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mise à jour du
11 novembre 2002
Surg Radiol Anat
1988; 10; 2; 107-12
lexique
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

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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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