Investigations of Respiratory System

A- Imaging Plain CXR A PA film provides information on the lung fields , heart ,mediastinum , vascular structures and the thorathic cage. additional information can be obtained from a lateral film. Structures of CXRs 1- Trachea , that should be central 2- Mediastinum, can be widened in many diseases like ( retrosternal goiter, Lymph nodes enlargement, aortic aneurysm and oesophageal dilatation) 3- The diaphragm , Rt side is usually slightly higher than the Lt side.

Causes of raised hemi diaphragm; collapsed lungs , phrenic nerve palsy, hepatomegaly and sub phrenic abscess) 4- Hila, Lt hilum is higher than the Rt hilum, and hila can be pulled up and down by fibrosis or collapse. 5- Bone and soft tissues 6- Lung fields, shadows can be divided in to; Nodular shadows; could be due Neoplasis ( primary lung Ca, metastasis, or adenoma) Infection ( pneumonia, hydatid cyst) Granuloma ( TB, sarcoidosis)

Reticular shadow; usually due to acute interstitial changes (cardiac or non cardiac). e.g pulmonary fibrosis. Alveolar shadow; usually due to pulmonary oedema , but could be due to ARDS, drugs, smoke inhalation.

CT scan It is superior to CXR in determining the position and size of a pulmonary lesion and whether calcification or cavitations is present. It is now routinely used in the assessment of patients with suspected lung cancer and facilitate guided percutaneous needle biopsy. HRCT (high resolution), that uses thin section to provide a detail assessment of pulmonary parenchymal diseases ( interstitial lung disease , bronchiectasis)

Ultra sound of chest cavity; is sensitive to detect plural effusion , may also be used to improve the diagnostic field of plural biopsy. Ventilation – perfusion scan; the main value of this technique is to detect pulmonary thrombi or embolism, a filling defect in the perfusion scan accompanied by preserved ventilation is highly suggestive of recent PE.

Positron Emission Tomography PET scan; In new technology to investigate pulmonary nodules , staging of mediastinal lymph nodes and distal metastasis. CT- pulmonary angiography Is widely available and gold standard to diagnose PE.

B- Endoscopic Examinations; Laryngoscopy; larynx may be inspected directly with a mirror or indirectly with a laryngoscope. Bronchoscopy; The trachea , large bronchi and lung segments can all be inspected by either flexible or rigid bronchoscope. Diagnostic indication of flexible bronchoscopy; Suspected cases of Lung ca, slowly resolving pneumonia, pneumonia in the immunocompramised patients, interstitial lung disease, and collecting lavage for AFB and culture in suspected cases of TB , with –ve sputum.

Mediastinoscopy; Through a small incision at the supra sternal notch under GA, to get an access to the mediastinum. C- Other investigations Plural aspiration and biopsy. Sputum examination , for microbiological ( AFB, Culture, Gram stain ) and cytological examinations Pulse oximetry Allow a non invasive assessment of peripheral O2 saturation, it provides a useful tool for monitoring those who are acutely ill or at risk of deterioration.

Peak expiratory flow rate (PEF). Is measured by a maximum forced expiration through a peak flow meter , it should be monitored regularly in asthmatic patients monitor response to therapy and disease control. Arterial blood gas analysis It is heparinized blood taken from , the radial , brachial and femoral arteries to check, PH, PaO2, PaCO2 and HCO3. Type I respiratory failure; PaO2 < 8Kpa , PaCO2 either Normal or reduced.( hypoxia only), PH is normal. Type II respiratory failure ; PaO2 < 8Kpa , PaCO2 >6Kpa ( hypoxia and hypercapnia), PH could be normal , high or low.

Pulmonary Function Tests. Are used to aid diagnosis, assess functional impairments and monitor treatment or progression of diseases. Abbreviations used in RFT FEV1 forced expiratory volume in 1 second FVC forced vital capacity VC vital capacity TLC total lung capacity FRC function residual capacity RV residual volume TLco Gas transfer factor for carbon monoxide Kco Gas transfer per unit lung volume.

FEV1 is disproportionately reduced in obstructive lung disease ( asthma, COPD, bronchial obstruction) and the ratio of FEV1/ VC will be <70%. When there is an airflow obstruction the test should be repeated following administration of inhaled or nebulised B2 agonist ( salbutamol) to see the reversibility to normal or >15% that would give the diagnosis of asthma . FEV1 and VC will both reduce in restrictive lung disease (Pulmonary Fibrosis) that will make the FEV1/VC ratio , >80%.

Flow volume loop , measures flow at various lung volumes , characteristic patterns are seen in intra thorathic airway obstruction like ( asthma , Emphysema), and extra thorathic airway obstruction( tracheal stenosis). Lung volume can be measured by dilution of inhaled gas ( usually helium), or by determining the pressure / volume relationship of the thorax by body plethysmography. Lung volume increases in obstructive diseases and decreases in restrictive diseases.

The gas transfer across the alveoli can be calculated by measuring carbon monoxide uptake from a single inspiration in a standard time ( usually 10 seconds) ,it is low in emphysema and lung fibrosis ( obstructive and restrictive ) , but very high in pulmonary haemorrhage.