Spirometry is the most common type of test for examining lung function. It measures the volume and speed of air breathed in and out by the lungs. The spirometer is an essential tool in assessing conditions like asthma, cystic fibrosis, Chronic Obstructive Pulmonary Disorder (COPD) and pulmonary fibrosis. A spirogram can differentiate between two types of abnormal breathing patterns, restrictive and obstructive.

In persons suffering from restrictive lung disease (RLD), the expansion of the lungs is impaired when breathing in. This causes a decrease in lung volume, making it more difficult for the person to breathe, impairing both oxygenation and ventilation. One type of condition underlying RLD is pulmonary fibrosis. Pulmonary fibrosis is associated with scarring of the lungs, resulting in a honeycomb-like appearance. While rare, the disease is poorly understood and is frequently fatal.

Other disorders that fall under the umbrella of RLD include the autoimmune condition, sarcoidosis; myscular dystrophy, amyotrophic lateral sclerosis (ALS), and obesity. Most patients present initially with difficulty breathing. Sarcoidosis is recognized by red, swollen lesions known as granulomas, mostly affecting the lungs and the skin. Some patients may suddenly develop symptoms that disappear spontaneously. Other people may never know they have sarcoidosis until they have an x-ray for another condition.

The main features of obstructive lung disorders are obstructed and reddened airways. Airflow is obstructed, resulting in difficulty breathing out and, inevitably, numerous visits to the hospital. A diagnostic feature of OLD is the inability to expire 70% of breath in one second. Examples of OLD include COPD, bronchitis and asthma.

Asthma, caused by inflammation of the airways, is a common respiratory condition most often characterized by coughing, wheezing and shortness of breath. Less common symptoms include sighing, fatigue and rapid breathing. Asthma is occasionally life-threatening.

The most serious symptom of CF is impaired breathing. Cystic fibrosis affects the lungs, pancreas, liver and intestine. Twenty-first century improvements in treatment and diagnosis have resulted in a much better prognosis than 50 or 60 years ago. In 1959, the median age of survival was only six months. As of 2008 in the United States, this had risen to 37.5 years; in Canada, it improved from 24 years in 1982 to 47.7 years in 2007. In Russia, the cost of medical treatment is often prohibitive and lung transplants do not take place. Here, the median age of survival is only 25 years.

The term COPD covers conditions like emphysema and chronic bronchitis. In emphysema, the delicate tissues lining the lungs become irreversibly damaged, most commonly from exposure to cigarette smoke. This limits the person's ability to exhale. While there is no cure for emphysema, smoking cessation will reduce disease progression.

Spirometers are essential devices for diagnosing both restrictive and obstructive lung conditions. Obstructive lung diseases include COPD, bronchitis and asthma. Restrictive lung disorders refer to sarcoidosis, muscular dystrophy, amyotrophic lateral sclerosis, pulmonary fibrosis and obesity hyperventilation syndrome.