Pulmonary Function Test & Spirometry
PULMONARY FUNCTION TESTS
Pulmonary function tests (PFTs) are a series of different breathing tests done by a trained pulmonary function technologist to learn about the lung health. It is also sometimes referred to as Spirometry.
Spirometry measures how much air a patient can inhale and exhale and how fast they can exhale. It is an objective measurement used for diagnostic evaluation.
Key measurements obtained by spirometry are:
1. (FVC) Forced vital capacity: The maximum amount of air that can be forcefully exhaled after a maximal inspiration. A decreased FVC may also indicate a restrictive pattern.
2. FEV1: The forced expiratory volume in one second. The degree of obstruction is determined by changes in the FEV1.
3. FEV1/FVC%: The forced expiratory volume in one second as a percent of the FVC. When the FEV1 and FEV1/FVC% are decreased, it is an indication of airway obstruction.
4. Peak Expiratory Flow (PEF) or Peak Flow (PF): It is the maximum flow achieved at the beginning of the FVC maneuver, but is patient effort dependent.
How is spirometry performed?
1. After informed consent and proper explanation and demonstration of proper technique, the patient takes a maximal deep breath. The patient then exhales forcefully and completely without hesitation for a prolonged period of time into a properly calibrated measuring device (Pneumotach).
2. The patient is usually asked to repeat the maneuver until three acceptable efforts are obtained, which consequently means that a patient might have to perform the procedure almost 5 to 8 times.
Other Pulmonary Function Tests (PFTs)
To differentiate between obstructing and restrictive patterns, lung volumes must be measured. The three most commonly used methods for measuring lung volumes are:
• Body Box – It is also known as plethysmography. It is performed while sitting in an enclosed clear chamber with performance of series of very small panting breaths. This is considered to be the most accurate way to measure lung volumes.
• Helium dilution – Done by normal breathing of gas, a mixture of helium and oxygen.
• Nitrogen Washout – Done by normal breathing of pure oxygen while exhaled gas is collected and analyzed.
Diffusing Capacity (DLCO)
Diffusing capacity of the lungs measures how well gases such as oxygen move from the lungs in to the blood.
Below is a list of few common abbreviations used in Pulmonary Function tests.
DLCO - Diffusing capacity of the lung; the capacity of the lungs to transfer carbon monoxide (mL/min/mm Hg)
DLCOc - The DLCO adjusted for hemoglobin (mL/min/mm Hg)
DLVA - The DLCO adjusted for volume (mL/min/mm Hg/L)
DLVC - The DLCO adjusted for both volume and hemoglobin (mL/min/mm Hg/L)
ERV - Expiratory reserve volume; the maximum volume of air that can be exhaled from the end-expiratory tidal position (L)
FET - Forced expiratory time; the amount of time the patient exhales during the FVC maneuver (seconds)
FEV1 - Forced expiratory volume in 1 second; volume of air forcibly expired from a maximum inspiratory effort in the first second (L)
FEV1/FVC ratio - Ratio of FEV1 to FVC. It is used to determine if the pattern is obstructive, restrictive or normal.
FRC - Functional residual capacity; the volume of air in the lungs following a tidal volume exhalation = ERV + RV (L)
FVC Forced vital capacity; the total volume that can be forcefully expired from a maximum inspiratory effort (L)
IC Inspiratory capacity; the maximum volume of air that can be inhaled from tidal volume end-expiratory level; the sum of IRV and VT (L)
IRV Inspiratory reserve volume; the maximum volume of air that can be inhaled from the end-inspiratory tidal position (L)
LLN Lower limit of normal; the lowest value expected for a person of the same age, gender, and height with normal lung function
PEF Peak expiratory flow; the highest forced expiratory flow (L/second)
RV Residual volume; the volume of air that remains in the lungs after maximal exhalation (L)
TLC - Total lung capacity; the total volume of air in the lungs at full inhalation.
TV or VT - Tidal volume; the volume of air that is inhaled or exhaled with each breath when a person is breathing at rest (L)
VC - Vital capacity; the maximum volume of air that can be exhaled starting from maximum inspiration, TLC can be measured either as slow vital capacity
(SVC) or forced vital capacity (FVC)
Pulmonary Function Test & Spirometry