28-10-22 – Diaphragm, Mechanics of Breathing, Surface Projections Flashcards
Learning outcomes
- Describe the attachments and functional anatomy of the diaphragm
- List the structures that pass through the diaphragm and give the vertebral levels at which they do so
- Describe the diaphragmatic and thoracic movements that occur during respiration
- Describe the surface anatomy (projections) of the pleura, lungs and their fissures (and their clinical significance)
- Explain what happens when a pneumothorax occurs and where would be the safest site to evacuate air
- List the boundaries of the “triangle of safety” for chest tube insertion
- Identify anatomical structures in cross-sections of the thorax
What is the diaphragm?
What does it close?
What is its structure like at the periphery and centrally?
What does the diaphragm consist of?
How high is each dome compared to each other?
Where does the diaphragm sit on full expiration?
Where is it intersected by the ribs on full inspiration?
- The diaphragm is the musculotendinous structure that separates the thoracic cavity from the abdominal cavity
- It closes the inferior thoracic aperture
- The diaphragm is muscular at its periphery, but tendinous centrally at the central tendon
- The diaphragm consists of 2 domes/hemidiaphragms, with the right hemidiaphragm sitting about 1cm higher than the left
- The diaphragm sits at the 4th/5th intervertebral space at full expiration
- The intervertebral disc space is typically defined on an X-ray photograph as the space between adjacent vertebrae
- The diaphragm should be intersected by the 5th to 7th anterior ribs in the mid-clavicular line on full inspiration
What are crura of the diaphragm?
What is their role?
How many crura are there?
What do they form together?
What 6 things does the diaphragm attach to?
- The crus of diaphragm (pleural is crura), refers to one of two tendinous structures that extends below the diaphragm to the vertebral column.
- There is a right crus and a left crus, which together form a tether for muscular contraction.
- 6 things the diaphragm attaches to:
1) Xiphoid process of the sternum (attaches at vertebral level T8/9)
2) Deep surface of the last 6 ribs and costal cartilages (costal margin)
3) Lumbar vertebrae
* Left crus is located at (L1-2)
* Right crus is located at (L1-3)
4) Median arcuate ligament
* Located at the medial borders of the crura
5) Medial arcuate ligament
* Condensation of psoas fascia – covers psoas major muscle
* Medial arcuate ligament is attached to transverse process of L1 (or L2)
6) Lateral arcuate ligament
* Condensation of thoracolumbar fascia
* Lateral arcuate ligament is attached to transverse process of L1 – rib 12
Where does the diaphragm insert?
Where is the central tendon located?
What type of joint is the xiphisternal joint?
What sits on the central tendon?
What is the central tendon fused to?
What does this prevent during forced inspiration?
What does further contraction of the diaphragm pull?
- The diaphragm inserts on the central tendon (Centrum tendineum)
- The central tendon is at the level of xiphisternal synchondrosis joint (T9)
- The heart sits on the central tendon
- The central tendon is fused to the pericardium
- This prevents the pericardium’s descent during forced inspiration
- Further contraction of the diaphragmatic muscle pulls on ribs 7 to 10 from the anchored central tendon
What is the level of the caval opening?
What does it pass through?
What 2 structures pass through the caval opening?
What is the level of the oesophageal opening?
What 3 structures pass through the oesophageal opening?
- The caval opening is At T8 level, through central tendon
- 2 structures that pass through the caval opening:
1) Inferior vena cava
2) Right phrenic nerve - The oesophageal opening is at T10 level, through the right crus (sphincter)
- 3 structures that pass through the oesophageal opening:
1) Oesophagus
2) Both vagus nerves
3) Left gastric vessels (part of control centre of stomach)
What level is the aortic hiatus?
What does is pass behind?
What 3 structures pass through the aortic hiatus?
What level are the crura?
What 3 structures pass through the crura?
What is the level of attachment of the medial arcuate ligament?
What structure passes behind the medial arcuate ligament?
