[Virtual Presenter] The direct PD Models such as Linear, Log-linear, Emax and Sigmoid Emax can be used to measure the immediate response of a drug in a patient. When a patient takes a drug, the amount of drug in their bloodstream and the immediate response to it can be measured by these models, which can be used to create a concentration and response plot. The plot will be parallel, with higher concentrations leading to higher responses. The plot can be either linear or curvilinear depending on the concentration range, with a linear plot created if the concentration range is small, and a curvilinear plot created if the range is large enough..