum urethral closure pressure (MUCP), and mean pressure/transmission ratio (PTR). Thirty women presenting to the urodynamics laboratory with symptoms of stress urinary incontinence were evaluated with both catheters. All subjects underwent two passive urethral pressure profiles and two dynamic (cough) urethral pressure profiles with each catheter. For FUL and MUCP, the means of the two passive measurements were compared between catheters. For PTR, the means of the two dynamic measurements were compared between catheters. There was no difference in FUL between the two catheter types. The FST measurements of MUCP and PTR were lower than the microtip measurements. Twenty per cent of patients would have been diagnosed with low-pressure urethra with the FST catheter, but not with the microtip catheter. Caution must be used when applying urethral measurements taken with the fiberoptic catheters to standards set with microtip catheters.     

A comparative study of water perfusion catheters and microtip transducer catheters for urethral pressure measurements

The aim of this study was to compare the maximum urethral closure pressure (MUCP) measures with two different techniques: water perfused catheter and microtip transducer catheters with respect to reproducibility and comparability for urethral pressure measurements. Eighteen women with stress urinary incontinence had repeat static urethral pressure profilometry on a different day using a dual microtip transducer and water perfused catheter (Brown and Wickham). The investigators were blinded to the results of the other. The microtip measurements were taken in the 45° upright sitting position with the patient at rest at a bladder capacity of 250 ml using an 8 Fr Gaeltec® double microtip transducer withdrawn at 1 mm/s, and the transducer was orientated in the three o’clock position. Three different measures were taken for each patient. Three water perfusion measurements were performed with the patient at rest in the 45° upright position at a bladder capacity of 250 ml using an 8 Fr BARD dual lumen catheter withdrawn at 1 mm/s. The mean water perfusion MUCP measure was 26.1 cm H₂0, significantly lower than the mean microtip measure of 35.7 cm H₂0. The correlation coefficient comparing each water perfusion measurement with the other water perfusion measures in the same patient was excellent, at 0.95 (p?=?0.01). Correlation coefficient comparing each microtip measure with the other microtip measure in the same patient was also good, ranging from 0.70 to 0.80. This study confirms that both water perfusion catheters and microtip transducers have excellent or very good reproducibility with an acceptable intraindividual variation for both methods.     

Fiber-optic versus microtip transducers in simultaneous urethrocystometry. A comparative study

A comparative study of a new fiber-optic transducer versus a microtip transducer was performed in 13 females. A good correlation was found on bladder pressure. The urethral pressure diverged considerably, as the pressures measured with the fiber-optic transducer were about two thirds of the pressures found with the microtip. The functional urethral length measured with the fiber-optic transducer was also shorter.     

Are the measurements of water-filled and air-charged catheters the same in urodynamics?

Introduction and hypothesis

The aim of our study was to compare air-charged and water-filled catheters simultaneously in the measurement of the intravesical, abdominal and detrusor pressure during urodynamic investigations.

Methods

Consecutive women with lower urinary tract symptoms, referred for urodynamics were prospectively studied. Readings of intravesical pressure (p_ves), abdominal pressure (p_abd) and detrusor pressure (p_det), recorded by both the air-charged and water-filled catheters, were displayed simultaneously and compared at the end of filling, on standing, on sitting prior to voiding and at the maximum involuntary detrusor contraction. The signals (pressures) recorded by both types of catheter were compared using the Bland–Altman plot and paired samples t test.

Results

Twenty women with a mean age of 49 (range 36–72) were recruited. One patient with normal urodynamics was excluded in view of the poor quality trace. At each of the four comparison points, the air-charged catheters consistently produced higher mean pressures than the water-filled catheters. There were wide variations in the difference between the readings produced by the two types of catheter.

Conclusions

Pressures measured using air-charged catheters are not comparable with water-filled catheters and are therefore not interchangeable. Caution must be used when comparing urodynamic parameters using air-charged and water-filled catheters.     

Characterization of pressure changes in the lower urinary tract during coughing with special reference to the demands on the pressure recording equipment

The exact demands on urodynamic equipment for measurement of coughs and cough associated pressure changes in the lower urinary tract have been analyzed from high-speed pressure recordings using a double microtip transducer and a storage oscilloscope. The equipment was tested in vitro by the step-test method. The natural frequency response was 175.6 Hz and the rise-time 2.5 ms, resulting in accurate measurements of frequencies up to about 60 Hz which is way above the clinically measured frequencies. Four men and 2 women, all of whom were healthy volunteers, were examined in the supine position with an empty bladder. Pressures were measured in the bladder and in the external sphincter zone of the urethra. The spectral power density of the bladder and urethral pressures were calculated by Fourier analysis. The pressure changes in the urethra were in all volunteers equal to or slower than in the bladder. The analysis of the spectral power density showed that 99% of the pressure changes could be recorded with an instrument capable of recording 9 Hz frequencies, i.e., with a sampling rate of 18 Hz or more. © 1994 Wiley-Liss, Inc.     

