Respiratory

Patterns of lung disease

Basics

Introduction

  • Understanding the patterns will make everything much easier. Not all patients and their diseases fit nicely into discrete categories but the differentiation into restrictive and obstructive is useful and is applicable to many respiratory illnesses

Spirometry/Pulmonary function testing

  • Tidal volume : volume of air shifted per normal quiet breath
  • FEV1.0 : amount of air expelled in the first second from a forced expiration at maximal inspiration
  • FVC : amount of air that can be expelled in a single breath
  • Residual volume : the volume of air remains in the lungs after full expiration. Can only be measured indirectly using total body plethysmography or helium dilution.
  • PEFR : the maximum rate at which air can be expelled from the lungs and used as a simple guide often in asthma to airways obstruction

Pulmonary function testing caveats

  • These measurements are dependent on the patient giving their best effort and the less the patient tries the worse the values
  • This can lead to misdiagnosis and overtreatment in the less compliant patients.
[picture of spirometry showing FEV and FVC]

Restrictive vs Obstructive

Restrictive:  Think of it as the Lungs getting smaller and stiffer

  • A diffuse parenchymal disease, Fibrosing lung disease
  • Reduced Vital capacity, Reduced FEV1, FEV/FVC normal, Reduced Transfer factor
  • CXR shows lung fibrosis
  • Type 1 Respiratory failure
  • Cyanosed, insp crackes, breathless, small poorly explanding lungs

Obstructive

  • An airways rather than parenchymal problem
  • Expiratory airways obstruction
  • Normal/increased Vital capacity, Reduced FEV1.0, Reduced FEV/FVC
  • CXR - Hyperexpanded lungs
  • Transfer factor reduced with emphysema
  • Type 1 and later disease Type 2 Respiratory failure
  • Pursed lips breathing, intercostal recession, breathless, hyperinflated "barrel" chest, loss of cardiac dullness

Investigations

Flow volume loops

  • Involves a subject taking a full inspiration and then full expiration. The plot is of flow vertically against lung volume horizontally.
  • Inspiration (negative flow) is below the line is semicircular in shape
  • Expiration (positive flow) is above the line and is a left slanted triangle
  • Expiratory obstruction such as COPD the loop below the line is unchanged but there is a rapid fall in expiratory flow rates as volume increases
  • In restriction the flow rates remain the same but the volumes on the x axis contract ?small lungs?.
[picture of flow volume loops]

Transfer Factor (TLCO/DLCO)

Introduction

  • Assesses pulmonary gas exchange
  • No smoking for 6 hours then inhale and hold air with (a very small concentration of) Carbon monoxide for 10 seconds
  • Measure CO content in expired air. Gives and idea of gas extraction as CO avidly bound to Hb (x270 times O2 binding)

A reduced DLCO is seen with

  • Emphysema
  • Idiopathic pulmonary fibrosis
  • Pulmonary oedema, Anaemia, Smoking
  • Wegener's Granulomatosis

Increased DLCO

  • Polycythaemia
  • Pulmonary haemorrhage
  • Left to right intracardiac shunts
  • Exercise
  • Asthma

Diffusion coefficient (KCO)

  • This divides the TLCO by the alveolar volume and so adjusts for smaller lungs.
  • Increases the abnormal results in emphysema as lung volume is large

Imaging in chest disease

  • CXR - see below
  • High resolution CT scan (HRCT)
    • HRCT has become one of the cornerstones of the management of pulmonary disease
    • Scanners now are faster and provide better resolution and diagnostic quality is better
    • Interventional radiologists can use them to guide the biopsy of lesions or insertion of drains etc
    • In a suspected lung tumour the liver and adrenals and sometimes brain can also be screened
    • CT-PA in which IV contrast is given at the same time is becoming the standard test for pulmonary embolic disease
  • PET scanning
    • Used to look for evidence of tumours and metastatic disease for tumour staging
    • Shows areas of increased metabolic activity using radiolabelled glucose as the metabolite under study.
  • MRI scan
    • Limited improvements over HRCT

Bronchoscopy

  • Examination of the upper airways and trachea and proximal branches of the trachea through and endoscope
  • Rigid and flexible scopes can be used - smaller endoscopes are now passed through the nose
  • This can be done under local anaesthetic and sedation and can be used diagnostically and therapeutically
  • Useful diagnostically to identify causes of haemoptysis and suspected lung tumours or for certain infections
  • Can also be used to remove obstructed material from foreign bodies to sputum plugs
  • Endobronchial tissue can be biopsied and Bronchoalveolar Lavage can be undertaken
  • More and more techniques are being identified
  • Patients are usually fasted before hand and clotting checked before hand and any coagulopathy reversed
  • Constant monitoring is needed throughout. Recognised complications include Pneumothorax,hypoxia, epistaxis.

CXR interpretation

Procedure

  • Check name, dob, date of CXR
  • Check orientation - markers for left/right
  • Check if AP or PA film (should be marked).
    • PA means X-rays pass from behind onto a radiographic plate against the patient's sternum. It is the best CXR to get.
    • AP means X -Rays pass from front to back and plate is behind patient and often done on ward or in extremis. Get a PA later if possible
  • See if it erect or supine and check rotation by comparing medial ends of clavicle
  • Adequate penetration should enable vertebral bodies to be well seen

Findings

  • Female - look for breast shadow and more importantly absence of one due to mastectomy
  • Lung fields - look for vascular markings. Absence of any markings at periphery look for a Pneumothorax
  • Describe lesions as upper zone, mid zone and lower zone and then go on to decide if you can identify lobe involved though a lateral may well be needed for this

Check

  • Heart size (less than 50% lateral diameter) and look for retrocardiac shadow
  • Mediastinum - enlarged, hilar nodes
  • Trachea - position
  • Apices - malignancy (pancoast), TB
  • Hilar - enlarged suggests infection, sarcoid, TB
  • Lung fields - describe what you see in lower zone, mid zone, upper zone. Is there the edge of a pneumothorax with absent vascular lung markings.
  • Diaphragm - elevated
  • Soft tissues - breast shadows ? mastectomy
  • Tubes - Endotracheal tube, NG tube (is it in airways (trachea) rather than (midline) oesophagus) , Tracheotomy tube, Central line, Pacemaker, ICD

Chest cavitation

  • Tuberculous and Atypical TB
  • Lung abscess
  • Wegener's granulomatosis
  • Malignancy - squamous cell, Melanoma, Cervical carcinoma, Sarcoma metastasis
  • Rheumatoid lung (Caplan's syndrome)
  • Vascular/septic emboli and abscess formation
  • Other infections TB (cavities suggests active disease and infectivity)
  • Fungal infections (coccidio, aspergillosis, cryptosporidium, nocardia)
  • Bacterial (esp. GNR, staph, strep) ,
  • Hydatid cyst
  • Congenital lesions, such as a bronchogenic cyst or communicating sequestration

Normal CXR despite breathless ill patient (useful list)

  • Asthma, COPD
  • Pulmonary embolism
  • Early pneumonia
  • Pneumocystis pneumonia - looks like LVF
  • Left lower lobe collapse
  • Fume inhalation but may develop ARDS with LVF picture
  • Diabetic ketoacidosis

Common CXRs in the exam

  • Lobar Consolidation
  • Pneumothorax
  • Pulmonary oedema
  • Fibrosing lung disease
  • Pleural effusion
  • Lobar Collapse
  • Pneumonectomy
  • Neoplastic lesion - mass
  • Tuberculosis
  • Hilar enlargement
  • NG tube in oesophagus or bronchus
  • Central line / Pacemaker
  • Endotracheal tube