PFT equipment and machines overview

PFT Equipment and Machines (Pulmonary Function Testing)

by | Updated: Jan 28, 2023

Pulmonary functioning testing (PFT) is a set of noninvasive tests that are used to measure how well a patient’s lungs are working. This is important in the diagnosis and treatment of those with respiratory diseases.

In order to perform the tests and obtain accurate results, it is important to use the right types of PFT equipment and machines. There are several different devices, which we will discuss in detail below.

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What is PFT Equipment?

PFT equipment is made up of a number of devices that are used to measure different aspects of lung function. This can include how well the lungs take in and expel air, how efficiently they transfer oxygen to the blood, and how much air the lungs can hold.

PFT’s measure lung volumes, capacities, and the amount of gas exchange, or lack thereof.

The results that are obtained can help respiratory therapists and physicians diagnose and create an optimal respiratory care plan.

Types of PFT Equipment

There are many different types of PFT equipment that are used in the various types of pulmonary function tests, including:

  • Spirometer
  • Peak flowmeter
  • Body plethysmograph
  • Pulmonary gas analyzer
  • Gas-conditioning device
  • Blood gas analyzer
  • Silverman pneumotachometer
  • Pulse oximeter

Each device is used to measure different aspects of a patient’s lung function.


A spirometer is a device that measures the volume and speed of air that a patient can inhale and exhale. It is helpful in diagnosing both obstructive and restrictive lung diseases.

Additionally, it is helpful in assessing if a medication is working in a patient with constricted airways.

Peak Flowmeter

A peak flowmeter is a hand-held device that measures the maximum speed of air that can be exhaled when a patient blows out as hard and fast as they can.

It is used to assess if a patient’s asthma is under control and can also be used to measure the effectiveness of certain medications.

peak flowmeter illustration

Body Plethysmograph

A body plethysmograph is a large box in which the patient enters that can measure the amount of air that is inhaled and the volume that remains in the lungs after exhalation.

This is one of the only PFT devices that is capable of measuring a patient’s residual volume (RV).

patient in PFT body plethysmograph box

Pulmonary Gas Analyzer

A pulmonary gas analyzer is a machine that is used to measure the concentration of oxygen and carbon dioxide in a patient’s exhaled breath. This information can be used to assess how well the lungs are exchanging gases.

This is important because, if too much CO2 accumulates in the blood, it can lead to respiratory failure and serious health complications. Additionally, if the oxygen concentration is decreased and hypoxemia is present, it is also problematic.

Gas-Conditioning Device

A gas-conditioning device is used to regulate the temperature and humidity of the air that is being delivered to the patient during a pulmonary function test.

This is important because changes in temperature and humidity can affect the results of the test.

Blood Gas Analyzer

A blood gas analyzer is a machine that measures the partial pressure of oxygen and carbon dioxide in a patient’s blood.

This information can be used to assess how well the lungs are exchanging gases and if there is too much CO2 accumulating in the blood.

Silverman Pneumotachometer

A Silverman pneumotachometer is a device that is used to measure the flow rate of gases during breathing. It uses multiple screens to act as a resistive element while helping ensure laminar flow.

Pulse Oximeter

A pulse oximeter is a device that measures the oxygen saturation of a patient’s blood. This is helpful in assessing how well the lungs are transferring oxygen to the blood and body tissues.

Hypoxemia is a condition in which the oxygen saturation is below normal. Using a pulse oximeter during a pulmonary function test helps ensure that a patient’s oxygen saturation stays within the acceptable range.

pulse oximeter illustration

PFT Equipment Practice Questions:

1. What are the 3 types of volume displacement spirometers?
Water-seal, dry-rolling seal, and bellows type.

2. What are the 5 types of flow-sensing spirometers?
Turbine device, heated wire flow sensors, pitot tube flow sensors, pressure differential flow sensors, and ultrasonic flow sensors.

3. What are the advantages of the water seal spirometer?
As a patient breathes in and out, the bell floats up or down proportionally. The pin is attached to the outer part of the bell, which marks the kymograph producing a recording of the amount and speed of the bell’s deflection. It is very sensitive to very small changes in volume. It maintains calibration over a long period of time.

4. What is the Collins water seal spirometer?
It has vertical a 7-10 L cylinder. It can calculate VC and FEV1. On inspiration, the bell float moves down while the pen moves up (expiration vice versa).

5. What are the disadvantages of the water seal spirometer?
Cumbersome and not very portable, potential contamination due to water spills, and challenging to keep the device clean.

6. What is a dry-rolling seal spirometer?
It has a horizontal 10-12 L cylinder. As the patient breathes in and out, a piston inside a cylinder is displaced back and forth to record volume displacement. It has very little resistance and considered the most effective volume displacement device.

7. What is a bellows type spirometer?
It has vertical or horizontal 7-8 L (smaller). It utilizes a kymograph to record volume displacement. Referred to as wedge or bellows type. It won’t work if dirt or particles got inside.

