Normal Values

19 Sep 23

Understanding normal values in spirometry: what to expect during a lung function test

Spirometry is by far the most useful test to detect and monitor abnormalities in the lung function. Whether patients are showing symptoms that may be indicators of respiratory problems or they’re just leading an unhealthy lifestyle – i.e. the patient is a chain smoker – a spirometry test can help identify lung diseases from an early stage.

Several different types of measurements can be obtained from a spirometry test, many of which may feel obscure or even intimidating to non-experts. In this article, we will try to make it easier to understand the most commonly used spirometric values.

  1. What happens during a spirometry test

When taking a spirometry test, patients are required to breathe into a device named spirometer, which will record the amount of air they can breathe in and out, as well as how fast and steadily they can exhale. The expiration time is generally measured in seconds, with six seconds being the standard duration for the test.

The results of the test can be used to identify conditions like asthma, COPD, restrictive lung diseases or other diseases related to pulmonary function.

  1. Normal values in spirometry: the most common parameters

It is important to keep in mind that the so-called normal values in spirometry may vary from patient to patient, according to parameters such as age, sex, body weight or height. Doctors usually calculate the reference values on the basis of these parameters and use them as reference for the test results. A result is considered normal if the value falls over 80% of the predicted score, while lower percentages are indicators of respiratory issues.

  1. FVC, Forced Vital Capacity

FVC measures the volume of air that a patient can exhale with a maximal forced expiration effort after a deep inhaling, simply put, how much air a patient can breathe out by blowing as fast as possible.

Average values in healthy patients aged 20-60 range from 5.5 to 4.75 liters in males and from 3.75 to 3.25 liters in females.

  1. FEV1, Forced Expiratory Volume in 1 Second

This parameter measures the amount, or volume, exhaled by a patient in the first second of the expiration after a full inspiration.

Average values in healthy patients aged 20-60 range from 4.5 to 3.5 liters in males and from 3.25 to 2.5 liters in females.

  1. FEV1/FVC Ratio

This parameter is calculated by dividing FEV1 by FVC, and is usually express as both a numerical (absolute) value and a percentage. This value is especially important for the detection of COPD, Cronic Obstructive Pulmonary Disease, as it can indicate resistance or obstructions to the expiratory airflow.

Healthy adults aged 20-60 should expect the percentage to be between 70% and 85%.

  1. Spirogram

This is a flow/volume graph showing a visual record of the expiration. The breath flow is usually shown on the X axis and expressed in liters per second, while the breath volume is shown on the Y axis and expressed in liters.

Non-medical personnel may find it hard to interpret the chart but, in general, a healthy patient’s curve will show a jump right after the start of the expiration, then a steady and quick raise to a sharp peak, and finally a smooth and slow fall.

Patients with respiratory problems may instead get different visuals, such as slow start or slow rises in the flow, an inconstant flow with several peaks, or even an abrupt interruption of the curve.

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