CPFT flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Spirometry contraindications

Avoid spirometry with pneumothorax, recent myocardial infarction or chest and abdominal surgery, active hemoptysis, thoracic or abdominal aneurysm, or unstable cardiovascular status.

Height measurement for prediction

Standing height is measured without shoes, heels together, head in the Frankfort plane, and recorded in centimeters; height, age, sex, and ethnicity generate predicted spirometry values.

Bronchodilator withholding times

Before testing, hold short-acting beta-agonists 4-6 hours, ipratropium 6-8 hours, long-acting beta-agonists 12-24 hours, and long-acting antimuscarinics 24 hours or longer per laboratory protocol.

Pre-test patient instructions

Patients should avoid smoking for 1 hour, vigorous exercise for 30 minutes, heavy meals for 2 hours, and alcohol for 4 hours before pulmonary function testing.

Infection control in PFT lab

Use a new mouthpiece or in-line bacterial filter for every patient, perform hand hygiene, wear gloves when handling secretions, and disinfect reusable surfaces between patients.

Pack-year calculation

Pack-years equal the number of packs smoked per day multiplied by the number of years smoked, where one pack contains 20 cigarettes; the value quantifies cumulative tobacco exposure.

Daily volume calibration

Inject a calibrated 3-L syringe at low, medium, and high flows; the spirometer must read within plus or minus 3%, meaning 2.91 to 3.09 L for a 3.00-L injection.

Spirometer leak test

Occlude the spirometer and apply slight positive pressure before calibration; a steadily falling volume signal identifies a leak that must be repaired before patient testing.

Biological control testing

A healthy nonsmoking reference subject is tested regularly on each device, values are plotted on a control chart, and trends or points outside laboratory limits prompt investigation.

DLCO calibration gas composition

Test gas usually contains 0.3% carbon monoxide, 0.3% helium or methane tracer, 21% oxygen, and balance nitrogen; analyzers are zeroed and spanned before each test day.

Blood gas analyzer quality control

Analyze low, normal, and high control materials at least every 8 hours and after maintenance; results must fall within established limits before patient samples are reported.

ATPS to BTPS conversion

Ambient spirometer volumes are converted to body conditions by multiplying by 310 divided by (273 plus ambient temperature) and by (barometric pressure minus 47) divided by (barometric pressure minus ambient water vapor pressure).

Acceptable FVC maneuver

A maximal inhalation to total lung capacity followed by a forceful blast without cough, glottic closure, leak, or extra breath, lasting at least 6 seconds or until a volume plateau.

End-of-test criterion

Forced expiration is complete when the volume change is less than 0.025 L over 1 second, or when 15 seconds of exhalation have elapsed, whichever occurs first.

Spirometry reproducibility criteria

The two largest acceptable FVC values and the two largest acceptable FEV1 values must agree within 0.150 L; perform at least three acceptable maneuvers and stop at eight.

Extrapolated volume limit

Back-extrapolated volume must not exceed 5% of FVC or 0.150 L, whichever is greater, which confirms a rapid, sharp start of the forced expiration.

Obstruction severity grading

With FEV1/FVC below the lower limit of normal, severity by FEV1 percent predicted is mild 70% or more, moderate 60-69%, moderately severe 50-59%, severe 35-49%, very severe below 35%.

Positive bronchodilator response

A significant response is an increase in FEV1 or FVC of at least 12% and at least 200 mL from baseline, measured 10-15 minutes after 400 mcg of albuterol.

Variable extrathoracic obstruction

Flattening of the inspiratory limb of the flow-volume loop with a preserved expiratory limb suggests variable extrathoracic obstruction, as in vocal cord paralysis or tracheomalacia.

Fixed airway obstruction loop

Flattening of both the inspiratory and expiratory limbs of the flow-volume curve suggests a fixed obstruction, such as tracheal stenosis or a large goiter.

Plethysmographic FRC principle

Body plethysmography measures thoracic gas volume at FRC using Boyle's law while the patient pants against a closed shutter, relating mouth pressure changes to box volume changes.

Helium dilution lung volumes

Closed-circuit helium dilution measures FRC after gas equilibration and underestimates lung volumes when poorly ventilated regions or trapped gas do not communicate with the circuit.

DLCO breath-hold requirements

Inhale test gas from residual volume to total lung capacity, hold the breath 10 seconds (acceptable 9-11 seconds), then exhale while discarding the washout volume before collecting the sample.

Decreased DLCO causes

DLCO falls in emphysema, interstitial lung disease, pulmonary vascular disease, anemia, and after pneumonectomy; values should be corrected for hemoglobin before final interpretation.

Increased DLCO causes

DLCO may rise with asthma, obesity, polycythemia, left-to-right shunts, and pulmonary hemorrhage because of increased pulmonary capillary blood volume or hemoglobin concentration.

Elevated RV/TLC ratio

The residual volume to total lung capacity ratio normally rises with age; values above the upper limit of normal indicate hyperinflation or gas trapping, typical of obstructive disease.

Modified Allen test

Compress the radial and ulnar arteries while the patient clenches the fist, release the ulnar artery, and confirm the palm flushes within about 5-15 seconds before radial puncture.

Arterial sample handling

Expel air bubbles, cap the syringe, mix the heparinized sample, and analyze within 15-30 minutes or place it on ice to limit changes in pH and PaCO2.

Alveolar gas equation

PAO2 equals FiO2 times (barometric pressure minus 47) minus PaCO2 divided by 0.8; the alveolar-arterial gradient is PAO2 minus measured PaO2.

Winter's formula

In metabolic acidosis, the expected PaCO2 equals 1.5 times serum bicarbonate plus 8, plus or minus 2 mmHg; a measured value outside this range indicates a second disorder.

Pulse oximetry limitations

SpO2 is unreliable with carboxyhemoglobin, methemoglobin, poor perfusion, dark nail polish, or motion, and readings below about 70% are inaccurate; it does not assess ventilation.

Methacholine challenge PC20

PC20 is the methacholine concentration causing a 20% fall in FEV1; a value below 16 mg/mL is generally considered a positive test for airway hyperresponsiveness.