The pressure flow study is the gold standard to assess the detrusor contractility and the bladder outlet obstruction (BOO). Nevertheless, it is invasive, time consuming and the cost. Non invasive urodynamics using tube test is a promising method to assess both; the ability of the bladder to adequately empty and detrusor contractility.

Two groups were studied; Benign prostate obstruction group and the control group. Each group had 20 patients. All had an initial uroflowmetry. Later, they were all asked to void into a uroflowmeter through a condom catheter fitted to the glans penis and the outflow tube guided into a vertical height of 10cm above the level of the symphysis pubis. The test was then repeated at increasing height resistances of 20, 30,40,50 and 60 cm at different days. Each patient was assessed using the conventional pressure flow study to compare both methods and for validation of the non invasive tube test.

All patients in the control group were able to continue the study without apparent difficulty and no complications. Only some difficulty during voiding was experienced with the 40,50 and 60 cm height resistance. Some patients tried to strain at theses heights. When this was observed, the test was repeated and the patient was instructed not to strain. At zero level the mean Qmax was 20ml/s.
At 10cm level, mean Qmax dropped to 16ml/s. The Qmax decreased with each increase of height resistance by small values ranging between  0.5 and 1.5 ml/s. At 60cm height, mean Qmax was 9.6ml/s. The PVR was 50 ml at zero level. No significant changes in PVR were noticed till 30 cm height resistance. PVR increased significantly at 40, 50 and 60 cm height resistance to a maximum of 153ml.
In the obstructed group, all patients cannot complete the test. They did reach 50cm height only . At zero level the mean Qmax was 9.4ml/s, mean PVR was 94.1ml. At 10 cm resistance, the mean Qmax was 7.5ml/s and then Qmax decrease with each increase in height resistance by small values reaching 7 ml/s at 50 cm height. The mean PVRincreased significantly to 181ml at 50 cm height. This was explained

The tubes test can be used as a primary tool for BPH assessment when the patients start to complain. Probably this test can be placed between the uroflowmetry and the conventional urodynamic study. Also it can be used for follow up of the patients on medical treatment to detect the efficacy of the treatment or occurrence of detrusor hypocontractility..  
The great advantages of using the tubes test are as follows: minimal discomfort, minimal risk of urinary tract infection, and low cost. This method can be repeated, permitting the evaluation of obstruction during clinical treatment.

The use of tube heights resistance test is non invasive, simple, feasible and not expensive with much less difficulty and lower complications.