Pulmonary Function Testing

The amount of air breathed in and out, or amount held in the lungs after exhalation

The amount of air the lungs can hold

How easily air flows through, to and from, the lungs

The performance of muscles like the diaphragm and costal muscles that help the lungs expand and contract—this is usually measured by proxy, using air flow in the lungs

How well the lungs perform gas exchange, the uptake and release of oxygen and CO2.

A breathing tube connected to a machine is used to measure the amount, speed and flow of air a patient inhales and exhales. A spirometer can also be used to measure lung capacity through a technique called gas dilution, in which the patient breathes in a solution containing a certain amount of helium gas, and concentration of the gas allows us to calculate the volume of the lung and airway space.

Used to measure a patient’s lung volumes and airway resistance. Plethysmography involves sitting in an airtight box in which air pressure can be measured very precisely; the patient briefly attempts to suck in air through a closed mouthpiece, opening the lungs and allowing the machine to calculate lung volume via changes in air pressure.

Another method in which the patient breathes through a tube attached to a machine. The machine uses a series of small changes in air pressure to calculate the space, pressure, and air flow in the lungs.

Often used to diagnose asthma. The patient is given medications that constrict the airways, and the amount of constriction is measured by a spirometer (patients with asthma respond more strongly). They may also then receive a medication that relaxes the airway; this can help distinguish asthma from chronic obstructive pulmonary disease (COPD), which isn’t affected by relaxant medication.

The patient breathes in a certain (nondangerous) amount of carbon monoxide, and a machine calculates how much of the gas was taken up by the lungs. This helps determine the lungs’ ability to perform their ultimate function, gas diffusion—and therefore measures the severity of conditions like bronchitis, emphysema, and COPD.

A blood sample is taken from an artery (usually in the wrist) to look at the concentration of different gases in the blood; like DLCO, this provides information on gas exchange in the lungs.

Testing a patient’s exercise capacity by measuring how far they can walk on a flat surface in the course of 6 minutes.

Used for patients who are on supplemental oxygen. A pulse oximeter (a device usually worn on the finger) is used to determine how much oxygen levels drop during exercise, and how much oxygen is needed to keep them stable.

Various measures of heart and lung function—such as oxygen use, blood pressure, blood oxygen levels, and heartbeat—are measured while a patient exercises, often on a stationary bike.

A physician feeds a thin, flexible viewing instrument called a bronchoscope in through the mouth or nose to examine a patient’s airways; tissue samples of the lungs or airways may also be taken.

A needle injected through the chest wall is used to remove fluid that has built up in the space around the lung lining (the pleural space), or to sample the fluid for analysis.