Uroflowmetry Combined with Simultaneous Measurement of Abdominal Pressure by Tocodynamometer

0022 5347 /93/1491-0335$03.00/0 THE JOURNAL OF UROLOGY Copyright© 1993 by AMERICAN UROLOGICAL ASSOC!AT!ON, !NC.

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Urological Neurology and Urodynamics UROFLOWMETRY COMBINED WITH SIMULTANEOUS MEASUREMENT OF ABDOMINAL PRESSURE BY TOCODYNAMOMETER YASUNORI TOMITA AND AKIMI OGAWA From the Department of Urology, Shinshu University School of Medicine, Matsumoto, Japan

ABSTRACT We used a guard-ring tocodynamometer to detect abdominal straining simultaneously with uroflowmetry in 19 normal volunteers, 63 patients with benign prostatic hyperplasia and 25 with a neurogenic bladder. The pressure curves obtained by the tocodynamometer were similar to the intrarectal pressure curves simultaneously measured by an intrarectal balloon. The frequency of straining in patients with benign prostatic hyperplasia did not differ significantly from that in normal volunteers and did not decrease postoperatively. In these patients abdominal straining did not produce a synchronously increased flow rate. Patients with a neurogenic bladder frequently voided with straining. Abdominal straining tended to produce a synchronously increased flow rate in patients with lesions in the sacral cord or peripheral nerves but not in patients with neural lesions above the sacral cord. The presence of urinary flow without straining was considered to signify an intact voiding reflex. We believe that this method is simple and provides much more information than uroflowmetry alone to evaluate voiding dysfunctions. KEY WORDS: urodynamics; pressure; prostatic hypertrophy; bladder, neurogenic

Uroflowmetry is a simple and noninvasive method to exam­ ine patients for the presence of voiding dysfunction. Urinary flow rates are the product of intravesical pressure against urethral resistance, and intravesical pressure during voiding is the sum of bladder contraction and abdominal pressure. If urinary flow rates and abdominal pressure are measured si­ multaneously, the results would be more useful in making a diagnosis. With surface electrodes on the abdominal wall Koff and Kass successfully detected abdominal straining during urodynamic studies in children. 1 However, our attempts to detect straining with this method were unsuccessful because even a slight movement of the patient during voiding obscured electromyographic changes elicited by straining. Obstetricians use a transducer attached to the abdominal wall to monitor abdominal pressure during labor. Unlike an intrarectal balloon to measure pressure, this monitoring does not cause any dis­ comfort to the patient. To measure abdominal pressure simul­ taneously with uroflowmetry, we applied the transducer devised by Smyth for labor pains. 2 Since the simultaneous measurement has been useful in making a differential diagnosis among pa­ tients with voiding dysfunction, the methods and results are presented.

tion, was asked to void into a uroflowmeter placed in a separate room. The pressure recorded before voiding was adjusted as 0 on the pressure scale. A total of 107 subjects underwent simultaneous measurement of urinary flow rates and abdominal pressure, including 19 male volunteers 23 to 48 years old (average 33) without any voiding disturbance who served as controls, 63 men 56 to 83 years old (average 71) with benign prostatic hyperplasia (BPH), and 17 male and 8 female patients 16 to 77 years old (average 52) with neurogenic bladder dysfunction. Diagnosis of a neurogenic

METHODS AND MATERIALS

A guard-ring tocodynamometer (Nihon model 45195) was used to measure abdominal pressure (fig. 1). A hard plastic plaque, 2 cm. in diameter and 5 mm. thick, was adhered to the sensor plate to increase the sensitivity. The tocodynamometer was connected to a recorder (Nihon model 363). The patient was given 20 mg. intravenous furosemide 20 minutes before the examination. The tocodynamometer was strapped to the lower abdomen and the patient, while in the upright or sitting posiAccepted for publication May 8, 1992. 335

FIG. 1. Tocodynamometer coiled for storage and strapped to lower abdomen.

