Diaphragm, Breathing Mechanism, Surface Anatomy PDF

Diaphragm; Mechanisms of Respiration; Surface Projections MD3001 September 2023 Dr. Alex Gardner [email protected] Learning Outcomes By the end of this lecture, time spent in the dissecting room, and further private study you should be able to: 1. Describe the attachments and functional anat...

Diaphragm; Mechanisms of Respiration; Surface Projections MD3001 September 2023 Dr. Alex Gardner [email protected] Learning Outcomes By the end of this lecture, time spent in the dissecting room, and further private study you should be able to: 1. Describe the attachments and functional anatomy of the diaphragm 2. List the structures that pass through the diaphragm and give the vertebral levels at which they do so 3. Describe the diaphragmatic and thoracic movements that occur during respiration 4. Describe the surface anatomy (projections) of the pleura, lungs and their fissures (and their clinical significance) 5. Explain what happens when a pneumothorax occurs 6. Define the boundaries of the “triangle of safety” for chest tube insertion 7. Identify anatomical structures in cross-sections of the thorax MD3001 2023 2 Sources N.B. Consult chapters on thorax and abdomen MD3001 2023 3 The (thoracic) diaphragm • Musculotendinous sheet separating thoracic and abdominal cavity • Central tendon, surrounded by muscle • Inverted “J” • Domed structure (right and left domes), right 1cm superior to left MD3001 2023 4 The diaphragm • Openings for several important structures • Main muscle for breathing • When maximally expired, right dome reaches rib 5 level, left = 5th intervertebral space MD3001 2023 5 Diaphragm attachments Attaches to margins of inferior thoracic aperture: Sternal part: • Xiphoid process (T8/9 vertebral level) Costal part: • Costal cartilages 7-10, ribs 11, 12 MD3001 2023 6 Diaphragm attachments Lumbar attachments: • Right and left crura • Median arcuate ligament • Medial arcuate ligaments • Lateral arcuate ligaments MD3001 2023 7 Diaphragm attachments Lumbar attachments: • Right and left crura – Left L1 to L2, Right L1 to L3 bodies, anterior longitudinal ligament and IV discs • Median arcuate ligament – Formed by crura MD3001 2023 8 Diaphragm attachments Lumbar attachments: • Medial arcuate ligaments – Thickened psoas major fascia spanning L1 vertebral body and transverse processes • Lateral arcuate ligaments – Transverse process L1 and tip of rib 12, thickened quadratus lumborum fascia MD3001 2023 Psoas major quadratus lumborum 9 Diaphragm attachments • Insertion to central tendon • Continuous with fibrous pericardium • Central tendon at level of Xiphisternal synchondrosis MD3001 2023 10 Diaphragm openings Three major openings • Caval opening • Oesophageal hiatus • Aortic hiatus MD3001 2023 11 Diaphragm openings Caval opening • Level of T8, through central tendon • Inferior vena cava and right phrenic nerve (and some lymphatics) • IVC connected to margins so diameter changes during action of diaphragm (widens during contraction) MD3001 2023 12 Diaphragm openings Oesophageal hiatus • Level of T10, within fibres of right crus (which have a sphincter function) • Accompanied by right and left vagal trunks, oesophageal branches of left gastric vessels MD3001 2023 13 Diaphragm openings Aortic hiatus • Level of T12, posterior to median arcuate ligament • Accompanied by thoracic duct • Sometimes azygous and hemiazygous veins (or sometimes these pass through the crura) • Aorta is not affected by actions of the diaphragm MD3001 2023 14 Diaphragm – smaller structures Also crossed by • Left phrenic nerve • Sympathetic trunks (posterior to medial arcuate ligaments) • Greater, lesser and least splanchnic nerves through crura • Intercostal nerves MD3001 2023 15 Diaphragm – smaller structures Also crossed by • Superior epigastric vessels (and lymphatics) • Musculophrenic vessels MD3001 2023 16 Diaphragm – neurovascular supply Arterial supply: Superior surface • Superior phrenic from thoracic aorta • Musculophrenic and pericardiophrenic from internal thoracic Inferior surface • Inferior phrenic from abdominal aorta MD3001 2023 17 Diaphragm – neurovascular supply Venous drainage: • Essentially, mirrors arteries • Superior phrenic vein on right Some posterior superior surface veins drain to azygous/hemiazygos system • N.B. left inferior phrenic vein also drains to suprarenal then renal vein MD3001 2023 18 Diaphragm – neurovascular supply Innervation: • Phrenic nerve (C3,4,5) • Motor, sensory to central diaphragm (and parietal pleura and pericardium) • Additional peripheral sensory innervation from intercostals (T5-11) and subcostal (T12) nerves MD3001 2023 19 Mechanics of breathing - overview • At rest, inspiration mostly driven by the diaphragm (external intercostal contribute) • Diaphragm contraction increases thoracic volume, drawing air into the lungs • Gaseous exchange occurs • Diaphragm relaxes, thoracic