Bodyplethysmography is a procedure to determine lung function in respiratory diseases. It involves measuring important respiratory physiologic variables such as breathing resistance, total lung capacity, and residual volume. The method is very reliable and provides more concrete information on lung function than conventional spirometry.
What is body plethysmography?
Bodyplethysmography is a method for determining lung function in respiratory diseases. The method is very reliable and provides more concrete information about lung function than conventional spirometry. Bodyplethysmography was introduced into clinical practice for lung function testing in 1956. Today, it is considered the procedure of choice in clinics and practices of pulmonary specialists. Another name for bodyplethysmography is whole-body plethysmography, since the respiratory volume of the whole body is determined. Plethys is the Latin term for volume, while the suffix “-graphy” indicates graphic representation. Bodyplethysmography is therefore used to display the volume of air inhaled and exhaled by the entire body. The capacity of lung function gives information about its efficiency. Three parameters in particular are of interest for measurement. These are the respiratory resistance, the residual volume and the total lung function. The breathing resistance represents the resistance that must be overcome during breathing. Residual volume describes the residual volume of air in the lungs after exhalation. Total lung capacity is characterized by different volumes such as respiratory gas volumes, respiratory volumes and lung volumes. By determining these parameters, bodyplethysmography is good at diagnosing obstructive and restrictive lung disease.
Function, effect, and goals
Bodyplethysmography is based on Boyle and Mariott’s law of physics. According to this law, if the temperature remains constant, the product of pressure and volume also remains constant. Thus, if the volume increases due to expansion, the pressure automatically decreases and vice versa. The measurement is carried out in an almost airtight cell. A tiny air leak ensures that the increase in cabin pressure is compensated by the patient’s body temperature. Breathing in through a spirometer causes the chest to rise, increasing the volume of the lungs. At the same time, the volume in the cabin decreases minimally, causing a slight increase in pressure. This change in pressure due to breathing is determined and the volume of air inhaled or exhaled is calculated from this. From this data, conclusions can be drawn about the three important parameters breathing resistance, residual volume and total lung capacity. For example, the residual volume (remaining volume after exhalation) in a healthy person is approximately 1.5 liters. Classic spirometry provides initial indications of lung disease. Only the inhaled and exhaled volume is measured, without taking pressure changes into account. Residual volume and airway resistance cannot be determined by this method alone because the intrapulmonary pressure is not measured. However, it is a prerequisite for distinguishing obstructive from restrictive lung disease. Obstructive lung diseases are characterized by narrowing or obstruction of the airways. Thus, obstructive lung diseases include such conditions as bronchial asthma, chronic bronchitis, or COPD (chronic obstructive pulmonary disease). These respiratory diseases are characterized by blockage of airflow. In restrictive lung diseases, the development of the lungs is impeded by scarring changes such as in pulmonary fibrosis or lung damage caused by asbestos. The normal residual volume of the lungs can no longer be achieved. With bodyplethysmography, respiratory diseases can be immediately assigned. Furthermore, bodyplethysmography also reliably indicates the severity of the lung disease. By measuring regularly, the course of the disease can be followed and treated quickly if there is a dramatic change. The measurement is combined with spirometry. The patient sits in the cabin and breathes in and out through a spirometer. In contrast to classical spirometry, the measurement is independent of the patient’s cooperation. Even breathing at rest is sufficient for the measurement. A computer program evaluates the slight changes in pressure in the cabin. The computer program also takes into account the patient’s age and gender.A sensor records the force of the breathing movements. The measured values show whether and how lung function has changed. In particular, it can be read whether the breathing resistance is too high (obstructive airway disease) or the residual volume too low (restrictive lung disease). Although the measurement is independent of the patient’s cooperation, the patient should still follow the physician’s instructions for inhalation and exhalation. The results are evaluated within a few seconds. An experienced pulmonologist can then already diagnose the first diseases. Very quickly it becomes clear which further tests need to be performed. These are usually diffusion tests, ergospirometry and provocation tests. For patients, bodyplethysmography is slightly more time-consuming than classic spirometry.
Risks, side effects, and hazards
There is no health risk associated with bodyplethysmography. There is no radiation or pressure exposure. The glass cabin is not locked and can be left at any time if respiratory problems or panic attacks occur. The examination method is therefore absolutely harmless and is performed even on small children without complications. Serious complications have hardly ever occurred. On the contrary, bodyplethysmography can greatly minimize the risk of lung diseases. Through regular measurements, the course of the disease can be monitored and treated concomitantly. For many patients it would be a risk not to use this method. Another advantage is that bodyplethysmography can be performed without the use of force during breathing. The procedure is essential for a definitive diagnosis. However, the equipment required and the acquisition costs are considerable. This also explains why bodyplethysmography is performed only in clinics and by specialists.
