A Pulmonary Function Test (PFT) is a non-invasive procedure that measures how well the lungs take in air, transfer oxygen, and move air out. These assessments, which often include spirometry, provide objective data on lung capacity and airflow to help diagnose and monitor conditions like asthma or Chronic Obstructive Pulmonary Disease (COPD). To ensure the measurements accurately reflect the lung’s true function, proper preparation is necessary. Preparing correctly means understanding and following specific guidelines regarding food, drink, medication, and physical activity leading up to the scheduled appointment.
Guidelines for Eating and Drinking
You should generally avoid consuming a large meal within two to three hours before a PFT. This restriction is in place because a full stomach expands and can press upward against the diaphragm, which is the primary muscle responsible for breathing. This pressure limits the diaphragm’s downward movement, preventing a full inhalation and potentially restricting the maximum lung volume that can be measured during the test.
High-fat meals should also be avoided because they require more oxygen for digestion, which may temporarily alter respiratory patterns. Light snacks, such as yogurt or fruit, may be permissible closer to the test time. It is also recommended to avoid alcoholic beverages for at least four to eight hours before the test, and some guidelines suggest abstaining for a full 24 hours.
Beverages containing caffeine, such as coffee, tea, and energy drinks, should be restricted on the day of the test. Caffeine acts as a mild bronchodilator, which may artificially open the airways and interfere with baseline measurements. Caffeinated drinks may also increase heart rate and breathing patterns, further skewing the results. Water intake is usually permitted and encouraged to maintain hydration, provided it is not consumed in excessive amounts immediately before the test.
Medications and Other Substances to Avoid
Careful consideration must be given to medications that chemically affect the airways. Bronchodilators, used to open the breathing tubes, must often be withheld for a specific period before the test to measure the patient’s baseline lung function without interference. The exact withholding time depends on the medication’s duration of action.
Short-acting beta agonists (SABAs), such as albuterol, are generally stopped four to six hours before the PFT. Longer-acting medications, including long-acting beta agonists (LABAs) or long-acting muscarinic antagonists (LAMAs), require a much longer cessation period, often ranging from 12 to 48 hours. For instance, ultra-long-acting agents may need to be stopped 36 hours before the test to ensure accurate measurements.
Other substances can also affect test results, including all forms of tobacco and nicotine products (cigarettes and vaping devices). Smoking should be avoided for at least six hours before the test, as it irritates the airways and can reduce measurements like the Forced Expiratory Volume in one second (FEV1). Antihistamines might also need to be withheld, sometimes for up to 48 hours before the procedure. Patients must confirm the precise holding instructions for all inhaled and oral medications with the ordering healthcare provider.
Ensuring Physical Readiness
Physical preparation is important for obtaining accurate PFT results. Patients should wear comfortable, loose-fitting clothing that does not constrict the chest or abdomen. Tight garments, belts, or restrictive waistbands can physically impede the ability to take the deep, full breaths required during the testing maneuvers.
Patients should avoid strenuous physical activity or vigorous exercise for at least 30 minutes to one hour before the appointment. Intense exertion can temporarily alter respiratory parameters and cause fatigue, making the required forced breathing more difficult. The respiratory system needs to be at a relaxed, resting baseline for the measurements to accurately reflect typical lung function.
It is advised to postpone the PFT if the patient has had a recent upper respiratory infection, such as a cold or the flu. Illness symptoms, including congestion or a productive cough, can significantly affect the ability to perform the test maneuvers correctly and may lead to inaccurate results. Minimizing anxiety also contributes to a better outcome, as anxiety can lead to rapid or shallow breathing that interferes with the measurements.