336

TOMITA AND OGAWA

bladder was made by positive neurological findings and the presence of voiding disturbance. Organic obstructions of the lower urinary tract were ruled out in men older than 50 years. Some patients underwent cystometry to confirm the diagnosis. Of 63 patients with BPH 24 were re-examined 2 or 3 months postoperatively. Of the subjects 2 volunteers and 14 patients with BPH simultaneously underwent intrarectal pressure measurement. A rubber balloon mounted on a No. 14 catheter was inserted into the rectum. The balloon was filled with saline and con­ nected to a pressure transducer. The intrarectal pressure re­ corded before voiding was adjusted as O on the pressure scale. When voiding was completed the patient was asked to perform the Valsalva maneuver. The correlation coefficient and linear regression equation between the abdominal and intrarectal pressures were deter­ mined in each subject (fig. 2). A total of 20 points was randomly sampled from the curve where the abdominal pressure reached peaks or bottoms in fluctuation. The abdominal and intrarectal pressures at each point were paired and underwent calculation. Statistical difference in the frequency of straining between the groups was evaluated with the chi-square test.

sure increase of instantaneous duration or occurring shortly before the end of voiding was not regarded as abdominal straining. The voiding pattern was classified according to the presence or absence of straining and whether this was accompanied by a synchronous increase in the flow rate (fig. 3). If straining did not synchronize with but was followed by an increased flow rate after a delay of more than 3 seconds, this was excluded from the category of the synchronous increase in flow rate (fig. 4). Table 1 shows the results of the voiding pattern in the subjects examined. Approximately one-fourth of the volunteers and nearly half of the patients with BPH voided with straining, most of whom did not produce a synchronously increased flow

RESULTS

All subjects successfully underwent the examination and the voided urine was more than 80 ml. The abdominal and intra­ rectal pressure curves fluctuated, synchronizing with respira­ tory movements. The amplitudes of intrarectal pressure were less than 5 cm. water. The correlation coefficient between the abdominal and intra­ rectal pressures ranged from 0.81 to 0.99 (mean 0.93 ± 0.06 standard deviation), indicating that both curves were almost similar. The linear regression equation was expressed as Y = aX + b, where Y is the abdominal pressure, X is the intrarectal pressure, a represents the regression coefficient and varied from 0.46 to 2.41 (mean 1.05 ± 0.4 7), and b represents the value of Y for X = 0 and varied from -12.1 to 8.64 (mean -2.5 ± 6.33). This finding indicated that the pressure measured by the ab­ dominal wall transducer was not necessarily equal to the intra­ rectal pressure. When the patient was asked to perform the Valsalva maneu­ ver, the abdominal pressure increased by more than twice the amplitude of the respiratory fluctuation at rest and lasted during the maneuver. Therefore, if the abdominal pressure increased by more than twice the respiratory amplitude and lasted for 1 or more respiratory movements, we regarded these findings as being due to abdominal straining. However, a pres-

I

FIG. 3. Simultaneous recordings of flow rate (upper curve) and abdominal pressure (lower curve) in patient with BPH. Note no strain­ ing during voiding.

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FIG. 4. Simultaneous recordings of flow rate (upper curve) and abdominal pressure (lower curve) in patient with cervical cord tumor. Frequent straining does not synchronize with urinary flow rate. TABLE 1. Voiding pattern according to clinical diagnosis

I FIG. 2. Simultaneous recordings of abdominal pressure (upper curve) and intrarectal pressure (lower curve) in patient with BPH. Both pressure curves are almost similar. Valsalva's maneuver produces marked increase in both pressures.

No. With No. With Neurogenic No. Bladder BPH Controls Voiding without straining Voiding with straining: No synchronously increased flow rate Synchronously increased flow rate Totals