Resting and stress urethral pressures as a clinical guide to the mechanism of continence in the female patient

Urethral closure pressures are examined with respect to continence and aging. An attempt is made to interpret the inherent orientation sensitivity of microtip transducer profilometry. The transmission of cough pressures along the length of the urethra is also examined, showing that incontinence is associated with low transmission.     

Time separation between cough pulses in bladder, rectum and urethra in women

Time separations between cough pulses detected by microtip transducer catheters in bladder, urethra and rectum were studied in 10 healthy female volunteers, 10 genuine stress incontinents, 10 motor urge incontinents and 9 motor urge incontinents after bladder retraining. From the measurements that could be analyzed in the group of volunteers, 25 per cent showed a significant advanced onset of the pressure rise in the urethra and 50 per cent a prolonged duration of the urethral cough pulses. None demonstrated delayed onset or shortened duration compared to the vesical pulses. In the genuine stress incontinent group none of the women had an advanced urethral start whilst the motor urge incontinents had figures somewhere in between, except for a remarkable prolonged duration of the urethral cough pulse in the bladder retrained women. The data obtained can be explained by introducing, besides the passive transmission of abdominal pressure, a 2nd component actively engaged in maintaining continence.     

Inadvertent ureteral catheterization with a microtip catheter at cystometry

Two patients in whom the right ureter was inadvertently catheterized at water cystometry are described. Accidental ureteral catheterization and filling was followed by colicky pain in the right flank and by an abrupt increase in the recorded pressure, up to 148 cmH₂O. The pain disappeared and the intravesical pressure returned to baseline after the microtip catheter was withdrawn.     

Peripheral neural lesion-induced stress urinary incontinence in anaesthetized female cats

OBJECTIVES

To characterize the effect of acute unilateral and bilateral lesion of the pelvic and pudendal nerves, and nerves innervating the iliococcygeous and pubococcygeous muscles during sneezing in anaesthetized female cats, on intravesical pressure (IVP), urethral pressure (UPs) and external urethral sphincter (EUS) activity.

MATERIALS AND METHODS

In seven anaesthetized female cats UPs along the urethra (UPs1–4) and IVPs were recorded in the emptied bladder during sneezing before and after unilateral and then bilateral peripheral neural lesions. UPs were measured using microtip transducer catheters with UP4 positioned in the distal urethra where the EUS is located. Urine leakage was also noted, after urethral catheter removal and bladder filling.

RESULTS

During sneezing, in intact cats, the magnitude of UP4 was larger than those of IVP and UPs1–3. The area under the curve of both anal sphincter and EUS electromyography was increased. There was no urine leakage. After unilateral neural lesions, the mean magnitude of response was similar all along the urethra and in the bladder. The distal UP response was significantly lower than that recorded in intact cats. In addition, there was urine leakage in six of the seven cats. Bilateral neural lesions caused permanent urine leakage and significant decreases in all the UP responses.

CONCLUSION

In female cats, during sneezing, neurally driven reflex contractions of EUS leading to an increase in distal UP contribute to active urethral closure mechanisms and ensure urinary continence.     

Simultaneous urethral pressure profilometry using a microtip transducer catheter in the bitch: Effects of bitch position and transducer orientation

Simultaneous urethral pressure profilometry using a microtip transducer catheter was perfonned in 14 bitches to determnine the effects of the position of the animal and the transducer orientation. The technique was carried out in three positions of the bitch (right lateral, dorsal, and left lateral recumbency) and four orientations of the transducers (Diorsal, right, ventral, and left). Both functional profile length and maximum urethral closure pressure were significantly affected by the orientation of the transducer relative to the position of the bitch. The optimum position of the bitch and orientation of the transducers were detennined by evaluating the proportion of profiles from which measurements could not be made, the diagnostic value of profiles, and the Proportion of artefacts in functional profile length. It was concluded that the bitch should be positioned in right lateral recumbency with the transducers orientated dorsally as these positions result in the highest proportion of diagnostic and measurable profiles and the lowest proportion of artefacts in functional profile length.     

