Autonomic testing

 Autonomic dysfunction can occur as a result of many
diseases that affect autonomic pathways.
 The clinician’s role is to seek out symptoms of
dysautonomia
 Necessary to determine if these symptoms are really
due to involvement of autonomic systems.

 The conceptual framework began 19th century .
 These original tests were developed over time .
 Widely used in clinical practice for 50 years
 Decades of extensive experience and thousands of
studies published on its use.

 1. To evaluate the severity and distribution of autonomic
function
 2. To diagnose limited autonomic neuropathy
 3. To diagnose and evaluate orthostatic intolerance
 4. To monitor the course of dysautonomia
 5. To monitor response to treatment
 6. As an instrument in research studies

 1. Cardiovagal innervation (parasympathetic innervation):
heart rate (HR) response to deep breathing, Valsalva ratio,
and HR response to standing (30:15 ratio)
 2. Adrenergic: beat-to-beat blood pressure (BP) responses to
the Valsalva maneuver, sustained hand grip, and BP and HR
responses to tilt-up or active standing
 3. Sudomotor: quantitative sudomotor axon reflex test
(QSART), thermoregulatory sweat test (TST), sympathetic
skin response (SSR).

 Beat to beat heart rate analysis
 Heart rate documented on ECG or on EMG equipment
 For ECG in EMG
 Low filter 1-5 Hz; High filter 500Hz
 Slow oscilloscope sweep time(0.2-1 secs)
 Sensitivity- 0.5 mv
 Active electrode midline posteriorly between inferior
angle of scapula; reference mid axillary line

 Heart rate is inversely related to RR interval
 Heart rate(R-R/min)=
 sweep speed(mm/s)÷RR interval x60
 BP sphygmomanometer
 Beat to beat BP measurement formerly required
invasive intra arterial measurement; but
plethysmography

 The variation of heart rate with respiration is known as
sinus arrhythmia
 Inspiration  increases the heart rate
 Expiration  decreases the heart rate
 This is also called Respiratory Sinus Arrhythmia (RSA)
 This is an index of vagal control of heart rate

 Due to changes in vagal control of heart rate during
respiration
 Probably due to following mechanisms
 Influence of respiratory centre on the vagal control of
heart rate
 Influence of pulmonary stretch receptors on the vagal
control of heart rate

 Connect the ECG electrodes for recording lead II
 Ask the subject to breath deeply at a rate of six
breaths per minute for 3 cycles
(allowing 5 seconds each for inspiration and
expiration)

 Record maximum and minimum heart rate with each
respiratory cycle
 Average the 3 differences
 Normal > 15 beats/min
 Borderline = 11-14 beats/min
 Abnormal < 10 beats/min

 Determine the expiration to inspiration ratio (E:I ratio)
 Mean of the maximum R-R intervals during deep
expiration to the mean of minimum R-R intervals
during deep inspiration

longest RR interval (expiration)
Ratio = -------------------------------------
shortest RR interval (inspiration)
E:I = 1.2

 An immediate response with an abrupt fall in systolic
and diastolic blood pressure and a visible acceleration
of heart rate (first 30 s),
 a phase of early stabilization, which occurs after
approximately 1-2 min,
 a response to prolonged orthostasis lasting for more
than 5 min.
 during the phase of stabilization , acceleration of heart
rate by about 10-15 beats per minute and a slight
decrease in systolic blood pressure, while diastolic
pressure increases by approximately 10 mmHg

 Evaluation of changes in heart rate (30/15 ratio) is
performed during the initial phase of adaptation to
orthostasis .
 On standing the heart rate increases until it
reaches a maximum at about
 15th beat (shortest R-R interval after standing)
 after which it slows down to a stable state at about
30th beat (longest R-R interval after standing)

 The ratio of R-R intervals corresponding to the 30th
and 15th heart beat  30:15 ratio
RR interval at 30th beat
 30:15 ratio= ------------------------------
 This ratio is a measure of parasympathetic response

 30:15 ratio = ------------------------------
 Normal > 1.04
 Borderline = 1.01-1.04
 Abnormal =<1.00

 Fluctuations of blood pressure are assessed based on
somewhat later responses to standing (first 4 min)
 they are expressed as the difference between the
baseline supine and the minimal blood pressure after
standing up.
 A decline in systolic blood pressure by more than 20
mmHg and by more than 10 mmHg for diastolic blood
pressure is considered abnormal

 OH- fall of 20 mm Hg systolic or 10 mm Hg diastolic
BP on standing- AAS ;AAN 1996
 30mmHg systolic; 20 mmHg diastolic BP- McLeod and
Tuck, 1987
 Diagnostic criteria of POTS include
 a) a sustained increase in heart rate (HR) of 30 beats
per minute (bpm) or greater during 10 minutes of
assuming an upright position,
 b) no associated hypotension, and
 c) symptoms of orthostatic intolerance, which must
be present for at least three months.
 In severe forms of the disease, HR may increase to
more than 120 bpm on standing.

