Effects of Transcutaneous Electrical Stimulation on the Autonomous Nerve System in Healthy Young People
Condition: Healthy Volunteers; Cardiovascular System; Autonomic Nervous System
Study type: Interventional

Summary: 
      Cardiovascular disease is one of the most important causes of death and disability in the
      world. An autonomic imbalance is associated to cardiovascular risks and disorders. Electrical
      stimulation (ES) applied by surface electrodes is a non-invasive therapeutic approach with
      low side-effects. In the last years, some studies had investigated the effects of ES on the
      autonomic nervous system and cardiovascular system. However, different intensities,
      frequencies and electrode locations had been used, which makes difficult to clarify the
      optimal parameters.

      The aim of this study is to analyze the effects of ES on autonomic nervous modulation in
      healthy subjects comparing three different locations of application for ES.

      Participants will be aleatory assigned to one of three groups for a single-session of
      20-minute transcutaneous ES: a) an auricular intermittent ES in an area that is believed to
      be connected to the vagal nerve (cymba conchae); b) an auricular sham intermittent ES,
      meaning a real ES but applied on an ear location not connected to the vagal nerve (scapha);
      and c) an upper back continuous ES (C7-T4), a placement that is thought to be connected to
      the stellate (sympathetic) ganglion. All the protocols will be stated at a non-painful
      intensity. After that, the hand grip exercise will be executed.

      The heart rate variability (HRV) and heart frequency (HR) will be measured in four main
      times: the baseline, in the final minutes of the ES, after the ES and after finishing the
      hand grip exercise. Blood pressure will be measured also at all the time points except during
      the ES due to the possibility of interferences. Adverse effects will be assessed after ES and
      48 h later. The study will provide initial knowledge about how different electrical
      stimulation locations contribute to reduce sympathetic excitation and improve the
      sympathovagal balance.
    

Detailed description: 
      Electrical stimulation (ES) of the nervous system, also denominated as neuromodulation, has
      been investigated for diverse conditions as cardiovascular diseases, chronic pain and
      psychiatric conditions. It is unknown which locations and parameters can be more effective
      and better tolerated. The transcutaneous ES is a non-invasive technique which has fewer
      side-effects than subcutaneous vagus nerve stimulation.

      The aim of this study is to analyze the acute effects of transcutaneous ES on autonomic
      nervous modulation by heart rate variability (HRV), heart frequency (HF) and blood pressure
      (BP) in healthy subjects comparing three different locations for the ES, before and after a
      hand-grip exercise. In addition, the tolerance to the current, the side-effects and the
      perceived exertion will be compared.

      Once the participants have given their informed consent and had been checked for exclusion
      criteria, are invited to an experimental session. Subjects will be advised to refrain from
      caffeine or alcohol for 12 h and vigorous exercise for at least 24h prior to the
      intervention.

      The participants will remain sitting during the entire session and will be instructed to stay
      awake and avoid movement. Grip strength will be evaluated by a hydraulic dynamometer (Saehan
      model SH5001). Participants will remain seated on a chair with their feet and trunk
      supported, shoulders adducted, elbows flexed at 90º, forearms in neutral position, and wrists
      with 0º-30º extension. Subjects will be instructed to perform a maximum isometric contraction
      for three to five seconds, and the peak force will be recorded. Three evaluations will be
      made with an interval of one minute between them. If the examiner would recognize some
      compensatory movement by the participant, a new measurement would be taken and registered.

      The volunteers will be randomized by sex to one of three groups: cymba conchae at the right
      ear (active group); C7-T4 placement (active group), scapha at the right ear (sham-group).
      These three arms will be denominated as Transcutaneous Vagus Electrical Nerve Stimulation
      (t-VNS); Transcutaneous Sympathetic Ganglion Electrical Nerve Stimulation (t-SNS); and Sham
      Transcutaneous Vagus Electrical Nerve Stimulation (sham t-VNS), and. Allocation concealment,
      stratified by sex, will be ensured by the use of sealed envelopes containing the treatment
      allocation. The sequence will be generated using a computer program by a researcher not
      implicated in the experimental sessions. The envelopes will be opened just before determining
      the amplitude for stimulation. The stimulation location will be wiped down with alcohol and
      the minimum intensity, at which the stimulus is perceived, will be evaluated for the
      auricular locations, whereas minimum amplitude for muscle contraction between the electrodes
      will be assessed in cervico-thoracic location.

      After 15 minutes of resting, the first assessment (baseline) will be taken (HRV, HR and blood
      pressure) for 5 minutes. The respiratory frequency will be checked every 5 minutes.

      Then the randomized ES will be applied for 20 minutes using the same TENSMED S82 (Enraf
      Nonius, The Netherlands) symmetrical and rectangular biphasic pulses, at 350 microseconds of
      phase duration. It will be applied at 10 Hz (t-VNS and sham t-VNS) or 5 Hz (t-SNS). Both the
      two protocols applied to the auricular region (t-VNS and sham t-VNS) will be delivered by
      trains, whereas a continuous ES will be selected for the (t-SNS). The minimum amplitude for
      auricular stimulations (t-VNS and sham t-VNS) will be twice the perception threshold, at a
      comfortable intensity under the discomfort threshold (pain onset). It will be increased
      during the stimulation only if the sensation is clearly decreased to a maximum of 9 mA. The
      perception threshold will be set increasing amplitude by 0.5 mA each 3 seconds from 0 mA.
      Amplitude in t-SNS will be set at a muscle contraction at a comfortable intensity (under
      discomfort threshold or pain onset). The motor threshold will be determined by increasing
      amplitude 0.5 mA each 3 seconds from the perception threshold until a motor contraction is
      observed. The initial amplitude will be 2 mA over this threshold. It will be increased during
      the stimulation only if the stimulus falls down (to a maximum of 25 mA).

