UROFLOWMETRY

0094-0143/96 $0.00

URODYNAMICS

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UROFLOWMETRY Jarrgen Balslev Jarrgensen, MD, DMSci, and Klaus Merller-Ernst Jensen, MD, DMSci

Despite ongoing controversy, functional studies of bladder and urethral function have gained widespread use in urology, pediatrics, and gynecology. The simplest study, the uroflow (measurement of urine volume passed per time unit), has been used for decades, although it has been refined over the years. The measured urinary flow is a product of detrusor contractility and urethral resistance, in some cases modified by abdominal straining. Therefore, uroflowmetry describes total voiding function only. The following discussion focuses on technical and methodologic aspects of uroflowmetry as well as clinical applications in men, women, and children. TECHNICAL AND METHODOLOGIC ASPECTS

The uroflow curve is obtained by means of a uroflowmeter, which may be based on any of a number of different physical principles. Among methods used are stop watch and calibrated glass, air displacement, ultrasound, and weight and rotating disc. Today most commercially available uroflowmeters are based on (1) weight transducers, measuring the voided volume and calculating flow rate by means of differentiation with respect to time; and (2) rotating disc, measuring the power necessary to maintain a constant rotation, whereas urine tends to slow down the

speed. The power reflects the urine flow rate. These flowmeters provide both the graphical presentation of the uroflow and a range of electronically read parameters. Generally these flowmeters are sufficiently precise for clinical practice when volume (error 1% to 8%) and flow rate (error 4% to 15%) are con15, 50 Also, dead times and time con~idered.~, stants have proved a ~ c e p t a b l e When . ~ ~ uroflowmetry is combined with simultaneous pressure measurements, a time lag exists from initiation of voiding until the stream is observed by the flowmeter. This time lag ranges from 1 to 1.4 seconds in females and from 1.1 to 1.6 seconds in males.54 The introduction of electronically read flow variables has introduced pitfalls in the evaluation of uroflowmetry results. The mictiograph reads the absolute maximum value uncritically, while observers evaluate the curve and neglect insignificant spikes or obvious artifacts. These spikes often are caused by the person directing the flow to different parts of the mictiograph funnel (the wag artifact). Urodynamically trained staff thus disagree with the electronic evaluation presented.29,42 The median difference in the maximum flow rate (Qmax) readings was shown to be 18.5% and was most pronounced in flow curves of abnormal shape and with low Qmax. The flow curve is characterized by the shape, the Qmax, the time to Qmax (Qmaxtime), and the flowtime (Fig. 1). From the

From the Department of Urology, University of Copenhagen, Copenhagen (JBJ); and the Department of Urology, Skejby Hospital, University of Aarhus, Aarhus (Kh4-EJ), Denmark

UROLOGIC CLINICS OF NORTH AMERICA VOLUME 23 * NUMBER 2 MAY 1996 0

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T

Qmax

Figure 1. The uroflow curve. Qmax = maximum flow rate; Qmaxtime = time in seconds to reach maximum flow; flowtime = time to void in seconds.

data obtained, the average flow rate can be calculated and a volume-corrected Qmax estimated from Qmax/square root of the voided volume. The latter is volume independent for volumes less than 450 mL.62,63 Finally the ratio Qmax/Qmax-time can be calculated to describe the flow acceleration from initiation until Qmax. The recommendations of the International Continence Society3 address the quantitative parameters obtained from the free-flow curve (i.e., Qmax, flowtime, and voided volume). Different flow-curve patterns have been described in association with voiding disabilities.6,28, 44, 45, 60, 70 Schafer et alS8 stated that "uroflow can demonstrate abnormal voiding and, perhaps, on the basis of the curve pattern, the underlying disease, but it cannot verify obstruction." Five flow-curve patterns have been defined39: Type 1. The normal flow curve is unbroken and bell shaped with only slight to moderate asymmetry of the "bell." Type 2. The prostatic curve is unbroken with pronounced asymmetry and an elongated, flattened course from Qmax to end of voiding. Type 3. The fluctuatingflow curve is unbroken but characterized by greater fluctuations without reaching zero before the end of voiding. Type 4. The fractionated flow curve is discontinuous (i.e., characterized by one or several episodes where flow is zero [dribbling not included]). Type 5. The platenu flow curue is unbroken and flattened and a large part of

