Autonomic Testing



Autonomic Testing


Louis H. Weimer



INTRODUCTION

Recognition of disorders producing autonomic dysfunction continues to increase the demand for noninvasive clinical testing in order to validate clinical diagnoses. Because autonomic systems affect virtually all organ systems, symptoms produced are multiple and varied, often affecting functions not considered by neurologists. Because many autonomic complaints can appear to be nonspecific, objective assessment is desirable in many instances. Laboratories testing autonomic function are increasingly available in part due to reliable noninvasive techniques. However, formal training opportunities in this neurologic specialty remain limited.








TABLE 27.1 Selected Tests of Autonomic Function



























































































































































Cardiovagal


Well established



HR variability to cyclic deep breathing



HR response to the VM (VR)



HR response to standing (30:15 ratio)


Other



Diving reflex/cold face test



HR variability at rest



HR response to cough



Spectral analysis of HR signals (frequency domain)



Transfer function analysis (nonlinear dynamics)


Adrenergic


Well established



BP response to the VM (phase IV and late phase II)



BP response to orthostatic stress




– Head-up tilt




– Standing


Other



Sustained handgrip test



Squat test



BP response to alternate stressors




– Lower body negative pressure




– Neck suction




– Lying down




– Liquid meal



Plasma catecholamine levels (supine/standing)



Microneurography



Mental stress tests



Cold pressor test



Spectral and transfer function BP analysis


Sudomotor


Well established



Sympathetic skin response (SSR)



Quantitative sudomotor axon reflex test (QSART)



Thermoregulatory sweat test (TST)



Silastic sweat imprint testing



Skin biopsy for sweat gland innervation


Additional or Investigational Methods



Pharmacologic challenges



Vasomotor testing



Pupillary testing (pharmacologic)



Pupillometry, pupillography



Urodynamics/cystometrogram with bethanechol



GI motility studies



GI manometry



Salivary testing/Schirmer test



Penile plethysmography, papaverine injection



Neuroendocrine tests



Neurogenic flare test



Quantitative direct and indirect test of sudomotor function (Q-DIRT)



Cardiac PET scanning


HR, heart rate; VM, Valsalva maneuver; VR, Valsalva ratio; BP, blood pressure; GI, gastrointestinal; PET, positron emission tomography.


Unlike other systems, autonomic function is not directly assessed. Instead, responses of complex overlapping reflex loops are measured after controlled perturbations, most commonly heart rate (HR), blood pressure (BP), and sweating. Techniques to evaluate autonomic function are numerous and continue to be devised, but only a limited number are considered to be suitable for routine clinical application (Table 27.1). Tests of cardiovagal, adrenergic, and sudomotor function are most commonly performed and are recognized, standard clinical measures. Consensus recommends use of a standardized testing battery in a controlled setting. Bedside screening tests complement a clinical evaluation; some techniques can be performed with limited equipment such as an electrocardiography (ECG) or electromyography (EMG) machine.
The primary testing goal is to identify autonomic failure and to assess and quantify disease severity. In some cases, determining the systems involved, such as parasympathetic, sympathetic, or panautonomic, can refine diagnostic possibilities. In most instances, localization to central, preganglionic, or postganglionic dysfunction is not possible. The effects of medications, environmental conditions, dehydration, and acute illness should be minimized during testing. Selected commonly performed tests are briefly discussed in this chapter.

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Jul 27, 2016 | Posted by in NEUROLOGY | Comments Off on Autonomic Testing

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