Spirometry is a fundamental diagnostic tool utilized to assess and monitor lung diseases.
Measuring the volume and flow of air that can be inhaled and exhaled offers clinicians valuable insights into the functional state of a patient’s respiratory system.
Particularly in conditions such as asthma, chronic obstructive pulmonary disease (COPD), and other pulmonary disorders, spirometry aids in diagnosis and tracking disease progression and the efficacy of therapeutic interventions.
This article will provide an in-depth overview of spirometry, including its principles, applications, and relevance in clinical settings.
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What is Spirometry?
Spirometry is a diagnostic pulmonary function test (PFT) used to measure the volume and flow of air a person can inhale and exhale. It’s vital for diagnosing and monitoring respiratory conditions such as asthma and COPD. The test provides quantitative data on lung function, aiding clinicians in assessing respiratory health.
Spirometry is indicated for a variety of clinical reasons, ranging from diagnosis to monitoring and even pre-operative assessment.
Here are the primary indications for spirometry:
- Diagnosis of Respiratory Disorders: To differentiate between obstructive and restrictive lung diseases, and to help identify specific conditions like asthma, COPD, and interstitial lung diseases.
- Monitoring Disease Progression: To track the course of chronic respiratory diseases over time, especially in conditions like asthma, COPD, and cystic fibrosis.
- Evaluating Treatment Efficacy: To assess the response to medications or other therapeutic interventions, such as the effect of bronchodilators in asthma or inhaled corticosteroids in COPD.
- Assessing Symptoms of Respiratory Dysfunction: In patients presenting with symptoms like chronic cough, wheezing, shortness of breath, or unexplained dyspnea.
- Preoperative Assessment: To evaluate lung function before surgeries, especially thoracic or upper abdominal surgeries, or in patients with known pulmonary conditions undergoing any major surgery.
- Screening for Occupational Lung Diseases: For individuals exposed to harmful agents or in occupations with a risk of lung diseases, such as coal miners, asbestos workers, or those exposed to silica.
- Disability or Impairment Evaluation: To determine the degree of lung impairment in cases of occupational health claims, insurance purposes, or legal matters.
- Evaluating Exercise Intolerance: In patients presenting with unexplained reduced exercise capacity or dyspnea on exertion.
- Bronchial Provocation Testing: To diagnose and evaluate the severity of bronchial hyperreactivity, especially in individuals with suspected asthma but normal baseline spirometry.
- Risk Assessment in Smokers: To assess the lung function in chronic smokers or those with a significant smoking history, even if they are asymptomatic, for early detection of COPD or other smoking-related lung diseases.
Note: While these are the primary indications, it’s essential for clinicians to interpret spirometry results in the context of clinical presentation, physical examination, and other diagnostic findings.
Respiratory Diseases Diagnosed with Spirometry
Spirometry is an essential tool in the diagnosis and monitoring of a variety of respiratory diseases.
Here are some of the primary diseases that spirometry can help diagnose:
- Asthma: Spirometry can detect airway obstruction and its reversibility after bronchodilator administration, aiding in the diagnosis of asthma.
- Chronic Obstructive Pulmonary Disease (COPD): It distinguishes between the obstructive patterns of COPD (which includes chronic bronchitis and emphysema) and other respiratory disorders.
- Chronic Bronchitis: While this is a subset of COPD, spirometry can help identify the reduced airflow commonly seen in chronic bronchitis patients.
- Emphysema: As another component of COPD, emphysema leads to alveolar damage. Spirometry can highlight the characteristic decrease in the forced expiratory volume.
- Bronchiectasis: Spirometry can help detect the airflow obstruction that occurs in bronchiectasis.
- Restrictive Lung Diseases: These include conditions like pulmonary fibrosis, sarcoidosis, and chest wall deformities. Spirometry can identify a reduction in lung volumes without a significant reduction in airflow.
- Pulmonary Tumors: While not definitive for tumors, spirometry can show airflow obstruction if a tumor is impeding an airway.
