What Is Spirometry?
Spirometry is also called a pulmonary function test. The device used to carry out the test is called a Spirometer or a Flow Meter.
It is a means to assess the integrated mechanical functioning of the lungs, respiratory muscles, and chest wall. This is done by measuring the total volume of air exhaled (Total Lung Capacity – TLC) to maximal expiration (Residual Volume – RV).
When To Do A Spirometry Test?
It is a valuable diagnostic and prognostic tool that can be used for the following purposes
- Early detection of airflow obstruction.
- Diagnosis of respiratory disorders in patients by evaluating results. The pattern of volume loop created points to the type of respiratory disorder but not the exact disease.
- Monitoring patient’s response to the treatment and course of respiratory illness.
- A guide to the further course of treatment and medical intervention.
- Investigation of non-respiratory diseases which may impact lung function.
Example: Connective tissue disorders and neuromuscular diseases.
- Screening or evaluation of persons at high risk for respiratory diseases
Example: Environmental or occupational exposure to radiation, asbestos, silica
- Preoperative risk evaluation prior to lung resection and cardiothoracic surgeries.
- Following lung transplant to detect signs of acute rejection, infection and obliterative bronchiolitis (chronic organ rejection).
- Evaluation of respiratory status before strenuous physical activity.
- Spirometry should ideally be performed regularly in persons above the age of 35 years with a history of cigarette smoking.
- Spirometry can effectively differentiate between psychosomatic and organic respiratory disorders.
- Spirometry can be performed in acute respiratory infections such as tuberculosis only if the risk of cross-contamination becomes negligible.
[Read – Immediate Effects of Smoking]
Persistence Of The Following Signs And Symptoms Are An Indication For A Spirometry Test
How To Do A Spirometry Test?
- The spirometry test is a relatively simple and quick procedure.
- It is to be performed in a sitting position with head slightly elevated or slightly leaned back.
- The nurse or technician will place the mouthpiece of the spirometer.
- The patient is asked to inhale rapidly and completely followed by forceful exhalation for as rapidly and as long as possible.
- Patients should not lean forward during the test.
- The patient should exhale for at least 6 seconds.
- This forceful inhalation and exhalation may have to be repeated for up to 4-5 times (maximum 8 number of times).
Spirometry Test Preparation
Patients Are Supposed To Observe The Below-Mentioned Guidelines Before A Spirometry Test As They Can Impact Test Results
- Patients are advised to not smoke at least an hour prior to the test.
- Patients reporting for the test should ensure that they do not eat a large meal at least 2 hours prior to the test.
- Patients should not consume alcohol at least 4 hours before reporting for the test.
- Patients should avoid vigorous exercises at least an hour before the test.
- Adequate care should be taken to avoid tight clothing when going for the test.
- Patients using false teeth can use it during the test unless it interferes while performing the test.
- Patients are usually explained about the test.
- Height and weight are measured before beginning the test.
Some Patients May Experience The Following Signs And Symptoms Due to Repeating The Test
Spirometry Test Results And Interpretation
Interpretation of spirometry test results depends entirely upon the test quality and how effectively it is performed by patients. A test which fails to meet the standard guidelines can yield unreliable results. The American Thoracic Society has laid down few guidelines for an acceptable spirometry test which includes
- Should start from full inflation
- Shows minimal hesitation at the start of forced expiration
- Shows an explosive start of the forced expiration
- Shows no evidence of a cough in the first second of forced expiration.
- There is no leak at the mouth
- No spirometry or test result can be rejected solely on the basis of poor repeatability.
- Meets one of the following three criteria that define a valid end-of-test (EOT criteria):
➢ The patient cannot or should not continue further exhalation. Patients can terminate expiration if they experience discomfort.
➢ The volume-time curve shows no change for more than 1 second and the person has tried to exhale for >/= 3 seconds or more in children less than 10 years of age and for >/= 6 seconds for patients above the age of 10 years.
➢ If the test fails to exhibit an expiratory plateau.
A final test report is generated for evaluation if the test meets the above-mentioned test quality parameters.
Spirometry Results Are Expressed As Graph Of Measure Of Volume Against Time. The First Graph Can Be Interpreted As Follows
- Forced Vital Capacity (FVC) – The volume of air that can be exhaled forcefully after maximal inhalation.FVC is less than 3 seconds in normal people.FVC is prolonged in patients with obstructive lung diseases.
- FEV1 – The volume of air exhaled in the first second of FVC.Normal persons can exhale up to 75 – 80% of FVC during the first second.The ration of FEV1/FVC helps to determine the type of lung disease.
- Forced Expiratory Flow (FEF) – Flow of air coming out of the lungs during the middle portion of forced expiration.FEF can be 25 – 75% in normal persons (FEF25-75%).A second graph is called the volume loop. In a volume loop, the part of the curve below baseline indicates inspiration and the curve above baseline indicates expiration.
This Graph Can Be Interpreted As Follows
- Peak Expiratory Flow (PEF) – It is the speed during maximal forced expiration after complete inhalation.
PEF is measured in liter per second. PEF of a normal person is 80 – 100%.
- Tidal Volume (TV) – It is the amount of air inhaled and exhaled during normal breathing.