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Respiratory Diaphragm Part 1

By Robert Libbey, RMT

Originally published in Massage & Myotherapy Australia Journal | 12 Issue 3 | Spring 2022

In Part 1, we will be looking at the research pertaining to Phrenic Nerve and Respiratory Diaphragm to advance your knowledge and understanding in an effort to improve your outcomes with your patients.

In part 2, we will look at research documenting 2 manual techniques applied to the Respiratory Diaphragm and share video links demonstrating the techniques. As an added bonus an “Alternative” manual technique will be demonstrated to expand the therapists’ options, improving your competence and confidence no matter what patient presents to your office.

The information presented before you is an opportunity to advance and update your knowledge of an area typically misunderstood often inappropriately and ineffectively treated by well-intentioned therapists.

Working within the Biopsychosocial framework, today’s therapist strives to incorporate simple, principle based, Bottom-Up and Top-Down, evidence-informed strategies into their clinical practice, in an effort to provide treatment which maximizes positive clinical outcomes while decreasing risk of harm.

This article is not meant to be an exhaustive piece documenting all potential positive and harmful influences and effects and common rehabilitation strategies focussing on the respiratory diaphragm, but is written as an introduction to therapists to provide a better understanding of the respiratory diaphragm and how manual therapy can contribute to a patients’ maintenance and potential improvement in their quality of life. This piece will contain a blending of information obtained from published research along with my own personal experiences treating patients with various conditions, pathologies and injuries and suggestions of manual applications to a patient to best influence improved function of the respiratory diaphragm.

Structure of the Diaphragm

Drawing (view from below) shows the large central tendon, which is formed by the transverse septum. The medial and lateral arcuate ligaments are thickened fascial bands that cover the anterior psoas and quadratus lumborum muscles, respectively. Note the crura and their attachments to upper lumbar vertebral bodies. (Nason LK, et al., 2012)

(Fig 8) Diaphragmatic attachments. (a) Drawing shows diaphragmatic slips or muscle bundles (*) attached to the anterior aspects of the lower six ribs. (b) Posteroanterior radiograph shows a scalloped contour of the diaphragm caused by the slips (arrows) at their insertions on anterior ribs. Their visibility is enhanced by the flattening of the diaphragm caused by chronic obstructive pulmonary disease. (c) Sagittal CT image shows the muscle bundles near the diaphragmatic dome (arrows).

The diaphragm is both the physical barrier that separates the thorax from the abdomen and the primary muscle of ventilation. The diaphragm has multiple attachments to the body wall. The two diaphragmatic crura attach the diaphragm posteriorly to the upper lumbar vertebral bodies and disks. The crura are joined by a fibrous median arcuate ligament. (Shin MS, et al., 1985) Posterior attachments include the paired medial and lateral arcuate ligaments. (Panicek DM, et al., 1988) Diaphragmatic slips or muscle bundles attach to anterior ribs. (Fig 8). (Chavhan GB, et al., 2010; Yeh HC, et al., 1990)

The medial arcuate ligaments extend over the anterior psoas muscles as fibrous attachments between the L1 or L2 vertebral body and the transverse processes of L1. The lateral arcuate ligaments are thickened fascial bands covering the quadratus lumborum muscle and extend from the transverse processes of T12 laterally to the midportion of the 12th ribs. Anterior and lateral attachments include the inferior sternum, xiphoid process, lower six ribs, and costal cartilage. (Kleinman PK, et al., 1985)


There are three main openings in the diaphragm that allow important structures to pass between the thorax and abdomen. (Panicek DM, et al., 1988) The Inferior Vena Cava hiatus is at the T8 level and contains the Inferior Vena Cava and branches of the right phrenic nerve. It passes through the midportion of the central tendon. This opening enlarges with inspiration, drawing blood into the heart.

The esophageal hiatus is at the T10 level and contains the esophagus, vagus nerve, and sympathetic nerve branches. It passes through the crossing of the muscle fibers of the right diaphragmatic crus, which form a ring around the esophagus. This ring functions as an anatomic sphincter by constricting with inspiration and helping prevent gastroesophageal reflux.

The aortic hiatus is at the T12 level and contains the aorta, thoracic duct, and azygos and hemiazygos veins. Diaphragmatic contractions do not affect this hiatus, as it is actually retrocrural.

Fascial connections

The respiratory Diaphragm is sandwiched between the Endothoracic and Endoabdominal/ Transversalis Fascia. (Apaydin N, et al., 2008)

Phrenic Nerve

Reprinted with permission from Robert Libbey, RMT (2022)

Interesting facts about the phrenic nerve.

In medical curricular globally, students learn the phrase “C3, 4, 5 keeps the diaphragm alive.” Research has documented that this classically taught branching pattern is not always the case.

Mendelsohn et al. documented substantial variability in phrenic branching. The most frequent pattern B (absent C5 contribution) was found in 26% of the specimens (regardless of side). The classically taught branching pattern A was found in only 22% of specimens while Pattern E was found in 21% of specimens. (Mendelsohn AH, et al., 2011)

The phrenic nerve consistently arises from the root of C4 (98%) with contributions from C3 (70%) and C5 (62%).