the voided volume is voided by a constant Qmax. It has been shown that urodynamically trained physicians, as opposed to untrained physicians, agreed in this classification both individually and compared with each other; that is, acceptable intra- and interobserver variations were obtained. The evaluation, therefore, should performed by the urodynamically trained physician who is examining and treating the patient. The urinary flow-curve pattern, to a large extent, is dependent on the methods used for registration and on the voided volume. The maximum amplitude and paper speed of the recorder used obviously determine the shape of the flow curves, but small voided volumes also may affect the curve shape. It would seem that the voided volume should be at least 150 to 200 mL if uroflow is to be interpreted c~rrectly.'~ Ryall and however, found no difference in Qmax relations obtained from small and large volumes. All the investigators agree that Qmax is volume dependent and that a Qmax/volume plot describes a hyperbolic curve from 0 to 300 mL voided volume. In volumes over 300 mL the relation becomes linear. In the evaluation of multiple-flow curves from the same person the learning effect21should be remembered. To ensure optimal voiding conditions and reproducible data, patients should void in privacy and in standing or sitting position, as they are used to, when normal desire to void is felt.21,31, 33, 64, 65 Reproducibility, however, still needs to be proved in larger populations. Poulsen and K i r k e b ~showed ~~ that although voided volume is largest in the morning, maximum flow rate is highest in the after-

UROFLOWMETRY

noon. Consequently, if multiple voidings are performed, they should take place at the same time of the day. Voiding should be considered initiated when flow exceeds 2 mL/s, and likewise, deviations from the zero line of less than 2 mL/s should be disregarded at the end of voidingz6 UROFLOWMETRY IN MEN

Uroflow in groups of normal younger men was primarily described one to two decades ago.2, 19, 26, 54, 59, 62. 63, 73 From these studies on younger normal persons, one can deduce that Qmax declines 1 to 2 mL/s/5 years and to a certain degree depends on the voided volume. Some agreement exists about normality, because Qmax greater than 15 mL/s is considered normal, whereas Qmax less than 10 mL/s is considered abnormal. GammelgaardZ4described a decline in Qmax from 35 mL/s at the age of 14 years to 15 to 20 mL/s at the age of 50 years. Siroky and Krane61 found that the normal voided volume in young persons was 250 mL + / - 100 mL. From the papers of Chancellor et al,14 Cucchi,16 Jargensen et a1,4O and SusseP it can be concluded that acceleration in young men is 3.21 mL/s/s and that it, as well as other flow variables, declines as a person grows older. Adding acceleration to the other flow variables, however, does not alter the fact that it is not possible to differentiate detrusor dysfunction from bladder outlet obstruction on the basis of uroflowmetry. Studies of populations of normal men over the age of 50 years', 7-10, 32, 36, 38, 40, 55 show that Qmax declines when compared with younger men and varies between 11.8 and 36 mL/s with a median value between 12.6 and 20.1 mL/s and voided volumes of 150 to 200 mL. According to Jargensen et a1,38,40 median Qmax reaches 10.5 mL/s at the age of 50 years versus 5.5 mL/s at the age of 80 years. Furthermore only 50% voided more than 200 mL. Forty percent to 50% of the flow curves were normal at the age of 50 years, versus only 10% at the age of 80 years. Over the years many studies have been performed based on patients with different degrees of prostatism.* From these investigations one can conclude that Qmax declines with advancing age. Residual urine increases *References 1, 4, 10, 13, 17, 20, 32, 34, 43, 46-49, 51, 59, 60, 71-73

