Asthma is a lung syndrome characterized by: (1) airway obstruction (or airway narrowing, the airways being the tubes to the lungs or in the lungs) that is reversible either spontaneously or with treatment, (2) airway hyperresponsiveness to a variety of stimuli, and (3) airway inflammation. Improvement in airflow following inhalation of a bronchodilator is generally accepted as indicative of reversible airway obstruction.
Each of the tests described help to rule in or rule out the presence of asthma or to characterize the asthma.
This test measures total volumes of air the lungs can hold and whether there are any problems with the flow of the air.
The illustration shows a handsome young man blowing into an office spirometer. For purposes of illustration, the nose clips are omitted. As long as personnel responsible for the test are well trained, spirometry can be done routinely in a doctor's office.
VERBAL EXPLANATION TO THE PATIENT
The patient takes a full breath in and then exhales as fast and as hard and as long as possible until they have no air left. They then relax. Children as young as age 5 or 6 can perform this test with some practice.
A normal individual should be able to force out 80% or more of their moveable air volume (the total air volume forced out, FVC) in 1 second (Forced Expiratory Volume at 1 second, FEV1). Asthmatics may not be able to do that because their airways are obstructed. However many children with asthma have values of their FEV1 that are with in the predicted normals and their FEV1/FVC, the percent of their total air volume that can be moved in 1 second is also within the normal range. As a result the test is often repeated after the child inhales a bronchodilator looking for an improvemt of 15% or more indicating that despite apparently normal values they have "reversible" obstruction. Because the absolute lung values of children increase as they grow, the results are often expressed as percent predicted (the predicted values have been established in normal children by gender, race, height etc. This is one more level of complexity and makes it worthwhile to do the test before and after a bronchodilator so the child becomes their own control.
This is a test that should be done in a specialized centre by trained technicians. It involves repeated performance of the forced expiratory volume manoeuver described above both before inhaling methacholine (to establish base-line FEV1) and after inhaling methacholine at increasing concentrations. Methacholine or an alternative histamine are chemicals that at certain concentrations can make the airways constrict i.e. go into spasm. In this test the patient inhales increasing concentrations of dilute methacholine. Initially the patient's base-line FEV1 is established and then a target value 20% below base-line is calculated. At a certain concentration of methacholine, the patient may feel chest tightness and may cough. The FEV1 falls 20% or more below the base-line and the test is over. (The patient is given a bronchodilator.) Asthmatics cannot breath as much of the methacholine as someone without asthma before they have this fall in their FEV1. The more of the dilutions of methacholine that the child can inhale, the better the results. Conversely the more hyperresponsive the airways are (i.e. the twitchier) the less they can inhale. Children often get fed up with the number of breathing tests that they have to perform and the technicians must be particularly adept at coaxing the children to maintain focus and do the best they can even when they are tired of doing the test.
This is a wonderful test that allows a relatively non-invasive assessment of the inflammation of the airways and can be done in children older than approximately 7 years of age.
It is now established that airway inflammation is a cardinal feature of asthma and is responsible for the pathophysiologic responses observed during an asthma attack and during periods of remissions and exacerbations. Consensus guidelines on the management of asthma have suggested that treatment of asthma should be primarily directed to reduce the inflammation. The evaluation of inflammation by examination of induced sputum has been observed to be a reliable, valid and responsive tool.
The technique of induced sputum has been extensively studied and validated as a measure of airway inflammation [1],[2],[3],[4],[5],[6]. Sputum has been shown to yield measures of airway inflammation that correlate well with the more invasive bronchoalveolar lavage in asthma. The technique of induced sputum allows the safe examination of the inflammatory events in the airways of children with asthma and/or cough when bronchoalveolar lavage or biopsy of the airways would not be practical or ethical./p>
The test and the test procedures to be described are those developed by Dr. Fred Hargreave and colleagues at the Firestone Institute for Respiratory Health, St. Joseph's Hospital, McMaster University, Hamilton, Canada. Through careful and methodical work, Dr. Hargreave and colleagues have established this test as reliable and reproducible.[Reference]
Sputum is induced with hypertonic saline and prepared for cytologic examination. After measuring the subject's FEV1 and finding it to be normal, the subject inhales hypertonic saline, nebulized with a Medix ultrasonic nebulizer, for 7-minute periods. The subject rinses their mouth with water, blows their nose and then is encouraged to cough up a sample of sputum into a chilled beaker. The sputum can be recognized by its consistency and that fact that it contains "plugs" i.e. tightly packed cells. Some children need a lot of encouragement to cough up material into the beaker and some, particularly little boys overenthusiastically spit saliva into the beaker. That should be discouraged sice it contaminates the sample. Three 7 minute saline inhalations are performed at 3%, 4% and 5% concentrations of saline. Each inhalational period is followed by an attempt to cough up sputum and the samples are all pooled.
The sample is taken by a technician who pulls the plugs out of the sample. Plugs are visible to the naked eye but can also be viewed in an inverted microscope. The plugs are then prepared to release their constituent cells and finally the cell material is spun onto a microscope slide which is stained with a Wright stain so that the cells can be visualized under light microscopy. The supernatant or fluid phase of the sample can be used to measure soluble cytokines and other measures of inflammation.