Pressure-flow study

The pressure-flow study is a fundamental urodynamic test that combines the simultaneous measurement of intravesical pressure and urinary flow during the voiding phase. It is the reference test for diagnosing bladder outlet obstruction. The principle is based on the relationship between the pressure generated by the detrusor muscle to expel urine and the resulting flow. In the case of obstruction (prostatic hyperplasia, urethral stricture), detrusor pressure is high but flow remains low. In the case of detrusor underactivity, both pressure and flow are reduced. The results are generally plotted on a nomogram (Abrams-Griffiths or Schäfer diagram) that classifies the patient into one of three categories: obstructed, equivocal or unobstructed. This classification is essential for treatment decisions, particularly in men with lower urinary tract symptoms. The pressure-flow study is particularly indicated before any prostatic deobstruction surgery, as it objectively confirms the obstruction and avoids unnecessary operations in patients whose symptoms are due to detrusor underactivity.