What does it mean when Ve exceeds its predicted during a CPET?

When I review the results from a CPET I am used to considering a maximum minute ventilation (Ve) greater than 85% of predicted as an indication of a pulmonary mechanical limitation. Recently a CPET report came across my desk with a maximum minute ventilation that was 142% of predicted. How is this possible and does it indicate a pulmonary mechanical limitation or not?

It is unusual to see a Ve that is greater than 100% of predicted. We derive our predicted max Ve from baseline spirometry and calculate it using FEV1 x 40. We have tried performing pre-exercise MVV tests in the past and using the maximum observed MVV as the predicted maximum Ve but our experience with this has been poor. Patients often have difficulty performing the MVV test correctly and realistically even if it is performed well the breathing maneuver used during an MVV test is not the same as what occurs during exercise. Since both Wasserman and the ATS/ACCP statement on cardiopulmonary exercise testing recommend the use of FEV1 x 35 or FEV1 x 40 as the predicted maximum minute ventilation we no longer use the MVV.

There are usually only two situations where a patient’s exercise Ve is greater than their predicted max Ve. First, when a patient is severely obstructed their FEV1 is quite low and FEV1 x 40 may underestimate what they are capable of since they are occasionally able to reach a Ve a couple of liters per minute higher than we expected. Second, if the FEV1 is underestimated due to poor test quality then the predicted max Ve will also be underestimated. In this case however, the baseline spirometry had good quality, was repeatable and the results did not show severe obstruction but instead looked more like mild restriction.

Pre_Exercise_FVLs

Effort 1: Effort 2: Effort 3:
FVC (L): 2.51 2.52 2.60
FEV1 (L): 1.86 1.87 1.95
FEV1/FVC %: 74 74 75
PEF: 6.26 6.46 6.37

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