Physiologic
variations of the internal jugular vein surface,
role of the omohyoid muscle, a preliminary
echographic study
Patra P, Gunness TK, Robert R, Rogez JM,
Heloury Y, Le Hur PA, Leborgne J, Laude M,
Barbin JY
Laboratoire anatomie
Faculté de médecine
Nantes
Variations physiologiques de surface de
la veine jugulaire interne, rôle du muscle
omo-hyoïdien, étude
échographique
préliminaire
L'action du muscle omo-hyoïdien sur
l'hémodynamique de la veine jugulaire
interne est controversée. Pour les uns,
la contraction de ce muscle, en tendant
l'aponévrose cervicale moyenne, facilite
le retour veineux jugulaire; pour les autres, le
muscle, en se contractant, comprime la veine
jugulaire dans son trajet cervical. Suivant
cette dernière hypothèse,
l'hémodynamique de la veine jugulaire
interne a été
étudiée dans son trajet cervical,
par échographie, chez 10 sujets sains
volontaires. Cent-vingt mesures de la surface de
la veine ont été
effectuées, au repos, bouche ouverte et
en inspiration profonde. Dans ces 2 derniers
cas, il a été mis en
évidence une augmentation statistiquement
significative de la surface de la veine,
au-dessus du muscle omo-hyoïdien. Ces
données confirmeraient le rôle de
compression de la veine par le muscle
omo-hyoïdien, entraînant des
modifications hémodynamiques veineuses
intracérébrales, qui pourraient
être impliquées dans le
bâillement.
Summary. The action of the omohyoid
muscle on the hemodynamics of the internal
jugular vein is controversial. For some authors,
contraction of this muscle, by tightening the
cervical fascia, promotes jugular venous retum.
For others, contraction of this muscle
compresses the jugular vein in its cervical
path. With this latter point in mind, the
hemodynamics of the intemal jugular vein have
been studied in its cervical path by echography
in 10 healthy volunteers. One hundred twenty
measurements of the venous surface we-re made at
rest, with the mouth open and during deep
inspiration. In the last 2 situations, evidence
of a significant increase in the venous surface
was found above the omohyoid muscle. These data
confirm the role of compression of the vein by
the omohyoid muscle, leading to modifications in
intracerebral venous hemodynamics, which can be
affected in yawning.
The descriptive anatomy of the omohyoid
muscle as well as its principal variations in
human beings is well-known. It belongs to the
group of infrahyoid muscles, which also includes
the stemothyroid and thyrohyoid muscles (forming
the deep layer), and the sternocleidohyoid
muscle forming with the omohyoid muscle the
superficial layer. This elongated, thin,
digastric and flat-ended muscle is in its modal
disposition directed obliquely in the
anterolateral region of the neck and extends
from the superior edge of the scapula to the
hyoid bone. It is composed of 2 fleshy portions,
the anterior and posterior bellies, seperated by
an intermediate tendon. Globally, this muscle
describes a posterior, external and superior
curve. It is frequently admitted that it is
innervated by fibers from the ansa cerficalis,
without any participation of the hypoglossal
nerve. However the exact constitution of the
ansa cervicalis is still the subject of much
controversy.
The physiologic role of the omohyoid muscle
is still not well-known. Its 2 attachments, the
direction of its fibers and its phylogenetic
connections with the other infrahyoid muscles
lead us to, believe that it contributes like
these muscles to, depressing the hyoid bone.
Moreover, it draws this bone backwards and helps
in its fixation. Bouyssou and Tricoire have
shown that the contraction of the omohyoid
muscle during opening of the mouth leads to
compression of the intemal jugular vein.
With this in mind, and with the help of vascular
echography, we have studied surface variations
of the intemal jugular vein with the mouth open
and during deep inspiration in order to, define
the action of the omohyoid muscle on the jugular
vein in its cervical path. significant
difference in surface variations between the
right and left vein at rest, whether the subject
is a lying or sitting position and with the
mouth opened and in deep inspiration.
[...
Discussion Despite all the work
devoted to the omohyoid muscle, it is strange
that its physiologic role is still not
wellknown. Its role during respiration also
remains controversial. Some authors believe that
it leads to a very small movementy of the hyoid
bone with reference to the cervical spine. For
others this muscle has no action during normal
respiration but may be involved in pathologie
situations such as hypoxia or sickness. In
physiologic conditions il could be that it
contributes to the prominciation of certain
vowels such as 'Y' and certain rolied
consonants, and during coughing or laughing as
well as during shouting and singing. The action
of the omohyoid can vary greatly according to
the position of the upper limb and simultaneous
movements of the scapula. This can explain
associated movements of the head and upper limbs
during difficulties in swallowing and during
certain special phonatory efforts.
We have been mostly interested in the action
of the omohyoid muscle in the hemodynamics of
the internai jugular vein. We shall first
consider this aspect and then we shall analyse
the possible consequences of variations of the
jugular pressure.
Role of the omohyoid muscle in the
hemodynamics of the internal jugular
vein
According to classical theory, the two
omohyoid muscles stretch the cervical fascia of
the pretracheal lamina which is crossed by veins
whose diameter vary according to the fascial
tension. During each inspiration the fascia
could become tense by the movements, of its bony
attachments (first rib, sternum, clavicle).
Hence, there is a blood-flow towards the base of
the neck.
