Pulmonary function tests – what do they tell us?

If you’ve got asthma or have cared for a patient with chronic lung disease, you might be accustomed to pulmonary function tests (PFTs). As an intensive care unit nurse, I did not have much experience with PFTs; I knew ventilator disconnection protocols and had knowledge of tidal volumes, vital capability, and minute ventilation, but I didn’t have a deep understanding of PFTs and the way these tests are helpful in diagnosing respiratory disorders and tailoring treatment.

What are PFTs and what do they tell us?

PFTs are used to diagnose lung disease, discover potential causes of shortness of breath, determine whether a functional abnormality is obstructive or restrictive, assess the severity of lung disease, monitor the effectiveness of therapy (i.e., bronchodilators), lung function, and assess lung function before treatment. and after surgery (Lippincott Advisor, 2019; Smith et al., 2021). The most typical PFTs include spirometry, lung volume, and diffusing capability.

Spirometry

Spirometry measures the utmost volume of air displaced in a single breath as a function of time (Smith et al., 2019). Spirometry measurements include total air volume during forced expiration after maximal inspiration (FVC); the quantity of air exhaled with great force in the primary second of exhalation (volume of forced exhalation in a single second, FEV1₁); and FEV₁/FVC ratio. FEV₁The /FVC ratio is vital in identifying obstructive airway disease and restrictive airway disease. To ensure accuracy, spirometry is repeated at the least thrice (as much as eight attempts), with the examiner observing a pointy peak within the flow curve and an exhalation that lasts longer than six seconds.

• Normal or decreased FVC and decreased FEV1₁ causes a discount in FEV1₁/FVC, indication of obstructive airway disease (i.e. COPD or asthma).
• Decreased FVC and normal or increased FEV1₁The /FVC ratio suggests restrictive disease if related to reduced lung volume (Kaminsky, 2022).

A is performed when the air flow in spirometry is proscribed. In this test, spirometry is repeated after inhalation of a bronchodilator (i.e. 4 puffs of albuterol). The patient is assessed for improvement or reversibility, as evidenced by a rise in FEV1₁ or FVC greater than 12 percent and greater than 200 m L. If FEV₁ and FEV₁/FVC results return to normal, which regularly indicates asthma (Smith et al., 2019).

Lung volume

Lung volumes are obtained to enhance spirometry. Body plethysmography is used to evaluate lung volume; common measurements include total lung capability (TLC), the entire volume of the lungs at maximum inflation; functional residual capability (FRC), the quantity of air remaining within the lungs after normal exhalation; and residual volume (RV), i.e. the quantity of air remaining within the lungs after the tip of maximum forced exhalation.

• Decreased lung volume suggests restrictive disease if accompanied by normal or increased FEV1₁/FVC ratio.
• Increased lung volume suggests hyperinflation as a result of obstructive airway disease combined with decreased FEV1₁/FVC ratio.
• Concomitant restriction and obstruction will be identified when TLC and FEV1₁/FVC are reduced (Kaminsky, 2022).

Diffusion capability of the lungs for carbon monoxide (DL_CON)

Diffusion capability of the lungs for carbon monoxide (DL_CON) assesses gas exchange by measuring milliliters of carbon monoxide (CO) dispersed per minute through the alveolar-capillary membrane.

• Reduced DL_CON with restrictive disease indicates intrinsic lung disease.
• Normal DL_CON with restrictive disease indicates a reason for restriction apart from pulmonary.
• Significantly reduced DL_CON with obstructive airway disease indicates emphysema.
• Reduced DL_CON with normal lung volume, it indicates possible pulmonary vascular disease.

PFT Additions (Kaminsiky, 2022)

Exercise tests are used to evaluate shortness of breath and exercise intolerance. Three commonly used tests are the six-minute walk test (6MWT), the incremental shuttle walk test (ISWT), and the endurance shuttle walk test (ESWT). Combined with pulse oximetry, the 6MWT provides information on distance traveled and exercise desaturation. The ISWT is a 12-level test wherein the patient walks at a step by step increasing speed for 12 minutes over a distance of 10 meters. The test stops when the patient is out of breath, unable to take care of the required speed, or has accomplished 12 levels. In ESWT, the patient walks between two markers 10 meters apart. Speed ​​relies on ISWT test results and the patient walks until they will now not maintain the pace or after 20 minutes.

Assessment of oxygen saturation pulse (SpO₂) at rest or during exercise will be used to discover problems with gas exchange and to find out the quantity of oxygen needed to take care of adequate oxygenation. Arterial blood gas (ABG) may help confirm carbon dioxide retention, increased bicarbonate levels, and/or chronic hypoxemia. ABGs also help determine the degree of gas exchange disturbance in patients with low normal SpO₂ (i.e. lower than 92%).

Contraindications/adversarial events

PFTs may cause adversarial effects in patients with conditions which might be adversely affected by increased intracranial, abdominal, intrathoracic, or intraocular pressure (Smith et al., 2021). PFTs could also be contraindicated in patients with acute coronary insufficiency, angina, or recent myocardial infarction. Assess these high-risk patients for respiratory distress, changes in heart rate and blood pressure, cough, bronchospasm, and physical exhaustion.

Patient education

• Before PFT (Lippincott Advisor, 2019)
  • Do not smoke or vape 12 hours before the test.
  • Before the test, it is best to eat a lightweight meal and avoid drinking an excessive amount of fluid.
  • Wear loose, comfortable clothing.
  • Hold bronchodilators as described below (Kaminsky, 2022):
    • Before the test, short-acting inhaled beta agonists (i.e. albuterol, salbutamol) must be withheld for 4 to 6 hours.
    • Prior to testing, the short-acting muscarinic antagonist ipratropium must be held for 12 hours.
    • Withhold long-acting beta agonist bronchodilators (i.e., salmeterol, formoterol) for twenty-four hours prior to testing.
    • Withhold ultra-long-acting beta agonists (i.e., indacaterol, olodaterol, vilanterol) for 36 hours before testing.
    • Long-acting muscarinic antagonists, also called anticholinergics, must be used (i.e., glycopyrrolate [glycopyrronium]tiotropium, aclidinium and umeclidinium) for 36 to 48 hours before the test.
• During some tests, you might be fitted with a nose clip and given respiration instructions to take a deep breath after which exhale forcefully and repeatedly into the mouthpiece of the spirometer.

Kaminsky, D. A. (2022, March 29). A review of pulmonary function tests in adults. . https://www.uptodate.com/contents/overview-of-pulmonary-function-testing-in-adults

Lippincott Advisor (2019, October 4). Pulmonary function tests. Lippincott’s advisor. https://advisor.lww.com/lna/document.do?bid=30&did=815890

Smith, W., Chinnis, S., Durham, C., and Fowler, T. (2021). Pulmonary function test for primary care nurse. , (12), 14–20. https://doi.org/10.1097/01.NPR.0000798216.19617.e4