Osteopathic Manipulative Treatment and Its Relationship to Autonomic Nervous System Activity
Condition: Healthy
Study type: Interventional

Summary: 
      The relationship between Osteopathic Manipulative Therapy (OMT) and the autonomic nervous
      system is poorly understood. This study quantifies that relationship and demonstrates a cause
      and effect. It is hypothesized that cervical myofascial release increases vagal tone.
    

Detailed description: 
      For most osteopathic physicians the validation of osteopathic manipulative treatment (OMT)
      has been largely observational and based on patient outcomes such as improvement in pain
      scales, range of motion, and other empiric measures.1,2 However, the osteopathic profession
      has long recognized a relationship between the autonomic nervous system and the function of
      the body in health and disease, although there is relatively little quantitative data
      evaluating the relationship between manipulation and the autonomic nervous system.3,4

      A theoretical basis for the action of OMT and its effect in the body has been advanced based
      on autonomic activation causing concomitant vasodilatation, smooth muscle relaxation, and
      increased blood flow, resulting in improved range of motion, decrease in pain perception, or
      change in tissue. Until recently this association remained largely a theoretical
      consideration due to the inability to accurately measure autonomic activity directly. Over
      the past two decades indirect methods have been developed and refined to provide noninvasive
      markers of autonomic balance,5,6 with heart rate variability (HRV) being commonly used. HRV
      is based on the inherent variation of the R-to-R intervals of a standard electrocardiogram
      (ECG), with these variations largely due to changes in autonomic balance at the sinus
      node.6-8

      Spectral analysis of heart rate variability has been used to study autonomic balance in
      humans, and it is generally accepted that the high frequency (HF) component (0.15-0.4 Hz) can
      be used as a marker for vagal modulation of heart rate. Although it is tempting to use the
      low frequency (LF) component (0.04-0.15 Hz) as a marker for sympathetic activity, its
      specificity is less clear. Pagani and colleagues9,10 have hypothesized that when the LF
      component is expressed in normalized units (LFnu) it becomes a better marker of sympathetic
      modulation of heart rate. For most studies using spectral analysis, the LF/HF ratio is used
      and considered by many to be a good index of sympathovagal balance.6,7,9,10

      The confidence given to the LF/HF ratio accurately reflecting autonomic balance is
      significantly influenced by experimental design. A tilt protocol involving postural change
      from horizontal to upright can be used to calibrate the change in the LF/HF ratio which
      occurs between the two positions and thus set a physiological range for sympathetic and vagal
      modulation of heart rate. An experimental procedure then can be implemented where comparisons
      are made of the changes in the LF/HF ratios that occur when the body is shifted from the
      horizontal to the upright position under conditions with application of an intervention
      versus without the intervention. In this manner, an experimentally mediated change in LF/HF
      ratio (i.e., with intervention) can be calibrated against a physiologically relevant change
      in ratio (i.e., without intervention).

      This approach was used by these investigators in a pilot study (n=9 healthy, adult
      volunteers, 3 females and 6 males) which showed that the LF/HF ratio changed from a mean of
      1.75+1.40 (mean+SD) in the horizontal position to a mean of 6.00+1.20 in the 50-degree
      head-up position. This change reflects an increase in sympathetic tone. Mean heart rate in
      these subjects increased from 61+7 bpm to 78+2 bpm in the head-up position. The subjects then
      were treated in the 50-degree head-up position with an OMT procedure, cervical myofascial
      release, which is thought to increase vagal tone. After the procedure was applied, the LF/HF
      ratio decreased back down to 1.75+1.58, even though the subjects were still in the head-up
      position. These data support the initial hypothesis that specific OMT procedures can modulate
      vagal tone, and also provide information relating to the significance of the LF/HF change.
      That is, the application of OMT reversed the increase in the ratio that occurs in the
      50-degree head-up position.

      We conducted a continuation project to further examine the association between OMT and
      autonomic nervous system activity as demonstrated by HRV, studying the hypothesis that
      cervical myofascial release increased vagal tone. In a within subjects (repeated measures)
      design, we examined the effect of OMT on HRV in comparison with sham treatment (touch only)
      and control (no touch) conditions.
    

Intervention name(s): Placebo; Sham; OMT
Intervention type(s): Procedure; Procedure; Procedure
Intervention description(s): No-touch control condition applied while subject was at a 50-degree head-up tilt.; Touch-only sham treatment applied while subject was at a 50-degree head-up tilt.; Cervical myofascial OMT applied while subject was at a 50-degree head-up tilt.
Allocation: Non-Randomized
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Relationship between Osteopathic Manipulative Therapy (OMT) and the autonomic nervous system; LF/HF ratio