The Anatomy of the Diaphragm

The diaphragm is a thin muscle that sits at the base of the chest

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A thin, skeletal muscle sitting at the base of the chest, the diaphragm is an unpaired muscle that separates the thorax from the abdomen. It plays an essential role in breathing function; when it contracts, the resulting vacuum effect expands and lets you inhale, and then you exhale when this muscle relaxes. Involuntary contraction of the diaphragm leads to hiccups—a common ailment experienced by almost all people—and this organ can also herniate, rip, or tear, due to either congenital or acquired conditions.

Anatomy

Structure & Location

The diaphragm is a dome-shaped sheet of muscle and tendon, and its convex upper surface represents the floor of the thoracic, or chest, cavity; this side directly accesses the lungs. The opposite, concave surface forms the roof of the abdomen and directly contacts the liver, stomach, and spleen. It’s asymmetrical, with a left dome dipping lower than a right one, something which is attributed to the presence of the liver to the right side. There’s also a depression between these two domes due to the fibrous membrane lining the heart (called the pericardium).

Doctors have identified three muscular parts to the diaphragm, all of which insert into its central tendon connected to the lower surface of the pericardium. These are:

  • Sternal: This portion arises as two slips coming from the rear side of the xiphoid process, a section of cartilage at the lower end of the sternum, which is not attached to any ribs.
  • Costal: Originating from the inner surfaces of the cartilages, just alongside the lower sixth ribs of both sides, the costal part is interlocked with transversus abdominis muscle (at the side of the upper body).
  • Lumbar: This part consists of four major sections. The medial and lateral lumbocostal arches are sections of tendons that attach to the L1 vertebra, with the latter of these also connecting to the lower border of the 12th rib. In addition, the right crus arises from the front and side portions of the upper three vertebrae as well as the discs that separate them. These fibers surround the orifice of the esophagus to form a kind of sling. The left crus originates from the top two vertebrae.  

Running through the diaphragm via openings called “hiatuses” are the esophagus, the phrenic and vagus nerves, as well as the descending aorta and inferior vena cava.

Anatomical Variations

Variations of the anatomy of the diaphragm are relatively rare. The most common of these is a birth defect in which peripheral attachments of the diaphragm are absent, leading to instability or even herniation of this organ. Such muscle slips can severely impact the functioning of this organ while giving it a serrated or scalloped appearance.

Dromedary diaphragm, also known as diaphragm eventration, is underdevelopment of one section of the organ that can influence its function. In addition, some people are born with an accessory diaphragm, in which the organ is duplicated, which can also affect breathing function. In other cases, the sternal section may be missing, or there may be differences in the locations that arteries pierce this organ.

Function

Generally speaking, there are four major functions of the diaphragm, the most important of which have to do with the physiology and mechanics of breathing. These include:

  • Muscle of inspiration: When breathing in, this muscle contracts, pulling the central tendon down. This elevates negative pressure inside the chest cavity, which draws air in, and the diaphragm flattens while the external intercostal muscles raise the front of the chest as the lungs expand. Relaxation of the diaphragm, allows everything to get back to the original position, letting air escape. 
  • Abdominal straining: Alongside muscles of the front abdominal wall, the diaphragm contracts to help with urination and defecation function.
  • Weightlifting muscle: When a person takes in and holds a breath, this organ helps the abdominal wall muscles retain and raise intra-abdominal pressure. This motion, called the Valsalva maneuver, is used to detect and augment heart murmurs by doctors.
  • Thoracoabdominal pump: The descending activity of the diaphragm as a person breathes in lowers pressure within the thorax while raising pressure within the abdomen. This places additional pressure on the inferior vena cava and aids in returning blood to the heart.

Associated Conditions

Given the importance of this muscle, issues or problems with the diaphragm can have significant effects. However, the most common ailment is relatively harmless and familiar to most—hiccups. These are involuntary contractions of the muscle, most often caused by eating or drinking too much in a short span of time.

Hiatal hernias of the diaphragm can also occur, with most of these being congenital in nature. As a result of these birth defects, abdominal organs may be able to penetrate and disrupt the formation, positioning, and function of the lungs. In many of these cases, the stomach ends up accessing the chest cavity.

In addition, blunt trauma or puncture—such as injury from a stabbing, severe fall, or car accident—can cause an acquired hernia of the diaphragm. As above, this can lead to improper positioning of abdominal organs, affecting breathing and other function.

Doctors will then surgically move the out of place abdominal organ or organs back to their original position. In cases of congenital hernia, surgeries can occur while the baby is still in the womb, or doctors may need to wait until after the baby is born. Acquired hernias are treated following injury regardless of age.

This surgery is usually performed either as an open procedure—in which the area is cut open—or laparoscopically, that is, using a specialized camera and tools to access and work on the diaphragm. The aim of surgery here is not only to restore proper anatomy, but to seal up any problematic areas within the diaphragm. This is done using with surgical staples, sutures, or, in rare cases, a prosthetic portion may be implanted. 

Tests

Herniation of the diaphragm can be severely disruptive, and in most cases, surgeries are required to correct these issues. As such, thorough assessment and testing are necessary. There are several key approaches taken:

  • Pulmonary testing: There are several tests doctors perform to assess diaphragm function. These include spirometry, which measures the amount of air that circulates during breathing; exercise oximetry, which looks at oxygen levels in the blood when the patient is active, as well as peak flow meter, a device that measures the level of exhalation.
  • Chest X-ray: One of the most common forms of imaging for diaphragm issues is chest X-ray. This involves using radiation to take pictures of problematic areas, and it's the approach that underlies the sniff test and CT scan approaches highlighted below.
  • Sniff test: Also known as diaphragm fluoroscopy, this test assesses overall function of the organ. Most often, it's used when doctors detect problems with inhaling (inspiration) following specific cases such as cerebral palsy or after stroke. Basically, this procedure involves using X-rays to create a real-time video of the affected area as the patient sniffs and exhales.
  • Computer tomography (CT) scan: This type of imaging also employs X-rays. Several beams access the diaphragm coming from different cross-sectional directions to render a three-dimensional image. This helps doctors assess any damage or malformation in this region.
  • Magnetic resonance imaging (MRI): Another form of chest imaging, MRI uses magnetic and radio waves to create composite images of the diaphragm. With this method, doctors use a contrast dye to improve contrast and increase what can be seen and captured.
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