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Techniques for Performing Autonomic Nerve Function Tests


Table 2.3 Scores according to Ewing classification


Grading

Score

Normal

0

Boundary

0.5

Abnormal

1

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(Source: Ewing, 1985 [51])


2.6 METHODS, TOOLS FOR MEASUREMENT AND DATA COLLECTION

2.6.1 Patient preparation

All tests are performed in the morning, after the patient has rested for 30 minutes.

Patients should not use stimulants (tobacco, tea, coffee) at least 3 hours before performing the tests.

On the day of the test: the patient temporarily stops taking drugs that can affect autonomic nerve function, including anticholinergics, antihistamines, cardiovascular drugs (beta-blockers, calcium channel blockers, corticosteroids), and drugs used to treat Parkinson's disease.

Instruct the patient to breathe 6 cycles/minute (the practitioner gives the command for the patient to inhale or exhale every 5 seconds).

Instruct the patient how to blow into the tube with resistance in the Valsalva test.

Instruct the patient to stand up quickly as required by the test when measuring heart rate and blood pressure in a standing position.

Total time to perform 6 tests is about 1 hour to 1 hour 30 minutes.



Figure 2.1 4-channel electromechanical machine, Natus, USA

(Source: photo taken at the electromyography room, International Neurosurgery Hospital)

2.6.2 Prepare tools

When doing the tests, the patient lies in a cool, quiet room.

The tests were conducted on the Viking Quest 4-channel electromyography machine, Natus, USA.

Automatic blood pressure monitor, arm cuff type, brand OMRON – IA2, made in Japan.

Mechanical blood pressure monitor, YAMASU brand, made in Japan.

All heart rate tests use electrocardiogram to measure in lead DII.

2.6.3 Techniques for performing autonomic nerve function assessment tests

Heart rate variability test during deep breathing :

Place two electrodes for recording the ECG on the chest, one at the 2nd intercostal space and one at the apex of the heart. The patient rests for 5 minutes, and the patient breathes normally for the first minute, then takes deep breaths (inhale deeply for 5 seconds and exhale for the next 5 seconds) at a rate of 6 times/minute for about 1 minute. Evaluate the difference in heart rate between inspiration (shortest R-R interval) and expiration (longest R-R interval).



Figure 2.2 Normal heart rate variability during deep breathing (∆HR = 21 beats/min)

(Source: patient Pham Tung B, born in 1973, performed test at the electromyography room, International Neurosurgery Hospital)

Figure 2.3 Abnormal heart rate variability during deep breathing (∆HR = 6 beats/minute)

(Source: patient Nguyen Van C, born in 1969, performed test at the electromyography room, International Neurosurgery Hospital)


Test for heart rate and blood pressure variability when changing position :

Have the patient lie supine on the bed, place two electrodes for recording the ECG on the chest. Measure the blood pressure in the lying position, then start to have the patient stand up. Measure the blood pressure at 2, 3 and 5 minutes after standing up. Assess the difference in blood pressure when lying down compared to standing.

Index 30:15 = RR interval of the 30th heart beat after standing/ R-R interval of the 15th heart beat after standing.


Figure 2.4 Normal heart rate variability when changing posture (Index 30:15 = 1.25)

(Source: patient Lam Hong D, born in 1971, performed test at the electromyography room, International Neurosurgery Hospital)


Figure 2.5 Abnormal heart rate variability when changing posture (Index 30:15 = 1.02)

(Source: patient Nguyen Thi H, born in 1954, performed test at the electromyography room, International Neurosurgery Hospital)


Heart rate variability test with Valsalva maneuver:

Have the patient take a deep breath and blow forcefully into a resistance tube (connected to a blood pressure monitor), so that a pressure of 40mmHg is created and maintained for 15 seconds. Then, let the patient rest for 3 minutes and repeat this test 2 more times. Choose the highest Valsalva ratio of the 3 times as the final result.

Valsalva ratio = fastest heart rate of phase 2/ slowest heart rate of phase 4 (longest RR interval of phase 4/ shortest RR interval of phase 2)


Figure 2.6 Normal heart rate variability with the Valsalva test (Valsalva index = 1.4)

(Source: patient Diep H, born in 1966, performed test at the electromyography room, International Neurosurgery Hospital)

Figure 2.7 Abnormal heart rate variability with Valsalva test (Valsalva index = 1.1)

(Source: patient Tran Huu L, born in 1967, performed test at the electromyography room, International Neurosurgery Hospital)


Test blood pressure variation during isometric exercise :

Have the patient hold the sphygmomanometer for 3 minutes, maintaining a pressure equal to 1/3 of the patient's maximum grip pressure. Assess the difference in blood pressure during isometric exercise compared to rest.

Figure 2.8 Isometric exercise test

(Source: patient Nguyen Thanh T, born in 1977, performed test at the electromyography room, International Neurosurgery Hospital)

Test recording sympathetic skin response:

Place recording electrode pairs on the hands and feet, with the active electrode on the palms and soles of the feet, and the reference electrode on the backs of the hands and feet. Stimulation is performed by electrical stimulation of the nerve. Observe the response potentials on the screen.

Evaluation of results:

Normal: the skin sympathetic response is a biphasic wave.

Abnormal: no response wave on the screen [41].


Figure 2.9 Sympathetic response waves of the skin, electrodes on the palms and soles of the feet (Source: patient Nguyen Minh T, born in 1960, tested at the electromyography room, International Neurosurgery Hospital)


Figure 2.10 No response wave to the sympathetic skin response test (Source: patient Nguyen Thi H, born in 1954, tested at the electromyography room, International Neurosurgery Hospital)

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