Pulmonary function testing measures the function of lung capacity and lung and chest wall mechanics to determine whether or not the patient has a lung problem. Pulmonary function testing is commonly referred to as “PFT” and such tests are usually performed by Certified or Registered Pulmonary Function Technologists (CPFT or RPFT) who are credentialed by the National Board for Respiratory Care (NBRC). When a patient is referred for pulmonary function testing, it means that a battery of tests may be carried-out including simple screening spirometry, static lung volume measurement, diffusing capacity for carbon monoxide, airways resistance, respiratory muscle strength, and arterial blood gases. Spirometry is the standard method for measuring most relative lung volumes; however, it is not capable of providing information about absolute volumes of air in the lung. Thus a different approach is required to measure residual volume, functional residual capacity, and total lung capacity. Two of the most common methods of obtaining information about these volumes are gas dilution tests and body plethysmography.
Body plethysmography is a very sensitive lung measurement used to detect lung pathology that might be missed with conventional pulmonary function tests. This method of obtaining the absolute volume of air within one’s lungs may also be used in situations where several repeated trials are required or where the patient is unable to perform the multibreath tests. The technique requires moderately complex coaching and instruction for the patient.
HOW IT WORKS
The plethysmography test is done by enclosing the subject in an airtight chamber often referred to as a body box. A pneumotachometer is used to measure airflow while a mouth pressure transducer with a shutter measures the alveolar pressure. The most common measurements made using body plethysmographs are thoracic gas volume and airway resistance. Using body plethysmography, doctors can examine the lungs’ resistance to airflow, distinguish between restrictive and obstructive lung diseases, determine the response to bronchodilators, and determine bronchial hyper reactivity in response to methacholine, histamine, or isocapnic hyperventilation.
SPACE REQUIREMENTS
The dimensions of the body box are approximately 30″ by 35″ by 71″ high with a footprint of about 7.5 square feet. The recommended area for the body box itself and an adjacent computer console is 54 square feet (7′ by 9′) to allow for opening the body box door.
THE GOLD STANDARD
The Body Box 5500 Series (Morgan Scientific, Inc.) is the gold standard in pulmonary function testing. It is a precise, elegant pulmonary function instrument that is designed to measure all the thoracic gas volume, whether in communication with the airways or not, to provide a true assessment of absolute lung volume. Patients can easily exit the body box should they feel uncomfortable and there is easy communication between the respiratory therapist and the patient for reassurance and testing instructions. The test can be carried out quickly with the least inconvenience to the patient. The body box interior is quiet, bright and easy to decontaminate.
This article is an update of previous post.