A glitch in time

This relatively odd DLCO testing error came across my desk today. Although it’s fairly unusual it brings up some interesting points about how the Breath-Holding Time (BHT) is determined and what effect it has on DLCO.

Specifically, at the beginning of the DLCO test the patient took a partial breath in, then exhaled, then took a complete breath in. The patient performed the DLCO test three times and did exactly the same thing each time despite being coached by the technician to only take a single breath in. I’m sure this says something about human nature but I’m not exactly sure what.

BHT_Glitch_1

Anyway, our test systems uses the Jones-Meade approach to measuring breath-holding time (the ATS/ERS recommendation). The J-M algorithm starts the measurement of BHT when the inhalation has reached 1/3 of the inspiratory time. In this case the computer detected the beginning of the first inspiration and detected when the patient had reached the end of inspiration (which is standardized at the point at which 90% of the final inhaled volume has been reached), but it ignored what happened in the middle. For this reason, the software set the beginning of the breath-holding time before the “real” inhalation.

Continue reading