James M. Nortona, Ph.D., Gretchen Sibleyb,
Richard Broder-Oldach, B.S.
Departments of Physiologya and Osteopathic Principles and
University of New England College of Osteopathic Medicine
11 Hill's Beach Road
Biddeford, ME 04005
Physiological rhythms within the neural, muscular, respiratory,
endocrine and other systems play a major role in the maintenance of
and appropriate conditions within the internal environment of the body.
Characterization of these rhythms, a major thrust of biomedical
rhythmogenesis (the cellular mechanisms responsible
for initiating and/or maintaining the rhythm), frequency
per sec, per min, per year, etc.), amplitude (magnitude of
range of concentration, amplitude of membrane potential, etc.), control
of the rhythm, and the interaction of a given rhythmic process
other homeostatic or compensatory mechanisms.
The cranial rhythmic impulse (CRI) has been identified and studied
a large number of osteopathic physicians and scientists ever since the
development of cranial osteopathy by Sutherland(1),(2).
The CRI is generally considered to be an independent rhythm occurring
a frequency similar to that of respiration (6-14 cycles/min(3),(4))
and has been described as "resembling the respiratory excursion of the
chest in minute form ..."(5). The
of the CRI is variously described as "strength" or "vitality" in a
subjective fashion; attempts to quantify CRI amplitude(6),(7),(8)
have been made with varying degrees of success.
This author recently published a tissue pressure model for the CRI(9)
that incorporated the cardiovascular and respiratory rhythms of both
and examiner as determinants of the perceived CRI frequency and
According to this model, the CRI would arise in the soft tissues of the
two participants (rhythmogenesis) and would have a frequency and
dependent upon the complex interaction of tissue fluid pressure
and the characteristics of the mechanoreceptors in the hands of the
The model therefore incorporates all the necessary characteristics of a
true physiological rhythm as described above and applies these
to the CRI in a testable hypothesis. The following article describes
of experiments designed to generate the kind of hard data concerning
frequency and amplitude required to test the validity of the tissue
subjects: The twenty-four (24) subjects who volunteered for
study were apparently healthy students and faculty members at the
of Osteopathic Medicine of the University of New England. All subjects
were informed in advance of the general nature of the project and of
nature of the physiological measurements that would be made, and gave
informed consent prior to participation in the study.
examiners: The twelve (12) examiners were osteopathic medical
students, teaching fellows with the UNE/COM Osteopathic Principles and
Practice Department, UNE/COM clinical faculty, and members of an
cranial osteopathy study group which meets regularly at the university.
The level of experience for the examiners in CRI palpation ranged from
two to fifteen years.
measurements and procedures: Subjects were asked to lie
on an examining table and the examiner was seated at the subject's
Examiners were asked to monitor the subject's CRI using a standard
hold. In order to assure that both subject and examiner were in a
state, the period of CRI monitoring was preceded by several minutes of
quiet rest, initially with no contact between examiner and subject,
with the examiner's hands on the subject's shoulders. The period of CRI
monitoring was usually about two (2) minutes in duration.
A switch attached to the leg of the examining table and activated by
examiner knee pressure was used to record the CRI. The examiners were
to depress the switch during the flexion phase of the CRI cycle,
producing in the time/event marker channel of a chart recorder an
deflection that corresponded to the flexion phase of the CRI as
by the examiner. The chart recording speed used throughout was 2
Following a period of monitoring and recording the CRI, the
were asked to quantify the amplitude of the subject's CRI using a
scale (1=well below average, 2=somewhat below average, 3=average,
above average, 5=well above average). This figure was recorded on the
record of the session.
analysis of the data: The basic data obtained for each
session using the protocol described above consisted of CRI cycle
(measured as the time between the beginning of one flexion and the
of the next), duration of flexion, and
CRI amplitude. Calculated
values derived from these basic measurements included average
for cycle length and for duration of the flexion phase (in
of the extension phase (in seconds, calculated as the difference
total cycle length and the duration of flexion), and CRI frequency
(cycles/min, calculated as 60 ÷ the cycle length in seconds).
frequencies were validated by visually counting the number of flexions
(or extensions) over a period of one minute on the permanent record.
Statistical analyses (simple and multiple linear regression, curvilinear regression, analysis of variance, and Student's t-test) were performed using commercially available software and statistical programs written by this investigator following standard formulae and procedures(10).