- Tuberculosis: In its advanced stages or when fibrosis occurs, tuberculosis can cause changes in lung function that can be detected by spirometry.
- Cystic Fibrosis: This genetic condition causes mucus buildup in the lungs. Spirometry can assess the degree of airflow obstruction and help monitor the disease’s progression.
- Occupational Lung Diseases: Conditions like asbestosis, silicosis, or other work-related diseases can cause lung function abnormalities detectable by spirometry.
Note: Regular spirometry testing is essential for diagnosis and monitoring disease progression, evaluating treatment efficacy, and guiding therapeutic interventions in these respiratory conditions.
What is a Spirometer?
A spirometer is a medical device used to measure the amount and speed of air a person can inhale and exhale.
It captures data during a forced breath maneuver to provide key metrics like forced vital capacity (FVC) and forced expiratory volume in one second (FEV1).
These measurements are essential for diagnosing and monitoring various obstructive and restrictive respiratory diseases.
Various types of spirometers are used in pulmonary function testing, including the following:
- Volume-Displacement: This type of spirometer involves a chamber that is fixed or attached to the patient’s mouth. As the patient breathes, the chamber’s volume changes, allowing for the measurement of lung volumes and capacities.
- Water-Seal: A classic and older design, this device utilizes a chamber submerged in water. As the patient breathes, the water level changes, reflecting lung volumes. It provides a seal that ensures no gas leaks during the testing process.
- Dry Rolling Seal: This design eliminates the need for water. Instead, it employs a rolling seal mechanism that maintains a closed system while allowing the volume measurement chamber to expand and contract with breathing.
- Bellows-Type: This design uses bellows, which expand and contract with inhalation and exhalation. The changes in the bellows’ size directly measure the volume of air displaced during breathing.
- Flow-Sensing: Instead of measuring the volume directly, this device measures the rate of airflow when a person breathes in and out. Various technologies, like pneumotachographs or hot-wire anemometers, are used to measure this flow, which is then integrated over time to obtain volume data.
- Portable: Designed for convenience, these are compact spirometers suitable for office or field settings. They often utilize electronic flow-sensing mechanisms and are beneficial for routine screening and monitoring, especially in primary care settings.
- Ultrasonic: This state-of-the-art device uses ultrasonic sensors to detect the velocity of the air breathed in and out. Two sensors, placed at a known distance apart, measure the speed of sound in the air flow, allowing for accurate calculation of flow rate and volume.
Note: Each of these spirometers has its own advantages and specific applications, making them suitable for different clinical and research settings.
How Does Spirometry Testing Work?
Spirometry testing measures the amount and speed of air a person can inhale and exhale.
Here’s a step-by-step breakdown of the process:
- Preparation: The patient sits comfortably, wears a nose clip to prevent air escape through the nostrils, and receives instructions on the test’s proper execution.
- Connection to the Spirometer: The patient tightly seals their lips around a mouthpiece connected to the spirometer.
- Taking Measurements: The patient inhales maximally and then exhales as forcefully and quickly as possible. This process measures the Forced Vital Capacity (FVC) and the amount of air exhaled in the first second (FEV1). The test is often repeated for consistency.
- Use of Bronchodilator (if necessary): For certain conditions, a bronchodilator may be given, and the test is repeated to assess any changes in lung function.
- Data Analysis: The spirometer charts the results on a flow-volume loop graph. Measurements like FVC and FEV1 are compared against predicted values based on patient demographics.
- Interpretation: Results help diagnose respiratory conditions, assess lung problem severity, and evaluate treatment effectiveness.
For accurate results, it’s vital for the patient to follow instructions closely and for the spirometer to be well-maintained and calibrated.
Spirometry Practice Questions
1. What is spirometry?
A pulmonary function test that is used to differentiate between obstructive and restrictive lung diseases and determine the extent or progress of the disease.
2. What is the role of spirometry in primary care?
It provides an objective measure of airflow restriction or obstruction and assists with both the initial diagnosis of asthma and the assessment of asthma control.
3. Can spirometry measure residual volume?
No, it cannot measure RV.
