Vital capacity is a parameter of spirometry. It provides information about lung function during inhalation and exhalation. If expiratory vital capacity is significantly different from inspiratory vital capacity, lung disease is probably present.
What is vital capacity
Vital capacity is a parameter of spirometry. It provides information about lung function during inhalation and exhalation. Spirometry measures lung function using a device called a spirometer. The lung function tests determine values for inspiration as well as values for expiration. That is, they look at both inhalation and exhalation. A core variable of all lung function tests is the so-called vital capacity. With reference to inhalation, we are talking about inspiratory vital capacity. The expiratory vital capacity, on the other hand, is the core variable for lung function during exhalation. Both variables can be measured during normal breathing or forced breathing. Forced breathing corresponds to breathing at maximum rate. The associated vital capacities are referred to as forced expiratory and forced inspiratory vital capacities. Other core variables of the pulmonary function test are lung volumes. They describe the volume of air that is in the lungs and airways during inspiration and expiration. Factors such as age and body size play a role in the target values of vital capacities and lung volumes.
Function and task
The lung is a paired organ that serves active respiration. Oxygen is absorbed from the air we breathe and transported to the individual tissues and organs of the body via the transport medium blood. This transport is vital. All cells in the human body are absolutely dependent on oxygen for their survival. If oxygen no longer reaches them, they die. However, the lungs are not only relevant for the uptake of oxygen, but play an equally important role in the removal of carbon dioxide, which is the end product of the body’s metabolism. If this removal is disturbed or interrupted, symptoms of poisoning set in. The main site of gas exchange is the alveoli of the lungs, which have a total surface area of 140 m2. As a medical specialty, pulmonology deals with the lungs and lung function. The pulmonologist uses various tests to determine lung volumes and vital capacities, which in turn allow conclusions to be drawn about lung function. He compares the determined values with the target values and makes a diagnosis if necessary. Vital capacity is the central parameter of lung function and is used as a parameter in spirometry. The inspiratory vital capacity provides information about lung function during inspiration. Expiratory vital capacity refers to exhalation. To determine the vital capacities, the patient breathes through a mouthpiece. Nasal breathing is prevented by a nasal clamp. In addition to physical relationships, such as air pressure or turbulence in the lungs, the cooperation of the patient influences the accuracy of the vital capacity measurement. The patient must inhale maximally and exhale maximally during the measurement. Static vital capacity refers exclusively to the air volume of the lungs themselves. Dynamic vital capacity also takes into account the flow of gas during inhalation and exhalation. Expiratory and inspiratory vital capacities are static vital capacities. The forced vital capacity is a dynamic parameter. Vital capacity has different target values depending on the patient’s age and body size. The equations VC_{m} =(27.63 – 0.112 a) cdot g quad (mathsf{in cm^3})and VC_{w} =(21.78 – 0.101 a) cdot g quad (mathsf{in cm^3}) are considered the basis for determining the target vital capacity. In it, g refers to body height in centimeters and a corresponds to age in years. Unlike inspiratory vital capacity, expiratory vital capacity is measured in three individual steps. The maximal expiration is followed by a slow maximal inspiration and finally the maximal expiration, which is used for the measurement.
Diseases and complaints
Normally, the physician always collects values on all vital capacities (expiratory, inspiratory, forced expiratory, forced inspiratory) during spirometry. If the capacities are not within the target range, lung disease is not necessarily present.The patient may simply have a below-average constitution. For disease diagnosis, the set point is less relevant than the approximate correspondence of the individual vital capacities. Thus, if the patient’s lungs are healthy, the four vital capacities should be relatively equal. If they differ greatly, there is probably obstructive lung disease. In this case, the inspiratory vital capacity is significantly greater than the expiratory vital capacity, which in turn significantly exceeds the forced vital capacity. In obstructive lung disease, there is a narrowing or obstruction of the airways called obstruction. Diseases from this group include bronchial asthma. The cause of this disease is a combination of genetic disposition and environmental factors. Climatic factors and psychological components can also be involved in asthma disease. In addition, the diseases from the group COPD belong to the obstructive lung diseases. These diseases are mainly caused by cigarette smoke. The lungs often become violently inflamed by the smoke and the airways become obstructed or narrowed as a result. Not only divergent vital capacities are frequently a smoker’s problem, but likewise abnormally low vital capacities.
