PFT
Spirometry
Spirometry is a common pulmonary function test (PFT) used to assess lung function. It measures the volume and flow of air that a person can inhale and exhale. Typically, it is used to diagnose respiratory conditions such as Chronic Obstructive Pulmonary Disease (COPD), asthma, and pulmonary fibrosis, as well as to monitor these conditions over time.
A device called a spirometer is used to record the volume of air exhaled and the speed of exhalation.
- The patient wears a nose clip and breathes into a mouthpiece connected to the spirometerspirometry.
- The test involves several breathing exercises, from maximum inhalation to forceful, sustained exhalation, usually lasting at least 6 seconds.
- To ensure consistency, the test is repeated multiple times.
- Diagnosing and managing lung disorders
- Assessing symptoms of breathlessness and distinguishing between respiratory and cardiac causes
- Monitoring lung function over time in conditions like occupational asthma
- Preoperative risk assessment for patients undergoing anesthesia or surgery
Spirometry is sometimes supplemented with additional tests to assess airway responsiveness or with a bronchodilator test to evaluate the reversibility of airflow obstruction. These tests are invaluable for diagnosing, managing, and tracking conditions and informing treatment decisions.
- Results can vary based on the patient’s cooperation, age, and any mental or physical impairments.
- Intermittent or mild asthma may show normal results if testing is conducted outside of an exacerbated state.
Forced Oscillation Technique (FOT)
The Forced Oscillation Technique (FOT) is a non-invasive method used to assess respiratory mechanics by applying small pressure oscillations during normal breathing. FOT has shown proven results in both clinical and research settings, as it requires minimal patient cooperation and does not alter airway smooth muscle tone, unlike spirometry.
Bronchodilation Sensitivity
While results may vary, FOT has shown promising outcomes in assessing bronchodilation, especially in pediatric cases.
Airway Obstruction Detection
This technique is particularly useful for children and those with bronchial hyperresponsiveness, as it does not require a deep breath.
Field and Epidemiological Studies
The simplicity and minimal cooperation required make FOT ideal for large population studies or for patients who are unable to perform complex maneuvers.
FOT technology is expanding its clinical applications beyond traditional uses. It is now being utilized to monitor respiratory mechanics during mechanical ventilation and sleep, offering valuable insights that support patient care.
While FOT is a valuable tool for assessing respiratory function, it may not fully capture the complex nature of the respiratory system, especially regarding its non-linear properties. This limitation often arises from its reliance on small oscillations, which can restrict the range of mechanical properties it can evaluate. However, its non-invasive nature makes it a versatile and useful tool in respiratory medicine.
Body Box Plethysmograph
Body Box Plethysmography also known as Pulmonary Plethysmography or Body Plethysmography, is a lung function test. Usually this test is considered to measure the volume of air in the lungs. The reason this procedure is named ‘body box plethysmography’ is, it is conducted in a sealed chamber.
Body Box Environment: The test subject enters a see-through plastic box, approximately the size of a small telephone booth, where machines measure lung function.
Initial Exhalation: At the end of normal expiration, the mouthpiece is closed.
Inspiratory Effort: The patient is then asked to make an inspiratory effort, and the machines measure the volume of air entering and leaving the lungs.
Body Plethysmography assesses lung function by determining:
Tidal volume (TV): the amount of air in the lungs after a deep breath
Residual volume (RV): the amount of air left in the lungs after exhaling as much as possible
This test helps diagnose and monitor respiratory conditions, such as asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis.
Body Plethysmography is a safe test, but deep breathing during the procedure may cause temporary lightheadedness or dizziness.
Diffusing capacity for carbon monoxide
Diffusing Capacity for Carbon Monoxide (DLCO) is a medical test that measures the ability of the lungs to transfer oxygen into the bloodstream. This test is a key indicator of lung function and is used to diagnose and monitor various pulmonary disorders. DLCO is usually expressed in mL/min/mm Hg or mmol/min/kPa, representing the volume of carbon monoxide transferred per minute for each unit of pressure difference across the available gas exchange surface in the lungs.
Understanding DLCO Readings Here is a guide to interpreting DLCO levels:
– Mild: >60% predicted DLCO
– Moderate: 40-60% predicted DLCO
– Severe: <40% predicted DLCO
DLCO Evaluation Applications DLCO is useful for assessing patients with,
-Dyspnea (shortness of breath)
-Hypoxemia (low oxygen levels in the blood)
-Emphysema
-Interstitial Lung Disease (ILD)
-Idiopathic Pulmonary Fibrosis (IPF)
DLCO can serve as an early indicator for conditions like IPF before spirometric changes appear, aiding in diagnosis, tracking disease progression, and evaluating response to therapy.
- Atmospheric pressure and/or altitude
- Hemoglobin levels
- Carboxyhemoglobin levels
- Age and sex
Reference Values Until 2017, there were no widely recognized reference values for DLCO. Currently, instrument manufacturers consider 80%-120% as the normal range.
A DLCO reading of <60% is generally considered a poor prognosis indicator for lung cancer resection. The test also assists in treatment decisions and in monitoring the response to therapy in patients with chronic lung diseases.