I don't know about Nisa. Never heard of it, but I am familiar with hollowcore. Typically the manufacturer will have load tables thatyou can use to pick a cross section size and even the strand configuration. The LECPres program is one that you can use, and there are several others: J&A Beam, Presto, Concise.
I work for a manufacturer that produces hollowcore. If you can give me more specifics I can steer you in the right direction if it is just sizing that you need, although the loading capacitys can vary some based on the cross-section. The Precast Prestressed Concrete Insitite (PCI) Handbook also has some standard load table to give you a starting point.
Typically the hollowcore producer will do the design calcuations, so you don't need to do it.