Description
Lung function tests, also known as pulmonary function tests, can help diagnose and monitor lung conditions such as asthma, chronic obstructive pulmonary disease (COPD), and lung fibrosis. The most common lung function tests include spirometry, which measures lung capacity and flow, and diffusing capacity, which measures the ability of the lungs to transfer oxygen into the bloodstream. They are usually interpreted in conjunction with other clinical information, such as symptoms, medical history, and a physical examination. A decrease in any of these values, or a decrease in the ratio of FEV1 to FVC, can indicate a lung condition such as COPD or asthma.
Summary Listen
- Pulmonary Function Tests (PFTs) are non-invasive assessments used to diagnose, evaluate, and monitor respiratory conditions. These tests provide insights into the respiratory system, including large and small airways, pulmonary parenchyma, and capillary beds. PFTs measure lung volumes, capacities, airflow rates, gas exchange efficiency, and oxygen-carbon dioxide levels.
- Indications for PFTs include persistent cough, breathlessness, abnormal chest auscultation findings, and abnormal chest X-rays. PFTs are also used in patients with connective tissue disorders, neuromuscular diseases, asthma, COPD, interstitial lung disease, and pulmonary vascular disease. Pre-operative evaluations for surgeries affecting the lungs and monitoring of individuals exposed to toxins or radiation also necessitate PFTs. Post-lung transplant surveillance relies on PFTs to detect rejection, infection, or obliterative bronchiolitis.
- Common types of PFTs are spirometry, lung volume measurement via body plethysmography, gas diffusion studies, cardiopulmonary exercise testing (CPET), pulse oximetry, and arterial blood gas (ABG) analysis. Spirometry measures how quickly air can be moved in and out of the lungs. Lung volume measurement assesses the total amount of gas the lungs can hold at various inflation states. Diffusion studies evaluate gas exchange across the alveolar membrane.
- Spirometry, a widely used PFT, assesses the integrated mechanical function of the lungs, chest wall, respiratory muscles, and airways. It measures the forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and the FEV1/FVC ratio. Acceptable spirometry requires at least three repeatable tests with FVC and FEV1 values within 150 ml of each other.
- Respiratory disorders are classified as obstructive or restrictive. Obstructive disorders, like asthma and COPD, narrow airways and hinder airflow out of the lungs, resulting in reduced FEV1 and an FEV1/FVC ratio below 70%. Restrictive disorders, like pulmonary fibrosis, reduce lung volume and compliance, leading to decreased FVC, while the FEV1/FVC ratio is typically above 70%. Bronchodilator testing helps diagnose asthma by assessing the reversibility of airway obstruction.
- Peak flow meters are portable devices for asthma patients to monitor their airway function. They measure the peak expiratory flow rate (PEFR) and help patients manage their condition at home. Readings are categorized into green, yellow, and red zones, guiding medication adjustments and when to seek medical attention. Peak flow measurements assist in diagnosing asthma, monitoring disease progression, and enabling self-management.
- Other PFTs, such as body plethysmography, determine lung volumes and capacities using Boyle's law. Gas diffusion studies assess alveolar membrane integrity by measuring the diffusion of gases. CPET measures exercise tolerance by assessing oxygen uptake, heart rate, and cardiac output during exercise. Potential risks of PFTs include dizziness, shortness of breath, cough, and asthma attacks. Contraindications include recent myocardial infarction, unstable angina, recent surgeries, and pneumothorax.
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