SPECIALTY TESTS MAY HELP IDENTIFY nOH IN SYMPTOMATIC PATIENTS

24-HOUR AMBULATORY BLOOD PRESSURE MONITORING (ABPM)

The wide variations in blood pressure (BP) experienced by patients with neurogenic orthostatic hypotension (nOH) may be recorded using 24-hour ABPM. If patients keep a diary noting posture and activity, hypotensive episodes captured with ABPM can help confirm a diagnosis of nOH and identify supine hypertension. ABPM may also be useful if a patient exhibits equivocal BP measurements in the office or on a tilt test.1,2

AUTONOMIC FUNCTION TESTS1-4

A specialized autonomic disorder center may be able to conduct additional specialty tests to diagnose nOH in symptomatic patients.

Test

What is evaluated

Pathways evaluated

Description of test

Sudomotor function

Quantitative sudomotor

axon reflex test (QSART)

Measures the functional integrity of the postganglionic sympathetic sudomotor axon

 

Defines distribution of sweat loss (of 4 sites—forearm, proximal leg, distal leg, foot)

Axon reflex

Sweat glands are stimulated via

iontophoresis of a cholinergic agent and sweat production is measured through a hygrometer

Thermoregulatory

sweat test (TST)

The integrity of thermoregulatory

sympathetic pathways from the hypothalamus to the eccrine sweat gland

 

Provides accurate patterns of anhidrosis; pattern can suggest site of lesion

Central, preganglionic,

postganglionic pathways

and eccrine sweat gland

Core body temperature is raised by increasing ambient room temperature,

raising blood and skin temperature

 

Sweat production visualized with an

indicator dye

Cardiovagal function

Heart rate variability (HRV)

Measures heart rate response to deep breathing

 

Determines normal or impaired cardiovagal function

Vagal afferent and efferent pathways

Patient breathes 6 breaths/minute and maximal heart rate minus minimal heart rate is averaged

Valsalva ratio

Determines normal or impaired cardiovagal function

Vagal pathway mediating

baroreflex function

Derived from the maximum heart rate divided by the lowest heart rate occurring within 30 seconds of the peak heart rate

Adrenergic function

Valsalva maneuver

Baroreflex function is evaluated by measuring adrenergic function and

baroreflex sensitivity

Baroreflex afferents and efferents

BP and heart rate are taken during the

Valsalva maneuver

 

Adrenergic function and baroreflex sensitivity are measured

Head-up-tilt/tilt table (HUT)

OH can be detected by evaluating baroreflex function

Baroreflex afferents and efferents

Heart rate and BP are measured in response to a patient placed on a tilt table at ≥60°

Plasma norepinephrine

supine/standing

Provides an index of postganglionic adrenergic fibers; response to standing

evaluates baroreflex unloading

Baroreflexes and adrenergic terminals

Plasma NE is measured while patient is supine and after a period of standing

Test

Sudomotor function

Quantitative sudomotor axon reflex test (QSART)

What is evaluated

Pathways evaluated

Description of test

Measures the functional integrity of the postganglionic sympathetic sudomotor axon

 

Defines distribution of sweat loss (of 4 sites—forearm, proximal leg, distal leg, foot)

Axon reflex

Sweat glands are stimulated via

iontophoresis of a cholinergic agent and sweat production is measured through a hygrometer

Test

Sudomotor function

Thermoregulatory sweat test (TST)

What is evaluated

Pathways evaluated

Description of test

The integrity of thermoregulatory

sympathetic pathways from the hypothalamus to the eccrine sweat gland

 

Provides accurate patterns of anhidrosis; pattern can suggest site of lesion

Central, preganglionic,

postganglionic pathways

and eccrine sweat gland

Core body temperature is raised by increasing ambient room temperature,

raising blood and skin temperature

 

Sweat production visualized with an

indicator dye

Test

Cardiovagal function

Heart rate variability (HRV)

What is evaluated

Pathways evaluated

Description of test

Measures heart rate response to deep breathing

 

Determines normal or impaired cardiovagal function

Vagal afferent and efferent pathways

Patient breathes 6 breaths/minute and maximal heart rate minus minimal heart rate is averaged

Test

Cardiovagal function

Valsalva ratio

What is evaluated

Pathways evaluated

Description of test

Determines normal or impaired cardiovagal function

Vagal pathway mediating

baroreflex function

Derived from the maximum heart rate divided by the lowest heart rate occurring within 30 seconds of the peak heart rate

Test

Adrenergic function

Valsalva maneuver

What is evaluated

Pathways evaluated

Description of test

Baroreflex function is evaluated by measuring adrenergic function and

baroreflex sensitivity

Baroreflex afferents and efferents

BP and heart rate are taken during the

Valsalva maneuver

 

Adrenergic function and baroreflex sensitivity are measured

Test

Adrenergic function

Head-up-tilt/tilt table (HUT)

What is evaluated

Pathways evaluated

Description of test

OH can be detected by evaluating baroreflex function

Baroreflex afferents and efferents

Heart rate and BP are measured in response to a patient placed on a tilt table at ≥60°

Test

Adrenergic function

Plasma norepinephrine supine/standing

What is evaluated

Pathways evaluated

Description of test

Provides an index of postganglionic adrenergic fibers; response to standing

evaluates baroreflex unloading

Baroreflexes and adrenergic terminals

Plasma NE is measured while patient is supine and after a period of standing

REFERENCES
  1. Low PA. Neurogenic orthostatic hypotension: pathophysiology and diagnosis. Am J Manag Care. 2015;21(suppl 13):s248-s257.
  2. Gibbons CH, Schmidt P, Biaggioni I, et al. The recommendations of a consensus panel for the screening, diagnosis, and treatment of neurogenic orthostatic hypotension and associated supine hypertension. J Neurol. 2017;264(8):1567-1582.
  3. Low PA, Tomalia VA, Park KJ. Autonomic function tests: some clinical applications. J Clin Neurol. 2013;9:1-8.
  4. llligens BMW, Gibbons CH. Sweat testing to evaluate autonomic function. Clin Auton Res. 2009;19(2):79-87.