8. What is a pneumotachometer?
It is a device that measures gas flow directly.

9. How do flow-sensing spirometers work?
The physical principle used to produce a signal proportional to gas flow. The signal is integrated to measure volume in addition to flow.

10. What is flow integration?
It is the process in which flow is divided into many small intervals (time). Volume from each interval is summed.

This textbook can serve as a great resource for learning more about PFT's.

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11. What are the advantages of flow-sensing spirometers?
It is smaller and easier to maintain and clean. It also uses disposable sensors. And it is very portable and may be used in any setting.

12. What is a turbine-type flow sensor?
It is a rotating vane that is mounted on jeweled bearings that drive reduction gears connected to the main dial. It has a limited measurement of high-flow greater than 300 L/min. It’s compact size makes it useful at the patient’s bedside.

13. What is a heated wire flow sensor?
It is based on a cooling effect of gas flow. Consists of a heated wire element. Gas flow past wire causes a temp decrease in proportion to the mass of gas and its flow. The flow signal integrated electronically or by software to obtain volume measurement. It is reusable with a bacterial filter.

14. Does the heated wire flow sensor meet ATS recommendations?
Yes, for accuracy and precision. It can do all types of PFT’s and is utilized by the CareFusion Vmax PFT system.

15. What is a pitot tube flow sensor?
It utilizes the pitot tube principle where the pressure of gas flowing against a small tube is related to the gas’s density and velocity. Flow is measured by placing a series of small tubes in the flow sensor and connecting them to a sensitive pressure transducer.

16. Does the pitot tube flow sensor meet ATS recommendation?
Yes, for accuracy and precision. It is utilized by Medgraphics company PFT. It is also reusable.

17. What is an ultrasonic flow sensor?
It is a tube with membranous ports on either side that permits high-frequency sound waves to be passed through a stream of gas. The ports angled so that sound waves speed up or slow down.

18. How can flow be measured accurately in ultrasonic flow sensors?
By measuring the transit time of sound pulses compared to conditions of no flow. This method allows an inexpensive disposable tube to be used and prevents contamination of the ultrasonic transducer.

19. What are portable office spirometers?
Flow sensing type. Many use disposable flow sensors. Sensors are pre-calibrated at the time and include calibration code for software.

20. What is a peak flow meter?
It consists of a resistor or flow tube and a movable indicator. The movable indicator is deflected in proportion to velocity of air flowing through the device.

21. What is peak expiratory flow (PEF)?
It is a method that is used to monitor patients with asthma. It can be read directly from the calibrated scale.

22. What is a low range peak flow meter?
It measures flows up to 400 L/min. Useful for small children or for patients who have marked obstruction.

23. What is a high range peak flow meter?
It measures flows as high as 800 L/min. It is designed for adult patients.

24. What are the two types of measuring devices?
Volume and flow.

25. What are volume-measuring devices?
Some examples include water-sealed and dry-rolling spirometers. They are very accurate but require leak checks. Also note that they are large and difficult to clean. They use a kymograph to graph the results. They can also measure time (x) and volume (y).

26. What type of device is also known as a spirometer?
Volume-measuring devices.

27. What are the types of volume measuring devices?
Water-sealed and dry-rolling devices.

28. Volume measuring devices are very accurate but require what?
Leak checks.

29. Leak checks in volume measuring devices are?
They are large and difficult to clean.

30. What does a volume-measuring device use to graph results?

31. Volume devices measure time on which axis?
The (X) axis.

32. Volume devices measure volume on which axis?
The (Y) axis.

33. What is PFT equipment controlled by?
ATS guidelines.

34. What are the different types of volume-measuring devices (spirometers)?
Water-sealed, bellows, and dry-rolling.

35. What do spirometers reflect as it expands and collects gases?

36. What does a spirometer’s speed of expansion reflect?
Flow rates.

37. Flow-measuring devices are called what?

38. What does a flow-measuring device measure?
They measure changes in pressure as it flows through minimal consistent resistance.

39. What are the uses of flow-measuring devices?
Screens, capillary tubes, fiber sheets, and filter paper.

40. Why are flow-measuring devices heated to body temperature?
To avoid condensation which could change resistance to flow (BTPS).

41. How closely a measured value is related to the true value of the quantity measured is referred to as what?
The accuracy.

42. What are the 5 things that accuracy depends on?
Linearity, frequency response, sensitivity to environmental conditions, calibration, and patient compliance.

43. What do you call the expression of an instrument’s ability to reproduce a measurement (repeatability)?

44. What is a device for measuring volume or flow changes in the airway openings?

45. How do you classify spirometers on what they measure?
Lung volume changes or airflow.

46. What are some examples of volume-displacement devices?
Water-sealed spirometer, bellows spirometer, and dry-rolling seal spirometer.

47. What are the flow-sensing devices that can measure airflow?
Thermal or hot wire anemometers, turbine or impeller device, and ultrasonic and differential pressure device.

