by W. Liu et al., August 1st 2017

And what did these analyses reveal?

Not surprisingly, when all was said and done, the authors report that “increasing [the] CO2 concentration to 3000 ppm at 35°C did not cause changes in any of the measured responses.” They did note, however, that the heart rates of the subjects were slightly reduced under elevated CO2 conditions (Figure 1, top left panel), although these reductions were not statistically significant.