- The aortic hiatus is At T12 level and passes behind median arcuate ligament
- 3 structures pass through the aortic hiatus:
1) Aorta
2) Thoracic duct
3) Azygos and Hemiazygos (±) - Left crus is at level L1-2
- Right crus is at level L1-3
- 3 structures pass through the crura:
1) Branches of left phrenic nerve
2) Splanchnic nerves
3) Azygos and Hemiazygos (±) - The medial arcuate ligament is attached to transverse process of L1 (or L2)
- The sympathetic trunk passes behind the medial arcuate ligament
What are the 4 different arterial supplies of the diaphragm?
- 4 different arterial supplies of the diaphragm:
1) Superior phrenic arteries
* Branch of thoracic aorta
2) Branches of musculophrenic arteries
* Supplies some of the anterior intercostal arteries
3) Branches of pericardiacophrenic arteries
4 Inferior phrenic artery
* Branch of abdominal aorta
What nerve roots make up the phrenic nerve?
What does it provide to the diagram?
What 3 things does the phrenic nerve supply sensory fibres to?
What other nerves supply sensory fibres to the diaphragm?
- The phrenic nerve is made from C3, C4, C5 (keeps the diaphragm alive)
- The phrenic nerve is the only motor supply to the diaphragm
- 3 things the phrenic nerve supplies sensory fibres to:
1) Central tendon of diaphragm
2) Parietal pleura
3) Pericardium - Intercostal nerves provide sensory fibres to the periphery of the diaphragm
What is the Boyle-Mariotte Law? When was it founded?
- The Boyle-Mariotte Law:
- The absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system
- Essentially means volume is inversely proportional to pressure
- R. Boyle (1662) and E. Mariotte (1679)
How can respiration vary?
What is respiration?
What 3 things change during inhalation?
How does exhalation occur?
- Respiration varies: Quiet (at rest) or Forced (during severe exercise or respiratory distress)
- Respiration = inspiration + expiration
- 3 changes during inhalation:
1) Diameters of thorax increase
2) Creation of a more negative intra-thoracic pressure (< atmospheric pressure) - Intrathoracic pressure is always negative, which acts like suction to keep the lungs inflated
3) Air is sucked into lungs due to the pressure gradient - Expiration (exhalation) is by muscle relaxation and elastic recoil of the elastic tissues in the lungs and bronchi
What are 3 mechanisms used to increase thoracic volume during inhalation?
- 3 mechanisms used to increase thoracic volume:
1) Movement of the diaphragm up and down
2) Movement of the ribs/sternum forwards and back (pump handle movement)
3) Movement of ribs upwards and laterally (bucket handle movement)
Movement of the diaphragm up and down.
What happens when the diaphragm contracts?
What 4 changes does this lead to?
How important is this mechanism?
How much air goes into the lungs for every 1cm of diaphragm descent?
- Movement of the diaphragm up and down
- When the diaphragm contracts, this flattens the domes
- When the domes of the diaphragm descend, this results in:
1) The vertical diameter of the thorax increasing
2) The volume of the thorax increasing
3) The intrathoracic pressure decreasing
4) Air being drawn into the lungs - Most important inspiratory activity in adult (responsible for 70% of air into lungs)
- Every 1cm of diaphragm descent allows 270ml of air into the lungs
Movement of the ribs/sternum forwards and back (pump handle movement).
How do anterior and posterior ends of ribs sit in relation to each other?
What do the external intercostal muscles do during inhalation?
What 4 changes does this lead to?
Why is this mechanism called a pump-handle movement?
- Movement of the ribs/sternum forwards and back (pump handle movement)
- The anterior ends of ribs are normally below the posterior ends of the ribs (similar to the thoracic inlet), with the posterior ends passing obliquely downwards
- During inhalation, the external intercostal muscles contract to raise the body of the rib towards the one above, while also lifting the sternum and pushing it anteriorly
- This leads to:
1) The sagittal diameter increasing
2) The volume of the thorax increasing
3) Intrathoracic pressure decreasing
4) Air being drawn into the lungs - In a pump handle movement, when the handle is pumped, it moves away from the midline
- This is similar to this mechanism, where the sternum moves away from the midline
Movement of ribs upwards and laterally (bucket handle movement).
How are costal cartilages 5-10 orientated towards the sternum?
