The lungs are a very powerful organ. It has the task of supplying our body with the vital oxygen and removing carbon dioxide with the exhaled air.
With every breath we draw in 0.5 liters of air in our lungs, that’s 10 liters per minute, 14400 liters a day and 5.265.000 liters a year. The lung is the organ that is most directly exposed to pollutants from all of our organs.
Not only these pollutants can damage our lungs, but also congenital disorders or infections can impair lung function. Characteristically, the values change here, which we can check with the help of spirometry (lung function test).
Spirometry is a simple, fast and non-invasive method for measuring lung volumes and respiratory flow strengths. The value of spirometry lies in the diagnosis of bronchoconstrictions such as asthma or chronic obstructive pulmonary disease (COPD). As already mentioned in the name of the COPD, we then speak of an obstruction. At the same time, we can test whether asthma sprays can help affected patients.
The lung function also serves to determine the severity of the obstruction and helps to assess the success of the therapy and the prognosis.
With the help of spirometry, statements can also be made about other disorders of lung function, which include gas exchange or the function of the respiratory pump. However, these measurement data can often only be clearly used with the help of additional diagnostic methods.
How is spirometry performed?
With the spirometer we use, we will first put a clip on your nose, because the breath maneuvers are measured only via the mouth. You will then receive the spirometer and will be asked to completely cover the mouthpiece with your lips and then inhale and exhale three cycles normally and then three times deeply or firmly.
During your breathing maneuvers, the static and dynamic lung function parameters and respiratory flows through the mouth are now measured. The measurements are carried out either with flow sensors or with the help of ultrasonic sensors or the hot wire anemometer, but also with volume sensors such as the turbine. For all mathematicians among us: With flow sensors, the volume is calculated numerically from the integration of the flow over time. In the case of the volume sensors, the flow is determined by differentiating the recorded volume.
When do we do spirometry?
We primarily use pulmonary function to diagnose suspected respiratory diseases (e.g. COPD, bronchial asthma). It is also used when a chronic cough needs further clarification.
The lung function is carried out as standard in our large check-up.
Other areas of application for spirometry are the early detection of damage caused by inhaled noxa, e.g. after smoke poisoning, suspected combined diseases of the lungs and heart, and musculoskeletal diseases with effects on breathing. However, lung function is also used when there is suspicion of diseases of the respiratory pump, which affect the respiratory center, the associated nerves or muscles, and when monitoring the course of bronchopulmonary diseases and their therapy control.
Additional areas of application include occupational health issues and preventive care (e.g. exposure to allergens, dusts, smoke pollution, etc.) and preoperative diagnostics
Which values are determined?
A distinction is made between static and dynamic parameters. Static lung volumes are lung volumes whose measured values are not a function of time. Dynamic parameters change over time (e.g. forced exhalation). The temporal profiles of the respiratory flow strengths and breathed volumes can be easily assigned in the flow-volume curve. During the investigation, you can also see the changes in the flow volume curve yourself. The most important parameters are summarized in the following figure and then explained.
Tidal volume (TV):
Volume that is inhaled or exhaled per breath. The turning point between exhalation and inhalation is the breath position.
Residual volume (RV)
The residual volume (RV) is the volume of air that remains in the lungs after maximum exhalation and thus denotes the amount of breathing air that is permanently held in the lungs and is approximately 1.5 liters in a middle-aged adult.
Functional Residual Capacity (FRC)
The functional residual volume (functional residual capacity) refers to the volume of air that remains in the lungs during normal breathing.
Vital capacity (VC)
The vital capacity VC is the volume difference that can be measured on the mouth between the breathing position with complete inhalation and with complete exhalation. We use the parameter of “inspiratory vital capacity”. To do this, we ask you to slowly exhale from normal resting breathing to the residual volume and then inhale quickly.
Expiratory vital capacity (EVC)
Volume that can be exhaled to the maximum after maximum inhalation. A distinction can be made between slow (“relaxed”) exhalation and forced exhalation. There are no relevant differences in healthy people. In obstructive pulmonary diseases, IVC can be larger than EVC and FVC. EVC is usually larger than FVC.
Forced vital capacity (FVC)
The maximum volume exhaled as quickly as possible after complete inhalation with the greatest effort (Tiffenau maneuver)
Functional residual capacity (FRC)
Volume that is still in the lungs after normal exhalation, i.e. ERC + RV. When using the helium dilution method, only the parts of the lungs that are ventilated are recorded. Physiologically corresponds to the TGV.
(Intra-) thoracic gas volume (TGV, ITGV)
Volume that is still in the lungs after normal exhalation, i.e. ERV + RV. When determined using body plethysmography, both the parts of the lung that are ventilated and the gas-filled parts that are not ventilated are recorded. If there is an Emphysema or trapped air can the TGV can be larger than FRC.
Residual volume (RV)
Volume that remains in the lungs after maximum exhalation and cannot be exhaled
Total capacity (TLC)
Volume that is in the lungs after maximum inhalation, i.e. VC + RV one-second capacity (FEV1, forced expiratory volume in one second) Volume that can be exhaled as quickly as possible in the first second after maximum inhalation with the greatest effort
Relative one-second capacity (FEV1%)
The volume exhaled as quickly as possible after maximum inhalation with the greatest effort in relation to vital capacity (FVC or VCin). It is expressed as a percentage of FEV1 in the FVC or VCin.
Peak flow (PEF)
maximum breath current during exhalation, flow rate that is reached when exhaling with the greatest effort after complete inhalation. Peak Inspiratory Flow (PIF) maximum breath current during inhalation, flow rate that can be reached during inhalation with the greatest effort after complete exhalation.
Maximum expiratory respiratory flow or flow velocity at the point in time at which 75% of the VC are still to be exhaled. (expiratory = when exhaling)
Maximum expiratory respiratory flow or flow rate at the point in time when 50% of the VC are still to be exhaled
maximum expiratory respiratory flow or flow velocity at the point in time when 25% of the VC are still to be exhaled
maximum expiratory respiratory flow or flow velocity in the volume section 75% -25% of the FVC still to be exhaled
maximum (forced) expiratory respiratory flow or flow rate at the point in time at which 25% of the VC were exhaled (= MEF75)
maximum (forced) expiratory respiratory flow or flow rate at the point in time at which 50% of the VC were exhaled (= MEF50)
maximum (forced) expiratory respiratory flow or flow rate at the point in time at which 75% of the VC were exhaled (= MEF25)
maximum expiratory respiratory flow or flow velocity in the volume section 25% -75% of the exhaled FVC (MEF75-25)
Airway resistance, flow resistance in the bronchi when breathing