Correlation between urinary flow rate, voided volume, and patient age in a community-based population.

This investigation is unique in that is the first study to use a large number of randomly chosen men from the community to establish the relationship between: 1) urinary flow rate and voided volume, 2) urinary flow rate and patient age, 3) voided volume and patient age, and 4) the time to achieve peak urinary flow rate and patient age. The results clearly indicate that both the peak and mean urinary flow rate decreases with advancing age. The voided volume also diminishes with increasing age. The time required to achieve the peak urinary flow rate, however, appears to be independent of the patient's age. Irrespective of age, approximately 9 seconds are required to achieve the maximum urinary flow rate. Because the urinary flow rate is dependent upon both the quantity of urine voided and the patient's age, it is necessary to account for the influence of both parameters when establishing the "normal range" for peak urinary flow rate. To this end, nomograms estimating the peak urinary flow rate percentile as a function of voided volume and patient age have been generated and are included in this report. These nomograms, based on a large, randomly selected population, should make peak urinary flow rate a more reliable diagnostic modality for assessing bladder outlet obstruction. They also should be most useful to the practicing clinician when interpreting the results of a peak urinary flow rate determination for a patient presenting with symptoms of prostatism.