Autonomic Nervous System Testing

By: Murtaza

Neurophysiology DeptAKUH Karachi

Introduction • The autonomic nervous system is a complex neural

network maintaining internal physiologic homeostasis, especially, or

• The autonomic nervous system is a control system that acts largely unconsciously and regulates heart rate, digestion, respiratory rate, pupillary response, sexual arousals and urination. This system is the primary mechanism in control of the flight-or-fight response and its role is mediated by two different components

The two main component of ANS– the sympathetic and – Parasympathetic

–1. Sympathetic nervous system–The sympathetic nervous system originates

in the spinal cord and its main function is to activate the physiological changes that occur during the fight or flight response. This component of the autonomic nervous system utilizes and activates the release of norepinephrine in the reaction.

2. Parasympathetic nervous system– The parasympathetic nervous system

originates in the spinal cord and medulla and works in concert with the sympathetic nervous system. Its main function is to activate the "rest and digest" response and return the body to homeostasis after the fight or flight response. This system utilizes and activates the release of the neurotransmitter acetylcholine

Symptoms of Autonomic Dysfunction

– orthostatic hypotension– heat intolerance– painful feet– constipation– diarrhea– incontinence– sexual dysfunction– dry eyes– dry mouth– loss of visual accommodation– pupillary irregularities– extreme fatigue, tachycardia, Parkinson's-like symptoms, gastrointestinal

tract distress, anhidrosis, and hyperhidrosis

Sympathetic nervous system• The sympathetic division is the “fight-or-flight” system• Involves E activities – exercise, excitement, emergency, and

embarrassment• Non-essential activities are dampened (GI/urinary)• Promotes adjustments during exercise – blood flow to

organs is reduced, flow to muscles is increased• Its activity is illustrated by a person who is threatened

– Heart rate increases, and breathing is rapid and deep– The skin is cold and sweaty, and the pupils dilate– Bronchioles dilate…increasing ventilation, delivering more oxygen

to cells– Constriction of visceral & cutaneous bv’s (blood is shunted to

skeletal mm)

Parasympathetic Nervous System

• Works to save energy, aids in digestion, and supports restorative, resting body functions.– Decrease in heart rate– Increased gastro intestinal tract tone and

peristalsis– Urinary sphincter relaxation– Vasodilation – decrease in blood pressure

Diseases causing Autonomic Dysfunction

• Diseases of the central nervous system

• Diseases of the peripheral nervous system

Diseases of the CNS• Neurodegenerative diseases

– Multiple system atrophy– Parkinson’s disease

• Trauma • Vascular diseases• Neoplastic diseases• Metabolic diseases

– Wernicke’s encephalopathy– Cobalamin deficiency

• Multiple sclerosis• Medications

Diseases of the PNS• Neuropathies

– Diabetes– Guillain–Barre´ syndrome– Lyme disease– Human immunodeficiency virus infection– Leprosy– Acute idiopathic dysautonomia– Amyloidosis– Porphyria– Uremia– Alcoholism– Familial neuropathies such as Riley–Day syndrome, Fabry’s disease, and familial

amyloidosis

• Diseases of the presynaptic neuromuscular junction such as botulism

Levels of ANS Control• The hypothalamus is the main integration center of

ANS activity• Subconscious cerebral input via limbic lobe

connections influences hypothalamic function• Other controls come from the cerebral cortex, the

reticular formation, and the spinal cord• Centers of the hypothalamus control:– Heart activity and blood pressure– Body temperature, water balance, and endocrine

activity– Emotional stages (rage, pleasure) and biological drives

(hunger, thirst, sex)– Reactions to fear and the “fight-or-flight” system

Levels of ANS Control

Testing Autonomic Function in Clinical Neurophysiology

• Tests of autonomic function– clinically useful– well validated – sufficiently straightforward to perform routinely– unambiguous interpretation

Testing Autonomic Function in Clinical Neurophysiology

• The specific aims of clinical and electrodiagnostic autonomic evaluation are

– to diagnose autonomic failure or dysfunction– to define the severity and distribution of autonomic failure– to define the site of the lesion