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but not as a direct consequence of the declining Qmax. Several nomograms of the Qmax/ 30, volume relation have been constr~cted,'~, 40, 62 but the only true nomogram is a threedimensional Qmax/volume/age nomogram. The clinical relevance of Qmax-nomograms is limited, however, because differentiation between normal and abnormal voiding in elderly men is almost impossible on the basis of uroflowmetry. Further, the diagnosis of infravesical obstruction per se does not predict risk of detrusor or renal impairment in patients suffering from benign prostatic hyperplasia. Flow-curve patterns seem to have some prognostic value with regard to the need for surgery, but they fail to differentiate between the obstructed and unobstructed bladder It is widely accepted that in patients with relative indications for prostatectomy, both symptoms and urodynamic evaluation should be considered. To demonstrate preoperative infravesical obstruction, one has to perform pressure-flow studies. From a realistic point of view, however, it appears justified to restrict pressure-flow studies to benign prostatic hyperplasia patients with Qmax over 10 mL/s. This approach would direct the need for full urodynamic investigation in 40% of benign prostatic hyperplasia patients with relative indications for treatment. Only 12% of these would require surgery for obstructi0n.3~ Uroflowmetry is an easily performed noninvasive investigation. It describes voiding disabilities objectively and the shape of the curve may even give some hints as to the cause of the disability. Two or more measurements should be performed and the investigation should be supplemented by adding information about residual urine and by keeping a voiding diary.

UROFLOWMETRY IN WOMEN

Uroflowmetry in women is characterized by the shorter urethra and no resistance, such as that caused by the prostate gland in the male. Thus, the only factor influencing normal female uroflow is the voluntary part of the sphincteric mechanism. Normal uroflow is described only briefly in the literature.12, 23, 25, 66, 68 Thus, one can conclude that in the normal uroflow in women Qmax reaches 20 to 36 mL/s. The flow curve is bell shaped,

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but flowtime is shorter than in men. Qmax is not dependent on age. Pregnancy does not seem to influence uroflow, but stress incontinence does seem to decrease Qmax, although the shape of the curve is more characteristic, resembling curves from men with lower urinary tract symptoms. Urodynamic investigation, as a part of preoperative evaluation of women with incontinence, has been shown to improve cure rate.22 In conclusion, the value of uroflowmetry in women is of some significance. The investigation is easy to perform and is a natural part of a urodynamic evaluation. If combined with a voiding diary it may give valuable hints as to further examinations needed to guide the most appropriate treatment. UROFLOWMETRY IN CHILDREN

Urodynamics for years has had a well-established place in evaluating lower urinary tract dysfunction in children.37Especially uroflowmetry (Qmax) has been advocated in screening and posttreatment control owing to its simplicity and noninvasiveness. Several studies on uroflowmetry variables37,67 have correlated flow variables with voiding volumes in both sexes and with age or body surface area. Interestingly, it was shown that in more than 90% of children the flow-curve patterns were identical to those of the normal adult bell-shaped flow curve. In the screening for functional infravesical obstruction or detrusor-sphincter dyssynergia in neurologically normal children, uroflowmetry proved inefficient as a single modality, whereas the combination of uroflowmetry with pressureflow electromyogram study and residual urine measurement yielded a consistent diagnosis, the incidence being approximately 20%.27, 37 Uroflowmetry as a single modality has only modest value in pediatric urology except in screening for occult voiding dysfunction. In a comprehensive study on nocturnal monosymptomatic it was shown that micturition disorders are not present in this disease entity. Similarly in children with vesicoureteral reflux, the cornerstone is not uroflowmetry but sophisticated overnight studies with monitoring of the bladder pressure.50 In the evaluation of patients with neurogenic bladder dysfunction, cystometry and 24-hour ambulatory urodynamic studies are prefera-

ble with special emphasis on the bladder leakpoint pressure as a predictor of risk of impairment of upper urinary tract.", 69

