When pyruvate dehydrogenase is inhibited, pyruvate accumulates and is used to regenerate NAD+, producing lactate as a byproduct.

“but if that enzyme preventative notice is not working but accumulates now because the cell needs a certain amount of NAD to nadh ratio to function in other words if that information drops too low the cell can die so the cell says okay I'm building up too much nadh what can I do to get more NAD and the cell says well in this emergency situation since I cannot get to oxygen which is the oxygen that can oxidize nadh back into NAD what other oxidizing agents do I have around me that can do this trick and that is peruvic so pyruvate acts as the emerging the oxidizing agents for nadh through an enzyme called lactate hydrogenase so pyruvate oxidizes nadh back to NAD but in the process becomes lactate”