Auricular Vagal Stimulation in Alcohol Craving
Condition: Alcohol Withdrawal; Psychophysiologic Reaction
Study type: Interventional

Summary: 
      Background: The cause of the vegetative symptoms is a sympathetic driven misbalance of the
      autonomous nervous system. To restore vegetative balance in alcohol withdrawal syndrome new
      neuro-modulatory methods, such as percutaneous auricular vagal stimulation (pVNS) could be
      used. Measuring the pupil size is a suitable method to assess imbalances or dysfunctions of
      the vegetative regulation in individuals. Objective: The objective of this study is to assess
      the pupil reaction to the cholinergic antagonist tropicamide in alcohol withdrawal syndrome
      as a biomarker of the vegetative balance before and after pVNS. Methods: 30 patients aged
      between 20 and 65 were recruited in this open-label, controlled pilot trial with repeated
      measure design. pVNS was administered at the left cymba conchae for 72 hours with intermitted
      stimulation. Pupillometric recording lasted about 60 min and was performed at baseline and
      following pVNS. The reaction of the pupil to an anticholinergic agent was measured as a
      receptor-test in terms of a psychophysiological feedback mechanism to pVNS.
    

Detailed description: 
      The chronic consumption of alcohol leads to a pathophysiological adaptation of the nervous
      system, by an increase in glutamatergic receptors and a decrease in GABAergic receptor
      functions. Autonomic and psychomotor hyperactive disorders, such as nausea, tremor,
      diaphoresis, hypersensitive reflexes, hypertension, and tachycardia, as well as negative
      emotional states, characterized by restlessness, anxiety, dysphoria, and irritability occur 6
      to 24 hours after cessation of alcohol consumption. The cause of the vegetative symptoms is a
      sympathetic driven misbalance of the autonomous nervous system. The negative state of health
      can last for a very long time and is the main reason for relapses.

      Pharmacological treatment of alcohol withdrawal syndrome consists of ether Benzodiazepines or
      GHB is an endogenous metabolite of γ-aminobutyric acid (GABA).

      The rate of successful treatment is lowest for alcohol dependence among all psychiatric
      disorders. Therefore, it seems important to carry out further interdisciplinary
      investigations in the direction of new and effective treatment methods. To restore vegetative
      balance in alcohol-withdrawal syndrome novel neuromodulatory approaches, such percutaneous
      auricular vagal stimulation (pVNS) could be beneficial.

      The pupil size changes, like other physiological markers, e.g., hyperventilation, blood
      pressure and heart rate, serves as psychophysiological marker of the autonomic nervous system
      (ANS). Beside the fact that pupil size is determined by balance between the parasympathetic
      ANS (PANS) and the sympathetic ANS (SANS), measuring the static and dynamic pupillary
      diameters are suitable parameters measuring imbalances or dysfunction of the vegetative
      regulation. The pupil diameter oscillates spontaneously at low frequencies, which is an
      almost constant oscillatory change in the pupil size. Like pupil size, it is generally
      assumed that pupil oscillation is regulated by a dynamic interaction between parasympathetic
      (cholinergic) and sympathetic (noradrenergic) activity.

      In this study, the investigator assessed the pupil reaction to the cholinergic antagonist
      tropicamide in alcohol withdrawal syndrome as a biomarker of the vegetative balance before
      and after pVNS. The Investigator hypothesized that pVNS will enhance the parasympathomimetic
      tone represented by a reduction of pupillary diameter in a parasympatholytic pharmacological
      challenge with tropicamide after vagal stimulation.

      Study Design

      The pilot study applied an open-label, unblinded, repeated measures design with three time
      points of pupillometry measurements at two testing days. For baseline measurements, the
      static pupil measurement was taken with the head fixed in a position and with open eyes (0').
      Followed by an administration one drop of 0.01% tropicamide-solution into the left eye. The
      dynamic pupil measure followed 20 minutes (20') and 40 minutes (40') after tropicamide
      application. In our protocol the investigator scheduled a 60' measurement, which was removed
      due to the finding, that a maximum dilation was measured after 40' and that patients became
      increasingly agitated and weary, often leading to biased recordings at baseline measurement.
      Absolute change (mm), and relative change (%) of the pupil diameter was calculated.

