ADS1292R ----the channel of respiration impacts on the signal of ECG

hello

Using the ADS1292R,I find the signal wave of ECG will change to bad if   using the channel of respiration.

please help me find the source of  problem.this is my schematic design.

this is 

In addition,if I dont use the low-pass filter circuit,should there be a resistor to match the input impedance?I find the resistors(100K) can decrease the amplitude of 50Hz wave.

thank you .

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