Block 2 Scenario 4


  1. Describe the form and subdivisions of the lung, the distribution of the bronchi, and the structure of alveoli and the alveolar membrane.
  2. Describe ‘breath sounds’ and give a simple explanation of what causes them.
  3. Outline the general principles of radiography.
  4. Describe the arrangement of the pleura and outline its function, and surface markings.
  5. Define pneumothorax and haemothorax, and outline how they are treated.

The Respiratory System

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The natural airway is through the nose - the nasal route remains open for respiration at all times, unlike the oral route. The nostril is the first point of entry of air into the respiratory system. This entrance is lined with coarse hairs which trap large particles from entering the nasal cavity. The nasal cavity is made of three turbinate bones which forces the air into turbulent eddies. The nasal cavity is lined with mucuous secreting goblet cells which trap almost all particles greater than 5 micrometres in size. (A RBC measures 8 micrometres across.) The nasal cavity also raises the temperature of the air to within 1 degree of body temperature and up to 95% humidity, maintaining internal moisture.

The oral cavity supports the hard palate (made of bone) and medially the soft palate which extends down to support the uvula in the centre of the mouth. Posterior to the oral cavity, the respiratory tract forms the pharynx - the throat- divided into the nasal-pharynx, the oro-pharynx, and the largyngo-pharynx. The Epiglottis points superior-posteriorly and acts as a cap during swallowing to stop bolus (food) from entering the trachea and direct it towards the oesophagus. This only becomes a problem because unlike the oesophagus which remains closed until swallowing, the trachea is made of 16-20 C- shaped hyaline cartilage rings which keep the trachea permanently open. Befored entering the trachea, the inspired air passes through the larynx - the voice box- whose main folds are the Vestibular (False) Folds and Vocal (True) Folds, separated by the Ventricle, or Laryngeal Sinus. .

The Trachea is generally 10-12cm long at terminates at the carina, at the level of the sternal angle (T4-T5.) At the Carina, the trachea splits in the right and left bronchi. The right bronchus is more vertical than the left (25 degrees from the midline, with the left at 45 degrees,)) and thus inhaled objects are more likely to pass into it. The right bronchi divides into three secondary bronchi, (the upper, middle and lower) whereas the left lung only divides into two (Upper and lower.) The primary bronchi stem to form secondary bronchi, tertirary bronchi and then bronchioles at about 1mm in diameter, and terminal bronchioles (about 0.5mm in diameter.) The respiratory bronchioles branch to each individual acinus which contain collections of alveoli which inflate and deflate with each breath. It is here that respiration takes place.

Breath Sounds

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Measuring Breath Sounds


Auscultate using the diaphragm of your stethoscope. Ask the patient not to speak and to breathe deeply through the mouth. You should listen to at least one full breath in each location. It is important that you always compare what you hear with the opposite side. Generally, you should listen to at least 6 locations on both the anterior and posterior chest. Begin by ausculating the apices of the lungs, moving from side to side and comparing as you approach the bases. If you hear a suspicious breath sound, listen to a few other nearby locations and try to delineate its extent and character.
external image PEFRONT.JPGexternal image PEBACK.JPG

Sounds to listen for...

Normal Breath Sounds

Heard over Trachea/Larynx. Clean, linear increase and decrease in pitch on inspiration and expiration, the Inspiration being louder.
Linear increase, but less evident expiratory phase.
VESTIBULAR (Lung Periphery)
Quiet inspiratory phase and almost silent on expiration.

Abnormal Breath Sounds

Crackles (Rales)
"Popping" Sounds which occur when obstructed airways suddenly open producing reverberations in the airways. Obstruction can be caused by Secretions or by airways closure due to inflammation or oedema in surrounding tissues. More common on inspiration.
Coninuous tone heard commonly at start of inspiration or end of expiration. They appear as collapsed lumen open gradually during inspiration and close during expiration.
Stridor (Rhonchi)
Intense Continuous Monophonic Wheeze loudest over extrathoracic airways. Stridor is often associated with obstructed upper airways. Caused by extrathoracic lumen collapsing as internal pressure is too low on inspiration.
Poorly defined/inconsistent term to describe harsh discontinuous crackling sounds over larynx or trachea. Sometimes describes as "snoring" sound.
Examples of these sounds can be heard here:

The Pleura pleura.JPG

The lungs are surrounded by two membranes, the pleurae. The outer pleura is attached to the chest wall and is known as the parietal pleura; the inner one is attached to the lung and other visceral tissues and is known as the visceral pleura. In between the two is a thin space known as the pleural cavity or pleural space. It is filled with pleural fluid, a serous fluid produced by the pleura.