14

33

4

5

26

8

0 19

4 63

13 25

337

UROFLOWMETRY WITH ABDOMINAL PRESSURE MEASUREMENT rate. No significant difference in the frequency of straining was found between these 2 groups (p >0.1). More than four-fifths of the patients with a neurogenic bladder voided with straining. Abdominal straining was significantly more frequent in these patients than in the others (p <0.01). The flow rate synchron­ ously increased with straining in most of the patients with a neurogenic bladder (fig. 5) and in a few with BPH. The latter patients strained continually throughout voiding, so that the urinary stream was never interrupted except for shortly before the end of voiding. Table 2 shows the preoperative and postoperative patterns of voiding in 26 patients with BPH. The frequency of straining did not decrease postoperatively. Some patients who had voided without straining preoperatively began to void with straining postoperatively and vice versa in some others. Table 3 shows the site of the lesion and the voiding pattern in the patients with a neurogenic bladder. Most of the pressure curves were interrupted because of intermittent straining. Ab­ dominal straining produced a synchronously increased flow rate in many of the patients who had lesions of the sacral cord or peripheral nerves and in some who had lesions of the brain. In contrast, in most of the remaining patients abdominal straining did not synchronize with an increased flow rate regardless of the site of the lesion. In a few patients straining sometimes synchronously increased the flow rate while at other times it did not (fig. 6). These patients maintained the urinary flow even while straining was interrupted. Eight patients with a neurogenic bladder underwent cystom­ etry. The bladder diagnosed as areflexic did not contract on intravesical instillation of more than 450 ml. saline. One patient with a normoreflexic bladder voided without straining. In 2 of 7 patients with an areflexic bladder who strained during voiding the straining did not produce a synchronously increased flow rate and the urinary flow continued while the patients did not strain. DISCUSSION

The results indicate that whether the patient strains during voiding can be determined with a pressure transducer on the

FIG. 5. Simultaneous recordings of flow rate (upper curve) and abdominal pressure (lower curve) in patient with spina bifida. Straining produces synchronously increased flow rate. Flow is absent when straining is interrupted. TABLE

abdominal wall. Using a guard ring tocodynamometer, Smyth was able to measure abdominal pressure, 2 and Sethia and Smith quantitatively measured intravesical pressure in patients with chronic urinary retention.3 In our study, however, the abdomi­ nal pressure measured with the same transducer did not reflect the intrarectal pressure quantitatively. The plastic plaque at­ tached to the sensor to increase the sensitivity possibly ac­ counts for this disproportional relationship. Nevertheless, ab­ solute values of abdominal pressure seem unnecessary to deter­ mine whether abdominal pressure affects the flow rate. Patients with organic bladder outlet obstruction, such as BPH, have been believed to strain during voiding as the disease progresses. Our results did not support this belief. Only half of the patients with BPH voided with straining and so did one­ fourth of the normal control subjects. The difference in the frequency between these 2 groups was not significant. Further­ more, the frequency of straining did not decrease after surgical removal of bladder outlet obstruction. Jensen et al stated that straining was unrelated to the degree of bladder outlet obstruc­ tion and did not disappear after transurethral resection of the prostate.4 Straining during voiding did not produce a synchronously increased flow rate in most of the subjects examined except those with neurogenic bladder dysfunction. This finding indi­ cates that increased abdominal pressure does not necessarily facilitate voiding. Griffiths stated that because abdominal straining exerts pressure not only on the bladder but on the urethra, it slightly increases the flow rate.5 Yalla et al reported that increased intravesical pressure caused by straining was less along the prostatic urethra and hardly exerted on the distal urethra.6 Another possible explanation is a reflex contraction of the urethral sphincter. An increase in abdominal pressure during urine storage leads to a synchronous contraction of the urinary sphincter to prevent stress incontinence. Koff and Kass demonstrated that two-thirds of the children strained during voiding and straining resulted in a decreased flow rate due to sphincteric contractions. 1 On the other hand, Hasegawa et al reported that straining increased the flow rate in female pa­ tients with stress incontinence and male patients with an anterior urethral stricture.7 Recently, Meffan et al reported similar effects in 3 normal male subjects.8 Normal subjects may void with straining. As noted by Jensen et al, whether to strain during voiding probably depends on personal habit, unless the bladder and urethra are neurologi­ cally damaged.4 Straining in neurologically normal subjects seems to increase the flow rate less efficiently than in neuro­ genic bladder patients. The results in patients with a neurogenic bladder reached our expectations. Abdominal straining led to a synchronously increased flow rate in most of the patients with lesions of the sacral cord or peripheral nerves, whereas it did not in most of those with neural lesions above the sacral cord. If the voiding reflex remains intact straining may trigger but does not synchronize with an increased flow rate. On the other hand, if the voiding reflex is damaged straining does not elicit reflex sphinc­ teric contractions and facilitate voiding. The presence of the urinary flow without straining signifies

2. Preoperative and postoperative voiding pattern in patients with BPH Postop. Voiding With Straining

Preop. (No. pts.)

