I’ve now been able to read the new iCPET paper a few times (I’m slow). As you know, I do love a CPET paper. My first thought is: good that a second group is using this methodology for replication purposes. Adds credibility to the findings if more than one group are finding them.
My second thought is: they didn’t seem to have any requirement for max tests. They mentioned respiratory quotient for their healthy controls, but not for their patients. Why is this important? The potential to compare apples with oranges: results of maximal and submaximal tests.
How do I know? The 25th percentile for RQ was below 1.15. This suggests a lot of variability around the median and potentially values below the generally accepted cut offs for achieving a maximal test. True that they observed the same spread in their healthy controls, but with a
low sample size, it could be enough participants to influence the results. Why does it matter? Well, cells will extract only enough oxygen necessary to function if one group is working harder than the other group on the test, it’s going to look like more oxygen is returning to
the heart then we might expect, giving the appearance of impaired peripheral oxygen extraction when it’s actually the case the participants did not exert at a similar psychological level with respect to their different levels of capacity.
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