Cranial Impedance Plethysmography 173

right frontal lobe was found arising from the Sylvian fissure. Old
clot extended down this fissure and back along the base of the
brain to the peduncular region where it pressed the left peduncle
against the tentorium and accounted for the misleading neurologi-
cal signs. The aneurysm was clipped; the patient recovered with
minor residua secondary to the operative trauma.

Once again it is impossible for these tracings to have arisen
from the external circulation. This case is, to the best of my
knowledge, the first case in which rheoencephalography was used
as the deciding factor in a clinical emergency in the United States;
rheoencephalography was first used by one of our group (S.Z.)
in November of 1960 to successfully lateralize a tumor despite
an equivocable clinical picture.

These cases are presented to indicate the potential value to
clinical medicine of this overlooked method and to stimulate
others in its investigation and use. While the exact significance
of these tracings is uncertain it is evident that rheoencephalo-

ANEURYSM OF RIGHT MIDDLE CEREBRAL ARTERY
1D. April 21962

Right side:

Calibration: i

Left side: Ir i fre i

Calibrations | ik

Ta ED

Fig. 9. Case No. 3 — Rheoencephalogram illustrating the effect of in-
creased intracranial pressure and restricted flow on the right.





Cranial Impedance Plethysmography 177

impedance plethysmograms taken from different electrode lo-
cations. The first figure (Fig. 1) shows the impedance plethys-
mogram of a normal, healthy man, forty-two years of age with
tracings taken in the order from top to bottom, 1) frontal-frontal,
2) frontal-occipital, 3) frontal-right mastoid, and 4) frontal-left
mastoid. There is a general similarity of the contour of all leads.
Thus, the contour does not differentiate extra-cranial and intra-
cranial circulation; the tracings may represent a mixture of both.
While the intracranial circulation is many times larger than the
extracranial circulation, this fact may not be reflected in the
record. The electrical field distribution between electrodes

PULSE CONTOUR AT VARIOUS ELECTRODE POSITIONS

Forehead "apart Occiput 2%" apart

Left Forehead - Left Occiput Right Forehead - Right Occiput
6" apart 6%" apart

Fig. 2



176 Cerebral Ischemia

various sizes and shapes of electrodes, different locations of elec-
trodes for placing, etc. I would like to show two slides, illustra-
tive of the controversial nature of this method and some of the
difficulties involved in its application. These tracings were
selected to show similarity and dissimilarity of the contours of

RIK PULSE CONTOUR FOR VARIOUS ELECTRODE POSITIONS

Male
42

right - left frontal

frontal - occipital

frontal « right mastoid

frontal - left mastoid .



Cranial Impedance Plethysmography 179

dicate considerable contamination of intracranial by extracranial
circulation. It is not unusual that divergent results are obtained
with variations in approach. Doctor Seipel’s data will contribute
importantly to any general evaluation of the problem. Cranial
impedance plethysmography is potentially a very useful method,
but it needs further exploration.
Dr. SEIPEL:

To all of which I say “Amen!”
Dr. Kennera Lursurrz: (Monsey, New York)

I wonder if Doctor Simonson and Doctor Seipel would com-
ment on the sizes of the electrodes they have been using? We
have been working with rheoencephalography for about three
years, and we find variations in results which depend upon the
size of the electrode used.

Dr. SEIPEL:

The same type and amplitude of pulse are obtained with a
wide range of electrode sizes. Therefore, for the purpose of com-
paring several instruments with each other, we are now using the
standard Jenkner aluminum blocks. In monitoring surgical pro-
cedures, we have also used the “Telemedics” adhesive plaster
stick-on electrodes which work quite well.

Dr. SrmMonson:

Doctor Otto Schmitt and I have done quite extensive experi-
ments on the shape and size of electrodes; the sites of electrode
location, pressures on electrodes equal or exceeding the systolic
blood pressure, etc. There is a critical size for the electrodes
(about 10 mm?), beyond which there is little variation. These
experiments were mainly performed for possible differentiation
between extracranial and intracranial circulation, but the results
were not definite.

Dr. Osnist:

The question I would like to ask is in connection with cere-
bral blood flow. I have heard you use the words blood flow and I
have seen the expression in the literature. It occurs to me that
this technique is primarily a measurement of blood volume, or, at
most, of relative changes in blood volume. I wonder if it isn’t a
little misleading to use the term, “blood flow?”



Am 8-4

CRANIAL IMPEDANCE
PLETHYSMOGRAPHY —
RHEOENCEPHALOGRAPHY AS A
METHOD OF DETECTION OF
CEREBROVASCULAR DISEASE*

J. H. Sewer, S. A. R. ZieMnowicz, anp D, S. O’DouErty

Reprinted from
CEREBRAL ISCHEMIA

Compiled and Edited by
Ernst Simonson, M.D. and Thomas Hodge McGavack, M.D.

CHARLES C THOMAS : PUBLISHER «¢ Springfield : Illinois : U.S.A.







