<Tr> <Td> PDD </Td> <Td> premenstrual dysphoric disorder </Td> </Tr> <Tr> <Td> PDE </Td> <Td> phosphodiesterase </Td> </Tr> <Tr> <Td> PDGF </Td> <Td> platelet - derived growth factor </Td> </Tr> <Tr> <Td> PDR </Td> <Td> Physicians' Desk Reference ((Profilarative Diabetic Retinopathy)) </Td> </Tr>

What is the meaning of px in medical term