Constant Flow vs. Constant Pressure Perfusion in Lungs

Lungs can be perfused by either constant flow or constant pressure. Although constant flow perfusion may mimic the in vivo situation more closely, it has the disadvantage that in case of vasoconstriction, hydrostatic edema becomes inevitable. Since lymph drainage is not possible in perfused lungs, extravascular water will accumulate quickly. For this reason, when using constant flow perfusion, small flow rates have been used to minimize hydrostatic edema. However, small flow rates may decrease lung functions such as serotonin metabolism and protein synthesis.

Constant pressure perfusion permits higher perfusate flow rates since in this case vasoconstriction decreases the perfusate flow and hydrostatic edema is unlikely to occur. Constant pressure allows the researcher to maintain lungs in a physiologically healthy way as well as to directly study edema formation caused by increased vascular permeability.If the vascular resistance is calculated, pressure and flow must be measured. In the case of flow measurement, flow can be measured directly by using an ultrasonic transit time flowmeter or indirectly by calculating the flow rate from the roller pump's speed (SCP module).

All IPL systems are supplied standard with the option of a simple switch between constant flow and constant pressure for maximum protocol and application flexibility.