178 Cerebral Ischemia

placed on the scalp in man is not precisely known. Moskalenko
and Naumenko found up to 50 per cent contamination by ex-
tracranial circulation. Differences between the contours of the
extracranial and intracranial pulses are to be expected. The next
tracing (Fig. 2) shows the cranial impedance plethysmogram of
a normal forty-five year old man. The electrode locations were:
for the upper left tracing, on the forehead; for the upper right
tracing, on the occipital region; for the lower left tracing, on the
left forehead-left occiput; and the lower right tracing, on the
right forehead-right occiput. There are great differences in con-
tour among the tracings taken at different locations. Such dif-
ferences have been considered by some clinicians as indicative of
cerebrovascular disease, but we found a large variation in con-
tour among 200 older normal men. This material is now in the
process of statistical evaluation. Perhaps one might argue that
the large differences between the contour from different elec-
trode sites may be an early sign of cerebrovascular disease. How-
ever, in this case, there was no development of overt clinical
symptoms of cardiovascular or cerebrovascular disease; the sub-
jects remained entirely asymptomatic.

We have performed a substantial number of unpublished ex-
periments regarding the effects of right and left carotid sinus
pressure in normal subjects, The results were quite variable, as
may be expected from animal experiments. Again, the normal
variability should be the basis for clinical application, but so far
as is known to me, no statistical analysis of the effects of carotid
pressure based on an adequate normal sample has yet been pub-
lished.

In a recent series of fifteen normal subjects, we found no
statistically significant change in the impedance plethysmo-
grams from forehead-mastoid locations, i.e., the same locations
which Doctor Jenkner and Doctor Seipel have been using, while
the subjects were breathing a mixture of 6 per cent CO, and air.
According to Kety and Schmidt's data, an increase of intracranial
circulation of about 100 per cent should have been expected.
Photoelectrically recorded skin circulation of the scalp with the
pickup placed between the impedance plethysmogram electrodes
increased slightly during breathing of 6% CO,. Our results in-


172 Cerebral Ischemia

The diagnosis of falsely localizing signs secondary to hemor-
thage on the right was made; the patient was transferred to this
hospital and explored. At operation a subdural and subarachnoid
collection of clot and blood measuring 8 mm. in thickness and 150
mm, in diameter overlying the anterior and lateral aspects of the



Cranial Impedance Plethysmography 163

of unconsciousness followed by right hemiparesis and partial
aphasia which cleared in several hours. At this time a bruit was
noted in the region of the left ear. Arteriography was performed
and disclosed an inoperable high left internal carotid occlusion
(Fig. 2).

The resting tracing indicates that the. instantaneous blood
volume on the two sides of the brain is essentially equal; however,
on right carotid compression the wave form radically decays, both
amplitudes decrease but much more so on the left, and the left

TO REG TO REG
Ss

ELECTRODE PLACEMENT

Fig. 1. Placement of electrodes for rheoencephalography. Two electrodes
are placed on the forehead and another two over the mastoids, each lateral
pair forming a separate circuit. The electrodes are placed so as to align
the included volume just above the base of the skull excluding as much as
possible the external carotid and basilar arterial fields. The lines on the
diagram connecting the electrodes delineate the presumed volume mon-
itored; the latter is represented by the symbol for a variable resistance. It
is particularly important to note that these electrodes must be positioned in
as identically symmetrical positions as possible; the tracings are comparable
only if equivalent volumes are monitored.



CRANIAL IMPEDANCE
PLETHYSMOGRAPHY —
RHEOENCEPHALOGRAPHY AS A
METHOD OF DETECTION OF
CEREBROVASCULAR DISEASE*

J. H. Semen, S. A. R. Zremnowicz, anp D. S. O’DouERtY

Cornesnovasconan DISEASE ranks third in causes of death in the
general population (1). Many of these approximately 200,000
fatalities (1) and the accompanying larger number who suffer
sublethal central nervous system damage are potentially salvage-
able if proper therapy can be instituted sufficiently early; those
patients suffering undiagnosed extracranial arterial occlusions are
the most tragic, for this disease can be treated surgically. These
patients have one factor in common—that of impairment of cere-
bral blood flow to the point where neuron loss took place.

There is an obvious need for a simple quick method that will
give a clinically reliable indication of the intracranial circulation,
preferably in both hemispheres simultaneously.

The purpose of this paper is to demonstrate by the presenta-
tion of several cases that rheoencephalography, no matter what
its tracings may represent in the way of biological variables, can
be used clinically as though it monitors intracranial circulation
(2, 3).

The electrode placement for rheoencephalography is indi-
cated in Figure 1.

Cases:
Case No. 1: The first case is that of R. K., a fifty year old white
male who experienced a suddenly occurring fifteen minute episode

*A contribution from the Georgetown Clinical Research Institute of the
Federal Aviation Agency, and the Neurological Research Laboratory of the
Georgetown University Hospital.

162