Voiding without straining (13) Voiding with straining (11): No synchronously increased flow rate Synchronously increased flow rate Totals

Voiding Without Straining

No Synchronously Increased Flow Rate

Synchronously Increased Flow Rate

8

5

0

3

8 0

0 0

0

IT

13

0

338

TOMITA AND OGAWA TABLE 3. Voiding pattern in patients with neurogenic bladder Brain

Diseases*

Voiding without straining Voiding with straining: No synchronously increased flow rate Synchronously increased flow rate Totals

Spinal Cord Diseases Above Sacral:j: Sacralt 0

3 1

3

7

Peripheral Nerve Diseases§

5

0

6

0

1 7

8

3

4

* Cerebrovascular accident, Parkinson's disease and others. t Spinal cord tumor, spinal cord injury and others. :j: Spina bifida, lumbar spinal cord injury and others. § Familial amyloidosis, status after radical hysterectomy.

interrupted flow curves, the presence or absence of an intact voiding reflex can distinguish between them. Urodynamic studies usually include recordings of intravesical and abdominal pressures, urethral pressure or electromyogra­ phy, and the flow rate. These are not only complicated but invasive because they need urethral catheterization. Voiding is a subtle act and easily influenced by psychological stress. In 2 patients with a neurogenic bladder the voiding reflex was not elicited by cystometry but recognized at uroflowmetry while wearing the abdominal wall transducer. Urethral catheteriza­ tion and asking to void while in the supine position may have inhibited the voiding reflex in these patients. Therefore, it seems necessary to confirm that the results obtained by invasive methods are consistent with those obtained by noninvasive methods. Uroflowmetry combined with simultaneous measurement of abdominal pressure by tocodynamometer is simple and makes it possible to void as usual. Unlike the intrarectal balloon method, this test can be repeated without causing discomfort to the patient. Therefore, we believe that the results obtained with this method are reliable and provide much more infor­ mation than uroflowmetry alone to evaluate voiding dysfunc­ tion, especially in neurogenic bladder patients. REFERENCES

FIG. 6. Simultaneous recordings of flow rate (upper curve) and abdominal pressure (lower curve) in patient with incomplete lumbar cord injury. Straining sometimes synchronously increases flow rate, while at other times it does not and flow continues (open arrows) while straining is interrupted (solid arrows).

an intact voiding reflex. Therefore, this method makes it pos­ sible to evaluate the voiding reflex. If the voiding reflex is absent, the bladder can be assumed to be areflexic. An intact voiding reflex and straining that does not produce a synchron­ ously increased flow rate suggests a hyperreflexic or normal bladder, or an organic bladder outlet obstruction. Although detrusor-sphincter dyssynergia and an areflexic bladder show

1. Koff, S. A. and Kass, E. J.: Abdominal wall electromyography: a noninvasive technique to improve pediatric uradynamic accu­ racy. J. Ural., 127: 736, 1982. 2. Smyth, C. N.: The guard-ring tocodynamometer. Absolute meas­ urement of intra-amniotic pressure by a new instrument. J. Obst. Gynaec. Brit. Emp., 64: 59, 1957. 3. Sethia, K. K. and Smith, J. C.: Non-invasive measurement of intravesical pressure. Brit. J. Ural., 58: 657, 1986. 4. Jensen, K. M.-E., Bruskewitz, R. C., Iversen, P. and Madsen, P. 0.: Abdominal straining in benign prostatic hyperplasia. J. Ural., 129: 44, 1983. 5. Griffiths, D. J.: The mechanics of the urethra and of micturition. Brit. J. Ural., 45: 497, 1973. 6. Yalla, S. V., Sharma, G. V. R. K. and Barsamian, E. M.: Micturi­ tional static urethral pressure profile: a method of recording urethral pressure profile during voiding and the implications. J. Ural., 124: 649, 1980. 7. Hasegawa, N., Kitagawa, Y., Takasaki, N. and Miyazaki, S.: The effect of abdominal pressure on urinary flow rate. J. Ural., 130: 107, 1983. 8. Meffan, P. J., Nacey, J. N. and Delahunt, B.: Effect of abdominal straining on urinary flow rate in normal males. Brit. J. Ural., 67: 134, 1991.