Autonomic Function Tests

1. Autonomic Function Tests
Dr Noorin Bhimani

2. Importance
• autonomic dysfunctions are common in metabolic diseases such as
diabetes, obesity, hypertension, hyperlipidemia, hyper and
hypothyroidism, etc. India is the epicenter of diabetes, hypertension
and heart diseases. Therefore, assessment of sympathetic and
parasympathetic functions by conventional autonomic function tests
(AFTs) is now part of routine clinical management.

3. CLASSIFICATION OF AFTs
• A. Tests for cardiovascular autonomic functions
• 1. Heart rate and Blood pressure (BP) response to
• standing
• 2. Heart rate and BP response to passive tilting
• 3. Assessing baroreceptor sensitivity (BRS)
• 4. Heart rate response to deep breathing
• 5. Valsalva ratio
• 6. BP response to hand grip
• 7. Cold pressure test
• 8. Nor-epinephrine spillage technique
• 10. Standing to lying ratio
• 11. Spectral analysis of heart rate variability (HRV)
• B. Tests for sudomotor functions
• 1. Sympathetic skin response
• 2. Thermoregulatory sweat test (TST)
• 3. Quantitative sudomotor axon reflex test (QSART)
• C. Vasomotor test
• 1. Laser Doppler Velocimetry for skin blood flow
• measurement
• 2. Cold pressor test
• C. Tests for pupillary functions
• 1. Cocaine test
• 2. Adrenaline test
• D. Tests for bladder functions
• 1. Test for sphincter-detrusor dysynergia
• 2. Cystometrogram
• E. Other methods
• 1. Muscle sympathetic nerve activity (MSNA)

4. Classification
• A. AFTs for assessment of sympathetic functions:
• 1. BP response to standing/tilt
• 2. Cold pressor test
• 3. Isometric hand grip
• 4. Galvanic/sympathetic skin response
• 5. Thermoregulatory sweat test
• 6. Tachycardia ratio
• 7. Valsalva ratio
• 8. NE spillage test
• 9. LF and LFnu of HRV
• B. AFTs for assessment of parasympathetic functions:
• 1. Resting heart rate: Basal heart rate is a good index
• of parasympathetic functions as heart rate in resting
conditions is a measure of vagal tone. Resting
• HR more 75 indicates poor vagal tone and is presently
considered as a CV risk.
• 2. 30:15 ratio
• 3. E:I ratio
• 4. Valsalva ratio
• 5. Bradycardia ratio
• 6. Baroreceptor sensitivity
• 7. Standing to lying ratio
• 8. HF and HFnu of HRV

5. Concept of Reactivity and Activity Tests and
CAFTs
• Reactivity Tests Tests that are
based on stimuli or disturbances
such as change in position
(standing, lying, dipping finger in
cold water, hand grip against
resistance, Valsalva maneuver etc.)
are called reactivity tests.
Accordingly, they are grouped as
sympathetic and parasympathetic
reactivity tests.
• Activity Tests Tests that are
performed without disturbing the
subject (subject at rest usually lying
on couch in a comfortable room for
15 to 20 min) are called activity
tests. 1. Recording of Resting HR
and BP, and HRV analysis are
examples. 2. Accordingly, they are
grouped as sympathetic and
parasympathetic activity tests. 3.
Resting heart rate is
parasympathetic test and resting
BP is sympathetic test.

6. • CAFTs CAFTs refer to conventional autonomic function tests. HR and
BP response to standing, HR response to deep breathing, isometric
hand grip, cold pressor test and Valsalva maneuver are CAFTs.

