The Spirometer, 1846 – A Window into Respiratory Disease

An old Sanskrit proverb, frequently used by modern practitioners of meditation, says: “Breath is life, and if you breathe well, you will live long on earth.” 

Scientists have likewise long been interested in measuring breathing and lung capacity to assess health. In 1846, English surgeon John Hutchinson, who was interested in tuberculosis, published a paper on lung capacity in more than 2000 people. He concluded that the volume of air forcibly expelled from fully inflated lungs predicted early death (a finding confirmed in many modern studies). He also found that adult lung capacity generally decreases with age.

To take measurements, Hutchinson placed a calibrated bell-shaped object immersed in water inside a tube to capture blown air, inventing the spirometer. His subjects ranged from wrestlers and people of short stature to cadavers. He tried to fill cadaver lungs with as much air as possible and measured the volume expelled during the chest’s elastic recoil.

Today, doctors measure lung function using modern versions of Hutchinson’s spirometers, testing the maximum volume and flow of air expelled as forcefully as possible after a deep breath. A graph of exhaled volume over time (for example, forced exhalation over six seconds) is used to assess conditions such as:

• Lung cancer
• Heart attack
• COPD (chronic obstructive pulmonary disease caused by narrowed airways, for example through chronic bronchitis and emphysema)
• Asthma
• Cystic fibrosis (airway blockage by mucus) 
• Pulmonary fibrosis (excess formation of fibrous connective tissue in the lungs)

Hutchinson was not the first to study human lung capacity, but thousands of clinical measurements using his new device led to his recognition as the spirometer’s inventor.

How Are Spirometry (Lung Function Test) Results Interpreted?

Spirometry is a medical test assessing lung function. It measures maximum breathing capacity, inhalation and exhalation rates, and other respiratory parameters. Results are interpreted using a range of measurements. The following describes their general interpretation:

1. Tidal Volume (VT): This is the air volume entering and leaving the lungs in a normal breath. A normal tidal volume is generally 500-800 ml. A lower value may indicate inadequate air exchange or limited respiratory function.
2. Forced Expiratory Volume in the First Second (FEV1): This is the volume exhaled during the first second after maximal inhalation. It generally reflects the lungs’ capacity to expel air. Normally, FEV1 should be at least 70-80% of the baseline value. A lower value may indicate restricted airflow or obstruction.
3. Baseline Value (FVC): This represents the difference between maximal inhalation and maximal exhalation. It normally varies with age, sex and body size. FVC reflects total lung capacity; a lower value may indicate restriction or limited air exchange.
4. Forced Expiratory Volume in the Second Second (FEV2): This is the volume exhaled during the second second after maximal inhalation. FEV2 reflects expiratory flow and is usually interpreted by comparison with FEV1. The FEV1/FVC ratio is used to assess obstructive breathing disorders.

A respiratory specialist or pulmonologist usually evaluates spirometry results. Normal values may vary with age, sex, height and other health factors.

Article image caption: An illustration showing how a spirometer is used.

Historical figures mentioned: John Hutchinson (1811–1861)

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