A total of 274 CRI cycles were recorded on twenty-four (24) subjects
by twelve (12) examiners; these data are summarized in Table
I. The most remarkable finding from these experiments is the
long average cycle length and the correspondingly low average CRI
of 3.7 cycles/min, considerably lower than previously published values.
The range of average cycle lengths among the twenty-four (24) subjects
was 11.7-22.3 seconds. Flexion occupied 46.5% of the average CRI cycle,
and little variation in this percentage was seen over the range of
lengths observed in these experiments. Amplitudes ranged from 2-4 on
arbitrary 5-point scale, with no values of "1" or "5" reported by any
No significant correlation was found between CRI frequency and
using standard linear regression techniques, although visual inspection
of the data suggested an inverse relationship between the two. The
duration of flexion and the calculated duration of extension were both
found to be linearly correlated with CRI cycle length (flexion: r2
= 0.877, p<.001; extension: r2 = 0.907, p<.001).
methodology and experimental conditions: The knee switch
for these experiments proved to be an effective method of allowing the
examiner to record palpatory findings while continuously monitoring the
CRI with both hands. The switch was silent, and the slight leg movement
required to activate it was imperceptible to the subjects. Using this
to record the CRI did not require the examiners to be constantly aware
of the passage of time, and allowed them to focus on their palpatory
All examiners questioned reported that they were able to monitor the
cranial rhythm in a manner consistent with their usual practice, and
there was nothing unusual about the rhythm(s) they were monitoring.
almost all of the examiners were surprised to find that the frequencies
were so much lower than expected.
relationship between CRI frequency and amplitude: Several
physiological rhythms demonstrate an inverse relationship between
and amplitude. For example, a given minute ventilation can be achieved
by a wide variety of ventilatory frequencies and tidal volumes; a
frequency requires a larger tidal volume, and vice versa.
The relationship between CRI frequency and amplitude for the subjects
this study suggested a similar pattern, but no statistically
relationship was found. The coarseness of the 5-point scale used by the
examiners and the narrow range of reported values for amplitude may
obscured a potentially significant inverse relationship, and a new
scale will be devised for future experiments.
CRI frequency and examiner experience: If the CRI represents
a true physiological rhythm that an examiner can be trained to
then CRI frequency, as a basic property of that rhythm, should be
palpated even by relatively unskilled examiners. Good agreement should
therefore exist among examiners with respect to the determination of
frequency, regardless of the examiners' levels of experience in cranial
techniques. The data collected during the experiments described above
a test of this hypothesis. One subject participated in experimental
with twelve (12) different examiners, ten of which examined the subject
within a three-hr period on a single day. The examiners were divided
three groups based on years of experience in cranial techniques, and
results of this data analysis are shown in Table
Although the average cycle length as determined by the most
examiners was longer, and the CRI frequency lower, than the
values for less experienced examiners, the differences among the three
groups were not statistically significant. Groups of examiners with
degrees of experience therefore appeared to agree on the basic CRI
of this one subject, supporting the hypothesis stated in the preceding
paragraph. The overall variability in each of the measured and
variables is least among the most experienced examiners, suggesting
inter-examiner agreement increases with increasing experience, as one
expect. Assuming the most experienced examiners to be the most
and accurate in identifying the CRI and its components, the low
determined by this group and the good agreement among the examiners
the accuracy of the generally low CRI frequencies documented in this
calculation of extension duration vs measurement of
duration: For a small group of subjects (n=3), an examiner was
first to indicate the flexion phase of the CRI with the knee switch for
1-2 min, then to indicate the extension phase for a similar period. The
results of these sessions are shown in Table III.
The average cycle lengths (and therefore CRI frequencies) determined
either flexion or extension were found to be the same. The extension
when measured directly rather than calculated, was found to occupy only
45.9% of the CRI cycle. An average of 17.6% of the cycle in these
was neither flexion nor extension, corresponding perhaps to the
zone" described previously(11). If each
CRI cycle does include time within such a "neutral zone", then the
described as "extension" in the results described above obtained on the
twenty-four (24) subjects should more appropriately be described as the
"non-flexion" component of the CRI. Incidentally, the examiner for the
sessions during which both flexion and extension were monitored
that the extension phase was more difficult to isolate and identify
was the flexion phase and that flexion appeared more "active".
