Effects of Power Extraction on Turbofan Compressor and Turbine Maps

The two diagrams below show the effects of power extraction (power offtake / power off-take) on a turbofan engine at a flight altitude of $H = 11km$ and a speed of $Ma = 0.8$, calculated with GasTurb 12:

Effects of Power Extraction on the Operating Line (Blue)

• Why are the operating lines (blue) of both the compressor and turbine shifted to the left towards the surge line?
• In particular, why does the non-dimensional corrected mass flow decrease, while the pressure ratio stays approximately constant?
• The same question from a different angle: Why does the pressure ratio not decrease at a constant mass flow?
  It seems logical that the non-dimensional corrected relative spool speed decreases, since power is extracted. However, I would assume that the decrease in spool speed would entail a decreasing pressure ratio for the same reason, while the mass flow would stay constant - which is apparently false.