Need help filtering a REST query

I'm trying to construct a REST query to get a list of devices that have a GlobalStatus of 'Warning' or 'Critical'

When I send the following query:

https://base_URI/Devices?GlobalStatus=16

It does work correctly, listing all of the devices in 'critical' status. When I try:

https://base_URI/Devices?GlobalStatus>4 

I get an error. (i've tryed several variations that I've seen in other REST APIs, such as 'GT4', GREATERTHAN4, even !=4)

I know I could just do two queries, for GlobalStatus=8 and GlobalStatus=16 but I would prefer to do a single query.

Also, is there a way to just return specific fields in the result set?

Thanks in advance.