Piezoelectric Sensor to Measure Respiration / Heart Rate

Hi guys!

For my summer research program, I was given the task to construct a respiration rate sensor given a piezoelectric sensor. How should I go about doing this?

Links:
Sensor:

User Manual:

The sensor outputs very low voltage, a few mV. There's isn't a lot of documentation, and I did learn that people put a 1M resistor in parallel, but how does that help?

Things I've tried:
I connected this to the arduino(A0 and GND) and read the data, the analog readings were around 0.2 out of 1023. (Simple analogRead function)

When I disconnected the GND pin from the arduino (just connected to A0 pin), the arduino read more data somehow... The peak data was around 160 this time. How is this working? It has no ground reference...

All in all, can you guys please help me figure this thing out? Should I amplify/filter it? What circuits? I just need be able to detect respiration rate, but I need to stick to this sensor.

Thanks!

No practical experience, but I think you need to use an extreme high impedance charge amplifier for those low breathing frequencies. Followed by high-pass and low-pass filters.
Leo..