In fact the increase in the venous surface
seems to be due to the contraction of the
omohyoid muscle which compresses the internal
jugular vein. The comparative hemodynamic study
of the jugular veins is not generally possible
in animals. In, fact in most mammals, except in
primates, the venous flow from the head is
through the external jugular vein, which is 10
times larger than the internal. Ligature of the
external jugular could palliate this
inconvenience, but would supplant the
physiological conditions.
Our study shows that opening the mouth and
deep inspiration lead to an increase in the
surface of the internal jugular vein and the
causes are very difficult to define (and in
particular it is difficult to specify if this is
caused by the elasticity of the vein), the
omohyoid muscle contracts when the mouth is
opened. It seems that the first phase, which
leads to the position of the half-open mouth, is
very easily realised, due to the weight of the
mandibula and is helped or started by
contraction of the infrayoid muscles, which with
then depress hyoid bone into contact with the
thyroid cartilage and fix il in this
position.
During opening of the mouth, the increase in
the surface of the internal jugular vein can
only be due to contraction of the omohyoid
muscle, which compresses the internal jugular
vein in a segmentary way and at the lower part
of the neck.
Our observations tend to confirm this
theory. Morever, they show that opening the
mouth and deep inspiration associated during
yawning have an identical action on the
internal jugular vein. Bouyssou and Tricoire
were the first to explore the hemodynamics of
the jugular vein by directly measuring the
pressures on each side of the omohyoid muscle
during opening of the mouth and by phlebography
a difficult technical approach. They showed that
the blood-flow, which is elsewhere normal,
presents a tight strangulation near the
tendinous intersection of the omohyoid muscle
during opening of the mouth. As far as we are
concerried, we have not been able to locate
precisely the position of the omohyoid muscle
and his because of its poor echogenecity. Hence
il bas not been possible to measure the surface
below the muscle or to make transverse sections
showing the muscle.
Hence the omohyoid muscle leads to a
bilateral direct localized and short compression
of the internal jugular veins, and this in spite
of possible diffuse compression by the
sternocleidomastoid muscle. The latter can
compress all the vascular elements of the neck
il covers, whatever the position of the head. We
would like to record that in our study this
muscle was not involved. However, it can play a
part during yawning. Other mechanisms
which can explain the increase in surface of the
jugular vein are : compression of main
blood-vessels and of the superior vena cava at
the apex of the thorax; terminaison valvules of
the internai jugular vein; pump effect in the
superior mediastinum by negative pressure at the
end of deep inspiration.
We can ask whether deep inspiration plays a
bigger role than mouth opening in the increase
of jugular vein surface. Statistical studies
make us believe that there is no difference
between these 2 situations. We have not been
able to show significant differences in surface
between the "mouth open" and "deep inspiration"
situations, be it on the right or left side or
in lying or sitting position. Hence, deep
inspiration is not more effective than maximum
opening. It is clear that the vein is at its
maximum dilatation at the end of inspiration or
during opening of the mouth. The combination of
these 2 actions does not seem to give a bigger
increase in surface than either of these
situations alone.
Apart from the hemodynamic consequences
which we shall now consider, it is quite
possible that compression of the jugular vein by
the omohyoid muscle leads to an antireflux
phenomenon, equivalent to venous valvules, which
plays an important role in cerebral protection
during situations of increased pressure induced
hy the sitting position, forced inspiration or
cough.
Role of pressure variations of the
internal jugular vein
Insofar as hemodynamic consequences due to
jugular vein compression are concerned, we note
that ligature or clamping of the internal
jugular veins leads to an increase in
cerebrospinal fluid (CSF) pressure in animals.
In human beings, compression of nech
bloodvessels leads to an increase in CSF
pressure in a few seconds. According to
Lazorthes, compression of the jugular veins can
"pressurize" the unvalved venous network,
whereas arterial pressure remains
unchanged.
Lepp has shown that opening the mouth leads
to an increase in CSF pressure on the cavernous
part of the pterygoid veinous plexus which may
act as a suction pump for cerebral venous blood.
In fact, for Bouyssou, this venous plexus has no
role. According to Braun, there is aspiration of
cerebral veinous blood by a "physiological
pump". This is to be considered with Dumpert's
theory, that blood is aspirated out of the brain
during inspiration.
If we combine these considerations with the
results of our study we can conclude that the
omohyoid muscle can play a role during
yawning. The very low and forward position
of the hyoid bone shows the action of the
infrahyoid muscles.
The exact role of yawning has never been
established. It occurs mostly during the sleepy
state, tiredness, a boring repetitive work...
Hence it might play an alarm function just
before sleeping. Yawning leads te, an
increase in CSF pressure by monohanisms
which have already been described. Schuller has
shown that the most important phenomenon is
represented not so by pressure variations as by
dynamic variations of the CSF. Yawning can
induce such dynamic variations of the CSF by 2
mechanisms : a flow of venous blood with
increase in pressure due to compression by the
omohyoid muscle and an increase in CSF pressure
resulting in wave percussion against the lining
of the interrial ependymal formations.
Conclusions
The results of our echographic study of the
interrial jugular vein confinn the compression
of the vein when there is contraction of the
omohyoid muscle. The sparse information in the
literature conceming the relations between
opening of the mouth and modifications of the
pressure suggests that the action of the
omohyoid muscle may be related to the yawning
effect, which is itself not well-known. A
comprehensive study of all these phenomena is
necessary.
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