Testing Autonomic Function in Clinical Neurophysiology

• Tests should be an extension of the clinical autonomic history and examination

• These tests assess end organ function, so the conclusions are largely extrapolative

Testing Autonomic Function in Clinical Neurophysiology

• Optimal evaluation requires

– appropriate patient selection– adequate patient preparation– an adequate panel of autonomic tests

Preparation of the Patient

• No food, coffee, or nicotine are permitted for 3 hours before the study

• Medications are stopped for five half lives– anticholinergic (including antidepressant, antihistamine,

and over-the-counter cough and cold medication) – sympathomimetic and– parasympathomimetic agents are forbidden for 48 hours

Evaluation of cardiovagal function using heart rate recordings

• Heart rate response to deep breathing (HRDB)

• Valsalva ratio

Protocol of HRDB

• Supine position with the head elevated to 30°

• Patient breathes deeply at six respirations per minute, allowing 5 s for inspiration and 5 s for expiration

• The maximal and minimal heart rates within each respiratory cycle and the mean variation are determined.

Protocol of HRDB

• The E to I ratio can be calculated as

– the sum of the six longest R-R intervals of each of the six respirations divided by the sum of the six shortest R-R

intervals.

Valsalva Ratio

• Normal Responses

– The Valsalva maneuver consists of respiratory strain which increases intrathoracic and intraabdominal pressures and alters hemodynamic and cardiac functions.

Protocol of Valsalva Ratio• The patient is supine or with head slightly elevated

to about 30°.

• Most labs have the patient strain against 40 mmHg applied for 15 s by blowing into a mouthpiece attached to a sphygmomanometer.

• The system should have a slow leak to ensure the patient strains continuously

• Following cessation of the Valsalva strain, the patient relaxes and breathes at a normal comfortable rate.

Protocol of Valsalva Ratio

• The ECG is monitored during the strain and 30–45 s following its release.

• The maximal heart rate of phase II actually occurs about 1 s following cessation of the strain

• The minimal heart rate occurs about 15–20 s after releasing the strain.

Protocol of Valsalva Ratio

• The ratio of the maximal-to-minimal heart rate is determined as a simple ratio.

• After a brief rest, the maneuver is repeated until three ratios are determined.

Sympathetic skin response (SSR)

• Thermoregulation is controlled by the sympathetic nervous system, with the parasympathetic system playing a minor role

• Sympathetic sudomotor cholinergic fibers innervate sweat glands to regulate evaporative heat loss

Indications of SSR• Progressive autonomic failure syndromes

• Peripheral neuropathies where autonomic or other small fiber involvement is suspected

• Distal small fiber neuropathies

• Diseases with sympathetically maintained pain

Protocol of SSR

• Low frequency (high pass) filter 0.1 or 0.5 Hz

• High-frequency (low pass) filter of 500 or 1000 Hz • The gain 500 µV /Div

• The sweep 0.5-1 s/Div

• Temperatures are standardized to over 30°C, preferably over 32°C

Protocol of SSR• The active electrodes are placed in the palm or sole and the

reference over the dorsum of the respective body part

• Electrodermal activity is brought out either directly or reflexly (electric depolarization of a sensory nerve, startling auditory sound or deep inspiratory gasps)

• Averaging should not be performed

Normal responses of SSR

• The morphology of the potentials are mono-, bi-, or triphasic

• Potentials are symmetric in homologous body regions.

• The potentials in the hands have larger amplitudes and shorter latencies than those in the feet.

• Generally absent responses are considered to be abnormal

Normal Values of SSR

• The SSR is age dependent– present in both hands and both feet in subjects under the

age of 60 years– only 50% of feet and 73% of hands in subjects older than

60years

• Mean latency in hands is 1.5 s, mean amplitude in hands is 0.450 mV, mean latency in feet is 1.9 s, and mean amplitude in feet is 0.15 mV

Advantages of SSR

• Sensitive, reproducible, semiquantitative, simple, fast, and readily obtained on most electrophysiologic equipment

• SSR is comparable in its sensitivity to the quantitative sudomotor axon reflex test (QSART) for the detection of autonomic dysfunction

Disadvantages of SSR

• Only semiquantitative

• May be difficult to elicit or be habituated and thereby be mistaken as abnormal