Analysis of Autonomic Control

The autonomic system is the part of the nervous system that we cannot control ourselves. It consists of two main parts - the sympathtic and the parasympa-thetic branches. Most tests of the function of the autonomic nervous system take advantage of the fairly easy access to continuous signals of blood pressure and heart rate. Thus almost all test involves these signals and the intactness of both branches of the autonomic nervous sytem is inferred from such recordings.

The more cumbersome tests of autonomic nevous activity outside the cardiovascular system include among others muscle sympathetic nerve activity, quantitative sweat test, and catecholamine turn-over.

Subjective symptoms of dysfunction in the autonomic nervous system can be quatified through the use of a standardized questionnaire (COMPASS 31)

Active Stand Test

Active stand test or orthostatic blood pressure measurement is a test using positional change from supine to standing to study the ability of the autonomic nervous system to regulate heart rate and blood pressure in response to gravitational changes in the distribution og blood volume.

There is no preparation for the study. During the actual examination, you are placed an a tilt table and connected to a computer by way of three electrodes on the chest and abdomen, a blood pressure cuff on the upper arm, and two small blood pressure cuffs on the 2. and 3. finger, respectively. In this way, we can record ECG, heart rate, blood pressure and breathing continuously throughout the study.

After resting for 10 minutes in the supine position, you will be asked to stand up from the tilt table and remain standing for 5 minutes, after which you lreturn to the resting supine position for another 5 minutes.

Valsalva Maneuvre

The Valsalva maneuvre is used to measure the ability of the autonomic nervous system to compensated for a short term reduction in the filling of the heart.

The test is performed in the sitting position on a tilt table and you will be connected to a computer by way of three electrodes on the chest and abdomen, a blood pressure cuff on the upper arm, and two small blood pressure cuffs on the 2. and 3. finger, respectively. In this way, we can record ECG, heart rate, blood pressure and breathing continuously throughout the test.

You will be asked to take a deep breath and the exhale in a connector creating a pressure of 40 mmHg - much like inflating a tight balloon.

The procedure is usually an integrated part og the active stand test and should be repeated twice with a 2-minute interval.

Deep Breathing

The deep breathing test analyses the coordination between respiration and heart rate level. This coordination is relayed through the parasympathetic part of the autonomic nervous system. Using slow respiration (6 breath per minute) gives the maximal response of this reflex.

During the actual examination, you are sitting on a tilt table and connected to a computer by way of three electrodes on the chest and abdomen. In this way, we can record ECG, heart rate, and breathing continuously throughout the study.

Sitting on the tilt table you will be asked to breath in deeply over 5 sec and exhale over 5 sec and to repeat this pattern for 2 minutes.

Isometric Handgrip

Isometric handgrip test serves three purposes. The first is to test your maximal voluntary stregth in the forearm muscles. The second is to test your endurance at 25 per cent of your maximum. The third is to monitor your heart rate and blood pressure response during the endurance.

We use the hangrip test to limit the muscle groups involved and thus to avoid post exertional malaise. The handgrip test is a classical test of the nervous systems response to muscular contraction.

ECG and blood prssure will be recorded as depicted in the other tests.

Active stand test

Both figures show heart rate (upper part - in red) and blood pressure (blue). The normal response (left panel) is a brief fall in blood pressure compensated by a transient increase in heart rate.

In POTS (right panel), heart rate remains at a high level throughout standing accompanied by strong oscillations in both heart rate and blood pressure. POTS is defined as an increase in heart rate of more than 30 beats per minute from supine to standing (40 for those under the age of 18 years). POTS is also characterised by the strong oscillations in heart rate and blood pressure.


Deep Breathing and Valsalva Maneuvre

The left panel shows heart rate (red) in response to deep breathing at a slow pace respiration. During inspiration heart rate increases and falls during expiration in response to reflex acitivty in the autonomic nervous system.

The right panel shows heart rate (red) and blood pressure in response to expiration against a resistance (begining at the first arrow). Lung pressure is elevated causing resistance to the blood returning to the heart. Thsi leads to a fall in blood pressure compensated by increases in heat rate and contraction of peripheral vessels