References 1. Abrams PH: Prostatism and prostatectomy: The value of urine flow rate measurement in the preoperative assessment for operation. J Urol 117:70, 1977 2. Abrams P H Urodynamic results of surgery. In Hinman F Jr (ed): Benign Prostatic Hyperplasia. New York, Springer Verlag, 1983, p 948 3. Abrams PH, Blaivas JG, Stanton SL, Andersen J T The standardization of terminology of lower urinary tract function. Scand J Urol Nephrol 114:5, 1988 4. Abrams PH, Griffiths DJ: The assessment of prostatic obstruction from urodynamic measurements and from residual urine. Br J Urol 51:129, 1979 5. Abrams PH, Torrens M: Urine flow studies. Urol Clin North Am 6:71, 1979 6. Andersen JT, Jacobsen 0, Gammelgaard P, et al: Mechanical and functional obstructions in the posterior urethra in males. Ugeskr Laeger 1372964, 1975 7. Andersen JT, Jacobsen 0, Worm-Petersen J, Hald T Bladder function in healthy elderly males. Scand J Urol Nephrol 12:123, 1978 8. Anikwe RM: Urinary flow rate in benign prostatic hypertrophy. Int Surg 61:109, 1976 9. Anikwe RM: Urodynamics in benign prostatic hypertrophy. Br J Urol50:20, 1978 10. Ball AJ, Smith PJB Urodynamic factors in relation to outcome of prostatectomy. Urology 28256, 1986 11. Bloom DA, McGuire EJ: Treatment of genitourinary dysfunction in children with myelodysplasia. Curr Opin Pediatr 4:488, 1992 12. Bottacini MR, Gleason DM: Urodvnamic norms in women. 1. Normals versus stress in;ontinence. J Urol 124:659, 1980 13. Brooks ME, Hanani D, Braf Z F Relationship between subjective complaints and urinary flow. Urology 22449, 1983 14. Chancellor MB, Blaivas JG, Kaplan SA, Axelrod S: Bladder outlet obstruction versus impaired detrusor contractility: the role of uroflow. J Urol 145:810, 1991 15. Christmas TJ, Chapple CR, Rickards D, et al: Contemporary flowmeters: An assessment of their accuracy and reliability. Br J Urol 63:460, 1989 16. Cucchi A: Acceleration of flow rate in obstructive detrusor instability. Br J Urol 66:26, 1990 17. Derrflinger T, Bruskewitz RC, Jensen KM-E, et al: Predictive value of low maximum flow rate in benign prostatic hyperplasia. Urology 27569, 1986 18. Drach GW, Ignatoff J, Layton T Peak urinary flow rate: Observations in female subjects and comparison to male subjects. J Urol 122:215, 1979 19. Drach GW, Layton TN, Binard WJ: Male peak urinary flow rate: Relationships to volume and age. J Urol 122:210, 1979 20. Drach GW, Steinbronn DV: Clinical evaluation of patients with prostatic obstruction: Correlation of flow rates with voided, residual or total bladder volume. J Urol 135:737, 1986 21. Dutartre D, Susset JG: Reproductibilite des courbes dkbitmetrie urinaire. J Urol (Paris) 80:484, 1974 22. Friis E, Hjortrup A, Nielsen JER, et a1 Urinary incontinence and genital prolapse: A prospective study of

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23. 24. 25. 26. 27. 28. 29. 30.

31. 32. 33. 34. 35.

36.

37. 38. 39.

40.

41.

42. 43.

