While spirometry is the most commonly used method for evaluating pulmonary function in clinical practice, there are times when it’s necessary to measure the volume of air the lungs cannot displace (static lung volumes). This is why body plethysmography with a booth remains an essential technique in pulmonary function testing.
The first test was conducted by DuBois in the 1950s, and while there have been numerous scientific advancements since then, today, body plethysmography using a body box is still considered the gold standard for measuring lung volumes. The body box plays a crucial role, as it allows the test to be performed under controlled environmental conditions, ensuring reliable data. For instance, it accurately measures various gas volumes, such as thoracic gas volume (TGV), functional residual capacity (FRC), residual volume (RV), and total lung capacity (TLC). This technique also measures total airway resistance (RawTOT), specific airway resistance (sRaw), airway conductance (Gaw), and specific airway conductance (sGaw).
In this article, we present scientific evidence confirming that body plethysmography with a booth is indispensable in today’s pulmonary function testing.
By América Torres
Differences Between Spirometry and Body Plethysmography
Before drawing conclusions, it’s important to understand the key differences between spirometry and body plethysmography. Spirometry, a test that requires calibration based on the atmospheric conditions of the test site, measures the volume of air a patient inhales or exhales, either absolutely or over time, and is expressed in a volume/time curve. With the addition of ultrasound technology, devices like the SpiroScout ultrasonic spirometer (which doesn’t require calibration) can measure flow and generate flow/volume curves (FEV1, FVC, SVC, and MVV).
Body plethysmography, on the other hand, allows simultaneous measurement of functional residual capacity (FRC) and provides precise, reliable measurements of airway resistance (Raw). This includes sRawtot (total specific airway resistance), sRaweff (effective specific airway resistance), sRaw 0.5, (specific airway resistance at flow +/- 0.5 L/s), and sRaw (specific airway resistance of the airway), among others.
Is the Body Plethysmograph Booth Truly Essential?
Once we define both tests, it becomes clear that each serves a different function. Rather than competing, spirometry and body plethysmography complement each other. But what do scientific studies say about plethysmography with a booth? Researchers have harnessed the power of this “magic box” to detect values that spirometry cannot. Let’s look at some interesting findings.
Scientific Studies Supporting Plethysmography
In the study “Correlation of Spirometry and Body Plethysmography During Exercise-Induced Bronchial Obstruction” by Johannes Schulze et al., it was concluded that changes in specific airway resistance (sReff) were more sensitive and provided a better indication of pulmonary deterioration than changes in FEV1, which underestimated the degree of hyperinflation.
In “Clinical Roles of Lung Volumes Detected by Body Plethysmography and Helium Dilution in Asthmatic Patients: A Correlation and Diagnosis Analysis”, researchers highlighted that body plethysmography is the optimal method for diagnosing asthma. They found that lung volumes assessed by body plethysmography, as well as the differences between plethysmography and helium dilution, can distinguish between mild vs. severe asthma, and moderate vs. severe asthma, but not mild vs. moderate asthma.
Finally, in “Pletismografía corporal: recomendaciones y procedimiento”, a document by Selene Guerrero-Zúñiga et al. from the National Institute of Respiratory Diseases “Ismael Cosío Villegas” in Mexico City, the authors affirm that while several techniques are available to assess pulmonary function, body plethysmography is still the gold standard for measuring lung volumes.
If spirometry results were sufficient, respiratory disease specialists wouldn’t follow up with body plethysmography testing. Wouldn’t you agree?
Calculating Isn’t the Same as Measuring
It’s true that lung volumes can be calculated using flow variables measured with spirometry techniques, but these calculations are only valid in healthy patients under ideal conditions. A pathological patient has unique conditions that aren’t accounted for in these calculations, making them ineffective for therapeutic decision-making. Calculating isn’t the same as measuring. Remember, there are patients, not diseases, and each patient is different. This is why, to date, nothing replaces the numerous advantages of body plethysmography with a body box.
The Body Box Plethysmograph: Still the Gold Standard
Body plethysmography remains the gold standard for lung volume measurement and pulmonary function testing. Despite advancements in spirometry, it provides unmatched accuracy and reliability, especially for complex conditions like asthma and obstructive pulmonary diseases. With its ability to measure critical lung volumes such as Functional Residual Capacity (FRC) and Total Lung Capacity (TLC), body plethysmography ensures precise, personalized diagnostics. As shown in numerous studies, this technique is indispensable for effective patient care.
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Body Plethysmography: Key Questions Answered
What is body plethysmography and how does it work?
Body plethysmography is a pulmonary function test that measures the total volume of air in the lungs, including the air that remains after a full exhalation (residual volume). The patient sits in an airtight booth (body box) and breathes through a mouthpiece. As the patient breathes against a shutter, the changes in pressure inside the box allow the system to calculate lung volumes using Boyle’s Law. It’s considered the gold standard for measuring static lung volumes and assessing conditions like restrictive or obstructive lung disease.
What are the clinical advantages of body plethysmography compared to spirometry?
While spirometry measures the air that a patient can inhale or exhale, body plethysmography provides a complete picture by assessing total lung capacity (TLC), residual volume (RV), and functional residual capacity (FRC). This allows for the detection of air trapping and hyperinflation—key markers in diseases like COPD and asthma. Body plethysmography also delivers more precise data for restrictive disorders, helping clinicians make accurate diagnostic and therapeutic decisions.
When should a clinician order a body plethysmography test?
Clinicians should order body plethysmography when they need a detailed assessment of lung volumes beyond what spirometry can provide. It is especially useful in evaluating patients with unexplained dyspnea, suspected restrictive lung disease, air trapping, or hyperinflation. It’s also recommended before and after bronchodilator testing or in pre-operative evaluations for patients with known or suspected respiratory conditions.