      Another 5-minute period after ES will be recorded and then the 3-minute hand grip exercise
      (SH5001, Saehan, Korea) at 30% of maximum strength will be required.

      The final assessment of cardiovascular and autonomous variables will be obtained during the
      last 15 minutes. The rating of perceived exertion will be asked (Borg-CR10) whereas a VAS (0
      denoting no sensation at all; 10 = indicating discomfort or pain onset) will be used to rate
      the tolerance to ES. The possible side-effects will be also checked.

      The participants will be asked upon completion of the session their presumed group
      assignment.

      Adverse effects will be checked again 48 h after finishing the experimental session.

      The ES and the acquisition of the data will be done by physical therapists, but analysis of
      the main variables will be done by a cardiologist with the assistance of one of the physical
      therapists with specific knowledge in the area. The data will be introduced by a third
      researcher, and accuracy of the data will be checked selecting 50% of the data from each arm,
      by random software. If some mistakes will emerge, then the complete check will be done. The
      traditional statistical analysis will be reinforced by Bayesian inferences.

      This is a pilot study. The objective is to check if there are statistically significant
      effects from the stimulation on the variables: cardiac variability, heart rate and blood
      pressure, before or after an isometric exercise of pressure.

      For the comparison of the results obtained in the three groups of subjects, the analysis of
      variance or rank test procedures will be used, based on the normality or non-normality of the
      data obtained.

      The effect of time will be assessed through a longitudinal data analysis that takes into
      account the dependence. For this purpose, the repeated measures Anova or Friedman's test will
      be used, in the parametric or non-parametric assumption, as a global comparison procedure.
      Possible interactions and dependence relationships between measured variables and time will
      be studied by means of linear regression analysis, generalised linear and/or generalised
      kernel-type non-parametric modelling.

      Comparisons between groups (Anova or its non-parametric equivalent) will be complemented by
      means of their equivalents in Bayesian analysis, in order to reinforce the information
      provided by the p-values obtained in each procedure. For this purpose, the corresponding
      Bayes factors (Kass and Raftery, 1995) and the posteriori distributions of the estimated
      parameters will be calculated, thus increasing the precision of the confidence intervals.
    

Intervention name(s): Transcutaneous Vagus Nerve Stimulation (t-VNS); Transcutaneous Sympathetic Ganglion Electrical Stimulation (t-SES); Sham Transcutaneous vagus nerve stimulation (Sham t-VNS)
Intervention type(s): Device; Device; Device
Intervention description(s): Type of device and current: portable machine, low frequency current, constant current Type of wave: square biphasic pulses Pulse duration: 350 microseconds Frequency: 10 Hz Number of channels: one Location and electrodes: cymba conchae at right ear (vagus branch nerve area); a clip electrode will be applied with its cathode on anterior cymba conchae, the anode placed behind.
Amplitude: from 2 times the perception threshold (individualized) at a comfortable, non-painful amplitude, and to a maximum of 9 mA. It will be increased, if necessary, each 5 minutes in order to maintain the same level of tingling sensation On-Off times: trains of 30 s on, 5 s rump up, 1 s rump down, 24 s off Duration: 20 minutes; Type of device and current: portable machine, low frequency current, constant current Type of wave: square biphasic pulses Pulse duration: 350 microseconds Frequency: 5 Hz Number of channels: two Location and electrodes: cervicothoracic area (stellate ganglion region); first channel: new 5 cm x 5 cm self-adhesive electrodes will be applied at 1-1.5 cm both sides of the vertebral spinous processes, approximately from C7 to T4, upper cathode on the left side of C7 and lower cathode on the right side.
Amplitude: 2 mA above the muscle contraction threshold (individualized) at a comfortable, non-painful amplitude and to a maximum of 25 mA. It will be increased, if necessary, each 5 minutes in order to maintain the same level of muscle contraction On-Off times: no trains, continuously delivered Duration: 20 minutes; Type of device and current: portable machine, low frequency current, constant current Type of wave: square biphasic pulses Pulse duration: 350 microseconds Frequency: 10 Hz Number of channels: one Location and electrodes: scapha at right ear (non vagus innervated region); a clip electrode will be applied with its cathode on anterior scapha, the anode placed behind.
Amplitude: from 2 times above the perception threshold (individualized) at a comfortable, non-painful amplitude, and to a maximum of 9 mA. It will be increased, if necessary, each 5 minutes in order to maintain the same level of tingling sensation On-Off times: trains of 30 s on, 5 s rump up, 1 s rump down, 24 s off Duration: 20 minutes
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: The study is a prospective, randomized, three-armed, sham-controlled, single-blind, exploratory clinical trial in healthy subjects
Masking: Single (Participant)
Primary purpose: Treatment
Keywords: Electric Stimulation Therapy; Transcutaneous Electric Nerve Stimulation; Parasympathetic Nervous System; Stellate Ganglion; Hearth Rate; Blood Pressure