7. Heart Rate Response to Standing
• Changing the posture from supine to standing, heart rate increases
immediately by about 10 to 20 beats per minute. 1. On standing, the
heart rate increases until it reaches a maximum at about the 15th
beat, after which it slows down to a stable state at about 30th beat. 2.
The ratio of R-R intervals corresponding to the 30th and 15th heart
beat is called the 30:15 ratio. 3. The 30:15 ratio is a measure of
parasympathetic function. 4. However, relative bradycardia at 30th
beat depends also on the sympathetic reactivity. 5. The normal 30:15
ratio is 1.15–1.12 at 21 to 30 years and 1.12 to 1.10 at 31 to 40 years
of age. 6. This ratio decreases with age. Ratio less than 1.04 is
considered abnormal.

8. Blood Pressure Response to Standing
• The changes in blood pressure on standing are studied to assess the
integrity of the sympathetic system. 1. Immediately on standing,
blood pressure falls, which activates baroreceptor reflex and blood
pressure returns to normal within 15 seconds. 2. When there is
sustained fall in systolic pressure more than 20 mm Hg or diastolic fall
more than 10 mm Hg within three minutes of standing, orthostatic
hypotension is said to be present.

9. Assessing Baroreceptor Reflex Sensitivity
(BRS)
• Baroreceptor reflex sensitivity is a newer method of assessing
autonomic reactivity to various stimuli, such as orthostatic challenge
and injection of chemicals and drugs that change the blood pressure.
1. This is assessed by continuous blood pressure variability (BPV)
measurement. Sensitivity of baroreceptors to change in dynamic
component (fluctuations) of blood pressure is an important marker of
sympathetic and parasympathetic systems. Thus, it is a reflection of
integration of both the components. 2. BRS is expressed as ms/mm
Hg. 3. BRS less than 20 ms/mm Hg reflect poor cardiovascular (CV)
health, and BRS less than 15 ms/mm Hg is an indicator of increased
CV risk. 4. BRS 25 ms/mm Hg or more indicates enhanced autonomic
tone and improved CV health.

10. Norepinephrine (NE) Spillage Technique
• Norepinephrine level in plasma is measured in supine position and
after 5 minutes of standing. The difference in level of NE represents
alteration in sympathetic-hormonal reactivity.

11. Heart Rate Response to Tilting
• Heart rate response to head up tilt (HUT) is a useful tool in the
diagnosis of autonomic dysfunctions. It is more accurate because the
active change of position is avoided by passively tilting the subject on
a tilt-table. Moreover, variation in time taken by individuals to stand
and the manner in which they stand from supine position is avoided
in this method. 1. On changing from recumbent to operate position
on a tilt table to 60 to 80 degrees HUT, pooling of about 30% venous
blood occurs in the peripheral vascular compartment, especially in
lower limbs. 2. This decreases cardiac filling pressure and stroke
volume by about 40%. 3. Heart rate rises immediately due to
withdrawal of parasympathetic activity and afterward due to
increased sympathetic activity

12. Standing to Lying Ratio (SLR)
• Heart rate (RR interval) response to lying down from standing posture
is assessed by continuous recoding of ECG. 1. Following lying from
standing position, increase in venous return produces reflex
bradycardia. 2. Longest RR interval in standing to shortest RR interval
in lying down is calculated as SLR. 3. Value of SLR below 1 is
considered as abnormal.

13. Heart Rate Response to Deep Breathing
• The variation of heart rate with respiration is known as sinus arrhythmia. Inspiration
increases and expiration decreases heart rate. 1. This is primarily mediated via
parasympathetic innervation of heart. Pulmonary stretch receptor, and cardiac
mechanoreceptors and baroreceptors contribute to sinus arrhythmia. 2. The difference
between the maximum and minimum heart rate during a deep breathing is called deep
breathing difference (DBD). 3. DBD is more than 15 beats per minute in normal
individual. It assesses the parasympathetic activity. DBD decreases with age. 4. It is one
of the best parasympathetic reactivity test. Normal values of DBD at different age group
are: 10 to 40 years : > 18 beats per minute 41 to 50 years : > 16 beats per minute 51 to
60 years : > 12 beats per minute 61 to 70 years : > 8 beats per minute Usually, subject is
asked to inhale deeply for five seconds and then exhale for five seconds for six cycles.
The ratio of shortest RR interval in inspiration to longest RR interval in expiration is
calculated for each, which is called expiration-inspiration ratio (E/I ratio). The average E/I
ratio of six cycles in a normal young individual is about 1:20. The E/I ratio decreases with
age (Table 34.1). Normally, instead of DBD expressed in terms of beats per minute, E:I
ratio is usually considered for assessing parasympathetic reactivity to deep breathing.
DBD is abnormal in multisystem atrophy, progressive autonomic failure, diabetes
mellitus, autonomic neuropathy and CNS depression.

