Figure 2
From: The quantitation of buffering action II. Applications of the formal & general approach
Buffering in conservative and non-conservative buffered systems, illustrated by blood pressure buffering. A-C, Conservative buffered system: Buffering individual flow against variations of total flow. Pipework model of circulation, where cardiac output corresponds to total volume flow Φ, and volume flows in individual organs to volume flows φi in individual tubes. A, Zero buffering. In a circulation comprising a single hydraulic conductor, a total volume flow (Φ) established by a pump (⊗) results in a partial flow (φ1) of equal magnitude in the conductor (red). Their quantitative relation can be represented in signal transduction formalism as a "transfer element" where input x corresponds to Φ, output y to φ1, and the transfer properties are characterized by a constant transfer coefficient of 1. B, Linear buffering. Total volume flow partitioning into two parallel hydraulic conductors. Changes of total flow Φ now elicit smaller changes of the partial flow φ1 (red) – due to "buffering" by the second conductor (blue). Transfer and buffering behavior with respect to the upper vessel can be expressed in terms of fixed, dimensionless fractions t and b. C, Nonlinear buffering. When one or both vessels have elastic walls, hydraulic conductance and thus responsiveness to changes in Φ will vary with the absolute value of Φ. Transfer and buffering coefficients become nonlinear functions of Φ. D, Non-conservative buffered systems: Buffering individual flow against variations of perfusion pressure. Organ volume flows φi are described as functions of perfusion pressure ΔP. With different physical dimensions for input and output (pressure vs. flow), the transfer coefficient for vessel 1 alone has the dimension of a hydraulic conducance LP1. With a second vessel added in series, changes of perfusion pressure translate into smaller changes of volume flow. This effect can be interpreted as "buffering" and expressed quantitatively using the buffering parameters t, b, T, and B. If one or both vessels are elastic, transfer and buffering functions become nonlinear functions of perfusion pressure ΔP.