How do you assess lung function and structure?

Comprehensive Lung Assessment: Structure and Function

The most effective approach to assess lung function and structure combines traditional physical examination techniques (inspection, palpation, percussion, and auscultation) with objective measurements like spirometry, supplemented by advanced imaging when necessary to evaluate morbidity, mortality, and quality of life outcomes.

Physical Examination Components

Inspection

• Observe the patient's breathing pattern, respiratory rate, use of accessory muscles, chest wall shape, and any visible abnormalities that might indicate respiratory distress 1
• Note chest wall symmetry during respiration and any signs of barrel chest (indicative of hyperinflation) 2
• Assess for cyanosis, clubbing of fingers, and general appearance that might suggest chronic respiratory disease 3

Palpation

• Evaluate chest expansion bilaterally to assess for symmetry of respiratory movements 1
• Assess for tactile fremitus (vibration felt when patient speaks), which may be increased with consolidation or decreased with pleural effusion or pneumothorax 2
• Palpate for any areas of tenderness or abnormal masses 3

Percussion

• Perform percussion in a systematic manner across all lung fields to identify areas of dullness (suggesting consolidation or pleural effusion) or hyperresonance (suggesting emphysema or pneumothorax) 1
• Compare percussion notes between corresponding areas on both sides of the chest 2
• Document any abnormal percussion findings that may indicate underlying pathology 3

Auscultation

• Listen systematically to all lung fields during both inspiration and expiration using the diaphragm of the stethoscope 2
• Identify normal vesicular breath sounds versus abnormal sounds such as crackles, wheezes, rhonchi, or pleural rubs 1
• Note any areas of diminished or absent breath sounds, which may indicate airway obstruction, pleural effusion, or pneumothorax 3

Objective Measurements

Spirometry

• Measure forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and the FEV1/FVC ratio to assess for obstructive or restrictive patterns 4
• Use spirometry for patients aged 40+ who smoke, or those with unexplained dyspnea, cough, wheezing, or excessive mucus production 4
• Monitor response to therapy in conditions like asthma, where improvements in FEV1 can be seen within 5 minutes after bronchodilator administration 5

Advanced Lung Structure Assessment

• For detailed structural assessment, use computed tomography (CT) which can provide quantitative data on air and tissue volumes, correlating significantly with histomorphometric estimates 6
• Consider multidetector computed tomography (MDCT) for reconstructing airways and blood vessels, which can identify the first 6-10 bronchial generations 6
• For highest resolution assessment, micro-CT can be used (primarily in research settings) to achieve 1-2 μm resolution for detailed structural analysis 6

Comprehensive Lung Volume Measurement

Clinical Methods

• Measure lung volume through techniques such as:
  • Saline immersion method: immersing the lung in saline and measuring volume displacement 6
  • Cavalieri method: serially slicing the lung at constant thickness and using point counting on cut surfaces 6
  • Radiologic imaging: using CT or MRI for in vivo volume assessment 6

Functional Assessment

• Evaluate the diffusing capacity of the lung, which depends on alveolar capillary blood volume, intra-acinar alveolar and capillary surfaces, and the harmonic mean air-blood barrier thickness 7
• Assess the air-blood barrier, which consists of alveolar epithelium, capillary endothelium, and their shared basement membrane 7

Combined Approach Benefits

• Using both spirometry and lung sound analysis significantly increases sensitivity for detecting pulmonary diseases compared to using either method alone (increasing from 71% to 87%) 8
• Combining physical examination with objective measurements provides early detection of lung abnormalities that may not be evident through a single assessment method 8
• This comprehensive approach allows for monitoring disease progression and treatment response over time 4

Structural Considerations

• Remember that the lung connects a small entrance to a massive alveolar gas exchange surface through sequential, irregular, dichotomous branching patterns 7
• Only 10-15% of lung volume consists of tissue and blood, while the remainder is air space designed to optimize gas exchange 7
• The airway tree follows a dichotomous branching pattern with the trachea as generation 0, where the number of branches in generation Z equals 2^Z 7