NIOSH SSS key terms

The total volume of air a person can blow out as forcefully and completely as possible after a full inhalation, measured in liters and reported at body temperature and pressure saturated (BTPS).

The volume of air exhaled during the first second of a forced expiratory maneuver, expressed in liters at BTPS; the most reproducible and widely used index of airflow obstruction.

The fraction of the forced vital capacity expelled in the first second, usually expressed as a percentage or decimal; a reduced value supports an obstructive pattern when compared with reference data.

The minimum requirements a single forced expiratory curve must meet, such as a good start, no cough in the first second, no glottic closure or leak, and a satisfactory end, before its values can be used.

The requirement that the two largest acceptable FVC and FEV1 values from a test session agree within a small fixed tolerance (typically 150 mL) so the reported result reflects consistent effort.

Conditions defining a complete blow: a plateau of at least one second with no further volume change, a forced expiratory time of at least six seconds (or reasonable duration in children), or the subject cannot continue.

The volume estimated by extending the steepest slope of the volume-time curve back to the start of exhalation; a large value signals a hesitant or slow start and can make a curve unacceptable.

Back-extrapolated volume expressed as a percentage of FVC; values above roughly 5 percent of FVC (or 150 mL, whichever is greater) indicate an unsatisfactory start to the maneuver.

A maneuver begun with a rapid, sharp rise in exhaled volume, showing peak flow and a steep volume-time slope with little hesitation, so that timed volumes are not underestimated.

The duration of the forced exhalation measured from the start of the maneuver; it is used to judge whether a plateau has occurred and whether the effort was sustained long enough.

A portion of the volume-time curve in which exhaled volume changes very little over at least one second, indicating the subject has emptied the lungs as far as possible.

The highest instantaneous flow achieved during a forced exhalation, read from the flow-volume curve; it depends heavily on effort and is not a reliable measure of obstruction on its own.

A graph plotting exhaled flow against volume; its shape helps identify a poor start, cough, glottic interruption, variable effort, or a characteristic pattern such as expiratory plateau in obstruction.

A graph plotting cumulative exhaled volume against elapsed time; it is used to judge start quality, plateau, forced expiratory time, and overall consistency of the maneuver.

The set of maneuvers performed during one visit, from which the best acceptable values are selected and which must satisfy reproducibility requirements before results are reported.

A single forced expiratory maneuver within a test session; typically at least three acceptable trials are needed, and testing continues until reproducibility is met or the subject cannot continue.

The standardized verbal encouragement and demonstration given during a maneuver, such as loud prompts to keep blowing, that improves effort without giving cues that alter the physiological result.

Showing the subject how to perform the maneuver, including posture, mouthpiece placement, full inhalation, and a hard blast, before asking them to attempt it themselves.

The complete sequence of inhaling fully, sealing the lips around the mouthpiece, and exhaling as hard and as long as possible while the spirometer records flow and volume.

The volume of air moved in or out during a normal quiet breath; it is used to check that the subject is breathing normally before the forced maneuver begins.

The largest volume exhaled during a slow, relaxed, complete exhalation after full inhalation; it can exceed FVC in some people and is used to detect air trapping or variable effort.

The change in FEV1 or FVC after inhaling a short-acting bronchodilator; a meaningful increase supports reversible airflow limitation but does not by itself confirm or exclude asthma.

A spirometric pattern in which the FEV1/FVC ratio is below the reference threshold, indicating reduced airflow out of the lungs, with severity graded by the FEV1 value.

A spirometric pattern suggesting reduced lung volumes, usually a low FVC with a preserved or high FEV1/FVC ratio; confirmation generally requires measurement of total lung capacity.

The fifth percentile of the reference population for a given measure; values below it are considered abnormal, avoiding the misclassification that fixed cutoffs cause across ages, sexes, and heights.

Predicted values derived from a defined healthy population, adjusted for factors such as age, height, sex, and ethnicity, against which a patient's measured spirometry is compared.

The structured process of comparing measured values with reference data, judging quality and reproducibility, and describing the pattern and severity in a report that answers the clinical question.

Clinical reasons to perform testing, such as diagnosing or monitoring asthma or COPD, evaluating unexplained breathlessness or cough, assessing preoperative risk, and screening people with occupational exposures.

Conditions in which testing should be deferred or avoided, such as recent myocardial infarction, pneumothorax, hemoptysis, unstable cardiovascular status, or active respiratory infection, because the effort could cause harm.

The pre-test check of identity, medical history, medications, recent illness, and contraindications, plus measurement of height and weight, done before any maneuver is attempted.

Practical steps before testing, including explaining the procedure, loosening tight clothing, removing gum or dentures if needed, correct upright posture, and a nose clip to prevent leakage.

Explaining the purpose, procedure, risks, and alternatives of spirometry and confirming the person agrees to proceed, documented according to local policy before testing begins.

A device placed on the nose during testing to prevent air escaping through the nostrils, which would otherwise reduce measured volumes and produce falsely low results.

Checking spirometer accuracy with a calibrated 3-liter syringe at several flow rates; measured volumes must fall within a small tolerance (commonly 3.5 percent) or the device needs service.

A precision 3-liter syringe used to deliver known volumes into the spirometer at low, medium, and high flows to verify that volume and flow measurements remain accurate over time.

The routine program of daily checks, calibration verification, biological control testing with a healthy staff member, and documentation that keeps spirometry results trustworthy and traceable.

Periodic testing of a healthy staff member whose results are tracked over time; a shift outside expected variability can reveal equipment drift or technique problems not caught by syringe checks.

The closeness of a spirometer's measured volumes and flows to true values, verified with a calibration syringe and maintained through service, leak checks, and attention to sensor condition.

A test for air escaping from the spirometer circuit, tubing, or mouthpiece seal; leaks cause falsely low volumes and must be corrected before participant testing proceeds.

The set of practices that reduce transmission of pathogens during spirometry, including hand hygiene, gloves, single-use mouthpieces and filters, and cleaning or disinfection of reusable components between participants.

A single-use device placed between the mouthpiece and the spirometer that traps microorganisms in exhaled air, protecting equipment and staff while adding minimal resistance to airflow.

Chemical or physical treatment that inactivates most pathogenic microorganisms on reusable spirometer parts; the level chosen depends on the device and on contact with mucous membranes or blood.

Cleaning hands with soap and water or alcohol-based rub before and after contact with participants or equipment; a basic, high-impact step in preventing cross-infection during testing.

Disposable gloves worn when handling mouthpieces, filters, or potentially contaminated surfaces; they supplement but never replace hand hygiene and must be changed between participants.

The tube the participant seals their lips around; it should be rigid, disposable or properly disinfected, and free of cracks so that no air leaks during the maneuver.

Retaining the curves, trial-by-trial values, calibration records, and interpretation in a retrievable form so results can be reviewed, audited, or compared with future tests.

Presenting the best acceptable values with predicted values, percent predicted, LLN, z-scores, a quality grade, and a clear interpretation so the referring clinician can act on the result.