Constant Flow vs. Constant Pressure Perfusion in Lungs
Lungs can be perfused by either constant flow or constant pressure. Althoughconstant flow perfusion may mimic the in vivo situation more closely, ithas the disadvantage that in case of vasoconstriction, hydrostatic edemabecomes inevitable. Since lymph drainage is not possible in perfusedlungs, extravascular water will accumulate quickly. For this reason, whenusing constant flow perfusion, small flow rates have been used to minimizehydrostatic edema. However, small flow rates may decrease lung functionssuch as serotonin metabolism and protein synthesis.
Constant pressure perfusion is a more physiologically relevant method ofperfusion which helps to extend the viability of the lung. By allowing thenormal regulation of vascular pressure through vasoconstriction, regionalflow is regulated naturally leading to minimal hydrostatic edema, often seenwith constant flow perfusion. As a result, perfusing the lungs under constantpressure conditions allows the investigator to study edema formation causedby changes in 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(PLUGSYS TTFM-2 module) or indirectly by calculating the flow rate from theperistatic pump’s speed (PLUGSYS SCP module).
All core IPL system packages are configured to include our PLUGSYS SCPcontrol module, suitable peristaltic pump capable of external analog speedcontrol, pressure transducer and amplifier. The pressure transducer amplifiersupplies a feedback signal to the SCP module which varies the pump speed tomaintain constant perfusion pressure. The output of the SCP module can becalibrated to allow measurement of the perfusion flow. A switch on the SCPmodule allows the user to choose or switch between either constant pressureor constant flow perfusion as needed.