Diaphragm

Diaphragm
The diaphragm is a curved musculofibrous sheet that separates the thoracic from the abdominal cavity It is pierced by structures that pass between these two regions of the body. The diaphragm is the primary muscle of respiration. It is dome shaped and consists of a peripheral muscular part and central tendinous part. The muscular part arises from the margins of the thoracic opening and gets inserted into the central tendon. The attachments to the thoracic wall are low posteriorly and laterally, but high anteriorly.

Origin of diaphragm 3 parts

Sternal part: It consists of small left and right strips that arise prom the posterior surface of the xiphoid process. Costal part: It consists of six slips that arise from the lower six ribs (rib 7 to rib 12) and their costal cartilages. Vertebral part: It arises by means of vertical columns, also known as crura, and from the arcuate ligaments.

Crura: The right crus from the bodies of first three lumbar vertebrae. The left crus, from the bodies of first two lumbar vertebrae. Arcuate ligaments: Lateral to the crura on both sides. Medial arcuate ligament is thickened upper margin of fascia that covers the psoas muscle. Lateral arcuate ligament is thickened upper margin of the fascia covering the quadratus lumborum muscle.

Insertion of diaphragm

The diaphragm is inserted into the central tendon that is trifoliate (like three leaves). On the superior side, the surface of the tendon is partially fused with the pericardium.

Anatomic positions

After forced expiration the right dome is level anteriorly with the fourth costal cartilage and therefore the right nipple, whereas the left dome lies approximately one rib lower. With maximal inspiration, the dome will descend as much as 10 cm, and on a plain chest radiograph the right dome coincides with the tip of the sixth rib.

When the body is lying on one side, the dependent half of the diaphragm will be considerably higher than the uppermost one.
Diaphragm will be higher in short, fat people than in tall, thin people Overinflation of the lung, as occurs for example in emphysema, causes marked depression of the diaphragm.

Openings in the diaphragm

Aortic opening: This opening transmits aorta, thoracic duct and azygous vein and lies anterior to the body of 12th thoracic vertebra between the crura. Esophageal opening: It transmits esophagus, left and right vagus nerves, esophageal branches of the left gastric vessels and lymphatics from lower third of the esophagus. It lies at the level of 12th thoracic vertebra in a sling of muscle fibers derived from the right crus. Caval opening: It transmits the inferior vena cava and terminal branches of right phrenic nerve. It lies at the level of 8th thoracic vertebra.

Other minor openings

Sympathetic trunk (pass posterior to the medial arcuate ligament on both sides)
Superior epigastric vessels (pass between the sterna and costal origins of the diaphragm on each side)

Left phrenic nerve (pierces the left dome of diaphragm)

Vascular supply

Lower five intercostal and subcostal arteries

Phrenic arteries
- supply the main central portion of the diaphragm. The phrenic arteries arise separately from the aorta, just above its coeliac trunk, or by a common aortic stem, or from the coeliac trunk.

The phrenic veins follow the corresponding arteries on the inferior diaphragmatic surface.

Nerve supply of diaphragm

The sensory supply of the central tendon of diaphragm that is covered by parietal and peritoneal pleura is from phrenic nerve. Sensory supply to the periphery of diaphragm is from lower six intercostal nerves. The motor nerve supply of diaphragm is only from the phrenic nerve.

Phrenic nerve

Mixed nerve that provides the sole motor supply to the diaphragm. Derived mostly from C4, but also receives contributions from C3 and C5

Phrenic nerve

Formed at the upper part of the lateral border of scalenus anterior and descends almost vertically across its anterior surface behind the prevertebral fascia and posterior to sternocleidomastoid

Phrenic nerve

At the root of the neck, it runs anterior to the second part of the subclavian artery, from which it is separated by the scalenus anterior, and posterior to the subclavian vein. The phrenic nerve enters the thorax by crossing medially in front of the internal thoracic artery.

Phrenic nerve

Within the thorax, the phrenic nerve descends anterior to the pulmonary hilum, between the fibrous pericardium and mediastinal pleura, to the diaphragm, accompanied by the pericardiophrenic vessels. In its thoracic course, each phrenic nerve supplies sensory branches to the mediastinal pleura, fibrous pericardium and parietal serous pericardium. The right phrenic nerve is shorter and more vertical than the left

Accessory phrenic nerve

Composed of fibres from C5 ventral ramus which run in a branch of the nerve to subclavius. This lies lateral to the phrenic nerve and descends posterior to the subclavian vein. The accessory phrenic nerve usually joins the phrenic nerve near the first rib, but may not do so until near the pulmonary hilum or beyond.

Phrenic nerve motor study

Recording site: Diaphragm muscle G1 2 finger breadths above the xiphoid process G2 over the anterior costal margin 16 cm from G1 Stimulation Site: Lateral neck Posterior to the sternocleidomastoid muscle, approximately 3 cm above the clavicle

Phrenic nerve motor study

Difficult study to perform in obese individuals. Firm pressure is needed when holding stimulator. If the stimulator is not in the correct location, The spinal accessory nerve can be stimulated (causing contraction of the trapezius). The brachial plexus can be stimulated (causing movement of the shoulder) Do not perform this study if there is an - external pacemaker, internal jugular catheter, implanted cardiac pacemaker, or cardioverter-defibrillator

Needle EMG of the diaphragm

Needle examination of the diaphragm can be challenging due to its location The safest and most accurate site for needle insertion is at the anterior axillary line, above the 8th rib (originally described by Bolton et al - Muscle Nerve 1992) Inaccurate needle placement can result in injury to the lungs, liver, spleen, or colon. Accurate localization is not always possible - e.g., when the diaphragm is completely paralyzed or very atrophic, in obese patients, patients with altered anatomy, or patients with severe obstructive pulmonary disease with hyperinflated lungs

The 7th, 8th, and 9th ribs at the mid-axillary line are identified, and the probe placed perpendicular to the ribs, centered over the 8th intercostal space. Subcutaneous tissue lies superficial to the ribs, and two layers of intercostal muscle bridge the space between. Deep to the ribs the diaphragm can be visualized The needle is inserted under real-time US guidance until the needle tip (arrow) enters the diaphragm muscle layer

We have started using US routinely in the Mayo EMG lab during needle examination of the diaphragm to enhance safety and augment the diagnostic utility of the test. Although not all the electromyographers in our laboratory have extensive experience with US imaging, most have found it a simple technique that they can utilize in their daily clinical practice when studying the diaphragm.

Advantages of US guided EMG

Direct visualization of the diaphragm in real time is particularly helpful, given the dynamic nature of the diaphragm. Less chance of injuring nearby structures. Confirmation of needle placement within the diaphragm by direct visualization is particularly helpful in patients with a paralyzed or severely atrophic diaphragm, where the normal sound of MUP firing cannot be relied on to confirm appropriate placement. In high-risk patients such as those on anticoagulants or with bleeding disorders, hematoma formation can be visualized immediately, allowing the examiner to terminate the examination and/or to intervene promptly if clinically indicated.