Lung

Respiration basics

Vesicular breath sounds

Vesicular breath sounds are the normal breath sounds heard over most of the lung surface in a healthy person on auscultation (i.e. listening to the lung sounds with a stethoscope).

Lung sounds available from https://meded.ucsd.edu/clinicalmed/lung.htm
Courtesy of Michael Wilkes, M.D. and Charlie Goldberg, M.D.

Breathing mechanism

Gas exchange

Lung defences

There are a wide range of lung defences that protect the lungs from infection. These include mechanical barriers and immune-mediated mechanisms.
In the nose, nasal hairs and mucus help to trap large microbial particles that are inhaled (5-10µm). The cough reflex ensures that any irritants impacting in the airways are coughed up.
Microbes that manage to get past these barriers may be trapped by the mucociliary apparatus in the conducting airways of the lungs. The mucociliary apparatus comprises the ciliated pseudostratified columnar epithelium and associated goblet cells that line the trachea, bronchi and larger bronchioles. The goblet cells produce mucus that sits on top of the epithelium like a raft; the mucus traps any particles (≥ 2µm) that it comes into contact with. The cilia, which are little hair-like structures on the luminal surface of the epithelial cells, beat in unison towards the top of the airway to propel the raft of mucus (with its trapped particles) out of the airways to where it may either be coughed out or swallowed.
Other protective mechanisms in the lungs include bronchus-associated lymphoid tissue (BALT), together with plasma cells that produce antibodies, particularly secretary IgA that lines the epithelium of the upper respiratory tract and helps to stave off foreign bacteria. Any microbes that do get past these defences end up within alveolar spaces, where resident phagocytic cells, the alveolar macrophages, may engulf and destroy foreign particles.

Mucociliary clearance

This video clip is a schematic animation of the mucociliary apparatus. Each ciliated cell may contain up to 200 cilia. The mucus is secreted by goblet cells. Note that there are two distinct mucus layers: the periciliary mucus layer that surrounds the cilia, and the mobile gel layer that lies on top of the periciliary layer. The cilia sweep back and forth, beating 12 to 15 times per second (In the video, the cilia have been deliberately slowed down to allow you to see the ciliary movements better). The so-called ‘effective stroke’ beats the cilia forwards; the cilia make contact with the overlying mobile gel layer and propel the mucus forward at a rate of several millimetres per minute. During the ‘recovery stroke,’ the cilia move back to their original position in the underlying periciliary fluid in order to minimise the drag on the overlying mobile gel layer travelling in the opposite direction. As there is a short lag phase between neighbouring cilia, the sequential actions of the recovery stroke result in the formation of a metachronal wave, which is essentially a ‘Mexican wave’ that travels in the opposite direction to the induced flow of mucus. (Bottier M, Peña Fernández M, Pelle G, Isabey D, Louis B, Grotberg JB, Filoche M. A new index for characterizing micro-bead motion in a flow induced by ciliary beating: Part II, modeling. PLoS Comput Biol. 2017 Jul 14;13(7):e1005552. doi: 10.1371/journal.pcbi.1005552).

Clearing the Lungs with Ciliogenesis
https://www.innovation.pitt.edu/innovations/clearing-the-lungs-with-ciliogenesis/

Lung Cilia, human origin
https://www.youtube.com/watch?v=LEE63XCFuoI

Overview

Pneumonia

Lung abscess

Lung abscesses may occur as a complication of typical bacterial pneumonia, mainly with infections caused by Staphylococcus aureus, Klebsiella pneumoniae or Streptococcus anginosus. However, most lung abscesses occur as complications of aspiration pneumonia and are typically caused by anaerobic bacteria from the mouth. Aspiration pneumonia typically occurs in persons with depressed levels of consciousness, such as may occur with alcohol intoxication, drug use or head trauma; the patients also commonly have periodontal disease such as gingivitis. Other, less common causes of lung abscess include airway obstruction (e.g. by a tumour or foreign body), infected (septic) emboli from infective endocarditis vegetations involving the right-sided heart valves (e.g. tricuspid valve) or haematogenous spread of pyogenic bacteria from other sites (e.g. pyaemic spread from bone with osteomyelitis). Penetrating lung injury (e.g. stab wound to the chest) is another possible cause. Complications of lung abscess include sepsis (most likely fatal complication), pyaemic spread to other organs (e.g. brain), sinus into the pleural cavity resulting in empyema thoracis, and bronchopleural fistula resulting in pyopneumothorax, the latter two of which are demonstrated in the Lung Abscess video.

Lung sounds

Crackles

Crackles (aka as rales or crepitations) are commonly heard on auscultation over consolidated lung segments in pneumonia. Crackles can be heard in many other respiratory disorders, including pulmonary oedema (e.g. due to congestive cardiac failure) and pulmonary fibrosis. Crackles are caused by an “explosive popping open" of small airways and alveoli that are collapsed by exudate (in the case of pneumonia) or transudate (in pulmonary oedema), or when “stiff” alveoli snap open in the case of pulmonary fibrosis. Crackles are much more commonly heard during inspiration than expiration.

Lung sounds available from https://meded.ucsd.edu/clinicalmed/lung.htm
Courtesy of Michael Wilkes, M.D. and Charlie Goldberg, M.D.

