Standardization of Controlled Vasoconstriction at the Finger Site for Pulse Oximeter Performance Assessment with Respect to a Perfusion Index

Abstract

Low perfusion at the sensor site of the finger is a challenge for pulse oximeter (PO) measurements. Since vaso-constriction is also a component of clinical pathophysiology, a measure to record changes in perfusion may assist in the diagnosis of patient status. Several perfusion indices have been established of which each depend on the manufacturer’s philosophy and development. Testing and calibration of sensors and pulse oximeters can only be established with controlled hypoxemia studies in healthy volunteers [1]. Hence standardized procedures should be available for testing the PO perfusion index (PI) compared to standardized and measurable changes with respect to perfusion and vasoconstriction. One procedure with a low risk and a reasonable modus operandi for introducing vasoconstriction at the fingers of healthy volunteers is the application of cooled air. In this study both arms were positioned in large tubes so that cold and warm air tempered between 40° and 10° C could be applied in a standardized bilateral manner. PO sensors and a laser Doppler system were fitted to the fingers in a randomized trial. Continuously recorded PI signals of the PO were compared to the laser Doppler signal and to the finger temperature as references for the effect of vasoconstriction. A standardized alteration of perfusion at the finger site with the establishment of steady state plateaus for both temperature and vasoconstriction was successful in 5 volunteers in a test and with 14 volunteers in a controlled randomised study. The perfusion at the finger site could be reduced to a PI lower than 0.3 (arbitrary unit) which in some cases caused a loss of the PO signal reading. Testing of pulse oximeter performance with respect to changes of perfusion due to cold induced vasoconstriction at the finger site can be established in a standardized and controlled manner.