How is Lung Capacity Measured?

Did you know that the maximum amount of your total lung capacity is about 6 liters? That is about three large soda bottles!

Typically, men have a greater lung capacity than women. At rest, a man’s lungs can hold about 1.5 pints of air, while women’s lungs can hold around 0.6 to 0.8 pints. However, most of us do not use our full lung capacity.

Your lung capacity naturally declines with age, starting at age 30. By the age of 50, your lung capacity may be reduced by as much as 50 percent. This means that the older you get, the harder it is for your lungs to breathe in and hold air.

There are several natural body changes that happen as you get older which may cause a decline in lung capacity. Muscles like the diaphragm can get weaker. Lung tissue that helps keep your airways open can lose elasticity, which means your airways can get a little smaller. Also, your rib cage bones can change and get smaller which leaves less room for your lungs to expand.

Lung capacity predicts health and longevity. A 29-year follow-up of the Buffalo Health Study concluded that pulmonary function is a long-term predictor of respiratory mortality and should be used as a tool for general health assessment.

Taking spirometry tests is a good way to measure lung function. Spirometry is the most common type of pulmonary function or breathing test. This test measures how much air you can breathe in and out of your lungs, as well as how easily and fast you can blow the air out of your lungs.

This test can help diagnose problems like asthma and COPD or can be done to check lung function before a surgery. You may also have spirometry done if you are being treated for a chronic lung disease, such as COPD, asthma, or pulmonary fibrosis, to determine if your disease is improving or worsening and whether your medications or inhalers are working properly. Spirometry can be done in the doctor’s office or in a special pulmonary function testing lab.

Spirometry measures two key factors: expiratory forced vital capacity (FVC) and forced expiratory volume in one second (FEV1). Your doctor also looks at these as a combined number known as the FEV1/FVC ratio. If you have obstructed airways, the amount of air you’re able to quickly blow out of your lungs will be reduced. This translates to a lower FEV1 and FEV1/FVC ratio.

During the test, you will be sitting upright. A clip is placed on your nose and you will be given a plastic mouthpiece connected to the spirometry machine. You will place your lips tightly around the mouthpiece and be asked to take in as big and deep a breath as possible and then blow out as hard and fast as you can. This maximal effort is very important, and testing will be repeated at least three times to get the best results. The testing takes about 30 to 45 minutes.

Spirometry will give your doctor information about why you may have a cough, shortness of breath, or noisy breathing and help diagnose certain lung problems. After the test, you can return to your normal daily activities.