2 - PFT Equipment

Info from 'Clinical Assessment in Respiratory Care,' 9th edition

types of spirometers

• volume displacement

• flow-sensing

volume displacement spirometers

• water-seal

• bellow

• dry rolling seal

• diaphragm

disadvantages of volume displacement spirometers

• equipment is large and bulky

• water levels have to be checked and replaced often

• leaks are likely

• manual calculations if no microprocessor

• infection control

advantages of volume displacement spirometers

• directly measures volumes

• low cost

• easy to operate

• water seal is gold standard

flow sensing spirometers

• pneumotachometer

• pressure differential

  • screen / pitot tube

• heated wire/mass flown sensor

• turbines

• ultrasonic

disadvantages of flow-sensing spirometers

• frequent, careful calibration

• moisture/secretions affect readings

• gas composition affects readings

• low flows

advantages of flow-sensing spirometers

• equipment is smaller and more portable

• computerized

• flow-volume loops

• easier infection control

heated wire (anemometer / mass flow sensor)

• type of flow sensing spirometer

• unidirectional

• cooling effect of gas flow

turbine

• type of flow-sensing spirometer

• measures bulk gas flow

• 3-300 L/min

ultrasonic

• type of flow-sensing spirometer

• high-frequency waves through flow of gas

• measures transit time

calibration of PFT equipment

• ATS standards

  • volumes: ≥8 L

  • flow: 0.5-12 L/sec

  • exhalation maneuvers for ≥15 seconds

• 3 L calibration syringe

• at least once a day:

  • volume: ±0.5%

  • flow: ±3% inspiration/expiration

body phethysmography box

• “body box”

• gold standard for measuring FRC/TGV (air trapping) and lung volumes

• can measure gas in ventilated and non-ventilated lung areas

• also used for spirometry, R_aw tests, DLCO

  • FVC, SVC, MVV, bronchial provocation tests

  • FRC, VC, IC, ERV, RV, TLC

  • R_aw & sGAW

• Boyle’s law

  • P₁V₁ = P₂V₂

  • V₁ = FRC & P₂ = P_B

  • FRC = (P_B × V₂) ÷ P₁

• cons: box is expensive

portable spirometers

• microprocessors

• laptop or stand alone

• flow-based

• issues with in-office (patient effort, technician)

determining which spirometer to use

• What is the intended function?

• Who will conduct the test?

• How many tests per day?

• What is the cost?

• Where will tests be done?

peak flow meters

• PFT device that aids in monitoring patients with asthma

• ranges

  • adults: up to 850 L/min

    • males: 450-750 L/min

    • females: 350-530 L/min

  • pediatrics: up to 400 L/min

    • values vary with height

• repeatability more important than accuracy