Because the nerve arises predominantly from C4, it is formally considered part of the cervical plexus. (Bordoni, B., & Zanier, E.,2013)

The nerve crosses the upper part of the lateral border of the anterior scalene muscle and then coursed obliquely, laterally to medially, crossing the anterior surface of the anterior scalene muscle behind its fascia at approximately Erb’s point. Erb’s point has been defined as a superficial point located 2-3 cm proximal to the clavicle and the posterior border of the sternocleidomastoid muscle

The cervical plexus consists of the anterior rami of the first 4 cervical nerves.

Four cutaneous branches termed:

Lesser occipital

Greater auricular

Transverse cutaneous


It then continues posterior to the sternocleidomastoid, parallel and posterior to the internal jugular vein, then enters the thorax by passing in front of the subclavian artery.

Phrenic-stellate anastomosis

The phrenic nerve meets the stellate ganglion between the subclavian artery and the anterior side of the pleural dome (Caliot P, et al., 1984). Stellate Ganglion is involved in conditions such as chronic regional pain syndrome I and II, craniofacial hyperhidrosis, refractory angina, atypical angina, postherpetic neuralgia, phantom limb pain, chronic post-surgical pain, post-traumatic stress disorder, neuropathic pain syndromes in cancer pain, vascular headaches including cluster, headache and migraine headache, raynaud syndrome, scleroderma, upper extremity embolism, meniere syndrome, refractory cardiac arrhythmias, sympathetically mediated pain, sudden loss of hearing accompanied by tinnitus (Mehrotra M, et al., 2021).


Within the thorax, it crosses medially in front of the internal thoracic artery, although this relationship may not always be consistent, as upon entering the thorax the phrenic nerve has been recorded to cross the internal thoracic artery either superiorly, lying between the internal thoracic artery and the first rib, or inferiorly where it is held against the artery by the adjacent lung and pleura as it passes into the mediastinum. The nerve passes downward and in front of the hilum of the lung between the fibrous pericardium and mediastinal pleura and is accompanied by the pericardiophrenic vessels toward the thoracic diaphragm (Wang YJ, et al., 2016).

Location at the heart

Reprinted with permission from Robert Libbey, RMT (2022)

(Wang YJ, et al., 2016).

Anatomically, both right and left phrenic nerves are accompanied along their courses by pericardiophrenic arteries and veins, which are wrapped together inside left and right pericardiophrenic bundles. The right and left phrenic nerve will continue to descend anteriorly to the root of the lung and between the mediastinal surface of the parietal pleura and fibrous pericardium. The right phrenic nerve passes lateral to the right atrium and right ventricle and will continue to descend through the vena cava hiatus in the diaphragmatic opening at the level of T8. The left phrenic nerve descends anterior to the pericardial sac of the left ventricle and terminates at the central tendon of the diaphragm (Wang YJ, et al., 2016).

The figure illustrates an axon and synapses (in green) near muscle fibers (orange), by means of a colored micrograph under a scanning electron microscope (SEM). The image is taken from the Don Gnocchi chemistry and research laboratory in Milan.

Both nerves always divide into a variable number of branches, from two to seven. The branches vary in size and the thickness bears no relationship to the area supplied. The average finding was three to five branches separating into anterior, lateral, and posterior directions. The posteromedial branch was usually the biggest, absolutely constant, and always running in the same direction.

The phrenic nerve receives afferents from the pericardium, liver, vena cava, and peritoneum, since it contains both sensory and motor fibers (Drake R, et al., 2002; Townend RE, & McConnell P., 2012).

The brachial and cervical plexuses are located in the region of the phrenic nerve. To give some examples, the roots that may be affected by phrenic disorders are C4–C5 (ie, the dorsal nerve of the scapula), and C5–C6, specifically, the axillary nerve, suprascapular nerve, musculocutaneous nerve, and subclavian nerve (Drake R, et al., 2009).

The electrical activity of the nervous system is not restricted to the mere distribution of efferent impulses in one direction; in fact, nerves not only convey electrical impulses but also release chemobiologic, neurotrophic and, at times, immune substances (Zhao T, et al., 2012; Yampolsky C, et al., 2012) (Russell FD, et al., 2000).

Along its pathway, the phrenic nerve anastomoses to the subclavian nerve, which innervates the subclavian muscle, specifically, the first rib and the clavicle (C5–C6) (Banneheka S., 2008). If there is a phrenic disorder, it is possible to contract the subclavius muscle, raising the first rib and reproducing a thoracic outlet syndrome, with the relevant symptomatology (Zhang Z, & Dellon AL., 2008; Laulan J, et al., 2011).

The scalene muscles, which are innervated by the cervical and brachial plexuses, are equally involved (Drake R, et al., 2009). It is worth emphasizing that a brachial disorder can provoke phrenic and diaphragmatic disorders. Kehr's sign is a classic example of referred pain: irritation of the diaphragm is signaled by the phrenic nerve as pain in the area above the collarbone. This is because the supraclavicular nerves have the same cervical nerves origin as the phrenic nerve, C3 and C4 (Franko OI, et al., 2008).