Cardiovascular autonomic nervous system testing

At rest, during tilt table provocation, active standing, Valsalva maneuver, and deep breathing, the following biosignals are derived continuously and noninvasively:

• Blood pressure (finger plethysmography, tonometry)
• Heart rate (3-channel ECG)
• Respiratory rate (breathing belt)
• Cerebral blood flow velocity (laser Doppler flowmetry)

These examinations provide information on cardiovagal and peripheral adrenergic function, as well as baroreflex arc functionality.

Measurement of the skin reflex using sympathetic sudomotor stimulus response

By applying an acoustic stimulus, the galvanic skin reflex can be measured. This test allows an assessment of the sympathetic-sudomotor innervation.

Measurement of the pupillary light reflex

The reflexive adaptation of the pupil (miosis) at light incidence is regulated by the autonomic nervous system. The parasympathetic part causes a reflexive contraction of the sphincters at light incidence, whereas the subsequent redilation of the pupil (mydriasis) is controlled by the sympathetic nervous system. The so-called pupillary light reflex can be quantitatively assessed by pupillography and allows an evaluation of the oculomotor efference.

Pupillographic sleepiness test

The pupillomotor instability or the oscillation tendency of the pupil can be determined with the help of an infrared camera and corresponding analysis software. As a measure of the temporal variability of the pupil diameter, the degree of daytime sleepiness can be determined from this. Thus, a high oscillation tendency indicates a high daytime sleepiness.

24-hour blood pressure monitoring

Using a portable blood pressure monitor, blood pressure can be recorded on an outpatient basis over 24 hours. This special form of blood pressure measurement allows assessment of circadian blood pressure rhythms. Thus, disturbances in blood pressure regulation (e.g. at night) can be detected and treated at an early stage.

To assess the function and structure of the vascular system, test methods not yet established in clinical routine are used within the framework of scientific studies. The following examination methods are available in the ANF laboratory:

• Ultrasound to detect vascular reactivity at the brachial artery after 5-minute occlusion of the forearm vessels (flow-induced dilation) and to assess the wall thickness (intima-media thickness) of the carotid artery.
• Fundus microscopy to determine structural vascular changes in the retina and to measure the flicker light response of retinal arteries and veins
• Applanation tonometry to evaluate pulse wave morphology and pulse wave reflection (pulse wave analysis) and pulse wave velocity as a measure of vascular stiffness
• Quantitative sudomotor axon reflex test with transcutaneous iontophoresis of acetylcholine and hygrometric measurement of sweat response for evaluation of postganglionic sudomotor efferents