Hello Raymond,
Thanks for using our community.
The MSL is the moisture level that an electronic device can stand without popping up in the soldering process (moisture expansion). All the pressure sensors like the MPX2300 has at least one pressure port. There is no MSL rating for ported devices since moisture expansion would not affect them.
As per the Highly Accelerated Stress Tests, I would like refer to the "Quality and Reliability" at DL200 Data Library at pages 1-3 to 1-14. Specifically page 1-8 "Accelerated Life Testing"
http://cache.freescale.com/files/sensors/doc/data_lib/DL200.pdf
(Please note that the size of the book will require ~25MB).
Hope it helps!
Josh