4. Why is spirometry effort-dependent?
Spirometry is highly effort-dependent and relies on the patient for accurate results. Poor effort leads to poor quality data and poor effort spirometry will result in an underestimation of true values.
5. When does a spirometer not need to produce a graphic display?
Only when the vital capacity is to be measured.
6. How are the normal predicted values of spirometry reported?
Normal predicted values vary with the patient’s sex, age, height, and race. The mean normal values for FEV1 and FVC are 100% of predicted and the normal range is 80-120% of predicted.
7. Is spirometry testing more focused on inspiration or expiration?
8. What is tidal volume?
The volume of gas that enters the lungs during normal breathing.
9. What is total lung capacity (TLC)?
The total volume of gas in the lungs at the end of a maximal inspiration.
10. What is vital capacity (VC)?
The volume of gas exhaled from maximal inspiration to maximal exhalation, which may be forced (FVC) or relaxed (SVC).
11. What is residual volume (RV)?
The gas remaining in the lungs after a maximal expiration. This volume of gas cannot be expelled, regardless of the maneuver performed.
12. What is functional residual capacity (FRC)?
The total volume of gas remaining in the lungs at the end of a tidal exhalation, which equals the sum of the RV and ERV.
13. What is inspiratory reserve volume (IRV)?
The volume of gas that must be inhaled at the end of a tidal inspiration to reach total lung capacity.
14. What is expiratory reserve volume (ERV)?
The volume of gas within the lungs that could still be exhaled after the end of a tidal exhalation.
15. What is normally recorded in either liters (L) or milliliters (mL) and is reported at body temperature, pressure, and saturation (BTPS)?
16. Two acceptable vital capacity maneuvers should be obtained within what parameters?
The volumes should be within 150 mL.
17. What is the maximum volume of gas that can be expired when the patient exhales as forcefully and rapidly as possible after a maximal inspiration?
18. What are the three distinct phases of the FVC maneuver?
Maximal inspiration, a ”blast” of exhalation, and continued complete exhalation to the end of the test.
19. What two ways can the FVC be displayed?
Volume-time recording and flow-volume recording.
20. Can spirometry measure gas exchange?
No, you can learn about a patient’s gas exchange from spirometry but not directly measure it. Spirometry only measures gas volumes and time (flow = volume/time).
21. The premature termination of a spirometry test leads to what?
An FVC that is falsely low.
22. What values cannot be measured with a spirometer?
Residual volume and total lung capacity.
23. What is the difference between TLC and RV?
24. What is FEV1?
Forced expiratory volume in 1 second
25. What does normal spirometry mean?
FVC greater than 80% of predicted, or 80-120% to fall within the normal range; FEV1/FVC ratio greater than or equal to 0.75.
26. What is the FEV1 in an obstructive lung disease?
The FEV1 will be less than 100% of the predicted value.
27. What is the FVC in an obstructive lung disease?
The FVC will be decreased or normal.
28. What is the FEV1/FVC ratio in an obstructive disease?
The FEV1/FVC ratio will be less than 0.75.
29. What are some clinical examples of obstructive lung diseases?
Asthma, emphysema, bronchiectasis, chronic bronchitis, and cystic fibrosis.
30. What will the expiratory curve look like in obstructive lung diseases?
There will be a rapid rise to a peak but usually, there will be a ‘scooped-out’ appearance/concavity. This is indicative of expiratory airflow obstruction, usually of the small airways.
31. What will the inspiratory curve look like in obstructive lung diseases?
The inspiratory curve is relatively well preserved. Remember, most clinical diseases have normal inspirations and it’s the expiration that is suboptimal.
32. In a restrictive disease, why is the peak flow of expiration greater than it is in a normal individual?
In restrictive disease, the lungs are very stiff and they empty more quickly than normal.
33. What is the FEV1 in a restrictive lung disease?
The FEV1 may be decreased or normal (if normal, it will be low-normal).
34. What is the FVC in a restrictive lung disease?
The FVC will be decreased (i.e., less than 80%). This is the key point wherein VC has to be low if you are going to call it a true restrictive pattern.
