Written by: Dawn Patterson, Supervisor Respiratory OverRead
On average, it costs $539 per person annually to treat an asthmatic and $4,150 to treat COPD. These costs reveal a need for improved symptom management and reduction in exacerbations that would reduce the need for escalated care and in return reduce overall costs. In addition, it would increase the quality of life for patients by avoiding or preventing an exacerbation event.
This post will address these three basic questions:
- Can spirometry be used to measure hyperinflation?
- Is inspiratory capacity a dependable parameter to measure hyperinflation?
- What impact does centralization have on inspiratory capacity?
Before we get started, let’s step back to basics for a minute: what is hyperinflation and why do we measure it?
Hyperinflation is the volume of air that is trapped in a patient’s lungs at the end of exhalation. The ability to fully exhale depends on the degree of airflow limitation and the time available for exhalation, which is why greater hyperinflation occurs during exacerbations or exercise. Because COPD is an irreversible disease characterized by a reduced expiratory airflow, COPD patients already start at a higher lung volume than that of a healthy individual. With increased activity, anxiety or if the patient becomes hypoxic, their respiratory rate increases, decreasing expiration time and ultimately creating dyspnea. As the disease progresses so does the hyperinflation, producing significant detrimental effects on a patient’s breathing.
There are several ways to confirm Hyperinflation including a physical exam, X-ray or CT scan. Another and more accurate way to confirm hyperinflated lungs is to measure lung volumes and capacities. Measurement of lung volumes provides a tool for understanding normal function of the lungs as well as disease states. The amount of air in the lungs is subdivided in two groups, lung volumes (VT, IRV, ERV and RV) and lung capacities (TLC, VC, IC, FRC). Measuring lung volumes in COPD patients can give us a better understanding of hyperinflation and how treatments work to improve their daily activity.
So, how do we measure IC? One way is by using body plethysmograph, also known as body box. Body Box is the GOLD standard for measuring lung volume. What is nice about the body box is that it not only measures spirometry, but also thoracic lung volumes and resistance. Most importantly it can be performed quickly and will give absolute values. However, it does have a few draw backs. Some COPD patients are claustrophobic and may not want to be placed in an airtight closed system. It’s also rather large and takes up a lot of room. In addition, severe COPD patients may require Oxygen and have other devices which may not be able to go into the body box. The most significant disadvantage, especially within clinical research, is having non-standardized equipment at each site. With sites using their own equipment, there is a possibility of equipment variability, poor equipment feedback (inconsistent assessment) and inconsistent site training – this will likely result in poor quality data, thus having inconclusive results. Having the same body box at each site will provide you with a greater percentage of acceptable data but unfortunately, it can be quite costly.
An alternative to the body box is spirometry. Spirometry (forced or slow) is used to confirm airway obstruction and physicians are in a position to detect COPD in its early stages. Spirometry is a relatively simple and noninvasive test which only takes a few minutes of the patient’s and technician’s time. There are many different devices to choose from which are smaller in size, and much lighter than the body box. More importantly, it’s affordable. According to the GOLD standard, FEV1 is the parameter of choice for diagnosis and monitoring progression of airway obstruction. It also provides a starting point for determining a patients initial treatment plan, however it does have its limitations. The changes in FEV1 value does not necessarily reflect changes in dyspnea and is limited to exercise performance. It is also limited in clinically assessing patients. For example, patients with mild and severe COPD may have similar FEV1s but they can be at complete opposite ends of the spectrum when it comes to quality of life.
Forced spirometry consists of a patient taking a deep breath in and forcefully expiring until the patient cannot exhale out any more, then the patient is asked to take another deep breath in. It is essential that the patient performing the test be clearly instructed in the procedure prior to the start of each test. A very enthusiastic demonstration by the technician is crucial so that the patient makes a maximum effort when carrying out the forced expiratory test. With this test, the forced expiration may cause airways to prematurely close and trap air, resulting in an inaccurate measurement.
The primary difference with slow spirometry is that the expiration into the spirometer is done slowly. Patients who have trouble with the force maneuver, due to an inability to complete a full exhalation, may do better with this test. Patients should be relaxed and asked to breathe regularly for several breaths until the end expiratory lung volume is stable (this usually requires at least 5 tidal breaths). They are then encouraged to take a deep breath to TLC with no hesitation, followed by an expiration. It is important, as with all the other tests, to make sure that it is done properly. If the inspiratory breath is too slow due to poor effort or hesitation, or if there is premature closure of the glottis, the IC may be underestimated. As with force, it is important for the patient’s cooperation and understanding of the test. The technician should be enthusiastic about the test but not as demanding.
In a study of 93 patients in a primary care setting, it was shown that in addition to measuring dyspnea and quality of life, IC is also an established reliable parameter in measuring hyperinflation. It has also been noted that Spirometry is highly reproducible and gives a clear indication of the extent of hyperinflation. After gathering all of the data, it is important to make sure that the data collected in clinical trials is of the best possible quality. The best way to eliminate any transcriptional errors and reduce variability is by having the data centralized.
Respiratory clinical trials can be challenging and centralizing IC data plays an important role in clinical research. Patients entering these trials already have breathing that is compromised, raising variability from the beginning. However, performance by the patient is extremely important to producing accurate results. Just as relying on the technician to be an enthusiastic motivator for the patient undergoing a test, it is important that the site is delivering data that is acceptable. A centralized approach to spirometry helps you increase data quality, by providing the ability to better see treatment effects. Centralization institutes quality control measures in each step of the clinical trial process so the study has the advantage of cleaner data, which in turn minimizes the negative impact to your data and your budget. For example, before centralization, there were 45,497 measurements with 6,094 (or 14%) that were unusable data. After having a team of expert reviewers assess the measurement and data quality based on the current ATS/ERS standards that percentage of unusable data dropped down to 9%.
As previously stated, improper training and poor patient effort will result in poor quality data and it is crucial to educate and monitor the technicians to improve the accuracy of data reporting. With centralizing, data is transmitted to a central database and is graded according to a combination of the ATS/ERS standards and pharmaceutical company specifications. The overread of data quality is reviewed proactively, so sites with a large amount of poor quality data can be targeted during the trial for retraining. As noted in the chart below, the most frequent error is repeatability. The 2005 ERS/ATS guideline on spirometry has established a repeatability criterion (highest to 2nd highest value) of 150 mL for Vital Capacity (VC), while for the Inspiratory Capacity (IC) there are no set established criteria. More studies need to be evaluated to estimate an achievable repeatability for IC. Some of the other errors are unstable baseline, cough, unstable breathing, breathing frequency, and improper procedure.
*Source: ERT Respiratory Solutions
In summary, although body plethysmography gives absolute values, it is an expensive way to monitor hyperinflation. IC together with spirometry on the other hand has been shown to be a dependable, inexpensive and simpler parameter that can indicate the presence and management of lung hyperinflation. The aim of centralization, standardized equipment and training, is to increase the percentage of acceptable data and provide the best quality data – resulting in greater patient retention, and increasing statistical power at a reduced price.
For more information on ERT’s Respiratory Solutions, please visit: http://www.ert.com/respiratory