CPFT key terms

Height measured with the patient barefoot, heels together, back against a vertical surface, and head in the Frankfort plane. It is combined with age and sex to select predicted values; arm span is substituted when height cannot be measured reliably.

Reference values derived from healthy people of similar age, sex, height, and ethnicity. They define the expected normal range used to interpret a patient's measured spirometry, lung volume, or diffusing capacity results.

The fifth percentile of values from a healthy reference population. Results below it are considered abnormal; it is preferred over a fixed 80% of predicted because it accounts for normal population variability.

Conditions in which forced breathing maneuvers risk harm, such as recent myocardial infarction, pneumothorax, recent eye or chest surgery, unstable cardiovascular disease, or active hemoptysis. These are screened for before testing begins.

Having patients stop bronchodilators for a set period before testing so results reflect baseline function. Typical intervals are 4 to 6 hours for short-acting and 12 or more hours for long-acting agents, following laboratory protocol.

Spirometry repeated after inhaling a bronchodilator, commonly 400 mcg of albuterol, after waiting about 10 to 15 minutes. Comparing it with baseline shows whether airflow obstruction is reversible.

Body temperature (37 degrees Celsius), ambient barometric pressure, and gas fully saturated with water vapor. Spirometry and lung volume results are corrected to these conditions so reported volumes reflect what occupies the lungs.

A precision syringe, usually 3 liters, that delivers a known volume to a spirometer. Comparing measured with delivered volume verifies that the device's volume and flow readings remain accurate.

A check for air escaping from tubing, valves, or the plethysmograph cabinet before testing. Leaks cause falsely low or unstable volumes, so systems are tested and repaired as part of routine quality control.

Confirming that a spirometer reads accurately across a range of volumes and flows, not just at one value. A syringe is emptied at different speeds and volumes, and each result must fall within the accepted tolerance.

A healthy staff member performs the same test repeatedly over weeks or months. Stable results suggest equipment and technique are consistent, while a sudden change signals possible device drift or calibration problems.

Setting the zero and span points of analyzers that measure carbon monoxide, helium, or other test gases, using known reference gases. This ensures reported concentrations are accurate during diffusing capacity and lung volume testing.

A device with a known, fixed diffusing capacity used to check the performance of the DLCO system. Testing it periodically confirms that analyzers, timing, and volume measurements still produce accurate results.

The greatest volume of air a person can exhale forcefully after a full inhalation. It is a core spirometry measurement and is reduced in both obstructive and restrictive lung disease.

The volume of air exhaled in the first second of a forced expiratory maneuver. It is the most reproducible and widely used spirometry value and is the main marker of airflow obstruction severity.

The proportion of the forced vital capacity exhaled in the first second, expressed as a fraction or percent. A reduced ratio indicates airflow obstruction; a normal or high ratio with a low FVC suggests restriction.

The average forced expiratory flow over the middle half of the FVC. It reflects small airway function, is more variable and effort dependent than FEV1, and is not used alone to diagnose obstruction.

The volume of air exhaled before the extrapolated start of the forced maneuver. A large value suggests a slow or hesitant start; it should be no more than 5% of FVC or 150 mL, whichever is greater.

Requirements showing a forced exhalation is complete: a volume plateau lasting at least 1 second, an expiratory time of at least 6 seconds (or 3 seconds in young children), or the patient cannot continue.

Standards a single spirometry maneuver must meet to be usable, including a good start, no cough or glottic closure in the first second, no leak or extra breaths, and a satisfactory end of test.

How closely a patient's repeated acceptable maneuvers agree. Current standards require the two largest FEV1 values and the two largest FVC values to be within 150 mL of each other.

A graph plotting airflow against exhaled or inhaled volume. Its shape helps distinguish obstruction, restriction, and variable intrathoracic or extrathoracic upper airway obstruction.

A significant improvement after bronchodilator, defined as a rise in FEV1 or FVC of at least 12% and at least 200 mL from baseline. It supports a diagnosis of reversible airflow obstruction.

The volume of gas in the lungs after a maximal inhalation. It is measured by plethysmography or gas dilution and is the key value for confirming true restriction.

The volume of gas remaining in the lungs at the end of a quiet expiration. It is the starting point for calculating residual volume and total lung capacity.

The gas remaining in the lungs after a maximal exhalation. It cannot be measured by spirometry alone and is calculated by subtracting vital capacity from total lung capacity.

A method in which the patient sits in a sealed cabinet and pants against a shutter while pressure changes are recorded. Using Boyle's law, thoracic gas volume and total lung capacity are calculated.

A technique for measuring lung volume by having the patient rebreathe a known helium mixture. The gas dilutes into the lung volume, and the final concentration reveals the volume it mixed with.

A measure of how readily carbon monoxide crosses from alveolar gas into blood. A single-breath test with a roughly 10-second breath hold assesses the alveolar-capillary membrane and pulmonary capillary blood volume.

The volume of gas in the lung that takes part in gas exchange during the DLCO maneuver, calculated from dilution of the tracer gas. It is used to correct DLCO for lung size.

The DLCO divided by alveolar volume, sometimes called the transfer coefficient. It reflects how efficiently each unit of lung volume transfers carbon monoxide and helps interpret a low DLCO.

The period the patient holds the test gas in the lungs during single-breath DLCO testing, targeted at about 10 seconds. Timing matters because carbon monoxide uptake continues during the hold and errors change results.

Analysis that directly measures pH, partial pressure of carbon dioxide, and partial pressure of oxygen in arterial blood. Bicarbonate and other derived values are calculated to assess ventilation and acid-base status.

The difference between calculated alveolar oxygen pressure and measured arterial oxygen pressure. It widens with ventilation-perfusion mismatch, shunt, or diffusion impairment and helps identify the cause of hypoxemia.

Pulse oximetry estimates the percentage of hemoglobin saturated with oxygen using light absorption through a pulsating vascular bed. Readings are unreliable with poor perfusion, abnormal hemoglobin, motion, or nail polish.

A laboratory method that measures the fraction of each hemoglobin type, including oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin, and methemoglobin, using multiple wavelengths. It is more accurate than pulse oximetry when abnormal hemoglobins are present.

A bedside check of collateral blood flow to the hand before radial artery puncture. The patient's fist is clenched while the radial and ulnar arteries are compressed, then color return is watched after releasing the ulnar artery.

The largest volume a person can breathe in and out rapidly, usually performed for 12 to 15 seconds and reported per minute. It reflects respiratory muscle endurance and is reduced in airflow obstruction.

A bronchoprovocation test in which increasing inhaled doses of methacholine are given to detect airway hyperresponsiveness. The provoking concentration that causes a 20% fall in FEV1, the PC20, is reported.

A submaximal exercise test measuring the distance a patient walks on a flat corridor in six minutes. It assesses functional exercise capacity, with oxygen saturation, heart rate, and dyspnea monitored during the walk.