 Assesses integrity of the baroreceptor reflex
 Measure of parasympathetic and sympathetic function
 It is “forced expiration against a closed glottis”

 The Valsalva maneuver
is performed by
attempting to forcibly
exhale while keeping
the mouth and nose
closed
 It increases
intrathoracic pressure
to as much as 80 mmHg

 Perform the Valsalva manoeuvre (forced expiration
against a closed glottis) by asking the subject to
breathe forcefully into a mercury manometer and
maintain a pressure of 40 mmHg for 15 seconds
 Record the ECG throughout and for 30 seconds
after the procedure

 4 phases
 Phase I
 Phase II
 Phase III
 Phase IV

 Transient increase in BP which lasts for a few seconds
 HR does not change much
 Mechanism: increased intrathoracic pressure and mechanical compression
of great vessels due to the act of blowing

 Early part – drop in BP lasting for about 4 seconds
 Latter part – BP returns to normal
 Heart rate rises steadily

Mechanism
 Early part
 venous return decreases with compression of veins by increased
intrathoracic pressure central venous pressure decreases 
BP decreases
 Latter part
 drop in BP in early part will stimulate baroreceptor reflex 
increased sympathetic activity  increased peripheral
resistance  increased BP ( returns to normal )
 Heart rate increase steadily throughout this phase due to vagal
withdrawal in early part & sympathetic activation in latter part

 Transient decrease in BP lasting for a few seconds
 Little change in heart rate

 Mechanical displacement of blood into
pulmonary vascular bed, which was
under increased intrathoracic pressure
 BP decreases

 BP slowly increases and heart rate proportionally decreases
 BP overshoots
 Occurs 15-20 s after release of strain and lasts for about a minute
or more

 Due to increase in venous return, stroke volume and
cardiac output

 Phase I Increase in BP
 Phase II Decrease in BP, Tachycardia
 Phase III Decrease in BP
 Phase IV Overshoot of BP, Bradycardia

 Measure of the change of heart rate that takes place
during a brief period of forced expiration against a
closed glottis
 Ratio of longest R-R interval during phase IV (within
20 beats of ending maneuver) to the shortest R-R
interval during phase II
 Average the ratio from 3 attempts

Longest RR
Valsalva Ratio = -----------------------------
Shortest RR
Values :> 1.4
 more than 1.21  normal
 less than 1.20  abnormal

 Valsalva maneuver evaluates
 1. sympathetic adrenergic functions using the blood
pressure responses
 2. cardiovagal (parasympathetic) functions using the heart
rate responses

 4. Cold pressor test
 Submerge the hand in ice cold water(1 minute)
 diastolic pressure by >15 mmHg
 HR>10/min
 5. Isometric handgrip test
 isometric pressing of a handgrip dynamometer at
approximately one third of the maximum contraction
strength for 3-5 min.
 Blood pressure measurements are taken at the other
arm at 1 min interval
 Rise of DBP>15/min

 • Patient refusal
 • Morbid obesity (technicians cannot tilt safely)
 • Unable to stand for long periods due to pain
 • Pregnancy
 • Recent (within 6 months) myocardial infarction or
stroke/TIA
 • A known tight stenosis anywhere (eg heart valve, LV
outflow obstruction, coronary or
carotid/cerebrovascular artery)

 Fast 2 or more hrs
 Rest supine 20-45 minutes
 Stop drugs affecting cvs or autonomic function;
minimum of 5 half life pretest
 Minimize lower limb movements
 Get the baseline blood pressure from the brachial
artery.
 Acquire the 5-10 minutes baseline
 Tilt angle and duration

 Tilt patient up. The tilt should be done at 70 degree. The
transition from supine to tilt position should smooth and of
duration 5-10 seconds.
 Obtain the blood pressure from a brachial artery every
minute.
 Observe subject for the presence of any discomfort, chest
pain, shortness of breath, dizziness, lightheadedness,
syncope
 Be prepared to terminate the tilt of any serious event occurs
during the tilt based on clinical judgment.
 The tilt can be continued if no obvious abnormalities are
detected but a clinical history is strongly suggestive of
dysautonomia or blood pressure instability.
 Tilt the patient back.

