Blood flow dynamics under venipuncture and viscosity estimation from pressure and flow variations

We have calculated the nonstationary flow of a viscous liquid in a narrow tube under the action of pressure variations with time. Such a flow accompanies venipuncture the procedure of taking a sample from a vein with a hypodermic needle. We show how the changes in the flow characterstics during venipuncture make it possible to actively estimate viscosity. This method is “nonperturbative” for blood in the sense that the measurement process weakly affects the measured quantity. It may find application in medicine.