the value of urodynamic evaluation. J Urol 128:764, 1982 Frimodt-Msller C, Hald T: Clinical urodynamics. Methods and results. Scand J Urol Nephrol 6(suppl 15):144, 1972 Gammelgaard J: Micturition patterns in normal adults. Ugeskr Laeger 136:2675, 1974 Gleason DM, Bottaccini MR Urodynamic norms in female voiding. 11. The flow modulating zone and voiding dysfunction. J Urol 127495, 1982 Gleason DM, Bottaccini MR, Perling D, Lattimer JK: A challenge to current urodynamic thought. J Urol 97935, 1967 Griffiths DJ, Scholtmeijr RJ: Detrusor-sphincter dyssynergia in neurologically normal children. Neurourol Urodyn 2:27, 1983 Griffiths DJ, Scholtmeijer RJ: Place of the free flow curve in the urodynamic investigation of children. Br J Urol56:474, 1984 Grino PB, Bruskewitz R, Blaivas JG, et al: Maximum urinary flow rate by uroflowmetry: autonomic or visual interpretation. J Urol 149:339, 1993 Haylen BT, Parys BT, Anyaegbunam WI, et al: Urine flow rates in male and female urodynamic patients compared with Liverpool Nomograms. Br J Urol 65:483, 1990 Heintz A, Hallwachs 0 Uroflowmetrie: der Einfluss der Tageszeit auf die Hamstrahlmessung. Urologe A 22:141, 1982 Jensen KM-E, Bruskewitz RC, Madsen PO: Urodynamic findings in elderly males without prostatic complaints. Urology 24:211, 1984 Jensen KM-E, Jsrgensen JB, Mogensen P: Reproducibility of uroflowmetry variables in elderly males. Urol Res 13:237, 1985 Jensen KM-E, Jsrgensen JB, Mogensen P: Urodynamics in prostatism. 1. Prognostic value of uroflowmetry. Scand J Urol Nephrol 22:109, 1988 Jensen KM-E, Jsrgensen JB, Mogensen P: Urodynamics in prostatism. 2. Prognostic value of pressure-flow study combined with stop-flow test. Scand J Urol Nephrol 114:72, 1988 Jensen KM-E, Jsrgensen JB, Mogensen P, Bille-Brahe NE: Some clinical aspects of uroflowmetry in elderly males. A population survey. Scand J Urol Nephrol 20:93, 1986 Jensen KM-E, Nielsen KK, Jensen H, et al: Uroflowmetry in neurologically normal children with voiding disorders. Scand J Urol Nephrol 19:81, 1985 Jsrgensen JB, Jensen KM-E, Bille-Brahe NE, Mogensen P: Uroflowmetry in asymptomatic elderly males. Br J Urol 58:390, 1986 Jsrgensen JB, Jensen KM-E, Klarskov P, et al: Intraand inter- observer variations in classification of urinary flow curve patterns. Neurourol Urodyn 9:535, 1990 Jsrgensen JB, Jensen KM-E, Mogensen P: Longitudinal observations on normal and abnormal voiding in men over the age of 50 years. Uroflowmetry and symptoms of prostatism. Br J Urol 72:413, 1993 Jsrgensen JB, Jensen KM-E, Mogensen P, et al: Urinary flow curve patterns and their prognostic value in males over the age of 50 years. Neurourol Urodyn 11:483, 1992 JsrgensenJB, Mortensen T, Hummelmose M, Sjsrslev 1: Mechanical versus visual evaluation of urinary flow curves and patterns. Urol Int 51:15, 1993 Kadow C, Feneley RCL, Abrams PH: Prostatectomy or conservative management in the treatment of benign prostatic hypertrophy. Br J Urol 61:432, 1988