 The normal responses in heart rate during the tilt is
heart rate increment within 10 - 15 beats per minute.
 At the same time the maximal heart rate should be less
than 120 beats per minute.
 Normal responses in the blood pressure during the tilt
modest rise of diastolic blood pressure ; slight fall of <10
mm Hg in SBP.

Through vasoconstriction of capacitance
and arteriolar vessels and through increased heart output, a healthy subject is able to reach orthostatic
stabilization in 60 seconds or less.
Within seconds of this sudden decrease in venous return,
pressure receptors in the heart, lungs, carotid sinus and aortic arch are activated and mediate an increase
in sympathetic outflow
about 300 to 800 mL of blood is forced downward to the abdominal area
and lower extremities

 From studies HUT testing (2 occasions), with a known
time interval,an average reproducibility of 81%
 However, as Behzad and collaborators and other
authors
 highlighted, negative results are much more
reproducible than positive ones (about 95% and 50%
respectively).
 depends strongly on population selection as it is
increased in patients with severe and frequent
orthostatic symptoms.

 Studies assessing the ability of the HUT test to diagnose
neurocardiogenic syncope averaged a sensitivity of 35%
without pharmacologic stimulation
 57% with pharmacologic stimulation
 Studies using HUT testing within the boundaries set by
the American College of Cardiology guidelines averaged
a sensitivity of 65%

 The specificity of the HUT test for neurocardiogenic
syncope 92% on average without pharmacologic
stimulation
 81% with pharmacologic stimulation
 Two investigator-HUT test-American College of
Cardiology guidelines-both yielded a specificity of
100%.

 Thermoregulatory sweat testing (TST) is used
 evaluate the integrity of central and peripheral
sympathetic sudomotor pathways from the CNS to the
cutaneous sweat glands
 The temperature is adjusted to 45–50 °C with a relative
humidity of 35–40%.

 Sweat produces a change in local pH resulting in the
indicator dye changing color
 marking the location of sweat production (sweat has a
pH of 4.5–5.5 at low sweat rates of 15–100nL/gland per
hour).
 Two common indicators include alizarin red powder
(alizarin red, corn starch, sodium carbonate, 1:2:1) and
iodine corn starch.

 Maximal sweating is achieved within 30–65 minutes.
 Heating time should not exceed 70 minutes to avoid
hyperthermia
 Sweating causes the indicator to change its color (from
yellow to dark red for alizarin red and from brown to
purple with iodine).
 Digital photographs are taken and a sweat density map
is generated on standard anatomical drawings
 Data are expressed as TST% which is the measured area
of anhidrosis divided by the area of the anatomic figure,
multiplied by 100

 Normal sweating patterns are generally symmetric but
vary in quantity
 Asymmetric sweat patterns and anhidrotic areas (focal,
segmental, regional, length dependent) are noted.
 The TST% can provide a general index of severity of the
autonomic failure

 Limitations
 TST can localize specific areas of sudomotor dysfunction
but can not differentiate preganglionic from
postganglionic lesions
 In combination with a test measuring postganglionic
sudomotor function (QSART, silicone impression) the
site of a lesion can be separated:
 preganglionic lesions show an abnormal TST, while the
QSART, or silicone imprints are normal.
 A postganglionic lesion will be abnormal in all tests

 Quantitative sudomotor axon reflex test (QSART) is
used to evaluate postganglionic sympathetic cholinergic
sudomotor function
 Axon-reflex mediated sweat response over time and
has achieved widespread clinical use.

 Clean the recording sites vigorously with the alcohol.
 Recording sites are:1) the medial forearm (75 %
distance from the ulnar epicondyle to the pisiform
bone);
 2) the proximal leg (5 cm distal to the fibular head
laterally);
 3) the distal leg (5 cm proximal to the medial
malleolus medially
 4) proximal foot over the extensor digitorum brevis
muscle.
 Place the ground for stimulation about 5 cm next to the
capsule.