14. Valsalva Ratio
• The Valsalva ratio is a measure of parasympathetic and sympathetic function. 1. In Valsalva maneuver
(named after scientist A M Valsalva, who described it), parasympathetic is the afferent and the efferent, and
sympathetic is the part of the efferent pathway. Therefore, Valsalva ratio assesses more of parasympathetic
(cardiovagal) than sympathetic functions. 2. The procedure is performed by closing both nostrils and then
blowing into a tube connected to sphygmomanometer. By putting strain, blowing pressure is maintained at
40 mm Hg for 15 seconds. Valsalva Maneuver Valsalva maneuver has four phases: Phase I: Phase I consists of
the onset of strain. In this phase, there is transient increase in blood pressure that lasts for a few seconds.
This occurs due to increased intrathoracic pressure and mechanical compression of the great vessels.
However, heart rate does not change much. Phase II: This is the phase of straining. In the early part of this
phase, venous return decreases, which in turn decreases cardiac output and blood pressure. This change
persists for 4 seconds. In the later part of this phase, blood pressure returns towards normal, which occurs
due to increased peripheral resistance as a result of sympathetic vasoconstriction. However, heart rate
increases steadily throughout this phase due to vagal withdrawal (in the early phase) and sympathetic
activation (in the later phase). Phase III: This phase occurs following the release of strain during which there
is transient decrease in blood pressure lasting for a few seconds. This is caused by mechanical displacement
of blood to pulmonary vascular bed, which was under increased intrathoracic pressure. There is little change
in heart rate. Phase IV: This is the phase that occurs with further release of strain. The blood pressure slowly
increases and heart rate proportionately decreases. It occurs following 15 to 20 seconds after release of
strain and lasts for about 1 minute or more. The cardiovascular changes occur due to increase in venous
return, stroke volume and cardiac out put.

15. • Valsalva ratio is the ratio of minimal heart rate in
• phase IV to maximum heart rate in phase II as depicted in
• terms of RR interval.
• Valsalva ratio = Longest R-R interval during phase IV
• Shortest R-R interval during phase II
• Clinical Correlation
• Valsalva ratio more than 1.45 is considered to be normal.
• 1. Ratio 1.2–1.45 is considered borderline, and ratio less
• than 1.2 is regarded abnormal.
• 2. The normal ratio is different at different age groups
• 3. Valsalva ratio is also affected by gender, posture of subject
in which recording is done, expiratory pressure, duration of
strain and level of yoga practice of the subject.
• Changes in Valsalva ratio occur due to changes in
• cardiac vagal efferent and sympathetic vasomotor activity,
which are stimulated by carotid sinus and aortic arch
• baroreceptors and other intrathoracic stretch receptors.
• Failure of heart rate to increase during strain suggests a
• sympathetic dysfunction and failure of heart rate to slow
• down after the strain suggests parasympathetic dysfunction.
If the cardiovascular response to Valsalva maneuver
• is abnormal but that to cold pressure test (see blow) is
• normal, the lesion is supposed to be present in the
baroreceptors or their afferent nerves. Such types of
abnormalities occur commonly in diabetes, other
neuropathies,
• multisystem atrophy and autonomic failure.