Differences in pressures of the popliteal, long saphenous, and dorsal foot veins

PURPOSE: The purpose of this study was to examine the relationship among pressures obtained simultaneously in the popliteal, long saphenous, and dorsal foot veins. METHOD: Eight limbs were studied. One limb had an isolated popliteal vein reflux, and two had moderate long saphenous vein incompetence. No perforator or short saphenous vein insufficiency was detected. Pressures and recovery times of the popliteal/tibial and long saphenous veins were obtained with cannulation at the ankle level and insertion of catheters with a pressure transducer tip. The dorsal foot vein pressure was measured with the insertion of a scalp needle (14-gauge) connected to an external transducer. During 10 toe stands, recordings were simultaneously made in the three veins at the level of the knee joint, in the middle third of the calf, and 5 to 7 cm above the ankle with all the transducers at the same level (ie, same reference point). RESULTS: In one limb the popliteal/tibial pressure increased at all calf levels, whereas pressures decreased in both saphenous and dorsal foot veins. The pressures decreased in all three systems in the remaining seven limbs. There was no statistical difference between the pressure drop in the long saphenous vein and the deep vein. However, the decrease of the dorsal foot venous pressure was significantly more marked compared with the other two veins at all levels. The recovery time was significantly increased in the long saphenous vein compared with the deep vein; recovery time was further prolonged in the dorsal foot vein. CONCLUSION: The dorsal foot, long saphenous, and popliteal/posterior tibial veins clearly exhibit different pressure waveforms in response to calf exercise. The postexercise pressure, the percentage pressure drop, and the recovery times are widely different, which indicates that the three veins behave hydraulically as separate compartments in limbs without significant venous insufficiency.     

Normal range for transdiaphragmatic pressures during sniffs with catheter mounted transducers.

BACKGROUND--Transdiaphragmatic pressure (sniff PDI) during maximal sniffs is a useful clinical test of inspiratory muscle function. Although a normal range has been established for sniff PDI using air filled balloons, no comparable data are available for catheter mounted pressure transducers. METHODS--Using a single catheter with two pressure transducers 15 cm apart, oesophageal and gastric pressures were recorded in 50 normal volunteers (25 women), five of each sex from each decade between the third and seventh decades of life. Each subject performed 10 maximal sniffs at functional residual capacity. RESULTS--Mean (SD) sniff PDI was 149 (32) cm H2O in men and 127 (22) cm H2O in women. The lower limits of normal for sniff PDI (mean -1.96 x SD) after logarithmic transformation of the data were 95 and 78 cm H2O in men and women respectively. CONCLUSIONS--With this technique transdiaphragmatic pressure can be measured using a single catheter which can easily be cleaned and reused. The values for sniff PDI are similar to those recorded previously with air filled balloons, suggesting that the method of recording pressure does not significantly affect the values obtained.     

Urethral pressure increment preceding and following bladder pressure elevation during stress episode in healthy and stress incontinent women

The urethral pressure elevation preceding and following pressure elevation in the bladder during cough was studied in 30 healthy volunteers and 30 genuine stress-incontinent women. The pressures were measured by means of a double microtip transducer catheter with the distal sensor in the bladder and the proximal sensor covered with a water-filled balloon and placed at the bladder neck, in the high-pressure zone, or distally in the urethra. In both groups of women a urethral pressure elevation was demonstrated before and after pressure elevation in the bladder during a cough. A urethral pressure elevation ≥ 5 cm H₂O both before and after bladder pressure elevation was demonstrated in one third and one fourth of healthy and stress-incontinent women, respectively. The initial urethral pressure rise in the mid- and distal urethra was statistically significantly higher in the healthy women. During abrupt coughing the initial urethral pressure rise disappeared. The pelvic floor as part of the demarcation of the abdominal cavity is positively taking part in the intraabdominal pressure generation during stress episodes, and the urethral pressure increment in advance of bladder pressure elevation reflects an active contraction. A lowering of this initial urethral pressure rise may be a contributing factor of the pathogenesis of genuine stress incontinence, although it does not necessarily result in stress incontinence.     

Initial urethral pressure increase during stress episodes in genuine stress incontinent women.

The urethral and bladder pressure increments registered during a cough were investigated in 30 woman with genuine stress incontinence (GSI) and compared with those from 30 previously investigated healthy women. The pressures were measured by means of a double microtip transducer catheter with the bladder sensor uncovered and the urethral sensor covered with a water-filled rubber cylinder and placed at the bladder neck, midurethrally, or distally in the urethra. In GSI women the pressure increment preceding the pressure spike produced by coughing was significantly higher in the bladder compared with the urethra, and the pressure increment seemed to be initiated in the bladder and all along the urethra simultaneously. In healthy women the pressure increment preceding a pressure spike was significantly higher in the midurethra compared with the bladder and it seemed to be initiated in the midurethra. These findings seem to reflect a defective active closure mechanism in GSI which may be a contributing factor in its pathogenesis.     