Bronchial breathing

Bronchial breath sounds are normally heard over large airways. Bronchial breathing over the peripheral lung fields is abnormal and is characteristically heard over consolidated lung parenchyma. When the lung becomes consolidated, air ceases to flow into the affected alveoli as these become filled with fibrinopurulent exudate. However, as sound travels better through solid tissue, consolidation results in increased sound transmission of the air entering and leaving the large airways, which is heard as bronchial breathing over the chest wall overlying the consolidated lung parenchyma. Compare bronchial breathing to the normal vesicular breath sounds in the Normal Lungs section.

Lung sounds available from https://meded.ucsd.edu/clinicalmed/lung.htm
Courtesy of Michael Wilkes, M.D. and Charlie Goldberg, M.D.

Normal CXR Lateral

0 Sternum

1 Heart

2 Right costophrenic angle

3 Left costophrenic angle

4 Thoracic vertebra

5 Hilar region

6 Trachea

7 Oesophagus

8 Scapula

Case courtesy of Dr Craig Hacking, Radiopaedia.org. From the case rID: 40794

Normal CXR PA

0 Right clavicle

1 Right 8th rib (posterior)

2 Right atrium

3 Left ventricle

4 Left costophrenic angle

5 Gastric bubble

6 Left hemidiaphragm

7 Aortic knuckle (distal aortic arch)

8 Descending thoracic aorta

9 Left hilum with left pulmonary artery

10 Right hilum with right pulmonary artery

11 Trachea

12 Right main bronchus

13 Spinous process, T1 vertebra

14 Coracoid process of left scapula

Part 1: Chest X-rays

CXR-1

The chest- X-ray shows widespread consolidation (seen as patchy opacity containing air-bronchograms) in the left upper lobe. Patchy consolidation is also present in the left lower zone.

For advanced learning only (you will not be examined on this): Sometimes it can be difficult to differentiate air space consolidation (fluid in the alveolar spaces) from atelectasis (lung collapse). Consolidation is opacity with air-bronchograms and implies an infective/inflammatory aetiology. Atelectasis is usually opacity with slight volume loss (volume loss is not always seen or difficult to delineate) and implies segmental/subsegmental collapse.

CXR-2

The chest- X-ray shows diffuse consolidation in the right mid to lower zone. Patchy consolidation is also present in the left lung, mainly around the hilum, together with patchy consolidation in the left lower zone.

Learning point: Please note that it can be hard to differentiate which lobe is affected on a single frontal chest X-ray; hence, when interpreting a chest X-ray, we often refer to 'zones' (e.g. upper, middle or lower zone) rather than ‘lobes.’ To help localise consolidation or collapse, we use the 'silhouette sign' where obliteration of the right hemidiaphragm suggests right lower lobe consolidation or obliteration of the right heart border suggests right middle lobe consolidation. We can also look for the relation of consolidation to the lung fissures. A lateral chest X-ray may be very helpful to localise the consolidation. For more information on the 'silhouette sign’ click here: https://radiopaedia.org/articles/silhouette-sign-x-rays

CXR-3

The chest- X-ray shows diffuse consolidation in the left lower lobe, as well as patchy consolidation in the left upper lobe, right hilum and right lower lobe.

Learning point: Strictly speaking, we would usually mention left upper ‘zone’ (rather than ‘lobe’) and right ‘basal zone’ (rather than right ‘lower lobe’); moreover, strictly speaking, the radiological changes in these areas are probably best described as hazy ‘opacity’ (rather than consolidation) as it is difficult to see ‘air-bronchograms’ in those areas (which you would need to qualify this as consolidation).

CXR-4

The chest- X-ray shows a thick-walled cavity in the mid to lower zone of the right lung containing an air-fluid level. The appearances are in keeping with a lung abscess. The presence of an air-fluid level suggests that the abscess has communicated with a bronchus.

Part 2: Macroscopic Lung Specimens

Left Lung

The specimen comprises a sagittal section of left lung, including the left upper lobe and lower lobe. There is a bronchopneumonia characterised by near-confluent consolidation of the left upper lobe (sparing only the apical portion). Small patchy areas of consolidation are also visible in the left lower lobe. An acute fibrinous pleuritis (pleurisy) is present along the visceral pleura in the oblique fissure.

Right lung

The specimen comprises part of the right lung, and includes the upper, middle and lower lobes. The lower lobe exhibits an almost uniform pale-grey consolidation that closely resembles the appearance of lobar pneumonia in the stage of grey hepatisation. The upper lobe shows multiple large areas of consolidation, which are also beginning to become confluent (bronchopneumonia).

Left lung

The specimen comprises part of the left lung. The lower lobe is uniformly consolidated (grey hepatisation) by lobar pneumonia. A possible area of consolidation is also discernible in the basal portion of the left upper lobe. There is a conspicuous acute fibrinous pleuritis (pleurisy) along the visceral pleura.

Right lung

The specimen comprises part of the upper lobe of the right lung, in the centre of which are two lung abscesses, the larger being 2.5cm in diameter. An abscess is a localised collection of pus, in this case in a cavity within the lung parenchyma.

Task 1

Case courtesy of Dr Hani Salam, Radiopaedia.org. From the case rID: 8755

XR-1

XR-2

Case courtesy of Dr Aneta Kecler-Pietrzyk, Radiopaedia.org. From the case rID: 53075

XR-3

Case courtesy of Dr Saikat Sarkar, Radiopaedia.org. From the case rID: 35156

XR-4

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