Vascular Function Curve

A graph of P plotted as a function of Q (Figure 4) has been termed a vascular function curve (Levy, 1979 Berne and Levy, 1981). From eq. 5, it is evident that the slope of the relationship between P and Q depends only on R, C and C . Changes in flow have an inverse effect on P, i.e., as 0 is increased, there will be a proportionate decrease in P. There is a limit to the reduction of P that can be produced by an increase in 0, however. At some critical maximum value of 0, sufficient fluid will be translocated from the venous to the arterial side of the circuit such that P, will drop below the ambient pressure. In a system of distensible tubes, the venous system will be collapsed by this negative transmural pressure (P minus ambient pressure). This will, of course, limit the maximum value of cardiac output regardless of the capabilities of the pump. 

Figure 4. Hypothetical cardiac and vascular function curves. (From Berne and Levy.)...

Kealey, S.M., et al.. User-defined vascular input function curves influence on mean perfusion parameter values and signal-to-noise ratio. Radiology, 2004. 231(2) p. 587-93. 

A typical clearance profile and curve-fitting of these bioconjugates in a rat with normal renal function is shown in Fig. 16. The time constant is the relevant quantifiable measure for how fast the agent clears from the vascular system. Figs. 17 and 18 compare the plasma clearance profile of different fluorescein conjugates in normal and ligated rat kidneys. The clearance profile followed the... 

Biomaterials are by definition materials that assume the functions of tissue in natural organs or organ parts. They must therefore imitate the properties of such tissue as well as possible. For example, a vascular prosthesis must exhibit a tension-expansion curve highly similar to that of a natural blood vessel, as well as a smooth inner surface which corresponds to the endothelial covering. In other words, a biomaterial must be made to act as much as possible like the natural tissue in Its biological environment - in the case of vascular prostheses in the environment of blood, tissue, and interstitial fluid -, it must withstand biodegradation and prove to be biocompatible (Table 1). 

One of the perils of any modeling analysis is the failure to obtain the input function to the system under study. For both single photon and PET imaging of the heart, the left ventricular cavity blood pool concentration-time curve gives the appropriate information when it is convoluted with the vascular transport function between the ventricular cavity and the coronary artery inflow. (Low order differential operators can be used to describe purely intravascular dispersive transport.)... 

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