PRACA ORYGINALNAREVIEW Janusz Kocjan1, Mariusz Adamek1, Bożena Gzik-Zroska2, Damian Czyżewski1, Mateusz Rydel1 1Chair and Department of Thoracic Surgery, Faculty of Medicine and Dentistry, Medical University of Silesia, Katowice, Poland 2Department of Biomaterials and Medical Devices Engineering, Silesian University of Technology, Zabrze, Poland Network of breathing. Multifunctional role of the diaphragm: a review The authors declare no financial disclosure Abstract The diaphragm is the primary muscle involved in active inspiration and serves also as an important anatomical landmark that separates the thoracic and abdominal cavity. However, the diaphragm muscle like other structures and organs in the human body has more than one function, and displays many anatomic links throughout the body, thereby forming a ‘network of breathing’. Besides respiratory function, it is important for postural control as it stabilises the lumbar spine during loading tasks. It also plays a vital role in the vascular and lymphatic systems, as well as, is greatly involved in gastroesophageal functions such as swallowing, vomiting, and contributing to the gastroesophageal reflux barrier. In this paper we set out in detail the anatomy and embryology of the diaphragm and attempt to show it serves as both: an important exchange point of information, originating in different areas of the body, and a source of information in itself. The study also discusses all of its functions related to breathing. Key words: diaphragm, breathing, diaphragm function Adv. Respir. Med. 2017; 85: 224–232 Introduction the diaphragm acts not only as a breathing mus- cle, but also plays multiple distinct physiological The scientific interest in diaphragm dates roles. Anatomically, the diaphragm only separates back to the end of the 19th c., when Sewall and thoracic and abdominal cavities. However, from Pollard investigated the relationship of movement a functional perspective, this muscle extends between the thoracic cavity and the diaphragm. from the trigeminal system to the pelvic floor, They assessed the diaphragmatic component of as well as has many links throughout the body respiration by observing changes of circumfer- and is an important crossroads of information ence of the abdomen and concluded that the dia­ involving the entire body. The phrenic nerve in- phragm contracts and descends into abdominal nervates the diaphragm, and runs from the roots cavity [1]. At the beginning of the nineteenth of C3 to C5. The pathway of the phrenic nerve century, Bell demonstrated that life could be involves the entire brachial plexus and the entire maintained by diaphragmatic breathing alone af- cervical plexus. Along its pathway, the phrenic ter injuries to the cervical spinal cord in a man [2]. nerve anastomoses with the vagus nerve, which is In the following decades researchers have investi- joined to the medial longitudinal fasciculus and gated physiological mechanisms, biomechanical is in contact with the spinal trigeminal nucleus functions, and anatomical attachments of the via afferent connections. Furthermore, the vagal diaphragm. Currently, it is well documented that nerve is firmly connected with the hypoglossal Address for correspondence: Janusz Kocjan, Chair and Department of Thoracic Surgery, Faculty of Medicine and Dentistry, Medical University of Silesia, Katowice, Poland, e-mail: [email protected] DOI: 10.5603/ARM.2017.0037 Received: 20.03.2017 Copyright © 2017 PTChP ISSN 2451–4934 224 www.journals.viamedica.pl Janusz Kocjan et al., Network of breathing. Multifunctional role of the diaphragm nerve, which is closely related to the trigeminal and the 12th rib posteriorly. The position also system and receives a multitude of presynaptic depends upon the posture of the body (lower impulses from the phrenic nerve. With reference when a person is sitting or standing and higher to neurological connections, dysfunction of the in supine position) and degree of distention of diaphragm can cause symptoms observed in the the abdominal viscera [6, 7]. region of the cervical base and eyes, as well as Structurally, the diaphragm comprises two in the floor of the mouth (poor swallowing or parts: a centrally placed, non­contractile tendon sleep apnoea). From lower side, the connection — a flat aponeurosis made of dense collagen fi- between the diaphragm and pelvic floor is less bers, and the peripheral muscle — that converge complicated. The respiration process has to be on the central tendon. The muscular portion is supported by the pelvic floor in order to properly divided into three parts based on fibers origin. control intra­abdominal pressure. During phys- Fibers of the sternal parts are short and arise iological diaphragmatic action (e.g. respiration, as small slips from the posterior surface of the coughing), when the diaphragm descends into xiphoid process. The costal region (laterally on the abdominal cavity, the corresponding action either side of the xiphoid) is made up of several of lowering of the pelvic floor is also observed. wide