The pleura runs a contrinuous loop on the outer surfaces of the lung and inner chest wall. The visceral layer forms the outer layer of the lung and is continuous in forming interlobar folds in each section of the lung. . The two layers are continuous with one another around and below the root of the lung.. When the lung collapses or when air or fluid collects between the two layers the cavity becomes apparent. The right and left pleural sacs are entirely separate from one another.Different portions of the parietal pleura have received special names which indicate their position: thus, that portion which lines the inner surfaces of the ribs and Intercostales is the costal pleura; that clothing the convex surface of the diaphragm is the diaphragmatic pleura; that which rises into the neck, over the summit of the lung, is the cupula of the pleura (cervical pleura); and that which is applied to the other thoracic viscera is the mediastinal pleura.

Surface Markings of the Lungs and Pleura

Anteriorly, the extent of the lungs run from its apex about 2.5cm above the clavicle to the lower border anteriorly at the 6th rib. To find this point the sternal angle (Angle of Louis) is used as it articulate with the 2nd rib and it is possible to palpate downwards to count ribs from here. At the 4th rib, on the midclavicular line the horizontal fissure is found which split the lung into upper, lower and middle lobes. Thus to auscultate the upper right lobe, this should be done anteriorly and above the 4th rib... likewise the lower lobe can be found posteriorly and below the 4th rib (but listen below the scapula,) with the middle lobe anteriorly below the 4th rib.

Both the lungs and the pleura extend farther down in the posterior thorax than in the anterior thorax. The pleura usually extends 2 intercostal spaces beyond the extent of the lung to allow for the lungs' expansion during inspiration. The oblique fissure in either lung starts posteriorly at T3 (sternal angle approx T3-T4 anteriorly as a guide,) and runs diagonally round to the midclavicular line at the 6th rib.

The figure to the left shows the surface marking point for the lung and pleura. These can be used as reference points to treat conditions such as pneumothorax outlined below.

Pneumothorax and Haemothorax


pneumothoraxsmll.jpg There are 3 types of pneumothorax: tension, open, and spontaneous.

A tension pneumothorax occurs when the lung or airway becomes damaged allowing air to escape into the pleural space. During inspiration air is forced out of the lung into the pleural space and is unable to leave because the wound is acting as a flap valve. This causes air to build up in the pleural cavity leading to the collapse of the lung on the affected side and the shift of the mediastinum to the opposite side putting further pressure on the lung on the uninjured side.

A tension pneumothorax is rare, but is a medical emergency. On a X-ray significant mediastinal shift may be evident from the increased pressure on one side. In an emergency, a cannular can be inserted on the anterior side of the 2nd rib in the midclavicular line. This equals the pressure and converts a tension pneumothorax to an open one.

An open pneumothorax occurs when there is damage to the thoracic wall allowing for direct communication between the internal and external environments. Because air flows along the path of least resistance air will enter the affected side via the hole and not via the trachea, thus the lung will not fill with air. During expiration the lung on the injured side receives air from the other lung and this partially reverses the situation.

The treatment of an open pneumothorax depends on the severity - if left, approximately 1.25% of the air with be absorbed each day. ie. if the air cavity takes up 50% of the lung space, it will take 40 days for the air to be absorbed if left. If problematic a chest drain can be inserted on the anterior side of the 5th rib on the midaxillary line, fed through a water-sealed jar. Persistant bubbles indicate air being released from the lung space.

A spontaneous pneumothorax is usually found in health young adult men up to the age of 40. Normally tall and lean. Results from a burst bleb (small blister) on the surface of the lung. (Normally during physical activity.)


A haemothorax occurs as a result of bleeding into the pleural cavity. The because the pleural cavity is enclosed the blood will accumulate, occupying the space that the lung otherwise would. This ultimately leads to lung collapse.
Haemothorax results more often from injury to a major intercostal vessel than from laceration of the lung.

Collapsed Lung

A collapsed lung (pulmonary collapse) occurs when the surface tension between the visceral and parietal pleura breaks down causing them to separate. When a lung collapses the potential pleural space becomes real space.
A collapsed lung can be caused by the accumulation of blood or air in the pleural cavity (haemothorax or pneumothorax) this forces the two pleura apart breaking the surface tension between then. The amount of air or blood in the cavity determines the extent of the collapse. Because each lung is enclosed by separate membranes it possible for only one side to be affected.