The Investigation of the Cardiovascular and Sudomotor Autonomic Nervous System—A Review

Abstract

The autonomic nervous system as operating system of the human organism permeats all organ systems with its pathways permeating that it is involved with virtually all diseases. Anatomically a central part, an afferent part and sympathetic and parasympathetic efferent system can be distinguished. Among the different functional subsystems of the autonomic nervous system, the cardiovascular autonomic nervous system is most frequently examined with easily recordable cardiovascular biosignals as heart rate and blood pressure. Although less widely established, sudomotor tests pose a useful supplement to cardiovascular autonomic assessment as impaired neurogenic sweating belongs to the earliest clinical signs of various autonomic neuropathies as well as neurodegenerative disorders and significantly reduces quality of life. Clinically at first, the autonomic nervous system is assessed with a detailed history of clinical autonomic function and a general clinical examination. As a lof of confounding factors can influence autonomic testing, subjects should be adequately prepared in a standardized way. Autonomic testing is usually performed in that way that the response of the autonomic nervous system to a well-defined challenge is recorded. As no single cardiovascular autonomic test is sufficiently reliable, it is recommended to use a combination of different approaches, an autonomic test battery including test to measure parasympathetic and sympathetic cardiovascular function (deep breathing test, Valsalva maneuver, tilt, or pressor test). More specialized tests include carotid sinus massage, assessment of baroreceptor reflex function, pharmacological tests or cardiac, and regional hemodynamic measurements. Techniques to measure functional integrity of sudomotor nerves include the quantitative sudomotor axon reflex sweat test, analysis of the sympathetic skin response as well as the thermoregulatory sweat test. In addition to these rather established techniques more recent developments have been introduced to reduce technical demands and interindividual variability such as the quantitative direct and indirect axon reflex testing or sudoscan. However, diagnostic accuracy of these tests remains to be determined. We reviewed the current literature on currently available autonomic cardiovascular and sudomotor tests with a focus on their physiological and technical mechanisms as well as their diagnostic value in the scientific and clinical setting.

Cardiac Autonomic Dysfunction in Multiple Sclerosis: A Systematic Review of Current Knowledge and Impact of Immunotherapies

“…Furthermore, age, patient medication, consumption of nicotine, alcoholics or caffeine or even room temperature in the examination room are important influencing factors in autonomic functional diagnostics. Therefore, strict standardization of patient preparation, test procedures and evaluation using standard values and test algorithms created for all laboratories is required [119].…”

The diagnostic usefulness of the combined COMPASS 31 questionnaire and electrochemical skin conductance for diabetic cardiovascular autonomic neuropathy and diabetic polyneuropathy

“…The study documents that ESC is associated with the presence of CAN and DPN and is related to the degree of impairment of neurological measures. Previous studies, using the gold‐standard for sudomotor function QSART, have shown weak correlations between sweat volume of lower limb and feet ESC, and recent reviews have described in detail the differences between these techniques assessing sudomotor function . Thus, the use of ESC as a marker of distal autonomic function seems to be supported although a conclusive demonstration of its direct assessment of sudomotor function is lacking.…”

“…ESC is based on an electrochemical reaction between sweat chloride and stainless steel electrodes in response to applied low voltage direct current, 35 thus it reflects the flow of chloride ions from sweat glands to the skin caused by an electric current through the activation of the sympathetic sudomotor fibers or a direct stimulation of sweat glands. 15,36…”

“…Sudomotor function was assessed by an operator unaware of the neurological assessment through ESC measured at the hands and feet using Sudoscan (Impeto Medical, Paris, France). ESC is based on an electrochemical reaction between sweat chloride and stainless steel electrodes in response to applied low voltage direct current, thus it reflects the flow of chloride ions from sweat glands to the skin caused by an electric current through the activation of the sympathetic sudomotor fibers or a direct stimulation of sweat glands . Participants were requested to avoid previous application of moisturizing creams, and instructed to put both palms and both feet simultaneously on electrodes.…”

“…Previous studies, using the gold-standard for sudomotor function QSART, have shown weak correlations between sweat volume of lower limb and feet ESC, 19,22 and recent reviews have described in detail the differences between these techniques assessing sudomotor function. 11,15,36 Thus, the use of ESC as a marker of distal autonomic function seems to be supported although a conclusive demonstration of its direct assessment of sudomotor function is lacking. Moreover, correlations between ESC and morphology of small fibers have been reported by some authors using skin biopsy parameters although weaker than expected 15,19,43 and denied by others using corneal confocal microscopy measures.…”