 Wait until the baseline sweat is flat, below 100
nanoliters/minute and all channels give similar baseline
sweat output (difference < 15 %,)
 Start stimulation at current 2 mA for 5 minutes, turn on
the marker.
 Record another 5 minute of the sweat (total 10
minutes), turn on the marker.
 Obtain the latencies and volumes at each site

Stable baseline of spontaneous sweating

 In normal individuals, the sweat output starts with a
delay of 1–2 minutes.
 The sweat output increases for up to 5 minutes after
stimulation until it reaches the inflection point and
decreases slowly.
 While males and females have similar latency the
sweat output differs.
 Mean sweat output for males is 2–3 μl/cm2
(approximate range 0.7–5.4 μl/cm2) and
 females 0.25–1.2 μl/cm2 (approximate range 0.2–3
μl/cm2) with some variation depending on the site of
stimulation
 Sweat response can be absent, decreased or increased.

 longer latency of the sweat onset can be seen as well as
a lack of recovery, the “hung up” response
 Increased sweat production is often a sign of axonal
excitability,
 seen in conditions such as diabetic neuropathy, reflex
sympathetic dystrophy and other small fiber
neuropathies.
 In diabetic neuropathy, especially during early stages,
a length-dependent pattern of sweat reduction can be
seen

 QSART measures the postganglionic sudomotor
response and will be unable to detect preganglionic
lesions.
 QSART is also time-consuming, requires special
equipment and is not widely available

 SSR, also referred to as galvanic skin response is a
measure of electrodermal activity
 Generated in deep layer of skin
 Reflex activation of sweat glands via cholinergic
sudomotor sympathetic efferent fibres.
 Provides a surrogate measure of sympathetic
cholinergic sudomotor function.

Historical aspects
 (SSR) is a change in skin potential following arousal
stimulation, described by Tarchanoff (1890).
 Method introduced by Sahani in 1984 and later by
Knezevic and Bjada

 SSR is a change in potential recorded from surface of
skin, representing sudomotor activity
 Can be evoked by different stimuli
 Acoustic; TMS C7, brain; startle; laser skin; reflex
hammer percussion on sternum
 Resende et al deglutition; blinking; skeletal
movements; biting; light stimuli; vocalization;
sphincteric contraction
 Stimulus modality determine the afferent tract

Electrical stimulation
of peripheral nerve
activates afferent part
of reflex consisting
thick myelinated
sensory fibres(typeII)
sensory spinal cord
tract
brain
stem(influenced by
hypothalamus,
medial and basal part
of frontal lobe and
medial part of
temporal lobe

originate from the
hypothalamus and
descend uncrossed
along the lateral
column of the
spinal cord to form
a small bundle
between the
pyramidal tract and
the anterior-lateral
tract. Terminates
on sympathetic
preganglionic
neurons in the
intermediolateral
cell column.
Myelinated
sympathetic
fibres from
intermediolateral
nucleus in T1- L2
of spinal cord
Paravertebral
sympathetic
ganglia
Post ganglionic
by non
myelinated( type
c); innervating
sweat gland

 Room temperature should be comfortable and the skin
surface temperature 32@C.
 potentials are increased during psychological stress and
may contaminate the evoked SSR.
 situation during recording has to be relaxed, without
acoustic disturbances

 Recording is done from glabrous skin and is referenced
against hairy skin whose sweat glands are not typically
active at normal ambient temperatures.
 The surface Ag-AgCl electrodes are placed on the palm
(active) and referenced against the volar forearm or
dorsum of the hand (indifferent);
 and on the sole of the foot (active) and referenced
against the shin or dorsum of the foot (indifferent)

 The recording time should be 5±10 s,
 the lower frequency limit 0.1±2 Hz (better,1 Hz), and
the upper limit 100±2000 Hz (not critical).
 Amplification should be 0.05±3 mV/division.

 Electrical stimulation is carried out with a constant
current stimulus (0.2 ms, supramaximal, 10±30 mA).
 Typically the median, posterior tibial, peroneal, sural
or supraorbital nerves are stimulated at a strength at
least three times the sensory threshold.
 it is applied at irregular time intervals and at a
frequency of approximately 1/min to avoid habituation.

 If electrical stimulation at one site does not evoke an
SSR, other sites of stimulation should be tried
 If the response to electrical stimulation is absent
 response to acoustic stimuli or to an inspiratory gasp
should be tried (Shahani et al. 1984).