48. What is an example of a flow-sensing device?

49. What do you call the water-sealed spirometer?

50. Water-sealed spirometers consist of a Bell that is sealed from?
The atmosphere by water.

51. What is attached to the pneumotachograph to prevent moisture and condensation build up on the capillary tube?
A heater.

52. What consists of a coiled tube that has a needle attached to a calibrated system via a gear mechanism?
Bourdon gauge.

53. What are the 3 different types of electromechanical transducers?
Strain gauge devices, variable inductance devices, and variable capacitance devices.

54. What pressure transducer uses a sensor that consists of a metal wire or semiconductor incorporated into a Wheatstone bridge circuit?
Strain gauge pressure transducer.

55. What transducer consists of a stainless-steel diaphragm that is positioned between two coils?
Variable inductance transducer.

56. With a variable inductance transducer, when not flexed, the two coils are equal with each other. The diaphragm flexes when what is applied, which changes the inductance between the two coils?

57. What transducer is like the inductance except the diaphragm of the device constitutes one plate of a capacitor and the other half of the plate is a stationary electrode?
The variable capacitance transducer.

58. Which transducers are commonly used for measuring respiratory and cardiovascular pressure?
Strain gauge and variable inductance transducers. They respond quickly to change and can respond to a wide range of pressure and are very insensitive to vibrations and shock.

59. What kind of transducers are large and very sensitive to vibration with a very poor frequency response?
Variable capacitance transducers.

60. What must be documented daily to show that quality control is being performed in the laboratory?
Volume verification, spirometry procedure manual maintenance, log that documents daily instrument calibration, problems encountered, corrective action required and system hardware changes should be maintained, biologic standards, known volume syringe, and monitor practitioner performance.

61. In volume verification (calibration) for at least daily before testing, use a calibrated known volume syringe with a volume of at least how many liters?
3 Liters. This is to ascertain that the spirometer reads a known volume accurately.

62. With calibration, the known volume should be injected and/or withdrawn at least three times, at flows that vary between?
2 – 12L/sec.

63. The known-volume syringe must be checked for accuracy at least quarterly using a second known-volume syringe with the spirometer in what mode?
In client-test mode, this validates the calibration and ensures that the client-test mode operated properly.

64. How do you calculate the % accuracy?
(measured volume – 3L/3L) x 100.

65. Why are accurate and reliable measurements of spirometry very important?
Otherwise, comparison with reference normal values is meaningless. One would have no confidence that a given result or change in results over time is real.

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66. What are the 4 things that the practice of spirometry requires an ongoing program of preventative maintenance and quality assurance?
Regular cleaning (manufacturer suggestions), calibration checks (spirometer manual), equipment maintenance to ensure that the spirometer is operating correctly, and regular review to ensure ongoing test quality.

67. A very useful and practical method of assessing the overall performance of the spirometer is to regularly test a healthy subject how often?
Every week. This is biological control.

68. Generally, a variation of more than 5% in FEV1 or FVC should alert you to a problem and the need to?
The need to have your instrument checked and serviced.

69. Ideally, when is regular calibration/validation usually performed with an accurate 3L syringe?
Before each testing session.

70. Can you use reusable mouthpieces on patients?
Yes, reusable mouthpieces must be cleaned and disinfected between patients. In the case of disposable mouthpieces, a new one must be used for each patient.

71. What are pneumotachometers used for?
To measure flow.

72. How would you describe a pneumotachometer?
Small, portable, easy to maintain, and disposable.

73. What flow should you not use with a turbine or respirometers flow sensors?
Greater than 300 L/min or 5 L/sec.

74. What can a Wright respirometer measure?
Vital capacity, but not forced vital capacity.

75. When does a Wright respirometer measure respiratory rate?
When the patient is breathing into the machine.


What is the Most Common Type of PFT Equipment?

The most common type of PFT equipment is the spirometer. It is used to measure the volume and speed of air that a patient can inhale and exhale.

Spirometry helps physicians diagnose and treat patients with both obstructive and restrictive lung diseases.

What are the Different Types of Spirometers?

There are several different types of spirometers, including:

  • Volume-displacement
  • Water-seal
  • Dry-rolling seal
  • Bellows-type
  • Flow-sensing
  • Portable
  • Ultrasonic

Each type of spirometer has the same ultimate goal; however, they all function slightly differently. The type of spirometer that is used will depend on the specific needs of the patient.

What are the Types of Plethysmography?

There are three primary types of plethysmography:

  1. Body
  2. Pressure
  3. Flow

Body plethysmography is the most common type and is able to measure a patient’s residual volume. As their names suggest, pressure and flow plethysmography can measure the changes in pressure and flow in the lungs, respectively.

Final Thoughts

Pulmonary function tests are important diagnostic tools that can be used to assess the functioning of a patient’s lungs. There are many different types of PFT equipment that are used in these tests, each of which measures different aspects of lung function.

By understanding the different types of equipment, you can better understand how PFTs are performed and what information they can provide.

To learn more, check out a guide on the basics of pulmonary function testing. Thanks for reading and, as always, breathe easy, my friend.

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.


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