Continuous recording of urethral activity in healthy female volunteers

The pressure variations at the maximal urethral closure pressure (MUCP) were continuously recorded in healthy female volunteers by means of a two-point microtip transducer catheter for one hour. Before the investigation a normal voiding was assured objectively and bladder instability was excluded. All women showed pressure variations both at the MUCP and more distally. The pressure variations, from 3 to 66 cm H₂O, showed rhythmicity and three frequency ranges could be identified. Slow pressure waves with a frequency of one in eight to 19 minutes were observed. Relatively fast-pressure waves were observed (one every one to four minutes) and relatively fast-frequency pressure waves were observed (rate: one to eight per minute). The pressure variations of the urethra seem to be an aspect of normal urethral physiology possibly contributing to continence and urinary tract infection prevention.     

Principles of pressure transducers,resonance, damping and frequency response

Blood pressure is a determinant of blood flow, and is the sum of hydrostatic and dynamic pressures. Intravascular pressures can be measured directly using intravascular pressure sensors, or with external transducers connected by a fluid column. Early pressure transducers consisted of wire strain gauges, but these have been superseded by semiconductor devices, which have become increasingly mass-produced and miniaturized, using production techniques common in microelectronics. Performance of pressure-monitoring systems is affected by physical factors including resonance and damping. This article examines the physical principles that underlie transducer design and function, and the sources of error and inaccuracy.     

Abnormal pelvic response to cough in women with stress urinary incontinence

AIMS: To assess how muscular fatigue deteriorates the modulation of pelvic contraction during increasing cough efforts. Furthermore, we investigated the correlation between the temporal course of pelvic floor activation during cough. METHODS: Informed consent was obtained from 20 women presenting with SUI and 6 continent women (overactive bladder syndrome [OAB]). Bladder pressure (BP) and external anal sphincter electromyographic activity (EAS EMGi) were recorded concomitantly during increasing cough efforts. Modulation of pelvic contraction was assessed before and after two types of intense pelvic exercise (Exercise #1: 10 successive strong cough efforts; Exercise #2: 10 pelvic contractions followed by a maximal pelvic contraction) at 0, 200, and 400 ml of bladder filling. We have also recorded electromyographic activity of external intercostal (EIC) muscles. RESULTS: Whereas the Exercise 1 had no effect on modulation, the Exercise 2 altered significantly the modulation of pelvic contraction during increasing cough efforts (P = 0.043) only in women presenting with SUI. The bladder filling volume seems to not significantly modify this modulation (P = 0.12). Median latency between the onset of the EAS EMGi and the onset of the EIC EMGi was -470 and -60 msec in OAB group and in SUI group, respectively (P = 0.012). There was a good correlation between mean latency (default of EAS EMGi pre-activation) and an altered modulation of pelvic contraction during increasing cough efforts (P = 0.040). CONCLUSIONS: Some women with SUI exhibit an altered pattern of the PFM response during increasing coughing efforts. The lack of this modulation of PFM response to stress may be one of the pathophysiologic factors of SUI.     

Urethral pressure profiles in the female canine implanted with sacral anterior nerve root electrodes

 The purpose of this work was to study the pressure distribution along the urethra in female canines with and without electrical stimulation of the sacral anterior roots innervating the bladder and urethra. Urethral pressure profiles were recorded in two orientations, dorsal and ventral, with microtransducer catheters. Two pulse types were applied at 1 Hz, 500 μs quasitrapezoidal pulses to selectively activate the small axons and 100 μs rectangular pulses. Four parameters were measured from each profile; maximum urethral pressure (MUP), bladder pressure (Pv), functional urethral length (FUL), and the position of the maximum peak from the bladder neck (PMP). Two derived measures, the estimated maximum urethral closing pressure (UCP) and the position of the maximum as a percentage of the FUL (PM%) were calculated. There were highly significant differences (P<0.01) in the value and position of the estimated UCP in the two orientations of the transducers. The highest pressures were recorded in the ventral orientation near the terminal portions of the urethra. Principal sphincter activity during electrical stimulation of the ventral sacral roots was also confined to this part. Selective small fiber activation did not result in any significant increase in this peak pressure from passive values.     

Clinical significance of axial variations in female urethral pressure profiles

It has been demonstrated that when urethral pressure profiles are measured with microtip transducers on relatively stiff catheters, there is an important difference in the profile when measured with the transducers facing anteriorly and posteriorly. It has been suggested that patients with demonstrable genuine stress urinary incontinence had notably lower posteriorly derived urethral pressure profiles than anteriorly derived pressure profiles. A clinical consideration of this factor has been studied in 25 patients; 19 had accepted urodynamic evidence of genuine stress urinary incontinence and 6 did not. The use of posteriorly derived pressure profiles in comparison with anteriorly derived as a test for genuine stress urinary incontinence showed a sensitivity of 84% and specificity of only 33.3%. However, when correlated with patients showing lack of anatomic support of vaginal and paraurethral structures, the sensitivity and specificity is significant. Anatomic considerations leading to these findings are suggested.