Phrenic Nerve

PHRENICUS NERVUS, thoraco-abdominal nerve, mixed nerve, predominantly motor nerve. It originates from C3, C4, C5, with the thickest root emerging from C4. It descends along the anterior surface of the m. scaleni ant. between the a. and v. subclavia and, together with the a. mammaria int., enters the thoracic cavity behind the articulatio sterno-cleido-mastoid. It then proceeds with the a. pericardiaco-phrenica over the dome of the pleura and anterior to the root of the lung toward the pericardium. Upon reaching the latter, it is situated between it and the pleura pericardiaca and is directed toward the diaphragm, near which it divides into its terminal branches. The course of the Ph. n. is different on both sides (see figure). On the right, it passes along the outer side of the v. anonymae and v. cavae sup. and reaches the diaphragma somewhat anteriorly and laterally from the foramen v. cavae. On the left, it is situated laterally from the arcus aortae in an anteriorly concave arc and reaches the diaphragma more anteriorly and laterally than on the right. The Ph. n. connects by anastomosis with the gangl. cerv. inf. or medius and, in addition, often receives a twig from the n. subclavius. The branches of the Ph. n.: a) ramus pericardiacus, usually only on the right side, goes to the anterior surface of the pericardium; b) rami pleurales, very thin twigs going to the pleura; c) rami diaphragmatici, more powerful than the other branches, in the main motor, but also containing sensory fibers; they innervate the sternal, lumbar, and most of the costal parts of the diaphragm; d) rami phrenico-abdominales pass through the diaphragm: on the right through the foramen v. cavae, on the left through the hiatus oesophageus and anastomose with the plexus phrenicus sympathici, sending twigs to the peritoneum, the area of the liver, and the adrenal glands. The function of the Ph. n. consists in innervating the movements of the diaphragma during the act of respiration. Therefore, in lesions of the Ph. n. leading to its paralysis, contractions are absent

The location of the n. phrenici in the thoracic cavity: 1-n. phrenicus sin.; 2-n. cardiacus sup.; 3-g. cardiacus sup. et vagi; 4-n. cardiacus med.; 5-n. vagus sin.; 6-n. recurrens sin.; 7-plexus cardiacus; 8, 11-v. phrenico-abdominalis; 9-diaphragma; 10-rr. musculares; 12-r. pericardiacus; 13-n. phrenicus dext.; 14-r. cardiacus inf.; 15-n. vagus dext.; 16-n. recurrens dext.; 17-v. anterior n. cervicalis IV.

of the diaphragma, which is expressed clinically in the limitation of mobility of the lungs and in the absence of protrusion of the epigastrium during inspiration; upon palpation, the descent of the diaphragma and liver during inspiration is not felt. Generally, a high position of the lungs is noted, which depends on the displacement of the diaphragma upward by the abdominal press. Dyspnoea in a quiet position is absent, but appears with every movement and can reach, in a pronounced bilateral paralysis, a very significant degree, which presents a particular danger when bronchitis or pneumonia is present, when there is an increased need for respiration. A particularly sensitive sign is the absence of Litten's phenomenon, consisting in the drawing in of the intercostal spaces inward and the wave-like displacement from top to bottom of a linear shadow, accompanying the separation of the diaphragma from the thoracic wall during inspiration (see Litten's phenomenon). In lesions of the Ph. n., a significant decrease in respiratory noises at the base of the lungs and the disappearance of electrical excitability of the diaphragma to faradic and galvanic current are also observed. In acute irritation of the Ph. n. (neuralgic form), phenomena from the side of sensitivity come to the forefront in the form of pains along the course of the nerve from the diaphragma to the neck, radiating to the shoulder, more often the left, and the presence of painful points upon pressure on the nerve in the neck in the area of the m. scaleni, laterally from the sterno-cleido-mastoideus or at the point of attachment of the 5th rib to the sternum. Tics of the diaphragma, changes in the rhythm of respiration, and an increase in blood pressure have also been observed. Diseases of the Ph. n. are not often observed. Among local processes, the most frequent causes are injuries to the spine and meningeal membranes at the level of C3 and C4, such as spondylitis, fracture or dislocation of the spine, tumors of the spine, spinal hemorrhages, pachymeningitis, luetic lesions of the membranes, compression of the Ph. n. by tumors of the neck and thoracic cavity, tuberculous process in the area of passage of the Ph. n. Direct injuries to the Ph. n., such as gunshot wounds, are very rarely encountered due to its protected position. The most important are paralyses of the Ph. n., caused by various toxic and infectious factors, such as alcoholic polyneuritis, diphtheria, acute articular rheumatism, syphilis, lead intoxication. Neuritis was also noted in anesthesia of the brachial plexus, progressive muscular atrophy. Neuralgic forms are most often associated with diseases of the heart, pericardium, large vessels. Hysterical paralyses also probably occur. For the latter, the absence of dyspnoea despite possibly significant acceleration of respiration and the general course of the disease, especially the great influence of psychogenic factors, is characteristic. - The course and outcome of the disease of the Ph. n. vary depending on etiology. In some cases, the process can subside and all phenomena are smoothed out, in others there is a persistent lesion of the nerve. Relatively favorable is the course in rheumatic and syphilitic forms, in lead poisoning. In diphtheritic paralyses, cases of recovery have also been repeatedly observed. On the contrary, a more severe course was noted in cases of neuritis of the Ph. n. in alcoholic polyneuritis. Therapy - depending on the main cause; symptomatic - the same as in neuritis of other nerve diseases (see Polyneuritides, Neuritides). In diphtheritic paralysis, good effect was produced by injections of strychnine.

G. Polyakov.