What Are Some Diagnostic Tests Taken for Asthma?

Asthma is a chronic lung disease that narrows and inflames the airways. Diagnosis of this condition involves a number of lung function tests such as spirometry, exhaled nitric oxide test, bronchial challenge test, chest X-ray or electrocardiogram (EKG), body plethysmography and negative inspiratory force (NIF).

Spirometry

• Spirometry is performed to detect conditions that affect the amount of air you can inhale. It also helps in tracing diseases that affect the rate at which you can exhale like asthma.

  Spirometry measures the amount and frequency with which you inhale and exhale air. The test involves two processes: (1) peak expiratory flow rate (PEFR), and (2) forced expiratory volume in 1 second (FEV1). PEFR tests the amount of air you can exhale as quickly as possible whereas FEV1 finds out the amount of air you can exhale in 1 second.

  You will be asked to take a deep breath and then release it as quickly as possible into a tube connected to the spirometer.

Exhaled Nitric Oxide Test

• Certain cell types produce nitric oxide (NO) in an inflammatory response to conditions such as asthma. The Exhaled Nitric Oxide (eNO) test detects the amount of nitric oxide exhaled in the breath. As the amount of eNO rises in patients suffering from asthma, the method is helps in diagnosing this condition.

Bronchial Challenge Test

• The patient is exposed to bronchoconstrictor such as nebulized methacholine. Bronchoconstrictors narrow the airways and the degree of narrowing is measured by spirometry. A person already suffering from airway hyperreactivity, such as an asthmatic, reacts to lower dose of the drug, allowing the condition to be diagnosed.

Chest X-ray or EKG

• These tests help determine whether some other disease or a foreign body is causing the symptoms.

Body Plethysmography

• This is a sensitive lung test that measures the absolute volume of air in a patient's lungs. This test is used when the patient is unable to perform multibreath tests.

  Body plethysmography is performed by enclosing the patient in an airtight chamber called the body box. The alveolar pressure is measured with a mouth pressure transducer whereas a pneumotachometer measures the airflow.

  The test helps in determining the lungs' resistance to airflow. It also distinguishes between obstructive and restrictive lung diseases, and determines the hyperreactivity of lungs to histamine or methacoline.

Negative Inspiratory Force

• NIF is used to assess respiratory strength of inspiratory muscles such as diaphragm. On the opposite, maximum expiratory pressure (MEP) is used to detect the strength of expiratory muscles such as abdominal muscles.