 In normal subjects, transcranial magnetic stimulation
of the motor strip
 elicited palmar and plantar SSRs similar
 both in latency and amplitude to those evoked by
median nerve stimulation.
Normal results
 The shape of the SSR is variable.
 The shortest latency to onset and the maximum peak
to trough amplitude of at least 5 recordings is used.

Latency
 The latency of the SSR includes
 1. afferent conduction (about 20 ms), 2.central
processing time (a few milliseconds),
3.and efferent conduction in pre- and
slow conducting postganglionic autonomic nerve.

 The mean conduction velocity of sudomotor nerve
fibers is about 1±2 m/s.
 Conduction in postganglionic C fibers as well as
activation time of sweat glands include about 95% of
the SSR latency
 of around 1.5 s at the hands and 2 s at the feet.
 differences in fast afferent conduction are not relevant
for the SSR latency and the site of stimulation is also
not significant

 Amplitude Measurements in theory should reflect the
density of spontaneously activable sweat glands.
 interaction of the two components, sweat gland and
epidermal, makes the absolute amplitude of the
evoked EDA difficult to interpret.
 the reproducibility of the electri-cally evoked SSR is
poor.
 Age- latency; amplitude
 SSR evoked by an auditory stimulus has less inter and
intrasubject latency and waveform variability than the
inspiratory gasp induced response.

 Still no consensus about the evaluation and processing
 Qualitative evaluation accepts only the absence of SSR
as a pathological sign
 Quantitative evaluation- different opinion

 SSR is a poor test of sympathetic sudomotor function.
 No close correlation between presence or absence of
SSR and the severity of autonomic dysfunction.
 polyneuropathy, erectile dysfunction, central
degenerative diseases, multiple sclerosis(50%), brain
infarction, reflex sympathetic dystrophies, spinal and
peripheral nerve lesions.

ASSESSMENT:
CLINICAL AUTONOMIC TESTING
Report of the Therapeutics and Technology Assessment Subcommittee
of the American Academy of Neurology
AAN 1996

 Distal small fiber neuropathy
 Sympathetic sudomotor fibers are affected, so that
QSART will show abnormalities at the feet and normal
sweating more proximally
 thermoregulatory sweat test shows anhidrosis that is
confined to the distal feet
 confined or becomes generalized.
 diabetes or amyloidosis can start with DSFN and
progress, while others do not

 e.g: Autonomic neuropathies and multiple system
atrophy.
 widespread loss of sweating, cardiovagal failure is
present, and OH with impaired baroreflexes is seen

 chronic idiopathic anhidrosis, gastroparesis

 Recent studies indicate that MSA is distinguishable
from PD using autonomic tests.
 PD is characterized by a length-dependent involvement
of postganglionic sudomotor fibers
 MSA is characterized by widespread, early and
preganglionic autonomic failure.
 MIBG or fluorodopa scan of the heart, which images
postganglionic adrenergic innervation, is typically
defective in PD and normal in MSA

 PD case showed very distal anhidrosis, affecting only
parts of the toes, and did not progress over time.
 In contrast, MSA causes widespread anhidrosis.
 If both QSART and TST are performed, normal
QSART volume in an anhidrotic region indicates that
the lesion is preganglionic in site.

 Plasma norepinephrine measured with the subject
supine and after a period of standing provides another
method of studying adrenergic function.
 A normal response consists of doubling of NE on
standing.
 The patient with generalized postganglionic adrenergic
failure, as in pure autonomic failure (PAF), will have
low supine NE.
 The patient with preganglionic lesion, as in MSA, will
typically have normal supine values (since the
postganglionic fibers are intact) but a failure to
increment on standing

 Mishra and kalita: clinical neurophysiology
 D. Clausa,* and R. Schondorf: Sympathetic skin
response; 1999 International Federation of Clinical
Neurophysiology.
 Kucera p, Goldenberg Z, Kurca E: SSR: Review of
method and its clinical use;Bratis1 Lek Listy 2004
 Ben M.W. Illigens, MD and Christopher H. Gibbons,
MD MMSc:Sweat testing to evaluate autonomic
function; Clin Auton Res. 2009 April
 Peter Novak:Video Article Quantitative Autonomic
Testing; 2011 Journal of Visualized Experiments

Autonomic testing

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