If you heat a gas in constant volume the temperature will go up according to pv = nrt. The change in the internal energy of the gas that relates to that temperature change can be found from the specific heat capacity of the gas.
What if you wanted to look at this from the point of view of pressure and how pressure affects internal energy. I could examine this indirectly by looking at temperature again...If you increase the pressure the temperature will go up. You can find the change in internal energy again from the heat capacity of the gas and teh temperature change. Is there an equation to tell you the change in internal energy from the pressure directly?