muscle segments originating from the in- In this point it is also important to mention that ternal surface of the caudal six ribs at the costal electrical activity of the pelvic floor muscle is cartilages (costal margin), while the lumbar part noticed before inhalation [3]. To summarise, of the diaphragm has its origins on the lumbar Caroline Stone states: ‘the diaphragm is one of vertebra by two crura and three arcuate ligaments. the most remarkable areas of the body in that The right crus attaches distally to the anterior it has so much influence and the consequences portions of the first through third lumbar ver- of its dysfunction can manifest anywhere from tebrae (L1­3) and the left crus attaches distally the head to the toes’ [4]. While Andrew Still, the on the first and second lumbar vertebrae (L1­2). founder of osteopathy and osteopathic medicine Anatomists name the crura left or right by their wrote: ‘by (diaphragm) action we live, and by its origin from the left or right side of the vertebral failure we shrink, or swell, and die’ [5]. bodies, but surgeons name the crura left or right by their relation to the esophagus. Lateral to the Anatomy and anatomic connections of the crura on both sides, the diaphragm arises from diaphragm the medial and lateral arcuate ligaments. Arcuate ligaments are thickened upper margin of fascia The diaphragm is a thin (2–4 mm), movable covering the psoas muscle on its anterior surface dome­shaped sheet of internal skeletal muscle (medial arcuate ligament) and the quadratus that separates the thoracic and abdominal cav- lumborum muscle (lateral arcuate ligament). The ities. It also plays a vital role in managing the paired lateral arcuate ligaments extend from the th information related to both cavities. In anatomic tip and lower margin of the 12 rib and arch over position, the diaphragm curves into right and left quadratus lumborum to the transverse processes domes (also known as cupolae). The right dome of L1 [6–8]. Although the lateral arcuate ligament is slightly higher than the left one and reaches is commonly described in anatomy books as as high as the upper border of the fifth rib. The attaching to the first lumbar vertebra (L1), other left dome may reach up to the lower border of the instances have been found in cadaver studies with fifth rib. The reason behind the right dome being attachments to either the second (L2) or third (L3) higher than the left one is probably the larger size lumbar vertebra [9]. Approximately in 5% of peo- of the right lobe of the liver. The central tendon, ple inferolateral extensions of the lateral arcuate which lies between the two domes, remains at the ligaments is present as thickened nodular areas level of the xiphisternal joint. The domes of the adjacent to the lateral diaphragmatic surface [10]. diaphragm support the right and left lung while The paired medial arcuate ligaments, in contrast the central tendon provides support to the heart. to the lateral ones, complete the journey arching The position and shape of the diaphragm is not over the psoas major from the tip of the transverse absolute, but varies with the phase of respiration. processes of L1 (sometimes also, of L2) to the With full exhalation, the dome of the diaphragm tendinous portion of each diaphragmatic crus. can rise to the level of the fourth intercostalspace The medial margins of the right and left crura anteriorly (nipple level). With full inhalation, the unites to form a poorly defined arch — the median diaphragm flattens, bringing the thoracic cavity arcuate ligament, through which pass the aorta, down to the level of costal margin anteriorly the azygos vein, and the thoracic duct [8]. www.journals.viamedica.pl 225 Advances in Respiratory Medicine 2017, vol. 85, no. 4, pages 224–232 The diaphragmatic ligaments are structures rently unclear whether the pleuroperitoneal folds that connect the diaphragm to the viscera. The in- are simply transient embryonic structures with ferior pulmonary ligament is a pleural thickening no adult derivatives or if they give rise to cells connecting the diaphragm to the base of the lungs. or tissues of the adult diaphragm. After the early The phrenopericardial ligament connects the di- diaphragm is formed, the dorsal mesentery of aphragm to the heart and is the fulcrum around the esophagus (third embryonic structure) fuses which the diaphragm is supported when it comes with the two previously mentioned structures to distribute its contractile tension laterally. The (septum transversum and the pleuroperitoneal hepatic ligaments (the falciform ligament and membranes) to form the median portion of the the right and left triangular ligaments) represent diaphragm, while the body wall tissue (fourth a subdiaphragmatic peritoneal thickening. The major component) splits into two layers as a result phrenicoesophageal ligament joins the esopha- of the enlargement of the lungs and the pleural gus and the diaphragm and is composed of loose cavities. The parts of the inner layer form the connective tissue.