volume falls and air is exhaled • Exhaling at rest is largely passive (elastic recoil) • Higher demand for O2/CO2 removal can involve accessory muscles • Smooth movement aided by the pleurae MD3001 2023 20 Mechanics of breathing - inspiration Inspiration – • peripheral muscle of diaphragm contracts • Domes descend MD3001 2023 21 Mechanics of breathing - inspiration Inspiration – • peripheral muscle of diaphragm contracts • Domes descend • External intercostals act to move ribs superiorly, and laterally • Thoracic volume increases and air is drawn in to compensate for the volume change Mostly ribs 2-6 Mostly ribs with oblique costal cartilages MD3001 2023 22 Mechanics of breathing Forced inspiration • Diaphragm can aid in increasing thoracic volume by raising ribs when anchored via pericardium • Minimises costodiaphragmatic recess • Accessory muscles can increase force/speed of inspiration but not alter the volume of air inspired – – – – SCM, scalenes, trapezius = fixing ribs Pectoralis major and minor (inspiration) Latissimus dorsi (inspiration and expiration) Abdominal wall muscles (expiration) MD3001 2023 23 Surface anatomy – lungs and pleurae Lungs and pleurae: • Apex – 3cm superior to mid clavicle • At middle from 2nd to 6th CC on right • Deviation laterally between 4th to 6th CC on left Lungs: • Midclavicular line – 6th rib • Midaxillary line – 8th rib • Scapular line and midline (posteriorly) – 10th rib Pleurae: Add 2 ribs to level of the lungs! • Midclavicular line – 8th rib • Midaxillary line – 10th rib • Scapular line and midline (posteriorly) – 12th rib MD3001 2023 24 Surface anatomy – lungs and pleurae Lungs and pleurae: • Apex – 3cm superior to mid clavicle • At middle from 2nd to 6th CC on right • Deviation laterally between 4th to 6th CC on left Lungs: • Midclavicular line – 6th rib • Midaxillary line – 8th rib • Scapular line and midline (posteriorly) – 10th rib Pleurae: Add 2 ribs to level of the lungs! • Midclavicular line – 8th rib • Midaxillary line – 10th rib • Scapular line and midline (posteriorly) – 12th rib MD3001 2023 25 Surface anatomy – oblique fissures Posteriorly, level T3/T4 MD3001 2023 Midaxillary line – 5th Intercostal space Anteriorly, following rib 6 26 Surface anatomy – horizontal fissure Moving lateral from sternum, 4th rib/intercostal space Merges with oblique fissure at 5th rib MD3001 2023 27 Surface anatomy – auscultation sites MD3001 2023 28 Surface anatomy – auscultation sites MD3001 2023 29 Lungs recesses Costodiaphragmatic • Space below lungs around periphery of diaphragm • Double fold of parietal pleura • Site of fluid collection e.g. in infection • Needle angled upwards at 9th intercostal space on midaxillary line during expiration can remove fluid Costomediastinal • Behind manubrium • Costal pleura and mediastinal pleura • More pronounced on left – cardiac notch • Lingula partly occupies during breathing MD3001 2023 30 Pneumothorax • Lungs tend to a collapsed state due to their elasticity • They are held in place against thoracic wall by surface tension of pleural fluid between the visceral and parietal pleurae • If air enters the pleural space then pneumothorax develops • Can be traumatic or spontaneous Mediastinum shifts to affected side MD3001 2023 Lung moved from thoracic wall https://radiopaedia.org/articles/pneumothorax Flattened hemidiaphragm 31 Chest drain • Used to evacuate air (pneumothorax) or fluid (pleural effusion, haemothorax, chylothorax) from the pleural space • Safety triangle MD3001 2023 32 Chest drain Safety triangle • Lateral border pectoralis major • Anterior border latissimus dorsi • Apex – towards axilla • Base – nipple/5th intercostal space • Incorrect placement risks perforating pericardium/heart/liver 45% of junior doctors misplacing chest drain, with many being too low From: British thoracic society MD3001 2023 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC174330 6/ 33 Flail chest • Occurs after severe trauma fracturing >3 ribs • 75% after a car crash • “Loose” section of thoracic wall is drawn inwards upon inspiration • Paradoxical chest wall motion https://www.youtube.com/watch?v=5QiQj8cBsAA NEJM youtube page MD3001 2023 34 Transverse thoracic sections T12 level Transverse colon duodenum liver spleen pancreas Costodiaphragmatic recesses MD3001 2023 35 Transverse thoracic sections T9 level Right ventricle Left ventricle IVC liver MD3001 2023 Lungs oesophagus Aorta Lungs 36 Transverse thoracic sections T5 level SVC Ascending aorta carina Pulmonary trunk Descending aorta Oesophagus Azygous vein MD3001 2023 37 Transverse thoracic sections T2 level Manubrium Clavicle Trachea Rib 1 Left Lung apex Images (and more) from: https://radiopaedia.org/cases/normal-ct-chest MD3001 2023 38 Lungs • Visceral and parietal pleura • Small amount of serous pleural fluid in fluid cavity • Note terminology for parietal pleura • This reduces friction during breathing MD3001 2023 39