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Overactive bladder—a condition in which the bladder churns and contracts uncontrollably causing urinary urgency and frequency and sometimes incontinence—has received a great deal of attention and clinical research. However, its younger sibling—underactive bladder—is an ailment that most people have not heard of and is a condition that is largely neglected with respect to clinical and scientific research. Underactive bladder is a disorder in which the bladder muscle is weak and incapable of contracting sufficiently to empty the bladder properly.
The medical term for the bladder muscle is the detrusor and the term for underactive bladder is detrusor underactivity. It is technically defined as “a bladder that contracts with reduced strength and/or duration, resulting in prolonged bladder emptying and/or failure to achieve complete bladder emptying within a normal time span.”
There is a significant overlap of symptoms of the conditions of underactive bladder, overactive bladder, and bladder outlet obstruction (an obstruction to the flow of urine, often from prostate enlargement, urethral scar tissue, or dropped bladder in females). The bottom line is that the bladder is “an unreliable witness” since lower urinary tract symptoms often do not accurately reflect the underlying condition.
One with an underactive bladder will typically experience incomplete emptying and as such their bladder always will remain partially full. In addition to experiencing obstructive symptoms (because of the weak bladder “motor”) like those with bladder outlet obstruction, they will also commonly experience irritative lower urinary tract symptoms including urgency and frequency and sometimes incontinence, like those with overactive bladder.
Causes of underactive bladder include neurological diseases that adversely affect the bladder, e.g., diabetes, multiple sclerosis, spinal cord injury, etc. Aging can affect bladder contractility adversely and may give rise to underactive bladder. Longstanding bladder outlet obstruction, classically from benign prostate growth, can ultimately cause bladder decompensation and underactive bladder. Ischemic bladder dysfunction based on impaired blood flow to the bladder is another cause of underactive bladder.
Tests to evaluate underactive bladder
- Uroflowmetry: This is a simple non-invasive test in which one urinates into a flow meter that measures flow rate and generates a flow curve.
- Post-void residual urine volume: This is a simple ultrasound scan that determines the quantity of urine left behind in the bladder after urinating.
- Urodynamics: These are sophisticated tests of bladder function that evaluate the storage and emptying phases of urination and can help distinguish between overactive bladder, underactive bladder, and bladder outlet obstruction.
Faucet and hose analogy to help understand the utility of urodynamics
Just as the “bladder is an unreliable witness,” so the flow out of a garden hose is not a good indicator of an underlying problem. If you have an outdoor faucet that is functioning well and gushes when it is turned on, when you attach a hose to it your expectation is a powerful flow of water through the hose. If the flow is meager, then there is obviously a kink (obstruction) of the hose. If you have an outdoor faucet that is functioning poorly and when it is turned on only generates minimal water pressure, when you attach a hose to it there will also be a meager flow through it. The conclusion is that poor flow through a hose can be caused by either a faucet functioning well that is obstructed or, alternatively, a poorly functioning faucet in the absence of obstruction. And so it is with the human bladder.
A weak urinary flow can be caused by a perfectly functioning bladder that is obstructed, or alternatively, by a poorly functioning (underactive bladder). Urodynamics measures the bladder contractility simultaneously with the flow and can make the distinction between the two entities. Obstruction is defined as excellent bladder contractility (high pressures) with poor flows versus underactive bladder that is defined as poor bladder contractility (poor pressures) with poor flows. The bottom line is that the only way to know what is going on with the bladder “faucet” is to measure its pressure at the time of voiding.
Management of underactive bladder
Because underactive bladder gives rise to incomplete emptying and residual urine remaining after voiding, it is important to make every effort to empty the bladder as completely as possible. This will minimize the occurrence of irritative lower urinary tract symptoms and urinary infections that may occur with incomplete bladder emptying. The following measures can facilitate emptying the bladder that does not have the muscle power to empty fully on its own:
- Relaxation: To empty the bladder efficiently the bladder muscle must contract synchronously with relaxation of the sphincter muscles. The sphincter muscles can be adversely affected by anxiety and nervous states. Sit to urinate, bring a magazine, take some deep breaths, try to assume a relaxed frame of mind, and patiently empty your bladder.
- Double and triple voiding: When seemingly finished voiding, give it a second and even a third try.
- Valsalva maneuver: This is the medical term for straining the abdominal muscles. Bearing down and squeezing generates increased pressure external to the bladder that may facilitate emptying.
- Crede maneuver: This is the medical term for applying external pressure to the lower abdomen to better empty one’s bladder. It can be thought of as “CPR for the bladder.” It is best performed with both hands placed on the lower abdomen between navel and pubic bone while leaning forward, pressing down firmly while trying to urinate.
- Suprapubic tapping: This involves tapping rhythmically over the region between navel and pubic bone to trigger a nerve reflex that will trigger urination. This is not effective in everyone, but worth a try.
- Medication: Unfortunately, there is no effective medication to increase bladder contractility; however, there are medications that decrease sphincter resistance and this class of medication (alpha-blockers) may be worthwhile on a trial basis.
- Self-catheterization: This is the mainstay of effective treatment for underactive bladder. Self-catheterization involves learning to pass a disposable catheter into the urinary bladder at least four times daily to empty it completely. Self-catheterization serves to empty the bladder completely and provides an opportunity to urinate spontaneously prior to each catheterization and enable measuring the voided (urinated) and residual (what remains in the bladder after a voiding attempt) volumes that will be indicative of improvement/resolution of the problem.
- Neuromodulation: Interstim device is a battery-powered neuro-stimulator (bladder “pacemaker”) that provides electrical impulses carried by a small lead wire to stimulate selected sacral nerves that affect bladder function. This can be considered in select cases of underactive bladder.