      Next, auriStim (AU0115, Multisana GmbH, Vienna, Austria) was placed for percutaneous vagal
      stimulation (pVNS). Patients were stimulated for 72 hours, with an intermittent stimulation
      mode, switching from active to resting state all three hours. After the stimulation period,
      patients placed their head in a fixed position for the second pupil measurement. For dynamic
      measurements, tropicamide was induced and measures were taken after 20' and 40'. Again, the
      investigator calculated absolute and relative changes of the pupil diameter. For each
      recording the investigator analyzed pupillary oscillations with a Fourier analysis as
      biomarker of the central nervous activation. All patients were tested at the same time of the
      day (between 9:00 and 10:00 a.m.) to exclude diurnal variation in pupillary diameter at day
      two and day five of the inpatient alcohol withdrawal.

      Percutaneous auricular vagal nerve stimulation (pVNS)

      For auricular vagal stimulation the investigator used auriStim (AU0115, Multisana GmbH,
      Vienna, Austria). Using a green light-emitting diode (LEDs) flashlight, blood vessels in the
      cymba conchae of the left ear side were detected. Minimal invasive needles (penetrating
      1-2mm) were placed close to the vessel-bifurcation to provide efficient stimulation of the
      auricular branch of the vagus nerve. The built-in microchip controls monophasic volt pulses
      of 1 ms, with alternating polarity, a frequency of 1 Hz and an amplitude of 4V. Stimulation
      lasted for 72h in total with alternating on/off periods of three hours. Thereafter, the
      device was removed, and patients continued their therapy consisting of anti-withdrawal
      medication.

      Quantitative pupillometry

      Before recording, patients were acquainted to the test environment (160 lux) in a
      noise-protected room (3 x 4 meters) for three minutes. With head held steady in a chin- and
      forehead rest, the patients positioned their left eye in front of the camera and fixed a
      black dot, at 1.6m distance, to prevent accommodation. Pupillometry was performed using a
      non-invasive, personal computer-based infrared digital video pupillometer system (TV
      pupillometer 1050, Whittaker Corporation., California, Los Angeles). Incorporated five
      milliwatts, infra-red LEDs provide continuous illumination of the eye, with a wavelength of
      850nm to achieve high contrast filming condition, and to which the pupil does not respond.
      The system integrates a calibrated light stimulation of fixed intensity (145 lux) and
      duration (300ms) to induce a light-evoked pupillary reaction. The system allows a precise
      (0.01mm limit) and rapid (50Hz) measure of the vertical diameter, and automatically
      determines static pupil size (averaged over the first 25.6sec of recording) and a series of
      dynamic pupillary parameters after light stimulation. Dynamic parameters include resting
      pupil diameter (pupil diameter just before light-stimulation), the latency for constriction
      (the latency time from the light flash exposure to the start of pupillary constriction), the
      amplitude of constriction (the value of the resting diameter minus the maximum constriction
      diameter), the constrictive ratio (amplitude of constriction/resting pupil diameter), the
      duration of constriction (time interval between the start of constriction, and the time point
      of maximum constriction) and peak constriction velocity. The recording of the pupillary
      diameter and response curve is shown as a graph of the pupillary diameter against time. Based
      on the measurement of static pupillary diameter (first 25.6sec) the pupillometer calculates
      pupillary oscillations by Fourier analysis (FA), reflecting the activation of the central
      nervous system. Prior to Fourier Analysis a linear interpolation was applied to artefacts
      such as blinking and missing data by a built-in noise removal program. For FA the
      investigator used five individual frequency bands: 0.0 - 0.2, 0.21 - 0.4, 0.41 - 0-6, 0.61 -
      0.8, 0.81 - 1 Hz and whole power spectrum 0.0 - 1 Hz.
    

Intervention name(s): auriStim, for auricular vagal stimulation
Intervention type(s): Device
Intervention description(s): For auricular vagal stimulation we used auriStim (AU0115, Multisana GmbH, Vienna, Austria). Using a green light-emitting diode (LEDs) flashlight, blood vessels in the cymba conchae of the left ear side were detected. Minimal invasive needles (penetrating 1-2mm) were placed close to the vessel-bifurcation to provide efficient stimulation of the auricular branch of the vagus nerve. The built-in microchip controls monophasic volt pulses of 1 ms, with alternating polarity, a frequency of 1 Hz and an amplitude of 4V. Stimulation lasted for 72h in total with alternating on/off periods of three hours. Thereafter, the device was removed, and patients continued their therapy consisting of anti-withdrawal medication.
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Diagnostic
Keywords: alcohol withdrawal; vagal stimulation; pupillometry