Background

The FIVC that follows the end of the forced exhalation should not exceed the FVC by the larger of 0.100 L or 5% of the FVC to confirm the forced exhalation started from full inflation. PFT operators often cite this addition to spirometry to be difficult for patients to do.The IVC of test gas for the DLCO test should not be less than 90% of largest VC measured that day.  We sought to characterize the relationship between these three parameters in a clinical trial for IPF. 

Methods

 We evaluated 177 same-day measurement of forced spirometry and DLCO in a clinical trial for IPF. 

Results

The FIVC was <90% of the FVC and could not evaluate full inflation in 15 measurements (8.5%). 40% of these tests were on the 1st 2 patients recruited by the site and all but 2 were successfully repeated. 151 of the remaining 162 measurements (93.2%) demonstrated a FIVC no more than 105% of the FVC.  11 measurements showed the forced exhalation started from a lung volume below full inflation because the FIVC was significantly larger than the FVC.

The IVC in 131 DLCO measurements (74.0%) was >90% of the FVC and demonstrated repeatability (Grade A).  16 measurements (9.0%) had IVC between 85% and 90% and demonstrated repeatability of VA with largest VA in acceptable effort (Grade B). 30 measurements (16.9%) showed IVC less than 85% of the FVC. 

93% of the measurements showed FIVC < 105% of FVC or 0.1L demonstrating full inflation,  86.7% of measurements where FIVC was <90% of FVC (n=15) were repeated successfully. 

Conclusions

The requirement to demonstrate full inflation is achievable in this patient population and most sites quickly became accustomed to coaching the FIVC after FVC.