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44. Klarskov I? Analysis of the method of measuring the urinary flow by means of the Glostrup Flowmeteret. Ugeskr Laeger 136:2679, 1974 45. Klarskov P: Urological diagnosis by investigation of the urinary flow with the Glostrup Flowmeter. Ugeskr Laeger 136:2684, 1974 46. Klarskov P, Andersen JT, Asmussen CF, et al: Symptoms and signs predictive of the voiding pattern after acute urinary retention in men. Scand J Urol Nephrol 22:23, 1987 47. McInemey PD, Robinson LQ, Weston PMT, et al: Assessment of poorly contractile or acontractile bladder in the older male in the absence of neuropathy. Br J Urol 65:161, 1990 48. McLoughlin J, Abel PD, Shaikh N, et al: Visual analogue scales distinguish between low urinary flow rates due to impaired detrusor contractility and those due to bladder outflow obstruction. Br J Urol 66:16, 1990 49. McLoughlin J, Abel PD, Williams G: Symptoms versus flow rates versus urodynamics in selection of patients for prostatectomy. Br J Urol 66:303, 1990 50. Nielsen JB, Nsrgaard JP, Ssrensen SS, et al: Continuous overnight monitoring of bladder activity in vesico-ureteral reflux patients: 11. Bladder activity types. Neurourol Urodyn 3:7, 1984 51. Nnhr SB, Jensen BN, Mortensen BB, Walther S: Hypertrophy of the prostate: Natural history. Subjective and objective changes during a period of six months. Ugeskr Laeger 153:1474, 1991 52. Nsrgaard JP: Pathophysiology of nocturnal enuresis. Scand J Urol Nephrol (suppl 140), 1991 53. Poulsen EU, Kirkeby HJ: Home monitoring of uroflow in normal male adolescents. Relation between flow-curve, voided volume and time of day. Scand J Urol Nephrol 114:58, 1988 54. Rollema HJ: Ultrasonic volumetry, a new principle for uroflowmetry: Comparison with the DISA mictiometer. Urol Int 33238, 1978 55. Rollema HJ: Uroflowmetry in males. Reference values and clinical application in benign prostatic hypertrophy. Rijksuniversiteit te Groningen, Drukkerij van Denderen BV, Groningen, 1981 56. Rowan D, James ED, Kramer AEJL, et al: Urodynamic equipment: Technical aspects. J Med Eng Techno1 11:57, 1987 57. Ryall RR, Marshall VR Normal peak urinary flow rates obtained from small voided volumes can provide a reliable assessment of bladder function. J Urol 127484, 1982 58. Schafer W, Rubben H, Noppeney R, Deutz F-J: Obstructed and unobstructed prostatic obstruction. World J Urol 6:198, 1989 59. Scott FB, Quesada EM, Cardus D: Studies on the dynamics of micturition: Observations on healthy men. J Urol 92455, 1964 60. Shoukry I, Susset JG, Elhilali MM, Dutartre D: Role of uroflowmetry in the assessment of lower urinary tract obstruction in adult males. Br J Urol47599,1975 61. Siroky MB, Krane RJ: Hydrodynamic significance of flow rate determination. In Hinman F Jr (ed): Benign Prostatic Hypertrophy. New York, Springer Verlag, 1983, p 507 62. Siroky MB, Olsson CA, Krane RJ: The flow rate nomogram: 1. Development. J Urol 122:665, 1979 63. Siroky MB, Olsson CA, Krane RJ: The flow rate nomogram: 2. Clinical correlations. J Urol 123:208, 1980 64. Susset JG: Development of nomograms for application of uroflowmetry. In Hinman F Jr (ed): Benign

242

65.

66.

67. 68.

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Prostatic Hyperplasia. New York, Springer Verlag, 1983, p 528 Susset JG: Relationship between clinical urodynamics and pathologic findings in prostatic obstruction. In Hinman F Jr (ed): Benign Prostatic Hyperplasia. New York, Springer Verlag, 1983, p 613 Susset JG, Shoukry I, Schlaeder G, et al: Stress incontinence and urethral obstruction in women: Value of uroflowmetry and voiding urethrography. J Urol 111:504, 1974 Szabo L, Fegyverneki S: Maximum and average urine flow rates in normal children-the Miskolc nomograms. Br J Urol 76:16, 1995 Tanagho EA, Stoller ML: Urodynamics: Uroflowmetry and female voiding patterns. In Oestergard DR, Bent AE (eds): Urogynecology and Urodynamics. Baltimore, Williams & Wilkins, 1991,

69. Thorup J: Urodynamic examination of the lower urinary tract in children with normal and congenital neurogenic bladder. Scand J Urol Nephrol (suppl 158), 1994 70. Tripathi VN, Sridhar M: Urodiagrams. A new method of uroflow pattern analysis. J Urol 130:309, 1983 71. Turner WR: The symptoms of bladder outlet obstruction. Detrusor dysfunction and the myth of prostatism. In Hinman F Jr (ed): Benign Prostatic Hypertrophy. New York, Springer Verlag, 1983, p 701 72. Turner WR, Whiteside CG, Arnold EP, et al: A urodynamic view of prostatic obstruction and the results of prostatectomy. Br J Urol 45:631, 1973 73. von Garrelts B: Micturition in the normal male. Acta Chirargica Scandinavica 114:197, 1957

Address reprint requests to Klaus Moller-Ernst Jensen, MD, DMSci Department of Urology Skejby Hospital University of Aarhus Brendstrupgardsvej 8200 Aarhus Denmark