35. What is the FEV1/FVC ratio in a restrictive lung disease?
The FEV1/FVC ratio will be greater than or equal to 0.75.
36. What are some examples of restrictive lung diseases?
Pulmonary fibrosis and pleural effusion.
37. What happens during quiet breathing?
Inspiration involves muscular contractions and expiration is passive with no accessory muscle usage.
38. What do you call breathing that involves active inspiratory and expiratory movements?
39. What is the amount of air that a patient expels if they inhale as deeply as possible and then blow the air out until they cannot exhale anymore?
40. What is the resting tidal volume?
It is the amount of air inhaled or exhaled with each breath under resting conditions. The normal value is 500 mL in both males and females.
41. What is the normal value for expiratory reserve volume (ERV)?
42. What is the normal value for residual volume?
The normal value for males is 1,200 mL and 1,100 mL for females.
43. What is the normal value for inspiratory reserve volume (IRV)?
The normal value for males is about 3,300 mL and 1,900 mL for females.
44. What is the formula for inspiratory capacity?
IC = TV + IRV
45. What is the formula for functional residual capacity (FRC)?
FRC = ERV + RV
46. What is the normal value for vital capacity?
The normal value for males is 4,800 mL and 3,400 mL for females.
47. What is the normal value for total lung capacity?
The normal TLC for males is 6,000 mL and 4,500 mL for females.
48. How many breaths can you take each minute?
The resting adult respiratory rate ranges from 12 to 18 breaths per minute with approximately one breath every four heartbeats.
49. When does an increased FRC occur?
In obstructive diseases like emphysema and chronic bronchitis.
50. When does a decreased or normal FRC occur?
In restrictive diseases like pulmonary fibrosis.
51. What is a forced expiratory volume?
It examines the percentage of the vital capacity that is exhaled during specific time intervals of the FVC test. Healthy people can exhale 75-85% of their FVC in the first second.
52. What does a lower pH change?
It changes the shape of the Hb molecules and they release their oxygen more readily.
53. What are the indications for using spirometry?
Diagnosis, monitoring, public health, and disability/impairment evaluations.
54. How do you establish an asthma diagnosis with spirometry?
Detailed medical history to determine episodic symptoms of airflow obstruction or hyper-responsiveness like a cough, wheezing, and shortness of breath with exercise. Next is the physical exam to assess the respiratory tract, chest, and skin. Lastly, reversibility is determined either by an increase in FEV1 by greater than 12% from the baseline.
55. What does the reliability of spirometry depend on?
Reproducible efforts and technique; 3 consistent, 6-second efforts.
56. What do predicted values in spirometry depend on?
The individual’s age, gender, height, and race.
57. What is the percent predicted?
The numbers are presented as percentages of the average expected in someone of the same age, height, sex, and race.
58. What can reduce a patient’s FVC?
Lung diseases, pleural cavity, chest wall restriction, or respiratory muscle weakness.
59. In a restrictive lung disease, what happens to the FEV1/FVC?
It decreases proportionately, hence the ratio is in the normal range.
60. What are the characteristics of flow-volume loops?
A classic flow-volume loop has a rapid peak and expiratory flow rate with a gradual decline in the flow back to zero. An obstructive pattern loop also has a rapid peak, but the curve descends more quickly than normal, taking on a concave shape. A restrictive pattern retains the shape of a normal curve, but the size of the curve appears smaller.
Spirometry is an indispensable test in the field of respiratory care, providing healthcare professionals with insights into a patient’s lung function.
With its essential role in diagnosing and monitoring various lung conditions, a comprehensive understanding of spirometry remains pivotal for any practitioner in the field of respiratory care.
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.
- Faarc, Mottram Carl Ba Rrt Rpft. Ruppel’s Manual of Pulmonary Function Testing. 11th ed., Mosby, 2017.
- Faarc, Kacmarek Robert PhD Rrt, et al. Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
- Lamb K, Theodore D, Bhutta BS. Spirometry. [Updated 2023 Jul 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023.