32 measured via the urethral catheter (Pves) and abdominal pressure is measured with an intrarectal catheter (Pabd). The difference between Pves and Pabd is the detrusor or bladder pressure (Pdet) and represents true intravesical pressure readings. With cystometry, an empty bladder is usually filled with sterile water or normal saline. While increasing the volume, the bladder is able to maintain approximately the same amount of Pves, also known as compliance. 122 The patient has to mark 3 phases of filling. 1) First sensation of filling. 2) First desire to void. 3) Strong desire to void. Any bladder contraction during filling phase is abnormal. In normal conditions, all three phases will be noticed. An impaired bladder, misses one or more phases and can be related with autonomic dysfunction.123,124 Uroflowmetry: Uroflowmetry is the analysis of the flow pattern during micturition, the voided volume and residual volume. The uroflowmeter is used to measure urinary stream in milliliters per second (mL/s). Additionally, it measures the voided volume. The residual volume is measured with an Ultrasound (US) scan.125 A normal flowpattern is continuous with good flow velocity. Decreased flow velocity with increased duration of micturition is indicative for obstruction. An intermitted flow can be indicative for impaired bladder contractility, obstruction or voiding with abdominal straining.126 A neurogenic bladder often misses the first sensation of filling around 100-200 ml. Normally, discomfort occurs at a filling volume of around 300-500 ml. However, patients with a neurogenic bladder can increase their capacity up to 2L. In neurogenic bladders, 2 patterns do present. The first shows a decreased peak flow and the second shows a prolonged intermitted flow pattern, with the need of abdominal straining to void.109 Sphincter electromyography: With sphincter electromyography (EMG), an electrode is placed in or near the sphincter muscle. Aside from some neurologic conditions, external anal sphincter EMG is the same as external urethral sphincter EMG. Normal voiding starts with relaxation of the sphincter, followed by contraction of the detrusor. EMG shows a slowly increasing activity, until the command to void. During voiding, no activity is measured. After voiding, a constant activity is measured. Several suprasacral spinal cord pathologies may cause detrusor external sphincter dyssynergia (DESD). DESD can result in huge EMG changes as the detrusor contracts involuntary against a relatively closed sphincter. This will result in high pressures and eventually may cause impaired bladder compliance. If no neurologic damage is present, the dyssynergia is behavioral.126 Urethral pressure profilometry Urethral pressure profilometry draws a pressure profile along the length of the urethra. A catheter with a pressure sensor is inserted in the urethra. The profile is measured during withdrawal of the sensor. The fluid pressure needed to just open a closed urethra is defined as the urethral pressure. Sympathetic cholinergic tests Sympathetic cholinergic tests are based on direct sweat response, after stimulation of M3 muscarinic receptors. Stimulation is achieved by iontophoresis, with thermal, electrical or mechanical stimuli. Methacholine, acetylcholine or pilocarpine are pharmacological substances used for iontophoresis of cholinergic agonist. Ionthophoresis stimulates the sweat glands in two ways. Binding to the M3 muscarin receptors on sweat glands results in a direct response of the corresponding sweat gland due to an impulse in orthodromic direction. However, acetylcholine also binds to nicotinergic receptors on the terminal nerve fibers, resulting in an indirect sweat response due to an impulse in antidromic direction.108 Thermoregulatory Sweat Testing (TST) TST is a unique technique that provides assessment of preganglionic, postganglionic and central nerve pathways. The patient is positioned nude in a special constructed sweat cabinet, for 40-60 minutes. The sweat cabinet maintains an environmental temperature of 43-460C and a relative humidity between 35-40%.109 This way, skin temperature is maintained between 38.5-39.50C and should not exceed 400C. A skin temperature above 400C may cause skin injury, confounding somatosympathetic reflex sweating and hydromeiosis (reduced sweat rating at high levels of skin moisture and high temperature).109 The patient is covered with an indicator that changes color in the presence of 2 34 2
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