ARTERIAL PULSE OXIMETRY LOOPS - A NEW METHOD OF MONITORING VASCULAR TONE

Objective. We report the off-line calculation of the vascular complian ce of the finger and suggest the continuous on-line use of this method ology as an aid to monitoring the peripheral vascular resistance. This method consists of the simultaneous analysis of the waveform signals from the pulse oximeter monitors and the arterial pressure as indicato rs of ''volume'' and pressure respectively to continuously calculate t he vascular ''compliance'' (volume change per unit pressure change). T his should be seen as a ''relative compliance'' as the pulse plethysmo graph signal is not calibrated. This new methodology allows for contin uous monitoring of peripheral vascular compliance as a beat-to-beat in dicator of peripheral vascular resistance. The vaso-constrictors, phen ylephrine and ephedrine, were shown to decrease the compliance as pred icted. Methods. The arterial pressure and pulse oximeter waveforms wer e obtained during routine anesthetic care. The waveforms were collecte d with a computer data-acquisition system and then analyzed ''off-line '' as an indirect indicator of total vascular tone. Demographic and cl inical information including drug administration were recorded. Result s. A case report is presented using this new: form oi analysis. Vascul ar compliance changes induced by phenylephrine and ephedrine were stud ied. A dose response curve of peripheral vascular compliance to phenyl ephrine was generated from these dat;. Conclusions. By plotting the pu lse oximeter waveforms versus the arterial waveforms, multiple volume versus pressure (relative compliance) loops were obtained. Analysis of these loops may assist in the monitoring oi vascular compliance.