Interpretation Answer

In this test we will be using the FEV₆ as a surrogate for the FVC.  The FEV₆ is obtained when the maneuver is shortened by terminating the maneuver after only 6-seconds of exhalation.  The FEV₆ is not recommended for use in occupational testing. 

The first step in interpreting results is to determine if you have a valid test.  In this test, we do have three acceptable maneuvers, but we do not have a repeatable test.  However, the lack of a repeatable test is not a sufficient condition to warrant failing to interpret the results -- particularly in patients with airways obstruction who have a greater difficulty in producing a repeatable test.  In this case, the FEV₁/FEV₆% is well below the LLN which would suggest an obstructive pattern.  However in these results, both the FEV₆ and FEV₁ are greater than 120% or the predicted values.  Since 100% is the average percent predicted in a normal population, these results are not consistent with an obstructive lung disease pattern. 

The explanation for these results is a flow zero error for the following reasons:
1. The test in not repeatable, particularly FEV₆ (FVC).
2. The percent predicted values (FEV₁ and particularly FEV6 or FVC) are above 120% with a low FEV₁/FEV₆ (FEV1/FVC%).
3. The volume is constantly increasing or there is a constant flow (see lines on graphs).  Even with airways obstruction, the volume-time curve should eventually plateau.  However, it is difficult to determine if the curve would not have eventually exhibited a plateau when only a 6-second maneuver is performed.  Some individuals, particularly those with airways obstruction, may require longer than 6-seconds to reach a plateau.  This is one of several reasons why the shortened maneuver of only 6-seconds (FEV₆) is not recommended for use in occupational testing as a surrogate for FVC.

Although the above criteria may occur without a flow-zero error, to see all three conditions in the same test is highly suggestive of a flow zero error.  Zero Errors can occur due to faulty electronic zeroing of the pressure transducer, resulting in either a false steady increase in flow or a false steady decrease in flow much like a leak.  Although it is dependent on the type of flow-spirometer, usually the faulty zeroing occurs when the sensor is moved or air is allowed to flow through the sensor while a zero is being determined.

The test should be repeated, taking greater care to keep the flow sensor still, without any air flowing through the sensor, while the instrument is performing a flow zero.  Regardless of whether there is a flow-zero error, the lack of a repeatable test would suggest some caution in interpreting the results as a mild obstructive lung disease pattern.

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