In reply to Rick Wicklin.

Rick,

Thank you for your response. I believe I can narrow down my complicated equation so I have my variable of interest as the 'y' and my other variables on the other side. There are 8 variables on the other side of y and I believe I'm going to need to take the derivative of all of them separately. I've been reading up on SAS and how to go about doing this, but I'm not sure of the code to use. Would i use the GETDER(Art,Fm) for example? The derivative of Art (which is arterial concentration-my y value), with respect to Fm (derivative of mammary blood flow-which is one of the other 8 variables)?