Venkatehswara | ||||
Occupational Health Centers | ||||
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(INDIAS FIRST OCCUPATIONAL HEALTH SERVICES AN ISO 9001-2008 CERTIFIED SERVICES) |
Purpose
Spirometry is the most commonly performed pulmonary function test (PFT). The test can be performed at the bedside, in a physician's office, or in a pulmonary laboratory. It is often the first test performed when a problem with lung function is suspected. Spirometry may also be suggested by an abnormal x ray, arterial blood gas analysis, or other diagnostic pulmonary test result. The National Lung Health Education Program recommends that regular spirometry tests be performed on persons over 45 years old who have a history of smoking. Spirometry tests are also recommended for persons with a family history of lung disease, chronic respiratory ailments, and advanced age.
Spirometry measures ventilation, the movement of air into and out of the lungs. The spirogram will identify two different types of abnormal ventilation patterns, obstructive and restrictive.
Common causes of an obstructive pattern are cystic fibrosis, asthma, bronchiectasis, bronchitis, and emphysema. These conditions may be collectively referred to by using the acronym CABBE. Chronic bronchitis, emphysema, and asthma result in dyspnea (difficulty breathing) and ventilation deficiency, a condition known as chronic obstructive pulmonary disease (COPD). COPD is the fourth leading cause of death among Americans.
Common causes of a restrictive pattern are pneumonia, heart disease, pregnancy, lung fibrosis, pneumothorax (collapsed lung), and pleural effusion (compression caused by chest fluid).
Obstructive and restrictive patterns can be identified on spirographs using both a "y" and "x" axis. Volume (liters) is plotted on the y-axis versus time (seconds) on the x-axis. A restrictive pattern is characterized by a normal shape showing reduced volumes for all parameters. The reduction in volumes indicates the severity of the disease. An obstructive pattern produces a spirogram with an abnormal shape. Inspiration volume is reduced. The volume of air expelled is normal but the air flow rate is slower, causing an elongated tail to the FVC.
A flow-volume loop spirogram is another way of displaying spirometry measurements. This requires the FVC maneuver followed by a forced inspiratory volume (FIV). Flow rate in liters per second is plotted on the y-axis and volume (liters) is plotted on the x-axis. The expiration phase is shown on top and the inspiration phase on the bottom. The flow-volume loop spirogram is helpful in diagnosing upper airway obstruction, and can differentiate some types of restrictive patterns.
Some conditions produce specific signs on the spirogram. Irregular inspirations with rapid frequency are caused by hyperventilation associated with stress. Diffuse fibrosis of the lung causes rapid breathing of reduced volume, which produces a repetitive pattern known as the penmanship sign. Serial reduction in the FVC peaks indicates air trapped inside the lung. A notch and reduced volume in the early segments of the FVC is consistent with airway collapse. A rise at the end of expiration is associated with airway resistance.
Spirometry is used to assess lung function over time, and often to evaluate the efficacy of bronchodilator inhalers such as albuterol. It is important for the patient to refrain from using a bronchodilator prior to the evaluation. Spirometry is performed before and after inhaling the bronchodilator. In general, a 12% or greater improvement in both FVC and FEV-1, or an increase in FVC by 0.2 liters, is considered a significant improvement for an adult patient.
Precautions
The patient should inform the physician of any medications he or she is taking, or of any medical conditions that are present; these factors may affect the validity of the test. The patient's smoking habits and history should be thoroughly documented. The patient must be able to understand and respond to instructions for the breathing maneuvers. Therefore, the test may not be appropriate for very young, unresponsive, or physically impaired persons.
Spirometry is contraindicated in patients whose condition will be aggravated by forced breathing, including:
In general, a normal result is 80–100% of the predicted value. Abnormal values are:
Resources
BOOKS
Braunwald, Eugene et al., editors. Harrison 's Principles of Internal Medicine. Philadelphia : McGraw-Hill, 2001.
PERIODICALS
Blonshine, S. and J.B. Fink. "Spirometry: Asthma and COPD Guidelines Creating Opportunities for RTs." AARC Times (January 2000): 43-7.
SPIROMETRY SCREENING
‘Spiro’ is the Greek word for breath and Spirometry is defined as the measurement of breathing.
Lung function tests have long been recognised as one of the most important tests available to assess lung impairment.
In recent years there has been an increase in the performance of these test in Occupational Health. The Control of Substances Hazardous to Health Regulations 2002, state that if an occupational asthma agent is present in the workplace, appropriate health surveillance is required. We do not yet know what all the agents are which induce occupational asthma, and the list is continually being added to.
In some cases the requirement for lung function testing is fairly obvious, i.e. isocyantes, solder flux, epoxy resin, curing agents. However, it can be all to easy to overlook many other commonplace industrial hazards such as wood dust, fibreglass, welding fumes, etc.
Given the lengthy development time of symptoms in occupational lung disease, the lung function test can form a valuable part of Pre-employment Screening, where prospective employees are likely to be exposed to a potential hazard.
Early knowledge of the incidence of disease made available by lung function testing makes it possible to take effective remedial action promptly and so minimise future liability.
SPIROMETRY SCREENING PROCESS
After completing a general respiratory questionnaire, the lung function test will be carried out using a Spirometer. Results will be discussed with the employee and a summary report of the results will be forwarded to the employer. If any abnormalities are detected, a referral will be made to the company Medical Officer or the employees GP.
Each test takes approximately 15 minutes and can be carried out at our medical centre or at company premises.
WHO SHOULD I SCREEN?
All employees who have been identified by your risk assessment as being exposed to respiratory irritants, sensitisers and nuisance dusts.
FREQUENCY OF TEST (as a guide)
Testing should be carried out annually for any employees exposed to sensitisers, irritants , dusts, fumes, etc.
For new employees, testing should be carried out initially at Pre-employment. If employees are working with respiratory sensitising agents the test will need to be repeated 6-weekly, 6-monthly, then annually thereafter.
If any abnormalities are detected then more frequent testing may be required to monitor the situation more closely.