16. BP Response to Sustained Hand Grip
• In hand-grip test is an isometric exercise in which the subject is asked to
maintain hand grip against resistance. 1. Resistance usually offered by
using a hand grip dynamometer at a 30% of maximum voluntary
contraction for 5 min. BP and heart (HR) are recorded before and after the
hand grip. 2. In hand-grip test, heart rate and blood pressure increase. 3.
These cardiovascular responses to isometric exercise are mediated partly
by central motor command and partly by mechanical changes or both, in
response to contraction of the muscles that activate small fibers in the
afferent limb of the reflex arch. 4. The normal response is rise in diastolic
pressure more than 15 mm Hg and rise in heart rate by about 30%. 5. The
blood pressure rise is due to increased sympathetic activity and heart rate
rise is due to decreased parasympathetic activity. 6. The responses to hand
grip test are usually not dependent on age. 7. Isometric handgrip test is
one of the best sympathetic reactivity tests.

17. Cold Pressure Test
• This test is performed by submerging the upper limb of the subject in
ice cold water at 4°C for 30 to 60 sec. and BP is recorded before and
after the procedure. The submersion of hand in cold water increases
systolic pressure by about 20 mm Hg and diastolic pressure by 10 mm
Hg. 1. The afferent limb of the reflex pathway is somatic fibers
whereas the efferent pathway is the sympathetic fibers. 2. Thus, it
assesses sympathetic activity. 3. Cold pressor test is one of the best
sympathetic reactivity tests.

18. Sympathetic Skin Response
• Sympathetic skin response (SSR) helps in studying the functions of
peripheral sympathetic cholinergic (sudomotor) fibers by evaluating
the changes in resistance of skin in response to electrical stimuli. 1.
SSR is age dependent and is present in both hands and feet till the
age of 60. 2. Composition of surface electrodes, stimulus frequency,
skin temperature, and mental state of the subject affect the
parameters of SSR. 3. The latency and amplitude of SSR are
measured. 4. The amplitude of SSR in hand is 1.6 mV and in feet is 2.1
mV. SSR is helpful in diagnosing multisystem atrophy, progressive
autonomic failure, diabetes, uremic patients and alcoholic neuropathy

19. Thermoregulatory Sweat Test (TST)
• Assessment of sweating response to heat also assesses sudomotor
functions. 1. The subject’s body temperature is raised to by 1°C by
exposing to heat of the electric heater. 2. Sweating response is
studied by demarcating the area of sweating with the help of iodide
starch or quinizarin powder that changes the color of the moist skin.
3. Absence of sweating in TST indicates sympathetic preand post-
ganglionic lesions.

20. Quantitative Sudomotor Axon Reflex Test
• Quantitative sudomotor axon reflex test (QSART) is a measure of
regional autonomic function by Ach-induced sweating. 1. In this test,
Ach is injected intradermally and the sweat production rate is
assessed. 2. Reduced or absence of sweating indicates post-ganglionic
lesion of sudomotor fibers (sympathetic fibers concerned with
sweating).

21. Tests for Pupillary Functions
• Cocaine Test Dilation of pupil is observed following instillation of 4%
cocaine on both eyes. Cocaine prevents reuptake of norepinephrine
at adrenergic nerve endings. Therefore, pupils dilate in response to
cocaine, but, Horner’s pupils do not. Adrenaline Test Instillation of
1:100 or 1% noradrenaline on eyes dilate Horner’s pupil more than
normal pupil. This is due to the mechanism of denervation
hypersensitivity of Horner’s pupil.

22. Tests for Bladder Function
• Cystometrogram (CMG) is performed to detect autonomic
dysfunctions of urinary bladder. CMG reveals decreased ability of
bladder to accommodate urine. Absence of accommodation to filling
indicates autonomic dysfunction. Also, contraction of bladder muscle
is poor in response to the act of micturition (evacuation).

23. Spectral Analysis of HRV