What occurs when the external intercostal muscles contract during inhalation?
How is this made possible?
What 4 changes does this lead to?
Why is this mechanism compared to a bucket-handle movement?
Why do costal cartilages 1-4 not really contribute to this mechanism?
- Movement of ribs upwards and laterally (bucket handle movement)
- The costal cartilages of ribs 5-10 are orientated obliquely to the sternum, meaning the costal cartilages and the anterior and posterior ends of these ribs will sit higher than the lateral edge of the ribs
- When the external intercostal muscles contract during inhalation, this lifts up the costal cartilages, displacing the ribs laterally and bringing them towards the level of their costal cartilages and anterior and posterior ends
- This lateral splay is made possible by the fact that the necks of ribs 5 to 10 lie obliquely
- This lateral splay leads to:
1) The transverse diameter of the thorax increasing
2) The volume of the thorax increasing
3) Intrathoracic pressure decreasing
4) Air being drawn into the lungs - This mechanism is compared to a bucket-handle movement as when we raise the ribs up, they move laterally
- Costal cartilages 1-4 are horizontal, meaning they basically sit at the same level of the whole rib
- When these costal cartilages are lifted on inspiration, the ribs won’t be laterally displaced, which won’t contribute to the increase in the volume of the thorax
- There is no lateral movement of the First Rib: its CC is horizontal, as is its neck
- Costosternal joint 1 is also a primary cartilaginous joint (synchondroses), which allows little movement or no movement
- Ribs 2 to 4 may twist slightly to increase lateral diameter (their CCs are short and horizontal)
Forced inspiration.
What are 2 ways excessive lowering of the diaphragm in inhalation prevented?
Why might this be prevented?
What can happen when the diaphragm is anchored by the pericardiophrenic ligament in during forced inspiration?
How does the roll of the central tendon change?
What 2 changes does this lead to?
What ribs does this mechanism occur in?
- Forced inspiration:
- Excessive lowering of the diaphragm is prevented by the pericardiophrenic ligaments attaching the central tendon of the diaphragm to the pericardium and also because of the liver
- This may be prevented due to the pericardium being anchored to the great vessels
- When the diaphragm is anchored by the pericardiophrenic ligament and can’t descend any further during forced inspiration, further muscle contraction pulls on the ribs and causes them to evert like lifting the handle of a bucket
- The central tendon is the insertion of the diaphragm, but when it becomes anchored, it becomes the origin in a way
- This leads to:
1) A small, additional increase in the lateral thoracic diameter and therefore the volume
2) Even more air being drawn into the lungs by this additional decrease in intrathoracic pressure - This mechanism occurs only in ribs 8 to 10 that have flat costo-transverse joints that allow gliding
What can accessory muscles be used for?
What can they contribute?
What 4 groups of muscles can be used as accessory muscles?
When are each of them used?
- Accessory muscles of respiration can be utilized when more power is required e.g during forced inhalation or respiratory distress
- They cannot further increase the thoracic diameters, but they add more power of contraction
- 4 groups of muscles can be used as accessory muscles:
1) Pectoralis major and minor (inspiration)
2) Latissimus dorsi (expiration and inspiration)
3) Abdominal wall muscles (expiration)
4) Neck and back muscles (trapezius, sternocleidomastoid, scalene muscles) help to fix the ribs
Why is it important know the surface anatomy of:
1) The 4 corners of the heart
2) The lung and fissures
3) The pleura and its reflections?
- It is important to know the surface anatomy of the 4 corners of the heart for auscultation of different chambers and valves of the heart and palpation of the apex beat
- It is important to know the surface anatomy of the lung and fissures so we can auscultate different lobes
- It is important to know the surface anatomy of the pleura and its reflections as fluid can accumulate in the pleural cavity, so we need to know where to drain it
Where does the pleura of the lungs rise to? Where is the pleura found at the:
1) 2nd CC
2) 4th Left CC
3) 6TH CC
4) 8th rib
5) 10th rib
6) T12
- The pleura of the lungs rise to level of neck of 1st rib, 2 cm above clavicle
- Where the pleura is found at different levels:
1) 2nd CC lie - adjacent in the mid line
2) 4th left CC - notch for the heart
3) 6th CC - deviate laterally
4) 8th rib - the midclavicular line
5) 10th rib - the mid axillary line
6) T12 - mid line (just below the 12th rib)
Where does the apex of the lung project into?
