Asthma Research Lab

Methacholine Challenge

The methacholine challenge is widely used by researchers and physicians to assist in the study and diagnosis of asthma.  Methacholine is a dry powder that we combine with a liquid (normal saline) to make different concentrations or "strengths" of solutions that can then be aerosolized and inhaled.  The test begins with the inhalation of normal saline.  Solutions of normal saline or methacholine are placed in a vial and nebulized (i.e. made into an aerosol) using compressed air or oxygen.  Attached to the nebulizer is a mouthpiece or face mask which "directs" the aerosol to you for inhalation (noseclips must be worn). The inhalation time period is two minutes during which you breath normally through the mouthpiece or via the face mask.  The timing of inhalations (i.e. from the start of one to the start of the next) is 5 minutes.  The number of inhalations you would be required to do depends on how your airway reacts to the methacholine.   Methacholine signals the muscles in your airway to contract causing constriction.  We measure the constriction by having you perform breathing tests (spirometry).  The test is considered positive if: a) the amount of air you forcefully exhale after inhaling methacholine decreases 20% compared to the amount of air you forcefully exhaled after being exposed to the normal saline; and b) if this occurs after inhaling a concentration of methacholine of 16mg/mL or less.  A methacholine inhalation challenge typically requires 1 hour of your time.

Spirometry

The results of this test will provide basic information on how well your lungs are functioning with respect to the amount of air you can inhale and exhale and with respect to how the air flows in and out of your lungs.  The test requires you to wear noseclips and breath through a mouthpiece into a handheld device that is attached to a computer.  The computer will analyze various breathing parameters and provide the information to us.

Allergen Challenge

The allergen challenge is very similar to the methacholine challenge in that it requires the inhalation (normal breathing through a mouthpiece connected to a nebulizer with noseclips on) of doubling concentrations of allergen.  Ten minutes after inhaling the allergen, breathing tests are performed and compared to values obtained before allergen was inhaled.  The inhalations are stopped when the level of constriction has reached at least 20%.  The time requirement for undergoing allergen challenges varies considerably, depending on both your response and the project being undertaken.

Skin Prick Tests

You may be wondering how we decide what allergen to "challenge" you with.  We do this by performing a skin prick test.  This test involves placing small drops of different allergens on the surface of your forearm.  We use about 25 different "common" allergens which include, for example, grass and cat.  We then scratch or "tent" the skin within the drop to introduce the allergen to your body.  We wait about 12 minutes and then we look for what is called the wheal and flare response.  This is basically a bump like a mosquitoe bite with some redness around it.  Yes, it will be itchy and no you are not allowed to scratch it!!!  We are able to select an allergen for the inhalation challenge based on the results of this test.  We then make a set of increasing (doubling) concentrations of this allergen and we perform another skin test with these to determine the concentration of allergen that produces a small wheal (2mm x 2mm or smaller) and we use this information together with the methacholine test result to mathematically determine a safe starting concentration for the allergen challenge.  Skin prick tests require about 30 minutes of your time.

Sputum Induction

This is really a very important part of what we do as it provides information about what's going on at the cellular level.  The procedure requires that you inhale three concentrations of "salty" water (i.e. hypertonic saline, 3%, 4% and 5%), each for seven minutes.  The salty water helps to draw out secretions from the tissue into the airway which you can then huff and cough and spit into a cup for us to analyze later.  The time required to induce sputum is about 40 minutes.

Exhaled Nitric Oxide Measurement

Nitric oxide is a gas that is normally produced by various tissues in the body.  In the adult lung, normal levels of nitric oxide range between 5 and 20 parts per billion (ppb).  Higher levels (>35ppb) and lower levels (<5ppb) may indicate airway disease.  To perform the test you inhale through your mouth via a filter that is connected to a handheld machine.  After you have inhaled as much as you can, you exhale through the filter into the machine for about 10 seconds.  The machine will then display the amount of nitric oxide exhaled.  Collecting this information takes about 10 minutes.