Your question is a little unclear. Are you trying to monitor when memory usage reaches those levels, and then perform some action (an alert email or something)?
Firstly you need to keep in mind that AIX automatically uses memory which is not used for computational work, as filesystem cache. It is therefor very common to see high overall memory usage at close to 100%, without any issues as a result of this. To monitor for problems you will therefore have to look at more than just total memory used. You need to look at the computational vs file/client memory separately, and also need to look at paging activity (both paging space usage and number of paging space IOs).
For scripting purposes a good starting point might be too look at the "svmon" command rather than nmon (assuming you are running nmon interactively).
If you want to just track memory usage over time, and report on it, your best bet is probably to run "nmon -x" to collect the data, and then graph it with one of the following tools:
* nmon analyzer - http://www.ibm.com/developerworks/wi...e/nmonanalyser
* pGraph - https://www.ibm.com/developerworks/w...kiPtype/pGraph
* nmon2rrd - http://www.ibm.com/developerworks/wi...WikiPtype/nmon
* nmon2web - http://users.ca.astound.net/~baspenc...nmon2rrdv3.htm