"still point": Related to the possible presence of a neutral
period or position within the CRI cycle is the concept of "still
frequently identified by examiners while monitoring the CRI of a
One subject in this study exhibited what the examiner described as a
point" in the middle of an experimental session. The characteristics of
this subject's CRI changed dramatically after this episode; the
of the flexion phase and the total cycle length increased, indicating a
decrease in CRI frequency. A copy of the experimental record of this
is shown in Figure 1.
The experiments described in this report were designed to provide
kind of quantitative information on the characteristics of the CRI that
is not available in the literature and that is essential for the
of any conceptual model for the origin of the cranial rhythmic
The authors would appreciate feedback concerning the data itself or the
methods by which the data were generated. The ultimate goal of research
in this area should be to gather and evaluate information on the CRI in
a manner that is both scientifically rigorous and clinically relevant
practitioners in the field.
CRI Cycle Characteristics(12)
duration of flexion (sec) 7.7 ± 1.4
duration of extension (sec)(13) 8.8 ± 1.6
CRI cycle length (sec) 16.5 ± 2.8
CRI frequency (cycles/min)(14) 3.7 ± 0.6
CRI amplitude(15) 3.0 ± 0.7
CRI Cycle Characteristics and Years of Examiner Experience(16)
years of experience < 5 5-10 > 10
number of examiners 6 3 3
duration of flexion
±2.3 ±1.8 ±0.9
duration of extension
±2.6 ±2.7 ±0.6
CRI cycle length
16.7 15.7 18.9
±4.9 ±4.2 ±1.2
CRI frequency (cycles/min)
±1.5 ±1.1 ±0.2
3.0 2.7 2.5
±0.7 ±0.5 ±0.5
Comparison of CRI Cycle Characteristics
Derived from Measuring Either Flexion or Extension
CRI phase monitored flexion extension
duration of flexion
duration of extension
CRI cycle length
CRI frequency (cycles/min)
(Figure 1 not available)
A tracing of a portion of the record of a subject who demonstrated a "still point" during an experimental session. The small vertical arrows represent the onset of flexion. The distance between arrows represents cycle length. The still point was detected by the examiner at the point indicated by the asterisk (*). Four cycles with relatively short flexions are followed by the still point, followed in turn by three cycles with clearly longer flexion phases and cycle lengths. CRI frequency prior to the pause, or "still point", was 4.4 cycles/min; after, 2.5 cycles/min. The horizontal bar represents 30 seconds.
1. Sutherland, W.G. The Cranial Bowl. Mankato, MN: Free Press Company, 1939.
2. Wales, A.L. The work of William Garner Sutherland. JAOA 71:788-793, 1972.
3. Upledger, J.E. and J.D. Vredevoogd. CraniosacralTherapy, Chicago: Eastland Press, 1983, p. 6.
4. Kappler, R.E. Osteopathy in the cranial field: its history, scientific basis, and current status. Osteopathic Physician Feb 1979, pp. 13-18.
5. Magoun, H.I. (ed). Osteopathy in the Cranial Field. Kirksville, MO: The Journal Printing Company, 1976, p. 86.
6. Frymann, V.M. A study of the rhythmic motions of the living cranium. JAOA 70:928-945, 1971.
7. Adams, T., R.S. Heisey, M.C. Smith, and B.J. Briner. Parietal bone mobility in the anesthetized cat. JAOA 92:599-621, 1992.
8. Upledger, J.E. and Z. Karni. Mechano-electric patterns during craniosacral osteopathic diagnosis and treatment. JAOA 78:782-791, 1979.
9. Norton, J.M. A tissue pressure model for the palpatory perception of the cranial rhythmic impulse. JAOA 91:975-984, 1991.
10. Dowdy, S. and S. Wearden. Statistics for Research. New York: John Wiley & Sons, 1983.
11. Upledger, J.E. and J.D. Vredevoogd. op. cit., p. 7.
12. Values given are mean ± standard deviation for twenty-four (24) subjects.
13. Calculated for each subject by subtracting the duration of flexion from the total cycle length.
14. Calculated for each subject as 60 divided by the cycle length in seconds.
15. Graded by the examiner on a relative scale of 1-5 as described in the text.
16. Values are expressed as mean ±
deviation; duration of extension, CRI frequency and CRI amplitude
as described previously.