Lung function test for asthma | Pulmonary function diagnostics for bronchial asthma

Lung function test for asthma

The clinical symptoms are usually already decisive in the diagnosis of asthma. Pulmonary function tests are used here to accurately assess the current lung function and to monitor the course of the therapy. Typically, various tests are performed to determine different pulmonary (lung) parameters.

These include, among others: The common procedures and their significance in asthma diagnostics are briefly described below:

• Spirometry
• Gank body plethysmography
• Pulse Oximetry
• Peak Flow Meter.

This procedure forms the basis of asthma diagnostics. Spirometry is a procedure in which patients breathe into and out of the spirometer through a mouthpiece. Nasal breathing is interrupted by a nose clip.

Spirometry can be used to determine various pulmonary parameters or volumes. For the diagnosis of obstructive diseases (diseases in which the airways are constricted, e.g. asthma), the one-second capacity as well as the vital capacity are of importance here. The vital capacity is the total amount of maximum inhaled and exhaled air.

The one-second capacity is obtained when the patient exhales the maximum possible volume into the spirometer after a deep inhalation with a strong breath. In patients with obstructive diseases, which include bronchial asthma, exhalation is more difficult. Therefore, the one-second capacity of this test is then reduced.

This test, in which the patient exhales forcedly within one second after maximum inhalation (therefore also “forced expiratory volume in one second = FEV1”) is called Tiffeneau test. In order to be able to compare the values better, this second capacity is set in relation to the vital capacity, which can also be determined in spirometry. If the second capacity is less than 80% of the vital capacity, this indicates an obstructive disorder such as bronchial asthma.

In practice, three measurements are usually taken, the highest value of which is then used for evaluation. Spirometry can be extended by an ergometer (ergospirometry). Ergospirometry is used to measure pulmonary volumes under stress.

Patients with pronounced bronchial asthma are generally less able to cope with stress than people without obstructive disease.This procedure, which is also called body plethysmography, is essential in the diagnosis of asthma. It is used to definitively confirm an obstruction and to differentiate asthma from other obstructive diseases. The patient sits in an airtight cabin and breathes in and out normally.

As he inhales and exhales, the pressure in the cabin changes. These pressure changes are recorded by measuring devices. With whole-body plethysmography, the airway resistance as well as the total intrathoracic gas volume, the gas volume of the entire thorax, can be recorded.

Lung patients with bronchial asthma show increased breathing resistance during exhalation. This is a clear indication of an obstruction, as it makes exhalation more difficult. The peak flow meter is used to monitor the progress of asthma diagnostics.

It is not suitable for identifying asthma. It is a medical measuring device that measures the maximum flow velocity during forced exhalation. The examination procedure is very simple.

The patient inhales once as deeply as possible and holds the air briefly. Then he takes the mouthpiece of the peak flow meter into his mouth and encloses it tightly with his lips. Now he has to exhale into the device with a strong breath.

A small resistance is built into the tube of the peak-flow meter, which is naturally shifted more the stronger the patient’s exhalation. A pointer then indicates a deflection. This rash is higher in healthy lung patients than in patients with bronchial asthma.

The peak flow meter is not suitable for making a diagnosis of asthma, as there is a wide interval of acceptable values. However, it is suitable for monitoring asthma progression for the following reason: The test can be repeated at certain intervals during asthma therapy, thus enabling the values to be compared with each other or with the patient’s best value. This shows, for example, whether the patient’s condition has improved or worsened somewhat as a result of therapy.

On the basis of this monitoring the therapy can be adjusted. Since peak-flow meters are not calibrated measuring devices, the same measuring device should always be used for follow-up. Pulse oximetry is the last method used in asthma diagnostics.

This method measures the oxygen saturation of the arterial blood in a non-invasive way. For this purpose, an adhesive sensor is preferably placed on the finger or earlobe. This method makes use of the fact that the hemoglobin of the blood absorbs light differently depending on the oxygen load.

The device can measure this and thus determine the oxygen saturation, which should normally be above 97%. In asthmatics, this oxygen saturation may be reduced because breathing and especially the exhalation of carbon dioxide is more difficult. General information on the procedure for a pulmonary function test can be found under Pulmonary Function Test.

In the diagnosis of asthma, various tests are carried out to assess lung function in addition to other examinations. These include spirometry, whole-body plethysmography, the peak flow meter and pulse oximetry. Spirometry provides initial indications of an existing obstruction, which are then confirmed by the obligatory body plethysmography.

The peak-flow meter then serves to monitor the progression of the asthma and can be very helpful in finding the optimal therapy. Pulse oximetry provides information about the oxygen saturation of the arterial blood, which can be reduced in lung diseases such as asthma.