How can this be represented?
At what levels it the lung 2 spaces higher than the pleural space?
Where is the lung found at the:
1) 2nd CC
2) 4th Left CC
3) 6TH CC
4) 8th rib
5) 10th rib
6) T12
- The apex of the lung projects into the neck
- This can be represented by a curved line, from the sternoclavicular joint to a point 2.5 cm above the junction of the medial and intermediate thirds of the clavicle
- Where the lung is found at different levels:
1) 2nd CC - lie adjacent in the mid line
2) 4th Left CC - cardiac notch
3) 6th CC - deviate laterally
4) 6th rib - the midclavicular line
5) 8th rib - the mid axillary line
6) 10th rib - the mid scapular line and mid line - At the 6th rib, 8th rib, and 10th rib, the lung is 2 spaces higher than the pleura e.g lung is at mid-axillary line at 8th rib, pleura is at midaxillary line at 10th rib
Do the lungs fill the pleural cavities during quiet respiration?
What does this lead to?
What can these recesses be the site of?
How does the surface tension between layers of pleura keep the lungs inflated?
What is this surface tension generated by?
- In quiet respiration, the lungs do not entirely fill the pleural cavities
- This results in recesses (potential spaces) in which two layers of pleura become unopposed
- The recesses are the potential sites of accumulation of fluids, from which they can be aspirated
- Surface tension between the parietal and visceral pleurae pulls the visceral layer (and lung) with the movements of the thorax wall
- Elastic recoil of the lung tissue means that lungs are tending to deflate
- The surface tension creates a slight negative pressure that maintains the lung in slight inflation even at the end of expiration
- This surface tension is generated by pleural fluid that lubricates potential spaces
Where is the costophrenic recess found?
Why do we need to know this boundary?
Where is the costomediastinal recess found?
- The costophrenic recess is a narrow potential space found between the ribs and the diaphragm
- We need to know this boundary in case fluid flows down here
- The costomediastinal recess is the potential space in the pleural cavity between the costal pleura and mediastinal pleura at approximately the level of the fifth intercostal space on the left-hand side.
Where does the oblique fissure run between?
Which lobes does the oblique fissure separate on both lungs?
Where does the horizontal fissure run between?
What lobes does it separate on the right lung?
- The oblique fissure is a curved line that begins between the spinous processes of the vertebrae T3 and T4, crosses the mid-axillary line at 5th intercostal space, and then follows the contour of rib 6
- The oblique fissure separates the middle and inferior lobes on the right lung
- The oblique fissure separates the superior and inferior lobes on the left rung
- The horizontal fissure follows the 4th intercostal space from the sternum until it meets the oblique fissure as it crosses rib 5
- The horizontal fissure separates the superior and middle lobes of the right lung
What happens if air enters the pleural cavity?
What 3 things can the affected side show?
- If air enters the pleural cavity, the surface tension and negative pressure are lost and the lung collapses (pneumothorax)
- If severe, the affected side shows:
1) No thoracic movement
2) Flat hemi-diaphragm
3) Shift of mediastinum to the unaffected side
What 3 things make up the triangle of safety for a chest tube?
Where is the apex of this triangle?
- 3 things make up the triangle of safety for a chest tube:
1) Anterior border of the latissimus dorsi
2) Lateral border of the pectoralis major muscle
3) Horizontal level of the nipple - The apex of this triangle is below the axilla
What can cause a flail chest?
What would this lead to? What is paradoxical respiration?
- Imagine severe chest trauma, such as hitting the steering wheel in a head-on collision, causing fracture of the ribs and sternum as shown on the diagram
- That whole segment would float freely, i.e. a flail segment or flail chest
- This would lead to paradoxical respiration
- Paradoxical respiration is when the flail chest is sucked in on inspiration instead of being raised up and outwards
