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.